CA1254601A - Anti-lock braking system - Google Patents
Anti-lock braking systemInfo
- Publication number
- CA1254601A CA1254601A CA000482572A CA482572A CA1254601A CA 1254601 A CA1254601 A CA 1254601A CA 000482572 A CA000482572 A CA 000482572A CA 482572 A CA482572 A CA 482572A CA 1254601 A CA1254601 A CA 1254601A
- Authority
- CA
- Canada
- Prior art keywords
- wheel
- hydraulic
- road surface
- control means
- wheels
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
- B60T8/32—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration
- B60T8/58—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration responsive to speed and another condition or to plural speed conditions
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
- B60T8/17—Using electrical or electronic regulation means to control braking
- B60T8/173—Eliminating or reducing the effect of unwanted signals, e.g. due to vibrations or electrical noise
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
- B60T2210/00—Detection or estimation of road or environment conditions; Detection or estimation of road shapes
- B60T2210/10—Detection or estimation of road conditions
- B60T2210/14—Rough roads, bad roads, gravel roads
Abstract
Abstract of the Disclosure:
An anti-lock braking system having a wheel brake, a hydraulic control circuit for controlling the supply of a hydraulic control pressure to the wheel brake, and a control means for energizing the hydraulic control circuit so as to reduce the hydraulic braking pressure applied to the wheel brake when the wheel is about to be locked due to the rotational speed characteristics thereof, characterized in that the control means has the function of detecting the condition of a road surface on which a vehicle runs, and is formed in such a manner that, when the control means judges that the road surface is rough, it is operated so as to reduce a rate of decrease in the hydraulic braking pressure. The control means is adapted to judge that, when the fluctuating frequency of a wheel speed is not less than a predetermined level, the road surface on which said vehicle runs is rough.
An anti-lock braking system having a wheel brake, a hydraulic control circuit for controlling the supply of a hydraulic control pressure to the wheel brake, and a control means for energizing the hydraulic control circuit so as to reduce the hydraulic braking pressure applied to the wheel brake when the wheel is about to be locked due to the rotational speed characteristics thereof, characterized in that the control means has the function of detecting the condition of a road surface on which a vehicle runs, and is formed in such a manner that, when the control means judges that the road surface is rough, it is operated so as to reduce a rate of decrease in the hydraulic braking pressure. The control means is adapted to judge that, when the fluctuating frequency of a wheel speed is not less than a predetermined level, the road surface on which said vehicle runs is rough.
Description
Tllls Inventlon relates to an antl-lock braklng system Includlng a wheel brake, a hydraullc controi clrcult for control-llng the supply of a hydraullc braklng pressure t~ the wheel brake, and a control means for determlnlng whether a wheel Is llkely to be locked, ~n the basls of the rotatlonal characterls-tlcs thereof, and for maklng operatlve the hydraullc control clr-cult when the wheel Is about to be locked, so as to reduce the hydraullc braklng pressure supplled to the wheel brake.
When a braklng operat10n Is carrled out whlle a vehlcle provided wlth a conventlonal antl-lock braklng system runs on a rough road, the braklng force applled to the w~eel varles due to the varlatlons In the ground-contacting condltlons thereof even lf the hydraullc bra~lng pressure Is constant. Consequently. the suspension of the vehlcle Is vlbrated longltudlnally. Thls causes the vehlcle speed to pulsaie li1 some cases. When such a pulsatlon of the vehlcle speed occurs, the control means Judges erroneously that there Is the posslblllty that the whee Is locked, even when there Is no suc'~ a posslblllty In practlce As a result, the hydrau~lc control clrcult Is energlzed so as to reduce the hydraullc braklng pressure. so that the brak1ng dls-tance Increases In some cases.
The present Inventlon provldes an antl-lock braklng system capable of preventlng a braklng dlstance from Increaslng whlle the vehlcle runs on a rough road.
In a flrst aspect of the present Inventlon, the control means Is constructed so that It has the functlons of detectlng the condltlon of the road surface on whlch the vehlcle runs, and reduclng the ra e of decrease In the hydraullc braklng pressure when thls means Judges tllat the condltlon of the road surface Is bad.
The present Inventlon also provldes an antl-lock brak-lng system capable of detecting a bad condltlon of the road sur-A
face easlly. and preventlng the braklng dlstance from Increaslng whlle the vehlcle runs on the bad road surface.
In a second aspect of the present Inventlon, the con-trol means Is constructed so that It has the functlons of Judglngthe road surface, on whlch the vehlcle rUns, to be bad when the fluctuatlon frequency of the vehlcle speed Is not lower than a predetermlned level, and so that the control means works so as to reduce the rate of decrease In the hydraullc braklng pressure when the road surface Is Judged to be In a bad condltlon.
Owlng to the speclfled constructlons as mentloned above. an unnecessary reductlon of the hydraullc braklng pressure can be prevented even If the control means Judges erroneously 1~ that the wheel Is about to be locked due to the varlatlons In the ground-contactlng condltlon of the wheel runnlng on a rough road surface, whereby the braklng effIclency does not decrease whlle the vehlcle runs on a rough road.
The present Inventlon Is caPable of detectlng automatl-cally wlth ease a slgnal Indlcatlng that the wheel of the vehlcle Is runnlng on a rough road surface.
Thus, accordlng to the present Inventlon there Is pro-vlded an antl-locklng braklng system for a vehlcle Includlng a palr of wheels, comprlslng wheel brakes for sald respectlve wheels; a palr of wheel detectors for detectlng rotatlonal speeds of the respectlve wheels and outputtlng slgnals Indlcatlve of the wheel speeds; hydraullc control clrcults for controlllng the sup-0 ply of hydraullc braklng pressUres to the respectlve wheel brakesfor antl-lock operatlons; and control means for placlng sald hydraullc control clrcults In operatlve state so as to control the hydraullc braklng pressures applled to the wheel brakes, on the basls of the slgnals from sald wheel detectors, when the wheels are about to be locked; whereln sald control means Includes a detectlon means for detectlng the condltlon of a road ~A
surface on which t~e vehlcle travels, and when sald detectlon means detects that the vehlcle Is travelllng on a rough road sur-face, the slgnals from sald wheel detectors are subJect to hlgh-selectlon and only the hlghest wheel speed value of the two wheel speed sl~nals Is employed ~y sald control means for operatlon of the hydraullc control clrcu~ts, whereas when sald detectlon means detects that the vehlcle Is travelllng on a regular road surface, sald slgnals from the respectlve wheel detectors are employed by sald control means for Independent operatlon of thelr respectlve tO hydraullc control clrcults. Sultably sald detectlon means Judges the vehlcle to be travelllng on sald rough road surface by detectIng the fluctuatlng frequency of a wheel sPeed belng not less than a predetermlned level. Deslrably when sald detectlon means detects that the vehlcle Is travelllng on sald rough road surface, sald control means operates to lessen the chance that the wheel brakes are subJect to antl-lock operatlon by the hydraullc control clrcult.
Advantageous features of the Inventlon wlll become apparent from the followlng descrlptlon of the preferred embodl-ments taken In conJunctlon wlth the acc~mpanylng drawlngs, In whlch:-Flg.s 1-5 show a flrst embodIment of the present Inven-tlon; whereln:
Fl~. 1 Is a dlagram of a hydraullc control clrcult;
Flg. 2 Is a slmpllfled clrcult dlagram showlng the con-structlon of a control means;
Flg. 3 Is a dlagram of an electrlc clrcult for use Inestlmatlng a vehlcle speed;
3~ Flg. 4 Is a dlagram showlng the operatlonal character-lstlcs of the electrlc clrcult of Flg. 3; and Fig. 5 Is a characterlstlc d I agram showlng the embodl-ment In antl-lock operatlon.
Flg. 6 Is a dlagram of an electrlc clrcult for use In estlmatlng a vehlcle speed In a second embodlment of the present Inventlon; and Flg. 7 Is a slmpllfled clrcult dlagram showlng the con-structlon of a control means In a thlrd embodlment of the present Inventlon.
ZO
~A
~3................................. ~ (J1 First, referring to Fig~ 1 showing a first embodi-ment of the present invention, a brake pedal 1 is operatively connected to a master cylinder M. When a driver steps on this brake pedal 1, the master cylinder M generates a hydraulic pressure in an oil passage 2. This oil passage 2 is connected to a hydraulic control circuit 3. A hydraulic braking pressure in accordance with the hydraulic pressure in the oil passage 2 is outputted from the hydraulic control circuit 3.
Wheel brakes are attached to the left and right front wheels and left and right rear wheels of a vehicle. The hydraulic braking pressure i5 supplied from the hydraulic control circuits 3 to these wheel brakes. The construction of the wheel brakes attached to these left and right front wheels and left and right rear wheels, and the construction of the hy-draulic control circuits 3 for supplying a hydraulic braking pressure to the wheel brakes are basically identical to one another. Therefore, only the wheel brake BQ for the left rear wheel and the wheel brake Br for the right rear wheel, and the hydraulic con-trol circuit 3 which is associated with these brakes B~, Br will now be described.
Oil passages 5, 6 extending from the hydraulic control circuit 3 communicate with the hydraulic braking pressure chambers 4 for the wheel brakes BQ, Br. When a hydraulic braking pressure is supplied to each braking pressure chamber 4, pistons 7, 8 are moved away from each other, so that brake shoes 9, 10 come into contact with a brake drum (not shown~, respectively, to generate a braking torque.
When the hydraulic braking pressure in the hydraulic braking pressure chamber 4 is too high, the braking torque generated between the brake shoes and brake drum becomes too high, so that the wheels are locked. In order to prevent this, when the wheels are about to be locked, the hydraulic braking pressure is reduced by the hydraulic control circuit 3, so that the locking of the wheels does not occur.
The hydraulic control circuit 3 is provided with modulators 11, 12 corresponding to the wheel brakes BQ, Br. Since these modulators 11, 1~ have the basically same construction, the construction of one modulator 11 alone will be described in detail.
The modulator 11 is provided with a cylinder 14 closed at both ends thereof and having a partition 13 at an intermediate portion of the interior thereof, and a rod 17 having pistons 15, 16 at both ends ~ thereof and penetrating through the partition 13 jA axiàlly and slidably at the portion thereof which is between the pistons 15, i6. The portion of the interior of the cylinder 14 which is between the partition 13 and one piston 15 is formed as a primarv hydraulic braking pressure chamber 18, which com-municates with the master cylinder M via oil passage 2. The portion of the interior of the cylinder 14 which is between the partition 13 and the other piston 16 is formed as secondary hydraulic braking pressure chamber 19, which communicates with the hydraulic braking pressure chamber 4 for the wheel brake BQ via the oil passage 5. An anti-lock hy-draulic control chamber 20 is formed between one end wall of the cylinder 14 and the piston 15, and a hydraulic discharge chamber 21 between the other i end wall of the cylinder 14 and the other piston 16, the hydraulic discharge chamber 21 communicating with a reservoir R in the master cylinder M. A
spring 22 urging the piston 16 away from the parti-tion 13 is provided in the secondary hydraulic brak-ing pressure chamber 19, and a spring 23 urging the piston 15 toward the partition 13 is provided in the anti-lock hydraulic control chamber 20.
An oil passage 24 is connected to the anti-lock ~5~
hydraulic control chamber 20. This oil passage 2~
is also connected to a hydraulic pump P via a nor-mally-closed inlet valve ViQ, and to an oil tank T
via a normally-opened outlet valve VoQ. An accumu-lator Ac is connected between the inlet valve ViQ
and hydraulic pump P.
Also, in the other modulator 12, a primary hydraulic braking pressure chamber 26 communi-cates with the master cylinder M, a secondary hy-draulic braking pressure chamber 27 with the wheel brake Br via passage 6, and a hydraulic discharge chamber 28 with the reservoir R. An anti-lock hydraulic control chamber 29 is connected to the hydraulic pump P via a normally-closed inlet valve Vir, and to the oil tank T via a normally-opened outlet valve Vor.
The inlet valves ViQ, Vir and outlet valves VoQ, Vor are solenoid valves, the opening and closing of them are controlled by a control means 32.
When the inlet valves ViQ, Vir are closed with the outlet valves VoQ, Vor opened, the anti-lock hydraulic control chambers 20, 29 are in communication with the oil tank T. When the brake pedal 1 is stepped to supply a hydraulic pressure from the master cylinder M to the primary hydraulic braking 1~'54~
pressure chambers 18, 26, the volumes of the secondary hydraulic braking pressure chambers 19, 27 decrease, and a hydraulic braking pressure cor-responding to the hydraulic pressure fed from the mas-ter cylinder M is supplied to the hydraulic braking pressure chambers 4 in the wheel brakes BQ, Br.
Accordingly, the braking torque increases freely in conformity with the driverls braking operation.
When the outlet valves VoQ, Vor are closed with the inlet valves ViQ, Vir closed~ the control oil in the anti-lock hydraulic control chambers 20, 29 is trapped therein. Consequently, the volumes of the secondary hydraulic braking pressure chambers 19, 27 are invariable whether or not the hydraulic pressure supplied to the primary hydraulic braking pressure chambers 18, 26 increases or decreases.
Hence, the braking torque during braking operation is maintained at a predetermined level irrespective of the driver's braking operation. Such opera-tional condition occurs when there is the possibility that the wheels are locked.
When the inlet valves ViQ, Vir are opened with the outlet valves VoQ, Vor closed, the anti-lock hydraulic control pressure is supplied to the anti-lock hydraulic pressure chambers 20, 29. Therefore, _ g _ l~t~
the volumes of the secondary hydraulic braking pressure chambers 19, 27 increase in spite of the fact that the hydraulic pressure from the master cy'inder M is applied to the primary hydraulic braking pressure chambers 18, 26, whereby the hydra~lic pressure in the braking oil chambers 4 in the wheel brakes BQ, Br decreases to lower the braking torque. Accordingly, if the inlet valves ViQ, Vir are opened with the outlet valves VoQ, Vor closed when the wheels are about to be locked, the locking of the wheels can be prevented.
The construction of a control means 32 will now be described with reference to Fig. 2. Since the construction for controlling the inlet valve ViQ and outlet valve VoQ which correspond to one wheel brake sQ, and that for controlling the inlet valve Vir and outlet valve Vor which correspond to the other wheel brake Br are basically identical, only the former construction will be described.
The control means 32 is provided with a judge-ment circuit 33 consisting of a microcomputer, for example, ar~
adapted to determine whether the wheels are locked or not. The judgement circuit outputs on the basis of this determination a signal for opening or closing the inlet valve ViQ and outlet valve VoQ.
The conditions constituting a judgement basis for determining to output a signal for carrying out an anti-lock control operation will now be discussed.
In general, the following four systems (a)-(d) have been proposed.
(a) A system in which a signal ~ is outputted when Vw the formula, wheel acceleration ~K referenGe wheel deceleration - VWO, is established, to lessen the braking pressure.
(b) A system in which a signal Sl is outputted when the formula, wheel speed Vw < first reference wheel speed Vrl, is established, to lessen the hydraulic braking pressure. In this case, Vrl = Vv ~
~ ic e, wherein Vv is a ~:hcc~ speed; and ~1 a suitable slip ratio of the wheel. Therefore, if the slip ratio is e~pressed by ~, Vw < Vrl has the same meaning as ~ ~ ~1' and, when Vw < Vrl or ~ > ~1 is establsihed, the signal 51 is outputted.
(c) A system in which the hydraulic braking pres-sure is lessened when either (a) or (b) above is established.
(d) A system in which the hydraulic braking pres-sure is lessened when (a) and (b) above is established concurrently.
In the system (a) above, the reference wheel deceleration - VwO is set to a level, usually, for example, -2.0 ~ 1.2G, which are not obtained during a braking operation carried out when there is no possibility that the locking of the wheels occurs.
However, according to this system, a wheel aecelera-tion of around -1.0 ~ -0.5G occurs in some cases during a braking operation carried out on a snow-covered xoad or a frozen road, and a signal for lessening the hydraulic braking pressure is not outputted in spite of the fact that the wheels are locked in the latter part of a braking operation.
While the vehicle runs on a rough road, the wheel acceleration Vw pulsates finely even druing a regular braking operation, and a signal ~ is outputted even when there is no possibility that the wheels are locked, to cause the braking efficiency to decrease.
In the system (b), when the wheel speed Vw is increasing, it is judged that the hydraulic braking pressure has been lessened sufficiently even if the slip ratio ~ is high, i.e., even if the signal Sl is outputted. The hydraulic braking pressure is necessarily lessened during this time as well, so that the braking efficiency decreases.
It is clear that the system (c) has the faults of the systems (a) and ~b).
Finally, in the system (d), the problem of a decrease in the braking efficiency during the driv-ing on a rough road, and the problem of a decrease in the braking efficiency due to a hydraulic braking pressure-lessening operation carried out while the wheel speed Vw increases are solved. Furthermore, if the reference wheel deceleration- VwO is set in the level in the range of wheel deceleration occurring during a braking operation carried out while the vehicle runs on a regular road surface, for example, -1.0 ~ OG, and preferably -0.3 ~ -0.6G, the locked wheels can be detected even when the wheel deceleration is -1.0 ~ -0.5G in a braking operation carried out on a snow-covered road or a frozen road, and the hydraulic braking pressure can thereby be lessened.
In the judgement circuit 33, a signal corre-sponding to a wheel speed Vw is inputted from the ehicle speed detector 34, and this wheel speed h~l Vw and a Y~b~e~e acceleration Vw, which is computed on the basis of the wheel speed Vw, are compared with a first reference wheel speed Vrland a reference wheel deceleration - Vw, respectively.
When Vw < - VwO and Vw < Vr1 are established, high-level signals ~, Sl are outputted from the judgement i circuit 33. These signals ~, Sl are inputted into an AND-gate 35, and, when both of these signals are in high levels, a transistor 36 is turned on, and a solenoid 38 is excited, the inlet valve ViQ being opened. When a high-level signal Sl is outputted, a transistor 37 is turned on, and a solenoid 39 is excited, the outlet valve VoQ being closed.
When the braking torque starts being reduced by the signals ~, Sl as mentioned above, the vehicle speed is still decreasing. At this time, the braking torque is still higher than the driving torque on the road surface, and the possibility of locking of the wheels has not yet been completely removed.
However, the system generally has an operational delay of around lOms. Accordingly, the hydraulic braking force :Ls further lessened after the braking pressure-lessening signal has been extinguished, so that this system generally enables a good effect to be obtained. However, in some cases, the braking pressure is not lessened sufficiently under certain conditions of the road surface to cause the wheel speed to vary in the locking direction. In order to prevent such a phenomenon, a braking pressure-lessening signal may be generated, when ~ > ~1' until the wheel speed Vw has started increasing 1 2 ~
certainly. However, in spite of the fact that a control operation can usually be carried out satis-factorily even when the generation of the braking pressure-lessening signal is stopped upon the A establishment of Vw > ~ , this signal is retained until Vw > 0 has been attained. This causes the braking torque to be lessened excessively. However, this poses no problems in practice in the wheels having a small braking load distribution.
A second reference wheel speed Vr2 which corresponds to a second reference slip ratio, at which A2 > Al is now set. Only when Vw < Vr2, i.e.
A > A2, so that the possibility that the wheels are locked has increased, the braking pressure-lessening signal is retained until the vehicle speed Vw has started increasing. In the judgement circuit 33, it is judged whether or not Vw < Vr2 or A > A2, and, when the conditions are satisfied, a signal S2 is outputted. In order to judge that the wheel speed Vw is increasing, a speedup reference value ~ Vw0 is set, and, when Vw > +Vw0, a signal ~ is outputted.
The signal S2 is inputted into one input ter-minal of an AND-gate 40 and an OR-gate 41. The signal ~ is inputted into the OR-gate 41, and in-verted and inputted into the AND-gate 40. The signal Sl is also inputted into ~e OR-gate 41, and an output fr~ ~e OR-gate 41 is applied to the base of transistor 37.
Outputs from both AND-~ates 35, 4~ are inputted into OR-yate 42 which in tu~n feeds an output to the base of transistor 36.
According to the control means 32, the level of any one of the signals Sl, ~, S2 has become high, the transistor 37 is turned on, the outlet valve VoQ is closed, and when the levels of both of the signals ~, Sl are high, or when the level of the signal ~ is high with that of the signal ~ low, the inlet valve ViQ is opened.
A method of setting first and second reference wheel speeds Vrl, Vr2 will now be described. These wheel speeds are determined ideally by detecting a vehicle speed Vv, and making calculations in accordance with the following formulae taking suitable reference slip ratios ~ 2 into consideration.
Vrl = Vv (1~
Vr2 = Vv (1-~2) However, no practical means for detecting a vehicle speed Vv has been found out up to the present time. Therefore, a system,for estimating a tentative vehicle speed Vr on the basis of,the condition of variations in the wheel speed Vw is generally used.
A basic circuit of this system is shown in Fig. 3.
Referring to Fig. 3, a wheel speed Vw is inputted into an input terminal 43, which is con-nected to an output terminal 47 through an ideal diode 44, a memory capacitor 45 and a constant current discharge circuit 46, and a vehicle speed Vr is outputted from this output terminal 47. By this system, as shown in Fig. 4, a peak value of the wheel speed Vw in an anti-lock operation is set to a level in the vicinity of the vehicle speed Vv with valleys of the wheel speed Vw connected with a predetermined gradient Gr, to estimate the tenta-tive vehicle speed Vr.
While a vehicle runs on a rough road, the wheel speed Vw pulsates, so that it is judged erroneously that the wheels are about to be locked, to cause the hydraulic braking pressure to decrease unnecessarily, and the braking efficiency to lower.
In ordex to prevent this, the control means 32 has the function of reducing the rate of decrease in the braking pressure when it is judged that the wheels are locked while the vehicle runs on a rou~h road.
The present inventor has experimentally ascer-tained that a pulsation frequency f of the wheel speed Vw during a braking operation carried out on a rough road is substantially equal to a natural frequency nO (generally 15-20Hz) of a suspension.
On the other hand, a fluctuating ~requency nm f the wheel speed ~w during a normal operation of an anti-lock braking system is generally not more than 10~lz. In the judgement circuit 33, it is judged that, when f > nm, the vehi~le is running on a rough road, and a signal E is outputted therefrom.
This signal E is inputted into a delay circuit 49. The terminal, from which the signal Sl is out-putted, of the judgement circuit 33, is grounded through a relay switch 50. The delay circuit 49 is adapted to output a signal for turning on a relay switch 5C when a high-level rough road detecting signal E has been inputted thereinto, and keep out-putting the same signal or a predetermined period of time, for example, 100ms after the level of the signal E has become low.
c.
When Vw ~ Vrl or ~ > ~1 has been established while the vehicle runs on a rough road, so that the judgement circuit 33 judges that the wheels are about to be locked, to output the high-level signal Sl, the level of the sign~l Sl is rendered low forcibly.
As a result, the rate of decrease in the hy-draulic braking pressure during travelling on a ~'Z5~
rough road decreases. Consequentl~, the hydraulic braking pressure does not decrease unnecessarily, so that a decrease in the braking efficiency can be prevented.
The operation of this embodiment will now be described with reference to Fig. 5. Fig. 5 shows an e~ample of a mode of operation of this anti-lock braking system. The lateral axis of this figure shows the time after the starting of a braking operation, and the vertical axis thereof a vehicle speed Vv, a wheel speed Vw and a first reference wheel speed Vrl and a second reference wheel speed Vr2 in the uppermost position, a wheel acceleration Vw, a speedup reference value +VwO and a reference wheel deceleration -VwO in the position under the mentioned position, signals ~, ~, Sl, S2 and the operational conditions of the solenoids 38, 39 in the position under the second-mentioned position, and a hydraulic braking pressure Pb in the lowermost position.
Immediately after a braking operation has been started at an instant t=O, the levels of the signals , Sl, S2 are low. The hydraulic braking pres-sure Pb increases gradually, and the wheel speed Vw and wheel acceleration Vw decrease gradually at ~5~
the same time.
When the wheel acceleration Vw has become lower than the reference wheel deceleration -Vw0 (Vw <
-Vw0) at an instant t1, the level of the signal ~
becomes high but the signal Sl remains to be in a low level since the level of the wheel speed Vw is higher than that of the first reference wheel speed Vrl at this time. Accordingly, the hydraulic brak-ing pressure Pb con inues to increase, and the wheel speed and wheel acceleration Vw to decrease.
When the wheel speed Vw has become lower than the first reference wheel speed Vrl at an instant t2, the level of the signal Sl becomes high, and the level of an output from the AND-gate 35 becomes high. Consequently, the levels of outputs from the OR-gates 42, 41 become high. As a result, the solenoids 38, 39 are excited to cause the inlet valve ViQ to be opened, and the outlet valve VoQ to be closed. The hydraulic braking pressure Pb then starts decreasing, and the wheel acceleration Vw resumes increasing. During this time, the wheel speed Vw continues to decrease.
When the wheel acceleration Vw has become higher than the reference wheel deceleration -Vw0 (Vw > -Vw0) at an instant t3, the level of the signal ~sLa~l ~ becomes low, and the level of an output from the AND-gate 35 low as well accordingly. Consequently, the solenoid 38 for the inlet valve ViQ is deexcited, and the inlet valve ViQ is closed. This enables the braking pressure Pb to be maintained in a con-stant level. Namely, the braking torque is main-tained in a substantially constant level. As a result, the wheel speed Vw starts increasing.
When the level of the wheel acceleration Vw has become higher than the speedup reference level +VwO
(Vw > +VwO) at an instant t4, the leve] of the signal ~ becomes high. When the wheel speed Vw has exceeded the first reference wheel speed Vrl at an instant t5, the level of the signal Sl becomes low.
When the value of the wheel acceleration Vw has become smaller than the speedup reference value ~VwO at an instant t6, the level of the signal becomes low, and the outlet valve VoQ is opene'd.
This causes the hydraulic braking pressure Pb to increase.
When the wheel acceleration Vw has become lower than the reference wheel deceleration -VwO (Vw <
-VwO) at an instant t7, the level of the signal ~
becomes high. When the wheel speed Vw has become lower than the first reference wheel speed Vr (Vw < Vrl) at an instant t8, the level of the signal Sl becomes high. Consequently, the level of an output from the AND-gate 35 becomes high to cause the inlet valve ViQ to be closed, and the outlet VoQ to be opened, the hydraulic braking pressure Pb beginning to decrease. When the wheel speed Vw has become lower than the second reference wheel speed Vr2 (Vw ~ Vr2) at an instant tgt so that the pos-sibility that the wheels are locked has become large, the level of the signal S2 becomes high. ~
~/ _ When the wheel acceleration Vw has become higher than the reference wheel deceleration -Vw at an instant t1o, the level of the signal ~ becomes low, and the hydraulic braking pressure Pb further decreases, the wheel speed Vw beginning to increase. When the wheel accelexation Vw has exceeded the speedup reference level +VwO at an instant tll, the level of the signal ~ becomes high, and the level of an output from the AND-gate 40 low. Since the level of an output from the AND-gate 35 is low duriny this time, the level of an output from the OR-gate 42 is lcw. Accordingly, exGitation is removed from solenoid 38, and the inlet valve ViQ is closed. As a result, the hydraulic braking pressure Pb is maintained in a constant level.
When the wheel speed Vw has exceeded the second reference wheel speed Vr2 at an instant tl2, the level of the signal S2 becomes low. When the wheel speed Vw has exceeded the first reference wheel speed Vrl at an instant tl3, the level of the signal Sl becomes low but the hydraulic braking pressure Pb is maintained in a substantially constant level to thereby enable the prevention of the locking of the wheels. When the wheel acceleration Vw has become lower than the speedup reference level -~VwO at an instance tl4, the level of the signal ~ becomes low, so that the outlet valve VoQ is ;4j ~
to be opened. Consequently, the hydraulic braking pressure Pb starts increasing.
When the wheel acceleration Vw has become lower than the reference wheel deceleration -VwO at an instant tl5, the level of the signal ~ becomes high.
When the-wheel speed Vw has become lower than the first reference wheel speed Vrl at the following instant tl6, so that the level of the signal Sl becomes high, the inlet valve ViQ is opened, and the outlet valve VoQ
closed. Consequently, the hydraulic braking pressure Pb starts decreasing, When the wheel acceleration Vw has exceeded the reference wheel deceleration -VwO at an instant tl7, the level of the signal ~ becomes low to cause the outlet valve VoQ to be opened, so that the hydraulic braking pressure is maintained in a constant level.
When the wheel acceleration Vw has exceeded the speedup reference level +VwO at an instant tl8, the level of the signal ~ becomes high. 'When the wheel speed Vw has exceeded the first reference wheel speed Vrl at an instant tlg, the level of the signal Sl becomes low. When the wheel acceleration Vw has become lower than the speedup reference level +Vw at an instant t20, the level of the signal ~ becomes low. As a result, the outlet valve VoQ is opened, and the hydraulic braking pressure Pb starts decreasing.
The vehicle speed then decreases with the wheels not locked, as the above-described operations are carried out in the same manner.
In the above embodiment, the level of ~he signal Sl is decreased to a low level forcibly by the relay switch 50. Only the braking pressure-lessening signal alone may be made ineffective by the signal E alone.
The delay circuit 49 may be omitted to drive the relay switch 50 directly by the signal E.
Fig, 6 shows a second embodiment of the present invention, in which larger and smaller values (Vrl 1 Vrl~2) are set as first reference wheel speeds Vrl 1 Vrl 2. In order to prevent the braking system from being operated erroneously on a rough road during the estimation of the vehicle speed Vr, a charging resistor 51 for a capacitor 45 is inserted between a diode 44 and the capacitor 45, and a constant current discharge circuit 46 is connected to a common contact of a relay switch 52, one independent contact of the relay switch 52 being connected to an arithmetic circuit 53, the other independent contact thereof being connected to an arithmetic circuit 54. One arithmetic circuit 53 is adapted to compute Vrl ~=Vr~(l~~l 1)~ and the other arithmetic circuit 54 to compute Vrl 2=Vr~ 2)~
The reference slip ratios ~1-1' A1_2 is set to ~1-1 > ~ and Vrl_l ~ Vrl_2. The relay switch 52 is adapted to be operated by the signal E outputted when a rough road is detected. While the vehicle is running on a rough road, the relay switch 52 is connected to the arithmetic circuit 53 as shown in Fig. 6.
Therefore, when Vw < Vrl-l or ~1-1 g running on a rough road, the signal Sl is outputted from the judgement circuit 33, and the number of outputting this signal decreases. Accordingly, a rate of decrease in the hydraulic braking pressure is reduced, and a decrease in the braking efficiency can be prevented.
Fig. 7 shows a third embodiment of the present invention, and the parts of this embodiment which correspond to those of the embodiment of Fig. 2 are designated by the same reference numerals. Moreover, the construction of the control means for the left and right wheel brakes and that of the control means for the left and right front wheels are completely the same, and, therefore, the embodiment of Fig. 7 wlll be described with only the parts of, for example, the left and right rear wheel brakes shown by reference numerals.
The left and right wheel detectors 34Q, 34r are connected to one contact of a relay switch ~ through 1~5~
diodes 61,62 which CQnStituteS a high select circuit s4, and the other contact of this relay switch 63 to a judgement circuit 33.
A relay coil 55 for driving the relay switch 63 is provided between an output terminal of the ~udgement circuit 33, from which a signal E is outputted, and the ground. When the level of the signal E becomes high to cause the rslay coil 55 to be turned on, the relay switch 63 is turned on.
While the vehicle runs on a rough road, the rel~y switch 63 is turned on, an signals from the wheel detectors 34 , 34r are inputted into the high select circuit 6~. As a result, in the high select circuit 64, the highest one of the values of the two wheel speeds is selected, and the selected value is inputted into the judgement circuit 33, in which this selected wheel speed is processed as the actual wheel speed to ~udge the locking state of the wheels. There is substantially no possibility that the wheels are erroneously ~udged to be nearly locked when there is no actual possibility of wheel locking, unless the phases of the rotation of the left and right wheels on their rotational speeds substantially agree with each other.
Accordingly, the rate at which the signal for reducing the hydraulic braking pressure during travelling on a rough road is outputted from the control means 32 decreases, so that an erroneous operation of the braking system can be prevented almost completely.
1~54~
In this embodiment, the highest wheel speed of the two wheel speeds at each axle is determined as the actual wheel speed at the axle, and a control operation is carried out on the basis thereof. Therefore, while the vehicle runs on a rough road, there is substantial-ly no possibility that the wheels are judged to be locked, unless the phases of the wheels agree with each other. Accordingly, while the vehicle runs on a rough road, the hydraulic braking pressure does not de-crease unnecessarily, so that the braking efficiency can be maintained at a high level.
. . .
When a braklng operat10n Is carrled out whlle a vehlcle provided wlth a conventlonal antl-lock braklng system runs on a rough road, the braklng force applled to the w~eel varles due to the varlatlons In the ground-contacting condltlons thereof even lf the hydraullc bra~lng pressure Is constant. Consequently. the suspension of the vehlcle Is vlbrated longltudlnally. Thls causes the vehlcle speed to pulsaie li1 some cases. When such a pulsatlon of the vehlcle speed occurs, the control means Judges erroneously that there Is the posslblllty that the whee Is locked, even when there Is no suc'~ a posslblllty In practlce As a result, the hydrau~lc control clrcult Is energlzed so as to reduce the hydraullc braklng pressure. so that the brak1ng dls-tance Increases In some cases.
The present Inventlon provldes an antl-lock braklng system capable of preventlng a braklng dlstance from Increaslng whlle the vehlcle runs on a rough road.
In a flrst aspect of the present Inventlon, the control means Is constructed so that It has the functlons of detectlng the condltlon of the road surface on whlch the vehlcle runs, and reduclng the ra e of decrease In the hydraullc braklng pressure when thls means Judges tllat the condltlon of the road surface Is bad.
The present Inventlon also provldes an antl-lock brak-lng system capable of detecting a bad condltlon of the road sur-A
face easlly. and preventlng the braklng dlstance from Increaslng whlle the vehlcle runs on the bad road surface.
In a second aspect of the present Inventlon, the con-trol means Is constructed so that It has the functlons of Judglngthe road surface, on whlch the vehlcle rUns, to be bad when the fluctuatlon frequency of the vehlcle speed Is not lower than a predetermlned level, and so that the control means works so as to reduce the rate of decrease In the hydraullc braklng pressure when the road surface Is Judged to be In a bad condltlon.
Owlng to the speclfled constructlons as mentloned above. an unnecessary reductlon of the hydraullc braklng pressure can be prevented even If the control means Judges erroneously 1~ that the wheel Is about to be locked due to the varlatlons In the ground-contactlng condltlon of the wheel runnlng on a rough road surface, whereby the braklng effIclency does not decrease whlle the vehlcle runs on a rough road.
The present Inventlon Is caPable of detectlng automatl-cally wlth ease a slgnal Indlcatlng that the wheel of the vehlcle Is runnlng on a rough road surface.
Thus, accordlng to the present Inventlon there Is pro-vlded an antl-locklng braklng system for a vehlcle Includlng a palr of wheels, comprlslng wheel brakes for sald respectlve wheels; a palr of wheel detectors for detectlng rotatlonal speeds of the respectlve wheels and outputtlng slgnals Indlcatlve of the wheel speeds; hydraullc control clrcults for controlllng the sup-0 ply of hydraullc braklng pressUres to the respectlve wheel brakesfor antl-lock operatlons; and control means for placlng sald hydraullc control clrcults In operatlve state so as to control the hydraullc braklng pressures applled to the wheel brakes, on the basls of the slgnals from sald wheel detectors, when the wheels are about to be locked; whereln sald control means Includes a detectlon means for detectlng the condltlon of a road ~A
surface on which t~e vehlcle travels, and when sald detectlon means detects that the vehlcle Is travelllng on a rough road sur-face, the slgnals from sald wheel detectors are subJect to hlgh-selectlon and only the hlghest wheel speed value of the two wheel speed sl~nals Is employed ~y sald control means for operatlon of the hydraullc control clrcu~ts, whereas when sald detectlon means detects that the vehlcle Is travelllng on a regular road surface, sald slgnals from the respectlve wheel detectors are employed by sald control means for Independent operatlon of thelr respectlve tO hydraullc control clrcults. Sultably sald detectlon means Judges the vehlcle to be travelllng on sald rough road surface by detectIng the fluctuatlng frequency of a wheel sPeed belng not less than a predetermlned level. Deslrably when sald detectlon means detects that the vehlcle Is travelllng on sald rough road surface, sald control means operates to lessen the chance that the wheel brakes are subJect to antl-lock operatlon by the hydraullc control clrcult.
Advantageous features of the Inventlon wlll become apparent from the followlng descrlptlon of the preferred embodl-ments taken In conJunctlon wlth the acc~mpanylng drawlngs, In whlch:-Flg.s 1-5 show a flrst embodIment of the present Inven-tlon; whereln:
Fl~. 1 Is a dlagram of a hydraullc control clrcult;
Flg. 2 Is a slmpllfled clrcult dlagram showlng the con-structlon of a control means;
Flg. 3 Is a dlagram of an electrlc clrcult for use Inestlmatlng a vehlcle speed;
3~ Flg. 4 Is a dlagram showlng the operatlonal character-lstlcs of the electrlc clrcult of Flg. 3; and Fig. 5 Is a characterlstlc d I agram showlng the embodl-ment In antl-lock operatlon.
Flg. 6 Is a dlagram of an electrlc clrcult for use In estlmatlng a vehlcle speed In a second embodlment of the present Inventlon; and Flg. 7 Is a slmpllfled clrcult dlagram showlng the con-structlon of a control means In a thlrd embodlment of the present Inventlon.
ZO
~A
~3................................. ~ (J1 First, referring to Fig~ 1 showing a first embodi-ment of the present invention, a brake pedal 1 is operatively connected to a master cylinder M. When a driver steps on this brake pedal 1, the master cylinder M generates a hydraulic pressure in an oil passage 2. This oil passage 2 is connected to a hydraulic control circuit 3. A hydraulic braking pressure in accordance with the hydraulic pressure in the oil passage 2 is outputted from the hydraulic control circuit 3.
Wheel brakes are attached to the left and right front wheels and left and right rear wheels of a vehicle. The hydraulic braking pressure i5 supplied from the hydraulic control circuits 3 to these wheel brakes. The construction of the wheel brakes attached to these left and right front wheels and left and right rear wheels, and the construction of the hy-draulic control circuits 3 for supplying a hydraulic braking pressure to the wheel brakes are basically identical to one another. Therefore, only the wheel brake BQ for the left rear wheel and the wheel brake Br for the right rear wheel, and the hydraulic con-trol circuit 3 which is associated with these brakes B~, Br will now be described.
Oil passages 5, 6 extending from the hydraulic control circuit 3 communicate with the hydraulic braking pressure chambers 4 for the wheel brakes BQ, Br. When a hydraulic braking pressure is supplied to each braking pressure chamber 4, pistons 7, 8 are moved away from each other, so that brake shoes 9, 10 come into contact with a brake drum (not shown~, respectively, to generate a braking torque.
When the hydraulic braking pressure in the hydraulic braking pressure chamber 4 is too high, the braking torque generated between the brake shoes and brake drum becomes too high, so that the wheels are locked. In order to prevent this, when the wheels are about to be locked, the hydraulic braking pressure is reduced by the hydraulic control circuit 3, so that the locking of the wheels does not occur.
The hydraulic control circuit 3 is provided with modulators 11, 12 corresponding to the wheel brakes BQ, Br. Since these modulators 11, 1~ have the basically same construction, the construction of one modulator 11 alone will be described in detail.
The modulator 11 is provided with a cylinder 14 closed at both ends thereof and having a partition 13 at an intermediate portion of the interior thereof, and a rod 17 having pistons 15, 16 at both ends ~ thereof and penetrating through the partition 13 jA axiàlly and slidably at the portion thereof which is between the pistons 15, i6. The portion of the interior of the cylinder 14 which is between the partition 13 and one piston 15 is formed as a primarv hydraulic braking pressure chamber 18, which com-municates with the master cylinder M via oil passage 2. The portion of the interior of the cylinder 14 which is between the partition 13 and the other piston 16 is formed as secondary hydraulic braking pressure chamber 19, which communicates with the hydraulic braking pressure chamber 4 for the wheel brake BQ via the oil passage 5. An anti-lock hy-draulic control chamber 20 is formed between one end wall of the cylinder 14 and the piston 15, and a hydraulic discharge chamber 21 between the other i end wall of the cylinder 14 and the other piston 16, the hydraulic discharge chamber 21 communicating with a reservoir R in the master cylinder M. A
spring 22 urging the piston 16 away from the parti-tion 13 is provided in the secondary hydraulic brak-ing pressure chamber 19, and a spring 23 urging the piston 15 toward the partition 13 is provided in the anti-lock hydraulic control chamber 20.
An oil passage 24 is connected to the anti-lock ~5~
hydraulic control chamber 20. This oil passage 2~
is also connected to a hydraulic pump P via a nor-mally-closed inlet valve ViQ, and to an oil tank T
via a normally-opened outlet valve VoQ. An accumu-lator Ac is connected between the inlet valve ViQ
and hydraulic pump P.
Also, in the other modulator 12, a primary hydraulic braking pressure chamber 26 communi-cates with the master cylinder M, a secondary hy-draulic braking pressure chamber 27 with the wheel brake Br via passage 6, and a hydraulic discharge chamber 28 with the reservoir R. An anti-lock hydraulic control chamber 29 is connected to the hydraulic pump P via a normally-closed inlet valve Vir, and to the oil tank T via a normally-opened outlet valve Vor.
The inlet valves ViQ, Vir and outlet valves VoQ, Vor are solenoid valves, the opening and closing of them are controlled by a control means 32.
When the inlet valves ViQ, Vir are closed with the outlet valves VoQ, Vor opened, the anti-lock hydraulic control chambers 20, 29 are in communication with the oil tank T. When the brake pedal 1 is stepped to supply a hydraulic pressure from the master cylinder M to the primary hydraulic braking 1~'54~
pressure chambers 18, 26, the volumes of the secondary hydraulic braking pressure chambers 19, 27 decrease, and a hydraulic braking pressure cor-responding to the hydraulic pressure fed from the mas-ter cylinder M is supplied to the hydraulic braking pressure chambers 4 in the wheel brakes BQ, Br.
Accordingly, the braking torque increases freely in conformity with the driverls braking operation.
When the outlet valves VoQ, Vor are closed with the inlet valves ViQ, Vir closed~ the control oil in the anti-lock hydraulic control chambers 20, 29 is trapped therein. Consequently, the volumes of the secondary hydraulic braking pressure chambers 19, 27 are invariable whether or not the hydraulic pressure supplied to the primary hydraulic braking pressure chambers 18, 26 increases or decreases.
Hence, the braking torque during braking operation is maintained at a predetermined level irrespective of the driver's braking operation. Such opera-tional condition occurs when there is the possibility that the wheels are locked.
When the inlet valves ViQ, Vir are opened with the outlet valves VoQ, Vor closed, the anti-lock hydraulic control pressure is supplied to the anti-lock hydraulic pressure chambers 20, 29. Therefore, _ g _ l~t~
the volumes of the secondary hydraulic braking pressure chambers 19, 27 increase in spite of the fact that the hydraulic pressure from the master cy'inder M is applied to the primary hydraulic braking pressure chambers 18, 26, whereby the hydra~lic pressure in the braking oil chambers 4 in the wheel brakes BQ, Br decreases to lower the braking torque. Accordingly, if the inlet valves ViQ, Vir are opened with the outlet valves VoQ, Vor closed when the wheels are about to be locked, the locking of the wheels can be prevented.
The construction of a control means 32 will now be described with reference to Fig. 2. Since the construction for controlling the inlet valve ViQ and outlet valve VoQ which correspond to one wheel brake sQ, and that for controlling the inlet valve Vir and outlet valve Vor which correspond to the other wheel brake Br are basically identical, only the former construction will be described.
The control means 32 is provided with a judge-ment circuit 33 consisting of a microcomputer, for example, ar~
adapted to determine whether the wheels are locked or not. The judgement circuit outputs on the basis of this determination a signal for opening or closing the inlet valve ViQ and outlet valve VoQ.
The conditions constituting a judgement basis for determining to output a signal for carrying out an anti-lock control operation will now be discussed.
In general, the following four systems (a)-(d) have been proposed.
(a) A system in which a signal ~ is outputted when Vw the formula, wheel acceleration ~K referenGe wheel deceleration - VWO, is established, to lessen the braking pressure.
(b) A system in which a signal Sl is outputted when the formula, wheel speed Vw < first reference wheel speed Vrl, is established, to lessen the hydraulic braking pressure. In this case, Vrl = Vv ~
~ ic e, wherein Vv is a ~:hcc~ speed; and ~1 a suitable slip ratio of the wheel. Therefore, if the slip ratio is e~pressed by ~, Vw < Vrl has the same meaning as ~ ~ ~1' and, when Vw < Vrl or ~ > ~1 is establsihed, the signal 51 is outputted.
(c) A system in which the hydraulic braking pres-sure is lessened when either (a) or (b) above is established.
(d) A system in which the hydraulic braking pres-sure is lessened when (a) and (b) above is established concurrently.
In the system (a) above, the reference wheel deceleration - VwO is set to a level, usually, for example, -2.0 ~ 1.2G, which are not obtained during a braking operation carried out when there is no possibility that the locking of the wheels occurs.
However, according to this system, a wheel aecelera-tion of around -1.0 ~ -0.5G occurs in some cases during a braking operation carried out on a snow-covered xoad or a frozen road, and a signal for lessening the hydraulic braking pressure is not outputted in spite of the fact that the wheels are locked in the latter part of a braking operation.
While the vehicle runs on a rough road, the wheel acceleration Vw pulsates finely even druing a regular braking operation, and a signal ~ is outputted even when there is no possibility that the wheels are locked, to cause the braking efficiency to decrease.
In the system (b), when the wheel speed Vw is increasing, it is judged that the hydraulic braking pressure has been lessened sufficiently even if the slip ratio ~ is high, i.e., even if the signal Sl is outputted. The hydraulic braking pressure is necessarily lessened during this time as well, so that the braking efficiency decreases.
It is clear that the system (c) has the faults of the systems (a) and ~b).
Finally, in the system (d), the problem of a decrease in the braking efficiency during the driv-ing on a rough road, and the problem of a decrease in the braking efficiency due to a hydraulic braking pressure-lessening operation carried out while the wheel speed Vw increases are solved. Furthermore, if the reference wheel deceleration- VwO is set in the level in the range of wheel deceleration occurring during a braking operation carried out while the vehicle runs on a regular road surface, for example, -1.0 ~ OG, and preferably -0.3 ~ -0.6G, the locked wheels can be detected even when the wheel deceleration is -1.0 ~ -0.5G in a braking operation carried out on a snow-covered road or a frozen road, and the hydraulic braking pressure can thereby be lessened.
In the judgement circuit 33, a signal corre-sponding to a wheel speed Vw is inputted from the ehicle speed detector 34, and this wheel speed h~l Vw and a Y~b~e~e acceleration Vw, which is computed on the basis of the wheel speed Vw, are compared with a first reference wheel speed Vrland a reference wheel deceleration - Vw, respectively.
When Vw < - VwO and Vw < Vr1 are established, high-level signals ~, Sl are outputted from the judgement i circuit 33. These signals ~, Sl are inputted into an AND-gate 35, and, when both of these signals are in high levels, a transistor 36 is turned on, and a solenoid 38 is excited, the inlet valve ViQ being opened. When a high-level signal Sl is outputted, a transistor 37 is turned on, and a solenoid 39 is excited, the outlet valve VoQ being closed.
When the braking torque starts being reduced by the signals ~, Sl as mentioned above, the vehicle speed is still decreasing. At this time, the braking torque is still higher than the driving torque on the road surface, and the possibility of locking of the wheels has not yet been completely removed.
However, the system generally has an operational delay of around lOms. Accordingly, the hydraulic braking force :Ls further lessened after the braking pressure-lessening signal has been extinguished, so that this system generally enables a good effect to be obtained. However, in some cases, the braking pressure is not lessened sufficiently under certain conditions of the road surface to cause the wheel speed to vary in the locking direction. In order to prevent such a phenomenon, a braking pressure-lessening signal may be generated, when ~ > ~1' until the wheel speed Vw has started increasing 1 2 ~
certainly. However, in spite of the fact that a control operation can usually be carried out satis-factorily even when the generation of the braking pressure-lessening signal is stopped upon the A establishment of Vw > ~ , this signal is retained until Vw > 0 has been attained. This causes the braking torque to be lessened excessively. However, this poses no problems in practice in the wheels having a small braking load distribution.
A second reference wheel speed Vr2 which corresponds to a second reference slip ratio, at which A2 > Al is now set. Only when Vw < Vr2, i.e.
A > A2, so that the possibility that the wheels are locked has increased, the braking pressure-lessening signal is retained until the vehicle speed Vw has started increasing. In the judgement circuit 33, it is judged whether or not Vw < Vr2 or A > A2, and, when the conditions are satisfied, a signal S2 is outputted. In order to judge that the wheel speed Vw is increasing, a speedup reference value ~ Vw0 is set, and, when Vw > +Vw0, a signal ~ is outputted.
The signal S2 is inputted into one input ter-minal of an AND-gate 40 and an OR-gate 41. The signal ~ is inputted into the OR-gate 41, and in-verted and inputted into the AND-gate 40. The signal Sl is also inputted into ~e OR-gate 41, and an output fr~ ~e OR-gate 41 is applied to the base of transistor 37.
Outputs from both AND-~ates 35, 4~ are inputted into OR-yate 42 which in tu~n feeds an output to the base of transistor 36.
According to the control means 32, the level of any one of the signals Sl, ~, S2 has become high, the transistor 37 is turned on, the outlet valve VoQ is closed, and when the levels of both of the signals ~, Sl are high, or when the level of the signal ~ is high with that of the signal ~ low, the inlet valve ViQ is opened.
A method of setting first and second reference wheel speeds Vrl, Vr2 will now be described. These wheel speeds are determined ideally by detecting a vehicle speed Vv, and making calculations in accordance with the following formulae taking suitable reference slip ratios ~ 2 into consideration.
Vrl = Vv (1~
Vr2 = Vv (1-~2) However, no practical means for detecting a vehicle speed Vv has been found out up to the present time. Therefore, a system,for estimating a tentative vehicle speed Vr on the basis of,the condition of variations in the wheel speed Vw is generally used.
A basic circuit of this system is shown in Fig. 3.
Referring to Fig. 3, a wheel speed Vw is inputted into an input terminal 43, which is con-nected to an output terminal 47 through an ideal diode 44, a memory capacitor 45 and a constant current discharge circuit 46, and a vehicle speed Vr is outputted from this output terminal 47. By this system, as shown in Fig. 4, a peak value of the wheel speed Vw in an anti-lock operation is set to a level in the vicinity of the vehicle speed Vv with valleys of the wheel speed Vw connected with a predetermined gradient Gr, to estimate the tenta-tive vehicle speed Vr.
While a vehicle runs on a rough road, the wheel speed Vw pulsates, so that it is judged erroneously that the wheels are about to be locked, to cause the hydraulic braking pressure to decrease unnecessarily, and the braking efficiency to lower.
In ordex to prevent this, the control means 32 has the function of reducing the rate of decrease in the braking pressure when it is judged that the wheels are locked while the vehicle runs on a rou~h road.
The present inventor has experimentally ascer-tained that a pulsation frequency f of the wheel speed Vw during a braking operation carried out on a rough road is substantially equal to a natural frequency nO (generally 15-20Hz) of a suspension.
On the other hand, a fluctuating ~requency nm f the wheel speed ~w during a normal operation of an anti-lock braking system is generally not more than 10~lz. In the judgement circuit 33, it is judged that, when f > nm, the vehi~le is running on a rough road, and a signal E is outputted therefrom.
This signal E is inputted into a delay circuit 49. The terminal, from which the signal Sl is out-putted, of the judgement circuit 33, is grounded through a relay switch 50. The delay circuit 49 is adapted to output a signal for turning on a relay switch 5C when a high-level rough road detecting signal E has been inputted thereinto, and keep out-putting the same signal or a predetermined period of time, for example, 100ms after the level of the signal E has become low.
c.
When Vw ~ Vrl or ~ > ~1 has been established while the vehicle runs on a rough road, so that the judgement circuit 33 judges that the wheels are about to be locked, to output the high-level signal Sl, the level of the sign~l Sl is rendered low forcibly.
As a result, the rate of decrease in the hy-draulic braking pressure during travelling on a ~'Z5~
rough road decreases. Consequentl~, the hydraulic braking pressure does not decrease unnecessarily, so that a decrease in the braking efficiency can be prevented.
The operation of this embodiment will now be described with reference to Fig. 5. Fig. 5 shows an e~ample of a mode of operation of this anti-lock braking system. The lateral axis of this figure shows the time after the starting of a braking operation, and the vertical axis thereof a vehicle speed Vv, a wheel speed Vw and a first reference wheel speed Vrl and a second reference wheel speed Vr2 in the uppermost position, a wheel acceleration Vw, a speedup reference value +VwO and a reference wheel deceleration -VwO in the position under the mentioned position, signals ~, ~, Sl, S2 and the operational conditions of the solenoids 38, 39 in the position under the second-mentioned position, and a hydraulic braking pressure Pb in the lowermost position.
Immediately after a braking operation has been started at an instant t=O, the levels of the signals , Sl, S2 are low. The hydraulic braking pres-sure Pb increases gradually, and the wheel speed Vw and wheel acceleration Vw decrease gradually at ~5~
the same time.
When the wheel acceleration Vw has become lower than the reference wheel deceleration -Vw0 (Vw <
-Vw0) at an instant t1, the level of the signal ~
becomes high but the signal Sl remains to be in a low level since the level of the wheel speed Vw is higher than that of the first reference wheel speed Vrl at this time. Accordingly, the hydraulic brak-ing pressure Pb con inues to increase, and the wheel speed and wheel acceleration Vw to decrease.
When the wheel speed Vw has become lower than the first reference wheel speed Vrl at an instant t2, the level of the signal Sl becomes high, and the level of an output from the AND-gate 35 becomes high. Consequently, the levels of outputs from the OR-gates 42, 41 become high. As a result, the solenoids 38, 39 are excited to cause the inlet valve ViQ to be opened, and the outlet valve VoQ to be closed. The hydraulic braking pressure Pb then starts decreasing, and the wheel acceleration Vw resumes increasing. During this time, the wheel speed Vw continues to decrease.
When the wheel acceleration Vw has become higher than the reference wheel deceleration -Vw0 (Vw > -Vw0) at an instant t3, the level of the signal ~sLa~l ~ becomes low, and the level of an output from the AND-gate 35 low as well accordingly. Consequently, the solenoid 38 for the inlet valve ViQ is deexcited, and the inlet valve ViQ is closed. This enables the braking pressure Pb to be maintained in a con-stant level. Namely, the braking torque is main-tained in a substantially constant level. As a result, the wheel speed Vw starts increasing.
When the level of the wheel acceleration Vw has become higher than the speedup reference level +VwO
(Vw > +VwO) at an instant t4, the leve] of the signal ~ becomes high. When the wheel speed Vw has exceeded the first reference wheel speed Vrl at an instant t5, the level of the signal Sl becomes low.
When the value of the wheel acceleration Vw has become smaller than the speedup reference value ~VwO at an instant t6, the level of the signal becomes low, and the outlet valve VoQ is opene'd.
This causes the hydraulic braking pressure Pb to increase.
When the wheel acceleration Vw has become lower than the reference wheel deceleration -VwO (Vw <
-VwO) at an instant t7, the level of the signal ~
becomes high. When the wheel speed Vw has become lower than the first reference wheel speed Vr (Vw < Vrl) at an instant t8, the level of the signal Sl becomes high. Consequently, the level of an output from the AND-gate 35 becomes high to cause the inlet valve ViQ to be closed, and the outlet VoQ to be opened, the hydraulic braking pressure Pb beginning to decrease. When the wheel speed Vw has become lower than the second reference wheel speed Vr2 (Vw ~ Vr2) at an instant tgt so that the pos-sibility that the wheels are locked has become large, the level of the signal S2 becomes high. ~
~/ _ When the wheel acceleration Vw has become higher than the reference wheel deceleration -Vw at an instant t1o, the level of the signal ~ becomes low, and the hydraulic braking pressure Pb further decreases, the wheel speed Vw beginning to increase. When the wheel accelexation Vw has exceeded the speedup reference level +VwO at an instant tll, the level of the signal ~ becomes high, and the level of an output from the AND-gate 40 low. Since the level of an output from the AND-gate 35 is low duriny this time, the level of an output from the OR-gate 42 is lcw. Accordingly, exGitation is removed from solenoid 38, and the inlet valve ViQ is closed. As a result, the hydraulic braking pressure Pb is maintained in a constant level.
When the wheel speed Vw has exceeded the second reference wheel speed Vr2 at an instant tl2, the level of the signal S2 becomes low. When the wheel speed Vw has exceeded the first reference wheel speed Vrl at an instant tl3, the level of the signal Sl becomes low but the hydraulic braking pressure Pb is maintained in a substantially constant level to thereby enable the prevention of the locking of the wheels. When the wheel acceleration Vw has become lower than the speedup reference level -~VwO at an instance tl4, the level of the signal ~ becomes low, so that the outlet valve VoQ is ;4j ~
to be opened. Consequently, the hydraulic braking pressure Pb starts increasing.
When the wheel acceleration Vw has become lower than the reference wheel deceleration -VwO at an instant tl5, the level of the signal ~ becomes high.
When the-wheel speed Vw has become lower than the first reference wheel speed Vrl at the following instant tl6, so that the level of the signal Sl becomes high, the inlet valve ViQ is opened, and the outlet valve VoQ
closed. Consequently, the hydraulic braking pressure Pb starts decreasing, When the wheel acceleration Vw has exceeded the reference wheel deceleration -VwO at an instant tl7, the level of the signal ~ becomes low to cause the outlet valve VoQ to be opened, so that the hydraulic braking pressure is maintained in a constant level.
When the wheel acceleration Vw has exceeded the speedup reference level +VwO at an instant tl8, the level of the signal ~ becomes high. 'When the wheel speed Vw has exceeded the first reference wheel speed Vrl at an instant tlg, the level of the signal Sl becomes low. When the wheel acceleration Vw has become lower than the speedup reference level +Vw at an instant t20, the level of the signal ~ becomes low. As a result, the outlet valve VoQ is opened, and the hydraulic braking pressure Pb starts decreasing.
The vehicle speed then decreases with the wheels not locked, as the above-described operations are carried out in the same manner.
In the above embodiment, the level of ~he signal Sl is decreased to a low level forcibly by the relay switch 50. Only the braking pressure-lessening signal alone may be made ineffective by the signal E alone.
The delay circuit 49 may be omitted to drive the relay switch 50 directly by the signal E.
Fig, 6 shows a second embodiment of the present invention, in which larger and smaller values (Vrl 1 Vrl~2) are set as first reference wheel speeds Vrl 1 Vrl 2. In order to prevent the braking system from being operated erroneously on a rough road during the estimation of the vehicle speed Vr, a charging resistor 51 for a capacitor 45 is inserted between a diode 44 and the capacitor 45, and a constant current discharge circuit 46 is connected to a common contact of a relay switch 52, one independent contact of the relay switch 52 being connected to an arithmetic circuit 53, the other independent contact thereof being connected to an arithmetic circuit 54. One arithmetic circuit 53 is adapted to compute Vrl ~=Vr~(l~~l 1)~ and the other arithmetic circuit 54 to compute Vrl 2=Vr~ 2)~
The reference slip ratios ~1-1' A1_2 is set to ~1-1 > ~ and Vrl_l ~ Vrl_2. The relay switch 52 is adapted to be operated by the signal E outputted when a rough road is detected. While the vehicle is running on a rough road, the relay switch 52 is connected to the arithmetic circuit 53 as shown in Fig. 6.
Therefore, when Vw < Vrl-l or ~1-1 g running on a rough road, the signal Sl is outputted from the judgement circuit 33, and the number of outputting this signal decreases. Accordingly, a rate of decrease in the hydraulic braking pressure is reduced, and a decrease in the braking efficiency can be prevented.
Fig. 7 shows a third embodiment of the present invention, and the parts of this embodiment which correspond to those of the embodiment of Fig. 2 are designated by the same reference numerals. Moreover, the construction of the control means for the left and right wheel brakes and that of the control means for the left and right front wheels are completely the same, and, therefore, the embodiment of Fig. 7 wlll be described with only the parts of, for example, the left and right rear wheel brakes shown by reference numerals.
The left and right wheel detectors 34Q, 34r are connected to one contact of a relay switch ~ through 1~5~
diodes 61,62 which CQnStituteS a high select circuit s4, and the other contact of this relay switch 63 to a judgement circuit 33.
A relay coil 55 for driving the relay switch 63 is provided between an output terminal of the ~udgement circuit 33, from which a signal E is outputted, and the ground. When the level of the signal E becomes high to cause the rslay coil 55 to be turned on, the relay switch 63 is turned on.
While the vehicle runs on a rough road, the rel~y switch 63 is turned on, an signals from the wheel detectors 34 , 34r are inputted into the high select circuit 6~. As a result, in the high select circuit 64, the highest one of the values of the two wheel speeds is selected, and the selected value is inputted into the judgement circuit 33, in which this selected wheel speed is processed as the actual wheel speed to ~udge the locking state of the wheels. There is substantially no possibility that the wheels are erroneously ~udged to be nearly locked when there is no actual possibility of wheel locking, unless the phases of the rotation of the left and right wheels on their rotational speeds substantially agree with each other.
Accordingly, the rate at which the signal for reducing the hydraulic braking pressure during travelling on a rough road is outputted from the control means 32 decreases, so that an erroneous operation of the braking system can be prevented almost completely.
1~54~
In this embodiment, the highest wheel speed of the two wheel speeds at each axle is determined as the actual wheel speed at the axle, and a control operation is carried out on the basis thereof. Therefore, while the vehicle runs on a rough road, there is substantial-ly no possibility that the wheels are judged to be locked, unless the phases of the wheels agree with each other. Accordingly, while the vehicle runs on a rough road, the hydraulic braking pressure does not de-crease unnecessarily, so that the braking efficiency can be maintained at a high level.
. . .
Claims (3)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An anti-locking braking system for a vehicle including a pair of wheels comprising wheel brakes for said respective wheels; a pair of wheel detectors for detecting rota-tional speeds of the respective wheels and outputting signals indicative of the wheel speeds; hydraulic control circuits for controlling the supply of hydraulic braking pressures to the respective wheel brakes for anti-lock operations; and control means for placing said hydraulic control circuits in operative state so as to control the hydraulic braking pressures applied to the wheel brakes, on the basis of the signals from said wheel detectors. when the wheels are about to be locked; wherein said control means includes a detection means for detecting the condi-tion of a road surface on which the vehicle travels, and when said detection means detects that the vehicle is travelling on a rough road surface, the signals from said wheel detectors are subject to high-selection and only the highest wheel speed value of the two wheel speed signals is employed by said control means for operation of the hydraulic control circuits, whereas when said detection means detects that the vehicle is travelling on a regular road surface, said signals from the respective wheel detectors are employed by said control means for independent operation of their respective hydraulic control circuits.
2. An anti-lock braking system according to claim 1, wherein said detection means Judges the vehicle to be travelling on said rough road surface by detecting the fluctuating frequency of a wheel speed being not less than a predetermined level.
3. An anti-lock braking system according to claim 1, wherein when said detection means detects that the vehicle is travelling on said rough road surface, said control means oper-ates to lessen the chance that the wheel brakes are subject to anti-lock operation by the hydraulic control circuit.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP11208184A JPS60255558A (en) | 1984-05-31 | 1984-05-31 | Anti-locking brake device |
| JP112081/84 | 1984-05-31 | ||
| JP112083/84 | 1984-05-31 | ||
| JP11208384A JPS60255560A (en) | 1984-05-31 | 1984-05-31 | Anti-locking brake system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1254601A true CA1254601A (en) | 1989-05-23 |
Family
ID=26451318
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000482572A Expired CA1254601A (en) | 1984-05-31 | 1985-05-28 | Anti-lock braking system |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4668022A (en) |
| CA (1) | CA1254601A (en) |
| DE (1) | DE3519549A1 (en) |
| FR (1) | FR2565181B1 (en) |
| GB (1) | GB2162262B (en) |
Families Citing this family (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6133353A (en) * | 1984-07-25 | 1986-02-17 | Honda Motor Co Ltd | Antilock braking device |
| JPH06104444B2 (en) * | 1985-12-23 | 1994-12-21 | 日産自動車株式会社 | Wheel slip prevention device simulated vehicle speed generator |
| CA1312129C (en) | 1986-03-04 | 1992-12-29 | Honda Giken Kogyo Kabushiki Kaisha (Also Trading As Honda Motor Co., Ltd .) | Traction control system for controlling slip of a driving wheel of a vehicle |
| US4755945A (en) * | 1986-09-24 | 1988-07-05 | General Motors Corporation | Adaptive mode anti-lock brake controller |
| JP2564816B2 (en) * | 1987-03-11 | 1996-12-18 | トヨタ自動車株式会社 | Vehicle drive wheel brake control device |
| JP2516780B2 (en) * | 1987-04-17 | 1996-07-24 | 本田技研工業株式会社 | Bad road detection device when the vehicle is running |
| JP2631474B2 (en) * | 1987-07-16 | 1997-07-16 | 住友電気工業株式会社 | Anti-lock control device |
| US4824184A (en) * | 1987-12-11 | 1989-04-25 | General Motors Corporation | Antiblock brake controller with brake mode filter |
| JPH01168556A (en) * | 1987-12-22 | 1989-07-04 | Honda Motor Co Ltd | Antilock controlling method for vehicle |
| JP2688948B2 (en) * | 1988-10-26 | 1997-12-10 | 株式会社曙ブレーキ中央技術研究所 | Vehicle anti-lock control method |
| JPH0316863A (en) * | 1989-06-14 | 1991-01-24 | Akebono Brake Res & Dev Center Ltd | Antilock control method for vehicle |
| JPH0367771A (en) * | 1989-08-08 | 1991-03-22 | Akebono Brake Res & Dev Center Ltd | Anti-lock control method for vehicle |
| JP2964044B2 (en) * | 1990-06-29 | 1999-10-18 | マツダ株式会社 | Vehicle traction control device |
| JP3153232B2 (en) * | 1990-10-25 | 2001-04-03 | ボッシュブレーキシステム株式会社 | Anti-skid brake control method |
| JP2855985B2 (en) * | 1992-08-19 | 1999-02-10 | 三菱自動車工業株式会社 | Anti-skid brake device |
| US5627755A (en) * | 1994-09-09 | 1997-05-06 | Kelsey-Hayes Company | Method and system for detecting and compensating for rough roads in an anti-lock brake system |
| JP3138603B2 (en) * | 1994-11-30 | 2001-02-26 | 三菱電機株式会社 | Anti-skid control device |
| DE19544445B4 (en) * | 1995-11-29 | 2007-09-06 | Continental Teves Ag & Co. Ohg | Method for improving the control behavior of an ABS for all-terrain vehicles |
| DE19601529A1 (en) * | 1996-01-17 | 1997-07-24 | Teves Gmbh Alfred | Process for improving the control behavior of an ABS in an off-road driving situation |
| US8327697B2 (en) * | 2009-10-15 | 2012-12-11 | Caterpillar Inc. | Wheel speed sensing system and method |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3554612A (en) * | 1968-08-21 | 1971-01-12 | Gen Motors Corp | Antilock brake control |
| US3727992A (en) * | 1971-03-15 | 1973-04-17 | Gen Motors Corp | Anti-lock brake control system |
| GB1405413A (en) * | 1971-10-22 | 1975-09-10 | Lucas Electrical Co Ltd | Braking systems for vehicles |
| US3843207A (en) * | 1972-06-02 | 1974-10-22 | Borg Warner | Control system regulated braking arrangement |
| GB1439928A (en) * | 1972-07-14 | 1976-06-16 | Lucas Electrical Ltd | Road vehicle anti-skid braking systems |
| US3802749A (en) * | 1973-05-04 | 1974-04-09 | Bendix Corp | Adaptive braking system control wheel selection by velocity comparison |
| DE2333126C3 (en) * | 1973-06-29 | 1981-05-21 | Wabco Fahrzeugbremsen Gmbh, 3000 Hannover | Anti-lock system |
| DE2706278A1 (en) * | 1977-02-15 | 1978-08-17 | Bosch Gmbh Robert | ANTI-LOCK CONTROL SYSTEM |
| DE2726738C2 (en) * | 1977-06-14 | 1988-03-24 | Wabco Westinghouse Fahrzeugbremsen GmbH, 3000 Hannover | Circuit arrangement for regulating the brake pressure in anti-lock vehicle brake systems |
| DE3026254A1 (en) * | 1980-07-11 | 1982-02-11 | Wabco Fahrzeugbremsen Gmbh, 3000 Hannover | ANTI-BLOCKING SYSTEM |
-
1985
- 1985-05-28 CA CA000482572A patent/CA1254601A/en not_active Expired
- 1985-05-29 US US06/739,267 patent/US4668022A/en not_active Expired - Lifetime
- 1985-05-30 GB GB08513592A patent/GB2162262B/en not_active Expired
- 1985-05-31 FR FR858508229A patent/FR2565181B1/en not_active Expired - Fee Related
- 1985-05-31 DE DE19853519549 patent/DE3519549A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FR2565181A1 (en) | 1985-12-06 |
| FR2565181B1 (en) | 1992-06-19 |
| GB2162262B (en) | 1988-05-25 |
| US4668022A (en) | 1987-05-26 |
| GB8513592D0 (en) | 1985-07-03 |
| DE3519549C2 (en) | 1990-01-11 |
| GB2162262A (en) | 1986-01-29 |
| DE3519549A1 (en) | 1985-12-05 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |