Speed Sensitive Electronic Fuel Control System for an Internal Combustion Engine

1. Field of Invention

The invention is related to electronic fuel control systems for internal combustion engines and in particular to speed sensitive electronic fuel control systems of the type taught by Reddy in U.S. Pat. No. 3,734,068.

2. Prior Art

The speed sensitive electronic fuel control disclosed by Reddy in U.S. Pat. No. 3,734,068 is illustrated in FIG. 1. This system embodies two capacitances 10 and 12 which are sequentially charged from two current sources respectfully designated RPM Signal Generator 14 and Ramp signal Generator 16. Electronically actuated switches, illustrated by mechanical ganged switch 18, controlled by an output signal from Switch Circuit 20, connects the two signal generators 14 and 16 to capacitances 10 and 12 in a manner so that when capacitance 10 is being charged by the RPM Signal Generator 14, capacitance 12 is being charged by Ramp Signal Generator 16 and vice versa. In this manner, both capacitances are sequentially charged, first by the output of the RPM Signal Generator 14, then by the output of the Ramp Signal Generator 16. At the end of each sequential charging period, the capacitance having been last charged by the output from the Ramp Signal Generator is discharged by means of a Discharge Circuit 22 to a predetermined value prior to the initiation of a new charging sequence.

The Switch Circuit may be a simple bi-stable flip-flop producing a square wave output signal in response to trigger signals designated TR 1 and TR 2. These trigger signals may be derived from the engine's crank shaft, flywheel or ignition system, and are indicative of predetermined angular positions of the engine, normally 180.degree. apart. Switch 18 responds to this square wave signal and assumes a first position in response to the positive portion and a second position in response to the ground or negative portion of the signal. Discharge Circuit 22 responds to the positive and negative transitions of the square wave and discharges the appropriate capacitance. The potential developed across both capacitances as they are being charged are communicated to the negative input of Comparator 24 by means of diodes 26 and 28. The output of a Load Signal Generator 30 is applied to the positive input to the Comparator 24. The Load Signal Generator 30 may be a pressure sensor generating a signal indicative of the pressure in the engine's air intake manifold as taught by Reddy in U.S. Pat. No. 3,734,068 or any other sensor generating a signal indicative of the engine's load.

The output of the comparator 24 is connected to the inputs of two parallel AND gates 32 and 34. The square wave output of the Switch Circuit 20 is applied directly to the alternate input of AND Gate 32 and indirectly to the alternate input of AND Gate 34 by means of an Inverting Amplifier 36. Alternately, the reciprocal or complementary square wave signal generated by the flip-flop may be applied directly to AND Gate 34.

The operation of this prior art circuit is described with reference to FIG. 1 and the waveforms shown on FIGS. 2A and 2B. It is assumed the Switch Circuit 20 is triggered by trigger signal TR 1 and its initial output signal is positive as shown on FIG. 2A. The positive output signal from the Switch Circuit 20 actuates switch 18 to the position shown on FIG. 1, activates Discharge Circuit 22 to discharge capacitance 12 to the predetermined value and enables AND Gate 32. Gates 32 or 34 to either Fuel Injector Group 1 or Group 2 depending upon which of the two AND gates is enabled by the square wave signal generated by the Switch Circuit 20.

The wave forms shown on FIG. 2B illustrate the change in the output 46 from the Comparator 24 when the engine speed has increased accompanied by an increase in the value of the load signal 44. The positive portion of the signal 46 is increased by two factors. Increasing the value of the load signal increases the positive portion of the Comparator's output by a first factor designated by the cross hatched area designated "a" indicative of the increased time it takes for the potential across capacitances 10 or 12 to reach the higher value of the load signal 44. The positive portion of the output signal generated by the Comparator 24 may also increased by a second factor, designated by the cross hatched section since the final value of the charge capacitances 10 or 12 is lower when switch 18 changes state in response to the square wave signal generated by the Switch Circuit 20. Obviously, if the only change in the waveforms illustrated on FIG. 2B was an increase in engine speed without a corresponding change in the load signal, the positive portion of the output signal from Comparator 24 would increase or decrease by the factor indicative of the time it would take the Ramp Signal Generator 16 to charge capacitances 10 or 12 to the value shown on Waveform 2A. Conversely, if the only change was an increase in the load signal without a corresponding change in the engine speed, the increase in the positive portion of the output from Comparator 24 would only proportional to the difference in time it would take the Ramp Signal Generator to charge either capacitance to the new value of the load signal.

Although this circuit works extremely well, it requires that the two capacitances 10 and 12 be a matched pair (identical) which require that they be tested prior to assembly to assure that the output signals generated by the Caparator 24 will be identical within permitted tolerances. Further, since both capacitances are charged by both the RPM and Ramp Generators, a severe restraint is placed on both signal generators to produce the desired wave forms. The disclosed invention eliminates both of these deficiencies.

The invention is an improved fuel control system of the type taught by Reddy in U.S. Pat. No. 3,734,068 in which the signal generated by a first signal generator charges a first capacitance to a value indicative of engine speed during a first predetermined interval of the engine's angular rotation. A charge transfer circuit, at the end of the first predetermined interval, transfers the charge on the first capacitance to the second capacitance from its initial value indicative of the engine's speed to a value equal to the value of the load signal.

The object of the invention is a speed sensitive electronic fuel control system in which the charge on the first capacitance indicative of the engine's speed is transferred to a second capacitance which is subsequentialy charged at a predetermined rate to the value of the load signal.

Another object of the invention is a fuel control circuit in which the two capacitances do not have to be a matched pair.

Another object of the invention is a fuel control system in which the value of the two capacitances do not have to be equal.

A final object of the invention is a fuel control system in which the output signal generated by the two signal sources are not constrained by the requirement that both capacitances have the same value.

These and other objects will become apparent from a reading of the Detailed Description of a Preferred Embodiment in conjunction with the drawings.

FIG. 1 is a block diagram of the prior art fuel control system as taught by Reddy in U.S. Pat. No. 3,734,068.

FIG. 2A is a series of waveforms used to discuss the operation of the system illustrated in FIG. 1 at a low engine speed.

FIG. 2B is a series of waveforms used to discuss the operation of the system illustrated in FIG. 1 at a higher engine speed.

FIG. 3 is a block diagram of the preferred embodiment of the disclosed system.

FIG. 4 is a circuit diagram of a preferred embodiment of the fuel control system shown on FIG. 3.

FIG. 5 is a series of waveforms used in explaining the operation of the circuit shown on FIG. 2A.

Referring to FIG. 3, there is shown a block diagram of the improved fuel control system of the type disclosed by Reddy in U.S. Pat. No. 3,734,068. For continuity purposes, common elements between this improved fuel control system and those of the prior art discussed with reference to FIG. 1 have the same identifying indicia. A comparable RPM Signal Generator 14 generates a reference signal which charges a first capacitance 10 to a potential having a value indicative of the engine's speed. As discussed with reference to FIG. 1, the RPM signal may be single valued as taught by Reddy in U.S. Pat. No. 3,734,068 or may vary as a function of time as taught in a commonly assigned copending patent application. A transfer circuit 50 is connected between the first capacitance 10 and a second capacitance 12 and transfers the potential stored on capacitance 10 to capacitance 12 in response to a transfer signal generated by a Switch Signal Generator 20 Capacitance 12 is further charged by a ramp signal generated by a Ramp Signal Generator 16. The ramp signal may be single valued as taught by Reddy in U.S. Pat. No. 3,734,068 or may vary as a function of time as shall be discussed hereinafter. A discharge Circuit 22 respectfully discharges capacitance 10 to a predetermined value determined by the Ramp Signal Generator 16 in response to signals generated by the Switch Signal Generator 20. The potential generated across capacitance 12 is communicated to the negative input of a Comparator 24 which also receives a load signal at its positive input from a Load Signal Generator 30. The Load Signal Generator 30 may be a pressure sensor generating a signal indicative of the pressure in the engine's air intake manifold or any other type of sensor generating a signal indicative of the engine's load as is known in the art. The Comparator may also receive an inhibit signal (not shown) from the Switch Signal Generator to disable the Comparator during the transfer process between the two capacitances. The output of the Comparator 24 is connected to the inputs of AND Gates 32 and 34. The alternate inputs of the AND Gates 32 and 34 receive complimentary flip-flop signals designated FF and FF from the Switch Signal Generator 20 which enable AND Gates 32 and 34 in an alternating sequence. The Switch Signal Generator 20 receives trigger signals TR #1 and TR #2 generated by a trigger signal generator (not shown). The trigger signals TR #1 and TR #2 are generated as a function of the angular rotational position of the engine's crankshaft, and are normally 180.degree. apart. These signals may be derived from sensors detecting the rotational position of the crankshaft itself such a cam actuated reed switches, or may be magnetic pick up detecting the position of the crank shaft or flywheel. Alternately the trigger signals may be generated by an inductive pick-up detecting the ignition signals or any other means known in the art.

FIG. 4 is a circuit diagram of the fuel control system shown in block form on FIG. 3. The terms B+ and ground as used herein have their usual meaning and represent the positive and negative inputs of a source of electrical energy normally associated with an internal combustion engine. This source may be a battery or any other engine driven source such as an alternator or generator. The trigger signals TR #1 and TR #2 are received at input terminals 100 and 102 respectively which are connected to the set and reset inputs of an RS flip-flop 104. The outputs Q and Q, a flip-flop 104 are connected to one of the inputs of AND Gates 32 and 34 respectively. The Q and Q signals are the FF and FF signals described with reference to FIG. 3. The Q and the Q outputs of flip-flop 104 are connected to one electrode of capacitances 106 and 108 respectively. The opposite electrodes of capacitances 106 and 108 are connected to B+ through resistances 110 and 112 respectively and to the cathodes of diodes 114 and 116. The anodes of diodes 114 and 116 are connected together and to B+ through a resistance 118 and to the input termed input of a comparator 120. The positive input of comparator 120 is connected to B+ and to ground through a resistance 122. The output of the comparator 120 is connected to B+ through a resistance 124 and to the base of a transistor 130 through a resistance 132. The 108 respectively. The opposite electrodes of capacitances 106 and 108 are connected to B+ through resistances 110 and 112 respectively and to the cathodes of diodes 114 and 116. The anodes of diodes 114 and 116 are connected together and to B+ through a resistance 118 and to the input termed input of a comparator 120. The positive input of comparator 120 is connected to B+ and to ground through a resistance 122. The output of the comparator 120 is connected to B+ through a resistance 124 and to the base of a transistor 130 through a resistance 132. The output of comparator 120 is also connected to the input of an inverting amplifier 130 and to the base of a transistor 132 through a resistance 134. Returning now to transistor 126, the emitter is connected to ground and to one electrode of a capacitance 136. The emitter of transistor 126 is connected to the positive inputs of comparators 138, 140 and 142 to B+ through resistance 144, and to the opposite electrode of capacitance 136.

The negative input of comparator 130 is connected to the center tap of a voltage dividing resistance network between B+ and ground consisting of resistances 146 and 148. In a like manner, negative input to comparator 140 is connected to the center tap of a voltage dividing network between B+ and ground consisting of resistances 150 and 152. Also, the negative input of comparator 142 is connected to a center tap of a voltage divider network between B+ and ground consisting of resistances 154 and 156.

The output of comparator 138 is connected to the control input of a bi-lateral switch 158 such as RCA-CD4106 or RCA-CD4066 manufactured by Radio Corporation of America, to B+ through a resistance 160 and to the input of an inverting amplifier 160. The output comparator 140 is connected to the control input of a bi-lateral switch 164, to B+ through a resistance 166, to the input of an inverting amplifier 168 and to the anode of a diode 170. The output of comparator 142 is connected to the control input of a bi-lateral switch 172 to B+ through a resistance 174, to the input of an inverting amplifier 176 and to the anode of diode 178. The output of inverting amplifier 162 is connected to the cathode of diode 170 and to the input of comparator 142 through diode 180 and to the control input of a bi-lateral switch 182 through a diode 184. The output of inverting amplifier 168 is connected to the cathode of diode 178 and to the control input of the bi-lateral switch 182 through a diode 186. The output of inverting amplifier 176 is also connected to the control input of the bi-lateral switch 182 through a diode 188 and to the output of inverting amplifier 130 through a resistance 190.

The outputs of the bi-lateral switches 158, 164, 172, and 182 are connected together and to the ungrounded electrode of a capacitances 10 and to the positive input of a comparator 192. The other electrode of capacitance 10 is connected directly to ground. The output of comparator 192 is connected to the emitter of transistor 132. The collector of transistor 132 is connected to the ungrounded electrode of capacitance 12, the negative input of comparator 192, the negative input of comparator 24 as shown on FIG. 3 and to output of the Ramp Signal Generator 16. The Ramp Signal Generator 16 may be a single current source as disclosed by Reddy in U.S. Pat. No. 3,734,068 or a multiple current source as taught herein with reference to the RPM Signal Generator. Because of the similarities of these circuits, the details of the Ramp Signal Generator need not be shown in detail for an understanding of the invention. The positive input of comparator 24 is connected to the Load Sensor 30 as shown on FIG. 3. The input to the bi-lateral switch 158 is connected by means of a resistance 194 to the center tap of a voltage divider resistance network consisting of resistances 196 and 198. The input of the bi-lateral switch 164 is connected by means of a resistance 200 to the center tap of a voltage dividing network consisting of resistances 202 and 204. The input to bi-lateral switch 172 is connected through resistance 206 to the center tap of a voltage divider network comprising resistance 208 and 210 connected between B+ and ground. The input to bi-lateral switch 182 is connected through resistance 212 to the center tap of a voltage divider network between B+ and ground comprising resistances 214 and 216. The output of comparator 24 is connected directly to the alternate inputs of AND Gates 32 and 34 as shown on FIG. 3 and to B+ through resistance 218.

The operation of the circuit will be described with reference to FIG. 4 and the waveforms shown on FIG. 5. Referring to FIG. 4, the trigger signals TR 1 and TR 2 are received by the flip-flop 104 which generates complimentary square waves at its Q and Q output as indicated on the waveforms of FIG. 5. The trailing edges of the square waves generated at the Q and Q outputs of flip-flop 104 produce a short negative going pulse 220 as shown on FIG. 5 at the junction between diodes 114 and 116 which is communicated to the negative input of comparator 120. The comparator 120 responds to these negative pulses generates a relatively short positive pulse signal 222 at its output which forward biases transistor 126 to discharge capacitance 136. The positive pulse output from comparator 120 is also communicated to the base of transistor 132 which disengages capacitance 12 to the potential on capacitance 10 as shall be explained hereinafter. After the termination of the pulse from comparator 120, capacitance 136 start to charge through resistance 144 and generates a ramp signal 224 which is applied to the positive inputs of comparators 138, 140 and 142. Termination of the positive pulse 222 also generates a positive signal at the output of inverter amplifier 130 which enables bi-lateral switch 182 which charges capacitance 10 to the value .alpha..sub.1 determined by the voltage divider network consisting of resistances 214 and 216. Resistance 212 determines the rate at which capacitance 10 is charged by this voltage divider network.

After a short period of time, the charge on capacitance 136 exceed the value of the potential applied to the negative input of comparator 142 as determined by the voltage divider network consisting of resistances 154 and 156. When the charge on capacitance 136 exceed this value, comparator 142 produces a positive output signal which activates bi-lateral switch 172. The positive output of comparator 142 also produces a negative or ground signal at the output of inverter amplifier 176 which turns off bi-lateral switch 182 through diode 188. Capacitance 10 is then charged to a value .alpha..sub.2 as determined by the voltage divider network consisting of resistances 208, and 210. The charge on the capacitor will either decrease as shown on FIG. 5, or increase depending on the value of the potential determined by the voltage divider network. After second time interval, the charge on capacitance 136 exceeds the potential of voltage divider comprising resistances 150 and 152 and comparator 140 produces a positive output enabling bi-lateral switch 164. The positive output of comparator 140 will also produce a negative signal at the output of inverter amplifier 168 which will be communicated to the input of bi-lateral switches 172 and 182 through diodes 186 and 188 respectively, thereby deactivating both of these bi-lateral switches. The potential generated at the center tap of the voltage divider network consisting of resistances 202 and 204 will then be communicated to capacitance 10 which will either charge or discharge to the potential .alpha..sub.3 established by the voltage divider network. After a third period of time, the charge across capacitance 136 will exceed the potential generated by the voltage divider network consisting of resistances 146 and 148 and comparator 138 will generate a positive output signal communicated to bi-lateral switch 158. Positive output of comparator 144 will also produce a negative or ground signal at the output of inverter amplifier 162 which will effectively deactivate electronic switches 164, 172 and 178 through diodes 170, 180 and 184. Capacitance 10 will then be either charged or discharged to a potential .alpha..sub.4 indicative of the potential generated by the voltage divider network consisting of resistances 196 and 198.

Referring now to the charge transfer portion of the circuit, capacitance 12 is charged by the signal from the Ramp Signal Generator 16 to a value well above the charge on capacitants 10 which is communicated to the negative input of comparator 192. Comparator 192 also receives the charge on capacitance 10 at its positive input. Since the charge on capacitance 12 is greater than the charge on capacitance 10, comparator 192 has a negative or ground output.

The positive pulse 222 generated by comparator 120 forward biases transistor 132 making it conductive. Capacitance 12 is then discharged through transistor 132 to the grounded output of comparator 192 until its value is equal to the value of the charge on capacitance 10. When the potentials on capacitances 10 and 12 are equal, the output of comparator 198 goes positive terminating the discharge of capacitance 12 and therefore capacitance 12 has a potential equal to the potential on capacitance 10. The termination of the positive output of comparator 120 back biases transistor 136 and capacitance 12 is charged by the output signal from the Ramp Signal Generator 16 increasing potential across capacitance 12 to a value greater than that transferred from capacitance 10. The rate at which capacitance 12 is charged by the Ramp Signal Generator 16 may be exponential as shown in FIG. 5, linear as shown in FIG. 2A or segmented.

As previously described with reference to FIG. 3, the output of the Load Sensor 30 is communicated to the positive input of comparator 24. As long as the charge on capacitance 12 is less than the value of the load sensor signal, the output of comparator 24 is a positive signal which is communicated to the alternate inputs of AND Gates 32 and 34. As previously indicated, AND Gates 32 and 34 are alternately enabled by the Q and Q outputs of flip-flop 104 and therefore alternately pass the positive output signal generated by the comparator 24. The output of comparator 24 transmitted through AND Gates 32 and 34 is a pulse width modulated injection signal indicative of the fuel requirements of the engine.

Having described the disclosed fuel control system with regards to a specific embodiment, it is not intended that the invention be limited to the embodiment discussed in the specification and illustrated in the drawings. It is recognized that a person skilled in the art could devise circuits to perform the same functions in the same way without departing from the spirit of the invention.