Electronic Fuel Injection System

Abstract

A sequential fuel injection system for an internal combustion engine has a separate electrical channel for each injector, each channel including a binary electronic counter. All said counters receive pulses from a voltage controlled generator whose frequency is set by the fuel demand. Engine operated timing means cause the counters to operate sequentially. An injector may be put into operation while a preceding injector is still being actuated, thus affording longer periods of injector operation.

Description

BACKGROUND OF THE INVENTION

Sequential fuel injection systems have been proposed in which the injectors are connected successively by a distributor to an output circuit. In engines having many cylinders, the period of operation of each injector may be very limited. This is a definite drawback, since the fuel supply must be varied over a very wide range. The present invention overcomes this difficulty by enabling the operating periods of the injectors to overlap. Another advantage of the invention is that it has a very low current consumption and this characteristic is taken advantage of to produce a high degree of stability with respect to the supply voltage. Still another advantage of the invention is that its operation is substantially independent of the duration and amplitude of the individual control pulses since only the frequency of the control pulses determines the amount of fuel supplied to the engine.

BRIEF DESCRIPTION OF THE INVENTION

The invention provides a digital electronic fuel injection system for a multi-cylinder engine. For each cylinder there is an injector, a circuit for operating the injector, and a digital divider circuit. A voltage controlled pulse generator is varied in frequency by sensors determining the fuel demand. The output fuel pulses of the pulse generator are supplied to all digital divider circuits. An engine operated timer or distributor supplies pulses to the divider circuits so as to place them in operation sequentially. Each divider circuit includes a binary counter and a NOR gate through which generator pulses are supplied to the input of the binary counter. The divider circuit also includes an AND gate through which the timing pulses are applied to reset the counter. After a predetermined number of pulses have been counted, the binary counter produces an output voltage which closes the NOR gate, and conditions the AND gate so that upon the occurrence of the next timer pulse and fule pulse supplied to that channel the AND gate will reset the counter and enable it to start a new count. A circuit is connected to the input of the AND gate to hold it closed when the NOR gate is open, in order to prevent timer pulses from reaching the binary counter while it is counting. Binary dividers or counters as used herein, are described in a publication of RCA Corporation entitled "COS/MOS Integrated Circuits Manual" copyrighted 1971 by RCA Corporation and printed in the United States of America in Mar., 1971. Pages 70 through 107 of the manual relate to counters and registers and the binary counter of FIG. 73 has utility in the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention is illustrated in the accompanying drawing, wherein:

FIG. 1 is a block diagram of a sequential fuel injection system according to the invention.

FIG. 2 is a block diagram of the digital divider for one channel.

FIG. 3 is a circuit diagram of the fuel rate converter.

DETAILED DESCRIPTION

Reference is made particularly to FIG. 1 of the drawing showing an embodiment of the invention for an 8-cylinder internal combustion engine. Timer 10, which may be in the form of a distributor of any suitable type synchronized with the engine, produces a series of pulses on lines 1, 2, 3, 4, etc. On each line the pulses 11 are 720 degrees, or two cycles, apart, and the pulses on the several lines are displaced 90 degrees from each other. The timing pulses are fed to a plurality of channels 12, there being a separate channel for each cylinder. Each channel includes a digital divider or counter 14, an injector operating circuit 16, and an injector 18, which may be a solenoid actuated valve. Each injector 18 is adapted to supply fuel to one cylinder and may be connected or mounted in a wall of the intake chamber immediately above the cylinder. The digital divider is also provided with fuel control pulses fed from a voltage controlled, variable frequency pulse generator 20 over lines 21 to all divider circuits. The frequency of pulse generator 20 is adapted to be varied by voltages representing the fuel demand of the engine. Each digital divider may have an output connection 22 from its first stage for supplying a starting pulse to injector circuit 16 for opening injector 18, and another output connection 24 from the last counting stage opening and for supplying closing pulses to determine the period of fuel injection. The closing pulse is also fed over line 26 to enable resetting of the digital divider 14 in response to a new timer pulse after completion of a cycle of operation. Output connection 22 may be omitted, since the start of the opening pulse on output connection 24, or a starting pulse from another part of the circuit, obviously may be used.

The operation of the system as disclosed in FIG. 1 is as follows: A timer pulse is fed from timer 10 to digital divider 14 to initiate operation of the digital divider. A series of fuel pulses is then fed from pulse generator 20 to the input of digital divider 14. The latter is set so as to send a pulse over line 24 to injector circuit 16 in response to the first pulse from generator 20 to open the injector and start a period of fuel injection into cylinder No. 1, say. The digital divider counts a predetermined number of pulses, which will be assumed to be 64 pulses, and then produces a high voltage pulse on line 24. This pulse causes injector circuit 16 to terminate the current fed to injector 18 to permit the latter to close. At the same time the closing pulse on line 24 is fed over line 26 to suitable reset circuits, which will be described in more detail hereafter. The digital divider 14 then remains inactive until the next timer pulse is impressed thereon. In the meantime, all other digital dividers are similarly operated at 90 degree intervals.

FIG. 2 discloses the circuitry and digital logic of one digital divider. Fuel pulses 30 from voltage controlled generator 20 are supplied to a NOR gate 32. These pulses are also fed to one input of a flip-flop circuit 34. The timer pulses 11 from timer 10 are impressed on terminal 38 of flip-flop circuit 34. NOR circuit 32 is connected to the input of binary divider 40 having a reset terminal 42. The output of flip-flop circuit 34 is fed by line 35 to one input of AND gate 44. The binary divider may consist of seven binary stages and is normally adapted to count to 64 and then produce an output pulse on line 24. The output pulse is fed to the injector circuit 16, and is also fed back to the second input of NOR gate 32 by line 26. The output of NOR gate 32 is connected by line 48 to a reset terminal 47 of flip-flop circuit 34. Voltage for binary divider 40, as well as other circuits of the channel are supplied from a regulated power supply. The latter includes a power transistor 50 on which battery voltage is applied through choke coil 52 and resistor 54. The output voltage is developed across a large capacitor 56, which may be of the order of a 100 mfd. The base of transistor 50 is connected to ground through a suitable zener diode 60 to produce a stabilized voltage of about 9 volts during normal operation. The control circuits disclosed herein can operate reliably on about 3 to 15 volts and have an average current drain of the order of a microampere. During cold engine startng the voltage regulator may turn off, allowing capacitor 56 to supply the required power. The capacitor will provide a far more than adequate voltage even after several minutes of steady cranking.

Assuming that binary divider 40 is set to begin a count, then output 24 will be at a low voltage and hold one terminal of gates 32 and 44 at a low voltage. The negative going portions of pulses 30 will then cause the output of NOR gate 32 to go high. The output from the NOR gate is fed over line 48 to reset flip-flop circuit 34 and make its output go low. AND gate 44 will then be closed. Pulses will be transmitted by NOR gate 32 to the input of binary divider 40 and the latter will produce an ON signal (low voltage) on line 24 until count 64 is reached. At that point, the voltage on line 24 will go high and impress a signal on one input of NOR gate 32 which will cause it to close. At the same time, the output from binary divider 40 will operate injector circuit 16 to close injector 18. Upon the closing of NOR gate 32, a low voltage will be fed from the output thereof to reset terminal 47 of flip-flop circuit 34, releasing it for operation. When the next timer signal 36 is impressed on flip-flop circuit 34, it will produce a high output which will be stored on a second input terminal of AND gate 44. Upon the next positive going pulse 30 supplied to the third input of AND gate 44, a reset pulse will be applied to reset terminal 42 of binary divider 40. This will cause the binary divider 40 to be reset so that all stages of the binary divider will be in their zero or low position and the output on line 24 will go low. The low output of binary divider 40 being applied to the inputs of NOR gate 32 and AND gate 44 will open the former and close the latter. NOR gate 32 is then in the condition to supply fuel pulses 30 to binary divider 40. Upon receiving the first pulse 30, the first binary stage of divider 40 will shift and the voltage on line 22 will go high and be fed to injector circuit 16 to cause opening of the injector for the start of a new injection period. The injection will last for a period of 64 pulses and consequently depend on the pulse repetition frequency which is determined by the fuel demand voltages impressed on pulse generator 20. Since the amount of fuel supplied to the engine is proportional to the time of opening of the injectors, the fuel supply will be in accordance with the engine fuel demand.

The circuit of pulse generator 20 is shown in FIG. 3. Fuel rate sensors 62 produce a voltage representing the fuel demand and this voltage is fed through choke coil 64 to capacitor C3 connected between the base of transistor Q6 and ground. The fuel rate sensors 62 can include sensing devices indicating engine variables such as manifold vacuum, engine speed, etc. Transistor Q1 and circuit elements connected thereto, including resistor R16, provide a temperature compensated current source for charging capacitor C1. Transistors Q5 and Q6 and their related elements form a comparator to sense when the charge voltage across capacitor C1 matches the fuel rate voltage of capacitor C3. When the match occurs, the comparator signal developed across resistor R11 is amplified by transistor Q8 and turns on transistor Q3. The circuit, including transistors Q3 and Q4 and capacitor C2, form a time-delay circuit designed to have a delay of several micro-seconds. During the delay period, the output of transistor Q3 turns on transistor Q2 to discharge capacitor C1 thorugh resistor R6. The output of transistor Q3 is transmitted through current limiting resistor R14 and transistor Q8, which serves as a buffer stage and supplies the fuel pulses 30 to output line 31.

Transistor Q1 may be provided with an enrichment circuit including resistors R1 and R4 and diodes D1 and D2, in which one or more of the resistors may be temperature responsive. This circuit is designed to suitably modify the rate of charge of capacitor C1 and thus change the frequency of the output fuel pulses by impressing a voltage on the network.

In operation, the cicuit of FIG. 3 charges capacitor C1 from a regulated voltage source through transistor Q1 at a constant rate. Capacitor C1 is charged to the level of the fuel rate voltage impressed on capacitor C3, and then capacitor C1 is discharged by transistor Q2 and clamped to ground for a fixed amount of time, such as several micro-seconds, and then the charge signal starts again. Thus, a continuous oscillation is maintained whose period is proportional to the fuel rate input voltage. Since the entire circuit is temperature compensated and depends upon voltage ratios rather whan absolute voltages, it is highly insensitive to supply voltage variations. It is also evident that a system has been provided which enables the injectors to be actuated independently in timed sequential order to supply the required amount of fuel, even if the fuel demand is so high that the operation of the fuel injectors overlap.

Claims

I claim:

1. An electronic fuel injection system for an internal combustion engine having a plurality of cylinders, comprising an electrically operated fuel injector for each cylinder; a channel connected to each injector for opening and closing it, each channel including a digital divider circuit for holding the injector connected thereto open during the counting of a predetermined number of input pulses; engine operated timing means for impressing voltage pulses on the divider circuits to start said circuits sequentially; a variable frequency fuel pulse generator connected to the inputs of all said divider circuits; and means connected to said pulse generator for controlling its frequency inversely in accordance with the fuel demand, whereby said injectors are actuated for periods proportional to the fuel demand.

2. A system according to claim 1, including means for preventing said pulse generator from impressing pulses on a divider circuit after receipt of said predetermined number of pulses thereby.

3. A system according to claim 2, wherein said last named means includes a NOR gate adapted to be closed by the output of the divider circuit after a count of said predetermined number of pulses.

4. A system according to claim 1, wherein each channel includes means connected between the timing means and a divider circuit for resetting said divider circuit so as to enable it to start a new count in response to the next timing pulse received thereby.

5. A system according to claim 4, wherein each said means for resetting a divider circuit includes an AND gate and means feeding the output of each divider circuit to one inout of the AND gate connected thereto to hold said gate open while the divider circuit is counting.

6. An elecronic fuel injector system for an internal combustion engine having a plurality of electrically operated fuel injectors; a binary electronic counter adapted to produce an output signal in response to a predetermined number of pulses impressed on the input thereof; a voltage controlled pulse generator connected to the input of said counter for supplying said pulses; means connected to said pulse generator for setting its frequency inversely in accordance with the fuel demand; engine operated pulse producing timing means; means connecting said timing means to said counter for initiating counting thereby; and means responsive to said timing means for opening a fuel injector and responsive to said output signal for closing said fuel injector.

7. A system according to claim 6, including means responsive to said output signal for terminating counting by said counter.

8. A system according to claim 6, including means responsive to said output signal for blocking the supply of pulses from the pulse generator to said counter.

9. A system according to claim 8, including means responsive to said output signal for resetting said counter in condition for starting a new count.

10. A system according to claim 9, wherein said means for resetting said counter operates to reset it only after receiving pulses from said timing means and said pulse generator.

11. A system according to claim 6, wherein said engine has a plurality of cylinders and a fuel injector for each cylinder, and a binary electronic counter connected to each fuel injector.