GB1591783A

GB1591783A - Fuel injection system with means to inhibit injection below a determined pressure

Info

Publication number: GB1591783A
Application number: GB20868/78A
Authority: GB
Original assignee: Allied Chemical and Dye Corp; Allied Chemical Corp
Current assignee: Allied Corp
Priority date: 1977-07-08
Filing date: 1978-05-19
Publication date: 1981-06-24
Also published as: IT7868613A0; CA1110736A; JPS5419021A; DE2829810A1; FR2396872A1; ES471306A1; SE7807309L

Description

(54) FUEL INJECTION SYSTEM WITH MEANS TO INHIBIT INJECTION BELOW A DETERMINED PRESSURE (71) We, ALLIED CHEMICAL COR PORATION, a Corporation organised and existing under the laws of the State of New York, United States of America, of Columbia Road and Park Avenue, Morris Township, Morris County, New Jersey, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: This invention relates to fuel injection systems for spark ignited internal combustion engines employing at least one injector fed by a constant pressure fuel supply, and more particularly to means to prevent fuel injection to the system during starting when the fuel delivery rate provided by the injector would be insufficient to prevent emission of high levels of unburned hydrocarbons.

In the specification of Application No.

45147/76 (Serial No. 1,567,041) where is disclosed a form of fuel injection system for a spark ignition internal combustion engine employing electrically energized fuel injectors disposed at each engine cylinder and connected to a common fuel line. During the engine operation the pressure in the fuel line and at the injectors is maintained at a regulated, relatively high value such as 100 psig by a camshaft driven fuel pressure booster. The latter is fed from a low pressure fuel supply pump. The regulated, high pressure fuel line ensures that the quantity ob fuel provided to a cylinder by an injector will always be at a predetermined value. The injectors are each energized into open condition by individual variable width pulse generators controlled by sensors which measure engine operating parameters, for example manifold vacuum.

Because the pressurized fuel delivery line is located in proximity to the engine, and the injectors are positioned in immediate proximity to the cylinders, the fuel within the line becomes heated during normal engine operation and cxpands. During normal engine operation the pressure booster retains regulated fuel pressure independent of the variable fuel density. After the engine stops, the booster is no longer oplerative, with the result that the cooling fuel will contract in volume and cause a drop in pressure in the fuel line.

Pressure wave converters employing flexible diaphragms connected to the line on one side and a reference pressure on the opposite side act to adjust automatically the high pressure fuel line volume as thernressure decays.

When the engine is restarted the initial fuel pressure may be substantially lower than the normal operating pressure. Such low fuel pressure will result in a diminution of the fuel charges provided to the cylinders by the injectors during starting. Since the variable width pulse generators that control the injectors as a function of measured engine operating parameters are programmed on the basis of an assumed constant pressure in the fuel line the lowered pressure will result in a decreased fuel flow rate through the injectors during actuati9n thereof.

If the engine has been allowed to cool to an appreciable degree below its normal operating temperature before restarting is attempted, the diminished fuel charge provided to the cylinders as a result of the drop in fuel line pressure may not inhibit starting. The variable width pulse generators are programmed to provide an excessive fuel charge during cold start. Moreover, at cooler engine starting tem peratures the fuel charge tends to accumulate, providing an air-fuel mixture that may be sufficient for ignition.

In the event that restarting is attempted while the engine is still close to operating tempgrature, however, the reduced fuel charge provided to the engine because of the lowered fuel line pressure may be insufficient to produce an ignitable air-fuel mixture quickly. The unburned hydrocarbons pumped into the ex haust system prior to ignition may substantially raise pollutants sufficiently to exceed limits imposed by government regulations.

After a period of cranking without combustion, the fuel booster or fuel pump will raise the fuel pressure, increasing the quantities of injected fuel to a level sufficient for starting of the engine. Further, the time period required for the pressure booster to raise fuel pressure to a level sufficient for clean combustion is increased by injection of diminished fuel charge during the starting mode.

According to the present invention there is provided a fuel injection system for a spark ignition engine having a supply of pressurized fuel, the system comprising an injector valve connected to the supply, sensors for measuring engine operating conditions, an electric circuit for energizing the injector in timed relation to the engine operation for periods controlled by the output of said sensors, means for sensing the pressure of the fuel in said supply and means actuatable by said pressure sensing means when the fuel pressure is below a preselected minimum pressure for inhibiting energization of the injector.

A further aspect of the invention provides a fuel injection system for a spark ignited internal combustion engine, comprising: a fuel source; a fuel supply line; means powered by the engine for feeding fuel from the source to the supply line to maintain a predetermined, operating fuel pressure in the supply line; an injector connected to the supply line; sensors connected to the engine to measure engine operating parameters; an electric circuit connected to the outputs of the sensors and to the engine operative to energize the injector at periods occurring in timed relation to the operation of the engine and having durations dependent upon the outputs of said sensors; and means actuated in response to the pressure of the fuel in said supplly line for inhibiting energization of the injector during starting of said engine, independent of the output of said electric circuit, until the pressure of said fuel in said supply line exceeds a preselected minimum pressure.

In one embodiment of the invention, described hereinafter in more detail, a pressure switch is connected to the fuel line and is set to switch at a pressure which is some substantial portion of the normal fuel pressure; for example, with a system having a normal fuel pressure of 100 psig, the pressure switch may be set to change outputs at 70 psig. A thermistor supported in proximity to the engine provides the variable width pulse generators with an electrical signal proportional to engine temperature. This signal is also compared to a reference value to derive a signal indicative of whether the engine rem- perature is above a predetermined level, below normal hot engine temperature.The system includes logic which receives the output of the pressure switch and the temperature signal and acts to prevent the generation of actuating pulses for the injectors when the pressure is below the level at which the switch actuates and the engine temperature is above the comparator level.

In another embodiment of the invention circuitry could be provided for comparing continuous functions of pressure and temperature so that the injectors would be inhibited at relatively low engine temperatures if the fuel pressure was very low and at higher temperatures if the fuel pressure was somewhat higher but still below full pressure.

The system prevents the injectors from operating while the engine is being cranked during a hot start until the booster or fuel pump raises the pressure in the fuel line above the required fuel pressure. This will typically only require a few turns of the cranking motor.

On continued cranking, the injectors are energized and the fuel flow through the injectors should be sufficient to create a fuel-air mixture which will sustain combustion, preventing the unburned fuel from being pumped into the engine exhaust.

The present invention will become further apparent from the following detailed description of a preferred embodiment of the invention given by way of example with reference to the accompanying drawings, in which: FIGURE 1 is a partially schematic, partially block diagram of a fuel invention system for an internal combustion engine, forming the prefered embodiment of the invention; FIGURE 2 is a more detailed schematic diagram of the circuitry of the present in vention which measures engine temperature and fuel line pressure to inhibit fuel injection during high temperature, low pressure starting conditions.

Referring to the drawings, FIGURE 1 schematically illustrates a system for providing fuel under a high, relatively constant pressure to eight fuel injectors or transducers 10 arranged to provide controlled bursts of fuel to the intake valve areas of an eight cylinder internal combustion engine, as well as relevant portions of the ignition system. The injectors 10 may be of any well-known type such as those disclosed in my U.S. Patent 3,412,718.

Electric signals applied to the injectors 10 through wires 12 open the injectors for con trolled periods of time based on measured engine operating conditions, such as manifold vacuum pressure, engine temperature, atmos pheric pressure and the like. The quantity of fuel provided by the injector during this signal period is a function of the pressure at the injector.

Fuel is provided to the injectors by a pair of conduits 14 termed fuel rails. Fuel for feeding the rails is derived from a fuel tank 16. A pump 18 receives fuel from the tank 16 through a one-way valve 17 and operates to feed fuel from the tank through a one-way valve 20. The pump 18 may be electrically powered or driven by the engine in the manner of a conventional automotive fuel pump. It must be capable of pumping fuel at a volumetric rate in excess of the engine requirements at the maximum throttle opening. For a relatively large 8-cylinder engine this may be in excess of 25 gallons per hour.

The outlet pressure of the pump 18 may be substantially lower than the 25-50 pounds per square inch provided by fuel pumps for typical injection fuel systems of the prior art.

In a preferred embodiment of the system a 5-10 pound per square inch outlet pressure will suffice. This pressure need not be well regulated and may vary with engine speed.

Accordingly, the pump 18 should be substantially simpler and lower in cost than fuel pumps used with previous injection systems.

A fuel pressure booster and regulator generally indicated at 22 receives fuel passed through the one-way valve 20 from pump 18 The booster and regulator is schematically illustrated as comprising a piston 24 movable within a cylinder 26 and biased by a spring 28. The spring biases the piston in a direction as to move the piston 24 to contract the volume of the cylinder 26 in communication with the fuel line 30. This increases the fluid pressure in the fuel line 30. The one-way valve 20 prevents this increase in pressure from forcing a reverse flow to the pump 18.

A reset mechanism 32 is schematically illustrated as being connected to the piston 24 to periodically move the piston against the bias of the spring 28 to enlarge the volume of the cylinder 26 in communication with the fuel line 30. The reset mechanism is cocked once each engine cycle by the engine cam shaft 33. This lowers the pressure in the fuel line 30 and allows momentary flow from the pump 18 trough the one-way valve 20.

A second one-way valve 34 is connected downstream of the booster and regulator 22.

When the piston 24 moves under the bias of the spring 28 to contract the volume of the cylinder 26, the valve allows the resulting high or elevated pressure to communicate with a fuel line 36 that connects to the fuel rails 14, thus imposing this higher pressure on the rails. When the reset mechanism 32 withdraws the piston against the force of the spring 28, allowing the pump 18 to force fuel into the low-pressure fuel line 30, the one-way valve 34 prevents backflow in the high pressure fuel line 36 toward the pressure booster 22 and thus maintains the high fluid pressure in the rails 14. In alternative embodiments of the invention a conventional high pressure regulated fuel pump could replace the booster and regulator 32.

Optionally, the far ends of the rails are connected together by a fuel line 38 to form a closed circuit. A constant bleed one-way valve 40 connects the fuel line 38 back to the fuel tank 16.

An accumulator acting as a fluid wave regulator or converter 42 is connected to the fluid line immediately upstream of the valve 20. The converter is essentially of the same typ!e disclosed in my U.S. Patent 3,507,263.

Schematically, it comprises an enclosed volume 44 separated from the fluid line by an elastic diaphragm 46. The diaphragm 46 assumes a position wherein the forces on its opposite sides are equal, thus when the line pressure increases, the diaphragm moves to contract the volume of the chamber 44 and thus pres surize the fluid sealed within that volume.

Conversely, when the line pressure falls the diaphragm moves to expand the sealed volume.

When the diaphragm 46 moves outwardly in response to a lowering in the fluid pressure in the line it effectively pumps a volume of fluid into the line. Conversely, when the diaphragm contracts in response to an increase in line pressure it increases the flow volume con nected to the line. The converter 42 thus acts as a flow regulator.

When the piston 24 is retracted against the bias of the spring 28 by the unit 32 so that the pressure in the line 30 falls below the outlet pressure of the pump 18, and the flow valve 20 opens, the decrease in pressure at the inlet to the converter 42 causes the dia phragm 46 to expand and supply a volume of fuel which replenishes the chamber 26. In the absence of this device the sharp low pres sure wave generated by expansion of the cylinder 26 might vaporize the fuel in the line between the pump and the booster.

A similar regulator or converter 48 is connected to the fuel line immediately downstream of the uni-directional valve 34. This converter provides a pressurized fuel source to the line during the short interval when the piston 24 is resetting and accordingly the valve 34 is isolating the line 30 from the line 36. The converter 18 also acts as a cushion to minimize the travel of expansion and com pression waves through the line 36.

In the preferred embodiment of the invention a pair of pressure converters 52 and 54 are connected adjacent to the input ends of the fuel rails 14. A second pair of converters 56 and 58 are connected adjacent to the outlet ends of the fuel rails, where they connect to the common fuel line 38. These converters all similarly act to regulate the pressure in the rails by cancelling pressure waves created in the system by injection of fluid from the booster 22 or ejection of fluid through the injectors 10.

FIGURE 1 also illustrates the circuitry for providing electrical power to the coils of the injector valves 10 over lines 12. One of the injectors 10 is illustrated as having a coil 60.

Considering the circuitry that derives the energization pulses for this coil, the ignition system includes a distributor generally indicated at 62 having an arm 64 rotated in timed relation to the engine operation to sequentially move into position with contacts that are connected to the engine spark plugs 66, only one of which is illustrated. The arm 64 is connected to the secondary of an ignition coil, generally indicated at 68, having its primary connected to the vehicle battery 70 through a pair of engine actuated breaker points 72. The breaker points are shunted by a capacitor 74.

The breaker points are also connected to a counter 76 forming part of the injector circuitry. The counter is advanced by one count each time the breaker points 72 close.

The counter 76 has a plurality of output lines 78 which connect to a number of variable width pulse generators 80, only one of which is illustrated. The various lines 78 are sequentially energized as the counter advances so that each line is energized once each engine cycle.

The variable width pulse generators each receive outputs from a group of engine sensors 82 which measure such operating variables as manifold pressure and the like. Each variable width pulse generator also receives an electrical output from a thermistor 84 supported relative to the engine to experience the engine temperature. The thermistor 84 is illustrated separately from the other engine sensors 82 because of its roll in the low pressure, high engine temperature inhibit circuitry.

The output of the variable width pulse generators 80 are provided to gates 86 and the outputs of the gates constitute the lines 12 which energize the injectors 10.

The gates 86 are controlled by an injection inhibit circuit 88. Only a single injection inhibit circuit services the gates 86 associated with each of the variable width pulse generators 80. The injection inhibit circuit 88 has inputs from the thermistor 84 and from a pressure switch 90 connected to the fuel line 14. The switch 90 preferably closes when the pressure in the line 14 is above a predetermined fraction of normal operating line pressure. In the case of the preferred embodiment, the normal operating line pressure may be 100 psi and the switch 90 may close when the pressure exceeds 65 psi.

The injection inhibit circuit 88 processes the output of the switch 90 and of the thermistor 84 to control the gate 86. The control is such that the gate 86 passes output pulses from the generator 80 to the injector coil 60 as long as the pressure switch is closed. When the pressure switch is open, indicating a pressure in the line 14 of less than 65 psi, the gate 86 still passes injector signals if the output of the thermistor 84 is such as to indicate that the temperature of the engine is below a predetermined value. In the preferred embodiment of the invention this value may be approximately 1500F as compared to a normal engine operating temperature of about 2000F.

When the pressure in the line 14 is less than 65 psi and the engine temperature is above 1500F the gate 86 is energized by the circuit 88 to prevent the application of firing pulses from the generator 80 to the coil 60.

This condition occurs when the engine is being restarted a relatively short period of time after it stopped while at or near operat ing temperature; i.e., within 520 minutes or thereabouts, depending upon the ambient temperature. Were the injectors not to be inhibited during this time the reduced fuel quantity that they would provide to the cylinders as a result of the lowered pressure in the line 14 would likely not result in a rich enough fuel/air ratio to achieve ignition and the unburned hydrocarbon vapors would be pumped out of the engine exhaust.

The injection inhibit circuit 88 can, alternatively, be provided with an input from the pressure switch 90 solely, making it operative in response to pressure of the fuel in line 14 to inhibit energization of the injector during starting of the engine until the fuel pressure exceeds a preselected minimum pressure in the order of about 65 psi.

FIGURE 2 illustrates the circuitry of the injection inhibit device 88 and its associates components in greater detail.

The thermistor 84 is connected in series with a resistance 100 between a positive vol tage provided by a power supply and ground so that the two act as a voltage divider. the mid-point of this voltage divider, which experiences a voltage dependent upon the resistance of the thermistor 84, is applied to one terminal of an operational amplifier 102 connected to a comparator mode. The reference input to the comparator 102 is provided by a voltage divider consisting of the series combination of two resistances 104 and 106. One end of resistance 104 is connected to ground and one end of resistance 106 is connected to a positive reference voltage. Resistance 104 is shunted by the pressure switch 90 which is closed when the pressure in line 12 exceeds the predetermined pressure such as 65 psig.

When the pressure is in excess of that value the switch 90 is closed and the comparator 102 cannot provide a high output, independent of the resistance of the thermistor 84. However, when the pressure is above 65 psi, so that the switch 90 is open, and the engine temperature and thus the thermistor temperature are above a predetermined value, such as 1500F, the voltage at the connection between the thermistor 84 and the resistance 100 will exceed the reference voltage and will pro vide an output from the comparator 102. This voltage is applied to the gates 86, one for each engine cylinder, through a plurality of isolating diodes 106. When the gates are activated by outputs from the comparator 102 the output pulses from the variable width pulse generators 80 are applied to the coils 60 of the injector 10.When the fuel line pressure is below the predetermined value and the engine temperature is above the comparator value, the output of the comparator 1012 will be such that the gates 86 will block pulses from the variable width generators from being applied to the injectors.

WHAT WE CLAIM IS: 1. A fuel injection system for a spark ignition engine having a supply of pressurized fuel, the system comprising an injector valve conected to the supply, sensors for measuring engine operating conditions, an electric circuit for energizing the injector in timed relation to the engine operation for periods controlled by the output of said sensors, means for sensing the pressure of the fuel in said supply and means actuatable by said pressure sensing means when the fuel pressure is below a preselected minimum pressure for inhibiting energization of the injector.

2. The fuel injection system of claim 1, wherein said means for sensing engine operating conditions includes a sensor for sensing engine temperature, the output of which is connected to said means for inhibiting energization of the injector, said means for inhibiting energization of the injector arranged to be disabled in response to the sensing of an engine temperature below a preselected value.

3. The fuel injection system of claim 1 or 2, wherein said means for sensing fuel pressure comprises a pressure transducer connected to the fuel supply, the transducer having a first output when the pressure in said supply is above a predetermined pressure, which is below the pressure in said supply during normal engine operation, and a second output when the pressure in said supply is below said predetermined pressure.

4. The fuel injection system of claims 2 and 3, wherein said temperature sensor is arranged to generate an electric signal having a property which is a function of engine temperature, the means for inhibiting energization of the injector comprising comparator means for receiving said electric signal and a reference signal, the comparator having a first output when the electric signal is greater than the reference signal and a second output when the electric signal is less than the reference signal.

5. The fuel injection system of claim 1, 2, 3 or 4, in which said temperature sensor comprises a thermistor connected to the engine to provide an electrical signal having a charac teristic which is a function of engine temperature and a pressure switch connected to said supply of fuel.

6. A fuel injection system for a spark ignited internal combustion engine, comprising: a fuel source; a fuel supply line; means powered by the engine for feeding fuel from the source to the supply line to maintain a predetermined, operating fuel pressure in the suplply line; an injector connected to the supply line; sensors connected to the engine to measure engine operating parameters; an electric circuit connected to the outputs of the sensors and to the engine operative to energize the injector at periods occurring in timed relation to the operation of the engine and having durations dependent upon the outputs of said sensors; and means actuated in response to the pressure of the fuel in said supply line for inhibiting energization of the injector during starting of said engine, independent of the output of said electric circuit, until the pressure of said fuel in said supply line exceeds a preselected minimum pressure.

7. The fuel injection system of claim 6, wherein said means for inhibiting energization of the injector during starting includes a pressure sensor connected to the fuel supply, a temperature sensor is connected to the engine and said means for inhibiting energization of the injector is disabled in response to the sensing of an engine temperature below a preselected value, said means for inhibiting energization of said injector being connected to the output of said temperature sensor.

8. The fuel injection system of claim 7, wherein said means for inhibiting energization of the injector acts to inhibit operation of the injector when pressure in the fuel supply is below a pressure which is itself below said operating pressure of the supply, and the engine temperature is above a predetermined temperature, which predetermined temperature is below the normal engine operating temperature after warm up.

9. A fuel injection system for a spark ignition engine constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

10. A spark ignited internal combustion engine including the fuel injection system of any preceding claim.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. activated by outputs from the comparator 102 the output pulses from the variable width pulse generators 80 are applied to the coils 60 of the injector 10. When the fuel line pressure is below the predetermined value and the engine temperature is above the comparator value, the output of the comparator 1012 will be such that the gates 86 will block pulses from the variable width generators from being applied to the injectors. WHAT WE CLAIM IS:

1. A fuel injection system for a spark ignition engine having a supply of pressurized fuel, the system comprising an injector valve conected to the supply, sensors for measuring engine operating conditions, an electric circuit for energizing the injector in timed relation to the engine operation for periods controlled by the output of said sensors, means for sensing the pressure of the fuel in said supply and means actuatable by said pressure sensing means when the fuel pressure is below a preselected minimum pressure for inhibiting energization of the injector.