JP4281825B2 - Fuel pressure control device for high pressure fuel injection system - Google Patents

Description

  The present invention relates to a fuel pressure control device for a high-pressure fuel injection system in which the fuel pressure in an accumulator pipe for supplying high-pressure fuel to the fuel injection valve is lowered by opening a relief valve provided in the accumulator pipe. About.

  In general, in an internal combustion engine having a pressure accumulating pipe such as a common rail, high pressure fuel is pumped from a fuel pump to the pressure accumulating pipe, and fuel is injected into the engine combustion chamber from a fuel injection valve connected to the pressure accumulating pipe. ing.

  The fuel pressure in the pressure accumulating pipe, in other words, the fuel injection pressure of the fuel injection valve is controlled to be a pressure corresponding to the engine operating state. In such fuel pressure control, for example, when the fuel pressure in the accumulator pipe detected by a pressure sensor or the like is lower than the target fuel pressure set according to the engine operating state, the fuel pumping amount of the fuel pump is increased and the reverse When the detected fuel pressure is higher than the target fuel pressure, the fuel pressure in the pressure accumulation pipe is controlled in such a manner that the fuel pumping amount of the fuel pump is decreased or the fuel pumping is stopped. By executing such fuel pressure control, the spray particle size of the injected fuel is adapted to the engine combustion state.

  However, if the target fuel pressure suddenly drops, such as when the engine operating state shifts from a high load operation to a low load operation within a short time, the fuel pumping by the fuel pump is limited or stopped. Even so, a predetermined time is required until the fuel pressure in the pressure accumulating pipe decreases to the target fuel pressure. In such a case, even temporarily, the fuel injection is executed based on the excessive fuel injection pressure, which may increase the combustion noise due to excessive atomization of the injected fuel. .

Therefore, conventionally, as described in Patent Document 1, for example, a pressure regulator (relief valve) attached to a common rail is configured with an electromagnetic valve that can be opened and closed, and the fuel pressure in the common rail is higher than the target fuel pressure. Sometimes, the relief valve is driven to open and discharge the fuel in the common rail to reduce the fuel pressure. By performing such pressure reduction processing, the difference between the fuel pressure and the target fuel pressure is quickly reduced, and it is also preferable to increase combustion noise due to fuel injection being executed based on an excessive fuel injection pressure. It will be suppressed.
Japanese Patent Laid-Open No. 10-54318

  However, the fuel pressure reduction process using such a relief valve is suitable for surely reducing the fuel pressure, but it adversely affects fuel injection, fuel pump fuel pump detection, or fuel pressure detection. There is a concern. For example, if fuel injection is executed during this decompression process, the fuel injection pressure changes greatly during fuel injection, and the fuel injection amount and injection rate also change with the change. Deterioration of control accuracy is unavoidable.

  The present invention has been made in view of such conventional circumstances, and an object of the present invention is to provide a high-pressure fuel injection capable of reliably reducing the fuel pressure in the pressure accumulating pipe while avoiding an adverse effect on the high-pressure fuel injection system. An object of the present invention is to provide a system fuel pressure control device.

In the following, means for achieving the above object and its effects are described.
In the first aspect of the present invention, the fuel supplied from the fuel pump is accumulated at a high pressure, and the pressure accumulation pipe that supplies the accumulated fuel to the fuel injection valve is provided in the pressure accumulation pipe. A relief valve that discharges fuel based on the valve opening operation, a fuel pressure in the pressure accumulating pipe is detected, and the relief valve is turned on in response to a pressure reduction request based on a comparison between the detected fuel pressure and the target pressure. A fuel pressure control device for a high-pressure fuel injection system comprising a fuel pressure control means for reducing the fuel pressure by opening the valve, wherein the fuel pressure control means is configured to supply fuel pressure to the fuel pump during the valve opening period of the relief valve. The relief valve is driven to open so as not to overlap the period.

  When the fuel pressure in the accumulator pipe is extremely higher than the target pressure, the fuel pump stops the fuel pumping, and the fuel pressure in the accumulator pipe is reduced by both the fuel discharge and the fuel injection by opening the relief valve. This is desirable in order to reduce the fuel pressure to the target pressure in a shorter time. On the other hand, when the fuel pressure in the pressure accumulation pipe is higher than the target pressure but the difference between the two is not so large, similarly, if the fuel pumping by the fuel pump is stopped, the fuel pressure in the pressure accumulation pipe becomes the target pressure. There is a concern that the pressure is suddenly reduced to below the pressure.

  Therefore, when the difference between the fuel pressure in the accumulator piping and the target pressure is not so large, the steady decrease in fuel pressure due to fuel injection etc. is offset by the increase in fuel pressure due to fuel pump fuel pumping. The difference between the fuel pressure in the pressure accumulating pipe and the target pressure is reduced by reducing the pressure by opening the relief valve, so that the fuel pressure can be controlled more stably.

  However, in such a case, if fuel pumping by the fuel pump and fuel discharging by opening the relief valve are performed at the same time, they will interfere with each other, and these fuel pressure pumping and discharging are performed separately. There is a possibility that the fuel pressure may be controlled to a value different from the case where it is performed.

  In this respect, according to the configuration of the invention described in claim 1, the fuel pressure in the pressure accumulating pipe can be avoided without adversely affecting the fuel pumping of the fuel pump by avoiding the mutual interference between the fuel pumping and the discharge. Can be reliably decompressed.

  According to a second aspect of the present invention, in the fuel pressure control device for a high pressure fuel injection system according to the first aspect, the fuel pressure control means sets a valve opening period of the relief valve based on the pressure reduction request. Determining whether the set valve opening period and the fuel pump fuel pumping period overlap, and when it is determined that they overlap, the relief valve opening period is overlapped with the fuel pump fuel pumping period. It is said that it is restricted so as not to become.

  According to such a configuration, it is possible to secure the relief valve opening period to the maximum within a range that does not overlap the fuel pumping period of the fuel pump. Therefore, in addition to the function and effect of the first aspect of the invention, the fuel pressure in the pressure accumulating pipe can be further reliably reduced.

  According to a third aspect of the present invention, in the fuel pressure control device for a high pressure fuel injection system according to the second aspect, the fuel pressure control means sets the valve opening period of the relief valve based on the pressure reduction request. The valve opening period is set in accordance with the magnitude of the differential pressure between the detected fuel pressure and its target pressure.

  According to such a configuration, in addition to the operational effect of the invention described in claim 2, the fuel pressure in the pressure accumulating pipe is reduced by an amount corresponding to the magnitude of the differential pressure between the detected actual fuel pressure and the target pressure. Therefore, more appropriate pressure reduction can be performed.

Hereinafter, an embodiment in which the present invention is applied to a control device that controls fuel pressure in a common rail provided in a diesel engine will be described.
FIG. 1 shows a schematic configuration of a four-cylinder direct injection diesel engine (hereinafter simply referred to as “engine”) 10 and its high-pressure fuel injection system according to the present embodiment.

  As shown in the figure, the high-pressure fuel injection system includes an injector 12 provided corresponding to each cylinder # 1 to # 4 of the engine 10, a common rail 20 to which the injectors 12 are connected, and a fuel tank 14 A fuel pump 30 that pumps the fuel to the common rail 20 and an electronic control unit (hereinafter referred to as “ECU”) 60 are provided.

  The common rail 20 has a function of accumulating the fuel supplied from the fuel pump 30 to a predetermined pressure, and the fuel injection pressure of the injector 12 is determined based on the internal fuel pressure (rail pressure).

  A relief valve 22 is attached to the common rail 20. The relief valve 22 is a normally closed solenoid valve that is energized and driven by the ECU 60 and is connected to the fuel tank 14 via the relief passage 21. When the relief valve 22 is opened, the fuel in the common rail 20 is discharged to the relief passage 21 and returned to the fuel tank 14 through the relief passage 21. In this way, the rail pressure decreases according to the amount of fuel discharged from the common rail 20, and the decrease amount is adjusted according to the length of the valve opening period of the relief valve 22.

  The injector 12 is an electromagnetic valve that is opened and closed by the ECU 60, and injects fuel supplied from the common rail 20 into the combustion chambers (not shown) of the cylinders # 1 to # 4. Each injector 12 is also connected to the fuel tank 14 via a relief passage 21, and the fuel leaked into the injector 12 is returned to the fuel tank 14 through the relief passage 21.

  The ECU 60 executes control related to the fuel pumping amount of the fuel pump 30, the fuel injection timing of the injector 12, and the fuel injection amount. The ECU 60 drives a memory 64 in which various control programs, function data, and the like are stored, a CPU 62 that executes various arithmetic processes, and an energization signal generated based on power supplied from the battery 59 to the injector 12 and the like. It comprises a plurality of drivers 63 and the like.

  The ECU 60 is connected to various sensors for detecting the operating state of the engine 10, the fuel pressure in the common rail 20, and the like, and detection signals are respectively input from these sensors.

  For example, a rotation speed sensor 65 is provided in the vicinity of the crankshaft (not shown) of the engine 10, and a cylinder discrimination sensor 66 is provided in the vicinity of the camshaft (not shown). The ECU 60 calculates the rotational speed of the crankshaft (engine rotational speed NE) and the rotational angle of the crankshaft (crank angle CA) based on the detection signals input from these sensors 65 and 66, respectively.

  An accelerator sensor 67 is provided in the vicinity of an accelerator pedal (not shown), and a detection signal corresponding to the amount of depression of the accelerator pedal (accelerator opening) is output from the accelerator sensor 67. A fuel pressure sensor 68 is provided on the common rail 20, and a detection signal corresponding to the rail pressure (actual fuel pressure PCR) is output from the fuel pressure sensor 68. A cylinder block (not shown) of the engine 10 is provided with a water temperature sensor 69 from which a detection signal corresponding to the temperature of the engine cooling water (cooling water temperature) is output. The ECU 60 detects the accelerator opening, the actual fuel pressure PCR, and the cooling water temperature based on the detection signals from these sensors 67 to 69, respectively.

  The fuel pump 30 is driven by a drive shaft 40 that is rotated by the crankshaft of the engine 10, a feed pump 31 that operates based on the rotation of the drive shaft 40, and a pair of cams that are formed on the drive shaft 40. Supply pumps (first supply pump 50a and second supply pump 50b) are provided.

  The feed pump 31 sucks the fuel in the fuel tank 14 from the suction port 34 through the suction passage 24 and supplies the fuel to the first supply pump 50a and the second supply pump 50b with a predetermined feed pressure. Thus, of the fuel sucked from the suction port 34, surplus fuel that is not supplied to any of the supply pumps 50a and 50b is returned from the relief port 36 to the fuel tank 14 through the relief passage 21.

  Both the first supply pump 50a and the second supply pump 50b are so-called inner cam pumps, and the fuel supplied from the feed pump 31 is further pressurized (for example, 25 based on the reciprocation of a plunger (not shown)). To 180 MPa), and the pressurized fuel is pumped from the discharge port 38 to the common rail 20 through the discharge passage 23.

The fuel pump 30 is provided with a first adjustment valve 70a and a second adjustment valve 70b for adjusting the fuel pumping amount of each of the supply pumps 50a and 50b.
Each of these regulating valves 70a and 70b is a normally closed electromagnetic valve that is energized and driven by the ECU 60 to open.

FIG. 2 is a timing chart showing the fuel suction / pumping timing in each of the supply pumps 50a, 50b, the rail pressure change mode in the steady state, and the like.
As shown in the figure, the intake of fuel in each of the supply pumps 50a and 50b is alternately performed in a state where the phase of the crank angle CA is shifted by 180 ° CA (CA: Crank Angle) for each of the pumps 50a and 50b. Yes. Similarly, the fuel pumps of the supply pumps 50a and 50b are alternately performed with the phases shifted by 180 ° CA (CA: Crank Angle).

  As shown in FIG. 5B, the first regulating valve 70a opens during the intake stroke of the first supply pump 50a to start the intake of fuel, while at a predetermined time (crank angle CA). The valve is closed and the intake of the fuel is stopped. All of the fuel sucked in this way is pressurized in the pumping stroke following the suction stroke, and pumped to the common rail 20 from the first supply pump 50a.

Thus, the fuel pumping amount of the first supply pump 50a is adjusted by changing the valve opening period of the first regulating valve 70a.
For example, as indicated by the arrows in FIGS. 5B and 5C, when the valve closing time of the first regulating valve 70a is delayed (retarded) to increase the valve opening period, the first supply pump The fuel intake amount of 50a increases. In addition, when the valve closing timing of the first regulating valve 70a is retarded in this way, the start timing of fuel pumping in the first supply pump 50a is advanced by an amount equal to the retard amount. As a result, the fuel pumping period becomes longer, and the fuel pumping amount of the first supply pump 50a increases.

  Conversely, if the valve closing period of the first adjustment valve 70a is advanced (advanced) to decrease the valve opening period, the fuel intake amount of the first supply pump 50a decreases. Further, when the closing timing of the first regulating valve 70a is advanced as described above, the start timing (crank angle CA) of fuel pumping in the first supply pump 50a is delayed by an amount equal to the advance amount. Is done. As a result, the fuel pumping period is shortened and the fuel pumping amount of the first supply pump 50a is decreased.

Note that, as described above, the fuel supply start timing of the first supply pump 50a can be uniquely determined based on the valve closing timing of the first adjustment valve 70a.
Similarly, with respect to the second supply pump 50b, the fuel pumping amount can be increased or decreased by retarding or advancing the closing timing of the second regulating valve 70b. The start timing (crank angle CA) can also be uniquely determined based on the valve closing timing of the second adjustment valve 70b.

  Incidentally, the valve opening timing and the valve closing timing of each of the regulating valves 70a and 70b are both defined with the crank angle as a unit, and the valve closing timing is set as a relative crank angle based on the valve opening timing. . For example, when stopping fuel pumping by the supply pumps 50a and 50b, the valve closing timing is set to “0 ° CA”, and the regulating valves 70a and 70b are held in the closed state during the intake stroke. Become so. On the other hand, when the fuel pumping amount is set to the maximum, the valve closing timing is set to “180 ° CA” corresponding to the crank angle change amount during the intake stroke, and each of the adjustment valves 70a and 70b is in the same intake stroke. The valve is always kept open.

  Further, the valve closing timing of each of the regulating valves 70a and 70b is set based on the rail pressure, the target fuel pressure, and the like each time fuel is sucked by the supply pumps 50a and 50b. Hereinafter, the procedure for setting the valve closing timing will be described with reference to the flowchart shown in FIG.

The ECU 60 executes an “adjustment valve drive timing calculation routine” shown in the figure as an interrupt process for each predetermined crank angle (every 180 ° CA).
In step 110 of this routine, the ECU 60 detects the actual fuel pressure PCR based on the detection signal from the fuel pressure sensor 68. The actual fuel pressure PCR detection timing, that is, the interrupt timing (angle) of this routine, as shown in FIG. 2 (g), is the timing (crank) after the fuel pumping of each supply pump 50a, 50b is completed. For example, the angle CA is set to a time when the angles CAA0 to CAA5 shown in FIG.

Next, in step 120, the ECU 60 calculates a target fuel pressure PCRTRG based on the fuel injection amount and the engine speed NE.
The relationship between the target fuel pressure PCRTRG, the fuel injection amount, and the engine rotational speed NE is obtained in advance by experiments so that the spray particle size of the injected fuel is adapted to the engine combustion state, and is stored in the memory 64 of the ECU 60. It is stored as function data for calculating the fuel pressure PCRTRG. The fuel injection amount is a value that is calculated based on the accelerator opening, the engine speed NE, and the like and stored in the memory 64 in a routine different from this routine.

  In step 130, the actual fuel pressure PCR is subtracted from the target fuel pressure PCRTRG, and the subtraction value (PCRTRG-PCR) is set as a deviation ΔPCR. In step 140, the basic valve closing angle ANGBASE is calculated based on the fuel injection amount, the actual fuel pressure PCR, and the engine speed NE.

  This basic valve closing angle ANGBASE is required when the fuel pump 30 is in a steady operation, that is, when the rail pressure is substantially equal to the target fuel pressure PCRTRG and the target fuel pressure PCRTRG is held substantially constant. It is determined based on the fuel pumping amount. The relationship between the basic valve closing angle ANGBASE and the fuel injection amount is stored in the memory 64 as function data for calculating the basic valve closing angle ANGBASE.

Next, the ECU 60 calculates the final valve closing timing (final valve closing angle ANGFIN) of each of the regulating valves 70a and 70b based on the following equation (1) in step 150.

ANGFIN = ANGBASE + Kp · ΔPCR (1)

Here, “Kp · ΔPCR” is a feedback correction term, and “Kp” is a proportional gain. As apparent from the above equation (1), when the target fuel pressure PCRTRG is larger than the actual fuel pressure PCR (ΔPCR> 0), the final valve closing angle ANGFIN is set relatively large, and conversely, the target fuel pressure When the pressure PCRTRG is smaller than the actual fuel pressure PCR (ΔPCR <0), the final valve closing angle ANGFIN is set to be relatively small.

  After calculating the final valve closing angle ANGFIN in this way, in steps 160 to 190, the final valve closing angle ANGFIN is compared with its upper limit set value “180 ° CA” and lower limit set value “0 ° CA”. If necessary, correct the final valve closing angle ANGFIN. That is, when the final valve closing angle ANGFIN exceeds “180 ° CA” (step 160: YES), the final valve closing angle ANGFIN is set equal to “180 ° CA” (step 170). If it is below “0 ° CA” (step 180: YES), the final valve closing angle ANGFIN is set equal to “0 ° CA” (step 190). Thereafter, the ECU 60 once ends this processing routine.

  Then, in a routine different from this routine, the ECU 60 alternately outputs an energization signal based on the final valve closing angle ANGFIN to the respective adjustment valves 70a and 70b via the driver 63, whereby the fuel of the fuel pump 30 is obtained. The rail pressure is controlled by adjusting the pumping amount.

  Further, the ECU 60 adjusts the fuel pumping amount of the fuel pump 30 as described above to control the rail pressure so that it matches the target fuel pressure PCRTRG, while the target fuel pressure PCRTRG rapidly decreases and the rail When the pressure cannot follow the decrease, a process of reducing the rail pressure by opening the relief valve 22 for a predetermined time (hereinafter referred to as “decompression process”) is executed.

Hereinafter, such a decompression process will be described with reference to FIGS.
FIG. 4 is a flowchart showing the processing contents of the “relief valve drive timing setting routine”, and FIG. 5 shows an energization signal output from the driver 63 of the ECU 60 to the relief valve 22, the open / close state of the relief valve 22 based on this energization signal, and the like. It is a timing chart which shows. FIG. 6 is a flowchart showing the processing contents of the “relief valve drive control routine”.

As shown in FIG. 5A, the energization signal output to the relief valve 22 is
The crank angle CA after a predetermined angle α from the detected angle of the actual fuel pressure PCR (for example, each angle of CAA1 to CAA3 shown in the figure) is set as a reference angle, and the crank angle CA is the reference angle (for example, CAB1, shown in the figure). Time from when each angle of CAB2 is reached to when energization of the relief valve 22 is started (non-energization time TCLOSE)
-Time from when energization to the relief valve 22 is started to when it is stopped (energization time TOPEN)
Are defined based on two parameters such as

  The relief valve 22 opens and closes based on this energization signal, but the opening and closing timing thereof does not completely coincide with the start timing and stop timing of energization of the valve 22, as shown in FIG. Then, it opens and closes after the elapse of predetermined response delay times ΔT1 and T2 from the start time and stop time of energization, respectively.

  Here, the non-energization time TCLOSE considers such a response delay of the relief valve 22, and the crank angle CA at which the relief valve 22 is actually opened is a predetermined angle β after the reference angle (CAB1, CAB2). Is set to coincide with the crank angle CA (for example, each angle of CAC1 and CAC2 shown in the figure, hereinafter referred to as “actual valve opening angle”).

  Further, the actual valve opening angles (CAC1, CAC2) are set in advance so that they are always later than the end timing of the fuel injection even when the fuel injection timing by the injector 12 is changed according to the engine operating state. Has been. Therefore, the fuel injection is always finished when the relief valve 22 is opened.

  On the other hand, the energization time TOPEN sets the valve opening time of the relief valve 22. By opening the relief valve 22 for a time equal to the energization time TOPEN, the actual fuel pressure PCR is reduced to the target fuel pressure PCRTRG. The pressure is set based on the differential pressure between the actual fuel pressure PCR and the target fuel pressure PCRTRG so that the pressure can be reduced.

Hereinafter, a detailed procedure for setting the non-energization time TCLOSE and the energization time TOPEN will be described with reference to FIGS. 4, 5, and 7.
The “relief valve drive timing setting routine” shown in FIG. 4 is executed by the ECU 60 after the completion of the “regulated valve drive timing calculation routine” as an interrupt process for each predetermined crank angle (every 180 ° CA).

  First, in step 210, the ECU 60 adds a predetermined value ΔP1 to the target fuel pressure PCRTRG, and executes a pressure reduction process whether or not the actual fuel pressure PCR is higher than the added value (PCRTRG + ΔP1). Determine if it is necessary.

  Here, if the pressure reduction process is executed even when the differential pressure (PCR-PCRTRG) between the actual fuel pressure PCR and the target fuel pressure PCRTRG is not so large, the rail pressure is increased as the relief valve 22 is opened. There is a concern of causing a so-called overshoot phenomenon that further decreases beyond the target fuel pressure PCRTRG.

  Accordingly, when the difference between the actual fuel pressure PCR and the target fuel pressure PCRTRG is not so large and the increase in combustion noise is in a negligible range, the fuel pump 30 is controlled while reducing the fuel pumping amount based on feedback control. Injecting or so-called ineffective injection, that is, by driving the injector 12 within the ineffective injection period and discharging the fuel in the common rail 20 to the relief passage 21 through the inside of the injector 12, the rail pressure is gradually reduced. It can be said that it is preferable to suppress the occurrence of the overshoot phenomenon.

  From this point of view, the predetermined value ΔP1 is set to a sufficiently large value within a range where combustion noise is not increased, and is set as a suitable value for suppressing the occurrence of the overshoot phenomenon.

If it is determined in step 210 that the decompression process is unnecessary, the energization time TOPEN is set to “0” in step 245, and the process of this routine is once ended.
On the other hand, if it is determined in step 210 that the pressure reducing process is necessary, in step 220, the ECU 60 calculates the non-energization time TCLOSE based on the response delay time ΔT1 of the relief valve 22 and the engine speed NE.

  For example, here, as the engine rotational speed NE increases, the time until the crank angle CA reaches the actual opening angle (CAC1, CAC2) of the relief valve 22 from the reference angle (CAB1, CAB2) becomes shorter. The energization time TCLOSE is set relatively short. The response delay time ΔT1 is obtained in advance as a response characteristic of the relief valve 22 based on experiments or the like, and is stored in the memory 64 as non-energization time TCLOSE calculation data.

  By the way, the fuel suction of each of the supply pumps 50a and 50b starts immediately after the crank angle CA becomes equal to the detected angle (CAA1 to CAA3) of the actual fuel pressure PCR (see FIG. 2). Under such a condition (PCR> PCRTRG + ΔP1), the fuel intake always ends before the crank angle CA reaches the reference angle (CAB1, CAB2). That is, the predetermined value ΔP1 and the reference angles (CAB1, CAB2) are set so as to satisfy such a relationship.

  Therefore, in step 220, even when the non-energization time TCLOSE is set to be the shortest and the energization start timing for the relief valve 22 is set to the earliest time, the adjustment valves 70a and 70b are energized. The energization of the relief valve 22 is never started.

  Incidentally, when the relationship (PCR ≦ PCRTRG + ΔP1) is established with respect to the actual fuel pressure PCR and the target fuel pressure PCRTRG, the final closing is performed as compared with the case where the relationship (PCR> PCRTRG + ΔP1) is established. Since the valve angle ANGFIN is set to be relatively large, the fuel suction in each of the supply pumps 50a and 50b is continuously executed even after the crank angle CA reaches the reference angle (CAB1, CAB2). However, in such a case, the depressurization process is not executed in the first place, so that the energization of the relief valve 22 is not started when the regulating valves 70a and 70b are energized.

  Next, in step 230, the ECU 60 calculates a pressure reduction speed K (> 0). When the relief valve 22 is opened, the fuel in the common rail 20 is discharged, so that the rail pressure is reduced. However, the speed at the time of the reduction is not constant and varies depending on the magnitude of the rail pressure. That is, as shown in FIG. 7, the speed at which the rail pressure decreases (the slope of the alternate long and short dash line in FIG. 7) tends to decrease as the rail pressure decreases. The pressure reduction speed K corresponds to the speed at which the rail pressure decreases, and is calculated based on the actual fuel pressure PCR. The relationship between the decompression speed K and the actual fuel pressure PCR is obtained in advance by experiments or the like and stored in the memory 64 as decompression speed K calculation data.

In step 240, the ECU 60 calculates the energization time TOPEN based on the following equation (2).

TOPEN = K · (PCR-PCRTRG) (2)

As is clear from the pressure reduction characteristics of the rail pressure shown in the above equation (2) and FIG. 7, if the rail pressure (actual fuel pressure PCR) when the relief valve 22 is opened is the same, the actual fuel pressure PCR and the target fuel As the differential pressure (PCR-PCRTRG) with respect to the pressure PCRTRG increases, the energization time TOPEN is set to be relatively long. If the differential pressure (PCR-PCRTRG) is the same, the rail pressure (actual The lower the fuel pressure PCR), the longer the energization time TOPEN is set.

  Here, the fuel pumping in each of the supply pumps 50a and 50b is performed immediately before the crank angle CA becomes equal to the detected angle (CAA1 to CAA3) of the actual fuel pressure PCR (see FIG. 2). The timing is changed to a retarded timing as the differential pressure (PCR-PCRTRG) between the actual fuel pressure PCR and the target fuel pressure PCRTRG increases. Therefore, when the energization time TOPEN is set to be relatively long, the fuel pumping periods of the supply pumps 50a and 50b are set to be relatively short. For this reason, the fuel pumping period of each of the supply pumps 50a and 50b and the valve opening period of the relief valve 22 do not overlap each other, and the fuel pumping by each of the supply pumps 50a and 50b and the fuel discharge due to the opening of the relief valve 22 are It takes place at different times.

  After calculating the energization time TOPEN in this way, in step 250, the ECU 60 calculates the maximum value TOPENMAX of the energization time TOPEN based on the response delay time ΔT2 (see FIG. 5) of the relief valve 22 and the engine speed NE.

  Here, the maximum value TOPENMAX is the maximum value of the energization time TOPEN on condition that the relief valve 22 is closed before the crank angle CA reaches the detection angle (CAA1 to CAA3) of the actual fuel pressure PCR. Incidentally, the maximum value TOPENMAX changes according to the engine speed NE, and is set shorter as the engine speed NE becomes higher.

  In step 260, the energization time TOPEN is compared with the maximum value TOPENMAX. If it is determined that the energization time TOPEN is greater than the maximum value TOPENMAX, the energization time TOPEN is set equal to the maximum value TOPENMAX in step 270.

  By limiting the energization time TOPEN to the maximum value TOPENMAX or less in this way, the relief valve 22 is always closed when the actual fuel pressure PCR is detected, and the detection timing of the actual fuel pressure PCR and the relief valve 22 are detected. The valve opening period will not overlap.

  Further, since the fuel injection by the injector 12 is always started after the actual fuel pressure PCR is detected, the relief valve 22 is always closed at the start timing of the fuel injection. Therefore, as described above, in consideration of the fact that the actual opening angle (CAC1, CAC2) of the relief valve 22 is always set to a time delayed from the fuel injection end time, the fuel injection period, that is, the injector 12 Both the valve opening period and the valve opening period of the relief valve 22 do not overlap.

  Further, the fuel suction of each of the supply pumps 50a and 50b is always started immediately after the actual fuel pressure PCR is detected, and the energization to the relief valve 22 is always ended when the actual fuel pressure PCR is detected. Therefore, the energization of the regulating valves 70a and 70b is started after the energization of the relief valve 22 is stopped. Therefore, as described above, considering that the energization of the relief valve 22 is not started during the energization of the regulating valves 70a and 70b, the energizing periods of the regulating valves 70a and 70b and the relief valve 22 do not overlap. Become.

  After executing the process of step 270 or when it is determined in step 260 that the energization time TOPEN is less than or equal to the maximum value TOPENMAX, the ECU 60 once ends the process of this routine.

Next, the processing of the “relief valve drive control routine” will be described with reference to the flowchart of FIG.
This routine is executed by the ECU 60 as an interrupt process for each predetermined crank angle (every 180 ° CA). The interrupt timing (angle) is set to the reference angle (CAB1, CAB2).

  First, in step 310, the ECU 60 determines whether or not the engine is stopped. Here, when the fuel injection is stopped in a state where the ignition switch of the engine 10 is operated to “OFF”, or when the engine speed NE is reduced to a predetermined speed or less, the engine is stopped. To be judged.

  If it is determined that the engine is not stopped, the ECU 60 generates an energization signal based on the non-energization time TCLOSE and the energization time TOPEN in step 320 and outputs it to the relief valve 22 via the driver 63.

  On the other hand, if it is determined in step 310 that the engine is stopped, in step 325, the relief valve 22 is energized and opened for a predetermined time. The valve opening time here is determined in advance by experiments or the like as the time during which the rail pressure can always be reduced below the target fuel pressure at the time of starting the engine regardless of the magnitude of the rail pressure when the engine is stopped. And stored in the memory 64. Incidentally, this valve opening time may be set as a fixed time or may be set as a function of the cooling water temperature when the engine is stopped.

After executing the processes of steps 320 and 325, the ECU 60 once ends the process of this routine.
As described above, when the actual fuel pressure PCR is higher than the target fuel pressure PCRTRG and the difference is larger than the predetermined value ΔP1, the rail pressure reducing process is executed.

  Incidentally, as such a pressure reduction process, a method of reducing the rail pressure by the above-described invalid injection of the injector 12 is generally known. However, in such a method, since it is necessary to discharge the fuel within an extremely short period such as the invalid injection period, there is a limit to the amount of fuel that can be discharged from the common rail 20 at a time, and it is not possible to secure a decompression amount that meets the requirements. In some cases.

  In this regard, in the pressure reducing process according to the present embodiment, the relief valve 22 is provided on the common rail 20 and the rail pressure is reduced based on the opening of the relief valve 22, so that a large amount of fuel is supplied to the common rail at a time. 20 can be discharged. Therefore, the rail pressure can be quickly and surely reduced to the vicinity of the target fuel pressure, and an increase in combustion noise can be suitably suppressed.

  (1) In particular, in this embodiment, when the relief valve 22 is driven to open by such pressure reduction processing, the valve opening period is set so as not to overlap with the valve opening period of the injector 12. Therefore, it is possible to avoid the change in the fuel injection amount and the injection rate due to the decrease in the rail pressure due to the opening of the relief valve 22, and the rail pressure can be reduced without adversely affecting the fuel injection. become able to.

  (2) Further, in addition to the opening period of the injector 12, the opening period of the relief valve 22 is set so as not to overlap with the detection timing of the actual fuel pressure PCR. Even if a pressure pulsation occurs in the common rail 20 when the accompanying fuel is discharged, the pressure pulsation does not adversely affect the detection of the actual fuel pressure PCR. Therefore, the actual fuel pressure PCR can be accurately detected, and for example, when calculating various control amounts based on the actual fuel pressure PCR, such as the fuel injection period, this can be accurately obtained.

  Further, as described above, when setting the valve opening period of the relief valve 22 so as not to overlap with the valve opening period of the injector 12 or the detection timing of the actual fuel pressure PCR, the valve opening period is set to the valve opening period of the injector 12. It is also possible to set the time as a sufficiently short fixed period in anticipation of changes and the like. However, in such a configuration, the valve opening period of the relief valve 22 can be set in advance so as not to overlap with the valve opening period of the injector 12 or the like, whereas the valve opening period of the relief valve 22 is set to the rail pressure. Even if this can be set longer in order to correspond to the differential pressure from the target fuel pressure, only a certain valve opening period can be secured.

  On the other hand, in the decompression process of the present embodiment, the determination value for determining whether or not the opening period of the relief valve 22 overlaps the opening period of the injector 12 and the detection timing of the actual fuel pressure PCR is described above. The maximum value TOPENMAX is calculated, the maximum value TOPENMAX is compared with the energization time TOPEN, and the energization time TOPEN is limited to the maximum value TOPENMAX only when the maximum value TOPENMAX is exceeded.

  (3) Therefore, the valve opening period of the relief valve 22 can be maximized within a range that does not overlap with the valve opening period of the injector 12 or the detection timing of the actual fuel pressure PCR, and the actual fuel pressure PCR and the target fuel pressure PCRTRG. The rail pressure can be reduced with an appropriate amount of pressure reduction corresponding to the pressure difference.

  Furthermore, in the decompression process of the present embodiment, the valve opening period of the relief valve 22 is set so as not to overlap with the fuel pumping periods of the supply pumps 50a and 50b, and the fuel is pumped and discharged at different times. I have to.

  Here, for example, when the reduced pressure of the rail pressure required in the pressure reducing process is “ΔPa” and the increased pressure required in the fuel pumping of each of the supply pumps 50a and 50b is “ΔPb”, such fuel pressure feeding. If the discharge and the discharge are not performed simultaneously, the final increase / decrease amount of the rail pressure should be (ΔPb−ΔPa). However, if the fuel is pumped and discharged at the same time, they will interfere with each other, so there is no guarantee that the amount of increase or decrease in rail pressure will be (ΔPb−ΔPa). It will have a negative impact on both emissions.

  (4) In this respect, according to the present embodiment, it is possible to avoid mutual interference between the fuel pumping by the supply pumps 50a and 50b and the fuel discharge by opening the relief valve 22, and the supply pumps 50a and 50b. The rail pressure can be surely reduced without adversely affecting the fuel pumping.

  (5) Furthermore, since the actual valve opening period is obtained based on the energization signal to the relief valve 22 and the response characteristics of the relief valve 22, the valve opening period can be obtained more accurately. it can. Accordingly, it is possible to surely avoid problems caused by the overlap of the valve opening period of the injector 12 and the detection timing of the actual fuel pressure PCR or the fuel pumping period of the supply pumps 50a and 50b and the valve opening period of the relief valve 22. In addition, the settable range of the valve opening period of the relief valve 22 can be expanded.

  (6) Since the energizing period of the relief valve 22 is set so as not to overlap with the energizing periods of the regulating valves 70a and 70b, the energizing period overlaps, so that the batteries 59 are connected to the valves 22, 70a and 70b. It is possible to avoid the occurrence of a situation where the amount of power supplied from the power source is insufficient and the valves 22, 70a, 70b cannot be reliably driven. Therefore, it is possible to avoid adverse effects on the fuel pumping of each of the supply pumps 50a and 50b, particularly the adjustment of the fuel pumping amount, and the relief valve 22 can be driven reliably.

  (7) Furthermore, in the present embodiment, the pressure reduction process execution condition is that the differential pressure (PCR-PCRTRG) between the actual fuel pressure PCR and the target fuel pressure PCRTRG is greater than a predetermined value ΔP1, and this predetermined value Δ P1 is set to be sufficiently large within a range in which the combustion noise is not increased. Therefore, even if the increase in combustion noise is negligible, it is possible to avoid a situation in which the rail pressure falls below the target fuel pressure by executing the pressure reduction process, and the engine accompanying the excessive decrease in the rail pressure. The deterioration of the combustion state can be suppressed.

  (8) In addition, in this embodiment, the energization time TOPEN, that is, the opening period of the relief valve 22 is determined based on the differential pressure (PCR-PCRTRG) between the actual fuel pressure PCR and the target fuel pressure PCRTRG and the pressure reduction rate K. Since the calculation is performed, the rail pressure can be accurately reduced to the target fuel pressure PCRTRG unless the energization time TOPEN is limited by the maximum value TOPENMAX.

  (9) Further, when it is determined that the engine is stopped in the pressure reducing process, the relief valve 22 is opened for a predetermined time so that the rail pressure is surely lowered from the target fuel pressure at the time of starting the engine. Therefore, an increase in combustion noise can be suitably suppressed not only during normal operation but also during engine restart.

  In particular, by variably setting the valve opening time in accordance with the coolant temperature when the engine is stopped, the rail pressure at the time of engine restart can be brought closer to the target fuel pressure, which preferably increases combustion noise. It is possible to ensure better engine startability while suppressing the engine.

The embodiment described above can be implemented by changing the configuration as follows.
In the above embodiment, the relief valve 22 is opened by setting the pressure difference (PCR-PCRTRG) between the actual fuel pressure PCR and the target fuel pressure PCRTRG to exceed the predetermined value ΔP1 as an execution condition of the decompression process. Although the period and the fuel pumping period of the fuel pump 30 are not overlapped with each other, for example, the following configuration can be adopted when setting the periods so that the periods do not overlap.

  That is, the fuel pump 30 start timing (crank angle CA) of the fuel pump 30 is calculated based on the final valve closing angle ANGFIN. Next, in the process of step 250 shown in FIG. 4, the maximum value TOPENMAX of the energization time TOPEN is calculated based on the response delay time ΔT2 of the relief valve 22 and the engine speed NE. However, here, the maximum value TOPENMAX is calculated on condition that the relief valve 22 is closed before the crank angle CA reaches the calculated fuel pumping start timing.

  When the energization time TOPEN exceeds the maximum value TOPENMAX by the processing after step 260, the energization time TOPEN is set equal to the maximum value TOPENMAX. As described above, the energization time TOPEN is limited to the maximum value TOPENMAX or less, so that the fuel pump 30 always starts the fuel pump 30 after the relief valve 22 is closed.

  According to such a configuration, the opening period of the relief valve 22 can be maximized within a range that does not overlap with the fuel pumping period of the fuel pump 30, and according to the pressure difference between the actual fuel pressure PCR and the target fuel pressure PCRTRG. The rail pressure can be reduced with an appropriate amount of pressure reduction.

  In the above embodiment, the energization time TOPEN is set based on the differential pressure (PCR-PCRTRG) between the actual fuel pressure PCR and the target fuel pressure PCRTRG and the pressure reduction speed K. For example, the energization time TOPEN is constant. It may be set as a value, and this energization time TOPEN may be limited to the maximum value TOPENMAX or less.

  In the above embodiment, the energization time TOPEN is limited to the maximum value TOPENMAX or less so that the detection timing of the actual fuel pressure PCR, the valve opening period of the injector 12 and the valve opening period of the relief valve 22 do not overlap. However, for example, by omitting the process for limiting the energization time TOPEN and setting the energization time TOPEN to a sufficiently short constant value, the valve opening period is set in advance to detect the actual fuel pressure PCR or to open the injector 12. It can also be set so as not to overlap the valve period.

  -In above-mentioned embodiment, when pressure reduction processing is performed, you may make it stop fuel pumping by the fuel pump 30 completely. According to such a configuration, the relief valve 22 and the driver 63 of each of the adjustment valves 70a and 70b can be shared, and the configuration can be simplified.

  In the above embodiment, the rail pressure is reduced only based on the relief valve 22 being opened. However, in addition to the pressure reduction processing based on the relief valve 22 being opened, the rail pressure based on the so-called invalid injection of the injector 12 is used. The pressure reduction may be executed. Further, in this case, when the differential pressure (PCR-PCRTRG) between the actual fuel pressure PCR and the target fuel pressure PCRTRG is equal to or higher than a predetermined pressure, the decompression process by opening the relief valve 22 is performed with the same differential pressure (PCR-PCRTRG). ) Is less than a predetermined pressure, each of the decompression processes may be executed in such a manner that the decompression process by the invalid injection of the injector 12 is selected.

In the above embodiment, the pressure reduction speed K is set as a function of the actual fuel pressure PCR, but this can also be set as a constant.
In the above embodiment, a mechanical pressure regulator that opens when the rail pressure rises to a pressure value higher than the pressure resistance of the fuel pumping system may be attached to the common rail 20 separately from the relief valve 22.

  In the above embodiment, the relief valve 22 is attached to the common rail 20, but the relief valve 22 is attached to a fuel passage that accumulates fuel at the same pressure as the fuel pressure in the common rail 20, such as the discharge passage 23, for example. May be.

  In the above embodiment, the pressure reduction process is executed on the condition that the differential pressure (PCR-PCRTRG) between the actual fuel pressure PCR and the target fuel pressure PCRTRG exceeds the predetermined value ΔP1, but for example, the actual fuel pressure The decompression process can also be executed on condition that the PCR has exceeded the target fuel pressure PCRTRG.

  In the above embodiment, the relief valve 22 is configured as a valve whose opening degree can be adjusted, and the opening degree is variably set according to the differential pressure (PCR-PCRTRG) between the actual fuel pressure PCR and the target fuel pressure PCRTRG. Thus, the decompression speed may be adjusted.

  In the above embodiment, the diesel engine is exemplified as the internal combustion engine to which the fuel pressure control device according to the present invention is applied. For example, the fuel pressure control according to the present invention is applied to a direct injection gasoline engine that directly injects fuel into the combustion chamber. A device can also be applied.

The schematic block diagram which shows a high pressure fuel injection system. The timing chart which shows the change mode of the rail pressure in a regular time, the operating state of a fuel pump, etc. The flowchart which shows the calculation procedure of the drive time of each control valve in a fuel pump. The flowchart which shows the setting procedure of the drive time of a relief valve. The timing chart which shows the output mode of the energization signal of a relief valve, the opening-and-closing state of the relief valve, etc. The flowchart which shows the control procedure at the time of driving a relief valve. The graph which shows the pressure reduction characteristic of the rail pressure at the time of valve opening of a relief valve.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Engine, 12 ... Injector, 14 ... Fuel tank, 20 ... Common rail, 21 ... Relief passage, 22 ... Relief valve, 23 ... Discharge passage, 24 ... Suction passage, 30 ... Fuel pump, 31 ... Feed pump, 34 ... Suction Port, 36 ... Relief port, 38 ... Discharge port, 40 ... Drive shaft, 42 ... Cam, 59 ... Battery, 60 ... ECU, 62 ... CPU, 63 ... Driver, 64 ... Memory, 65 ... Speed sensor, 66 ... Cylinder Discrimination sensor, 67 ... Accelerator sensor, 68 ... Fuel pressure sensor, 69 ... Water temperature sensor, 50a ... First supply pump, 50b ... Second supply pump, 70a ... First adjustment valve, 70b ... Second adjustment valve.

Claims (3)

Based on the valve opening operation of the pressure accumulation pipe which accumulates the fuel supplied from the fuel pump to a high pressure and supplies the accumulated fuel to the fuel injection valve and the pressure accumulation pipe. The relief valve to be discharged and the fuel pressure in the pressure accumulating pipe are detected, and the relief valve is driven to open in response to a pressure reduction request based on a comparison between the detected fuel pressure and its target pressure. A fuel pressure control device for a high-pressure fuel injection system comprising a fuel pressure control means for lowering,
The fuel pressure control device for a high pressure fuel injection system, wherein the fuel pressure control means drives the relief valve to open so that a valve opening period of the relief valve does not overlap a fuel pumping period of the fuel pump. The fuel pressure control device for a high-pressure fuel injection system according to claim 1,
The fuel pressure control means sets a valve opening period of the relief valve based on the pressure reduction request, and determines whether the set valve opening period and a fuel pumping period of the fuel pump overlap, A fuel pressure control device for a high-pressure fuel injection system, wherein when the overlap is determined, a valve opening period of the relief valve is limited so as not to overlap a fuel pumping period of the fuel pump. The fuel pressure control device for a high-pressure fuel injection system according to claim 2,
When the fuel pressure control means sets the relief valve opening period based on the pressure reduction request, the fuel pressure control means sets the valve opening period according to the magnitude of the differential pressure between the detected fuel pressure and its target pressure. A fuel pressure control device for a high-pressure fuel injection system.

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