GB2332241A

GB2332241A - Accumulator (common rail) fuel injection system for vehicle diesel engines

Info

Publication number: GB2332241A
Application number: GB9827266A
Authority: GB
Inventors: Yoshihiro Narahara; Ken Uchiyama; Mamoru Oki; Hideo Naruse
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 1997-12-11
Filing date: 1998-12-10
Publication date: 1999-06-16
Anticipated expiration: 2018-12-10
Also published as: DE19857260A1; DE19857260B4; DE19857260A8; GB2332241B; GB9827266D0; GB2332241A9

Abstract

An accumulator fuel injection system comprises a common rail 3 pressurised by a high pressure pump 5 and connected to a number of fuel injection valves 1 via solenoid valves 1a. If, for example, the engine stalls or the vehicle driver switches the engine off after high load operation and immediately restarts it, releases the accelerator pedal or tries repeatedly to start the engine, the pressure in the common rail 3 may be greater than is appropriate for starting, leading to excessive injection quantity and combustion noise. The system of the invention responds to such conditions by draining the pressurised fuel from the common rail 3 through the injectors 1 thereby keeping the fuel pressure in the common rail at a level suitable for the following engine start up. For draining, the solenoid valve 1a may be opened for a period of time shorter than the normal time lag between opening the solenoid valve and the beginning of opening movement of the needle valve 37 to drain high pressure fuel from the controlled chamber 43 of the injector to the fuel tank 9.

Description

2332241

SPECIFICATION

ACCUMULATOR FUEL INJECTION SYSTEM FOR DIESEL ENGINE OF AUTOMOTIVE VEHICLES The present invention relates generally to an improvement on an accumulator fuel injection system for automotive vehicles designed to store fuel transported from a fuel pump within a common rail under high pressure and to inject the fuel into cylinders of a diesel engine through fuel injectors.

Typical accumulator fuel injection systems monitor operating conditions of a diesel engine (e.g., engine speed and load) to calculate the fuel pressure within a common rail (referred to as common rail pressure below), the injection quantity, and the injection timing, to adjust the amount of fuel discharged from a fuel pump under feedback control to bring an actual common rail pressure into agreement with a target common rail pressure, and to control turning on and off of fuel injectors injecting the fuel stored within the common rail into cylinders of the diesel engine based on the calculated in ection quantity and injection timing. j Such accumulator fuel injection systems raise the drawback in that when a vehicle operator turns off an ignition switch to stop a diesel engine after operating the engine at high loads or racing it and then restarts the engine immediately, it will cause a large amount of fuel to be injected into each cylinder of the engine at a pressure level more than required, thereby resulting in undesired combustion noise.

Specifically, during high load operations and racing of the diesel engine, the target common rail pressure is set to a higher level for increasing an engine output, so that the common rail pressure is elevated. When the ignition switch is turned off to stop the engine, the fuel injection is disabled immediately, so that the common rail pressure is kept near the target level determined before the engine stop. Therefore, when the engine is restarted immediately, the common rail pressure will be more than a level suitable for starting the engine, thereby resulting in injection of fuel from each injector at a pressure level higher than required, which will cause the combustion noise to be produced at the beginning of burning of the fuel.

Such a combustion noise may also arise at a time when the engine is activated after the vehicle operator turns on and off a starter switch repeatedly for a failure in starting the engine. Specifically, when the starter switch is turned on to rotate a crankshaft of the engine, the accumulator fuel injection system makes a fuel pump run at full loads to tra-nsport the fuel to the corm-non rail at a maximum rate for increasing the common rail pressure quickly up to a level enabling the fuel injection through injectors. The repeated on-off operations of the starter motor for a failure in starting the engine may thus cause the common rail pressure to be elevated more than required. which produces the combustion noise at the beginning of burning of the fuel immediately after the engine is started.

It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.

It is another object of the present invention to provide an accumulator fuel injection system for a diesel engine of an automotive vehicle which is designed to keep the pressure within a common rail at a suitable level at all times.

According to one aspect of the present invention. there is provided an accumulator fuel injection apparatus for a diesel engine of a vehicle which comprises: (a) a fuel line; (b) an accumulator chamber accumulating therein fuel supplied from a fuel pump through the fuel line; (c) a fuel injector injecting the fuel stored in the accumulator chamber into a cylinder of the engine, (d) a draining mechanism draining the fuel out of the accumulator chamber to a portion of the fuel line lower in pressure than the accumulator chamber to reduce a pressure in the accumulator chamber; (e) an on-off switching detecting circuit detecting a switching operation of an ignition switch of the vehicle from an onstate to an off-state to provide an on-to-off switching signal indicative thereof; and (fi a controller responsive to the on-to- off switching signal from the on-off switching detecting circuit to activate the draining mechanism to reduce the pressure in the accumulator chamber.

In the preferred mode of the invention, the fuel injector includes an injecting portion. a drive portion, and a solenoid valve.

2 5 The injecting portion has disposed therein a valve member which is applied with a pressure of the fuel transported from the accumulator chamber through a first passage portion of the fuel line -4 to move to open a spray hole for injecting the fuel into the engine. The drive portion applies the pressure of the fuel transported from the accumulator chamber through a second passage portion of the fuel line to drive the valve member to close the spray hole. The solenoid valve constitutes the draining mechanism and is opened when energized to establish fluid communication between a third passage portion of the fuel line connecting with the portion of the fuel line lower in pressure than the accumulator chamber and the second passage portion of the fuel line to reduce the pressure of the fuel applied to the valve member of the drive por-tion of the fuel injector so that the valve member moves to open the spray hole. The controller opens the solenoid valve for a preselected period of time shorter than a time lag occurring between opening of the solenoid valve and the beginning of movement of the valve member for draining the fuel out of the accumulator chamber to reduce the pressure in the accumulator chamber.

The controller opens the solenoid valve for the preselected period of time at regular intervals in response to the on-to-off switching signal from the on-off switching detecting circuit.

The controller is responsive to the on-to-off switching signal from the on-off switching detecting circuit to activate the draining mechanism for a given period of time as long as the ignition switch is kept off.

The controller determines whether the pressure of the fuel within the accumulator chamber is higher than a given pressure level or not. The controller allows the draining mechanism to be activated as long as the pressure of the fuel within the accumulator chamber is higher than the given pressure level.

According to another aspect of the invention, there is provided an accumulator fuel injection apparatus for a diesel engine of a vehicle which comprises: (a) a fuel line., (b) an accumulator chamber accumulating therein fuel supplied from a fuel pump through the fuel line; (c) a fuel injector injecting the fuel stored in the accumulator chamber into a cylinder of the engine; (d) a draining mechanism draining the fuel out of the accumulator chamber to a portion of the fuel line lower in pressure than the accumulator chamber to reduce a pressure in the accumulator chamber; (e) an on-off switching detecting circuit detecting a switching operation of a starter switch for starting the engine from an on-state to an off-state; (f) an engine speed determining circuit determining whether a speed of the engine is lower than a preselected speed or not when the on-off switching detecting circuits detects the switching operation of the starter switch from the on-state to the off-state; and (g) a controller activating the draining mechanism to reduce the pressure in the accumulator chamber when the engine speed determining circuit determines that the speed of the engine is lower than the preselected speed.

In the preferred mode of the invention, the fuel injector includes an injecting portion, a drive portion, and a solenoid valve. The injecting portion has disposed therein a valve member which is applied with a pressure of the fuel transported from the accumulator chamber through a first passage portion of the fuel line to move to open a spray hole for injecting the fuel into the engine.

The drive portion applies the pressure of the fuel transported from the accumulator chamber through a second passage portion of the fuel line to drive the valve member to close the spray hole. The solenoid valve constitutes the draining mechanism and is opened when energized to establish fluid communication between a third passage portion of the fuel line connecting with the portion of the fuel line lower in pressure than the accumulator chamber and the second passage portion of the fuel line to reduce the pressure of the fuel applied to the valve member of the drive portion of the fuel injector so that the valve member moves to open the spray hole.

The controller opens the solenoid valve for a preselected period of time shorter than a time lag occurring between opening of the solenoid valve and the beginning of movement of the valve member for draining the fuel out of the accumulator chamber to reduce the pressure in the accumulator chamber.

The controller opens the solenoid valve for the preselected period of time at regular intervals when the engine speed determining circuit determines that the speed of the engine is lower than the preselected speed.

When the engine speed determining circuit determines that the speed of the engine is lower than the preselected speed, the controller activates the draining mechanism for a given period of time as long as the star-ter switch is kept off.

The controller dete=ines whether the pressure of the fuel within the accumulator chamber is higher than a given pressure level or not. The controller allows the draining mechanism to be activated as long as the pressure of the fuel within the accumulator chamber is higher than the given pressure level.

According to the third aspect of the invention, there is provided an accumulator fuel injection apparatus for a diesel engine of a vehicle which comprises: (a) a fuel line, (b) an accumulator chamber accumulating therein fuel supplied from a fuel pump through the fuel line: (c) a fuel injector injecting the fuel stored in the accumulator chamber into a cylinder of the engine in synchronism with revolutions of the engine; (d) a pressure reduction condition determining circuit; (e) a draining mechanism; and (f) a controlling circuit.

The fuel injector includes an injecting portion, a drive portion, and a solenoid valve. The injecting portion has disposed therein a valve member which is applied with a pressure of the fuel transported from the accumulator chamber through a first passage portion of the fuel line to move to open a spray hole for injecting the fuel into the engine. The drive portion applies the pressure of the fuel transported from the accumulator chamber through a second passage portion of the fuel line to drive the valve member to close the spray hole. The solenoid valve is opened when energized to establish fluid communication between a third passage portion of the fuel line connecting with a portion of the fuel line lower in pressure than the accumulator chamber and the second passage portion of the fuel line to reduce the pressure of the fuel applied to the valve member of the drive portion of the fuel injector so that the valve member moves to open the spray hole.

The pressure reduction condition determining circuit determines whether a preselected pressure reduction condition that a pressure of the fuel within the accumulator chamber is to be reduced is met or not. The draining mechanism drains the fuel out of the accumulator chamber to the portion of the fuel line lower in pressure than the accumulator chamber to reduce a pressure of the fuel in the accumulator chamber. The controlling circuit activates the draining mechanism at regular intervals to reduce the pressure in the accumulator chamber when the pressure reduction condition determining circuit determines that the preselected pressure reduction condition is met.

In the preferred mode of the invention, the controlling circuit determines whether a speed of the engine is higher than a preselected speed or not when the pressure reduction condition determining circuit determines that the preselected pressure reduction condition is met. The controlling circuit activates the draining mechanism at the regular intervals when it is determined that the speed of the engine is lower than the preselected speed and activates the draining mechanism in synchronism with revolutions of the engine when it is determined that the speed of the engine is higher than the preselected speed.

According to the fourth aspect of the invention, there is provided an accumulator fuel injection apparatus for a diesel engine of a vehicle which comprises: (a) a fuel line; (b) an accumulator chamber accumulating therein fuel supplied from a fuel pump through the fuel line; (c) a fuel injector injecting the fuel stored in the accumulator chamber into a cylinder of the engine in synchronism with revolutions of the engine: (d) a pressure reduction condition determining circuit; and (c) a controlling circuit.

The fuel injector includes an injecting portion, a drive portion, and a solenoid valve. The injecting portion has disposed therein a valve member which is applied with a pressure of the fuel transported from the accumulator chamber through a first passage portion of the fuel line to move to open a spray hole for injecting the fuel into the engine. The drive portion applies the pressure of the fuel transported from the accumulator chamber through a second passage portion of the fuel line to drive the valve member to close the spray hole. The solenoid valve is opened when energized to establish fluid communication between a third passage portion of the fuel line connecting with a portion of the fuel line lower in pressure than the accumulator chamber and the second passage portion of the fuel line to reduce the pressure of the fuel applied to the valve member of the drive portion of the fuel injector so that the valve member moves to open the spray hole. The pressure reduction condition determining circuit determines whether a preselected pressure reduction condition that a pressure of the fuel within the accumulator chamber is to be reduced is met or not. The controlling circuit opens the solenoid valve of the fuel injector for a preselected period of time shorter than a time lag occurring between opening of the solenoid valve and the beginning of 10- movement of the valve member at regular intervals in asynchronism with revolutions of the engine when the pressure reduction condition determining circuit determines that the preselected pressure reduction condition is met for draining the fuel out of the accumulator chamber to the portion of the fuel line lower in pressure than the accumulator chamber to reduce a pressure of the fuel in the accumulator chamber.

In the preferred mode of the invention, the controlling circuit determines whether a speed of the engine is higher than a preselected speed or not when the pressure reduction condition determining circuit determines that the preselected pressure reduction condition is met. The controlling circuit opens the solenoid valve of the fuel injector at the regular intervals when it is determined that the speed of the engine is lower than the preselected speed and opens the solenoid valve of the fuel injector in synchronism with revolutions of the engine when it is determined that the speed of the engine is higher than the preselected speed.

The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying dravi-ings of the prefer-red embodiment of the invention, which, however, should not be taken to limit the invention to the specific embodiment but are for explanation and understanding only.

In the drawings:

Fig. 1 is a circuit diagram which shows an accumulator fuel injection system according to the first embodiment of the invention; - 1 1 - Fig. 2(a) is a time chart which shows an on-off operation of solenoid valve installed in an injector; Fig. 2(b) is a time chart which shows the pressure within a controlled chamber of an injector:

Fig. 2(c) is a time chart which shows the amount of lift of a needle disposed in an injector; Fig. 3 is a flowchart which shows a common rail pressure control program; Fig. 4 is a flowchart of a short valve activation decision program for deciding whether a solenoid valve of an injector should be subjected to short valve activation control or not, Fig. 5 is a flowchart of a regular interruption program for performing short valve activation control of a solenoid valve of an injector; Fig. 6 is a flowchart of a short valve activation decision program according to the second embodiment of the invention; Fig. 7 is a flowchart of a short valve activation decision program according to the third embodiment of the invention; Fig. 8 is a flowchart of a short valve activation decision program according to the fourth embodiment of the invention:

Fig. 9 is a circuit diagram which shows an accumulator fuel injection system according to the fifth embodiment of the invention; Fig; 10 is a flowchart of an injection control program performed in the accumulator fuel injection system shown in Fig. 9; Fig. 11 is a flowchart of a short valve activation decision program for deciding whether a solenoid valve of an injector should be subjected to short valve activation control or not; Fig. 12(a) is a time chart which shows a cylinder discriminating signal outputted each time a crankshaft reaches a given angular position in every two rotations of the crankshaft of an engine; Fig. 12(b) is a time chart which shows a crank angle signal outputted every 30" rotation of a crankshaft of an engine; Fig. 12(c) is a time chart which shows a target injection quantity; Fig. 12(d) is a time chax-t which shows an on-off operation of a solenoid valve; Fig. 12(e) is a time chart which shows an actual common rail pressure and a target common rail pressure; Fig. 13 is a flowchart of a short valve activation decision program according to the sixth embodiment of the invention; Fig. 14 is a flowchart of a regular interruption program for performing short valve activation control of a solenoid valve of an injector', Fig. 15 is a flowchart of a crank angle interruption program for short valve activation control of a solenoid valve of an injector which is executed when an encrine speed is higher than a given speed; I Fig. 16(a) is a time chart which shows a cylinder discriminating signal outputted each time a crankshaft reaches a given angular position in every two rotations of the crankshaft of an 25 engine; Fig. 16(b) is a time chart which shows a crank angle signal I outputted every 30 rotation of a crankshaft of an engine, Fig. 16(c) is a time chart which shows a Larget injection quantity; Fig. 16(d) is a time chart which shows an on-off operation of a 5 solenoid valve, and Fig. 16(e) is a time chart which shows an actual common rail pressure and a target common rail pressure.

Referring now to the drawings, particularly to Fig. 1, there is shown an accumulator fuel injection system according to the first embodiment of the invention.

The shown accumulator fuel in ection system is used in a fourj cylinder diesel engine and consists essentially of four injectors 1, one for each cylinder, a common rail (i.e., a high-pressure fuel reservoir chamber) 3 accumulating therein fuel under high pressures, a high-pressure pump 5 supplying the fuel to the common rail 3, and an electronic control unit (ECU) 7 controlling system operations based on operating conditions of the engine. Note that Fig. 1 illustrates controlled electric and fluid circuits for one of the injectors I for the brevity of illustration.

The high-pressure pump 5 is of a known ty pe capable of changing the volume of fuel to be discharged and is designed to suck in the fuel transported from a fuel tank 9 through a low pressure pump 11 in response to a command signal from the ECU to pressurize and supply it to the common rail 3 through a supply line 13.

Each of the injectors 1 is connected through an inlet line 15 to the common rail 3 and injects the fuel in the common rail 3 into one of cylinders of the engine through on-off operations of a solenoid valve la installed therein. The injectors 1 each include a cylindrical holder body 21, two orifice plates 23 and 25, a piston 27, a piston pin 31, a nozzle body 35, and a needle 37. The orifice plates 23 and 25 are laid to overlap each other on an upper end of the holder body 21. The piston 27 is slidably disposed within a cylinder formed in the holder body 21. The piston pin 31 extends from the bottom of the piston 27 and has disposed on the head thereof a flange 29. The nozzle body 35 is connected to the bottom of the holder body 21 through a chip packing 33. The needle 37 is disposed slidably within the nozzle body 35.

The needle 37 has a large-diameter portion 37a from which a connecting rod 37b extends through the chip packing 33 and connects with the flange 29 within the holder body 21. Disposed between the flange 29 and an inner upper wall of the holder body 21 is a coil spring 39 which urges the needle 37 downward at all times.

The holder body 21 has formed therein a fluid passage 41 communicating with the common rail 3 through the inlet line 15.

The fluid passage 41 extends vertically, as viewed in the drawing, and communicates at one end with a controlled chamber 43 through an orifice 23a and a fluid passage 23b formed in the orifice plate 23 and at the other end with a fuel sump 47 through the chip packing 33 and a fluid passage 45 formed in the nozzle body 35.

The controlled chamber 43 is defined within the holder bodv 21 by an end (i.e., a back face) of the piston 27. The fuel sump 47 is formed in the nozzle body 35 around a portion of the needle 37 beneath the largediameter portion 37a.

The nozzle body 35 has formed in the head thereof spray holes 49 leading to the fuel sump 47. The spray holes 49 are normally closed by the head of the needle 37 urged by the spring pressure of the coil spring 39 into engagement with a valve seat 35a of the nozzle body 35.

The controlled chamber 43 is connected through an orifice 25a formed in the orifice plate 25 to a fluid passage 51 leading to the fuel tank 9. The fluid passage 51 has disposed therein the solenoid valve la which is electrically controlled by the ECU 7 to establish and block fluid communication between the fuel tank 9 and the controlled chamber 43.

The fuel transported from the common rail 3 through the inlet line 15 flows both to the controlled chamber 43 and to the fuel sump 47 through the fluid passage 41 and to the fluid passage 45, respectively. The needle 37 is urged downward (i.e., in a valveclosing direction) by elevated pressure within the controlled chamber 43, while it is lifted upward (i.e., a valve-opening direction) by elevated pressure within the fuel sump 47.

The back face of the piston 27 exposed to the controlled chamber 27 is greater in area than a surface of the large-diameter portion 37a of the needle 37 on which the fuel pressure within the fuel sump 47 acts. Thus, when the ECU 7 turns off the solenoid valve la, the downward pressure acting on the piston 27 is superior to the upward pressure acting on the needle 37.

Specifically, when the solenoid valve la is turned off, the head of the needle 37 is urged into constant engagement with the valve seat 35a to close the spray holes 49, so that the fuel is not injected into the cylinders of the engine. Alternatively, when the solenoid valve 1 a is turned on by the ECU 7 so that it is opened, it will cause the pressurized fuel supplied from the common rail 3 to the controlled chamber 43 of the injector 1 to be drained to the fuel tank 9 on a lower pressure side through the orifice 25a of the orifice plate 25 and the fluid passage 51, so that the fuel pressure within the fuel sump 47 acts on the needle 37 to move it out of engagement with the valve seat 35a, thereby opening the spray holes 49 to initiate the fuel injection into the cylinders of the engine.

Therefore, when the solenoid valve la is opened, as shown in Fig. 2(a), the fuel pressure within the controlled chamber 43 is decreased, as shown in Fig. 2(b). Afterward, when the sum of a downward force produced by the fuel pressure in the controlled chamber 43 and the spring pressure of the spring 39 becomes smaller than an upward force produced by the fuel pressure in the fuel sump 47, the needle 37 starts to move in the valve-opening direction, In Fig. 2(c), the amount of lift of the needle indicates a displacement in the valve-opening direction.

The fuel flow from the controlled chamber 43 to the fuel tank 9 is restricted by the orifice 25a of the orifice plate 25, which will cause, as shown in Figs. 2(b) and 2(c), the time lag tm (about 0.4 ms) to occur between energization or opening of the solenoid valve la and the becinning of movement of the needle 37 in the valve- zn opening direction.

When the ECU 7 turns off or closes the solenoid valve la, it will cause the fuel pressure within the controlled chamber 43 to be elevated again, thereby moving the needle 37 downward to close the spray holes 49.

The ECU 7, as clearly shown in Fig. 1, includes a microcomputer consisting essentially of a CPU 61, a ROM 63 storing therein programs to be executed by the CPU 61, and a RAM 65 temporarily storing therein results of operations of the CPU 61.

The ECU 7 also includes a power supply circuit 81, an input circuit 77, and an output circuit 79. The input circuit 77 connects with a crank angle sensor 67, an accelerator sensor 69, a coolant temperature sensor 71, a cylinder discriminating sensor 73, and a common rail pressure sensor 75 and inputs sensor signals therefrom into the CPU 61. The crank angle sensor 67 outputs a crank angle signal CS in the form of a pulse every rotation of a crankshaft of the engine through a given angle (e.g., 309. The accelerator sensor 69 measures an effort of an accelerator pedal or an opening of a throttle valve (also called an accelerator opening) indicative of an engine load and provides an accelerator opening signal Ac indicative thereof. The coolant temperature sensor 71 measure the temperature of coolant of the engine to provide a coolant temperature signal THW. The cylinder discriminating sensor 73 outputs a cylinder discriminating signal KS in the form of a pulse each time the crankshaft reaches a given angular position in every two rotations of the crankshaft of the engine. The common rail pressure sensor 75 measures the pressure of fuel stored in the common rail 3 and provides a common rail pressure signal Pc. The output circuit 79 receives command signals from the CPU 71 to drive the solenoid la of each of the injectors 1 and the high pressure pump 5. The power supply circuit 81 supplies the voltage VDD to the CPU 61, the ROM 63, the RAM 65, etc.

The power supply circuit 81 converts a battery voltage into the voltage VDD. The battery voltage is supplied from a supply line 83 connecting with a positive terminal of a battery BT mounted in an automotive vehicle through an ignition switch IGS or from a supply line 87 connecting with the positive terminal of the battery 1 0 BT through contacts of a main relay 85.

The ECU 7 also has a transistor Tr which is responsive to a command issued from the CPU 61 through the output circuit 79 to excite a coil L of the main relay 85 to close the contacts establishing the electric communication between the battery BT and the power supply circuit 81.

The ECU 7 codes through the input circuit 77 the voltage level appearing at the supply line 83 and the voltage level appearing at a supply line 89 connecting with the positive terminal of the battery BT through a starter switch STS to produce binary signals of a high level (W or a low level (OV). Based on these signals, the CPU 61 determines the on-off state of the ignition switch IGS and the starter switch STS.

The ignition switch IGS and the starter switch STS are installed in a known key cylinder. When a key is inserted into the key cylinder and turned, it will cause the ignition switch IGS and the starter switch STS to be turned on in sequence. Specifically, when the starter switch STS isturned on, the ignition switch IGS is 19- always turned on. The turning on of the starter switch STS causes the battery voltage to be applied to a starter motor SM through the supply line 89. When the starter motor SM is turned on, it cranks to start the engine.

Accordingly, when the ignition switch IGS is turned on, it will cause the voltage VDD to be outputted from the power supply circuit 81 to operate the ECU 7. The ECU 7 first turns on the transistor Rr to close the relay 85. The ECU 7 also executes an injection program, as will be discussed in detail later, to inject the fuel into the engine during turning on of the ignition switch IGS and is responsive to turning off of the ignition switch IGS to execute an engine stopping program, after which the transistor Tr is turned off to open the main relay 85. When the main relay 85 is opened, it cuts off the supply of the battery voltage to the power supply circuit 81, thereby stopping the output of the voltage VDD from the power supply circuit 81 to disable the ECU 7. Specifically, the main relay 85 serves as a power supply relay for a period of time even after the ignition switch IGS is turned off.

When the ECU 7 is activated by turning on of the ignition switch IGS, it executes in the CPU 61 the injection program, as discussed below, which is stored in the ROM 63.

First, the ECU 7 receives outputs of the sensors 67, 69, 71, 73, and 75 to monitor engine operating conditions such as engine speed Ne, accelerator opening Ac, coolant temperature THW, and common rail pressure Pc in a cycle. The engine speed Ne is determined by measuring time intervals of outputs of the crank angle signal CS from the crank angle sensor 67. The accelerator opening Ac, the coolant temperature THW, and the common rail pressure Pc are determined by A/D converting analog signals outputted from the accelerator sensor 69, the coolant temperature sensor 71, and the common rail pressure sensor 75.

The ECU 7 executes an interruption program, as shown in Fig. 3, in synchronism with revolutions of the engine to determine a target common rail pressure PF which develops a fuel injection pressure for optimizing the combustion in the engine according to the engine operating conditions and to drive the high-pressure 1 0 pump 5 under feedback control so as to bring the actual common rail pressure Pc into agreement with the target common rail pressure PF.

After entering the program in Fig. 3, the routine proceeds to step 200 wherein the ECU 7 reads in the engine speed Ne, a target injection quantity g, and the actual common rail pressure Pc- The routine proceeds to step I 10 wherein the target common rail pressure PF is determined based on the engine speed Ne and the target injection quantity Q. Note that the target injection quantity g is determined in a fuel injection control operation, as will be described later in detail, and that the target common rail pressure PF is increased essentially according to increases in engine speed Ne and target injection quantity indicated by the target injection quantity g.

The routine proceeds to step 120 wherein the high-pressure pump 5 is driven to transport the fuel to the common rail 3 so that the actual common rail pressure Pc may reach the target common rail pressure PF, after which the common rail pressure control is terminated.

When the crankshaft of the engine starts to be rotated by the starter motor SM, the ECU 7 drives the high-pressure pump 5 at full loads to supply the fuel to the common rail 3 at a maximum rate in order to quickly develop the common rail pressure (e.g., 15 MPa) required to initiate the fuel injection from the injectors 1. After the crankshaft of the engine experiences a given number of rotations, the ECU 7 executes the above common rail control operation to feedback control the pressure in the common rail 3.

Further, the ECU 7 executes the fuel injection control operation, as discussed below, every 180' rotation of the crankshaft of the engine to turn on and off the solenoid valve la of one of the injectors 1 for controlling the injection of fuel into the engine. Specifically, in the fuel injection control operation, the target injection quantity Q is determined based on the engine speed Ne and the accelerator opening Ac. The target injection quantity Q is, as already described, increased as either of the engine speed Ne and the accelerator opening Ac is increased. Next, based on the engine speed Ne, the target injection quantity g, and the actual common rail pressure Pc, a solenoid valve-opening duration Tg (> the above described time lag tm) that is the length of time the solenoid valve la of each of the injectors 1 is opened as a function of the quantity of fuel to be injected into the engine and a solenoid valve-opening time T7 that is an instant at which the solenoid valve 1 a is turned on and that corresponds to fuel injection timing are determined. When the solenoid valve-opening time TT is reached, the solenoid valve la is turned on to be opened for the solenoid valve-opening duration TQ.

The ECU 7 also executes a short valve activation decision program, as shown in Fig. 4, and a regular interruption program for short valve activation control, as shown in Fig. 5, periodically to open the solenoid valve la of each of the injectors 1 for a period of time shorter than the time la(y tm between the opening of the solenoid valve la and the beginning of movement of the needle 37 in the valve- opening direction when the ignition switch IGS is switched from the on- state to the off-state, thereby draining the 1 0 high-pressure out of the controlled chamber 43 of the injector 1 to the fuel tank 9 to decrease the pressure of fuel within the common rail 3.

The short valve activation decision program and the regular interruption program will be discussed below in detail with reference to Figs. 4 and 5. The short valve activation decision program is executed at regular intervals of 16 ms. The regular interruption program is executed at regular intervals of 4 ms.

After entering the program in Fig. 4, the routine proceeds to step 200 wherein it is determined whether the ignition switch IGS is turned on or not. If a YES answer is obtained, then the routine proceeds to step 210 wherein the transistor Tr is turned on to close the main relay 85. The routine proceeds to step 220 wherein a short valve activation control flag FK is set to zero (0) indicating that the short valve activation control is not to be performed, that is.

that the solenoid valve la is not to be turned on. The routine proceeds to step 230 wherein a counter value C 1 is reset to zero (0) and then terminates.

If a NO answer is obtained in step 200 meaning that the ignition switch IGS is not turned on, then the routine proceeds to step 240 wherein it is determined whether the ignition switch IGS has been switched from the onstate to the off-state in this program cycle or not, that is, whether a YES answer was obtained in step 200 one program cycle earlier and a NO answer is obtained in step 200 of this program cycle or not.

If a YES answer is obtained in step 240, then the routine proceeds to step 250 wherein an inlet valve installed in an induction system (not shown) is closed to make the engine misfire so that the engine is stopped slowly. The routine proceeds to step 260 and waits 0.2 sec. The routine then proceeds to step 270 wherein the fuel injection from the injectors 1 is stopped. The routine proceeds to step 280 wherein the high-pressure pump 5 is turned off to stop the transportation of fuel to the common rail 3. The routine proceeds to step 290 wherein the short valve activation control flag FK is set to one (1) indicating that the solenoid valve la is to be turned on and then terminates.

If a NO answer is obtained in step 240 meaning that the 1 ignition switch IGS is kept turned off, and that the negative answers have been obtained both in this program cycle and in the immediately proceeding program cycle, then the routine proceeds to step 300 wherein the counter value Cl is incremented by one (1).

The routine proceeds to step 310 wherein it is determined whether the counter value Cl is greater than a reference value N 62) corresponding to one second or not. If a NO answer is obtained, then the routine terminates. Alternatively, if a YES answer is obtained meaning that one second has passed since the ignition switch IGS is turned off, then the routine proceeds to step 320 wherein the short valve activation control flag FK is set to zero (0) indicating that the short valve activation control is not to be performed. The routine proceeds to step 330 wherein the transistor Tr is turned off to open the main relay 85 and then terminates.

When the main relay 85 is opened, it blocks the supply of power from the battery BT to the power supply circuit 81, so that the ECU 7 is turned off.

Upon initiation of the regular interruption program as shown in Fig. 5, the routine proceeds to step 400 wherein it is determined whether the short valve activation control flag FK is one (1) or not. If a NO answer is obtained meaning that the short valve activation control is not to be performed, then the routine terminates. Alternatively, if a NO answer is obtained, then the routine proceeds to step 410 wherein the short valve activation control is performed. Specifically, the solenoid valve la of each of the injectors 1 is activated or opened for the per-iod of time Tq (e.g., 500 is) shorter than the time lag tm to reduce the pressure in the common rail 3, after which the routine terminates. In step 410, one or some of the injectors 1 may alternatively be opened or all the injectors 1 may be opened in sequence.

It is advisable that the period of time Tq during which the solenoid valve la is opened be deter-mined depending upon the coolant temperature THW or the temperature of combustion in the engine. This is because when the coolant temperature THW or the combustion temperature is low, the viscosity of fuel becomes high thus resulting in a decreased rate at which the cornmon rail pressure drops. Therefore, a stable rate of decrease in common rail pressure may be achieved by prolonging the period of time Tq during which the solenoid valve la is opened as the coolant temperature THW or the combustion temperature is lowered.

The operation of the accumulator fuel injection system in execution of the short valve activation decision program and the regular interruption program in Figs. 4 and 5 will be described 1 0 below.

When the ignition switch IGS is changed from the on-state to the offstate and when the positive answer is obtained in step 240 of the short valve activation decision program in Fig. 4, the engine is stopped through steps 250 to 280, and the short valve activation control flag FK is set to one (1) in step 290. Each time the regular interruption program in Fig. 5 is performed, the positive a-nswer is thus obtained in step 400. In the following step 410, the solenoid valve la of each of the injectors 1 is activated for a short time. Specifically, every execution of the regular interruption program, that is, every 4 ms, the solenoid valve la is opened for the period of time Tq shorter than the time lag tm occurring between the opening of the solenoid valve la and the beginning of movement of the needle 37 in the valve-opening direction, thereby decreasing the actual common rail pressure Pc.

As long as the ignition switch IGS is kept off, the counter value Cl is incremented by one (1) every execution of the short valve activation decision program in Fig. 4. When about one second has passed following turning off of the ignition switch IGS, the positive answer is obtained in step 3 10 in Fig. 4. The short valve activation control flag FK is, thus, set to zero (0). The main relav 85 is turned off.

Therefore, even if the regular interruption program is performed between turning off of the main relay 85 and deactivation of the ECU 7, the negative answer is obtained in step 400, so that the solenoid valve la is not opened.

When the i:nition switch IGS is turned on again before the C.

positive answer is obtained in step 310, that is, before one second passes following turning off of the ignition switch IGS, the positive answer is obtained in step 200 in Fig. 4. The short valve activation control flag FK is, thus, reset to zero (0) in step 220, and the counter value Cl is reset to zero (0) in step 230. Subsequently, when the ignition switch IGS is switched from the on-state to the off-state, the solenoid valve la of each of the injectors 1 is opened every execution of the regular interruption program in Fig. 5 (i.e., every 4 ms).

Accordingly, even if a vehicle driver turns off the ignition switch IGS just after operating the engine at high loads or racing it and turns on the ignition switch IGS and the starter switch STS immediately to start the engine again, the accumulator fuel injection system of this embodiment decreases the pressure in the common rail 3 sufficiently before the engine is restarted, thereby preventing a large quantity of fuel from being injected into the engine at a t) 1 - pressure level higher than required when the engine is restarted, which would cause uncomfortable combustion noise that is objectionable in the conventional accumulator fuel injection systems, as discussed in the introductory part of this application.

Such a combustion noise, as already described, also arises at a time when the engine is started after the vehicle operator turns on and off the starter switch STS many times because of a failure in starting the engine. Specifically, when the starter switch STS is turned on to rotate the crankshaft of the engine, the accumulator fuel injection system drives the high-pressure pump 5 at full loads to transport the fuel to the common rail 3 at a maximum rate for increasing the common rail pressure quickly up to a level enabling the fuel injection through the injectors 1. The repeated on-off operations of the starter motor SM because of a failure in starting the engine may thus cause the common rail pressure to be elevated more than required, which produces the combustion noise at the beginning of burning of the fuel immediately after the engine is started.

The accumulator fuel injection system of this embodiment, however, is responsive to the turning off of the ignition switch IGS to open the solenoid valve la of each of the injectors 1 to reduce the pressure in the common rail 3, thus avoiding the combustion noise caused by the above.

An accumulator fuel injection system according to the second embodiment will be described blow which is a modification of the first embodiment designed to execute a short valve activation decision program, as shown in Fig. 6, instead of the one shown in Fid. 4. Other arrandements and operations are identical, and C) 1t5 explanation thereof in detail will be omitted here.

In Fig. 6, the same step numbers as employed in Fig. 4 refer to the same operations. Only differences between Figs. 4 and 6 will be discussed below.

After, in step 220, the short valve activation control flag FK is reset to zero (0), the routine terminates.

After, in step 280, the high-pressure pump 5 is stopped, the routine proceeds to step 285 wherein it is determined whether the actual common rail pressure Pc is higher than a set pressure level PM (e.g., 2 MPa) or not. If a YES answer is obtained, then the routine proceeds to step 290 wherein the short valve activation control flag FK is set to one (1) and then terminates. Alternativelv, if a NO answer is obtained in step 285, then the routine proceeds to step 287 wherein the main relay 85 is turned off and then terminates.

If a NO answer is obtained in step 240 meaning that the ignition switch IGS is kept turned off, and that the negative answers has been obtained both in this program cycle and in the immediately proceeding program cycle, then the routine proceeds to 315 wherein it is determined whether the actual common rail pressure Pc is higher than the set pressure level PM or not. If a YES answer is obtained, then the routine terminates. Alternatively, if a NO answer is obtained, then the routine proceeds to step 320 wherein the short valve activation control flag FK is reset to zero (0). The routine proceeds to step 330 wherein the main relay 85 is turned off and then terminates.

Accordingly, when the ignition switch IGS is switched from the on-state to the off-state (YES in step 240), and when the actual common rail pressure Pc is greater than the set pressure level PM (YES in step 285), the short valve activation control flag FK is set to one (1) (step 290) to open the solenoid valve la of each of the injectors 1 in execution of the regular interruption program in Fig. 5. Afterwards, when the actual common rail pressure Pc is decreased below the set pressure level PM (NO in step 315), the short valve activation flag FK is reset to zero (0) (step 320) to close the solenoid valve la.

Specifically, the accumulator fuel injection system of this embodiment is responsive to the turning off of the ignition switch IGS to open the solenoid valve la at regular intervals until the actual common rail pressure Pc is smaller than the set pressure level PM. An accumulator fuel injection system according to the third embodiment will be described blow which is different from that in the first embodiment in two points below. Other arrangements and operations are identical, and explanation thereof in detail will be omitted here. (1) The ECU 7 executes shown in Fig. 7. (2) The ECU 7 executes a program corresponding to the short valve activation decision program in Fig. 6 from which steps 220, 240, 285, 290 to 330 are omitted for controlling an on-off operation of the main relay 85, which will be discussed below with reference to Fig. 6.

If the ECU 7 determines that the ignition switch IGS is turned c) a short valve activation decision program, as on (YES in step 200), it turns on the main relay 85 (step 210). Alternatively, if the ECU 7 determines that the ignition switch IGS is turned off (NO in step 200), it performs the operations in steps 250 to 280 to stop the engine and turns off the main relay 85 (step 287).

The short valve activation decision program in Fig. 7 is executed at time intervals of 16 ms.

After entering the program, the routine proceeds to step 500 wherein it is determined whether the starter switch STS is turned on or not. If a YES answer is obtained, then the routine proceeds to step 510 wherein the short valve activation control flag FK is reset to zero (0). The routine proceeds to step 520 wherein the counter value C2 is reset to zero (0) and then terminates.

If a NO answer is obtained in step 500, then the routine proceeds to step 530 wherein it is determined whether the starter switch STS has been switched from the on-state to the off-state in this program cycle or not, that is, whether a YES answer was obtained in step 500 one program cycle earlier and a NO answer is obtained in step 500 of this program cycle or not. If a YES answer is obtained, then the routine proceeds to step 540 wherein it is determined whether or not the engine speed Ne is lower than a given speed M (e.g., 300 rpm) that is lower than a typical idling speed. If a NO answer is obtained meaning that the engine has started, then the routine terminates. -,,kltemativelv, if a YES answer is obtained in step 540 meaning that the starter switch STS has been turned on, but the engine is not started, that is, that the vehicle driver has failed to start the engine, then the routine proceeds to step 550 wherein the short valve activation control flag FK is set to one (1) indicating that the solenoid valve la of each of the injectors 1 is to be opened and then terminates.

If a NO answer is obtained in step 530 meaning that the starter switch STS is kept off, then the routine proceeds to step 560 wherein it is determined whether the short valve activation control flag FK indicates one (1) or not. If a NO answer is obtained meaning that the engine is running normally, then the routine terminates. Alternatively, if a YES answer is obtained meaning that the engine has failed to start, then the routine proceeds to step 570 wherein the counter value C2 is incremented by one (1). The routine proceeds to step 580 wherein it is determined whether the counter value C2 is greater than a given value N (= 62) corresponding to one (1) second or not. If a NO answer is obtained, then the routine terminates. Alternatively, if a YES answer is obtained meaning that one second has passed since the starter switch STS was turned off, in other words, since the engine has failed to be started, then the routine proceeds to step 590 wherein the short valve activation control flag FK is reset to zero (0) and then terminates.

Specifically, if the engine speed Ne is lower than the given speed M (= 300 rpm) when the starter switch STS is switched from the on-state to the off-state, the positive answers are obtained both in steps 530 and 540 in the short valve activation decision program in Fig. 7, and the short valve activation control flag FK is set to one (1). Therefore, every execution of the regular interruption program in Fig. 5, the positive answer is obtained in step 400, so that the solenoid valve la of each of the injectors 1 is opened in step 410. Specifically, the solenoid valve la is opened at regular intervals of 4 ms that are program execution cycles of the regular interruption program in Fig. 5 to reduce the actual common rail pressure Pc.

If the starter switch STS remains turned off, the counter value C2 is incremented in step 570 every execution of the short valve activation decision program in Fig. 7. After a lapse of one second following the turning off of the starter switch STS, the positive answer is obtained in step 580, and the short valve activation control flag FK is reset to zero (0) (step 590) to turn off or close the solenoid valve la of each of the injectors 1.

If the starter switch STS is turned on again before the positive answer is obtained in step 580, that is, before one (1) second passes following the turning off of the starter switch STS, the positive answer is obtained in step 500, the short valve activation control flag FK is reset to zero (0) in step 510, and the counter value C2 is reset to zero (0) in step 520.

Therefore, when the starter switch STS is turned off subsequently, and when the engine speed Ne is lower than the given speed M, the solenoid valve la of each of the injectors 1 is opened at regular intervals of 4 ms again to reduce the fuel pressure in the common rail 3.

As clearly from the above discussion, the accumulator fuel injection system of this embodiment is so designed that if it is determined that the engine has failed to be started when the engine speed Ne is lower than the given speed M after the starter switch STS is switched from the one-state to the off-state, the solenoid valve la of each of the injectors 1 is opened to drain the fuel out of the common rail 3 to the fuel tank 9 for decreasing the fuel pressure in the common rail 3. This causes the actual common rail pressure Pc to be lowered before the vehicle driver turns on the starter switch STS again following a failure in starting the engine, thereby avoiding an excessive elevation in fuel pressure within the common rail 3 caused by repeated turning on and off of the starter switch STS which would contribute to the combustion noise at the 10 engine start up.

Specifically, the accumulator fuel injection system of this embodiment is capable of avoiding the excessive elevation in fuel pressure within the common rail 3 even if the vehicle driver turns on and off the starter switch STS repeatedly while keeping the 15 ignition switch tuned on.

An accumulator fuel injection system according to the fourth embodiment will be described blow which is different from the third embodiment in a short valve activation decision program in Fig. 8. Other arrangements and operations are identical, and 20 explanation thereof in detail will be omitted here.

The short valve activation decision program in Fig. 8 emits steps 520, 570, and 580 as executed in Fig. 7 and adds steps 545 zn and 585.

Specifically, after the short valve activation control flag FK is reset to zero (0) in step 510, the routine terminates. If a YES answer is obtained in step 540 meaning that the engine speed Ne is lower than the criven speed M, then the routine proceeds to step t5 545 wherein it is determined whether the actual common rail pressure is higher than the set pressure level PM (e.g., 2 MPa) or not. If a YES answer is obtained, then the routine proceeds to step 550 wherein the short valve activation control flag FK is set to one (1) and terminates. Alternatively, if a NO answer is obtained meaning that the actual common rail pressure Pc is lower than the set pressure level PM, then the routine terminates without setting the short valve activation control flag FK to one (1).

Further, if a YES answer is obtained in step 560 meaning that the short valve activation control flag FK indicates one (1), then the routine proceeds to step 585 wherein it is determined whether the actual common rail pressure Pc is higher than the set pressure level PM or not. If a YES answer is obtained meaning that the actual common rail pressure Pc is still higher than the set pressure level 1 5 PM, then the routine terminates. Alternatively, if a NO answer is obtained, the routine proceeds to step 590 wherein the short valve activation control flag FK is reset to zero (0) and terminates.

Specifically, the accumulator fuel injection system of this embodiment determines, similar to the third embodiment, that the engine has failed to start if the engine speed Ne is lower than the given speed M (YES in step 540) after the starter switch STS is switched from the on-state to the off-state (YES in step 530), but it sets the short valve activation control flag FK to one (1) to open the solenoid valve la of each of the injectors 1 only when the actual common rail pressure Pc is higher than the set pressure level PM (YES in step 545). 1ifterwards, when the actual common rail pressure Pc drops below the set pressure level PM (NO in step 585), the short valve activation control flag FK is reset to zero (0) (step 590) to close the solenoid valve la of each of the injectors 1.

In other words, the accumulator fuel injection system of this embodiment is so designed that when the engine has failed to start, the solenoid valve la of each of the injectors 1 is opened at the regular intervals until the actual common rail pressure Pc is decreased below the set pressure level PM.

Fig. 9 shows an accumulator fuel injection system according to the fifth embodiment of the invention. The same reference 0 numbers as employed in Fig. 1 refer to the same parts, and explanation thereof in detail will be omitted here.

The accumulator fuel injection system of this embodiment is designed to alleviate the following problem. Usually, when the vehicle operator releases depression of an accelerator pedal to decelerate the diesel engine quickly, a target quantity of fuel to be injected into the engine is set to zero (0) to stop the fuel injection from injectors. Subsequently, when the vehicle operator depresses the accelerator pedal to accelerate the vehicle, the target injection quantity is determined based on an operating condition of the engine, and the fuel injection is resumed. The pressure in the common rail, however, is not reduced sufficiently because of the stop of the fuel injection accompanied by the quick deceleration of the engine, so that it is kept near a target pressure level determined prior to the deceleration of the engine. This may cause the common rail pressure when the fuel injection is resumed to be higher than the target pressure level depending upon an operating condition of the engine, so that as soon as the injectors are opened, the fuel is injected into the engine at a higher rate in a short time, which will result in excessive combustion noise and mechanical shocks of the engine at acceleration. The ECU 7 includes, as shown in Fig. 9, the input circuit 77, C> the RAM

65, the CPU 61, the output circuit 79, and the ROM 63. The input circuit 77 inputs to the CPU 61 sensor signals from the crank angle sensor 67, the accelerator sensor 69, the coolant temperature sensor 71, the cylinder discriminating sensor 73, and the common rail pressure sensor 75. These sensors and circuit elements of the ECU 7 are identical with those shown in Fig. 1, and explanation thereof in detail will be omitted here.

Fig. 10 shows a fuel injection control program performed by the ECU 7 every 180' rotation of the crankshaft of the engine to turn on and off the solenoid valve la of each of the injectors 1 for controlling the injection of fuel into the engine.

The fuel injection control program is initiated in response to the first output of the crank angle signal CS from the crank angle sensor 67 (i.e., at time ti), as shown in Fig. 12(b), after the cylinder 1 discriminating signal KS, as shown in Fig. 12(a), is outputted from the cylinder discriminating sensor 73. Subsequently, the fuel injection control program is performed every six outputs of the crank angle signal CS (i.e., t2, t3, - - -). In Fig. 12(b), each numeral Z_ indicates an angular position of the crankshaft of the engine if defined as zero (0) when the fuel injection control program is performed.

After entering the program, the routine proceeds to step 1200 wherein the engine speed Ne and the accelerator opening Ac are read in the CPU 7. The routine proceeds to step 1210 wherein the target injection quantity g is determined based on the engine speed Ne and the accelerator opening Ac. The target injection quantity Q is increased as the accelerator opening Ac is increased.

The routine proceeds to step 1220 wherein it is determined whether the target injection quantity 9 is lower than zero (0) or not. If a NO answer is obtained meaning that the fuel should be injected into the engine, then the routine proceeds to step 230 wherein the short valve activation control flag FK is reset to zero (0). The routine proceeds to step 1240 wherein based on the engine speed Ne, the target injection quantity Q, and the actual common rail pressure Pc, the solenoid valve-opening duration TQ (> the above described time lag tm) that is the length of time the solenoid valve la of each of the injectors 1 is opened as a function of the quantity of fuel to be injected into the engine and the solenoid valve-opening time TF that is the timing with which the solenoid valve I a is turned on and that corresponds to fuel injection timing are determined. When the solenoid valve-opening time TT is reached, the solenoid valve la is turned on to be opened for the solenoid 2 0 valve- opening duration TQ.

If a YES answer is obtained in step 1220 meaning that the fuel injection is not needed, then the routine proceeds to step 1250 wherein a short valve activation decision program, as shown in Fig.

C 11, is performed. The routine proceeds to step 1260 wherein the solenoid valve la of each of the injectors 1 is disabled to stop the fuel injection.

Upon initiation of the program in Fig. 11, the routine proceeds to step 1300 wherein it is determined whether a difference between the actual common rail pressure Pc and the target common rail pressure PF (PC - PF) is greater than a given pressure level H (e.g., 2 MPa) or not. If a NO answer is obtained, then the routine proceeds to step 1310 wherein the short valve activation control flag FK is reset to zero (0) and terminates.

Alternatively, if a YES answer is obtained meaning that the pressure in the common rail 3 should be decreased, then the routine proceeds to step 1320 wherein the high-pressure pump 5 is turned off to stop the transportation of fuel to the common rail 3. The routine proceeds to step 1330 wherein the short valve activation control flag FK is set to one (1) and then terminates. Note that the deactivation of the high pressure pump 5 in step 1320 is released when it is determined in step 1300 that the pressure difference (Pc - PF) is smaller than the given pressure level H.

In parallel with execution of the program in Fig. 11, a regular interruption program identical with the one shown in Fig. 5 is performed at time intervals of 4 ms to open the solenoid valve la of each of the injectors 1 for the period of time Tq (e.g., 500 LLs) which is shorter than the time lag tm between the opening of the solenoid valve la and the beginning of movement of the needle 37 in the valve-opening, direction for reducing the pressure in the common rail 3. The short valve activation control may alternatively be performed for one or some of the injectors 1 or for all the injectors 1 in sequence.

The operation of the accumulator fuel injection system in execution of the programs in Figs. 3, 5, 10, and 11 will be described W below.

If the target injection quantity Q determined in step 1210 in the injection control program of Fig. 10 executed at time ti, as shown in Fig. 12(b), is greater than zero (0), as shown in Fig. 12(c), the negative answer is obtained in step 1220, so that the normal fuel injection control is performed in step 1240. Thus, when the solenoid valve-opening time Tr is reached after time ti, the solenoid valve la of corresponding one of the injectors I is turned on to be opened for the solenoid valve-opening duration TQ for injecting the fuel into one of the cylinders of the engine. In Fig. 12(d), the solenoid valve-opening time Tr is defined near the top dead center #ITDC in a compression stroke of the first cylinder of the engine which is shifted in rotation of the crankshaft 90' apart from time t 1.

The fuel injection into the engine causes, as shown by a broken line in Fig. 12(e), the actual common rail pressure Pc to drop below the target common rail pressure PF slightly, but it is returned quickly to the target common rail pressure PF under the common rail pressure control in Fig. 3.

If the vehicle operator releases depression of the accelerator pedal, and the target injection quantity g determined in step 1210 in the injection control program of Fig. 10 executed at time U, as shown in Fig. 12(b), is smaller than zero (0), as shown in Fig. 12(c), the positive answer is obtained in step 1220. The short valve activation control is, thus, performed in step 1250, and the fuel injection is stopped in step 1260.

The releasing of the accelerator pedal causes the accelerator opening Ac to be zero (0), so that the target common rail pressure PF determined in step 110 of Fig. 3 decreases. When the pressure difference (PC - PF) between the actual common rail pressure Pc and the target common rail pressure PF becomes, as shown in Fig. 12, greater than the given pressure level H, the positive answer is obtained in step 1300 in the short valve activation decision program executed at time U. The high pressure pump 5 is, thus, turned off in step 1320, and the short valve activation control flag FK is set to one (1). This causes the positive answer to be obtained in step 400 every execution of the regular interruption program in Fig. 5, or at time intervals of 4 ms, so that the solenoid valve l a of each of the injectors 1, as shown in Fig. 12(d), is opened for the period of time Tq shorter than the time lag tm, thereby reducing the actual common rail pressure Pc gradually, as shown in a broken line of Fig.

1 5 12 (e).

Subsequently, when the vehicle operator depresses the acceleration pedal again, the accelerator opening Ac is increased more than zero (0). The fuel injection quantity Q is, thus, determined to be greater than zero (0) in step 1220 of the injection control program in Fig. 10 executed, for example, at time t3. The fuel injection is performed similar to the one between ti and t2.

As will be apparent from the above discussion, when the depression of the accelerator pedal is released, and when the pressure difference (Pc - PF) between the actual common rail pressure Pc and the target common rail pressure PF increases above the given pressure level M, the solenoid valve la of each of the injectors 1 is subjected to the short valve activation control at time -41 intervals of 4 ms until the pressure difference (Pc PF') is smaller than or equal to the given pressure level M, thereby avoiding the excessive combustion noise at acceleration, as discussed above.

An accumulator fuel injection system according to the sixth embodiment will be described blow with reference to Figs. 13 to 16(e) which is different from the fifth embodiment in three points below. Other arrangements and operations are identical, and explanation thereof in detail will be omitted here.

(1) The ECU 7 executes a short valve activation decision program, as shown in Fig. 13, in step 1250 in the injection control program of Fig. 10.

(2) The EW 7 executes a regular interruption program, as shown in Fig. 14, instead of the one in Fig. 5.

(3) The ECU 7 executes a crank angle interruption program, as shown in Fig. 15, in response to output of the crank angle signal CS from the crank angle sensor 67 (i.e., even, crank angle of 30% 1 In Fig. 13, the same step numbers as employed in Fig. 11 to the same operations, and explanation thereof in detail will be omitted here.

If a YES answer is obtained in step 1300 meaning that the pressure difference (Pc PF) between the actual common rail pressure Pc and the target common rail pressure PF is greater than the given pressure level M, the routine proceeds through step 1320 to step 1322 wherein it is determined whether the engine speed Ne is greater than a preselected speed (e.g., 2500 rpm) or not. If a NO answer is obtained, then the routine proceeds to step 1324 wherein an angle synchronization flag FN is reset to zero (0) indicating that the short valve activation control is not to be performed in synchronization with revolutions of the engine. The routine proceeds to step 1330 wherein the short valve activation control flag FK is set to one (1) and then terminates.

Alternatively, if a YES answer is obtained in step 1322, then the routine proceeds to step 1326 wherein the angle synchronization flag FN is set to one (1) indicating that the short valve activation control is to be performed in synchronization with revolutions of the engine. The routine proceeds to step 1330 wherein the short valve activation control flag FK is set to one (1) and then terminates.

In the regular interruption program of Fig. 14, if a YES answer is obtained in step 400 meaning that the short valve activation control flag FK indicates one (1), then the routine proceeds to step 405 wherein it is determined whether the angle synchronization flag M is zero (0) or not. If a NO answer is obtained, then the routine terminates. Alternatively, if a YES answer is obtained, then the routine proceeds to step 410 to perform the short valve activation control in asynchronism with revolutions of the engine.

Every input of the crank angle signal CS from the crank angle 1 sensor 67 into the ECU 7, the crank angle interruption program, as shown in Fig. 15 is executed.

Upon initiation of the program, the routine proceeds to step 1500 wherein it is determined whether the short valve activation control flag FK is one (1) or not. If a YES answer is obtained, then Itly the routine proceeds to step 1510 wherein it is determined whether the angle synchronization flag FN is one (1) or not. If a YES answer is obtained, then the routine proceeds to step 1520 wherein it is determined whether or not the angular position of the crankshaft of the engine (i.e., the crank angle) has reached one of 30', 90', and 150' if the crank angle at which the injector control program is executed is defined as 0'. If a YES answer is obtained, then the routine proceeds to step 1530 wherein the short valve activation control is performed in the same manner, as in step 410 of Fig. 14, and terminates.

If a NO answer is obtained in either of steps 1500, 15 10, and 1520, then the routine terminates without executing step 1530.

Specifically, the accumulator fuel injection system of this embodiment is designed to subject the solenoid valve la of each of the injectors 1 to the short valve activation control at regular intervals of 4 ms in asynchronism with revolutions of the engine (step 410 in Fig. 14) if it is determined that the common rail pressure is to be decreased (YES in steps 1220 and 1300) when the engine speed Ne is lower than the preselected speed, for example, 2500 rpm (NO in step 1322). Alternatively, if it is determined that the common rail pressure is to be decreased (YES in steps 1220 and 1300) when the engine speed Ne is higher than the preselected speed (YES in step 1322). the solenoid valve la of each of the injectors 1 is subjected to the short valve activation control every 60' rotation of the crankshaft of the engine in execution of the crank angle interruption program in Fig. 15.

For example, between t4 to t5 in Figs. 16(a) to 16(e) where the 1 0 target injection quantity g is calculated as zero (0), and the pressure difference (PC - PF) between the actual common rail pressure Pc and the target common rail pressure PF is greater than the set pressure level H, the solenoid valve la of each of the injectors 1 is subjected to the short valve activation control each time the crank angle reaches one of 30', 90', and 1500 when the engine speed Ne is greater than the preselected speed (e.g., 2500 rpm), thereby reducing the actual common rail pressure Pc stepwise, as shown by a broken line in Fig. 16(e). When the engine speed Ne is greater than 2500 rpm. the execution cycle of the crank angle interruption program in Fig. 15 becomes shorter than 4 ms that is the execution cycle of the regular interruption program in Fig. 14. The reduced rate of the common rail pressure Pc, thus, increases as the engine speed Ne increases, resulting in a quick reduction in common rail pressure as a function of the engine speed Ne.

In Fig. 16(b), times t4, t5, and t6 each indicate an instant at which the injection control program in Fig. 10 is executed. The target common rail g and an operation of the solenoid valves la after t5 are identical ivith those before U in Figs. 12(c) and 12(d). Specifically, between t5 and 56, when the solenoid valve-opening time TI7 defined near the top dead center "'3TDC in a compression stroke of the third cvIinder:.3 of the engine which is shifted in rotation of the crankshaft 90' apart from time t5 is reached, the solenoid valve la of corresponding one of the injectors 1 is opened for the solenoid valve-opening duration Tg for injecting the fuel into one of the cvIinders of the engine.

The execution cycle of the programs in Figs. 5 and 14 is not limited to 4 ms, but may be changed depending upon the coolant temperature THW and/or the combustion temperature in the engine. It is advisable that the execution cycle be shortened as the coolant temperature THW and/or the combustion temperature is decreased. This is because the decrease in the coolant temperature THW and combustion temperature usually produce excessive combustion noise of the engine, thus requiring a quick drop in pressure in the common rail 3 for minimizing the combustion noise and because the short valve activation control is prevented from being executed in cycles shorter than required under conditions that the coolant temperature THW and combustion temperature are high, thereby minimizing thermal loads of the injectors 1 and dr-ive circuits thereof.

It is advisable that the period of time Tq during which the solenoid valve la is opened be determined depending upon the coolant temperature THW or the temperature of combustion in the engine. This is because when the coolant temperature THW or the combustion temperature is low, the viscosity of fuel becomes high.

thus resulting in a decreased rate at which the common rail pressure drops. Therefore, a stable rate of decrease in common rail pressure may be achieved by prolonging the period of time Tq during which the solenoid valve la is opened as the coolant temperature THW or the combustion temperature is lowered.

In the injection control program of Fig. 1.0, if it is determined in step 1220 that the target injection quantity g is less than or equal to zero (0), the short valve activation control in Fig. 11 or 13 1 is performed, but may alternativelv be performed if it is determined that the target injection quantify g is less than a preselected value more than zero (0).

The above fifth and sixth embodiments determine whether the common rail pressure should be decreased or not based on the difference between the actual common rail pressure Pc and the target common rail pressure PF, but such a determination may be made based on another condition.

For example, it may be determined that the common rail 1 0 pressure should be decreased when an engine stall takes place.

Specifically, in the fifth embodiment, when the engine speed Ne becomes zero (0), that is, when output of the crank angle signal CS from the crank angle sensor 67 stops, it is deter-mined that the engine stall has taken place, and the short valve activation control flag FK is set to one (1). This avoids the combustion noise in the engine when a vehicle operator restarts the engine after the engine stall takes place.

In the sixth embodiment, when the engine speed Ne is greater than the preselected speed (e.g., 2500 rpm), the short valve activation control is performed at 30', 90', and 150' angular positions of the crankshaft of the engine to open the solenoid valves la, but the number of angular positions at which the solenoid valves la are to be opened may be increased as the engine speed Ne decreases.

While the present invention has been disclosed in terms of the prefer-red embodiment in order to facilitate a better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modification to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in the appended claims.

Claims

1. An accumulator fuel injection apparatus for a diesel engine of a vehicle comprising: a fuel line, an accumulator chamber accumulating therein fuel supplied from a fuel pump through said fuel line., a fuel injector injecting the fuel stored in said accumulator chamber into a cylinder of the engine; a draining mechanism draining the fuel out of said accumulator chamber to a portion of said fuel line lower in pressure than said accumulator chamber to reduce a pressure in said accumulator chamber; an on-off switching detecting circuit detecting a switching operation of an ignition switch of the vehicle from an on-state to an off-state to provide an onto-off switching signal indicative thereof; and a controller responsive to the on-to-off switching signal from said on-off switching detecting circuit to activate said draining mechanism to reduce the pressure in said accumulator chamber.

2. An accumulator fuel injection apparatus as claimed in claim 1. wherein said fuel injector includes an injecting portion, a drive portion, and a solenoid valve, the injecting portion having disposed therein a valve member which is applied with a pressure of the fuel transported from said accumulator chamber through a first passage portion of said fuel line to move to open a spray hole for injecting the fuel into the engine, the drive portion applying a pressure of the fuel transported from said accumulator chamber through a second passage portion of said fuel line to drive the valve member to close the spray hole, the solenoid valve constituting said draining mechanism and being opened when energized to establish fluid communication between a third passage portion of said fuel line connecting with the portion of said fuel line lower in pressure than said accumulator chamber and the second passage portion of said fuel line to reduce the pressure of the fuel applied to the valve member of the drive portion of said fuel injector so that the valve member moves to open the spray hole, and wherein said controller opens the solenoid valve for a preselected period of time shorter than a time lag occurring between opening of the solenoid valve and beginning of movement of the valve member for draining the fuel out of said accumulator chamber to reduce the pressure in said accumulator chamber.

3. An accumulator fuel injection apparatus as claimed in claim 2, wherein said controller opens the solenoid valve for the preselected period of time at regular intervals in response to the on-to-off switching signal from said on-off switching detecting circuit.

4. An accumulator fuel injection apparatus as claimed in any one of claims 1 to 3, wherein said controller is responsive to the on-tooff switching signal from said on-off switching detecting circuit to 1 1 activate said draining mechanism for a given period of time as long as the ignition switch is kept off.

5. An accumulator fuel injection apparatus as claimed in any one of claims 1 to 3, wherein said controller determines whether the pressure of the fuel within said accumulator chamber is higher than a given pressure level or not, said controller allowing said draining mechanism to be activated as long as the pressure of the fuel within said accumulator chamber is higher than the given pressure level.

6. An accumulator fuel injection apparatus for a diesel engine of a vehicle comprising:

a fuel line; an accumulator chamber accumulating therein fuel supplied from a fuel pump through said fuel line; a fuel injector injecting the fuel stored in said accumulator chamber into a cylinder of the engine; a draining mechanism draining the fuel out of said accumulator chamber to a portion of said fuel line lower in pressure than said accumulator chamber to reduce a pressure in said accumulator chamber; an onoff switching detecting circuit detecting a switching operation of a starter switch for starting the engine from an on-state to an off-state:

an engine speed determining circuit determining whether a t C1) W speed of the engine is lower than a preselected speed or not when said onoff switching detecting circuits detects the switching operation of the starter switch from the on-state to the off-state; and a controller activating said draining mechanism to reduce the pressure in said accumulator chamber when said engine speed determining circuit determines that the speed of the engine is lower than the preselected speed.

7. An accumulator fuel injection apparatus as claimed in claim 6, wherein said fuel injector includes an injecting portion, a drive portion, and a solenoid valve, the in ecting portion having disposed j therein a valve member which is applied with a pressure of the fuel transported from said accumulator chamber through a first passage portion of said fuel line to move to open a spray hole for injecting 1 5 the fuel into the engine, the drive portion applying a pressure of the fuel transported from said accumulator chamber through a second passage portion of said fuel line to drive the valve member to close the spray hole, the solenoid valve constituting said draining mechanism and being opened when energized to establish fluid communication between a third passage portion of said fuel line connecting with the portion of said fuel line lower in pressure than said accumulator chamber and the second passage portion of said fuel line to reduce the pressure of the fuel applied to the valve member of the drive portion of said fuel injector so that the valve member moves to open the spray hole, and wherein said controller opens the solenoid valve for a preselected period of time shorter than a time lag occurring between opening of the solenoid valve and beginning of movement of the valve member for draining the fuel out of said accumulator chamber to reduce the pressure in said accumulator chamber.

8. An accumulator fuel injection apparatus as claimed in claim 7, wherein said controller opens the solenoid valve for the preselected period of time at regular intervals when said engine speed determining circuit determines that the speed of the engine is 10 lower than the preselected speed.

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9. An accumulator fuel injection apparatus as claimed in any one of claims 6 to 8, wherein when said engine speed determining circuit determines that the speed of the engine is lower than the preselected speed, said controller activates said draining mechanism for a given period of time as long as the starter switch is kept off.

10. An accumulator fuel injection apparatus as claimed in any one of claims 6 to 8, wherein said controller determines whether the pressure of the fuel within said accumulator chamber is higher than a given pressure level or not, said controller allowing said draining mechanism to be activated as long as the pressure of the fuel within said accumulator chamber is higher than the given pressure level.

11. An accumulator fuel injection apparatus for a diesel engine of a vehicle comprising: a fuel line: an accumulator chamber accumulating therein fuel supplied from a fuel pump through said fuel line; a fuel injector injecting the fuel stored in said accumulator chamber into a cylinder of the engine in synchronism with revolutions of the engine, said fuel injector including an injecting portion, a drive portion, and a solenoid valve, the injecting portion having disposed therein a valve member which is applied with a pressure of the fuel transported from said accumulator chamber through a first passage portion of said fuel line to move to open a spray hole for injecting the fuel into the engine, the drive portion applying a pressure of the fuel transported from said accumulator chamber through a second passage portion of said fuel line to drve the valve member to close the spray hole, the solenoid valve being opened when energized to establish fluid communication between a third passage portion of said fuel line connecting with a portion of said fuel line lower in pressure than said accumulator chamber and the second passage portion of said fuel line to reduce the pressure of the fuel applied to the valve member of the drive portion of said fuel injector so that the valve member moves to open the spray hole; a pressure reduction condition determining circuit determining whether a preselected pressure reduction condition that a pressure of the fuel within said accumulator chamber is to be reduced is met or not; a draininer mechanism draining the fuel out of said t> accumulator chamber to the portion of said fuel line lower in pressure than said accumulator chamber to reduce a pressure of the fuel in said accumulator chamber; and a controlling circuit activating said draining mechanism at regular intervals to reduce the pressure in said accumulator chamber when said pressure reduction condition determining circuit determines that the preselected pressure reduction condition is met.

12. An accumulator fuel injection apparatus as claimed in claim 11, wherein said controlling circuit determines whether a speed of the engine is higher than a preselected speed or not when said pressure reduction condition determining circuit determines that the preselected pressure reduction condition is met, said controlling circuit activating said draining mechanism at the regular intervals when it is determined that the speed of the engine is lower than the preselected speed and activating said draining mechanism in synchronism with revolutions of the engine when it is determined that the speed of the engine is higher than the preselected speed.

13. An accumulator fuel injection apparatus for a diesel engine of a vehicle comprising: a fuel line; an accumulator chamber accumulating therein fuel supplied from a fuel pump through said fuel line; a fuel injector injecting the fuel stored in said accumulator chamber into a cylinder of the engine in synchronism with revolutions of the engine, said fuel injector including an injecting portion, a drive portion, and a solenoid valve, the injecting portion having disposed therein a valve member which is applied with a pressure of the fuel transported from said accumulator chamber through a first passage portion of said fuel line to move to open a spray hole for injecting the fuel into the engine, the drive por-tion applying a pressure of the fuel transported from said accumulator chamber through a second passage portion of said fuel line to drive the valve member to close the spray hole, the solenoid valve being opened when energized to establish fluid communication between a third passage portion of said fuel line connecting with a portion of said fuel line lower in pressure than said accumulator chamber and the second passage portion of said fuel line to reduce the pressure of the fuel applied to the valve member of the drive por-tion of said fuel injector so that the valve member moves to open the spray hole; a pressure reduction condition determining circuit determining whether a preselected pressure reduction condition that a pressure of the fuel within said accumulator chamber is to be reduced is met or not: and a controlling circuit opening the solenoid valve of said fuel injector for a preselected period of time shorter than a time lag occurring between opening of the solenoid valve and beginning of movement of the valve member at regular intervals in asmchronism w-ith revolutions of the engine when said pressure reduction condition determining circuit determines that the preselected pressure reduction condition is met for draining the fuel out of said accumulator chamber to the portion of said fuel line lower in pressure than said accumulator chamber to reduce a pressure of the fuel in said accumulator chamber.

14. An accumulator fuel injection apparatus as claimed in claim 13, wherein said controlling circuit determines whether a speed of the engine is higher than a preselected speed or not when said pressure reduction condition determining circuit determines that the preselected pressure reduction condition is met, said controlling circuit opening the solenoid valve of said fuel injector at the regular intervals when it is determined that the speed of the engine is lower than the preselected speed and opening the solenoid valve of said fuel injector in synchronism with revolutions of the engine when it is determined that the speed of the engine is higher than the preselected speed.