Fuel pressure control device for high pressure fuel injection system

Abstract: In a fuel pressure control apparatus for a high-pressure fuel injection system provided with a common rail (15), a supply pump (13) for force-feeding fuel to the common rail, and a fuel injection valve (17) attached to each cylinder of a diesel engine (1) and connected at one end to the common rail (15), an attempt is made to securely reduce a surplus of fuel pressure making use of a limited period during which normal fuel injection is not carried out. In exclusively performing pressure-release of fuel in the common rail (15) by driving the fuel injection valve (17) within an invalid injection period, the fuel injection valve (17) is driven in a cycle that does not depend on an operational condition of the engine (1), while adjusting a timing for driving the fuel injection valve (17) in such a manner as to prevent interference with the normal fuel injection control.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel pressure control apparatus for a high-pressure fuel injection system according to claim 1. 2. Description of the Related Art From EP 0 896 144 a fuel injection control apparatus for an accumulator type engine is known, which efficiently reduces fuel pressure in an accumulator pipe if the fuel pressure exceeds a target pressure, thereby ensuring stable combustion. With this known apparatus injectors of a diesel engine are connected to a common rail provided commonly for all the cylinders of the engine. The common rail is connected to a supply pump by a supply pipe. Each injector has a mechanism that injects fuel into the corresponding one of the cylinders when an electromagnetic valve provided in the injector is driven, and that releases fuel to reduce the fuel pressure in the common rail during an early period (ineffective injection time) after the start of the driving of the electromagnetic valve. An electronic control unit executes an ineffective injection control during the ineffective injection control time to reduce the fuel pressure in the common rail if the target injection amount is "0" and the actual fuel pressure is greater than the target fuel pressure. The ineffective injection control time is set to greater values as the fuel temperature decreases. In an internal combustion engine provided with an accumulator line such as a common rail, the high-pressure fuel that is force-fed from a supply pump upon starting operation of the engine is temporarily accumulated in the accumulator line. The accumulated high-pressure fuel is supplied through injection to respective combustion chambers of the engine in response to open-driving of a fuel injection valve connected to the accumulator line. At this moment, the injected fuel and the high-pressure fuel accumulated in the accumulator line are at an equal pressure level. An electronic control unit controls a fuel pressure in the accumulator line, namely, an injection pressure of fuel injected from the fuel injection valve such that the fuel pressure suits an operational state of the engine such as an engine rotational speed and a required injection amount. This control is normally performed through feedback control based on a detection value of a pressure sensor disposed in the accumulator line. That is, if the fuel pressure detected by the pressure sensor is lower than a target fuel pressure calculated based on an operational state of the engine, the amount of fuel force-fed from the supply pump is increased so that the fuel pressure in the accumulator line is increased. On the contrary, if the detected fuel pressure is higher than the target fuel pressure, the amount of fuel force-fed is reduced or the force-feeding of fuel is suspended so that the fuel pressure in the accumulator line is reduced. However, when the internal combustion engine installed in a vehicle restores a normal injection state out of a fuel-cutting state, for example, at the time of a transition from abrupt deceleration of the vehicle to low-load running of the vehicle, there arises an unignorable inconvenience because the fuel pressure in the accumulator line can follow the target fuel pressure only to a certain extent. At the time of a transition from the fuel-cutting state to the normal injection state, operation of the supply pump is temporarily suspended and fuel is kept from being force-fed to the accumulator line. During this period, no fuel in the accumulator line is consumed. Therefore, at the time of restoration of normal injection, the fuel pressure in the accumulator line becomes higher than the target fuel pressure, so that fuel injection may be carried out at an excessively high pressure for the engine. The performance of fuel injection at such an excessively high pressure leads to an increase in combustion noise and the like. In view of this problem, according to a related art as disclosed in Japanese Patent Application Laid-Open No. HEI 2-191865, the fuel injection valve is driven within an invalid injection period so as to exclusively perform pressure-release of the fuel in the accumulator line (invalid injection), whereby reduction of a surplus of fuel pressure is achieved. During this invalid injection control, since fuel in the accumulator line is returned to a fuel tank without being injected from the fuel injection valve, the fuel pressure in the accumulator line is reduced smoothly. Thus, even at the time of restoration of the normal injection, performance of fuel injection at an excessively high pressure for the engine is inhibited, and moreover, the combustion noise or the like is suitably inhibited from increasing. As described hitherto, there is no doubt that the invalid injection control is extremely effective in reducing a surplus of fuel pressure in the accumulator line. However, this control is performed, because of its property, making use of a period during which the normal fuel injection is not carried out, for example, a transitional period of restoration of normal injection out of the aforementioned fuel-cutting state. Accordingly, the control can only be performed at a limited number of timings, and the degree of freedom regarding performance of the control is severely restricted. For example, in order to more effectively reduce a fuel pressure in the accumulator line through the invalid injection control, it is desirable that this control be performed more often. However, when taking into account an operational condition of the engine and interference with other control operations at the time of restoration of normal injection or the like, it is not a simple task to set a condition for performing the invalid injection control. SUMMARY OF THE INVENTION The present invention has been made in view of the aforementioned circumstances. It is an object of the present invention to provide a fuel pressure control apparatus for a high-pressure fuel injection system that is capable of securely reducing a surplus of fuel pressure making use of a limited period during which normal fuel injection is not performed. The above-described object is achieved by combination of features stated in the main claim. Further advantages of the present invention are apparent from the dependent claims. In order to achieve the above-stated object, the fuel pressure control apparatus for a high-pressure fuel injection system according to the present invention, which is designed to control a fuel pressure of high-pressure fuel supplied to an internal combustion engine provided with an accumulator line, is characterized by comprising normal injection control means for supplying through injection fuel accumulated in the accumulator line to the internal combustion engine by driving a fuel injection valve connected to the accumulator line, invalid injection control means for releasing a pressure of fuel accumulated in the accumulator line by driving the fuel injection valve within an invalid injection period, and adjustment means for adjusting timings for driving the fuel injection valve through the fuel injection control means and the invalid injection control means. In the aforementioned aspect of the present invention, under whatever condition the normal injection control of the fuel injection valve and the driving control of the fuel injection valve through the invalid injection control means are performed, the fuel injection valve is prevented from undergoing any interference at the time of a transition of those control operations. Thus, even if the fuel injection valve is driven by the invalid injection control means making use of a limited period during which normal fuel injection is not carried out, for example, under a condition that the fuel pressure exceeds a target fuel pressure, the invalid injection control can securely be performed, and moreover, a surplus of fuel pressure in the accumulator line can securely be reduced. Although this summary does not disclose all the features of the present invention, it is to be understood that any combination of the features stated in the dependent claims is within the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 schematically shows the overall structure of a fuel pressure control apparatus for a high-pressure fuel injection system according to an embodiment of the present invention. Fig. 2 is a cross-sectional view schematically showing the internal structure of a fuel injection valve. Fig. 3 is a timing chart showing an output pattern of a rotational speed sensor in relation to a rotational phase of a crank shaft. Fig. 4 is a state transition table showing patterns of implementation of adjustment and retardation processings of the apparatus of the embodiment. Fig. 5 is a flowchart showing control performed by the apparatus of the embodiment in relation to the state transition table exemplified in Fig. 4. Fig. 6 is a flowchart showing control performed by the apparatus of the embodiment in relation to the state transition table exemplified in Fig. 4. Fig. 7 is a flowchart of crank angle synchronous control ("NE=3 synchronous processing") of the apparatus of the embodiment. Fig. 8 is a flowchart of an invalid injection pulse-off interruption handling of the apparatus of the embodiment. Fig. 9 is a flowchart of crank angle synchronous control ("NE=7 synchronous processing") of the apparatus of the embodiment. Fig. 10 is a timing chart showing a control pattern relating to the crank angle synchronous control of the apparatus of the embodiment. Fig. 11 is a timing chart showing a control pattern relating to the crank angle synchronous control of the apparatus of the embodiment. Fig. 12 is a flowchart of temporal synchronous control of the apparatus of the embodiment. Fig. 13 is a timing chart of the temporal synchronous control of the apparatus of the embodiment. Fig. 14 is a timing chart showing a control pattern relating to the temporal synchronous control of the apparatus of the embodiment. Fig. 15 is a graph showing an example of a calculation pattern of a target fuel pressure at the time of start of the engine. Fig. 16 is a timing chart showing a control pattern based on a detected fuel pressure of the temporal synchronous control. DESCRIPTION OF PREFERRED EMBODIMENT An embodiment of a fuel pressure control apparatus of a high-pressure fuel injection system according to the present invention will be described with reference to the drawings. Fig. 1 schematically shows the structure of a fuel pressure control apparatus of the present embodiment. The apparatus is composed of a high-pressure fuel injection system 10 for supplying high-pressure fuel to a diesel engine 1 (having four cylinders) through injection, a control system 20 for controlling a fuel pressure of the high-pressure fuel injection system 10, and a detection system 30 made up of various sensors. Detection data obtained from the various sensors of the detection system 30 are inputted to the control system 20 as part of control data. The high-pressure fuel injection system 10 is provided with a supply pump 13, which sucks fuel accumulated in a fuel tank 11 through a feed line 12, pressurizes the fuel and discharges it as high-pressure fuel. The high-pressure fuel that has been pressurized and discharged by the supply pump 13 passes through a feed line 14 and is accumulated in a common rail 15, which is an accumulator line. Basically, the high-pressure fuel accumulated in the common rail 15 is supplied to a fuel injection valve 17 through a feed line 16, and supplied through injection to a corresponding cylinder of the diesel engine 1 based on the driving of an electromagnetic valve 24 constituting the control system 20. Although only one cylinder is shown in Fig. 1, each one of the cylinders is supplied with fuel through a corresponding fuel injection valve. The supply pump 13 has an intake port 13a connected to the feed line 12, a discharge port 13b connected to the feed line 14, and a return port 13c connected to a return line 18a. A pressure control valve 25, which constitutes the control system 20, controls an amount of fuel discharged from the supply pump 13. A surplus of fuel that has not been discharged from the discharge port 13b is returned to the fuel tank 11 through the return port 13c and return lines 18a, 18. The common rail 15, in which high-pressure fuel is accumulated, is provided with four output ports 15a through 15d corresponding to the respective cylinders of the diesel engine 1 and with a pressure regulator 15e. The fuel that has been excessively pressurized for some reason is returned to the fuel tank 11 through the pressure regulator 15e and the return lines 18b, 18. The fuel injection valve 17 has an internal structure shown in Fig. 2. This structure enables so-called invalid injection control wherein not only injection of fuel to the diesel engine 1 but also discharge of the fuel accumulated in the common rail 15 based on the driving of the electromagnetic valve 24 within an invalid injection period is performed. As shown in Figs. 2A through 2C, the fuel injection valve 17 has a casing 71 provided with a feed port 17a. The fuel accumulated in the common rail 15 passes through the feed port 17a and is introduced into a lower fuel reservoir chamber 72 that is formed in a lower portion of the casing 71. Also, the feed port 17a communicates with an upper fuel reservoir chamber 74 through an orifice 73. The lower fuel reservoir chamber 72 and the upper fuel reservoir chamber 74 are slidably provided with a nozzle needle 75. A nozzle hole 17b, which is formed in a lowermost portion of the casing 71, comes into communication with the lower fuel reservoir chamber 72 through an upward movement of the nozzle needle 75. The nozzle needle 75 is composed of a tip portion 76 serving as a valve body, a large-diameter portion 77, a small-diameter portion 78 and a piston portion 79, which are arranged in this order in a down-to-up direction. The large-diameter portion 77 can vertically slide along an upper section of the lower fuel reservoir chamber 72, and the piston portion 79 can vertically slide along a lower section of the upper fuel reservoir chamber 74. A spring 80 for the needle is provided around the small-diameter portion 78. The nozzle needle 75 is urged downwards in Fig. 2 by an urging force of the spring 80. Thereby, the tip portion 76 of the nozzle needle 75 normally abuts on a seat portion 81 in the vicinity of the nozzle hole 17b. Further, the upper fuel reservoir chamber 74 communicates with an electromagnetic valve accommodation chamber 83 through an orifice 82. The electromagnetic valve 24 is composed of a valve body 24a, a solenoid 24b, a spring 24c for the valve body, and the like, which are accommodated in the electromagnetic valve accommodation chamber 83. The valve body 24a is provided in a lower section of the electromagnetic valve accommodation chamber 83. The spring 24c for the valve body, which is disposed so as to abut on the valve body 24a and a ceiling portion of the electromagnetic valve accommodation chamber 83, urges the valve body 24a downwards in Fig. 2. Thereby, the orifice 82 is normally closed by the thus-urged valve body 24a, so that the upper fuel reservoir chamber 74 is out of communication with the electromagnetic valve accommodation chamber 83. When excited by an electronic control unit 21 (Fig. 1) constituting the control system 20, the solenoid 24b draws the valve body 24a upwards against an urging force of the spring 24c for the valve body. An upper portion of the valve body 24a is shaped like a flange, in which a penetration hole H is formed. A return port 17c, through which fuel from the electromagnetic valve accommodation chamber 83 escapes, is formed in the casing 71. Under a predetermined condition, a surplus of fuel is returned from the return port 17c through the return lines 18c, 18 to the fuel tank 11. A space where the spring 80 for the needle is provided communicates with the electromagnetic valve accommodation chamber 83 through a communication passage 84. The fuel that gradually leaks out into the space where the spring 80 for the needle is provided flows into the electromagnetic valve accommodation chamber 83 through the communication passage 84, and gradually flows out into the return line 18c through the penetration hole H and the return port 17c. Next, it will be described how the fuel injection valve 17 operates. Fig. 2A shows an internal state of the fuel injection valve 17 when the solenoid 24b of the electromagnetic valve 24 is not excited. In this state, the valve body 24a is urged downwards by an urging force of the spring 24c for the valve body, so that the upper fuel reservoir chamber 74 is out of communication with the electromagnetic valve accommodation chamber 83. The fuel that is introduced from the feed port 17a is evenly supplied to the lower fuel reservoir chamber 72 and the upper fuel reservoir chamber 74, whereby a balance of pressure is maintained. Hence, the nozzle needle 75 is urged downwards by an urging force of the spring 80 for the needle, and the tip portion 76 also remains abutting on the seat portion 81 in the vicinity of the nozzle hole 17b. That is, in this case, there is no fuel injected from the nozzle hole 17b, and the fuel that is accumulated in the upper fuel reservoir chamber 74 does not flow out rapidly through the return port 17c. If the solenoid 24b is excited, the valve body 24a moves upwards against an urging force of the spring 24c for the valve body, so that the upper fuel reservoir chamber 74 comes into communication with the electromagnetic valve accommodation chamber 83 (Fig. 2B). In this case, the fuel accumulated in the fuel reservoir chamber 74 passes through the electromagnetic valve accommodation chamber 83 and the penetration hole H and flows out to the return port 17c. It is to be noted herein that fuel flows out to the electromagnetic valve accommodation chamber 83 from the fuel reservoir chamber 74 through the orifice 82. Thus, after the solenoid 24b has been excited, the differential pressure between a fuel pressure in the lower fuel reservoir chamber 72 and a fuel pressure in the upper fuel reservoir chamber 74 is kept smaller than an urging force of the spring 80 for the needle for a while. While the urging force of the spring 80 for the needle is greater than the differential pressure, the nozzle needle 75 does not move, and the tip portion 76 remains abutting on the seat portion 81. That is, with no fuel being injected from the nozzle hole 17b, only the fuel accumulated in the upper fuel reservoir chamber 74 swiftly flows out to the return line 18c through the return port 17c. This period corresponds to an invalid injection period during which discharge of the fuel accumulated in the common rail 15 is performed exclusively. After a certain amount of fuel has been discharged from the upper fuel reservoir chamber 74, if the differential pressure between a fuel pressure in the lower fuel reservoir chamber 72 and a fuel pressure in the upper fuel reservoir chamber 74 becomes greater than the urging force of the spring 80 for the needle, the nozzle needle 75 moves upwards due to the fuel pressure in the lower fuel reservoir chamber 72 (Fig. 2C). In this state, the tip portion 76 of the nozzle needle 75 is detached from the seat portion 81, whereby the lower fuel reservoir chamber 72 comes into communication with the nozzle hole 17b. Then, high-pressure fuel is supplied through injection from the nozzle hole 17b to a corresponding cylinder of the diesel engine 1. In a state shown in Fig. 2B or 2C, the excitation of the solenoid 24b is then suspended, whereby the fuel injection valve 17 again assumes the internal state shown in Fig. 2A. Then, the fuel injection valve 17 stops discharging fuel or injecting fuel as described above. As described hitherto, in the apparatus of the present embodiment exemplified in Fig. 1, the fuel injection valve 17 constituting the high-pressure fuel injection system 10 assumes three states (a) to (c) depending on whether or not the electromagnetic valve 24 (solenoid 24b) is being driven and how long it has been driven. In the state (a), the fuel injection valve 17 neither injects fuel to the diesel engine 1 nor discharges the fuel accumulated in the common rail 15 (Fig. 2A). In the state (b), the fuel injection valve 17 only discharges the fuel accumulated in the common rail 15 (performs invalid injection) (Fig. 2B). In the state (c), the fuel injection valve 17 injects fuel to the diesel engine 1 (performs normal injection) after the invalid injection (Fig. 2C). The amount of fuel injected from the fuel injection valve 17 during the normal injection is controlled and set in accordance with an excess of the driving period of the electromagnetic valve 24 over the invalid injection period. The control system 20 shown in Fig. 1 is composed of the electronic control unit 21, the electromagnetic valve 24 drivingly controlled through the electronic control unit 21, and the pressure control valve 25. The electronic control unit 21 is mainly provided with a microcomputer 22 for controlling a fuel pressure of the high-pressure fuel accumulated in the common rail 15, and with a driver 23 for driving the electromagnetic valve 24 under the control of the microcomputer 22. Based on various control programs stored in a memory (not shown), the electronic control unit 21 performs crank angle synchronous control and temporal synchronous control, which will be described later. In the control system 20, the electronic control unit 21 is supplied with electric power from a vehicle-mounted battery B based on the turning-on of an IG (starter) switch 26, and thus becomes ready to perform its control operations. In response to the turning-on of the IG switch 26, the microcomputer 22 turns on an internal contact of a relay 27, thereby supplying electric power from the vehicle-mounted battery B to the electronic control unit 21. If the IG switch 26 is turned off, the microcomputer 22 turns off the internal contact of the relay 27 after having terminated a predetermined post-processing. That is, after the IG switch 26 has been turned off, the microcomputer 22 performs the predetermined post-processing and then stops supplying electric power from the vehicle-mounted battery B to the electronic control unit 21. As shown in Fig. 1, the detection system 30 is composed of an accelerator sensor 31, a coolant temperature sensor 32, a rotational speed sensor 33, a cylinder discriminating sensor 34 and a fuel pressure sensor 35. The accelerator sensor 31, which is provided in the vicinity of an accelerator (not shown), detects an opening degree (depression amount) thereof. The coolant temperature sensor 32, which is provided in a water jacket of the diesel engine 1, detects a temperature of coolant. Detection signals from the accelerator sensor 31 and the coolant temperature sensor 32 are both introduced into the microcomputer 22 as suitably A/D (analog-digital)-converted signals. The rotational speed sensor 33 is, for example, composed of a rotor 33a attached to a crank shaft of the diesel engine 1, and of an electromagnetic pick-up 33b that is provided in the vicinity of the rotor 33a and detects passage of protrusions provided at predetermined intervals along the outer periphery of the rotor 33a. Normally, an output from the electromagnetic pick-up 33b undergoes waveform shaping and is introduced into the microcomputer 22 as a pulse signal (NE pulse) corresponding to a rotational speed (rotational phase) of the crank shaft, as is apparent from Fig. 3. In the present embodiment, as shown in Fig. 3, eighteen NE pulses 0 through 17 are outputted for each cylinder of the diesel engine 1. In the later-described crank angle synchronous control, the processing for controlling a driving pattern of the fuel injection valve 17 is performed in synchronization with the "3" pulse and the "7" pulse of the NE pulses. The cylinder discriminating sensor 34 is composed of a rotor 34a attached to the cam shaft of the diesel engine 1, and of an electromagnetic pick-up 34b that is provided in the vicinity of the rotor 34a and detects passage of protrusions provided along the outer periphery of the rotor 34a for the purpose of cylinder discrimination. Normally, an output from the electromagnetic pick-up 34b is also introduced into the microcomputer 22 as a waveform-shaped pulse signal. The fuel pressure sensor 35, which is provided in the common rail 15, detects a pressure of high-pressure fuel accumulated inside the common rail 15. A detection signal from the fuel pressure sensor 35 is also introduced into the microcomputer 22 as a suitably A/D-converted signal. Based on the aforementioned construction, the fuel pressure control apparatus of the present embodiment performs invalid injection control of the fuel injection valve 17 while there is no requirement for cylinder injection by the diesel engine 1 and the fuel pressure in the common rail 15 is excessively high. In this manner, the fuel pressure control apparatus reduces the fuel pressure in the common rail 15 down to a suitable pressure. In the invalid injection control, the driving cycle of the fuel injection valve 17 during an invalid injection period is set to a predetermined length of time that does not depend on an operating condition of the diesel engine 1 or the like. As a result, the effect of reduction in fuel pressure is ensured. The invalid injection control is performed not only during a temporary fuel-cutting period, such as a transition period from abrupt deceleration to low-load running of the vehicle, but also upon fulfillment of a condition for stopping the engine 1. This is because fuel injection may be carried out at an excessively high pressure, which results from the fact that the fuel pressure in the common rail 15 does not decrease to a target fuel pressure at the time of start of the engine even in the case where the engine restarting operation has been performed immediately after the turning-off of the IG switch 26 (IG-off operation) during the racing of the engine 1 (the operation of raising a rotational speed of the engine in the presence of an almost negligible external load), or in the case where the engine restarting operation has been performed immediately after stall of the engine 1 in a running state of the vehicle. However, the invalid injection control of the fuel injection valve 17 that is performed on the basis of a predetermined length of time may interfere with the normal injection control of the fuel injection valve 17 that is performed on the basis of a crank angle (NE pulse) of the engine 1. Even with regard to invalid injection control, the invalid injection control that is performed during a fuel-cutting period may interfere with the invalid injection control that is performed upon fulfillment of a condition for stopping the engine. For example, at the time of making a transition from the normal injection control to the invalid injection control, it is important whether or not there is a normal driving requirement for the fuel injection valve 17 at the timing when the fuel injection valve 17 starts being driven through the invalid injection control. If the normal driving requirement exists at the timing when the fuel injection valve 17 starts being driven through the invalid injection control, the precision in controlling an amount of fuel injection may deteriorate. This also holds true at the time of making a transition from the invalid injection control to the normal injection control. If the timing for starting driving the fuel injection valve 17 through the invalid injection control arises after the lapse of an extremely short length of time since termination of the driving of the fuel injection valve 17 through the normal fuel injection, the stability in driven state of the fuel injection valve 17 may deteriorate. This also holds true at the time of making a transition from the invalid injection control to the normal injection control. In the case where the condition for stopping the engine 1 has been met during performance of the normal injection control, if the remaining period for driving the fuel injection valve 17 overlaps with the timing for starting driving the fuel injection valve 17 through the invalid injection control, the precision in controlling an amount of fuel injection may deteriorate despite fulfillment of the condition for stopping the engine. Further, even in the case where the condition for stopping the engine 1 has been met during performance of the invalid injection control, if the remaining period for driving the fuel injection valve 17 through the invalid injection control prior to fulfillment of the stop condition overlaps with the timing for starting driving the fuel injection valve 17 through new invalid injection control after fulfillment of the stop condition in response to commencement of new control associated with fulfillment of the stop condition, the fuel injection valve 17 may end up being driven over an unnecessarily long period. Also, if the timing for starting driving the fuel injection valve 17 through the invalid injection control arises after the lapse of an extremely short length of time since termination of the driving of the fuel injection valve 17 upon fulfillment of the condition for stopping the engine 1, the stability in driven state of the fuel injection valve 17 may deteriorate. In view of all these possibilities, according to the apparatus of the present embodiment, (i) if the fuel injection valve 17 undergoes a transition from the normal injection control to the invalid injection control, or (ii) if the fuel injection valve 17 undergoes a reversed transition from the invalid injection control to the normal injection control, adjustment is made such that the periods for driving the fuel injection valve 17 do not overlap with each other, and (iii) if the fuel injection valve 17 undergoes a transition from the normal injection control to the invalid injection control during suspension of the engine, or (iv) if the fuel injection valve 17 undergoes a transition from the invalid injection control to the invalid injection control during suspension of the engine, adjustment is made by retarding performance of the invalid injection control during suspension of the engine by a predetermined period, so that control interference is avoided and the pressure of a surplus of fuel can securely be reduced within a certain length of time. Fig. 4 is a state transition table showing how adjustment including a retardation (delay) processing performed in the present embodiment is made in various states of the diesel engine 1 and the IG switch 26. Before explaining concrete procedures of individual processings, the gist thereof will now be described with reference to Fig. 4. A state block C1 represents a control pattern of the fuel injection valve 17 during normal operation of the diesel engine 1. In this state block C1, if a predetermined condition for performing invalid injection control is met (e.g. when the vehicle makes a transition from abrupt deceleration to a low-load running state), a transition is made from a normal injection control mode to a state of performance of invalid injection control (an invalid injection control mode). The aforementioned predetermined condition is met, for example, when the fuel pressure in the common rail 15 is higher than a target fuel pressure calculated based on an operational state at the time of a transition from a state of performance of normal injection control (a normal injection control mode) to a fuel-cutting state. In the present embodiment, at the time of a transition from the normal injection control mode to the invalid injection control mode, the timings for driving the fuel injection valve 17 are adjusted such that the periods for driving the fuel injection valve 17 through the respective control modes do not overlap with each other. Further, in the state block C1, if the condition for performing the invalid injection control is not met, for example, when a requirement for injection is restored in the invalid injection control mode, the normal injection control mode is restored. Also, at the time of such a transition from the invalid injection control mode to the normal injection control mode, the timings for driving the fuel injection valve 17 are adjusted such that the periods for driving the fuel injection valve 17 do not overlap with each other. If the IG switch 26 has been turned off in a state indicated by the state block C1, a transition to a state block C2 is made. The state block C2 indicates a control pattern of the fuel injection valve 17 when the IG switch 26 is off. In the state block C2, the control pattern in the state block C1 is continued until a predetermined time T1 (e.g. about 0.2 sec) elapses after turning-off of the IG switch 26. After the lapse of the predetermined time T1, it is determined that the condition for stopping the diesel engine 1 has been met, and a transition to a state block C21 is made. In the state block C21, regardless of whether the injection control mode immediately before fulfillment of the stop condition is the normal control mode or the invalid injection control mode, the driving of the fuel injection valve 17 is temporarily suspended upon fulfillment of the stop condition, as a measure for adjustment. After the delay processing has been performed for a predetermined length of time, if a later-described condition for performing the invalid injection control during suspension of the engine is met, the invalid injection control is performed. If the condition for performing the invalid injection control has not been met after the delay processing, the driving of the fuel injection valve 17 remains suspended. In a control state indicated by the state block C1, if the diesel engine 1 has stalled despite the fact that the IG switch 26 is on, a transition to a state block C3 is made. The state block C3 indicates a control pattern of the fuel injection valve 17 at the time of stall of the engine 1 while the IG switch 26 is on. In the state block C3, as in the state block C21, the driving of the fuel injection valve 17 is temporarily suspended upon fulfillment of the condition for stopping the engine 1, and the delay processing is performed for a predetermined length of time. After that, if the later-described condition for performing the invalid injection control during suspension of the engine has been met, the invalid injection control is performed. If the condition for performing the invalid injection control has not been met, the driving of the fuel injection valve 17 remains suspended. If the IG switch 26 has been turned off in a control state indicated by the state block C3, or if the engine 1 has stalled in a control state indicated by the state block C2 or the state block C21, a transition to a state block C4 is made. The state block C4 indicates a control pattern of the fuel injection valve 17 at the time of stall of the engine 1 while the IG switch 26 is off. Also in the state block C4, basically in the same manner as in the state block C21, the driving of the fuel injection valve 17 is temporarily suspended upon fulfillment of the condition for stopping the engine 1, and the delay processing is performed for a predetermined length of time. After that, if the later-described condition for performing the invalid injection control during suspension of the engine has been met, the invalid injection control is performed. If the condition for performing the invalid injection control has not been met, the driving of the fuel injection valve 17 remains suspended. It is to be noted herein that in the state block C4, the control state immediately after a transition from the state block C2, C21 or C3 is continued. Therefore, for example, the delay processing (adjustment) upon fulfillment of the condition for stopping the engine is actually performed only once. Then, after having confirmed that the driving of the fuel injection valve 17 is suspended, the microcomputer 22 turns off the relay 27 and stops supplying electric power to the electronic control unit 21 (in a state C5). Figs. 5 and 6 show a flowchart of the overall control corresponding to the state transition table exemplified in Fig. 4. First of all, under the confirmation (step S1) that the IG switch 26 has been turned on, the electronic control unit 21 starts driving control of the fuel injection valve 17 in the normal injection control mode (step S10). In that state, if the engine 1 has not stalled and the IG switch 26 has not been turned off and the condition for performing the invalid injection control has not been met (if the results in steps S11 through S13 are all negative), the driving control of the fuel injection valve 17 in the normal injection control mode is maintained. Although stall of the engine 1 or turning-off of the IG switch 26 has not been confirmed (although the results in steps S11 and S12 are negative), if fulfillment of a condition for performing the invalid injection control has been confirmed (if the result in step S13 is affirmative), a transition to the invalid injection control mode is made and the driving control of the fuel injection valve 17 is started (step S20). As described above, the aforementioned condition for performing the invalid injection control is met, for example, when the fuel pressure in the common rail 15 is higher than a target fuel pressure calculated based on an operational state at the time of a transition to the fuel-cutting state. At this moment, as described above, the timings for driving the fuel injection valve 17 are adjusted such that the last portion of the period for driving the fuel injection valve 17 in the normal injection control mode does not overlap with the first portion of the period for driving the fuel injection valve 17 in the invalid injection control mode. Then, if the engine 1 has not stalled and the IG switch 26 has not been turned off and the condition for restoring the normal injection has not been met (if the results in steps S21 through S23 are all negative), the driving control of the fuel injection valve 17 in the invalid injection control mode is maintained. Then, although stall of the engine 1 or turning-off of the IG switch 26 has not been confirmed, if the condition for restoring the normal injection such as restoration of a requirement for injection has been met (if the condition for performing the invalid injection control has not been met), a transition to the normal injection control mode is made again (step S23 → step S10). Also at this moment, as described above, the timings for driving the fuel injection valve 17 are adjusted such that the last portion of the period for driving the fuel injection valve 17 in the invalid injection control mode does not overlap with the first portion of the period for driving the fuel injection valve 17 in the normal injection control mode. If stall of the engine 1 has been confirmed in the normal injection control mode or in the invalid injection control mode (if the results in steps S11 and S21 are affirmative), it is determined that the condition for stopping the engine 1 has been met, and the delay processing is performed as a measure for adjustment (step S30). After that, it is determined whether or not the condition for performing the invalid injection control during suspension of the engine has been met (step S31). Further, if turning-off of the IG switch 26 has been confirmed in the normal injection control mode or in the invalid injection control mode (if the result in step S12 or S22 is affirmative), the lapse of the predetermined time T1 is judged to be fulfillment of the condition for stopping the engine 1 (the result in step S14 or S24 is affirmative). Then, likewise, the processings in steps S30 and S31 are performed. Then, if fulfillment of the condition for performing the invalid injection control during suspension of the engine has been confirmed in step S31 (if the result in step S31 is affirmative), the invalid injection control during suspension of the engine is performed (step S32), and then, the relay 27 is turned off (step S33). If the condition for performing the invalid injection control during suspension of the engine has not been met (if the result in step S31 is negative), the relay 27 is turned off without performing the invalid injection control. Figs. 7 through 14 show concrete procedures and patterns of controlling a fuel pressure based on the invalid injection control of the fuel injection valve 17. With reference to these drawings, the fuel pressure control including the adjustment and the delay processing will be described in detail. In the present embodiment, the timing for performing driving control of the fuel injection valve 17 in the normal injection control mode and the timing for starting driving the fuel injection valve 17 in the invalid injection control mode are determined based on crank angle synchronous control, which is performed on the basis of a crank angle of the diesel engine 1. After a transition to the invalid injection control has been made, the driving cycle of the fuel injection valve 17 within the invalid injection period is set to a predetermined time that does not depend on an operational condition of the engine 1 or the like. Repeated driving of the fuel injection valve 17 based on the predetermined time is realized by pulse-off interruption of invalid injection pulses. The timing for confirming fulfillment of the condition for stopping the engine 1 and the timing for starting driving the fuel injection valve 17 in the invalid injection control mode during suspension of the engine based on fulfillment of the stop condition are determined based on temporal synchronous control, which is performed on the basis of a predetermined time. Also in this case, after a transition to the invalid injection control has been made, the driving cycle of the fuel injection valve 17 during the invalid injection period is set to a predetermined time. Repeated driving of the fuel injection valve 17 is realized by pulse-off interruption of invalid injection pulses. Especially as regards the invalid injection control during suspension of the engine, the period for performing the control is also supervised. As for these control operations, concrete procedures and control patterns will now be described sequentially in detail. First of all, the aforementioned crank angle synchronous control will be described in detail based on Figs. 7 and 9. As described above with reference to Fig. 3, in the crank angle synchronous control, the processing for controlling a driving pattern of the fuel injection valve 17 is performed in synchronization with the "3" pulse and the "7" pulse of the NE pulses that are outputted in accordance with a rotational angle of the crank shaft of the engine 1. More specifically, the microcomputer 22 constituting the electronic control unit 21 repeatedly counts NE pulses according to the pattern exemplified in Fig. 3, based on outputs from the rotational speed sensor 33 and the cylinder discriminating sensor 34. Every time the microcomputer 22 confirms the "3" pulse and the "7" pulse of the NE pulses, it repeatedly performs an "NE=3 synchronous processing" shown in Fig. 7 and an "NE=7 synchronous processing" shown in Fig. 9 respectively. In the "NE=3 synchronous processing", as a processing of step S101 in Fig. 7, a fuel injection period Tq required in a momentary operational state of the engine 1 is calculated. The injection period Tq is calculated as a value obtained by converting an amount, which is obtained by suitably correcting a basic injection amount calculated based on outputs from the accelerator sensor 31, the rotational speed sensor 33 and the like, into a driving period of the fuel injection valve 17. The fuel injection timing, namely, the timing for starting driving the fuel injection valve 17 is preliminarily calculated through a separate processing. Normally, this fuel injection timing is calculated in the form of "x ms (milliseconds) or xµs (microseconds) after the y-th pulse of the NE pulses". In a processing of step S102, it is determined whether or not the condition for restoring the normal injection control mode has been met. As the condition for restoring the normal injection control mode, a logical product (AND) of the following conditions is adopted. These conditions are: (A1) that the fuel injection period Tq calculated in a preceding cycle (i-1) of the "NE=3 synchronous processing" is zero µs (Tq i-1 = 0µs); (A2) that the fuel injection period Tq calculated in the present cycle (i) of the "NE=3 synchronous processing" is longer than zero µs (Tq i > 0µs); and (A3) that a later-described normal-time invalid injection performing flag XN is on. That is, in the processing of step S102, only if a requirement for restoring the normal injection control has just arisen for the first time after the invalid injection control of the fuel injection valve 17, an affirmative determination is made (YES). In all the other circumstances, a negative determination is made (NO). If the affirmative determination has been made, as a processing of the following step S103, the fuel injection period Tq (> 0µs) that has been calculated this time is unconditionally set to "0µs". Then, the normal injection restoration flag is turned on and the routine is terminated temporarily. On the other hand, if the negative determination has been made in the processing of step S102, the routine is terminated temporarily without performing any other processings. As described hitherto, in the "NE=3 synchronous processing", it is monitored, in conjunction with calculation of the fuel injection period Tq, whether or not the condition for restoring the normal injection control mode has been met. Only if fulfillment of the condition for restoration has been confirmed, the calculated fuel injection period Tq is unconditionally set to "0 µs" (no injection). On the other hand, in the "NE=7 synchronous processing" that is activated based on confirmation of the "7" pulse of the NE pulses, as shown in Fig. 9, it is first determined as a processing of step S201 whether or not a prerequisite for the invalid injection control during normal operation has been established. As the prerequisite for the invalid injection control during normal operation, a logical product (AND) of the following conditions is adopted. These conditions are: (B1) that the IG switch 26 is on or that the predetermined time T1 (see Figs. 4 and 5) has not elapsed yet after turning-off of the IG switch 26; and (B2) that a prerequisite flag for the temporal synchronous control is off. That is, if the condition for performing the temporal synchronous control and the like upon fulfillment of the condition for stopping the engine has not been met during normal operation of the engine 1, it is determined affirmatively (YES) that normal control is in operation at the moment. In all the other circumstances, a negative determination is made (NO). If the affirmative determination has been made, as a processing of step S202, the prerequisite flag for the invalid injection control during normal operation is turned on. If the negative determination has been made, as a processing of step S203, the prerequisite flag for the invalid injection control during normal operation is turned off. Thereafter, as a processing of step S204, it is determined whether or not the condition for performing the invalid injection control during normal operation has been met. As the condition for performing the invalid injection control during normal operation, a logical product (AND) of the following conditions is adopted. These conditions are: (C1) that the prerequisite flag for the invalid injection control during normal operation is on; (C2) that the value of a fuel pressure in the common rail 15 detected by the fuel pressure sensor 35 is equal to or greater than a value obtained by adding an arbitrary value a to a target fuel pressure calculated based on a momentary operational state of the engine 1; (C3) that the normal injection restoration flag is off; and (C4) that the fuel injection period Tq calculated in the present cycle (i) of the "NE=3 synchronous processing" is zero µs (no requirement for injection) (Tqi = 0µs). That is, in a processing of step S204, it is determined whether or not the condition for performing the invalid injection control during normal operation, such as a transition to the aforementioned fuel-cutting state, has been met. In the case of an affirmative determination, it is determined whether or not a normal-time invalid injection performing flag XN is off (step S205). If the result is NO in step S205, the routine is terminated temporarily. If the result is YES, the invalid injection performing flag XN is turned on (step S206), and a first one of invalid injection pulses, which is a driving pulse for the invalid injection control of the fuel injection valve 17, is set (step S207). Then, the routine is terminated temporarily. The invalid injection pulse is set as two periods of time, namely, an off-time Ta prior to the rising of the invalid injection pulse and an on-time Tb from the rising to the falling of the invalid injection pulse. The on-time Tb corresponds to what is called a pulse width. As is the case with the driving pulse for the normal injection control of the fuel injection valve 17, the microcomputer 22 itself sets the invalid injection pulse for an output port corresponding to the driver 23. Due to the setting of the driving pulse, the driver 23 drives the fuel injection valve 17 (the electromagnetic valve 24) for the on-time (Tb) after the lapse of the off-time (Ta). If a negative determination is made in the processing of step S204, as processings of steps S208 and S209, the invalid injection performing flag XN and the normal injection restoration flag are turned off respectively. Then, the routine is terminated temporarily. As described hitherto, in the "NE=7 synchronous processing", it is determined whether or not the prerequisite condition and the performance condition of the invalid injection control during normal operation of the diesel engine 1 have been met. Only if these conditions are first met, the normal-time invalid injection performing flag XN is turned on, and the first pulse of the invalid injection pulses is set. If either the prerequisite condition or the performance condition becomes unfulfilled, the normal-time invalid injection performing flag XN is turned off immediately. If the normal injection restoration flag has been turned on in the aforementioned "NE=3 synchronous processing", the normal injection restoration flag is turned off. In the present embodiment, the invalid injection control during normal operation is performed on the aforementioned condition (C4) that "there is no requirement for injection this time". Thus, as indicated by the aforementioned (i), even in the case where the fuel injection valve 17 undergoes a transition from the driving through the normal injection control to the driving through the invalid injection control, the control operations relating to the driving of the fuel injection valve 17 do not interfere with each other. If the first pulse of the invalid injection pulses has been set through the "NE=7 synchronous processing", based on the pulse-off interruption of the thus-set invalid injection pulse, the second and following pulses are sequentially set. Fig. 8 shows a procedure relating to the invalid injection pulse-off interruption. Every time an invalid injection pulse that has been set in advance is turned off, the microcomputer 22 starts the interruption handling shown in Fig. 8. At the time of the interruption handling, the microcomputer 22 monitors a state of the invalid injection performing flag (including a later-described stop-time invalid injection performing flag XT). If the flag is on (if the result in step S401 is affirmative), the microcomputer 22 sets the second and following pulses at the output port corresponding to the driver 23 (step S402). The interruption handling is then terminated temporarily. In this manner, the invalid injection pulse-off interruption is activated on the condition that the invalid injection pulses are preliminarily set at the output port corresponding to the driver 23. Then, if the invalid injection performing flag (XN/XT) remains turned on, the subsequent (the second and following) invalid injection pulses are set. Hence, once the invalid injection pulses are set, the driving of the fuel injection valve 17 is repeated based on a set of invalid injection pulses, thus on the invalid injection pulses at intervals of the sum of the off-time Ta and the on-time Tb, as long as the invalid injection performing flag (XN/XT) remains turned on. In this case, the off-time Ta represents a period of time for securing accumulation of electric power necessary and sufficient for the driver 23 to drive the fuel injection valve 17. The on-time Tb represents an arbitrary length of time within the invalid injection period of the fuel injection valve 17. On the other hand, once the invalid injection pulse is set under the aforementioned condition, even if the invalid injection performing flag (XN/XT) is thereafter turned off, the driving of the fuel injection valve 17 based on the invalid injection pulse is carried out. That is, if there is an invalid injection pulse that has been set immediately before the turning-off of the invalid injection performing flag (XN/XT), even after the invalid injection performing flag (XN/XT) has been turned off, the driving of the fuel injection valve 17 based on that invalid injection pulse is carried out. Thus, as indicated by the aforementioned (ii), the aforementioned operation alone cannot prevent a final driving timing in the invalid injection control from becoming unclear in the case where the fuel injection valve 17 restores the driving through the normal injection control out of the driving through the invalid injection control. Therefore, according to the present embodiment, when the fuel injection valve 17 restores the driving through the normal injection control out of the driving through the invalid injection control, the first fuel injection period Tq is unconditionally set to "0 µs" (no injection) through the aforementioned "NE=3 synchronous processing" so as to prevent interference with the unclear invalid injection pulse. Fig. 10 is a timing chart showing changes in the normal-time invalid injection performing flag XN (a), the invalid injection pulse (b), the normal injection restoration flag (c) and the normal injection pulse (d) based on the crank angle synchronous control and the invalid injection pulse-off interruption handling, in the case of the aforementioned (i), namely, in the case of a transition from the normal injection control to the invalid injection control of the fuel injection valve 17. As shown in Fig. 10, in the normal injection control mode, the fuel injection valve 17 is driven based on the fuel injection period Tq calculated through the "NE=3 synchronous processing" (the injection timing is calculated separately)(see (d)). If the fuel-cutting operation is started in such a state and fulfillment of the aforementioned conditions (B1) to (B2) and (C1) through (C4) is confirmed in the "NE=7 synchronous processing" at least on the condition that the fuel injection period Tq calculated through the "NE=3 synchronous processing" is "0 µs" (no injection), the invalid injection performing flag XN is turned on at a timing t11 (see Fig. 10 (a)) and the first pulse of the invalid injection pulses is set (see Fig. 10 (b)). Thereafter, as long as all the aforementioned conditions (B1) to (B2) and (C1) through (C4) are met, the invalid injection pulses are repeatedly set based on the invalid injection pulse-off interruption handling, and the fuel injection valve 17 is repeatedly driven in the invalid injection control mode through the invalid injection pulses that have been set. Fig. 11 shows a timing chart in the case of the aforementioned (ii), namely, in the case where the fuel injection valve 17 restores the normal injection control out of the invalid injection control. In this case, the invalid injection performing flag XN is turned on at a timing t21 (see Fig. 11(a)). After that, while the fuel injection valve 17 is being driven in the invalid injection control mode, it is assumed that the requirement for injection has been restored by the "NE=3 synchronous processing" at a timing t22 (see Fig. 10 (c)). At this moment, the aforementioned conditions (A1) through (A3) are met. Therefore, the normal injection restoration flag is turned on through the "NE=3 synchronous processing" and the fuel injection period Tq (≠ 0) that has been calculated by that time is unconditionally set to "0 µs" (Tq = 0). That is, the driving of the fuel injection valve 17, which is to be driven intrinsically in the normal injection control mode at the fuel injection timing that has been preliminarily calculated in accordance with the requirement for injection, for example, at a timing t23, is prohibited (see Fig. 10 (d)). At this moment, at least the aforementioned condition (C3) becomes unfulfilled in the "NE=7 synchronous processing" at a timing t25, and the invalid injection performing flag XN is turned off (see Fig. 10 (a)). However, the subsequent invalid injection pulse has already been set through the invalid injection pulse-off interruption handling in response to the pulse-off of the invalid injection pulse that has risen at a timing t24 immediately before the timing t25. Thus, even after the timing t25 when the invalid injection performing flag XN is turned off, the fuel injection valve 17 is driven based on the last invalid injection pulse PLSr. At this moment, as described above, the driving of the fuel injection valve 17 in the normal injection control mode is prohibited. Hence, the fuel injection valve 17 undergoes no interference of those control operations. After that, according to the pattern indicated by (d), the driving of the fuel injection valve 17 in the normal injection control mode is resumed. If the fuel-cutting operation is performed again in the normal injection control mode, the invalid injection control is performed again according to the pattern exemplified in Fig. 10 on the condition that the aforementioned conditions (B1) to (B2) and (C1) through (C4) are met. In the present embodiment, as described hitherto, at the time of a transition from the normal injection control mode to the invalid injection control mode, adjustment is made according to a pattern in which the invalid injection pulse is set, at least on the condition that there is no requirement for injection. At the time of restoration of the normal injection control mode out of the invalid injection control mode, adjustment is made according to a pattern in which the first fuel injection relating to the restoration is prohibited. Thus, it is possible to suitably prevent interference of those control operations relating to the driving of the fuel injection valve 17. While the engine 1 is in normal operation, the driving period of the fuel injection valve 17 relating to the normal injection control and the first driving timing of the fuel injection valve 17 relating to the invalid injection control are managed unitarily. As a result, such adjustment is facilitated. Next, the temporal synchronous control, which manages the driving of the fuel injection valve 17 in the invalid injection control mode during suspension of the engine based on confirmation of fulfillment of the condition for stopping the engine 1 and on fulfillment of the stop condition, will be described in detail with reference to Fig. 12. The temporal synchronous control is repeatedly performed at intervals of a predetermined time (e.g. 16 ms) through the microcomputer 22 constituting the electronic control unit 21. In the temporal synchronous control, as a processing of step S301, it is first determined whether or not the prerequisite condition of the temporal synchronous control has been met. As the prerequisite condition for the temporal synchronous control, a logical product (AND) of the following conditions is adopted. These conditions are: (D1) that the time T1 (see Figs. 4 and 5) has elapsed after turning-off of the IG switch 26; and (D2) that stall of the engine 1 has been confirmed and the IG switch 26 is not at a position for driving the starter of the engine 1 (a third position other than the on- and off-positions of the IG switch 26: not shown). That is, in a processing of step S301, it is determined whether or not the diesel engine 1 or the IG switch 26 assumes any of the states indicated by the state blocks C21, C3 and C4 exemplified in Fig. 4. If it is confirmed that the diesel engine 1 or the IG switch 26 assumes any of those states, an affirmative determination is made. In all the other circumstances, a negative determination is made. If the affirmative determination is made, the prerequisite flag for the temporal synchronous control is turned on (step S302) and the normal-time invalid injection performing flag XN is turned off (step S303). Also, a delay counter internally defined in a temporal synchronous control program is incremented (step S304). The delay counter is a counter used for the delay processing that has been described with reference to Fig. 4 or Fig. 6. If the negative determination is made in the processing of step S301, the prerequisite flag for the temporal synchronous control is turned off (step S305) and the delay counter is cleared (step S306). Thereafter, in the temporal synchronous control, as a processing of step S307, it is determined whether or not the condition for performing the temporal synchronous control has been met. As the condition for performing the temporal synchronous control, a logical product (AND) of the following conditions is adopted. These conditions are: (E1) that the counter value of the delay counter is equal to or greater than a predetermined value DCa that permits completion of the aforementioned delay processing (the delay counter value ≥ DCa); (E2) that the value of fuel pressure in the common rail 15 detected by the fuel pressure sensor 35 is equal to or greater than a predetermined pressure value Pa that requires performance of the invalid injection control (the detected fuel pressure ≥ Pa); and (E3) that the counter value of a temporal synchronous control performing counter that is internally defined in the temporal synchronous control program in the same manner as the delay counter is equal to or smaller than a predetermined value ECa that is set in accordance with a period that is longer than that required for performance of the invalid injection control during suspension of the engine 1 (the temporal synchronous control performing counter value ≤ ECa). That is, in the processing of step S204, it is determined whether or not the condition for performing the invalid injection control during suspension of the engine has been met. For example, as a comparison value DCa in the aforementioned condition (E1), which corresponds to the delay period in the delay processing, a value more or less equal to "2" is adopted. That is, in the case where the temporal synchronous control is activated in a cycle of 16 ms, the comparison value DCa is set to a value corresponding to a period of time equal to about "32 ms", which is twice as long as the cycle. This is a period necessary and sufficient for secure avoidance of interference of the control operations at the time of a transition of the fuel injection valve 17, in the case of the aforementioned (iii) where the fuel injection valve 17 undergoes a transition from the normal injection control to the invalid injection control during suspension of the engine, or in the case of the aforementioned (iv) where the fuel injection valve 17 undergoes a transition from the invalid injection control to the invalid injection control during suspension of the engine. In this temporal synchronous control, if an affirmative determination is made in the processing of step S307, on the condition that the stop-time invalid injection performing flag XT has been turned off, the invalid injection performing flag XT is turned on and the first pulse of the invalid injection pulses is set (steps S308 through S310). As in step S207 of the aforementioned "NE=7 synchronous processing", the invalid injection pulse is set as an off-time Ta and an on-time Tb. As in the case of the aforementioned control, the first pulse of the invalid injection pulses is set in step S310, whereby the invalid injection pulse-off interruption handling is activated at the time of the pulse-off. Thereafter, while the invalid injection performing flag XT is kept on, the invalid injection pulse is repeatedly set and thus the fuel injection valve 17 is repeatedly driven based on the pulse at intervals of a predetermined time, namely, in a cycle of the sum of the off-time Ta and the on-time Tb. After the first pulse of the invalid injection pulses has been set in step S310, the temporal synchronous control performing counter is incremented as a processing of step S311, and the routine is terminated temporarily. Every time an affirmative determination is made in the processing of the aforementioned step S307, the processing in step S311 is repeated. If a negative determination is made in the processing of step S307, the stop-time invalid injection performing flag XT is turned off (step S312), and the temporal synchronous control performing counter is cleared (step S313). The routine is then terminated temporarily. Thus, in the temporal synchronous control, as soon as the condition for stopping the diesel engine 1, namely, the condition of a logical product (AND) of the aforementioned conditions (D1) and (D2) is met, the normal-time invalid injection performing flag XN is turned off. Then, the delay processing is started on the basis of a counter value of the delay counter. After the lapse of the predetermined delay period, if the condition for performing the invalid injection control during suspension of the engine has been met, as in the case of the aforementioned crank angle synchronous control, the fuel injection valve 17 starts being driven in the invalid injection control mode through the setting of the invalid injection pulses. However, in the temporal synchronous control during suspension of the engine, the period for performing the invalid injection control (the active period) is also monitored on the basis of a counter value of the temporal synchronous control performing counter. Even if the aforementioned condition (E2) is met, the stop-time invalid injection performing flag XT is turned off when the counter value reaches the aforementioned value ECa. Fig. 13 is a timing chart showing changes in the stop-time invalid injection performing flag XT (a), the temporal synchronous control prerequisite flag (b), the counter value of the delay counter (c), the invalid injection/normal injection pulse (d) and the counter value of the temporal synchronous control performing counter (e) based on the temporal synchronous control and the invalid injection pulse-off interruption handling, in the case of the aforementioned (iii), namely, in the case of a transition from the normal injection control of the fuel injection valve 17 to the invalid injection control during suspension of the engine. As described above, in the normal injection control mode, the fuel injection valve 17 is driven based on the fuel injection period Tq calculated through the aforementioned "NE=3 synchronous processing" (the injection period is calculated separately)(see (d) in Fig. 13). In such a state, if fulfillment of the condition for stopping the engine (the condition of a logical product of the aforementioned (D1) and (D2)) is determined through the temporal synchronous control at a timing t31, the temporal synchronous control prerequisite flag is turned on (b) at the timing t31. At the same time, the operation of incrementing the delay counter, namely, the delay processing is started (c). After that, the delay processing is continued through repeated performance of the temporal synchronous control, until the counter value of the delay counter reaches the predetermined value DCa. When the counter value reaches the value DCa (when the aforementioned condition (E1) is met), the delay processing is terminated. Meanwhile, at least the fuel injection valve 17 is not driven in the invalid injection control mode. Thus, even if the final driving of the fuel injection valve 17 based on the normal injection control has been carried out, the fuel injection valve 17 undergoes no control interference. After such a delay processing, if the aforementioned condition (E2) is met, the invalid injection performing flag XT is turned on through the temporal synchronous control at a timing t32 ((c) and (a)). At the same time, the first pulse of the invalid injection pulses is set (d) and the operation of incrementing the temporal synchronous control performing counter is started (e). At this moment, the aforementioned condition (E3) is met undoubtedly. Because the first pulse of the invalid injection pulses has thus been set, as long as all the aforementioned conditions (E1) through (E3) as well as the logical product conditions (D1) and (D2) are met, the setting of the invalid injection pulse based on the invalid injection pulse-off interruption handling and the driving of the fuel injection valve 17 through the thus-set invalid injection pulse in the invalid injection control mode are thereafter repeated (d). After that, even though the aforementioned condition (E2) is met, if it is confirmed in the temporal synchronous control at the timing t33 that the counter value of the temporal synchronous control performing counter has reached the predetermined value ECa, the invalid injection performing flag XT is turned off at the timing t33 ((e) and (a)) so that the invalid injection control is terminated. Also in this case, the subsequent invalid injection pulse is already set through the invalid injection pulse-off interruption handling in response to the pulse-off of the invalid injection pulse that has risen immediately before the turning-off of the invalid injection performing flag XT. Therefore, even after the timing t33 when the invalid injection performing flag XT is turned off, the driving of the fuel injection valve 17 based on the last invalid injection pulse PLSr is carried out. However, after the timing t33, the fuel injection valve 17 is not driven again until the engine 1 is restarted. Thus, in this case, the fuel injection valve 17 undergoes no control interference. Fig. 14 is a timing chart showing changes in the invalid injection performing flag XN/XT (a), the temporal synchronous control prerequisite flag (b), the counter value of the delay counter (c), the invalid injection/normal injection pulse (d) and the counter value of the temporal synchronous control performing counter (e) based on the temporal synchronous control and the invalid injection pulse-off interruption handling of the present embodiment, in the case of the aforementioned (iv), namely, in the case of a transition from the normal-time invalid injection control of the fuel injection valve 17 to the invalid injection control during suspension of the engine. As regards (a), for the sake of convenience, the normal-time invalid injection performing flag XN and the stop-time invalid injection performing flag XT are illustrated along a single time axis. When the fuel injection valve 17 is being driven in the invalid injection control mode based on the state where the normal-time invalid injection performing flag XN is on, if fulfillment of the condition for stopping the engine (the logical product condition of the aforementioned (D1) and (D2)) is confirmed through the temporal synchronous control at a timing t41, the temporal synchronous control prerequisite flag is turned on at the timing t41 (b). At the same time, the normal-time invalid injection performing flag XN, which has been turned on, is turned off (a), and the delay processing through the aforementioned counting operation of the delay counter is started (c). Thereafter, the delay processing is terminated when the counter value of the delay counter reaches the predetermined value DCa. Also at this moment, the subsequent invalid injection pulse is already set through the invalid injection pulse-off interruption handling in response to the pulse-off of the invalid injection pulse that has risen immediately before the turning-off of the invalid injection performing flag XN. Therefore, even after the timing t41 when the invalid injection performing flag XN is turned off, the driving of the fuel injection valve 17 based on the last invalid injection pulse PLSr is carried out. However, in the present embodiment, after the timing t41, the driving control of the fuel injection valve 17 is not started again at least until the delay processing is terminated. Thus, also in this case, the fuel injection valve 17 undergoes no control interference. After that, if the aforementioned condition (E2) is met when the delay processing is terminated based on the temporal synchronous control at the timing t42, the stop-time invalid injection performing flag XT is turned on at the timing t42 ((c) and (d)). At the same time, the first pulse of the invalid injection pulses is set (d) and the counting (incrementing) operation of the temporal synchronous performing counter is started (e). As described above, because the first pulse of the invalid injection pulses has thus been set, as long as all the aforementioned conditions (E1) through (E3) as well as the logical product conditions (D1) and (D2) are met, the setting of the invalid injection pulse based on the invalid injection pulse-off interruption handling and the driving of the fuel injection valve 17 through the thus-set invalid injection pulse in the invalid injection control mode are thereafter repeated (d). After that, even though the aforementioned condition (E2) is met, if it is confirmed in the temporal synchronous control at the timing t43 that the counter value of the temporal synchronous control performing counter has reached the predetermined value ECa, the invalid injection performing flag XT is turned off at the timing t43 ((e) and (a)) so that the invalid injection control is terminated. This represents the same control as exemplified in Fig. 13. As described hitherto, in the present embodiment, even at the time of a transition from the normal injection control mode or the invalid injection control mode to the invalid injection control mode during suspension of the engine, the performance of the invalid injection control during suspension of the engine is retarded by a predetermined length of time through the delay processing based on the temporal synchronous control. Hence, even at the time of a transition to the invalid injection control mode, the driving of the fuel injection valve 17 through the invalid injection control can be carried out securely while preventing the fuel injection valve 17 from undergoing any control interference. Besides, in performing the temporal synchronous control during suspension of the engine, the period for performing the invalid injection control (the active period) is also managed based on the counter value of the temporal synchronous control performing counter. Therefore, it is possible to suitably inhibit the unnecessary invalid injection control from being performed when the diesel engine 1 is out of operation. After the invalid injection control during suspension of the engine has thus been terminated, or after the driving of the fuel injection valve 17 has been suspended without the conditions (E1) through (E3) for performing the temporal synchronous control being met, the relay 27 is turned off as described above, so that the electronic control unit 21 is stopped from being supplied with electric power. As described hitherto, the fuel pressure control apparatus according to the present embodiment enables achievement of many splendid effects which will be described hereinafter. The fuel injection valve 17 is driven in the invalid injection control mode in a cycle of a predetermined length of time that does not depend on an operational condition of the diesel engine 1 or the like. Thus, a surplus of fuel pressure in the common rail 15 can securely be reduced. Because the surplus of fuel pressure in the common rail 15 is thus reduced securely, the amount of pressure decrease can easily be estimated. In circumstances where other control or diagnosis operations such as control for force-feeding fuel into the common rail 15, diagnosis of the high-pressure fuel injection system 10 and the like are also performed, the estimation of an amount of pressure decrease also constitutes an important factor. During normal operation of the diesel engine 1, the driving of the fuel injection valve 17 in the normal injection control mode and the timing for starting driving the fuel injection valve 17 in the invalid injection control mode are controlled based on the crank angle synchronous control that is performed on the basis of the crank angle. Therefore, the normal injection control mode and the invalid injection control mode can be managed unitarily. Thus, the fuel injection valve 17 is prevented from undergoing control interference in the respective control modes, whereby the overall adjustment is also facilitated. In the crank angle synchronous control, on the condition that there is no requirement for injection at least in the normal injection control mode, the first driving of the fuel injection valve 17 in the invalid injection control mode is permitted. Thereby, the fuel injection valve 17 is securely prevented from undergoing interference of control operations in the respective control modes. Thus, the deterioration of emission properties, the damage inflicted on the engine and the like at the time of a transition from the normal injection control mode to the invalid injection control mode are also suitably avoided. Also, the off-time Ta of the invalid injection pulse relating to the first driving of the fuel injection valve 17 in the invalid injection control mode is set to a time that is necessary and sufficient for the driver 23 to drive the fuel injection valve 17. Therefore, the first driving of the fuel injection valve 17 is secured at least in the invalid injection control mode. Further, in the crank angle synchronous control, at the time of restoration of the driving of the fuel injection valve 17 in the normal injection control mode out of the driving of the fuel injection valve 17 in the invalid injection control mode, only the first driving of the fuel injection valve 17 in the normal injection control mode is unconditionally prohibited. Thus, even in the case where the driving of the fuel injection valve 17 in the invalid injection control mode is carried out in the invalid injection pulse-off interruption handling, the fuel injection valve 17 is securely prevented from undergoing interference of control operations in the respective control modes. Basically, the period of prohibition can be set arbitrarily. However, as described in the present embodiment, if the driving cycle of the fuel injection valve 17 in the invalid injection control mode is sufficiently shorter than the driving cycle of the fuel injection valve 17 during the normal injection control that is performed on the basis of a crank angle, the period of prohibition is just set to an amount corresponding to the first driving movement. Thus, the normal injection control mode can be restored most smoothly out of the invalid injection control mode while preventing the fuel injection valve 17 from undergoing control interference. Further, fulfillment of the condition for stopping the diesel engine 1 is confirmed, and the first timing for driving the fuel injection valve 17 in the invalid injection control mode during suspension of the engine based on the fulfillment of the stop condition is set based on the temporal synchronous control, which separately manages the timing with a predetermined time being set as a criterion. Therefore, after fulfillment of the condition for stopping the engine 1, the driving of the fuel injection valve 17 in the invalid injection control mode is securely carried out regardless of a rotational speed of the engine 1. Further, since the invalid injection control is thus performed during suspension of the engine, even if the operation for restarting the engine 1 has been performed immediately after turning-off of the IG switch 26 during racing of the engine 1 or even if the operation for restarting the engine 1 has been performed immediately after stall of the engine 1 during the running of the vehicle, the fuel pressure in the common rail 15 can preliminarily be reduced down to a suitable value. If the engine is left as it is for a sufficient period of time after it has been stopped, the fuel pressure in the common rail 15 also decreases sufficiently. However, as described above, in the case where the operation of restarting the engine is performed abruptly, fuel injection is carried out at an excessively high pressure because the fuel pressure in the common rail 15 does not decrease to a target fuel pressure at the time of the start of the engine. Also, there is a considerable possibility that an increase in combustion noise or the like might be incurred. In the temporal synchronous control of the present embodiment, the first timing for driving the fuel injection valve 17 in the invalid injection control mode through the delay processing is retarded by a predetermined length of time. Thus, after fulfillment of the condition for stopping the engine 1, a transition to the invalid injection control mode can securely be made while preventing interference with the control performed before the fulfillment. Further, after a transition to the invalid injection control mode during suspension of the engine has been made, the period for performing the invalid injection control (the active period) is also managed. If the active period has reached a predetermined period, the invalid injection control is suspended. In this manner, it is also possible to suitably inhibit the unnecessary invalid injection control from being performed when the engine 1 is out of operation. As one of the factors for determining whether or not the condition for performing the invalid injection control has been met in the temporal synchronous control (Fig. 12) of the present embodiment, the following condition is set. This condition is: (E2) that the value of fuel pressure in the common rail 15 detected by the fuel pressure sensor 35 is equal to or greater than a predetermined pressure value Pa that requires performance of the invalid injection control (the detected fuel pressure ≥ Pa). It is to be noted herein that the predetermined pressure value Pa may be set as a variable which is the function of a coolant temperature detected by the coolant temperature sensor 32. At the time of the start of the diesel engine 1, the target fuel pressure in the common rail 15 is calculated using the coolant temperature as a parameter, for example, according to a pattern exemplified in Fig. 15. On the other hand, as described above, if the operation for restarting the engine 1 has been performed immediately after turning-off of the IG switch 26 during racing of the engine 1 or if the operation for restarting the engine 1 has been performed immediately after stall of the engine 1 during the running of the vehicle, the coolant temperature during suspension of the engine is normally maintained substantially at the same level as the coolant temperature at the time of the start of the engine. Thus, when the fuel pressure in the common rail 15 upon fulfillment of the condition for stopping the engine is controlled by means of the invalid injection control through the temporal synchronous control, the predetermined pressure value Pa serving as a threshold value may be set to a variable which is the function of a coolant temperature. In this case, when restarting the engine 1, feedback control of fuel pressure is started in a relationship "the target fuel pressure ≈ the actual fuel pressure". That is, while the frequency of unnecessary performance of the invalid injection control is reduced, the convergency of the feedback control of fuel pressure in restarting the engine can substantially be enhanced. Fig. 16 shows a relationship between the predetermined pressure value Pa and the aforementioned temporal synchronous control in the form of a timing chart corresponding to Figs. 13 and 14. Referring to Fig. 16, (f) represents changes of fuel pressure in the common rail 15 detected by the fuel pressure sensor 35, and a relationship of the predetermined value Pa to such changes. That is, as indicated by (a), the invalid injection performing flag XT during suspension of the engine is turned on through the temporal synchronous control at a timing t51. If the invalid injection control is performed according to a pattern indicated by (d), as long as the force-feeding of fuel through the supply pump 13 is not carried out during this period, the fuel pressure in the common rail 15 decreases according to a pattern exemplified by (f) in accordance with the driving of the fuel injection valve 17 in the invalid injection control. If it is determined that the detected value of fuel pressure has reached a predetermined value Pa through the temporal synchronous control at a timing t52, even though the counter value of the temporal synchronous control performing counter has not reached the predetermined value ECa, the invalid injection performing flag XT is turned off at the timing t52 (a). This does not apply if a timing t53 when the counter value of the temporal synchronous control performing counter reaches the predetermined value ECa is earlier than the timing t52. That is, as exemplified in Fig. 13 or 14, the invalid injection performing flag XT is turned off at the timing when the counter value reaches the predetermined value ECa. Further, the predetermined pressure value Pa under the aforementioned condition (E2) can also be set to a predetermined value corresponding to a target fuel pressure based on experiments or the like. Also in this case, the fuel pressure in the common rail 15 can suitably be prevented from becoming abnormally high in restarting the engine. Further, in the aforementioned embodiment, as one of the factors for determining whether or not the condition for performing the invalid injection in the temporal synchronous control exemplified in Fig. 12 has been met, the following condition is set. This condition is: (E3) that the counter value of the temporal synchronous control performing counter is equal to or smaller than the predetermined value ECa that is set in accordance with a period that is longer than that required for performance of the invalid injection control during suspension of the engine 1 (the temporal synchronous control performing counter value ≤ ECa). It is to be noted herein that the predetermined value ECa may be set as a variable which is the function of an engine rotational speed (NE) detected by the rotational speed sensor 33. If the diesel engine 1 is in operation, operation noise of the fuel injection valve 17 is not displeasing to the passenger. However, after fulfillment of the condition for stopping the engine 1, if the operation noise of the fuel injection valve 17 in the invalid injection control mode remains in stopping the engine, the operation noise causes discomfort to the passenger. In view of this, if the predetermined value ECa is set as a variable which is the function of an engine rotational speed (NE), the driving of the fuel injection valve 17 in the invalid injection control mode can be prohibited, for example, on the condition that the rotational speed of the engine 1 drops below a certain rotational speed. Hence, such discomfort can be eliminated. In the aforementioned embodiment, the normal-time invalid injection performing flag XN is turned on simultaneously with the setting of the first pulse of the invalid injection pulses through the "NE=7 synchronous processing" as the crank angle synchronous control. However, it is not always necessary to perform these two processings simultaneously. For example, after the normal-time invalid injection performing flag XN has been turned on through the "NE=7 synchronous processing", the first pulse of the invalid injection pulses may be set in synchronization with the following "NE=8" or the like. Also in this case, at the time of a transition to the invalid injection control mode, the first driving of the fuel injection valve 17 can securely be carried out while preventing control interference of the fuel injection valve 17. The setting of the timings for performing the "NE=3 synchronous processing", the "NE=7 synchronous processing" and the like as the aforementioned crank angle synchronous processing is merely an example. What is important is that an appropriate processing is performed on the basis of a suitable timing before a top dead center (TDC) of the piston according to a crank angle detecting pattern of a diesel engine system to which the present invention is applied. Further, in the aforementioned embodiment, when driving the fuel injection valve 17 in the invalid injection control mode, only the first pulse of the invalid injection pulses is set through the crank angle control or the temporal synchronous control, and then the second and following pulses of the invalid injection pulses are sequentially set through the invalid injection pulse-off interruption handling exemplified in Fig. 8. The pattern of producing invalid injection pulses can be determined arbitrarily, as long as the produced pulses rise only within an invalid injection period in a cycle of a predetermined time under a predetermined condition that the invalid injection performing flag XN or XT is kept on. That is, a known pulse-producing circuit using a logic element or the like can also be employed suitably. Further, the cycle time of the invalid injection pulse does not have to be constant. The time serving as the repetition cycle of the pulses may be set as a variable that changes in accordance with a momentary fuel pressure, a momentary fuel temperature, other requirements and the like. However, in the case where the cycle time is set as a constant, the response characteristic associated with a decrease in fuel pressure in the common rail 15 is also basically constant all the time. As a result, estimation of the aforementioned amount of decrease in fuel pressure and the like can further be facilitated. Further, in the aforementioned embodiment, the means for adjustment performs the following processings through the crank angle synchronous control and the temporal synchronous control. These processings include: (1) setting invalid injection pulses at least on the condition that there is no requirement for injection at the time of a transition from the normal injection control mode to the invalid injection control mode; (2) prohibiting the first fuel injection relating to restoration at the time of restoration of the normal injection control mode out of the invalid injection control mode; and (3) retarding by a predetermined time a first set of the invalid injection pulses in the invalid injection control mode during suspension of the engine at the time of a transition to the invalid injection control mode during suspension of the engine. However, what is essential is that adjustment is made in such a manner as to prevent the driving of the fuel injection valve 17 through the invalid injection control from interfering with the normal driving of the fuel injection valve 17 that is not based on the invalid injection control. Thus, even in the case where the fuel injection valve 17 is driven through the invalid injection control making use of a limited period of time in which the normal fuel injection is not carried out, the performance of the operation is ensured, and moreover, a surplus of fuel pressure in the common rail 15 can securely be reduced. Especially, the means for adjustment can be designed such that the setting of periods in which neither the invalid injection control nor the normal injection control is performed is controlled within the range of control demands at the time of respective transitions. In this case, even though the fuel injection valve 17 is also driven through the invalid injection control, the driving control of the fuel injection valve 17 exhibits enhanced reliability. The high-pressure fuel injection system designed to control a fuel pressure in the present invention is not limited to a high-pressure fuel injection system whose main component is a common rail of a diesel engine system. For example, if there is a gasoline engine or the like of a cylinder direct injection type wherein high-pressure fuel accumulated in an accumulation line is supplied to the engine by driving a fuel injection valve connected to the line, the fuel pressure control apparatus of the present invention can also be applied to that engine in a manner similar to the aforementioned embodiment.

Claims: A fuel pressure control apparatus for a high-pressure fuel injection system, for controlling a fuel pressure of high-pressure fuel supplied to an internal combustion engine (1) provided with an accumulator line (15), comprising: normal injection control means (20) for supplying through injection fuel accumulated in the accumulator line (15) to the internal combustion engine (1) by driving a fuel injection valve (17) connected to the accumulator line (15); invalid injection control means (20) for releasing a pressure of fuel accumulated in the accumulator line (15) by driving the fuel injection valve (17) within an invalid injection period; characterized by adjusting means for adjusting timings for driving the fuel injection valve (17) through the normal injection control means (20) and the invalid injection control means (20) so that the driving timings of the fuel injection valve (17) of the normal injection control by the normal injection means (20) and the invalid injection control by the invalid injection control means (20) are prevented from overlapping each other, if: a) the fuel injection valve (17) undergoes a transition from the normal injection control to the invalid injection control, or b) the fuel injection valve (17) undergoes a reversed transition from the invalid injection control to the normal injection control; and an adjustment is made by retarding performance of the invalid injection control during suspension of the engine by a predetermined period, so that control interference is avoided and the pressure of a surplus of fuel can securely be reduced within a certain length of time, if: c) the fuel injection valve undergoes a transition from the normal injection control to the invalid injection control during suspension of the engine, or d) the fuel injection valve (17) undergoes a transition from the invalid injection control to a new invalid injection control during suspension of the engine. The fuel pressure control apparatus according to claim 1, characterized in: that the adjustment means (20) controls setting of a period during which neither driving control of the fuel injection valve (17) through the invalid injection control means (20) nor the driving control of the fuel injection valve (17) through the normal injection control means (20) is performed, within a range of control demands. The fuel pressure control apparatus according to claim 1 or 2, characterized in: that the adjustment means (20) is provided with crank angle synchronous control means (20) for controlling a first timing for driving the fuel injection valve (17) through the invalid injection control means (20) and a timing for driving the fuel injection valve (17) through the normal injection control means (20), using a crank angle of the internal combustion engine (1) as a criterion. The fuel pressure control apparatus according to claim 3, characterized in: that the crank angle synchronous control means (20) allows driving of the fuel injection valve (17) through the invalid injection control means (20) to be started if there is no requirement for driving of the fuel injection valve (17) through the normal injection control means (20). The fuel pressure control apparatus according to claim 3, characterized in: that the crank angle synchronous control means (20) prohibits driving control of the fuel injection valve (17) through the normal injection control means (20) for a predetermined period when making a transition from a driving control state of the fuel injection valve (17) through the invalid injection control means (20) to a driving control state of the fuel injection valve (17) through the normal injection control means (20). The fuel pressure control apparatus according to any of claims 1 to 5, characterized in: that the adjustment means (20) prohibits driving control of the fuel injection valve (17) through the invalid injection control means (20) based on fulfillment of a condition for stopping the internal combustion engine (1), and is further provided with temporal synchronous control means (20) for controlling setting of a timing for starting driving the fuel injection valve (17) through the invalid injection control means (20) in synchronization with a predetermined time. The fuel pressure control apparatus according to claim 6, characterized in: that the temporal synchronous control means (20) retards by a predetermined period a timing for starting driving the fuel injection valve (17) through the invalid injection control means (20), the timing being set based on fulfillment of the condition for stopping the internal combustion engine (1). The fuel pressure control apparatus according to claim 6 or 7, characterized in: that the temporal synchronous control means (20) also controls setting of an active period of driving control of the fuel injection valve (17) through the invalid injection control means (20). The fuel pressure control apparatus according to claim 8, characterized in: that the temporal synchronous control means (20) sets an active period of driving control of the fuel injection valve (17) through the invalid injection control means (20) based on either a temperature of coolant in the internal combustion engine (1) or a target fuel pressure in the accumulator line (15). The fuel pressure control apparatus according to claim 8 or 9, characterized in: that the temporal synchronous control means (20) sets an active period of driving control of the fuel injection valve (17) through the invalid injection control means (20) based on a rotational speed of the internal combustion engine (1). The fuel pressure control apparatus according to any of claims 1 to 10, characterized in: that the adjustment means (20) sets a driving cycle of the fuel injection valve (17) to a predetermined time. The fuel pressure control apparatus according to claim 11, characterized in: that the predetermined time is constant.

Inventors: KATOU YUUICHIROU, SUGIYAMA TATSUMASA, KATOU, YUUICHIROU, SUGIYAMA, TATSUMASA, Katou, Yuuichirou c/o Toyota Jidosha K.K., Sugiyama, Tatsumasa c/o Toyota Jidosha K.K.
Applicants: TOYOTA MOTOR CO LTD, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 2000
Main classification: F02D41
IPC codes: F02D41, F02B3, F02M37, F02M55