Fuel Injection System For An Internal Combustion Engine

Abstract

A fuel injection system for diesel engines is provided comprising an electronic control system for controlling fuel injection pumps made with electrostrictive material, to provide proper pilot injection of fuel followed by main fuel injection.

Description

BACKGROUND OF THE INVENTION

This invention relates to fuel injection systems for internal combustion engines of the compression ignition type and more particularly to improvements therein.

In the operation of internal combustion engines of the compression ignition principle, commonly referred to as diesel engines, compression of the fuel takes place as a result of increase in temperature of the air charge that is compressed adiabatically. Fuel is injected into the partially compressed charge of air some time before the piston reaches the top of its stroke. An ignition delay period occurs, following which the first droplets of fuel to be injected ignite, releasing heat to the surrounding compressed air. During the ignition delay period, two processes continue. The piston continues its upward stroke raising compression pressure (and consequently temperature), and injection of the fuel proceeds. Consequently, after the initiation of combustion, the total fuel that has been injected during the delay period tends to ignite instantly giving a high rate of rise of cylinder pressure and a high peak pressure, producing a characteristic "diesel knock" and heavily stressing components of the engine such as the piston, wrist pin, connecting rod, large- and small-end bearings and the crankshaft.

The roughness and noise associated with rapid cylinder pressure rise discourages the use of compression ignition engines for passenger cars despite the superior economy of these engines when compared with spark ignition engines.

Furthermore, the peak cylinder pressure achieved, dictates the strength and weight of the engine components mentioned above. These components have a cumulative influence on operating limitations since, for example, a stiffer piston pin boss will increase piston weight demanding increases in small end diameter, connecting rod section, big-end bearing area, and a heavier crankshaft. The increased reciprocating weight requires heavy crankshaft balance weights which in turn reduce the natural frequency of torsional vibration of the crankshaft and reduce the limit of rotational speed at which it may be operated. It may consequently be appreciated that peak cylinder pressure and rate of pressure rise are parameters that presently set the design boundaries for diesel engine operation, limit the specific power output that may be obtained, and restrict application to vehicles where noise and roughness may be tolerated.

In the past, efforts have been made to eliminate noise and roughness by utilizing two distinct periods of fuel injection. A small quantity of fuel was fed to the engine in a short duration, high pressure injection, timed slightly in advance of the normal injection point. After a time equivalent to the ignition delay period, which is approximately independent of speed and load, injection of the remainder of the fuel charge was effected. The injection of a small fuel quantity early in the compression stroke permitted ignition delay to occur without the continuing feed of additional fuel and after igniting, the heat release was of sufficient magnitude to insure that subsequent injection resulted in immediate combustion of the fuel particles. Factors influencing the crank angle that was rotated whilst ignition delay occurred, such as speed, fuel cetane rating, cylinder head temperature, etc., had little or no effect on the desired timing of the main injection which was dependent principally on the injection pressure and degree of atomization achieved. Consequently, whilst the first or pilot injection required to be variable in relation to crank angle, the second or main injection was preferably fixed in relation to crank angle.

Three methods were developed for achieving pilot injection. One was to employ a second pump and injector, timing, duration and quantity being variable independently of the main fuel injection. This layout was expensive and imposed installational difficulties on the engine unit since the cylinder head required two injector bosses thus limiting intake and exhaust valve sizes while a separate pump drive had to be provided.

A second method utilized a fuel pump cam having two lift periods. Jerk pumps are typically driven by cams which must accelerate the pump plunger to a working velocity and a spring mechanism is arranged to decelerate the plunger to zero velocity at full stroke, then to accelerate it again, while the cam form provides final deceleration to zero at the completion of the return stroke. The pump discharges fuel only after attaining maximum (or close to maximum) velocity. This provision is effected by the plunger edge occluding a spill-port at about a quarter of the stroke and reopening it upon completion of pumping, by the coincidence of a helical pressure relief groove cut in the plunger. Consequently, when two lift periods were employed to give pilot injection, the cam dynamics necessitated wider spacing of pilot and main injections than is desirable from combustion criteria. Time separation of pilot and main injections varied with speed and the chosen compromise gave errors at the extremities of the speed range of the engine, greatly reducing the effectiveness of the principle.

A third method of pilot injection which was used to employ a two-stage spill-cutoff by providing two relief grooves, one circumferential and one helical, thus producing one injection of a fixed quantity of fuel followed by a second injection of a variable quantity spaced from the first by a crank angle dependent upon the width of the first relief groove. This method also suffered from the disadvantage described above, of having a pilot to main injection spacing fixed in crank angle and not in time. Applied to a fixed speed engine it gave good results but for vehicle applications it was inadequate.

OBJECTS AND SUMMARY OF THE INVENTION

This invention provides a novel and practical arrangement for injecting a pilot quantity of fuel with independent control of timing, duration and quantity of the pilot injection and of the lead or spacing of the pilot injection from the main injection. These parameters may be progressively and independently varied, if necessary, while the engine is operating, in response to combustion requirements. This invention utilizes a pump employing an electroexpansive driver element, which may use piezoelectric material, and is exemplified in, for example, U.S. Pat. Nos. 3,354,327, 3,150,592 or 3,194,162. Such a pump is operated electrically and has the ability to respond to voltage pulses with delay periods typically varying down to 100 microseconds. Consequently, the pressure response is almost instantaneous so that no allowance is required to be made for the pump plunger to accelerate, and dribble of the fuel discharge nozzle is avoided. Accordingly, both startup and cutoff of fuel injection may be effected substantially instantaneously in response to electrical signals.

Operation of such a pump is controlled by circuitry which is operated to provide the correct timing of signals which establish pilot injection and the timing between pilot injection and main injection. The basic timing requirements are that main injection should occur at approximately a fixed crank angle, and that pilot injection occur at approximately a fixed time, but a varying crank angle, before main injection. The timing signal for main injection can be obtained by a means exemplified by a cam, driven from the engine camshaft, and a switch means to initiate main injection at the desired crank angle. However, pilot timing cannot be obtained directly from a cam on a variable speed engine because the switch means will operate at a given crank angle, and the time between pilot injection and main injection would vary with engine speed. Because it is not possible to measure the time before an event occurs, it is necessary to predict the time of occurrence of the event. For this purpose, this invention includes a Pilot Leadtime Computer, described below, which predicts the time of main injection and causes pilot injection to occur at a fixed time period before the predicted time of main injection.

The operation of the Pilot Leadtime Computer, herein exemplified by but not limited to analog electronic circuitry, is as follows. Basic timing is obtained from a cam attached to the engine camshaft and three switch means, which may be mechanically operated, optically operated, or operated in any desired manner, herein designated Start Switch, Main Switch, and Reset Switch. The switches are located so that a predetermined crank angle is rotated between closure of the start switch means and the main switch means and a possibly different crank angle is rotated between closure of the main switch means and the reset switch means. Closure of the main switch means initiates main injection. Pulse shaping circuits generate pulses at the moment of closure of the switch means and these pulses are used to initiate action in the computer circuitry. The leadtime computer, on a given cycle, generates, by means of a first voltage ramp generator, a voltage proportional to the time between closure of the start switch means and the main switch means. This voltage is stored in a sample and hold circuit to be used on the next cycle of the engine. This stored voltage is used to predict on the next cycle the time interval between closure of the start switch means and main injection (i.e. of main switch closure). The computer also generates a pilot lead voltage proportional to the desired fixed time interval between pilot and main injection. This pilot lead voltage is subtracted from the stored voltage by electronic or other means to give a resultant voltage proportional to the computed time between closure of the start switch means and the instant at which pilot injection should occur.

The pilot lead voltage is derived from a circuit having a number of input settings both manually and automatically regulated. A setting is provided for adjustment, at the engine manufacturer's plant, of the basic pilot leadtime found suitable for quiet operation of the engine on a fuel of known cetane value. This setting adjusts by resistive or other means, the voltage level obtained from the vehicle's voltage regulator to produce a voltage proportional to the desired pilot leadtime. A further circuit provides adjustment for fuels of different cetane number and manual selection is provided for a range of cetane values commonly encountered in vehicle fuels. The voltage output of this output is proportional to the change in pilot leadtime that is desirable with fuels differing in cetane value from a datum test fuel. A further circuit is provided for adjustment of pilot leadtime with the engine's cylinder head temperature. A temperature sensitive element fitted to the cylinder head automatically modifies the voltage obtained from the vehicle's voltage regulator to produce a voltage adjustment proportional to the change in desired pilot leadtime that occurs with cylinder head temperature changes. A further circuit is provided to accept signals from any engine parameter found from tests to influence ignition delay time. Such an influence may, for example, be produced by engine speed, as a secondary effect, owing to the reduction in air charge heat loss as speed increases.

The voltage outputs of all circuits influencing pilot leadtime are applied to a summing amplifier and the resultant pilot lead voltage is subtracted as already described.

A second ramp voltage generator generates a voltage proportional to the time elapsed since closure of the start switch means, the constant of proportionally being the same as that of the first ramp voltage generator. This second ramp voltage, proportional to time since closure of the start switch means, is continuously compared with the resultant voltage proportional to the computed time between closure of the start switch means and the required instant of pilot injection. When the amplitudes of these two voltages are equal, a pilot, high voltage, pulse generator is actuated which enables the electroexpansive material pump to provide pilot injection to the cylinder. Voltage comparison is performed by means of known voltage comparator circuits or other desired means. A pilot suppression switch is included to suppress pilot injection during starting or at any other time that pilot injection suppression is desired.

Closure of the reset switch means occurs after main injection, and causes the output of the first and second voltage ramp generators to be reset to zero volts and to remain at zero volts until the next closure of the start switch means.

The above description has been for an engine with a single cylinder. Operation of a multicylinder engine can be accomplished by having one pilot time computer, one power supply unit and one electroexpansive pump per cylinder. This is not meant to preclude the sharing between two or more cylinders of components belonging to the system of one cylinder.

When starting, a pilot injection suppression switch is opened to prevent pilot injection from occurring because the pilot computer on first starting would signal injection at the point of closure of the start switch means and might cause a reverse kick on the crankshaft whilst the starter is engaged.

In summary of the foregoing, the main fuel injection will, at all times except when starting the engine, occur at the same crank angle. However, the crank angle relative to the main fuel injection at which the pilot fuel injection should occur varies in accordance with the speed of the engine and other factors.

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block schematic diagram exemplary of an arrangement in accordance with this invention for fuel injection control. A four cylinder engine is taken by way of example, and not by way of a limitation.

FIGS. 1A and 1B are a block schematic diagram of the fuel injection control circuit required for each cylinder in accordance with this invention.

FIG. 2 is a timing chart showing the sequence of events in FIG. 2. The engine is shown accelerating to show how voltage levels change with speed.

FIG. 3 is a block schematic diagram illustrating a fuel control governor which may be used with this invention.

FIG. 4 is a block schematic diagram illustrating, by way of example, a four cylinder embodiment of the invention.

FIG. 5 is a block schematic diagram illustrating a simplified arrangement of a four cylinder embodiment of the invention.

Referring now to FIGS. 1A and 1B, there may be seen the details of a fuel injection control circuit together with a fuel injection control constant circuit. FIG. 2 shows a timing chart which should also be considered. An engine-driven cam 30 is assigned to each fuel injection control circuit. Associated with the cam is a start switch 32, a main switch 34, and a reset switch 35. These are cam-driven switches. Switch 32 is shown in its operated position and switches 34 and 35 are shown in the unoperated position. Closure occurs on the trailing edge of the cam lobe.

The cam surface and the positioning therealong of the cam switches for operation thereby is determined as follows. The main cam switch 34 is positioned so that it is operated substantially at the proper and customary crankshaft angle for obtaining the main fuel injection. The start cam switch is positioned in advance of the main cam switch a distance which will provide the largest crank angle desired for the pilot fuel injection to occur before main fuel injection at the fastest engine speed. The reset cam switch 35 is positioned to operate after main injection and before closure of the start switch on the next cycle.

When operated, start switch 32 applies a voltage from a voltage regulated power supply 33 taking current from the vehicle's electrical system, to a pulse shaping circuit 40, which respectively generates a pulse at the moment of switch closure. This is represented as waveform 40A in FIG. 2. This pulse is applied to a first ramp voltage generator 42 and also to a second ramp voltage generator 44. In response both the first ramp voltage generator 42 and the second ramp voltage generator 44 are triggered into starting the generation of a ramp voltage. See waveforms 42A and 44A in FIG. 2.

As the engine continues to operate, the main switch 34 is operated by the cam 30 and applies a voltage from the voltage regulated power supply 33 to a pulse shaping circuit 46, which applies a pulse (see waveform 46A in FIG. 2) to the ramp voltage generator 42 causing it to stop. Its output is now a voltage proportional to the time between closure of start switch 32 and closure of main switch 34. The pulse from the main pulse shaping circuit 46 is applied, with a short delay (up to 10 microseconds), by delay circuit 48, to a sample and hold circuit 50, commanding it to sample. When the sample and hold circuit 50 receives a sample command pulse, it rapidly sets itself at a voltage equal to the output voltage of ramp generator 42 and remains at that voltage until commanded to sample again. (See waveform 50A in FIG. 2.) The output of the main pulse shaping circuit 46 is also used to initiate main fuel injection in a manner to be described below.

The output of the sample and hold circuit 50, which has an amplitude proportional to the time between closures of the start switch 32 and main switch 34, is applied to a subtractor circuit 52 which subtracts from it a voltage proportional to the desired time between pilot and main injection giving resultant (waveform 52A shown in FIG. 2 and designated V.sub.4). This voltage is established by adding voltages from a factory set voltage source 54, a fuel cetane number voltage source 56, a voltage established by an engine temperature sensor 58, and a voltage representing any other engine variable, from a source 60, which can be converted to an electrical signal by means of a transducer and which it may be desired to have considered. The above voltage sources 54, 56, 58 and 60, may be derived from resistors, fixed or variable, connected to voltage regulated power supply 33; or may be derived from any other transducer with an electrical output. These voltages are applied to summing amplifier 62, whose output, designated as V.sub.3, is the sum of the input voltages. The system is designed such that the output of the summing amplifier 62 is a voltage proportional to the proper time between pilot and main injection for the engine variables at that instant. This voltage is applied to the subtractor 52 which subtracts if from the voltage proportional to the time between closure of the start switch 32 and the main switch 34 which is designated as V.sub.2.

The subtractor 52 applies its output voltage, V.sub.4, proportional to the difference between the input voltages V.sub.2 and V.sub.3, to a comparator circuit 62, of a known type. The comparator circuit compares the output voltage of ramp generator 44, designated as V.sub.5, with the output voltage V.sub.4 of the subtractor 52 such that when voltage V.sub.5 is less than voltage V.sub.4 the output voltage V.sub.6 will be at some preset low or negative voltage, but when voltage V.sub.5 is greater than voltage V.sub.4 the output voltage V.sub.6 of the comparator circuit will be some preset high value. At the point when voltage V.sub.5 increases to equal voltage V.sub.4 the output voltage V.sub.6 will change rapidly from the preset low to the preset high voltage. A pulse shaping circuit 64 shapes the comparator output voltage into a pulse to trigger pilot injection in a manner described below.

Upon closure of the main switch 34, a voltage is applied to the pulse shaping circuit 46, which in response, delivers a pulse to a cold start switch 66, as well as to ramp generator 42, and to sample and hold circuit 50, as described above. When the cold start switch 66 is in its normal position, the applied pulse is transmitted to an amplifier 68, of the main power supply unit.

If the cold start switch 66 is placed in the start position, (for example by operation of the engine starter solenoid 69,) the pulse may be applied to time delay circuits 72 and 74 by the operation of an ambient temperature sensitive switch element as well as by time delay circuit 70. Time delays 70, 72 and 74 have fixed delay times set to provide retardation of injection to produce injection closer to piston top dead center under cold starting conditions. Time delays 72, 74, etc., are introduced progressively with lower temperature by means of a temperature sensitive switch 110 to provide for multiple main injections on a single cycle of the engine at cranking speed. The delay time of time delays 72,74 are set to the shortest interval required for the main power supply unit to recharge its capacitor after the previous injection. The outputs of time delay circuits 70, 72, 74 are all applied to amplifier 68.

As the motor continues to operate, the reset switch 35 is operated by the cam 30 such that it closes after both pilot and main injections are completed, but before closure of the start switch 32 on the next cycle. Closure of the reset switch 35 applied a voltage from the voltage regulated power supply 33 to the reset pulse shaping circuit 80, which generates a reset pulse in response thereto. This pulse is applied to ramp generators 42 and 44 to reset their respective outputs to zero volts, in preparation for the next cycle.

Timing signals are generated by the pilot time computer, which has been described above. These timing signals are applied to the switch 92, which actually switches electrical energy from the pilot power supply 84 into the electroexpansive pump 82. The pilot power supply unit obtains electrical power from the vehicle's electrical power system (not shown). This power is converted to the proper voltage and power level for pilot injection by the pilot power supply 84. The actual voltage level of the pilot power supply 84 is set by the pilot quantity adjust circuit 86, which may be preset at the factory with possible corrections for engine operating conditions. The pilot quantity adjust 86 may be a voltage regulator of a type suitable for operation with automobile engines.

The output of the pulse shaping circuit 64 is applied to an amplifier 88. This amplifier amplifies the trigger signal to the proper voltage level to trigger an electronic switch 92. The pulse from the amplifier 88 is applied through a pilot suppression switch 90 to the electronic switch 92 and a pilot pulse width control circuit 94. When the pilot suppression switch 90 is open there will be no pilot fuel injection. This pilot suppression switch may be connected to the starter solenoid or to the operator's controls in such a manner that it will be operated to suppress pilot injection when such suppression is found desirable; for example, during starting as already described.

When the pilot suppression switch is closed the pulse from the amplifier 88 is applied to the trigger of the electronic switch 92 and to the pilot pulse width control circuit 94. The pilot pulse width control circuit is a fixed time delay circuit of a well-known type, such as a one shot circuit, and applies the trigger pulse after time delay to the trigger of an electronic switch 96. When the electronic switch 92 receives a trigger pulse, the switch is made conductive and enables voltage from the pilot power supply to charge the electroexpansive element pump to approximate the voltage generated in the pilot power supply. This causes pilot fuel injection to occur. After the electroexpansive element pump 82 is charged to the voltage of the pilot power supply 84, the electronic switch 92 is automatically turned off. The delayed pilot trigger from pilot pulse width control 94 is then applied to electronic switch 96, causing it to conduct. This switch serves the function of discharging the electrical charge from the electroexpansive pump 82, thus ending pilot injection. It should be noted that the electronic switches may be thyratrons or silicon-controlled rectifiers, for example.

Power from the vehicle's electrical system (not shown) feeds a main injection power supply 100, which converts this power to the proper voltage and current for the main injection phase of the electroexpansive element pump. At the proper time for main injection, a pulse is received by the amplifier 68 from the main pulse shaping circuit 46. The amplifier 68 amplifies this trigger pulse to the proper level to trigger electronic switch 102 and to drive the main pulse width control circuit 104. This is a time delay circuit of a known type similar to the circuit 94, and may be preset at the factory. When the trigger pulse from amplifier 68 is applied to electronic switch 102, the electronic switch conducts and applies voltage from the main injection power supply 100 to the pump 82. When this charging is completed, electronic switch 102 is automatically turned off. After a preset time delay, the main pulse width control circuit 104 applies a trigger pulse to an electronic switch 106 which then conducts and removes the electrical charge from the pump 82 terminating main fuel injection.

This completes the fuel injection cycle.

The system described above is for a single cylinder engine but may be extended to a multicylinder engine by having one such system for each cylinder of the engine. This does not exclude the possibility that some components of the system may be shared by a number of cylinders and need not be duplicated.

The quantity of fuel which is injected by the electroexpansive pump may be determined either by the amplitude of the voltage applied thereto from the main injection power supply, on the length of time this voltage is applied. This is true whether the pump is operated in response to a single pulse or in response to a plurality of pulses supplied during the main fuel injection interval. Since with different conditions of engine speed and load, it is necessary to vary the amount of fuel supplied a fuel control governor apparatus 108 is provided. Normally the amount of fuel supplied to the engine is controlled by a foot pedal which is represented by "operator's control" 109. The operator's control apparatus may be a potential source across which is a potentiometer, or voltage divider which can be varied in response to a foot pedal, to produce an output signal in response to which the fuel control governor 108 can determine the main injector power supply output voltage or the delay interval of the main pulse width control circuit or both. Alternatively, the fuel control and governor apparatus can include linkages which vary potentiometer values within the main injection power supply or main pulse width control circuit itself, whereby these are controlled for the purposes intended. Such controlled power supplies and variable delay circuits are known and commercially purchasable.

The fuel control governor 108 may have an additional input from the main pulse shaping circuit 46 for the purpose of smoke limitation. This input is a voltage proportional to the speed of the engine and is used to program the quantity of fuel to be supplied to the engine. The function of such programming is to provide speed governing or to prevent the emission of exhaust smoke by limiting maximum fuel in a predetermined relationship with engine speed. Such governing is performed with present-day diesel engines in which the maximum amount of fuel for a given engine speed is limited or governed. The details of a preferred arrangement for a fuel control governor 108, which has smoke control capability are shown in FIG. 3.

In summary of the foregoing, start switch 32 and main switch 34 are spaced to be operated responsive to the cam 30, so that the time interval therebetween at maximum engine speed is slightly larger than the maximum time interval desired between pilot and main fuel injection. The time interval between switches grows larger with diminishing engine speed since the start and main switch positions are fixed.

Ramp generator 42 is used to generate a voltage, the amplitude of which represents the time interval between closures of switches 32 and 34. This voltage is diminished by another voltage whose amplitude represent the desired time interval between pilot and main injection and is the net output of a pilot fuel injection control constants circuit. The resultant voltage represents the predicted desirable time lapse between closure of switch 32 and the instant of pilot injection on the next engine cycle.

The second ramp generator 44 together with the comparator 62 cooperate to identify the point in time at which this time interval has elapsed and to signal initiation of pilot injection. Since one cannot compute the pilot leadtime and then go back in time before a main injection to produce a pilot fuel injection at the interval computed, the computed pilot injection lead interval is converted to a computed pilot injection lag interval after the next closure in sequence of the start switch 32. Since there is essentially no large time difference between adjacent cycles of engine operation, the fact that the pilot injection lagtime is computed from a time interval measured in the preceding cycle of engine operation has no significant effect upon the accuracy of the computation.

Thus, in operation, there is first a closure of a start switch means followed by a closure of a second switch means signalling main injection. A resetting switch then operates, then a succeeding closure of the start switch means followed by a pilot injection and then a main injection again followed by operation of the reset switch means.

The aschematic circuit illustrative of a fuel control and governor 108 is shown in FIG. 3. A pulse from main pulse shaping circuit 46 is applied to an electronic tachometer 110. This may be a well-known type of tachometer such as a monostable multivibrator and averaging circuit in accordance with tachometers which are commercially available. Other types of electrical or electronic tachometers may be used. In response to a pulse train input, the output of this tachometer is a voltage proportional to actual engine speed. This voltage is applied to a comparator circuit 112 which compares this with a voltage from a source 114 which is proportional to the maximum desired engine speed. As the voltage out of the tachometer 110 approaches close to the maximum, the comparator output goes negative and therefore a negative voltage is applied to an amplifier 116 through a diode 117 and resistor 118. Diode 117 becomes conductive and the resulting voltage drop at the input to the amplifier 116 is determined by the relative values of series connected resistances 118 and 120 and the gain of comparator 112. The drop in voltage at the input to amplifier 116 as the speed approaches the maximum value limits the quantity of fuel so that the engine will not exceed the preset maximum speed. When the engine speed is below the maximum, the output of the comparator 112 is positive. Diode 117 does not conduct and the comparator output does not affect the amplifier.

The voltage proportional to speed from the tachometer is also applied to a programmed nonlinear network 122 of a well-known type, such as the resistor diode networks commonly used in analog computers for producing an output voltage having a predetermined amplitude relationship with an input voltage amplitude. The programmed nonlinear network 102 is programmed so that the amount of fuel injected per stroke will not be so much as to cause smoke. This limit is a function of engine speed and is programmed at the factory. The voltage out of the programmed nonlinear network 122 is connected through a diode 125 to the output of the amplifier 116, thus limiting the output so that it can be less than the programmed limit but never greater. When the output voltage exceeds the programmed limit, the diode 125 becomes conductive causing a voltage drop across resistor 124 and thus reducing voltage to the main injection power supply. The amount of fuel injected will be proportional to the output of amplifier 116. The primary control of the output of amplifier 116 is the operator's control 109 which is applied to the input of amplifier 116. The output of the amplifier, and therefore the quantity of fuel injected, will be proportional to the operator's control unless the speed approaches closely to the preset maximum or the quantity of fuel approaches the programmed limit. In either of these two cases, the output will be limited by the governor or the programmed smoke limit control.

The operator's control may be connected to control speed rather than quantity of fuel. In that case, the operator's control can be connected to comparator 112 in place of the maximum speed setting in such a way that maximum speed will never be exceeded. Fuel quantity is automatically increased until the engine reaches the smoke limit. The gain of the comparators can be set to give a smooth control.

An embodiment of the pilot leadtime computer showing the specific structure required for a four cylinder engine is shown in FIG. 4. The numbering in FIG. 4 is the same as the numbering in FIGS. 1A and 1B for identically functioning structures except that the duplicated devices are shown with a, b and c following the numbers. The power handling part of the circuit consisting of the pilot and main injection power supplies, the electronic switches and the pulse width controls are not shown in FIG. 4.

The components of the power unit which must be duplicated for each cylinder are electronic switches 92, 96, 102 and 106; amplifiers 68 and 88; pilot pulse width control 94, main pulse width control 104, and the electroexpansive pump 82. The pilot power supply 84, the pilot quantity adjust 86 and the main injection power supply 100 and the fuel control 108 need not be duplicated for each cylinder.

Certain components of the pilot leadtime computer are duplicated for each cylinder. They are: the main switch 34, the pulse shaping circuit 46, the ramp generator 44, the comparator 62 and the pulse shaping circuit 64. The other components of the pilot leadtime computer are not duplicated. A separate pilot suppression switch 90 is required for each cylinder.

The switches 34a, 34b, 34c and 34d serve as main injection switches for the corresponding cylinders. These switches are disposed at equal angular intervals, 360.degree. divided by the number of cylinders, apart (i.e. 90.degree. on a four cylinder engine) and are operated by cam 30 driven by a 1/2 crank speed shaft. These switches also serve the function of the start switch (switch 32 in FIG. 2) for the next cylinder in the firing order. That is, switch 34d serves as the start switch for the first cylinder and also as the main and the reset switch for the preceeding cylinder in the firing sequence. Because these switch closures are spaced at equal angular intervals of crank rotation, the time intervals between the first pair and the last pair in the firing sequence in any one cycle of the engine will be substantially equal. Consequently computations based upon the time interval occurring between the first pair of closures will be valid for the last pair of closures. Inertia of the rotating parts of the engine prevents significant changes in angular velocity from occurring in the period of one engine cycle. However, should these changes cause operational difficulty additional circuitry deriving a signal proportional to the angular acceleration of the engine may be incorporated. The switches also serve as timing sources for the circuitry, which computes the voltage proportional to the time interval between closure of the start switch and the computed instant of pilot injection.

Operation of this system on a four cylinder engine will now be described.

Closure of switch 34d, which now has the same function as switch 32 in FIG. 1A, causes pulse shaping circuit 46d to emit a pulse which starts ramp generator 42. A later closure of switch 34a causes the ramp generator to stop and commands the sample and hold circuit 50 to sample the output of the ramp generator. The factory preset voltage proportional to the desired lead time, coming out of amplifier 62, is subtracted from the voltage out of the sample and hold circuit 50 by the subtractor circuit 52 giving a resulting voltage V.sub.4 which is proportional to the time interval between closure of the start switch and the computed instant of pilot injection. This voltage V.sub.4 is applied to the comparators 62a, 62b, 62c and 62d for all four cylinders. The computing cycle is completed by closure of switch 34b which causes the ramp generator 36 to be reset. The voltage V.sub.4 is computed once per cycle of the engine and is used to fix the instant of pilot injection for each of the four cylinders.

The timing of pilot injection for the first cylinder is determined in the following manner. Closure of switch 34d applies a voltage to pulse shaping circuit 46d which in turn applies a pulse to ramp generator 44a and this pulse starts the voltage ramp operation. The voltage output of ramp generator 44a is proportional to the time elapsed since closure of switch 34d and is applied to a comparator 62a. When this voltage reaches the level of voltage V.sub.4 out of the subtractor, the output of the comparator 62a goes from a low level to a high level. This high level voltage is applied to the pulse shaping circuit 64a which forms a trigger pulse to initiate pilot fuel injection in cylinder No. 1. A short time later, the cam 30 causes switch 34a to close applying a voltage level to pulse shaping circuit 46a which generates a pulse which then initiates main fuel injection for cylinder No. 1. This pulse, which occurs upon closure of switch 34a, is also used to start the ramp generator 44b for the cylinder next in firing order, and to reset the ramp generator 44a in preparation for the next start signal on cylinder No. 1. The ramp generators 44b, 44c, 44d, comparators 62b, 62c, 62d, and pulse shaping circuits 64b, 64c, 64d follow, for each cylinder, the same operation cycle as described for cylinder No. 1. Each cylinder uses the computed voltage V.sub.4 which is computed to be proportional to the time interval between closure of a start switch corresponding to that cylinder and the desired instant for pilot injection for that cylinder at the prevailing speed and operating conditions of the engine.

This description shows the manner in which this invention can be applied to a four cylinder engine. The system shown is exemplary and other arrangements of components to suit any number of cylinders may be employed. Individual components may be combined into one unit without departing from the principles of operation described.

Further reductions in number of components for a pilot leadtime computer is possible for a multicylinder engine. An example of one such reduction is shown for a four cylinder engine in FIG. 5. This system does not require individual ramp generators, comparators and pulse shaping circuits for each cylinder, and it also eliminates ramp generator 42 which was used in the previous systems. Elimination of ramp generator 42 is made possible by using a sample and hold circuit which can take its sample in a few microseconds and then hold that value for seconds, if required. Such circuits are well known.

Switches 134a, 134b, 134c and 134d are single-pole double-throw switches each having a front contact respectively connected to pulse shaping circuits 146a, 146b, 146c, 146d respectively and a back contact connected to AND gates 148a, 148b, 148c and 148d respectively. Closure of switch 134a to its front contact applies a voltage level to pulse shaping circuit 146a. The output pulse from the pulse shaping circuit is used to initiate main fuel injection for the corresponding cylinder and is also applied to the OR gate 149. A pulse is derived from the OR gate whenever there is a pulse on any of its four inputs (from any one of pulse shaping circuits 146a,...146d). The pulse out of the OR gate 149 is applied to the sample and hold circuit 150 in response to which it samples the voltage of ramp generator 152, and holds this voltage level. The output of the OR gate 150 is also applied to a time delay circuit 154 which has a time delay (of a few microseconds) long enough for the sample and hold circuit 150 to complete its sample before the ramp generator 152 is reset.

At the end of the delay interval the ramp generator 152 is reset by the output from the time delay circuit 154 and this output is also applied to time delay circuit 156, which has a time delay longer than the time required to reset the ramp generator (less than 1 millisecond). At the end of the delay interval produced by time delay 156, the ramp generator 152 is enabled to start a new ramp voltage which will be proportional to the time interval elapsed since the closure of switches 134a, minus the sum of the time delay intervals established by delay circuits. At the closure of switch 134b, the output of the ramp generator is sampled and stored again. This sample voltage is now proportional to the time interval between closure of two adjacent switches (134a, 134b) minus the sum of the time delay intervals. This voltage is applied to subtractor 158. The voltage proportional to the computed leadtime derived from summing amplifier 62 is subtracted and the resultant is the voltage V.sub.4. The voltage V.sub.4 is then compared, by comparator 160 with the output voltage of ramp generator 152. When they are equal a voltage is applied to pulse shaper 162 which can provide a pilot trigger pulse at the instant that the two voltages are equal (i.e. at the computed instant for pilot injection). The process of comparison eliminates the effects of the time delays on the output of the ramp generator 152, so long as the time delays remain constant from cycle to cycle.

The system now described differs from systems described earlier in that a pilot trigger pulse is generated at a common connection for each closure of one of the switches 134a, 134b, 134c, 134d. This pulse must be applied to the correct cylinder, which is the function of the AND gates, 148a, 148b, 148c, 148d. There is a pulse out of the AND gate only when a pulse is applied to one input simultaneously with a voltage level at the other input. By applying a voltage level to a selected AND gate, the pilot trigger pulse is steered to the corresponding cylinder.

The voltage level to select the proper cylinder is obtained by a cam 130 that rotates at half crankshaft speed and has a dwell duration slightly less than the angular spacing between switches 134a, 134b, 134c, 134d. The cam lobe is adjusted so that only one switch is lifted by the cam at any given time to close to its back contact thus selecting a corresponding one of the AND gates to emit a pulse when a signal appears at its other input.

For example, FIG. 5 shows the cam 130 in such a position that the back contacts of switch 134b are closed selecting and opening AND gate 148b. If a pilot injection pulse were to come from pulse shaping circuit 162 at this instant the pilot pulse would pass through AND gate 148b to initiate pilot injection in the corresponding cylinder, but the pilot pulse would be blocked by the other AND gates which are still closed. When the cam has rotated a few degrees counterclockwise, switch 134b will close to the front contacts and switch 134c will close its back contacts. It will then be the only switch with its back contacts closed and only AND gate 148c will be opened so that the next pilot pulse will be steered to the cylinder corresponding to AND gate 148c. The operation of the remaining switches to generate main injection pulses and to enable the correct one of the AND gates should now be apparent.

There has been described herein a novel and useful pilot fuel injection system employing a pilot leadtime computer in conjunction with an electroexpansive fuel injector which calculates the correct leadtime for the pilot fuel injection. In an embodiment of the invention which was built and successfully operated, not only did the usual diesel "knock" disappear, but the engine operated more smoothly and the emission of toxic constituents from the engine muffler was significantly reduced.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and consequently it is intended that the claims be interpreted to cover such modifications and equivalents.

Claims

We claim:

1. A fuel injection system for an internal combustion engine of the compression ignition type which drives a crankshaft comprising:

an electroexpansive fuel injection pump for each cylinder,

first means operated responsive to said engine for generating, independently of any crankshaft angle but at a substantially fixed time prior to the time of generating a second control signal, a first control signal timed for and representative of a pilot fuel injection for each cylinder,

second means operated responsive to said engine for generating, at a crankshaft angle, said second control signal timed for and representative of a main fuel injection for each cylinder,

means for operating said electroexpansive pump for each cylinder responsive to each said first control signal, and

means for operating said electroexpansive pump for each cylinder responsive to each said second control signal.

2. A fuel injection system as recited in claim 1 wherein said first means includes a first switch means,

said second means includes a second switch means and there are cam means driven responsive to said engine for successively operating said first and second switch means,

means operative responsive to operation of said first and second switch means for generating a first voltage having an amplitude representative of the time interval elapsing between the operation of said first and second switches,

means for establishing an engine constant voltage having an amplitude representative of a desired leadtime for pilot fuel injection before main fuel injection,

means for subtracting said motor constant voltage from said first voltage to provide a resultant voltage having an amplitude representative of the required pilot fuel injection leadtime for the prevailing operating conditions of said engine,

means for converting said resultant voltage into a first control signal, and

means responsive to operation of said second switch means for generating said second control signal.

3. A fuel injection system for an internal combustion engine as recited in claim 2 wherein said means operative responsive to operation of said first and second switch means for generating said first voltage is a first ramp voltage generator,

means for initiating operation of said first ramp voltage generator responsive to operation of said first switch means,

means for stopping operation of said first ramp voltage generator responsive to operation of said second switch means,

said means for converting said resultant voltage to a first control signal includes a second ramp voltage generator,

means for initiating operation of said second ramp voltage generator responsive to operation of said first switch means, and

comparator means for comparing said resultant voltage amplitude with said second ramp voltage amplitude and providing a first control signal as an output when the amplitudes are equal.

4. A fuel injection system as recited in claim 1 wherein there is included means for disabling said first means during engine startup time, and means operative upon engine startup and responsive to the temperature of said engine for delaying the application of said second control signal to said means for operating said electroexpansive pump by an interval required to compensate for the effects of said engine temperature.

5. A fuel injection system as recited in claim 3 wherein there is inclined a third switch means operative responsive to said cam driven means following operation of said second switch means for resetting said first and second ramp voltage generators.

6. A fuel injection system as recited in claim 1 wherein said second means operated responsive to said engine for generating a second control signal timed for and representative of a main fuel injection for each cylinder includes a switch means for and associated with each cylinder,

a cam means driven responsive to said motor for successively operating each switch means, and

means operated responsive to operation of each said switch means for generating a second control signal for the associated cylinder.

7. A fuel injection system as recited in claim 6 wherein said first means operated responsive to said engine for generating a first control signal timed for and representative of a pilot fuel injection for each cylinder includes a first ramp voltage generator,

means for initiating operation of said first ramp voltage generator responsive to operation of a first of said switch means,

means for terminating operation of said main ramp voltage generator responsive to operation of a second of said switch means,

a second ramp voltage generator for and associated with each cylinder,

means for initiating operation of each said second ramp voltage generator responsive to the operation of a switch means associated with a preceding cylinder,

means for resetting each second ramp voltage generator responsive to the operation of a switch means associated with the same cylinder as said second ramp voltage generator,

means for generating an engine constant voltage having an amplitude representative of a desired leadtime for pilot fuel injection over main fuel injection,

means for subtracting said main ramp voltage generator output voltage from said motor constant voltage to provide a voltage difference signal, and

comparator means for each cylinder for comparing the amplitude of said voltage difference signal with the output of each said second ramp voltage generator and generating a first control signal for the cylinder when said amplitudes are substantially equal.

8. A fuel injection system as recited in claim 7 including switch means operative responsive to engine startup for preventing application of the first control signal to each serial means for operating said electroexpansive pump for each cylinder during engine startup time.

9. A fuel injection system as recited in claim 7 wherein said means for generating an engine constant voltage includes means for generating a first voltage responsive to engine temperature, a second means for generating a second voltage responsive to fuel cetane number, means for generating a third voltage responsive to engine constants and means for combining said first, second and third voltages to produce said engine constant voltage.

10. A fuel injection system as recited in claim 6 wherein each said first means operated responsive to said engine for generating a first controlled signal timed for and representative of a pilot fuel injection for each cylinder, includes:

Or gate means to the input of which each of said second control signals are applied,

a first delay circuit,

a second delay circuit having its input connected to the first delay circuit output and having a longer delay time than said first delay circuit,

a sample and hold circuit,

means for connecting the output of said OR gate means to the sample and hold circuit to enable it to sample and hold a voltage signal applied to its input in response to a pulse signal received from said OR gate,

means for connecting said OR gate means output to said first time delay circuit input,

a ramp generator,

means for applying said first delay circuit output to said ramp generator to reset said ramp generator,

means for applying said second delay circuit output to said ramp generator input to initiate operation of said ramp generator,

means for applying the output of said ramp generator to said sample and hold circuit input,

means for generating a motor constant voltage having an amplitude representative of a desired pilot fuel injection leadtime,

means for subtracting said motor constant voltage from the voltage of said sample and hold circuit to provide a resultant voltage,

means for comparing said resultant voltage with said ramp generator voltage and providing a first control signal when they are substantially equal, and

means for directing said first control signal to a selected one of said means for operating an electroexpansive pump responsive to a first control signal for a cylinder.

11. A fuel injection system as recited in claim 10 wherein said means for directing said first control signal to a selected one of said means for operating an electroexpansive pump responsive to a first control signal for a cylinder includes:

a two input AND gate for each of said cylinders each AND gate having its output connected to one of said means for operating an electroexpansive pump,

means applying said first control signal to one input of all of said AND gates, and

means operative responsive to each said switch means for applying an enabling signal to a selected one of said AND gates second inputs.

12. A fuel injection system as recited in claim 10 wherein there is provided switch means operative responsive to startup operation of said engine for preventing application of said pilot fuel injection signals to said electroexpansive fuel pumps.

13. A fuel injection system as recited in claim 2 wherein there is included a governing means operative responsive to operation of said second switch means for limiting the fuel injected into the cylinders of said engine to provide a speed and smoke emission governing device.

14. A fuel injection system as recited in claim 13 wherein said governing means includes tachometer means responsive to the operation of said second switch means for providing an output signal having an amplitude representative of the speed of said engine:

means for establishing a speed voltage having an amplitude representative of a desired maximum speed,

means for comparing the output of said tachometer means and said speed voltage to provide a resultant signal, and

means responsive to said resultant signal to limit the amount of fuel injected into said engine cylinders to thereby limit said engine speed.

15. A fuel injection system as recited in claim 13 wherein there is included programmable filter means to which the output of said tachometer is applied for producing an output signal for establishing the maximum amount of fuel for a given engine speed which will not cause smoking, and means for applying said output signal to each said electroexpansive pump.

16. A fuel injection system as recited in claim 15 wherein there is included a manual means for independently controlling the quantity of fuel injected in each of two or more discrete injection periods per engine cycle, and manual means for independently controlling the duration of fuel injection for two or more discrete injection periods per engine cycle.

17. A fuel injection system as recited in claim 15 wherein there are included means for sensing engine temperature, and delay means for delaying the application by said means for applying each main fuel injection to cause said injection to occur close to top dead center for a relatively cold engine than for a relatively warm engine.

18. A fuel injection system as recited in claim 1 wherein there is included means for disabling said first means during engine startup time:

means operative upon engine startup and responsive to the temperature of said engine for delaying the application of said second control signal to said means for operating said electroexpansive pump by an interval required to compensate for the effects of said engine temperature, and

means operative upon engine startup and responsive to the temperature of said engine for applying a plurality of second control signals in sequence and during an engine cycle to assist the cold starting of the engine.

19. A fuel injection system for an internal combustion engine of the compression ignition type comprising:

an electroexpansive fuel injection pump for each cylinder of said engine,

a first ramp voltage generator,

a second ramp voltage generator for each cylinder of said engine,

a plurality of switch means, a different one of said plurality being assigned to a different one of said cylinders,

engine driven cam means for sequentially and successively operating each of said switch means,

means for initiating operation of said first ramp voltage generator responsive to operation of a last of said plurality of switch means,

means for terminating operation of said first ramp voltage generator responsive to operation of a first of said plurality of switch means,

means for resetting said first ramp voltage generator responsive to operation of a second of said plurality of switch means,

means responsive to operation of a switch means for initiating operation of the second ramp generator assigned to the engine cylinder succeeding the one to which the switch means which has been operated is assigned,

means responsive to the operation of the switch means assigned to the same cylinder as that assigned to the operated second ramp generator to reset the second ramp generator,

means for generating an engine constant voltage having an amplitude representative of a desired leadtime for a pilot fuel injection before a main fuel injection into a cylinder,

means for subtracting said first ramp voltage generator output voltage at the time its operation is terminated from said engine constant voltage to provide a resultant voltage,

comparator means for each cylinder for comparing said resultant voltage with the output of the second ramp generator for each cylinder and providing a pilot injection pulse signal when they have substantially the same amplitude,

means for operating the electroexpansive fuel pump of each cylinder responsive to the pilot injection pulse signal output of the comparator means for that cylinder, to provide a pilot fuel injection,

means for generating a main injection pulse signal for each cylinder responsive to operation of the switch means for that cylinder, and

means for operating the electroexpansive fuel pump of each cylinder responsive to the main injection pulse signal from the switch means associated with that cylinder to provide a main fuel injection.

20. A fuel injection system for an internal combustion engine of the compression ignition type comprising:

an electroexpansive fuel injection pump for each cylinder of said engine,

a plurality of switch means, a different one of which is assigned to a different one of said engine cylinders, each switch means having a first and second contact and swinger means for making connection with either said first or said second contact,

engine driven cam means for sequentially operating the swinger means of a switch means to its first contact and the swinger means of the succeeding switch means to its second contact,

a ramp voltage generator,

means responsive to the operation of a swinger means to a first contact for generating a first pulse,

sample and hold means responsive to said first pulse to sample and hold the output of said ramp voltage generator,

first time delay means for resetting the ramp generator responsive to a first pulse after a first predetermined time delay,

second time delay means for initiating operation of said ramp generator responsive to the output of said first time delay means after a second predetermined time delay,

means for establishing an engine constant voltage having an amplitude representative of a desired leadtime for a pilot fuel injection before a main fuel injection into a cylinder,

means for subtracting said engine constant voltage from the output of said sample and hold circuit and providing a resultant voltage,

comparing means for comparing the output of said ramp voltage generator with said resultant voltage and providing a pilot lead pulse signal output when the amplitudes are substantially the same,

means for generating a steering pulse responsive to a switch means swinger operated to a second contact,

means responsive to a steering pulse and a pilot lead pulse signal for causing the electroexpansive pump for the cylinder associated with the switch means whose swinger is connected to the second contact to provide a pilot fuel injection,

means responsive to a first pulse generated when the said switch means swinger is next operated to its first contact for causing the electroexpansive pump for the cylinder associated with the said switch means to provide a main fuel injection pulse.