JP5884710B2 - Fuel pressure control device - Google Patents

Description

  The present invention relates to a fuel pressure control device applied to, for example, a high pressure fuel supply system of a diesel engine.

  As a high-pressure fuel supply system such as a diesel engine, a fuel pump that discharges fuel at a high pressure and a common rail (accumulation pipe) that stores high-pressure fuel discharged from the fuel pump are provided, and the high-pressure fuel stored in the common rail is stored in the common rail. A common rail fuel injection system that supplies fuel to an engine via a fuel injection valve has been put into practical use. In this common rail fuel injection system, it is necessary to accurately control the fuel pressure in the common rail so that the fuel injection rate of the fuel injection valve is an appropriate value corresponding to the engine operating state. Conventionally, in the common rail fuel injection system, the fuel pressure in the common rail is made to follow the target value corresponding to the engine operating state by controlling the discharge amount of the fuel pump. In addition, when it is necessary to reduce the target pressure with changes in the engine operating state, the fuel in the common rail is leaked by driving the pressure reducing valve provided in the common rail, and the fuel pressure in the common rail is reduced. (For example, refer to Patent Document 1).

JP 2010-90845 A

  By the way, there is a case where the next pressure reducing valve is opened (energized) by grasping the state of pressure reduction change caused by opening (energizing) the pressure reducing valve. In this case, if the pressure change continues even after the pressure reducing valve is closed (de-energized), the fuel pressure in the common rail cannot be detected accurately, and the fuel pressure to be reduced by the next pressure reducing valve drive is accurately grasped. There are things that cannot be done. For this reason, the driving amount of the pressure reducing valve (for example, the amount of fuel leaked from the pressure reducing valve, etc.) cannot be obtained accurately, and as a result, the controllability of the common rail pressure may be reduced.

  This invention is made | formed in view of the said subject, and makes it a main objective to provide the fuel pressure control apparatus which can improve the controllability of the fuel pressure in pressure accumulation piping.

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

  The present invention is applied to a fuel supply system for an engine including a pressure accumulation pipe that stores high-pressure fuel discharged from a fuel pump, and a pressure reducing valve that opens when energized to leak fuel in the pressure accumulation pipe. The present invention relates to a fuel pressure control device that reduces the fuel pressure in the pressure accumulating pipe by controlling the driving of the pressure reducing valve in synchronization with the rotational position of a rotary shaft of a pump.

  According to the first aspect of the present invention, in the case where the pressure detecting means for detecting the fuel pressure in the pressure accumulating pipe and the subsequent pressure reducing valve driving are implemented following the previous pressure reducing valve driving, After the energization of the pressure reducing valve is stopped, a determination unit that determines whether or not the rotational position has reached a predetermined calculation position for calculating a driving amount of the pressure reducing valve in the subsequent driving of the pressure reducing valve; When it is determined that the calculated position is reached, the fuel pressure detected by the pressure detecting means at the timing when the calculated position is reached and the timing when the calculated position is reached from the timing when the previous pressure reducing valve drive is stopped. Based on the required time required for rotation or a correlation parameter thereof, a pressure estimated value that is the fuel pressure after the pressure reduction by the previous pressure reducing valve driving is completed, and the pressure estimated value A driving amount calculating means for calculating the driving amount in the subsequent pressure reducing valve driving based on the driving amount calculated by the driving amount calculating means after the pressure reducing by the previous pressure reducing valve driving is completed. And a decompression control means for performing decompression valve driving.

  In short, when the subsequent pressure reducing valve drive is performed following the previous pressure reducing valve driving, the pressure reduction by the previous pressure reducing valve driving is not completed at the time of calculating the drive amount of the pressure reducing valve in the subsequent pressure reducing valve drive. There is. In this case, it is impossible to accurately grasp the fuel pressure after completion of pressure reduction by the previous pressure reducing valve drive. In addition, the pressure reduction incomplete amount is the time required from the timing of stopping energization of the pressure reducing valve in the previous pressure reducing valve drive to the timing for calculating the pressure reducing valve drive amount in the subsequent pressure reducing valve driving (time required for rotation) ).

  Focusing on this point, in the above configuration, the fuel after the pressure reduction by the pressure reducing valve driving is completed based on the actual fuel pressure at the calculation timing of the pressure reducing valve driving amount and the time required for rotation or the correlation parameter thereof. The pressure is estimated, and the pressure reducing valve drive amount in the subsequent pressure reducing valve drive is calculated based on the estimated pressure value. Further, after the pressure reduction by the previous pressure reducing valve driving is completed, the subsequent pressure reducing valve driving is performed based on the calculated pressure reducing valve driving amount. According to this configuration, even when the pressure reduction by the previous pressure reducing valve drive does not complete at the calculation timing of the pressure reducing valve drive amount, the pressure reducing valve drive amount for the subsequent pressure reducing valve drive is accurately determined. Can be calculated. As a result, the controllability of the fuel pressure in the pressure accumulating pipe can be improved.

  The drive amount of the pressure reducing valve is a variable value set in accordance with the deviation between the fuel pressure (actual value) in the pressure accumulating pipe and the target value. For example, the fuel flow rate that leaks from the pressure accumulating pipe by driving the pressure reducing valve In addition, a rotation angle period (energization duty ratio) in which the pressure reducing valve is energized is included.

The block diagram which shows the outline of the common rail type fuel injection system of an engine. The figure explaining pressure reduction control of common rail pressure. The figure which shows the condition of the pressure reduction change according to a pump rotational speed. The figure which shows the condition of the pressure reduction change according to the electricity supply duty ratio of the previous pressure reducing valve drive. The flowchart which shows the process sequence of pressure reduction control. The figure which shows an example of the map for pressure correction.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings. In this embodiment, the present invention is embodied in a common rail fuel injection system for a diesel engine for a vehicle. The system controls the fuel pressure (common rail pressure) in the common rail, which is an accumulator piping for high-pressure fuel, with an electronic control unit (hereinafter referred to as ECU) as the center. An overall schematic configuration diagram of this system is shown in FIG.

  In FIG. 1, the fuel tank 11 is connected to a fuel pump 13 via a fuel pipe 12. The fuel pump 13 is a mechanical pump that sucks and discharges fuel by being driven as the engine 15 rotates. Specifically, the fuel pump 13 includes a pump rotation shaft 17 that rotates as the output shaft (crank shaft 16) of the engine 15 rotates, and a plunger that reciprocates as the pump rotation shaft 17 rotates. The plunger reciprocates in synchronization with the rotation of the engine 15 to suck and discharge fuel. An electromagnetically driven suction metering valve (SCV) 18 is provided in the fuel suction portion of the fuel pump 13, and low-pressure fuel from the fuel tank 11 passes through the suction metering valve 18 to fuel the fuel pump 13. It is introduced into the pressure chamber. In the fuel pump 13, the pressure in the fuel pressurizing chamber is increased by the reciprocation of the plunger, and the high-pressure fuel is discharged.

  The intake metering valve 18 is a normally open valve that is maintained in an open state (fully open state) when the electromagnetic solenoid is not energized, and the opening area of the fuel intake passage is changed in accordance with the value of the commanded current to the electromagnetic solenoid. By changing the opening of the intake metering valve 18, the amount of fuel supplied to the fuel pump 13 is adjusted, and the amount of fuel discharged from the fuel pump 13 (pump discharge amount) is adjusted.

  A common rail 26 is connected to the fuel pump 13 via a fuel pipe 25. High pressure fuel discharged from the fuel pump 13 is sequentially supplied to the common rail 26. Thereby, the fuel in the common rail 26 is held in a high pressure state. The common rail 26 is provided with a rail pressure sensor 27, and the rail pressure sensor 27 detects the actual value of the fuel pressure in the common rail 26 (actual rail pressure Pc).

  The common rail 26 is provided with a pressure reducing valve 28 as pressure reducing means for leaking fuel in the common rail 26. The pressure reducing valve 28 is a normally closed valve that is held in a shut-off state (fully closed state) when the electromagnetic solenoid is not energized, and is held in an open state (valve open state) when the electromagnetic solenoid is energized. When the electromagnetic solenoid is energized to open the pressure reducing valve 28, the common rail 26 and the fuel tank 11 are communicated with each other via the leak pipe 29. Thereby, the fuel in the common rail 26 is discharged to the fuel tank 11 side, and the rail pressure decreases.

  The engine 15 is a diesel engine, and is configured as a four-cylinder engine in the present embodiment. The engine 15 is provided with an electromagnetically driven injector 31 for each cylinder. High pressure fuel is supplied from the common rail 26 to the injector 31 through the high pressure fuel pipe 32, and fuel is injected and supplied to each cylinder of the engine 15 by driving the injector 31. A part of the high-pressure fuel supplied to the injector 31 is returned to the fuel tank 11 through the return pipe 33. As the fuel injection valve (injector 31), it is possible to use a piezo drive type instead of the electromagnetic drive type.

  The pump rotation shaft 17 is provided with a pump rotation angle sensor 20 as a rotation angle sensor that outputs a rectangular detection signal for each predetermined rotation angle. The pump rotation angle sensor 20 includes a pulsar (rotary disk) 21 that rotates integrally with the pump rotation shaft 17 and an electromagnetic pickup unit 22 provided near the outer periphery thereof. Protrusions 23 are provided on the outer peripheral portion of the pulsar 21 at a predetermined interval (10 ° C. A interval in this embodiment), and one or more protrusions (protrusions of two teeth in this embodiment) are missing in a part thereof. A missing tooth portion 24 is provided. In the present embodiment, one missing tooth portion 24 is provided on the outer peripheral portion of the pulsar 21. When the pulser 21 rotates with the rotation of the pump rotating shaft 17, a detection signal is output from the electromagnetic pickup unit 22 each time the protrusion 23 of the pulser 21 approaches the electromagnetic pickup unit 22 (basically every 10 ° C. A).

  In the present embodiment, 34 pulse detection signals are output from the pump rotation angle sensor 20 within a period of one rotation of the pump rotation shaft 17 (within a period of 360 ° C.). Each of these signals is given pulse numbers of 0 to 17 in sequence with a period of 180 ° C. as one period, of which pulse numbers 15 and 16 are missing teeth 24. Based on the detection signal from the pump rotation angle sensor 20, the rotation speed of the pump rotation shaft 17 (pump rotation speed Np) is calculated.

  The ECU 40 is an electronic control device including a known microcomputer including a CPU, a ROM, a RAM, and the like. In addition to the detection signals of the rail pressure sensor 27 and the pump rotation angle sensor 20, the ECU 40 includes a crank angle sensor 41 as a rotation angle sensor for detecting the rotation speed of the engine 15 (engine rotation speed), and an accelerator operation amount. Detection signals are sequentially input from various sensors such as an accelerator sensor to be detected. The crank angle sensor 41 is of an electromagnetic pickup type like the pump rotation angle sensor 20. The ECU 40 determines an optimal fuel injection amount and injection timing based on engine operation information such as engine rotation speed and accelerator operation amount, and outputs an injection control signal corresponding to the fuel injection amount to the injector 31. Thereby, the fuel injection from the injector 31 to the combustion chamber is controlled in each cylinder.

  Further, the ECU 40 sets a target pressure Pt that is a target value of the common rail pressure (injection pressure) based on the engine speed and fuel injection amount at each time, and the actual rail pressure Pc detected by the rail pressure sensor 27 is set. The fuel discharge amount of the fuel pump 13 is feedback-controlled so that the target pressure Pt is reached. Actually, the fuel discharge amount of the fuel pump 13 is determined based on the deviation between the actual rail pressure Pc and the target pressure Pt, and the opening of the intake metering valve 18 is controlled according to the pump discharge amount. At this time, if the target pressure Pt is higher than the actual rail pressure Pc, the suction metering valve is controlled by controlling the command current value (drive current) for the electromagnetic solenoid of the suction metering valve 18 according to the deviation. 18 opening degree is adjusted. Thereby, the amount of fuel discharged from the fuel pump 13 is adjusted, and the actual rail pressure Pc is increased to the target pressure Pt. In the present embodiment, a one-injection one-pressure feed type in which the fuel pump 13 performs fuel pumping once for one combustion fuel injection of the engine 15 is employed.

  On the other hand, when the actual rail pressure Pc is higher than the target pressure Pt, the pump discharge amount is reduced to zero and the energization time (energization duty ratio) of the pressure reducing valve 28 to the electromagnetic solenoid is controlled. Adjust the valve opening time. As a result, the reduced pressure flow Qd, which is the amount of fuel leaking from the common rail 26 to the fuel tank 11 side, is adjusted, and the actual rail pressure Pc is reduced to the target pressure Pt.

  The common rail pressure reduction control by the pressure reducing valve 28 which is a premise of the present embodiment will be described in detail below. In the present embodiment, the common rail pressure is reduced by controlling the drive of the pressure reducing valve 28 in synchronization with the rotational position of the pump rotating shaft 17 (hereinafter also referred to as the pump rotational position). Specifically, a predetermined rotation angle period (180 ° C. A period in the present embodiment) of the pump rotating shaft 17 is set as a pressure reduction period, and a predetermined first rotation position within the pressure reduction period is set as a calculation timing of the reduced pressure flow Qd, The predetermined second rotational position, which is a position rotated by a predetermined angle α from the first rotational position, is fixed as the energization start timing of the pressure reducing valve 28 and the pressure reducing valve 28 is driven. The first rotation position corresponds to a “predetermined calculation position”, and the second rotation position corresponds to a “predetermined start position”. In each decompression cycle, an upper limit is set for the energization period per drive of the decompression valve for reasons such as suppressing heat generation in the decompression valve 28 accompanying energization continuation, and in principle the maximum duty ratio D1 ( For example, the pressure reducing valve 28 is energized at an energization duty ratio of 40% duty or less. The energization period is a rotation angle period from the energization start timing to the energization end timing of the pressure reducing valve 28. Therefore, for example, when the target pressure Pt of the common rail pressure is changed in accordance with a change in the engine operating state, if the amount of change of the target pressure Pt is a predetermined value or more, the actual rail pressure Pc is not reduced to the target pressure Pt all at once. Instead, the common rail pressure is reduced to the target pressure Pt by performing the pressure reducing valve drive a plurality of times by repeating the pressure reducing cycle.

  In this embodiment, for example, when the system is abnormal, such as when fuel is excessively discharged from the fuel pump 13, the duty ratio of the pressure reducing valve 28 is set to the abnormal duty ratio D2 (for example, 80% Duty). The depressurization valve 28 is energized at the abnormal duty ratio D2.

  The pressure reduction control by the pressure reducing valve 28 will be specifically described with reference to FIG. In FIG. 2, the target pressure Pt of the common rail pressure is changed from the target pressure Pt1 at the time of high engine load (for example, 250 MPa) to the target pressure Pt2 at the time of idle operation (for example, 30 to 40 MPa) as the engine operating state changes. It assumes a transient operation. The pressure reducing control by the pressure reducing valve 28 is performed in an angle synchronization in which the period during which the pump rotating shaft 17 rotates by 180 ° C. is one cycle (pressure reducing cycle).

  For each decompression cycle, the ECU 40 calculates [1] calculation of the decompression flow rate Qd as the decompression valve drive amount, [2] calculation of the energization period (energization duty ratio) of the decompression valve 28, and [3] energization of the decompression valve 28 ( (Open valve) and [4] Stop energization of the pressure reducing valve 28 (close valve). Specifically, in FIG. 2, when the target pressure Pt is changed from Pt1 to Pt2, the timing at which the pump rotational position becomes the predetermined first rotational position, here, the detection of the pulse number θ1 from the pump rotational angle sensor 20 is detected. At a timing t11 when the signal is input, a decompression component flow Qd by one decompression valve drive is calculated. For example, if the system is normal, a reduced pressure flow Qd corresponding to the deviation ΔP between the actual rail pressure Pc detected by the rail pressure sensor 27 at the timing t11 and the target pressure Pt is calculated among the flows below the upper limit. The Further, when a system abnormality such as pump overpressure occurs, a reduced pressure corresponding to the abnormal duty ratio D2 is set. That is, the timing t11 at which the pump rotational position becomes the first rotational position is also a timing for determining whether or not the next pressure reducing valve drive is to be performed with the abnormal duty ratio D2.

  In order to enable energization of the pressure reducing valve 28 with the abnormal duty ratio D2, the energization period is ensured by determining whether or not to drive with the abnormal duty ratio D2 at the earliest possible timing within the decompression cycle. There is a need to. Therefore, in this embodiment, the start reference position of the decompression cycle, and in this embodiment, the input timing (t11) of the detection signal of the pulse number θ1 is used as the calculation timing of the decompression partial flow Qd. Further, when energization is performed with the abnormal duty ratio D2, the timing when the pump rotation position becomes the predetermined third rotation position is set as the energization start timing. In this embodiment, the timing when the detection signal of the pulse number θ2 is input is energized. It is the start time.

  Subsequently, at the timing when the pump rotation position becomes the predetermined second rotation position, in this embodiment, at the timing t12 when the pulse number θ4 is input from the pump rotation angle sensor 20, the energization period of the pressure reducing valve 28 is calculated. Energization of the pressure reducing valve 28 is started. Specifically, the energization period (energization duty ratio) is set based on the decompression flow rate Qd as the decompression valve drive amount calculated at timing t11 and the fuel flow rate (unit flow rate Qu) from the decompression valve 28 per unit time. calculate. The unit flow rate Qu differs depending on the common rail pressure, and increases as the common rail pressure increases.

  In the present embodiment, the energization end timing of the pressure reducing valve 28 is variable based on the second rotation position, which is the energization start timing, in accordance with the deviation ΔP between the common rail pressure Pc and the target pressure Pt, that is, in accordance with the reduced pressure flow Qd. Set (end time setting means). Therefore, after the energization of the pressure reducing valve 28 is started at the timing t12, the energization of the pressure reducing valve 28 is stopped at the timing when the energization period corresponding to the reduced pressure flow Qd has elapsed. For example, when the maximum duty ratio D1 is set, the energization of the pressure reducing valve 28 is stopped at the timing immediately before the start reference position of the next pressure reducing cycle, in this embodiment, at the rising timing t13 of the pulse number θ5. After the energization of the pressure reducing valve 28 is stopped, when the pump rotational position becomes the first rotational position, the pressure reducing flow rate Qd for driving the next pressure reducing valve is calculated at the timing t14, and then the pump rotational position is the second rotational position. At the timing t15 when the position is reached, energization of the pressure reducing valve 28 is started and pressure reduction by the pressure reducing valve 28 is performed.

  In the present embodiment, the fuel injection from the injector 31 is performed after the pressure reducing valve 28 is closed until the common rail pressure becomes stable until the next pressure reducing valve driving is started (the second rotation position is reached). In this embodiment, fuel injection is performed with reference to the pulse number θ3 (pulse number between θ2 and θ4). Therefore, when calculating the reduced pressure flow Qd, it is desirable to calculate the reduced pressure Qd by the next drive of the pressure reducing valve, taking into account the reduced pressure of the fuel pressure due to fuel injection. In addition, since the fuel injection from the injector 31 is performed after the common rail pressure becomes stable after the pressure reducing valve 28 is closed, at the second rotational position that is the energization start timing of the pressure reducing valve 28, The pressure reduction by the previous pressure reducing valve driving is completed.

  By the way, when changing the energization state (on / off) of the pressure reducing valve 28 and switching the open / close state of the pressure reducing valve 28, the rail pressure sensor 27 does not immediately detect the change in the common rail pressure accompanying the switching of the energized state. And a predetermined delay time occurs. Further, during this delay time period, since the pressure reducing valve 28 is before being fully closed, the common rail pressure continues to decrease even after the pressure reducing valve 28 is turned off. Therefore, in the case where the pressure reducing state by the previous pressure reducing valve driving is grasped and the next pressure reducing valve driving is performed, the pressure reduction by the previous pressure reducing valve driving is reduced at the timing of calculating the pressure reducing flow Qd of the next pressure reducing valve driving. In some cases, the decompression flow Qd for driving the subsequent pressure reducing valve cannot be accurately calculated. Specifically, by calculating the reduced pressure flow Qd using a pressure value higher than the common rail pressure at the time of starting energization of the pressure reducing valve 28, the current duty ratio of the pressure reducing valve 28 is set larger than the actual. End up. In this case, the decompression flow Qd in the subsequent decompression valve drive becomes excessive, and the fuel pressure in the common rail 26 may not be accurately controlled.

  Therefore, in the present embodiment, when the subsequent pressure reducing valve driving is performed following the previous pressure reducing valve driving, the calculation timing of the pressure reducing partial flow Qd at the time of the subsequent pressure reducing valve driving, that is, the pump rotational position is the first rotational position. At this time, the actual rail pressure Pc at that timing is the time required from the previous stop timing of energization of the pressure reducing valve drive to the calculation timing of the reduced pressure flow Qd of the subsequent pressure reducing valve drive. By correcting by the required time or the correlation parameter, the common rail pressure after the pressure reduction by the previous pressure reducing valve driving is completed is estimated. Further, based on the estimated pressure value Pc * that is the estimated common rail pressure, a reduced pressure flow Qd is calculated as a pressure reducing valve drive amount in the subsequent pressure reducing valve drive. By performing the subsequent pressure reducing valve driving based on the pressure reducing flow rate Qd calculated in this way, the pressure reduction by the previous pressure reducing valve driving is not completed at the time of calculating the pressure reducing partial flow rate Qd. In the case of driving 28, it is possible to accurately grasp the fuel pressure to be reduced by driving the pressure reducing valve.

  In particular, in the present embodiment, as the correlation parameter of the required rotation time, the engine rotation speed and the energization period (previous energization period) in the previous pressure reducing valve drive are used, and the reduced pressure flow is based on the engine rotation speed and the previous energization period. The estimated pressure value Pc * is calculated by correcting the actual rail pressure Pc at the calculation timing of Qd.

  The reason is as follows. First, for the pump rotation speed Np, the time interval (pulse width) for inputting the detection signal from the pump rotation angle sensor 20 differs according to the pump rotation speed Np, and the pulse width becomes shorter as the pump rotation speed Np is higher. For this reason, the higher the pump rotation speed Np, the shorter the time from the energization stop timing of the previous pressure reducing valve drive to the calculation timing of the reduced pressure flow Qd for the subsequent pressure reducing valve drive. For example, in FIG. 2, the time from timing t13 (pulse number θ5) to t14 (pulse number θ1) becomes shorter as the pump rotation speed Np is higher. In such a case, the higher the pump rotation speed Np, the earlier the calculation timing of the reduced pressure flow Qd comes before the completion of the pressure drop, and the time required for the pressure drop cannot be secured sufficiently. The deviation amount of the actual rail pressure Pc at the calculation timing of the reduced partial flow rate Qd with respect to the original common rail pressure is increased. For this reason, the higher the pump rotation speed Np, the larger the calculation error of the reduced pressure flow Qd.

  This will be further described with reference to FIG. In FIG. 3, when energization of the pressure reducing valve 28 is started at the rising timing t21 of the pulse number θ4, the common rail pressure is lowered after a predetermined delay time has elapsed from the energization start timing t21 due to a delay in response of the pressure accompanying the start of energization. Appears as the sensor value. Further, when the maximum duty ratio D1 is set, energization of the pressure reducing valve 28 is stopped at the pulse number immediately before the pulse number θ1, that is, the rising timing t22 of the pulse number θ5 here. In this case, due to the response delay of the pressure accompanying the end of energization of the pressure reducing valve 28, the change in the common rail pressure accompanying the end of energization does not immediately appear as a sensor value at the energization end timing t22, and the rail after a certain delay time td has elapsed. It is detected by the pressure sensor 27. That is, the actual rail pressure Pc detected by the rail pressure sensor 27 continues to decrease within the delay time td.

  After the pressure reducing valve 28 is deenergized, at the rising timing t23 of the pulse number θ1, the reduced pressure flow Qd in the next pressure reducing cycle is calculated. At this time, for example, at a predetermined low rotation speed of the pump (for example, 1,000 rpm), the energization of the pressure reducing valve 28 is stopped at timing t22. The pressure reduction by the valve drive has been completed. Therefore, the actual rail pressure Pc at the calculation timing t23 of the reduced pressure flow Qd and the actual rail pressure Pc at the next energization start timing t24 are substantially the same. On the other hand, at a predetermined high rotation speed (for example, 4,500 rpm), the pressure reduction by the previous pressure reducing valve driving is not completed at the calculation timing t23 of the next pressure reducing flow rate Qd, and the common rail pressure continues to decrease. . Therefore, the actual rail pressure Pc at the calculation timing t23 of the reduced pressure flow Qd is different from the actual rail pressure Pc at the next energization start timing t24, and the actual rail pressure Pc at the calculation timing t23 is higher by Δpn. It has become. Therefore, in this embodiment, the estimated pressure value Pc * is calculated by correcting the actual rail pressure Pc at the calculation timing of the reduced pressure partial flow Qd based on the pump rotation speed Np, and based on the estimated pressure value Pc *, The pressure reduction flow Qd for the next pressure reducing valve drive is calculated.

  Further, the pressure Δpn for the incomplete decompression at the calculation timing of the decompression flow Qd is different depending on the energization period (previous energization period) in which the decompression valve 28 is energized by the previous decompression valve drive. This is because the energization end timing is set according to the deviation ΔP with reference to the energization start timing of the pressure reducing valve 28, and therefore the pressure reduction in the subsequent pressure reducing valve drive from the energization end timing of the previous pressure reducing valve drive according to the deviation ΔP. This is because the time until the calculation timing of the partial flow rate Qd is different. This point will be described with reference to FIG. In FIG. 4, the case where the duty ratio of the previous pressure reducing valve drive is the maximum duty ratio D1 is indicated by a solid line, and the case where the duty ratio is smaller than the maximum duty ratio D1 is indicated by a one-dot chain line. In these two modes, the pump rotation speed Np is set to the same rotation speed.

  As shown in FIG. 4, the longer the previous energization period (the greater the energization duty ratio), the more the energization end timing of the pressure reducing valve 28 is, ) Further, as the energization end timing approaches the pressure reduction partial flow rate calculation timing, the pressure Δpn for the pressure reduction incomplete at the pressure reduction partial flow rate Qd calculation timing increases. Therefore, in the present embodiment, the estimated pressure value Pc * is calculated by correcting the actual rail pressure Pc at the calculation timing of the reduced pressure flow Qd based on the previous energization period, and the next value is calculated based on the estimated pressure value Pc *. The pressure reducing flow rate Qd for driving the pressure reducing valve is calculated.

  Next, the processing procedure of the common rail pressure reduction control of this embodiment will be described with reference to the flowchart of FIG. This process is executed by the microcomputer of the ECU 40 at a calculation cycle in which the period during which the pump rotating shaft 17 rotates at 180 ° C. is one cycle. Note that FIG. 5 illustrates a normal state of the fuel supply system.

  In FIG. 5, in step S101, it is determined whether or not the pump rotation position is the first rotation position, that is, whether or not it is the input timing of the detection signal of the pulse number θ1 (determination means). When step S101 becomes Yes, it progresses to step S102, the actual rail pressure Pc detected by the rail pressure sensor 27 is acquired, and deviation (DELTA) P (= Pc-Pt) of the acquired actual rail pressure Pc and the target pressure Pt. ) Is calculated. In the following step S103, it is determined whether or not the deviation ΔP is larger than 0, that is, whether or not the actual rail pressure Pc is higher than the target pressure Pt. If step S103 is No, the process proceeds to step S104, and a pump (not shown) The fuel pump 13 is driven by the driving routine.

  On the other hand, when Step S103 is Yes, it progresses to Step S105, and it is judged whether the previous pressure reducing valve drive has been carried out, that is, whether or not it is the second and subsequent pressure reducing cycles after the change of the target pressure Pt. If the previous pressure-reducing valve drive is not performed, that is, if it is the first pressure-reducing cycle after the change of the target pressure Pt, the process proceeds to step S109, and the pressure-reducing amount is reduced based on the deviation ΔP between the actual rail pressure Pc and the target pressure Pt. The flow rate Qd is calculated. On the other hand, if step S105 is Yes, that is, if the subsequent decompression drive is performed following the previous decompression valve drive, the process proceeds to step S106.

  In step S106, the pump rotation speed Np detected by the pump rotation angle sensor 20 is acquired, and the previous energization period is acquired. In step S107, the pressure correction coefficient fp is calculated based on the acquired pump rotation speed and the previous energization period. The pressure correction coefficient fp is a coefficient for correcting the actual rail pressure Pc acquired in step S102 in consideration of the pressure Δpn (see FIG. 3) of the pressure reduction incomplete pressure that has not fallen at the time of calculation of the pressure reduction flow rate Qd. In the present embodiment, it is represented by the ratio (≦ 1) of the expected pressure after the completion of the pressure reduction with respect to the actual rail pressure Pc. Regarding the pressure correction coefficient fp, in this embodiment, the relationship among the pump rotation speed Np, the previous energization period, and the pressure correction coefficient fp is determined in advance and stored as a pressure correction map.

  FIG. 6 shows an example of the pressure correction map. In the pressure correction map of FIG. 6, the higher the pump rotation speed Np or the longer the previous energization period (the greater the energization duty ratio), the lower the pressure side relative to the actual rail pressure Pc at the calculation timing of the reduced pressure flow Qd. The pressure correction coefficient fp is set to a small value so that the ratio of the correction amount to is increased.

Returning to the description of FIG. 5, in step S108, the estimated pressure value Pc * is calculated by the following equation (1) based on the acquired actual rail pressure Pc (corresponding to the pressure at the time of calculation) and the pressure correction coefficient fp. In step S109, the reduced pressure flow Qd is calculated based on the differential pressure between the estimated pressure value Pc * and the target pressure Pt (drive amount calculation means). That is, when the subsequent pressure reducing valve driving is performed following the previous pressure reducing valve driving, the pressure estimated value Pc * is used instead of the actual rail pressure Pc, and the deviation between the pressure estimated value Pc * and the target pressure Pt is used. The reduced pressure flow Qd is calculated so as to be a value corresponding to ΔP.
Pc * = Pc × fp (1)

  In the subsequent step S110, it is determined whether or not the pump rotation position has reached the second rotation position, that is, whether or not it is the rising timing of the detection signal of pulse number θ4. When step S110 becomes Yes, it progresses to step S111, calculates an energization period (energization duty ratio) based on the calculated reduced pressure flow Qd, and starts energization of the pressure reducing valve 28 at step S112 (decompression control means). . In step S113, it is determined whether or not the energization end time has come. When the energization end time is reached, the process proceeds to step S114, the energization of the pressure reducing valve 28 is terminated, and this routine is terminated.

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  In the case where the subsequent pressure reducing valve drive is performed subsequent to the previous pressure reducing valve driving, when the pump rotational position becomes the first rotational position after the power supply to the pressure reducing valve 28 in the previous pressure reducing valve drive is stopped, After the pressure reduction by the previous pressure reducing valve drive is completed based on the actual rail pressure Pc and the time required for rotation from the current stop timing of the previous pressure reducing valve drive to the timing at which the first rotation position is reached or its correlation parameter The estimated pressure value Pc * was calculated as the common rail pressure. Further, based on the calculated pressure estimated value Pc *, a pressure reducing valve drive amount in the subsequent pressure reducing valve drive is calculated, and on the basis of the pressure reducing valve drive amount, after the pressure reduction by the previous pressure reducing valve drive is completed, The pressure reducing valve is driven. According to such a configuration, even when the pressure reduction by the previous pressure reducing valve drive is not completed at the time of calculating the pressure reducing valve drive amount in the subsequent pressure reducing valve drive, the pressure reducing valve drive for the subsequent pressure reducing valve drive is completed. The amount can be calculated accurately. Moreover, the controllability of the common rail pressure can be enhanced by driving the pressure reducing valve 28 using the pressure reducing valve drive amount calculated as described above.

  The pump rotational speed Np is included as a parameter correlated with the required rotation time, and the estimated pressure value Pc * is calculated by correcting the actual rail pressure Pc at the calculation timing based on the pump rotational speed. Since the pulse width of the detection signal of the rail pressure sensor 27 varies depending on the pump rotation speed, the time from the previous depressurization valve drive energization stop timing to the subsequent depressurization valve drive drive amount calculation timing also differs. Therefore, by adopting the above-described configuration, it is possible to accurately calculate the drive amount of the pressure reducing valve regardless of the pump rotation speed, and to improve the controllability of the common rail pressure.

  The estimated current value Pc * is calculated by correcting the actual rail pressure Pc at the calculation timing based on the previous energization period as a parameter correlated with the required rotation time. The longer the previous energization period is, the closer the energization end timing of the previous pressure reducing valve drive approaches the timing for calculating the drive amount of the subsequent pressure reducing valve drive. The time until the drive amount calculation timing is shortened. Therefore, with the above-described configuration, the pressure reducing valve drive amount can be accurately calculated regardless of the length of the previous energization period, and as a result, the controllability of the common rail pressure can be improved.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  In the above embodiment, the energization end timing is variably set based on the energization start timing of the pressure reducing valve 28. However, the present invention is configured to variably set the energization start timing based on the energization end timing of the pressure reducing valve 28. Can also be applied. Even in the configuration in which the energization start timing is variably set based on the energization end timing of the pressure reducing valve 28, the required rotation time from the previous deenergization driving timing of the pressure reducing valve drive to the timing when the pump rotational position becomes the first rotational position. Accordingly, the incomplete amount of pressure reduction by the previous pressure reducing valve drive is different at the timing when the first rotational position is reached. Specifically, for example, based on the pump rotation speed Np, the pressure estimation value Pc * is calculated by correcting the calculation-time pressure that is the actual rail pressure Pc at the calculation timing of the reduced pressure partial flow Qd, and the pressure estimation value The pressure reducing valve 28 is driven using Pc *.

  In the above embodiment, the pressure reducing valve drive amount calculated at the predetermined calculation position (first rotation position) is the reduced pressure flow Qd as the fuel flow rate leaking from the common rail 26. However, the pressure reducing valve drive amount is the reduced pressure flow rate. Other than Qd, for example, the energization period or the energization duty ratio of the pressure reducing valve 28 may be used.

  In the above embodiment, the pump rotation shaft 17 rotates with the rotation of the crankshaft 16. Therefore, instead of the configuration in which the pressure reducing valve 28 is driven in synchronization with the rotational position of the pump rotation shaft 17 based on the detection signal output from the pump rotation angle sensor 20, the detection signal output from the crank angle sensor 41 is used. The pressure reducing valve 28 may be driven. In other words, the pressure reducing valve 28 may be driven in synchronization with the rotational position of the crankshaft 16, and as a result, the pressure reducing valve 28 may be driven in synchronization with the rotational position of the pump rotating shaft 17. In this case, instead of the pressure correction map of FIG. 6, the relationship among the engine speed Ne, the previous energization period, and the pressure correction coefficient fp is determined in advance and stored as a pressure correction map. In the pressure correction map in this configuration, the higher the engine speed Ne or the longer the previous energization period (the greater the energization duty ratio), the greater the ratio of the correction amount to the reduced pressure side with respect to the actual rail pressure Pc. Thus, the pressure correction coefficient fp is set to a small value.

  In the above embodiment, the pressure detecting means for detecting the fuel pressure in the common rail 26 is provided with the rail pressure sensor 27 provided on the common rail 26. However, the pressure detecting means is not limited to this, for example, an injector The pressure sensor provided in 31 may be provided, and the pressure-reducing valve 28 may be driven based on the pressure value detected by the pressure sensor.

  In the above embodiment, the pump rotation speed Np and the previous energization time are used as the correlation parameters of the required rotation time from the timing when the depressurization valve 28 is energized to the timing when the pressure is reduced to the first rotation position. Based on the above, the calculation-time pressure, which is the actual rail pressure Pc at the first rotational position, is corrected. Instead of this, it may be configured to actually measure the time required from the timing of stopping energization of the pressure reducing valve 28 to the timing when the first rotational position is reached, and to correct the calculated pressure based on the measured time.

  In the case where the actual rail pressure Pc is reduced to the target pressure Pt by repeating the decompression cycle, the number of repetitions of the decompression cycle may be a plurality of times. That is, for example, the present invention may be applied when the actual rail pressure Pc is reduced to the target pressure Pt by executing the pressure reducing cycle twice, and the actual rail pressure Pc is set to the target pressure by executing the pressure reducing cycle three times or more. The present invention may be applied in the case of decreasing to Pt.

  In the above embodiment, instead of the configuration in which the estimated pressure value Pc * is calculated using a map that defines the relationship between the previous energization period (energization duty ratio) and the pressure correction coefficient fp, the energization end timing and the pressure correction coefficient fp The pressure estimated value Pc * may be calculated using a map that defines the relationship between

  The rotation angle sensor may be other than the electromagnetic pickup type as long as it outputs an angle signal at a predetermined interval as the output shaft rotates, and may be a Hall element type, photoelectric type sensor or the like.

  The present invention can be applied to a vehicle other than a common rail fuel injection system for a diesel engine. For example, the present invention can be applied to a pressure accumulation type fuel injection system of a direct injection type gasoline engine. It can also be applied to engines other than those for vehicles.

  DESCRIPTION OF SYMBOLS 13 ... Fuel pump, 15 ... Engine, 17 ... Pump rotating shaft, 20 ... Pump rotation angle sensor, 26 ... Common rail (accumulation piping), 27 ... Rail pressure sensor (pressure detection means), 28 ... Pressure reducing valve, 31 ... Injector ( (Fuel injection valve), 40... ECU (determination means, drive amount calculation means, decompression control means), 41... Crank angle sensor.

Claims (5)

Fuel for an engine (15) comprising a pressure accumulating pipe (26) for accumulating high-pressure fuel discharged from the fuel pump (13) and a pressure reducing valve (28) for opening the valve when energized to leak fuel in the pressure accumulating pipe A fuel pressure control device that is applied to a supply system and that controls the drive of the pressure reducing valve in synchronization with the rotational position of the rotary shaft (17) of the fuel pump to reduce the fuel pressure in the pressure accumulating pipe;
Pressure detecting means for detecting fuel pressure in the pressure accumulating pipe;
In the case where the subsequent pressure reducing valve drive is performed following the previous pressure reducing valve driving, after the power supply to the pressure reducing valve in the previous pressure reducing valve drive is stopped, the rotational position of the pressure reducing valve in the subsequent pressure reducing valve drive is Determination means for determining whether or not a predetermined calculation position for calculating a driving amount has been reached;
When it is determined by the determination means that the calculated position is reached, the calculated pressure that is the fuel pressure detected by the pressure detecting means at the timing when the calculated position is reached, and the energization stop timing of the previous pressure reducing valve drive Based on the required rotation time from the time when the calculation position is reached or its correlation parameter, a pressure estimation value that is the fuel pressure after the pressure reduction by the previous pressure reducing valve drive is completed is calculated, Drive amount calculation means for calculating the drive amount in the subsequent pressure reducing valve drive based on the estimated pressure value;
Pressure reducing control means for performing the subsequent pressure reducing valve driving based on the driving amount calculated by the driving amount calculating means after the pressure reducing by the previous pressure reducing valve driving is completed;
A fuel pressure control device comprising: Including the pump rotation speed which is the rotation speed of the rotating shaft as the correlation parameter;
2. The fuel pressure control device according to claim 1, wherein the drive amount calculation unit calculates the pressure estimated value by correcting the calculation-time pressure based on the pump rotation speed.   3. The fuel pressure control according to claim 2, wherein the drive amount calculation means calculates the pressure estimated value such that the higher the pump rotation speed, the larger the ratio of the correction amount to the pressure reduction side with respect to the calculated pressure. apparatus. The timing at which the rotational position becomes a predetermined start position is the energization start timing of the pressure reducing valve,
Means for variably setting the energization end timing of the pressure reducing valve based on the start position according to the deviation between the fuel pressure in the pressure accumulating pipe and the target value;
As the correlation parameter, including a previous energization period that is a rotation angle period in which the pressure reducing valve is energized in the previous pressure reducing valve drive,
4. The fuel pressure control device according to claim 1, wherein the drive amount calculation unit calculates the pressure estimated value by correcting the calculation-time pressure based on the previous energization period. 5.   5. The fuel pressure control according to claim 4, wherein the drive amount calculation unit calculates the pressure estimation value such that the ratio of the correction amount to the pressure reduction side with respect to the calculated pressure increases as the previous energization period increases. apparatus.

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