US 3576350 A
Description (OCR text may contain errors)
United StatesPatent  lnventor Lester J. Larsen South Bend, Ind. 211 Appl. No. 756,259  Filed Aug. 29, 1968  Patented Apr. 27, 1971  Assignee The Bendix Corporation  ANTI'SKID SYSTEM 5 Claim, 10 Drawing Figs.
 US. Cl 303/21, 188/ 18], 303/6, 303/22  Int. Cl B60t 8/08, B60t 8/26  Field oiSearch 303/6, 6 (C),2l,22,24;183/181  References Cited UNITED STATES PATENTS 3,995,522 6/1963 Packeret a1. 303/21 H I I 200 3,479,094 1 1/ 1969 Chovings 303/21X 3,486,800 12/1969 Ayers 303/21 1,926,296 9/ 1 933 Merchie 303/21X 2,088,185 7/1937 Borde 303/21 2,181,161 11/1939 Wolf 303/21UX 3,093,422 6/1963 Packer et a1 303/21 3,443,842 5/1969 Pier 303/22X Pn'rfiary Examiner-Mi1ton Buchler Assistant Examiner-John J. McLaughlin Attomeys-Richard G. Geib and Plante, Arens, Hartz and OBrien ABSTRACT: A means to regulate hydraulic system pressure based upon a function of the work produced by one set of actuators and having a device to monitor the pressure from said means to another set of actuators as a function of the comparison of their work required with the work done by the one set of actuators.
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WESSMME? ATTORNEY PATENTEU M27197! 3576350 Y SHEET UF 6 /6 m we M2 INVENTOR LESTER J- LABSEN ATTORNEY PATENTED m Re zsn 3578350 sum 5 or 6 v m I .96 -32lfl$933d INVENTOR LESTER J. LARSEN BY i ATTORNEY ANTI-SKID SYSTEM SUMMARY In the development of antiskid systems, it has been shown that maximum benefits of (l) retained steerability, (2) retained directional stability, and (3) reduced stopping distances as compared to locked wheel stopping distances are obtainable by systems which affect the braking of all four wheels individually in response to a sensed performance characteristic of the respective wheel which is being controlled. Such a system is very expensive in that it requires four wheel characteristics sensors, four brake pressure modulating devices, and four channels of control logic. In a first attempt to reduce the cost and complexity of such a system, it has been shown to be practical to combine the control of the two rear-axle mounted wheels into a single control channel using a single brake pressure modulator while continuing to control the front wheels individually. Initial efforts in this direction also involved the use of a single sensor mounted on the vehicle drive shaft. These efforts failed because the derived signals were not truly indicative of actual wheel performance because of the presence of the differential gear mechanism.
A successful rear-axle antiskid control has been developed. This system involves the use of individual wheel sensors and a single logic and control channel which selects that wheel indication which is provided by the wheel operating at the lowest speed. An antiskid control of this character, in effect, is regulating the braking effort in proportion to the lowest coefi'rcient road surface contacted by either one of the wheels of the respective axle. Such systems are referred to as select low systems. Due to factors which need not be explained in relation to the current invention, such systems are capable of showing improved stopping distances under most circumstances.
OBJECTS In the present invention the inventor has attempted to accomplish a further reduction in the number of components required for the system while, at the same time, providing performance which, under most operating conditions, shows measurable gains in all three of the categories previously enumerated. In this system braking pressure supplied to all four wheels is controlled by an antiskid pressure modulator in accordance with front wheel behavior measured by individual wheel sensors mounted on each of the front wheels which transmit their indications to a logic and control channel operating on a select low" or "select high basis. The pressure to the rear brakes is further modified by operation of a load sensing proportioning valve constructed and arranged substantially in accordance with that shown in US. Pat. No. 3,362,758 issued Jan. 9, 1968 by the common assignee.
The load sensing proportioning valve is designed to reduce pressure to the rear brakes as a function of the distance between the rear axle housing and the vehicle frame or body. This distance changes in response both to variations in static load and braking deceleration due to the well-known weight shift characteristic which results from the fact that the vehicle center of gravity is always positioned substantially higher than the road surface.
DRAWING DESCRIPTION One embodiment of my invention is illustrated in the accompanying drawings in which:
FIG. 1 is a schematic system diagram;
FIG. 2 is a longitudinal sectional view of an antiskid brake pressure modulator of a type suitable for use in the subject system;
FIG. 2a is a partial cross section of the modulator piston of FIG. 2 showing a tandem cylinder for controlling a dual brake system;
FIG. 3 is a longitudinal sectional view of a brake proportioning valve installed in a manner suitable to operation in the subject system;
FIG. 4 is a graph of the relationship between rear brake pressure and front brake pressure as determined by the operation of the load sensing proportioning valve;
FIG. 5 is a longitudinal section through a front disc brake installation showing a wheel characteristic sensor installed for the purpose of measuring the required wheel performance characteristics;
FIG. 6 is a lateral cross section view of the sensor and brake shown in FIG. 5;
FIG. 7 is an axial cross section of the sensor per se; and
FIGS. 8 and 9 are reproductions of oscillograph recordings of actual vehicle performance under control of the system of this invention.
DETAILED DESCRIPTION cylinder 24. A conduit 26 conducts brake fluid to an antiskid modulator designated generally by the numeral 28. A conduit system designated only by the numeral 30 extends from the outlet port of the pressure modulator 28 to each of the front disc brakes and to the inlet port of the load sensing proportioning valve which is designated generally by the numeral 32. If the barking system is of dual nature then there would be two conduits from the master cylinder to the modulator and one conduit therefrom to the front brakes and another conduit therefrom to the load sensing proportioning valve. The load sensing proportioning valve is shown mounted on the rear axle housing 34 and is provided with an operating lever 36 having one end a notch 38 in which one end of an extension spring 40 is secured. A bracket 42 extending from a portion of the vehicle frame 44 provides a point of attachment at 46 for the other end of the extension spring 40. A conduit 48 extends from the outlet port of the load sensing pressure modulating valve to the wheel cylinders 50 and 52, respectively, of the drum brakes 14 and 16. Since the power brake master cylinder unit 22-24 is of completely conventional configuration, I do not feel it necessary to describe or show its interior construction.
Referring to FIG. 2, the antiskid brake pressure modulator 28, which does not in itself comprise part of my invention, consists of a vacuum chamber housing made up of two cupshaped stampings 54 and 56 whose rims are clamped together in sealed relationship with the flange 58 of a conventional rolling diaphragm 60. The rolling diaphragm 60 is mounted on a piston 62 and the diaphragm and piston divides the housing into two chambers, which I will designate as a vacuum chamber 64 and a vacuum-air chamber 66. A very powerful spring 68 is located in the vacuum chamber 64 and urges the piston 62 to the right-hand end of the unit. A hydraulic cylinder 70 is mounted concentrically with the cup member 56 and extends into the vacuum chamber forming a guide for the right-hand portion of the vacuum piston 62. A tube 72 is secured in the cup member 54 to serve as a guide for the lefthand end of the vacuum piston 62. The hydraulic cylinder 70 is formed with an interior bore 74 in which is seated a hydraulic piston 76 which projects through a seal 78 in the leftward end of the cylinder 70 and engages the vacuum piston 62. The hydraulic cylinder 70 is formed at its right end with an inlet port which receives the conduit 26 leading from the master cylinder and with a port 82 which receives the conduit 30 leading to the front brakes and the load sensing proportioning valve. A check valve 84 is located in the port and, in the normal or released position of the pressure modulator, a pin 86, forming a rightward extension of the hydraulic piston 76, holds this check valve away from its seat. In this condition, it will be observed that brake fluid under pressure can flow freely from conduit 26 to the brakes through conduit 30.
A vacuum connection 88 is connected to a conduit 90 which is, in turn, connected to the intake manifold 92 of the vehicle engine 94, as seen in H6. 1. The vacuum connection 88 is formed as a plastic molding in the shape of a T, one branch 89 of which enters the vacuum chamber 64. The third arm of the T 91 is connected by a conduit 94 to a normally open solenoid valve, designated generally by the numeral 96, mounted on the right-hand end of the cup member 56. A rubber disc check valve 98 is positioned in the vacuum inlet chamber in such a way that vacuum is trapped in anns 90 and 92 even though the engine stops and atmospheric pressure is established at vacuum connection 88. A normally closed solenoid valve 100 is also mounted on the right-hand end of cup 56 and is provided with an air inlet 102 which admits air to the vacuum-air chamber 66 through a passage 104 when the solenoid valve 100 is energized. The normally open solenoid valve 96 permits vacuum to communicate through a passage 106 with the vacuum-air chamber 66 whenever it is not energized, and, when energized, it interrupts the connection between the vacuum conduit 104 and the passage 106, preventing increase of vacuum in the chamber 66.
in FIG. 2a the cylinder 70a is for a dual brake system. It has separate inlets 80a and 80b, separate outlets 82a and 82b and separate check valves 84a and 8412. Two pistons 76a and 76b control valves 84a and 84b by pins 86a and 86b. These pistons extend beyond the cylinder into abutment with the vacuum piston 62 so that the valves 84a and 84b would be controllable by segregated master cylinder pressures and by the piston 62.
Referring now to FIG. 3, the load sensing proportioning valve 32 comprises a cast housing 108 having a central bore 110 having a closed end 112 and an open end which is partially closed by a threaded plug 114. The plug 114 is formed with a concentric longitudinal bore 116 of substantially smaller diameter than the housing bore 110. A stepped piston 118 has its large end 120 positioned in fitted relationship to the housing bore 110 and its smaller end 122 extends in fitted relationship through the passage 116 in the plug 114. The clearance between the small end 122 of the piston 118 and the bore 116 of the plug 114 is protected against the entrance of contaminants by a rubber boot 124. Escape of pressure fluid through this same clearance is prevented by a cup seal 126 installed in a suitable annular groove formed in the piston. The housing bore 110 constitutes a chamber having an upper portion 128 defined by a portion of bore 110, by portions of stepped piston 118, and the inner end face of the nut 114. This chamber 128 is provided with an inlet port 130 to which is connected the conduit leading from the antiskid brake pressure modulator. The chamber formed by the housing bore 110 also has a lower portion 132 defined by a portion of the walls of the bore 110, the lower face of the piston 118 and the closed end 112 of the housing. An outlet port 134 communicates with this chamber and is connected to the conduit 48 which leads to the rear brake wheel cylinders 50 and 52. A cup seal 136 is seated in a suitable groove formed in the large end 120 of the piston 118 and is oriented to seal against passage of fluid from the upper chamber 128 to lower chamber 132. The construction of this seal is such that passage of fluid from chamber 132 to chamber 128 will not be inhibited if a pressure difference exists in that direction. The stepped piston 118 is formed with a longitudinal passage 138 extending from the lower face of the large end 120. A threaded bushing 140 is screwed into suitable threads formed in the lower end of this passage. The upper end of this bushing constitutes a valve seat upon which is seated a valve ball 142. A small spring 144 serves to urge this ball on to its seat.
A pin 146 is slidably disposed in the bore of the threaded bushing 140 and is of such length that when the piston 118 is urged to its lowermost position in contact with the end wall 112 of the housing bore 110, the valve ball 142 will be lifted from its seat. The pin 144 is of noncircular cross section so as to from a fluid passage whereby fluid may flow through a lateral passage 148 into the passage 138 past the check ball 142 through the bore in the bushing 140 to the chamber 132.
The cast housing 108 is formed with a bracket 150 to which the lever 36 is swingably secured on a pin 152. The lever 36 rests in contact with the projecting end 122 of the stepped piston 118 and with the spring 40 installed as described in relation to FIG. 1, the force of the spring is exerted on the piston 118 to urge it to its lowermost position in contact with housing end wall 112 and hold it there at some predetermined force. It will be observed, however, that as the distance between the axle housing 34 and vehicle frame 44 varies, the spring 44 will be either stretched or relaxed in such a way as to increase or decrease this predetermined force.
Referring to FIGS. 5,6, and 7, installation of suitable wheel operating characteristic sensors is shown although this does not constitute a part of my invention per se. In these FIGS. is shown a front wheel spindle 154 upon which a wheel hub 156 is pivoted on suitable bearings 157. A brake disc 158 is secured to the wheel hub 156 by suitable studs 160. Pivoted on the wheel hub 156 and secured thereto by machine screws 162 is a heat insulating ring 164 formed with an annular groove 166 in which is seated a friction drive ring 168 of suitable elastomeric material. A bracket 170 (see FIG. 7) is secured to a portion of the wheel spindle 154 by bolts 172 and the sensor, which I will designate generally by the numeral 174, is pivotably mounted to said bracket by a pin 176. The sensor 174 is provided with a drive roller 178 and a mousetrap spring 180 resiliently urges the sensor to swing about its pivot pin 176 to bring the drive roller 178 into driving contact relationship with the friction element 168. Thus, it will be seen that the sensor drive roller 178 will be driven at a speed in a fixed relationship to the speed of rotation of the vehicle wheel. Referring specifically to the sectional view of HO. 7, the sensor 174 comprises a generally circular cast housing 182. A toothed wheel 184 is enclosed within the cavity of said housing by a cover plate 186 secured by suitable screws 188. The toothed wheel 184 is mounted on a shaft 190 carried in suitable bearings 192 in a hub 194 which is formed integrally with the housing 182. The friction drive roller 178 is secured to the outer end of the shaft 190, A magnetic proximity sensor 196 is threaded into a lateral opening in the housing 186 in such a way that its magnetic pole portion 198 is positioned in close proximity to the ends of the teeth on the toothed wheel 184. The sensor 196 is provided with a permanent magnetic element and an induction coil of suitable characteristics and the toothed wheel has teeth of correct shape and proportion to generate electrical impulses upon the passage of each tooth past the pole face.
Referring back to FIG. 1, the sensors 174 are shown electrically connected by cables 200 to an electronic unit designated generally by the numeral 202. This unit is provided with electric energy from the vehicle battery 204. A switch 206 positioned so as to be actuated by initial movement of the brake pedal 18 is also electrically connected to the unit 202 so as to energize it upon initiation of braking and make it ready to perform the antiskid function as required. The unit 202 includes logic and control elements which, in detail, are not a part of my invention but which may be of the type shown in US. Pat. No. 3,494,671. The signals received from the wheel sensors 174 are connected into control signals and electrical energy is transmitted through electric wires 208 and 210 to the normally open and normally closed solenoid valves 96 and 100, respectively, for the purpose of making the antiskid brake pressure modulators function in a manner which will be described subsequently. As I have described them, the wheel sensors 174 constitute pulse generators which produce an alternating current at a frequency proportional to wheel speed. This pulsing, or alternating, current is passed through a frequency converter which produces a DC voltage proportional to wheel speed. The voltages from the two sensors are compared and the lower voltage is passed through a discriminator to the control system. Since this voltage represents wheel frequency and the antiskid system is best controlled in relation to wheel acceleration, both positive and negative, this signal voltage is processed to produce a first derivative which is proportional to the acceleration of the wheel. It is well known in antiskid technology that the maximum rate of vehicle deceleration is approximately lg, so if wheel deceleration exceeds a value slightly higher than lg, it is obvious that this wheel is approaching a lockup condition. This can be established as the first set point at which the control system signals the pressure modulator to reduce braking pressure by closing valve 84 and retracting piston 76, or valves 84a and 84b and pistons 76a and 7611 as the case may be. As braking pressure is reduced, the rate of wheel deceleration reduces and at some point the wheel will begin to accelerate back to synchronous speed. Some level of acceleration is established as a second set point and, upon receiving this intelligence from the wheel sensor, the control system signals the pressure modulator to stop reducing pressure and instigates a slow rate of pressure increase by displacing piston 76 or 76a and 76b, with spring 68 upon a reduction of pressure in vacuum-air chamber 66. At some point later in time, if the first deceleration set point has not been exceeded again, a high rate of pressure rise will be instigated. Shortly thereafter, the said first deceleration set point should be exceeded again and the control cycle will repeat itself.
It should be fairly obvious to most persons familiar with conventional automobile brake performance that controlling the brake pressure to the rear brakes, in the same manner as l have just described with relation to the front brakes, would not prevent the rear brakes from locking was a result of normal weight shift when the vehicle is being rapidly decelerated on a good road surface. For this reason, as an important element of my invention, I have incorporated into the system the load proportioning valve 32, which in itself is not novel in the brake industry. In the previously identified Pat. application relating to such a valve, it has been explained that the valve can be built to automatically vary the relationship of front and rear brake pressure to compensate both for static load variations such as the addition or removal of extra passengers or luggage, and also for variations of rear wheel load caused by the previously mentioned weight shift due to the efiects of inertia upon the mass of the vehicle while braking. However, in an otherwise conventional automobile equipped with a load sensing proportioning valve for the rear brakes, if the driver attempts to make an emergency stop and applies sufficient energization to the-brake system to cause the front brakes to lock, the rear brakes will also receive sufiicient pressure to enable them to be locked. However, in a vehicle equipped in accordance with my invention, since the pressure to the front brakes is regulated by the antiskid mechanism in such a way that locking of a front wheel is impossible, it can be understood that the functioning of the load sensing pressure modulator will simultaneously prevent the locking of either or both of the rear wheels.
FIGS. 8 and 9 represent tracings of actual oscillograph recordings of the behavior of a vehicle equipped with an antiskid system built in accordance with my invention. FIG. 8 was recorded during a stop on smooth, dry asphalt, constituting a relatively high frictioncoefficient surface. FIG. 9 was recorded during a stop on a surface made up of loose gravel and cinders and, in view of the deceleration attained, about ftjsecfi, should be considered a medium coefficient surface. The difference in cycling behavior illustrates the manner in which the system adapts to road surfaces having different characteristics.
Referring to FIG. 8, Trace 01 represents rear brake pressure, that is, pressure in the conduit 48/ Trace 02 represents front brake pressure, or the brake pressure in the conduit 30. Trace 03 represents vehicle deceleration. Trace 04 represents the speed of the left front wheel. Trace 05 represents the speed of the right front wheel. Trace 06 represents the speed of the left rear wheel. It should be noted that the Traces 01 and 02 both begin at zero brake pressure; and that Traces 04, 5, and 6 end at zero wheel speed. They are shown spaced for clarity.
With this in mind, the operation of my brake system is clearly presented to show the system of FIG. 1 to be working from the beginning of brake application, or point A of this FIG. Moreparticularly, from point A to point B the following has occurred:
At about 900 p.s.i. front brake pressure and 400 p.s.i. rear brake pressure the modulator 28 has been activated to close check valve 84 and lock out further supply of pressure from master cylinder 24. In doing this, the modulator also relieves pressures by increasing displacement in that piston 76 follows up the movement of piston 62 to return the front brake pressure to approximately 500 p.s.i. whereupon atmospheric air is cut off from passage 104 by solenoid valve 100.
During this the rear brake proportioning valve 32 has sensed a weight shift via the spring 40 to close the valve ball 142 at approximately 150 p.s.i. to proportion the rear brake pressure as a function of the inlet and outlet areas of stepped piston I18. As seen in FIG. 8 the rear brake pressure climbs to 400 p.s.i. and then is relieved by the modulator increasing the displacement in thesystem between it and the proportioning valve.
At the time of closure of the solenoid valve the front brake pressure has been reduced by 400 p.s.i. and the rear brake pressure by I00 p.s.i. and wheel lock has not occurred while vehicle deceleration, as represented by Trace 03 has reached a maximum value permitted by the electronic unit 202.
Unit 202 which senses the result of these braking pressure changes now reopens the solenoid valve 96 so that spring 68 will move piston 76 to begin redevelopment of front brake pressure to 900 p.s.i., as the rear brake proportioning valve maintains approximately 300 p.s.i. in the rear brakes called for by the center of gravity shift of the vehicle as a maximum rear brake pressure for maximum rear brake effectiveness.
When the front brake pressure reaches 900 psi. again the sensors 174 tell the unit 202 to apply atmosphere to chamber 66 of modulator 28 and the brake system pressure is again reduced and reestablished, as before.
Therefore, braking was initiated at point A and the stop was completed at point B. The antiskid control system cycled three times during this period, which represents an elapsed time of 2 /4 seconds. In this particular case, the left front wheel appeared to be the controlling wheel, and it will be noted that while it approached the locked condition briefly at the beginning of the last cycle, no actual lockup occurred during the entire stop. A high average deceleration was maintained during the entire stop and in all testing to date stopping distances have been consistently lower than locked wheel stopping distances of the same vehicle on the same surfaces.
Referring to FIG. 9, the cycling rate increased to about 10 cycles/second and the pressure and velocity excursions were substantially reduced.v In this FIG. the trace designations are the same as in FIG. 8 with the suffix a applied, and the trace for rear brake pressure is omitted.
1. In a wheeled vehicle with front and rear wheels having a pressure operated brake system, said brake system comprising:
a booster type brake unit;
separate actuation means for each wheel of said vehicle,
said actuation means being responsive to pressure from said booster type brake unit;
sensor means for detecting the rotational velocity of at least one wheel of said wheeled vehicle and generating a sensor output signal for each detected wheel;
control means for converting said sensor output signals into a control signal; modulation means interposed between said booster type brake unit and said separate actuation means, said modulation means being operated by said control signal to reduce brake pressure and prevent wheel skidding; proportioning means interposed between said modulation means and said separation actuation means for the rear wheels, said proportioning means automatically redistributing braking effort between the front and rear wheels as a function of load shift; and
said modulation means having valve means to operate said modulation means in response to said control signal, said control signal operating said valve means to provide multiple build rates in said brake pressure.
2. The brake system of claim 1 wherein said control signal is a function of the front wheel turning at the slower velocity.
3. A braking system for a wheeled vehicle having antiskid control, said system comprising:
a brake master cylinder for generating pressurized fluid in response to a brake application;
actuating means for applying the brakes of said vehicle braking system in response to said pressurized fluid from said brake master cylinder;
sensor means for detecting the rotational velocity of the wheels of said wheeled vehicle, said sensor means generating a signal proportional to said rotational velocity;
control means for converting said proportional signal to control signals, said control signals being generated when there is an imminent skid condition;
modulator means for removing operator control and varying said pressurized fluid received by said actuation means from said brake master cylinder in response to said control signals being received from said control means;
valve means operatively connected to said modulator means wherein said control signals operate said valve means to give multiple pressure build and decay rates in said actuation means; and I proportioning means interposed between said modulator means and said actuating means of certain wheels of said wheeled vehicle, said proportioning means automatically redistributing braking effort between said certain wheels and the rest of the wheels of said wheeled vehicle as a function of load shift.
4. The braking system having antiskid control, as recited in claim 3, wherein said valve means comprises solenoid valves located at a fluid input and a fluid output of said modulator means, said control signals operating said solenoid valves to give said multiple pressure build and decay rates.
5. The braking system having antiskid control, as recited in claim 4, wherein said control signals are generated when predetermined rates of change of said rotational velocity have been detected by said control means, said control signals being repeated as long as said predetermined rates of change occur on subsequent cycles of the same brake application.