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Publication numberUS3581720 A
Publication typeGrant
Publication dateJun 1, 1971
Filing dateNov 22, 1968
Priority dateNov 22, 1968
Publication numberUS 3581720 A, US 3581720A, US-A-3581720, US3581720 A, US3581720A
InventorsBlevins Ronald E, Hemphill Lewis W
Original AssigneeSilicon Systems Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electronic engine r.p.m. limiting device
US 3581720 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

United States Patent [72] Inventors Lewis W. Hemphill; 3,153,746 10/1964 Atkinson 123/118 Ronald E. Blevins, both of Balboa, Calif. 3,220,396 12/1965 Heidner 123/148 [211 App]. No. 778,173 3,402,327 9/1968 Blackburn. 317/31 (22] Filed Nov. 22. 1968 3,430,615 3/1969 Chauis 1. 123/102 [451 Patented June 1,1971 [731 Assignee Silicon Systems, Incorporated j f EmmuierMark Newman Newpofl Beach Calm sslstan! ExammerRonald B. Cox

AttorneyFowler, Knobbe & Martens [54] ELECTRONIC ENGINE R.P.M. LIMITING DEVICE 22 Claims, 4 Drawing Figs.

123M021 23/148 ABSTRACT: In the ignition system of an internal combustion 1 Int. engine a witching means is connected in eries the pri.

F029 1 1/08 mary winding of an ignition coil. The switching means opens of Search I l8, and closes to interrupt current flow through the primary wind- 148 D; 317/19 ing generating ignition pulses in the secondary winding of the i nition coil at a fre uenc determined b the s eed of the en- [56] References g ine. A sensing 11162318 is rgsponsively cou pled t8 the switching UNITED STATES PATENTS means and generates an output signal when the engine reaches 2,519,801 8/1950 Tognola 171/97 a predetermined r.p.m. A silicon-controlled rectifier con- 3,182,648 5/1965 Schneider et a1. 123/148 nected in parallel with the switching means is gated on by the 3,235,742 2/1966 Peters 250/233 output signal of the sensing means to short out the switching 3,356,082 12/1967 .Iukes 123/102 means and thereby disable the ignition system. The silicon- 3,363,615 1/1968 Meyerle 123/148 controlled rectifier is turned off by the sensing means when 3,410,362 1 1/1968 Fales 180/ 1 10 the engine speed returns to an rpm. below the predetermined 2,377,591 6/1945 Taylor 123/118 rpm. to allow the ignition system to function in a normal 2,726,647 12/1955 Molyneux 123/1 18 manner.

50 {Z 1; 1 Li. 42

I6 i 1% '32 l 1o 25 54 101 l4 PATENTED JUN 1 Ian SHEET 2 UF 2 FOWLER, A/NOBEE 6 Mnerews 14 T TOIPNE Y5.

ELECTRONIC ENGINE R.P.M. LIMITING DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ignition systems for internal combustion engines and, more particularly, to an electronic device for limiting the r.p.m. of an internal combustion engine.

2. Description of the Prior Art A conventional device for limiting the r.p.m. of an internal combustion engine includes a sensing means for measuring the engine speed. The sensing means is generally responsive to the rate at which the mechanical breaker points, which are in series with the ignition coil open and close. When the breaker points are closing at a predetermined rate, the sensing means will actuate a control means which will disable the ignition system to cause the engine to slow down. Mechanical breaker points, however, begin to bounce or chatter as the speed of the engine increases. Thus, the sensing means will inaccurately measure the engine speed due to the point bounce and will prematurely disable the ignition system. This result is highly undesirable.

In the conventional device the control means is usually a mechanical device such as a relay. The relay will have a pair of contacts which are connected in parallel with the mechanical breaker points. When the sensing means actuatcs the relay,

the contacts will close to disable the ignition system by placing a short circuit across the breaker points. If the engine upon which the r.p.m. limiting device is mounted is subjected to strong vibrations, the contacts of the relay are likely to be vibrated between the open and closed positions resulting in spurious ignition pulses. These ignition pulses may cause engine damage.

SUMMARY OF THE INVENTION The present invention provides a solid-state electronic circuit means for accurately limiting the r.p.m. of an internal combustion engine to prevent engine damage due to excessive engine speed. Further, the circuit means is adaptable for use with conventional engine ignition systems or the relatively new transistorized ignition systems. i

In accordance with the preferred embodiment of the present invention a switching means is connected in a series with the primary winding of the ignition coil on an internal combustion engine. The switching means may be either the mechanical breaker points in a conventional ignition system or a switching transistor in a transistorized ignition system. The switching means actuates at a frequency proportional to the engine speed interrupting the current flow through the primary winding of the ignition coil to cause the ignition coil to generate ignition pulses to the spark plugs in the engine. A solid-state sensing means is responsive to the rate at which the current flow through the primary winding is interrupted and generates an output signal to a control means when the engine speed exceeds a predetermined value. The control means will disable the ignition system until the engine speed has been reduced to a speed below this predetermined value at which time it will automatically reenable the ignition system.

In accordance with one aspect of the present invention the sensing means includes a charging capacitor coupled to a direct current source and a discharge means responsively coupled to the switching means. The charging capacitor is charged by a charge current from the direct current source and is discharged each time the switching means interrupts the current through the primary winding. The discharge means is immune to the phenomenon of point bounce present in ignition systems using mechanical breaker points and will discharge the charging capacitor only when the ignition coil generates an ignition pulse. The average value of the charge current to the charging capacitor therefore is proportional to the engine speed. A detector means is also included in the sensing means and is responsive to the average value of the charge current. The detector means will generate an output signal to the control means when the average value of the charge current exceeds a value corresponding to the predetermined engine speed.

The present invention provides both an extremely accurate means for sensing engine speed and, due to its solid-state components, a device having a high reliability and immunity from engine vibration. BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic diagram of the preferred embodiment of the present invention used with an ignition system which employs the conventional mechanical breaker points;

FIG. 2 is a schematic diagram of the preferred embodiment of the present invention modified to be used with a transistorizcd ignition system;

FIG. 3 is a diagrammatic representation of the voltage waveform which would normally appear across the switching means used to interrupt current flow through the primary winding of an ignition coil; and

FIG. 4 is a diagrammatic representation of the voltage waveform appearing across the switching means as modified by the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodiment of the present invention as adapted for use with a conventional ignition system in an internal combustion engine is shown in FIG. I. The ignition system comprises a direct current source I0, such as the 12 volt storage battery in an automobile, connected through an ignition switch 16 and a ballast resistor 18 to one side of the primary winding 12 of an ignition coil I4. The opposite side of the primary winding 12 is connected to ground through a power switching means comprising breaker points 20. The secondary winding 22 of the ignition coil 14 is connected to a distributor 24 having a rotatable wiper arm 26. The wiper arm 26 distributes the ignition pulses generated in the secondary winding 22 through a plurality of ignition wires 28 to one electrode of a correspondingplurality of spark plugs 30 in an internal combustion engine 32. The other electrodes of the spark plugs 30 are connected to ground. An engine output shaft indicated by dotted line 34, drives the wiper arm 26 and the breaker points 20. Accordingly, the breaker points 20 will open and close at a frequency determined by the speed of the engine 32. Each time the breaker points 20 are closed a current from the direct current source 10 will flow through the primary winding 12 to ground. When the breaker points 20 are opened, the current flow through the primary winding 12 will be interrupted resulting in an ignition pulse being generated in the secondary winding 22. The ignition pulse in the secondary winding 22 is connected to the appropriate spark plug in the engine 32 by the wiper arm 26. A capacitor 35 is ordinarily connected in parallel with the breaker points 20 to reduce the arcing and the burning of the contacts of the breaker points 20 during system operation.

Referring now to FIG. 3, there is shown a waveform 37 which represents the voltage that would appear at the terminal 36 in FIG. 1 for one cycle of the breaker points 20. Time t in FIG. 3, corresponds to the instant in time that the breaker points 20 are opened to interrupt the current flow through the primary winding 12. When the current flow through the primary winding 12 stops, at time t the flux in the core of the ignition coil 14 will begin to collapse and a positive voltage pulse in the order of 300 volts will occur at the terminal 36. Further, it can be seen that the voltage will oscillate decreasing in amplitude between times t and t ,as the energy in the core of the coil 14 is exchanged between the coil 14 and the capacitor 35. Note that although the oscillating voltage in FIG. 3 is decreasing in amplitude, each voltage peak is only slightly less than the preceding voltage peak. At time 1,, the appropriate spark plug in the engine 32 fires resulting in a constant voltage across the primary winding 12 such as segment 38. When the wiper arm 26 has removed the ignition pulse in the secondary winding 22 from the particular spark plug 30,

the voltage at terminal 36 will oscillate a few more cycles and will eventually damp out to the voltage potential of the battery 10, represented by segment 39. At time I the breaker points 20 will close grounding terminal 36 until time r of the next cycle when the breaker points 20 will again open to interrupt the current flow through the primary winding 12.

The preferred embodiment of the present invention as seen in FIG. I includes a diode 40 connected in parallel with the breaker points 20 having its anode connected to ground and its cathode connected to terminal 36. The diode 40 modifies the voltage waveform seen in FIG. 3 to a waveform such as waveform 41 seen in FIG. 4. In FIG. 4, it can be seen that at time t when the breaker points 20 open, a voltage pulse in the order of 300 volts appears at the terminal 36 as was the case in FIG. 3 (diode 40 has no affect on a positive pulse). Note, however, that the diode 40 will clamp the terminal 36 to ground potential during the negative portions of the voltage oscillation. The diode 40 will not only eliminate the negative portions of the voltage oscillation, but will also reduce the amount of energy exchanged between the capacitor 35 an the coil 14. This reduced exchange of energy will cause the frequency of the oscillations to be smaller and the amplitude of the positive pulses after the first pulse to be significantly diminished from what they would normally be. The polarity of the diode is such that it can have no effect until after the first positive pulse has occurred. For example, the first pulse occuring after time t in both FIG. 3 and FIG. 4 has an amplitude in the order of 300 volts. The second oscillation of the voltage in FIG. 3 has an amplitude only slightly less than 300 volts, whereas the second positive pulse in FIG. 4 has an amplitude of approximately 50 volts. The diode 40, then, significantly alters the energy exchange between the capacitor 35 and the coil 14 so that a distinguishing pulse occurs at the terminal 36 when the breaker points 20 open.

It is significant to note that most of the energy for this first positive pulse is stored in the leakage inductance" of the primary winding 12 of the ignition coil 14. Accordingly, this pulse occurs due to a characteristic of the coil 14 which is essentially unaffected by conditions existing in the secondary circuit which includes the secondary winding 22, distributor 24, wires 28 an spark plugs 30. Thus, any abnormal condition in the secondary circuit such as a disconnected spark plug wire, open or shorted spark plug, or other abnormality will not affect the first pulse.

A silicon-controlled rectifier (SCR) 42 is connected in series with a resistor 44 across the breaker points 20 from the terminal 36 to ground. The conductive state of the SCR 42 is controlled by a signal appearing on line 46 which is connected to its gate electrode. When an appropriate signal appears on the line 46, the SCR 42 will become conductive and will short out the breaker points 20 thus disabling the primary circuit of the ignition system. The resistor 44 is a very low value so that the terminal 36 is at approximately ground potential even though it is not connected directly to ground when the SCR 42 becomes conductive.

A sensing means 48 is responsive to the voltage potential appearing on the terminal 36 and 'will generate an output on the line 46 to cause the SCR 42 to become conductive when the frequency of the voltage pulses appearing on terminal 36 indicates that the engine 32 has reached a predetermined rpm.

The sensing means 48 includes an RC charging network comprising a capacitor 60 which is charged by the direct current source through a charge path including a resistor 58 connected between the capacitor 60 and the direct current source 10 and diodes 62 and 64, connected in series with resistors 66 and 68 between the capacitor 60 and ground.

The sensing means 48 also includes a discharge means comprising a Zener diode 50, resistors 52 and 54, and a transistor 56. The reverse breakdown voltage of Zener diode 50 is selected so that current will be conducted from terminal 36 through resistors 52 and 54 to ground only when the voltage at terminal 36 exceeds a value, 100 volts for example, which is less than the first voltage pulse occurring after the breaker points 20 open, as seen in FIG. 4, and yet is significantly higher than the second voltage pulse. Referring again to FIG. 4, it can be seen that the Zener 50 will become conductive only when the first pulse occurs in each ignition cycle. Each time Zener diode 50 conducts, a positive voltage potential will appear on the base electrode of the transistor 56 causing it to become conductive. The transistor 56 will therefore have a conduction rate determined by the conduction rate of the Zener diode 50.

The breaker points in virtually all mechanical breaker point ignition systems will bounce or chatter as they are closing causing current pulses through the primary winding 12. These current pulses, however, do not have a significant duration and will not store enough energy in the ignition coil 14 to cause a voltage pulse at the point 36 of sufficient amplitude as the breaker points chatter to cause the Zener diode 50 to conduct. A voltage pulse of the required magnitude will appear at the point 36 only after the points 20 have settled down and been closed for a significant period of time and are then opened. The conduction rate of the transistor 56 therefore is unaffected by this phenomenon ofpoint bounce."

The transistor 56 has its collector electrode connected between the resistor 58 and the capacitor 60 and its emitter electrode connected to ground. A diode 74 has its anode connected to the emitter electrode of the transistor 56 and its cathode connected between the capacitor 60 and the diode 62, Accordingly, each time the Zener diode 50 becomes conductive, causing the transistor 56 to turn on, the charge built up on the capacitor 60 is discharged through a path including the transistor 56 and the diode 74. The diode 62 prevents any reverse current from flowing from ground through the resistors 66 and 68 when the capacitor 60 is discharged. When the voltage potential on terminal 36 decreases to a value such that the Zener diode 50 becomes nonconductive a charge current from the direct current source 10 will charge the capacitor 60 through the resistor 58.

A Zener diode 72 is connected from one side of the capacitor 60 to ground and will determine the maximum charge which may be placed on the capacitor 60. Accordingly, since the capacitor 60 is charged to a fixed value, as determined by the Zener diode 72 each time the transistor 56 becomes nonconductive, the average current flowing in the charge path for the capacitor 60 is proportional to the switching frequency of the transistor 56 and hence the frequency at which the breaker points 20 are operating.

Advantageously, in a system wherein the direct current source 10 has a voltage potential of l2 volts, the Zener diode 72 will allow the capacitor 60 to charge to 9 volts before it becomes conductive. The value of the resistor 58 is chosen to limit the current which will pass through the Zener diode 72, after the capacitor 60 has been charged, to a value for which the Zener diode 72 has been temperature compensated, 5 milliamps for example.

A current-amplifying means 99 will amplify the current flowing in the capacitor 60 charge path. The diode 64 and the resistors 66 and 68 are connected in series between the base electrode of a transistor 76 and ground. A resistor 82 is connected between emitter electrode of the transistor 76 and ground. The output from the current-amplifying means 99 appears on the collector electrode of the transistor 76. A terminal 63 intermediate the diodes 62 and 64 is the input terminal for the current-amplifying means 99.

A capacitor 70 is connected between the terminal 63 and ground. The capacitor 70 has a value large enough, 1,000 microfarads for example, to prevent current spikes, due to the charging current pulses through the capacitor 60, from flowing into the terminal 63. The capacitor 70 will filter the current flowing into the current-amplifying means 99 so that it is substantially a direct current with a ripple content of2 percent or less. This low ripple current enhances the accuracy of the device.

The collector electrode of the transistor 76 is connected to the direct current source through a series-connected resistor 78 and diode 80. The amount of current flowing in the capacitor 60 charge path, that is, into the terminal 63 and through the diode 64 an resistors 66 and 68, determines the conductivity of the transistor 76. Accordingly, the current flowing from the direct current source 10 into the collector electrode of the transistor 76 is proportional to the current flowing into the terminal 63. This proportionality is the current gain or amplification factor of the current-amplifying means 99 and is determined by the ratio of the sum of the values of the resistors 66 and 68 divided by the value of the resistor 82. The resistor 68 is a variable resistor and hence may be varied to change the gain of the current-amplifying means 99. The diode 64 serves to compensate for changes in the base-emitter voltage of the transistor 76 which occur as a result of changes in the ambient temperature. This feature allows the amplification factor of the current-amplifying means 99 to remain constant in spite of ambient temperature changes.

Advantageously, the current amplifier 99 is a temperature compensated, constant gain current amplifier. The constant gain of the current amplifier is achieved by selecting a current gain of the transistor 76 so that it is much higher, ten times as high for example, as the value of the sum of the resistors 66 and 68 divided by the resistor 82. For example, in an eightcylinder engine, the amplifier will operate satisfactorily with a gain of 5. Accordingly, the current gain of the transistor 76 should be approximately 50.

As the current flow from the direct current source 10 through the resistor 78 and the transistor 76 increases with an increasing charge current flowing into the terminal 63, the voltage potential of the collector electrode of the transistor 76 will decrease. A detector means is responsive to the voltage potential on the collector of the transistor 76 and generates an output signal on line 46 to a control means l0l which includes the SCR 42 when the collector potential of transistor 76 corresponds to a predetermined engine rpm.

The detector means includes a Zener diode 84, having its anode connected to the collector of transistor 76 and its cathode connected to the direct current source 10 through a resistor 86. The base electrode of a transistor 88 is connected intermediate to the cathode of the Zener diode 84 and the resistor 86. The emitter electrode of a transistor 88 is connected to the direct current source 10 and its collector electrode is connected to the gate electrode of the SCR 42 through a resistor 89.

When the collector current of the transistor 76 increases to a value such that the voltage drop across the resistor 78 is equal to the breakdown voltage of the Zener diode 84, the Zener diode 84 will become conductive and conduct current from the direct current source 10 through the base-emitter junction of transistor 88 causing transistor 88 to become con ductive. This in turn causes SCR 42 to turn on disabling the ignition system due to a direct current flow from the direct current source 10 through the transistor 88, resistor 89, and the gate SCR 42 to ground. The transistor 88 will remain conductive until the current flow into the collector of the transistor 76 decreases sufficiently, due to a decrease in the engine speed, to stop the conduction of the Zener diode 84. The resistor 89 minimizes the power dissipation in the transistor 88 when it is conductive.

Thus, it can be seen that the SCR 42 will be turned on when the current into the collector of the transistor 76 (Le. the output signal of the current amplifier 99) reaches a value equal to the Zener voltage of the Zener diode 84 divided by the value of the resistor 78. Since a fixed output current from the current amplifier 99 is required to turn on the transistor 88 and hence the SCR 42, varying the amplification factor of the current amplifier 99 will vary the input current to the terminal 63 required to turn on the transistor 88 and the SCR 42. The variable resistor 68 thus provides a means for adjusting the input current, and hence the engine r.p.m. required to turn on the SCR 42. For example, decreasing the value of the resistor 68 reduces the gain of the current amplifier 99, increasing the required current input, and hence engine rpm, to turn on the transistor 88 and the SCR 42. The resistor 86 serves the dual purpose of reducing the leakage current of transistor 88 at high temperatures and insuring that sufficient current must flow through Zener diode 84 before transistor 88 can be turned on. The first condition insuresthat SCR 42 will not he accidentally turned on at high temperatures. The second condition assures that the Zener diode 84 is at the Zener breakdown voltage before transistor 88 can be turned on. To maintain the accuracy of the circuit, the current flow through resistor 86, when transistor 88 is biased on, should be much lower than the current through the resistor 78 under the same condition. For example, the current through the resistor 78 might be 100 times as high as the current through the resistor 86 which includes the base drive current for the transistor 88.

The diode provides compensation for changes in the base-emitter voltage of the transistor 88 which may occur due to changes in ambient temperature. This assures that the value of the current which is required to flow through the resistor 78 to cause conduction of the Zener diode 84 will be stable. To assure the accuracy of the circuit, resistors 66, 68, 78, 82 and capacitor 60 should be temperature stable types.

A resistor 90 and a capacitor 92 are also included in the control means 101 and are connected in parallel between the gate electrode and the cathode electrode of the SCR 42. The resistor 90 and the capacitor 92 will act as a filter to prevent spurious voltage pulses on line 46 from inadvertently turning the SCR 42 on. A capacitor 93 is connected in parallel with the SCR 42 and acts as a filter to prevent any high frequency voltage spikes which might appear on the terminal 36 from turning the SCR 42 on. The value of the capacitor 93 is selected to be as large as possible without affecting the resonant relationship between the capacitor 35 and the primary winding 12. Advantageously, the value of the capacitor 93 is approximately l0 percent to 15 percent of the value of the capacitor 35.

When the SCR 42 is conductive, current will flow from the direct current source 10 through the primary winding 12 to ground through the SCR 42 and resistor 44. The resistor 44 has a small value, one ohm'for example, resulting in a small voltage drop across the resistor when the SCR 42 is conductmg.-

Although the SCR 42 shorts out the breaker points 20 when it is conducting, the breaker points 20 continue to operate at a frequency proportional to the speed of the engine 32. The current which would normally pass through the SCR 42 will be shunted to ground each time the breaker points 20 close due to the lower resistance of the path through the breaker points 20. Accordingly, when the SCR 42 is conducting a voltage waveform will appear across the resistor 44 and will approximate a square wave having a frequency equal to the actuation frequency of the breaker points 20.

The voltage waveform appearing across the resistor 44 is coupled to the base electrode of the transistor 56 through a diode 94 and a resistor 96. Each time the breaker points 20 open, causing the voltage potential across the resistor 44 to increase, the diode 94 will become conductive causing the transistor 56 to turn on. The resistor 96 limits the base current into the transistor 56 to a reasonable value. Therefore, although the breaker points 20 are shorted out when the engine speed reaches the predetermined value and no pulses appear at the terminal 36, the transistor 56 will continue to function at a frequency proportional to the speed of the engine 32. Accordingly, the charge current through capacitor 60 will continue to be proportional to the speed of the engine 32 even though the ignition system has been disabled.

It can be seen that the transistor 88 will turn on to cause the SCR 42 to become conductive when the engine speed reaches a predetermined value and will turn off to remove the gate control signal from the SCR 42 when the engine speed falls below this value.

When the transistor 88 is turned off, the SCR 42 will not become nonconductive until the current flowing through it is actually removed. Accordingly, although the signal on line 46 is removed from the gate electrode of the SCR 42, the SCR 42 will not become nonconductive until the breaker points 20 close. This aspect of the present invention insures that a spurious ignition pulse will not be generated in the secondary winding 22 when the SCR 42 is disabled. That is, the mere removal of the gate signal on line 46 will not cause the current flowing through the primary winding 12 to be interrupted and result in a mistimed ignition pulse.

The diode 94 connected between the cathode electrode of the SCR 42 and the base electrode of the transistor 56 is provided to prevent the current which flows through the Zener diode 50 each ignition cycle to the base electrode of the transistor 56 from being shunted to ground through the low resistance path provided by the resistors 95 and 44.

Advantageously, the value of the capacitor 60 is selected large enough so that the charging current through the resistors 66 and 68 will result in the transistor 88 being turned on for the lowest engine speed for which the resistor 68 may be adjusted. The value of the capacitor 60 is also selected to be small enough so that it will become fully charged during each cycle of the waveform, seen in FIG. 4, at the maximum engine speed. These constraints on the size of the capacitor 60 are minimized by the method of discharging the capacitor 60. The pulse that turns on the transistor 56 lasts for only a small percentage of a total ignition cycle so that the capacitor 60 is discharged in about l percent of the time that it is charged. Thus, the allowable time to charge the capacitor 60 is maximized. Since the time required to fully charge the capacitor 60 is determined by its capacitive value and the series charging resistance, which is mostly accounted for by resistor 58 whose value is fixed by the characteristics of Zener diode 72, maximizing charging time maximizes the allowable value of capacitor 60. Thus, this approach will allow operation at the lowest possible engine speeds.

The present invention, as seen in FIG. 1, may be slightly modified for use with an electronic ignition system, such as the ignition system disclosed in my copending US. application, Ser. No. 758,209, filed Sept. 9, I968, entitled Transistorized Ignition System. The ignition system as described therein is shown in FIG. 2.

In general, the ignition system seen in FIG. 2 is the same as the ignition system seen in FIG. I, with the exception of the power switching means which controls the current flow through the primary winding 12. It can be seen in FIG. 2 that the mechanical breaker points 20 have been replaced by a transistorized switching means.

In the system shown in FIG. 2, the direct current source is connected to the primary winding 12 through the ignition switch 16 and ballast resistor 18 as in the system in FIG. I. A transistor 98, however, having its collector connected to the terminal 36 and its emitter connected to ground, performs the current switching function of the breaker points and is turned on and off by the electronic ignition system to generate the ignition pulses in the secondary winding 22. The capacitor 35 connected in parallel with the transistor 98 performs the same function as it did in the system seen in FIG. 1. A Zener diode 100 having its anode connected to ground and its cathode to the terminal 36, protects the transistor 98 from an overvoltage when the transistor 98 is turned off.

The timing function of the electronic ignition system is performed by a photoelectric timing means comprising a photocell 102 coupled to the direct current source 10 through a resistor I04, and a light source 106 which is coupled to the direct current source 10 through a resistor 108. A shutter wheel 110 having a plurality of spaced accurate segments 112, corresponding to the number of spark plugs in the engine 32, is driven by the engine shaft 34. Light rays from the light source 106 incident upon the photocell 102, will cause the photocell 102 to become conductive. As the shutter wheel 110 is rotated, the light rays from the light source 106 will be interrupted causing the photocell 102 to become nonconductive. The voltage potential across the photodiode 102 will alternate between the voltage potential of the base electrode of a transistor I14 when the photodiode 102 is noneonductive and ground when the photocell 102 is conductive.

A signal amplifier comprising transistor 114 is responsive to the voltage potential across the photodiode 102 and will generate an amplified output signal at point 115.

A pulse shaping means including transistors I16 and H8 will respond to the signal at point 115 and generate a square wave output, appearing at the collector of the transistor 118 and also at points 120 and 122, having the same frequency as the signal appearing at point 115.

The square wave appearing at point 122 is applied to the base electrode of a transistor 123 and will turn the transistor I23 on and off at a frequency corresponding to the frequency of the square wave. Accordingly, the voltage potential on the collector electrode of the transistor 123 is also a square wave. The base electrode of the transistor 98 is connected to the collector of the transistor 123. The transistor 98 will be turned on when the transistor I23 is nonconductive, and will be turned off when the transistor 123 is conductive.

The square wave appearing at point 120 on the output of the pulse-shaping means is an input to the sensing means 48 on a line 124.

The sensing means 48, seen in FIG. 2, functions in the same general manner as was described in conjunction with FIG. 1. That is, the transistor 56 is turned on and off to discharge the capacitor 60 at a frequency proportional to the speed of the engine 32. The charging current for the capacitor 60 is amplified by the current-amplifying means 99. The transistor 88, included in the detector means, is responsive to the current amplifier 99 output and will become conductive to generate an output signal on the line 46 when the charging current for the capacitor 60 exceeds a predetermined value. The signal on the line 46 will cause the SCR 42 to become conductive to short out the switching transistor 98 and disable the ignition system.

The only significant difference between the engine r.p.m. limiting device seen in FIG. 2 and the one seen in FIG. 1 is the source of the timing signals used to control the transistor 56. Since the timing signals from the collector electrode of the transistor 118 used in the device of FIG. 2 to control the transistor 56 provides a precise definition of the engine speed, the Zener diode 50 and the diode 40 which are employed in the device of FIG. 1 to insure that the transistor 56 will become conductive but once every ignition cycle may be eliminated. Another advantage derived from using these timing signals is that the diode 94 and the resistors 44 and 96 of the device seen in FIG. 1 may also be eliminated since these signals are present regardless of the conductive state of the SCR 42.

It should be noted, however, that the source of the timing signals used to control the transistor 56 in FIG. 2 could be the same as the source in FIG. 1 if the Zener diode 50, diode 94 and the resistors 44 and 96 were retained.

Iclaim:

1. An electronic device for limiting the speed of an internal combustion engine having an ignition coil including a primary winding and a direct current source series connected to one side of said primary winding, said limiting device comprising:

switching means connected in series with said series connected primary winding and direct current source and responsive to said engine speed for alternate actuation to allow current flow through said primary winding and deactuation to interrupt said current flow at an actuation frequency proportional to said engine speed;

sensing means responsively coupled to said switching means for generating an output signal when said actuating frequency reaches a predetermined value;

a silicon-controlled rectifier connected across said switching means and having a gate electrode, said output signal generated by said sensing means being coupled to said gate electrode, said silicon-controlled rectifier becoming conductive to allow continuous current fiow through said primary winding when said output signal is generated by said sensing means.

2. The device as described in claim 1 wherein said sensing means includes (i) an RC charging network including a charging capacitor coupled to said direct current source, and (ii) discharge means responsively coupled to said switching means for discharging said each time said switching means interrupts said current flow through said primary winding, said direct current source charging said charging capacitor to a predetermined voltage potential by a charging current intermediate said discharges, the average value of said charging current being proportionalto said engine speed.

3. The device as described in claim 2 wherein said sensing means further includes a detector means responsive to said charging current for generating said output signal to said gate electrode of said silicon-controlled rectifier when the average value of said charging current reaches a predetermined value.

4. The device as described in claim 3 wherein said switching means comprises mechanical breaker points and wherein said sensing means further includes a diode coupled in parallel with said mechanical breaker points.

5. The device as described in claim 3 wherein said switching means comprise a transistorized circuit including a switching transistor connected in series with said primary winding said switching transistor becoming alternately conductive and nonconductive at a frequency proportional to said engine speed.

6. The device as described in claim 5 wherein said switching means further includes a photoelectric timing means coupled to said engine for generating an output timing signal having a frequency proportional to said engine speed, said timing signal being coupled to the base electrode of said switching transistor.

7. The device as described in claim 1 wherein said siliconcontrolled rectifier is series connected with a resistor, said series connected silicon-controlled rectifier and resistor being connected in parallel to said switching means, and wherein said sensing means is responsive to current flowing through said series connected silicon-controlled rectifier and resistor when said silicon-controlled rectifier is conductive.

8. A solid-state device for limiting the speed of an internal combustion engine having a direct current source connected to the primary winding of an ignition coil, said limiting device comprising:

means driven by said engine for generating timing signals synchronized with the speed of said engine;

pulse-shaping means responsive to said timing means for generating a square wave having a frequency determined by said timing signals;

switching means in series with said primary winding and responsive to said pulse shaping means, said switching means allowing current fiow through said primary winding when actuated and interrupting said current flow when deactuated, said ignition coil generating an ignition pulse when said current flow is interrupted;

sensing means responsive to said engine speed for generating an output signal when said engine speed exceeds a predetermined value; and

a silicon-controlled rectifier connected in parallel with said switching means and having a gate electrode coupled to said sensing means output signal, said silicon-controlled rectifier becoming conductive when said sensing means generates said output signal to allow continuous current flow through said primary winding.

9. The device as described in claim 8 wherein said sensing means includes (i) an RC charging network having a charging capacitor coupled to said direct current source and (ii) a discharge means coupled to said charging capacitor and responsive to said engine speed for discharging said charging capacitor at a rate proportional to said engine speed, said direct current source charging said charging capacitor by a charging current intermediate said discharges, the average value of said charging current being proportional to said engine speed.

10. The device as described in claim 9 wherein said sensing means further includes a detector means responsive to said charge current for generating said output signal when the average value of said charging current reaches a value corresponding to a predetermined engine speed.

ll. In an internal combustion engine having an ignition system including an ignition coil having a primary and a secondary winding, and a direct current source coupled to one side of said primary winding an engine r.p.m. limiting device comprising:

switching means having a first terminal connected to ground and a second terminal coupled to the other side of said primary winding and responsive to the speed of said engine for actuating to allow current flow from said direct current source through said primary winding and deactuating to interrupt said current flow at an actuation frequency proportional to said engine speed, said ignition coil generating an ignition pulse when said current flow is interrupted;

a diode having an anode and a cathode connected to said first and second terminals respectively of said switching means;

a silicon-controlled rectifier having (i) an anode electrode coupled to said second terminal of said switching means, (ii) a cathode electrode coupled to said first terminal of said switching means, and (iii) a gate electrode, said silicon-controlled rectifier becoming conductive to disable said ignition system when an appropriate signal is applied to said gate electrode;

a resistor connected intermediate said cathode electrode of said silicon-controlled rectifier and said first terminal of said switching means, and

a sensing means coupled to said second terminal of said switching means and responsive to said ignition pulses generated by said ignition coil for generating an output signal to said gate electrode of said silicon-controlled rectifier to disable said ignition system when saidignition pulses occur at a frequency corresponding to a predetermined engine speed, said control means being further responsive to current flow through said series connected silicon-controlled rectifier and resistor to maintain said output signal to said gate electrode when said ignition system is disabled until said engine speed slows to a value below said predetermined value.

12. The device as described in claim 11 wherein said sensing means includes anRC charging network including a charging capacitor coupled to said direct current source and discharge means responsive to said ignition pulses generated by said ignition coil and coupled to said charging capacitor for discharging said charging capacitor at a frequency determined by the frequency of said ignition pulses, said direct current source charging said charging capacitor with a changing current intermediate said discharges, the average value of said charge current being proportional to said engine speed.

13. The device as described in claim 12 wherein said sensing means further includes a detector means responsive to said charge current for generating said output signal when the average value of said charging current reaches a value corresponding to a predetermined engine speed.

14. The device as described in claim 13 wherein said switching means comprises mechanical breaker points.

15. The device as described in claim 13 wherein said switching means comprises a photoelectric timing means responsive to said engine speed for generating a timing signal proportional to said engine speed, and a switching transistor connected in series with said primary winding said switching transistor having a base electrode responsively coupled to said timing signal.

16. The device defined in claim 1 wherein said current flow through said silicon-controlled rectifier is limited when said silicon-controlled rectifier is conductive, to inhibit ignition pulses while allowing sufficient current changes in said primary circuit to allow actuation of said sensing means, thereby allowing operation of said device while the ignition system is disabled.

17. The device defined in claim 1 additionally comprising:

a diode, parallel connected to said switching means, said diode eliminating spurious signals from said switching means and thereby allowing said sensing means to produce said output signal at a frequency no lower than said predetermined frequency.

18. A solid-state device for limiting the speed of an internal combustion engine having a direct current source connected to the primary winding of an ignition coil, said limiting device comprising:

means driven by said engine for generating timing signals synchronized with the speed of said engine;

pulse shaping means responsive to said timing means for generating a square wave having a frequency determined by said timing signals;

switching means in series with said primary winding and responsive to said pulse shaping means, said switching means allowing current flow through said primary winding when actuated and interrupting said current flow when deactuated, said ignition coil generating an ignition pulse when said current flow is interrupted;

a capacitor;

means responsive to said engine speed for charging said capacitor;

sensing means responsive to said capacitor charging means for generating an output signal when said engine speed exceeds a predetermined value; and

a silicon-controlled rectifier connected in parallel with said switching means and having a gate electrode coupled to said sensing means output signal, said silicon-controlled rectifier becoming conductive when said sensing means generates said output signal to allow continuous current through said primary winding.

19. The device as described in claim 18 wherein said capacitor charging means charges said capacitor with a charging current the average value of which is proportional to said engine speed.

20. An electronic device for limiting the speed of an internal combustion engine having an ignition coil including a primary winding and a direct current source series connected to one side of said primary winding, said limiting device comprising:

switching means connected in series with said series connected primary winding and direct current source and responsive to said engine speed for alternately actuating to allow current flow to be said primary winding and deactuating to interrupt said current flow at an actuation frequency proportional to said engine speed;

a diode parallel connected with said switching means, to control the waveform produced by said switching means; and

control means responsive to said switching means for inhibiting the operation of said ignition coil when said actuation frequency reaches a predetermined level.

21. An electronic device for limiting the speed ofan internal combustion engine having an ignition coil including a primary winding and a direct current source series connected to one side of said primary winding, said limiting device comprising:

switching means connected in series with said series connected primary winding and direct current source and responsive to said engine speed for alternate actuation to allow current fiow through said primary winding and deactuation to interrupt said current flow at an actuation frequency proportional to said engine speed;

sensing means responsively coupled to said switching means for generating an output signal determined by said actuation frequency; and

a solid-state switch connected across said switching means and having a gate electrode, said output signal generated by said sensin means being coupled t0 said ate electrode, said so id-state switch becoming con uctlve to allow continuous current flow through said primary winding when said actuation frequency reaches a predetermined value.

22. An electronic device as defined in claim 21 additionally comprising:

a resistor, series connected with said solid-state switch, said series resistor and solid-state switch being connected in parallel with said switching means, said solid-state switch, when conductive, allowing current flow through said coil primary and said resistor when said switching means is deactuated, said resistor having a value which is sufficiently low that changes in the current flow through said primary winding caused by actuation and deactuation of said switching means when said solid-state switch is conductive will not produce ignition pulses; and

sensing means is responsive to changes in the current flow in said primary winding caused by actuation and deactuation of said switching means regardless of actuation or deactuation of said solid-state switch.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3.581.720 Dated un 1971 Inv Lewis W. Hemphill et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 21, "an" should read and line 42, an should read and Column 5, line 5, "an" should read and Column 7, line 17, "95" should read 96 Column 9, line 9, after "said", first occurrence, insert charging capacitor line 26, "comprise" should read comprises Column 10, line 16, should not have started new paragraph after "from"; line 35, after "means" the comma should be a semicolon.

Signed and sealed this 4th day of January 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Patents FORM PO-IOSO (IO-69 USCOMM-DC 6Q376-F'69 u 5, GOVERNMENT PRINTING OFFICE: 1909 o-sss-au

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Classifications
U.S. Classification123/335
International ClassificationF02P9/00
Cooperative ClassificationF02P9/005
European ClassificationF02P9/00A1