JP5217514B2 - Engine fuel supply system - Google Patents

Description

  The present invention relates to an engine fuel supply apparatus, and more particularly to an apparatus for starting an engine by directly injecting fuel into a combustion chamber of an engine in a compression stroke.

The fuel supply device for an engine described in Patent Document 1 estimates the fuel pressure acting on the fuel injection valve at the fuel injection timing when the predetermined timing (injection timing calculation timing) before the fuel injection timing comes. The fuel injection is prohibited while the estimated fuel pressure is less than the permitted fuel pressure by comparing the estimated fuel pressure at the fuel injection timing with the predetermined permitted fuel pressure when starting the engine. Then, the compression stroke injection is permitted when the estimated value of the fuel pressure becomes equal to or higher than the injection permitted fuel pressure. Here, the injection permission fuel pressure is set to a fuel pressure suitable for stratified combustion.
JP 2006-307800 A

  However, in Patent Document 1, since the amount of fuel leakage at the high-pressure fuel pump is not considered when calculating the estimated value of the fuel pressure at the fuel injection timing, the estimated value of the fuel pressure at the fuel injection timing and the actual value There will be a difference between the values.

  For this reason, in Patent Document 1, even when the estimated value of the fuel pressure at the fuel injection timing is equal to or higher than the permitted fuel pressure, and the actual value of the fuel pressure at the fuel injection timing is less than the permitted fuel pressure. The compression stroke injection may be permitted.

  In this case, since the compression stroke injection is performed before the actual value of the fuel pressure at the fuel injection timing reaches the fuel pressure suitable for stratified combustion, good stratified combustion is not performed due to poor atomization of the fuel, and exhaust emission is not performed. There is a problem that the startability deteriorates with worsening.

  In view of such a problem, an object of the present invention is to accurately estimate the fuel pressure at the fuel injection timing when the injection timing calculation timing is provided before the fuel injection timing.

Therefore, the present invention includes a high-pressure fuel pump that discharges fuel at a high pressure, and a fuel injection valve that directly supplies high-pressure fuel from the high-pressure fuel pump to the combustion chamber of the engine. A fuel pressure estimated value calculating means for calculating in advance an estimated value of the fuel pressure acting on the fuel injection valve at the fuel injection timing when the predetermined timing before the fuel injection timing in the compression stroke is reached. By comparing the estimated value of the fuel pressure at the fuel injection timing with the predetermined injection permitted fuel pressure when starting the engine, the fuel injection is prohibited while the estimated fuel pressure value is less than the permitted fuel pressure. And a fuel injection prohibition / compression stroke injection permission determining means for permitting the compression stroke injection when the estimated value becomes equal to or higher than the injection permission fuel pressure. Further, the fuel pressure estimated value calculating means has means for calculating the amount of fuel leakage in the high-pressure fuel pump in accordance with the engine operating conditions, and the means for calculating the fuel leakage amount is the engine speed and the engine cooling. A map showing the relationship between the water temperature and the amount of fuel leakage is provided. The higher the engine speed, the smaller the fuel leakage amount, and the lower the engine cooling water temperature, the smaller the fuel leakage amount. The estimated value of the fuel pressure at the fuel injection timing is calculated by correcting with the amount of fuel leakage.

Further, in the present invention, the volume of the pump chamber is changed by the reciprocating motion of the pump plunger, the fuel is sucked into the pump chamber in the stroke in which the pump plunger is lowered, and the pressure in the pump chamber is increased in the stroke in which the pump plunger is raised. The high pressure fuel pump that discharges the fuel and the fuel injection valve that directly supplies the high pressure fuel from the high pressure fuel pump to the combustion chamber of the engine. The fuel that acts on the fuel injection valve at the fuel injection timing of the cylinder at a predetermined timing before the fuel injection timing of the cylinder for the cylinder in which the fuel injection timing in the compression stroke exists during the stroke A fuel pressure estimated value calculating means for calculating an estimated value of the pressure in advance, and a fuel injection timing of the cylinder at the start of the engine. By comparing the estimated value of the fuel pressure with a predetermined permitted fuel pressure for injection, the fuel injection of the cylinder is prohibited while the estimated value of the fuel pressure is less than the permitted fuel pressure for injection. And a fuel injection prohibition / compression stroke injection permission judging means for permitting the compression stroke injection of the cylinder when the pressure becomes equal to or higher than the pressure. Further, the fuel pressure estimated value calculating means has means for calculating the amount of fuel leakage in the high-pressure fuel pump in accordance with the engine operating conditions, and the means for calculating the fuel leakage amount is the engine speed and the engine cooling. A map showing the relationship between the water temperature and the amount of fuel leakage is provided. The higher the engine speed, the smaller the fuel leakage amount, and the lower the engine cooling water temperature, the smaller the fuel leakage amount. The estimated value of the fuel pressure at the fuel injection timing is calculated by correcting with the amount of fuel leakage.

  According to the present invention, the estimated value of the fuel pressure at the fuel injection timing is calculated based on the fuel leakage amount at the high-pressure fuel pump at a predetermined timing (injection timing calculation timing) before the fuel injection timing. Accordingly, it is possible to suppress the deviation between the estimated value and the actual value of the fuel pressure at the fuel injection timing, so that the compression stroke injection can be reliably performed at the fuel pressure equal to or higher than the injection permission fuel pressure. Thereby, since stable stratified combustion can be realized at the time of engine start, deterioration of exhaust emission can be suppressed. In addition, since the robustness of the fuel pressure is improved, it is possible to suppress variations in exhaust emission.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an engine fuel supply device showing an embodiment of the present invention, and FIG. 2 is a diagram showing suction / discharge operations of a high-pressure fuel pump.

  In FIG. 1, the engine fuel supply apparatus mainly includes a fuel tank 1, a low-pressure fuel pump (feed pump) 2, a high-pressure fuel pump 3, a common rail (fuel gallery) 4, and fuel injection valves 5 </ b> A to 5 </ b> D. Prepare for.

  The low-pressure fuel pump 2 is driven by the electric motor 6 and pumps the fuel in the fuel tank 1 to the fuel supply passage 7. Fuel filters 8 are provided on the upstream side and the downstream side of the low-pressure fuel pump 2, respectively. In order to regulate the discharge pressure of the low-pressure fuel pump 2 to a predetermined pressure, a low-pressure pressure regulator 10 is provided in the return passage 9 that branches from the fuel supply passage 7 and returns to the fuel tank 1.

  The fuel discharged from the low pressure fuel pump 2 is supplied to the high pressure fuel pump 3 via the fuel supply passage 7. The fuel supply passage 7 is provided with a damper 11 for absorbing fuel pressure pulsation.

  The high-pressure fuel pump 3 is mainly composed of a plunger pump 12. The plunger pump 12 changes the volume of the high-pressure chamber (pump chamber) 12b by the reciprocating movement of the plunger 12a driven by the cam 13, and enters the high-pressure chamber 12b via the suction check valve 14 in the downward stroke (suction stroke) of the plunger 12a. The fuel is sucked, and the fuel in the high-pressure chamber 12b is discharged through the discharge check valve 15 in the upward stroke (discharge stroke) of the plunger 12a. The pump drive cam 13 is connected to the intake valve camshaft.

  The high-pressure fuel pump 3 further includes a control solenoid 16. The control solenoid 16 is provided for the suction check valve 14, and can hold the suction check valve 14 in an open state by an electromagnetic force generated by energization regardless of the pressure in the high pressure chamber 12b.

  The high-pressure fuel pump 3 is connected to a leaked fuel passage 17 that collects leaked fuel from the cylinder 12 c of the plunger pump 12 and the sliding portion of the plunger 12 a and returns it to the fuel tank 1.

Next, the operation of the high-pressure fuel pump 3 will be described with reference to FIG.
FIG. 2 shows the suction / discharge operation of the high-pressure fuel pump 3 (and the start of energization of the solenoid).

  In the suction stroke in which the plunger 12a descends from the maximum lift position (time t1), the suction check valve 14 is opened by the negative pressure in the high pressure chamber 12b, and fuel is sucked into the high pressure chamber 12b.

Thereafter, when the plunger 12a reaches the minimum lift position (time t2), the solenoid ON signal is raised and the control solenoid 16 is energized.
After the plunger 12a reaches the minimum lift position (time t2), it rises and enters the spill stroke. In this spill stroke, the intake check valve 14 is held in the open state by the control solenoid 16, so that the fuel in the high pressure chamber 12b flows back to the suction side due to the rise of the plunger 12a. As a result, the fuel in the high pressure chamber 12b The pressure does not increase, the discharge check valve 15 is kept closed, and no discharge operation is performed.

  Thereafter, the solenoid ON signal is terminated at an arbitrary timing (t3) during the lift of the plunger 12a, the energization of the control solenoid 16 is terminated, and a substantial discharge stroke is started. In this discharge stroke, the energization of the control solenoid 16 is finished, so the suction check valve 14 is closed. For this reason, the pressure in the high pressure chamber 12 b rises due to the rise of the plunger 12 a, and the fuel in the high pressure chamber 12 b is discharged through the discharge check valve 15. This discharged fuel is supplied to the common rail 4 through the orifice 18 shown in FIG. 1 until the plunger 12a reaches the maximum lift position (time t4).

  Therefore, the amount of fuel corresponding to the closing timing of the intake check valve 14 due to the end of energization of the control solenoid 16, specifically the closing period of the intake check valve 14 in the discharge stroke, is discharged from the high-pressure fuel pump 3, and the common rail 4 To be supplied.

  Returning to FIG. 1, a safety valve 19 is provided at the rear end of the common rail 4. When the actual common rail fuel pressure exceeds the allowable pressure, the safety valve 19 is opened and a part of the high-pressure fuel in the common rail 4 is returned to the fuel tank 1.

  The high-pressure fuel stored in the common rail 4 is distributed to the fuel injection valve of each cylinder. FIG. 1 shows a case of a four-cylinder engine, in which high-pressure fuel stored in the common rail 4 acts on the four fuel injection valves 5A, 5B, 5C, and 5D.

  When the fuel injection valves 5A to 5D are opened at a predetermined timing in accordance with the ignition timing of each cylinder, fuel is supplied to the combustion chamber of the cylinder having the opened fuel injection valve. Further, the common rail fuel pressure is reduced by the disappearance of a predetermined amount of fuel from the fuel injection valve.

  Therefore, the engine control unit (ECU) 20 has a target fuel pressure of the common rail 4 corresponding to the engine load and the engine speed as a map in advance, and the actual common rail fuel pressure detected by the fuel pressure sensor 21 is The discharge amount of the high-pressure fuel pump 3 is controlled via the control solenoid 16 so as to coincide with the target fuel pressure according to the engine load and the engine speed at that time. For example, when the actual common rail fuel pressure is lower than the target fuel pressure, the control solenoid 16 increases the discharge amount of the high-pressure fuel pump 3 by increasing the closing period of the intake check valve 14 in the discharge stroke to increase the actual common rail fuel pressure. To bring it closer to the target fuel pressure. On the other hand, when the actual common rail fuel pressure is higher than the target fuel pressure, the control solenoid 16 shortens the closing period of the intake check valve 14 in the discharge stroke to reduce the discharge amount of the high-pressure fuel pump 3 and lower the actual common rail fuel pressure. To bring it closer to the target fuel pressure.

  When the engine load and engine speed are determined, the required fuel amount per cylinder and cycle is uniquely determined. When the required fuel amount per cylinder and cycle and the common rail fuel pressure are determined, the fuel injection valve is opened. The valve pulse width is determined. Accordingly, the ECU 20 has a map of the required fuel amount per cylinder per cycle corresponding to the engine load and the engine speed, and the required fuel per cylinder per cycle from the engine load and the engine speed at that time. A map of the amount is searched to obtain the required fuel amount per cylinder and one cycle, and the valve opening pulse width to be given to the fuel injection valve is calculated from the required fuel amount per cylinder and one cycle and the common rail fuel pressure. When the injection timing is reached, the fuel injection valve is opened with this valve opening pulse width to supply fuel to each cylinder.

  In the present embodiment, the fuel injection valves 5A to 5D are provided facing the combustion chambers of the respective cylinders, and the ECU 20 performs the compression stroke injection for each cylinder at the start of the engine (during cranking). Control is performed to cause stratified combustion.

  Next, with respect to the influence of the common rail fuel pressure due to the fuel leakage in the high pressure fuel pump in the case of using the conventional technology (for example, the technology described in Patent Document 1) that does not assume the fuel leakage in the high pressure fuel pump, FIG. 3 and FIG. 4 will be described.

  FIG. 3 is a waveform diagram showing changes in the common rail fuel pressure when the engine is started when the conventional technology is used. FIG. 4 is a waveform diagram for explaining the relationship between the plunger lift, the injection timing, and the rising timing of the REF signal. Here, T1 to T8 shown in FIG. 3 correspond to T1 to T8 shown in FIG. In addition, as shown in FIG. 1-4 correspond to cylinder numbers. In the injection timing of FIG. 3, the solid line indicates the injection timing at which fuel injection is performed, while the dotted line indicates the injection timing at which fuel injection is not performed.

3 shows the change in the common rail fuel pressure from the time when the starter switch is turned on and engine cranking is started (T0 in FIG. 3).
In this common rail fuel pressure, a solid line indicates an actual value of the common rail fuel pressure, and a dotted line indicates an estimated value of the common rail fuel pressure calculated by using the conventional technique at an injection timing calculation timing (T5) described later.

Further, the section in which the common rail fuel pressure is increased corresponds to the upward stroke (discharge stroke) of the plunger lift in FIG.
In the prior art, the rising timing (T1, T3, T5, T7 in FIG. 3) of the REF signal of each cylinder is adopted as the injection timing calculation timing, and it is determined whether or not the compression stroke injection is permitted at this injection timing calculation timing. To do. Here, the REF signal is a known signal and is a signal of a crank angle reference position for each cylinder. For example, as described later, there is a REF signal that rises at 110 ° before compression top dead center of each cylinder for a four-cylinder engine.

Specifically, the prohibition / permission determination of the compression stroke injection at the injection timing calculation timing is performed as follows.
First, for cylinders where fuel injection timing exists during the pump plunger ascending stroke (discharge stroke), the estimated value of the common rail fuel pressure is calculated in advance at the fuel injection timing of the cylinder when the injection timing is reached. To do. This estimated value of fuel pressure is the actual value of the common rail fuel pressure at the injection timing calculation timing, and the common rail fuel pressure increase from the injection timing calculation timing to the injection timing calculated without assuming fuel leakage at the high-pressure fuel pump. It is calculated by the sum with the minute ΔP.

Next, the estimated value of the fuel pressure at the fuel injection timing of the cylinder is compared with the injection permitted fuel pressure (see FIG. 3).
The fuel injection of the cylinder is prohibited while the estimated value of the fuel pressure is less than the permitted fuel pressure for injection, and the compression stroke injection of the cylinder is permitted when the estimated value of the fuel pressure exceeds the permitted fuel pressure for injection. To do.

Here, the common rail fuel pressure increase ΔP calculated without assuming fuel leakage in the high-pressure fuel pump will be described with reference to FIG.
FIG. 4 shows the plunger lift of the high-pressure fuel pump 3 with the horizontal axis as the crank angle. The intake valve camshaft makes one rotation with respect to two rotations of the crankshaft, and the pump drive cam 13 lifts twice during one rotation. As a result, one cycle of the plunger lift is 360 ° in crank angle. become. For simplicity, it is assumed that the pump drive cam 13 is connected to the intake valve camshaft so that the plunger lift becomes zero at the compression top dead center position of the first cylinder. It is assumed that it rises at the timing of T3 110 degrees before the dead center. If the ignition sequence of the 4-cylinder engine is 1-3-3-4-2, the cylinder immediately before the 1st cylinder is the 2nd cylinder, and the REF signal of this 2nd cylinder is higher than the REF signal of the 1st cylinder. Furthermore, it rises at the timing of T1 180 ° before.

  On the other hand, the injection timing of the first cylinder is a crank angle of T4 delayed from the rising of the REF signal of the first cylinder (T3), and the injection timing of the second cylinder is the rising of the REF signal of the second cylinder (T1). It is assumed that the crank angle of T2 is later than).

  For the 3rd and 4th cylinders, the REF signal for the 3rd and 4th cylinders comes to the position of the REF signal for the 2nd and 1st cylinders at the position where the plunger lift is shifted to the 360 ° advance side. Since the injection timings of the third cylinder and the fourth cylinder come to the crank angles of T2 and T4 which are later than the rising of the REF signal of the second cylinder and the first cylinder, the REF signals for these third and fourth cylinders, The injection timing is shown in parentheses in FIG.

  In this case, in the cylinder in which the rising timing and the injection timing of the REF signal are on the plunger lift rising side, that is, the second cylinder (or the third cylinder), the common rail at the rising timing (T1) of the REF signal of the second cylinder. The common rail fuel pressure at the injection timing (T2) of the second cylinder rises by the timing difference rather than the fuel pressure. This common rail fuel pressure increase ΔP is estimated at the rising timing of the REF signal.

When the above-described prior art is applied to the third cylinder shown in FIG. 3 and the compression stroke injection is prohibited / permitted at the injection timing calculation timing, there are the following problems.
In the third cylinder shown in FIG. 3, since there is an injection timing calculation timing (T5) and an injection timing (T6) during the lift stroke (discharging stroke) of the plunger lift, at the injection timing calculation timing of T5, It is determined whether or not to permit the compression stroke injection at the injection timing (T5) by comparing the estimated value of the common rail fuel pressure and the injection permission fuel pressure.

  In this determination at T5, the estimated value of the common rail fuel pressure at T6 is assumed to be the actual value of the common rail fuel pressure at the injection timing calculation timing (T5) (fuel pressure at the time of determination) and fuel leakage at the high-pressure fuel pump. It is calculated by the sum of the calculated common rail fuel pressure increase ΔP.

As a result of this calculation, since the estimated value of the common rail fuel pressure at T6 exceeds the injection permission fuel pressure, the compression stroke injection is permitted at the injection timing calculation timing (T5).
However, the actual value (injection fuel pressure Pf) of the common rail fuel pressure at the injection timing (T6) may be lower than the injection permission fuel pressure. This is because the common rail fuel pressure at the injection timing (T6) decreases due to fuel leakage in the high-pressure fuel pump.

  For this reason, there is a possibility that the compression stroke injection may be performed before the actual value of the common rail fuel pressure at the injection timing (T6) reaches the fuel pressure suitable for stratified combustion, and stable stratified combustion cannot be performed. There is.

  Therefore, in the present invention, the compression stroke injection is performed before the actual value of the common rail fuel pressure reaches the fuel pressure suitable for stratified combustion by calculating the estimated value of the common rail fuel pressure in consideration of the fuel leakage in the high pressure fuel pump. Suppress it.

Next, a change in the common rail fuel pressure at the time of engine start in the present embodiment will be described with reference to FIG.
FIG. 5 is a waveform diagram showing changes in the common rail fuel pressure when the engine is started in this embodiment.

Differences from the prior art shown in FIG. 3 will be described.
In the present embodiment shown in FIG. 5, the compression stroke injection prohibition / permission determination at the injection timing calculation timing is performed as follows.

  First, for cylinders where fuel injection timing exists during the pump plunger ascending stroke (discharge stroke), the estimated value of the common rail fuel pressure is calculated in advance at the fuel injection timing of the cylinder when the injection timing is reached. To do. The estimated value of the fuel pressure is calculated from the sum of the actual value of the common rail fuel pressure at the injection timing calculation timing and the common rail fuel pressure increase ΔP (see FIG. 4). It is calculated by correcting by subtracting Δpl.

Next, the estimated value of the fuel pressure at the fuel injection timing of the cylinder is compared with the injection permitted fuel pressure (see FIG. 5).
The fuel injection of the cylinder is prohibited while the estimated value of the fuel pressure is less than the permitted fuel pressure for injection, and the compression stroke injection of the cylinder is permitted when the estimated value of the fuel pressure exceeds the permitted fuel pressure for injection. To do.

The case where the compression stroke injection prohibition / permission determination is applied to the third cylinder (injection timing T6) and the second cylinder (injection timing T10) shown in FIG. 5 will be described.
In the third cylinder (injection timing T6), there are an injection timing calculation timing (T5) and an injection timing (T6) during the lift stroke (discharging stroke) of the plunger lift. It is determined whether or not the compression stroke injection at the injection timing (T5) is permitted by comparing the estimated value of the common rail fuel pressure with the injection permission fuel pressure.

  In the determination at T5, the estimated value of the common rail fuel pressure at T6 is obtained from the sum of the actual value of the common rail fuel pressure (determination fuel pressure) at the injection timing calculation timing (T5) and the common rail fuel pressure increase ΔP. Unlike the case where the above-described conventional technique is applied, the estimated value of the common rail fuel pressure at T6 is the injection permitted fuel, because the calculation is performed by subtracting the fuel pressure drop Δpl due to fuel leakage at the high pressure fuel pump. Below pressure. Therefore, the compression stroke injection is not permitted (prohibited) at the injection timing calculation timing (T5).

  On the other hand, in the second cylinder (injection timing T10), there is an injection timing calculation timing (T9) and an injection timing (T10) during the upward stroke of the plunger lift (during the discharge stroke), so at the injection timing calculation timing of T9, It is determined whether or not the compression stroke injection at the injection timing (T10) is permitted by comparing the estimated value of the common rail fuel pressure at T10 and the injection permitted fuel pressure.

  In this determination at T9, the estimated value of the common rail fuel pressure at T10 is obtained from the sum of the actual value of the common rail fuel pressure (determination fuel pressure) at the injection timing calculation timing (T9) and the common rail fuel pressure increase ΔP. The correction is made by subtracting the fuel pressure drop Δpl due to fuel leakage at the high-pressure fuel pump. Since the estimated value of the common rail fuel pressure at T10 exceeds the injection permission fuel pressure, the compression stroke injection is permitted at the injection timing calculation timing (T9).

Next, fuel injection control executed by the ECU 20 will be described with reference to FIGS.
FIG. 6 is a flowchart of fuel injection control in the present embodiment, FIG. 7 is a flowchart of calculating an estimated value of fuel pressure in the present embodiment, and FIG. 8 is an engine speed and fuel leakage amount ΔL (fuel pressure decrease Δpl due to fuel leakage). 9 is a diagram showing the relationship between the engine coolant temperature and the fuel leakage amount ΔL (the fuel pressure drop Δpl due to fuel leakage).

  In step S1, the ECU 20 determines whether or not the engine is starting. Specifically, when the signal from the starter switch is ON, it is determined that the engine is being started (cranking). If it is not at the time of starting the engine, the process proceeds to step S8 to perform fuel injection control during normal operation. In this fuel injection control, for example, engine speed and engine load are used as parameters, and on the low load side where large engine output is not required, stratified combustion is performed by compression stroke injection, while fuel efficiency is increased. On the high load side, the required output is ensured by performing homogeneous combustion by intake stroke injection.

  If it is determined in step S1 that the engine is being started, the process proceeds to step S2, where an elapsed time T from the engine start is compared with a predetermined time Ts to determine whether the elapsed time T is less than the predetermined time Ts. Judgment is made. Here, the elapsed time T is measured by a timer provided in advance in the ECU 20 with the time when the signal from the starter switch is turned ON as the start time. The predetermined time Ts is a threshold value for determining whether to start the engine by stratified combustion or homogeneous combustion. When the elapsed time T is equal to or longer than the predetermined time Ts, the process proceeds to step S9, and in order to ensure startability, the engine is started with homogeneous combustion by intake stroke injection.

  When the elapsed time T is less than the predetermined time Ts in step S2, the process proceeds to step S3, and whether or not the actual common rail fuel pressure Pr detected by the fuel pressure sensor 21 is less than the injection permission fuel pressure Ps. Make a decision. Here, the injection permission fuel pressure Ps is a common rail pressure that permits the compression stroke injection, and specifically, a value of about 3 MPa is set. When the actual common rail fuel pressure Pr is equal to or higher than the injection permission fuel pressure Ps, the process proceeds to step S6, fuel injection is permitted at the next injection timing, and compression stroke injection is executed in step S7.

  When the actual common rail fuel pressure Pr detected by the fuel pressure sensor 21 in step S3 is less than the injection permission fuel pressure Ps, the process proceeds to step S4, and the estimated value Pest of the common rail pressure is calculated by the flow shown in FIG. To do.

Here, calculation of the estimated value Pest of the common rail pressure will be described based on the flow shown in FIG.
In step S11 of FIG. 7, it is determined whether or not the rising timing (injection timing calculation timing) of the current REF signal is that of the second cylinder or the third cylinder. If the rising timing of the current REF signal is that of the second cylinder or the third cylinder, it is determined that the common rail fuel pressure increases from the injection timing calculation timing to the injection timing, which is the current timing, and the process proceeds to step S12. The common rail fuel pressure increase ΔP that can be boosted from the current timing to the injection timing is calculated. The common rail pressure increase ΔP is calculated by calculating the plunger lift amount of the plunger 12a from the cam profile of the pump drive cam 13 and using a map stored in advance based on the plunger lift amount. Thereafter, the process proceeds to step S13.

  On the other hand, if the rising timing of the current REF signal is not that of the second cylinder or the third cylinder in step S11, that is, the rising timing of the REF signal of the first cylinder or the fourth cylinder, the current timing. It is determined that the common rail fuel pressure does not increase before the injection timing, and the process proceeds to step S22 to set the common rail fuel pressure increase ΔP = 0, and then proceeds to step S13.

  In step S13, a common rail fuel pressure drop Δpl due to fuel leakage at the high-pressure fuel pump 3 is calculated. Here, FIGS. 8 and 9 are used to calculate the fuel pressure drop Δpl.

  FIG. 8 shows the relationship between the engine speed and the fuel leak amount ΔL (the corresponding fuel pressure drop Δpl), and FIG. 9 shows the engine coolant temperature and the fuel leak amount ΔL (corresponding to this). It shows the relationship with the fuel pressure drop Δpl). In this embodiment, FIGS. 8 and 9 preliminarily include a fuel leakage amount ΔL (a corresponding fuel pressure decrease Δpl) due to deterioration of the high-pressure fuel pump 3.

  In FIG. 8, the higher the engine speed, the smaller the fuel leak amount ΔL (the corresponding fuel pressure drop Δpl). This is because the higher the engine speed, the stronger the negative pressure on the suction side of the high-pressure fuel pump 3 and the greater the inertial force of the fuel on the discharge side.

  In FIG. 9, the higher the engine coolant temperature, the greater the fuel leakage amount ΔL (the corresponding fuel pressure drop Δpl). This is because the higher the engine coolant temperature, the higher the fuel temperature and the lower the fuel viscosity.

  As a method for calculating the fuel leakage amount ΔL (the corresponding fuel pressure drop Δpl), in addition to the above, the engine speed, the engine coolant temperature, and the fuel leakage amount ΔL (the corresponding fuel pressure) A map showing the relationship with the decrease Δpl) is created in advance, and using this map, the fuel leakage amount ΔL (corresponding to the fuel pressure decrease corresponding to this) is determined based on both the engine speed and the engine coolant temperature parameters. Δpl) may be calculated.

  After calculating the common rail fuel pressure drop Δpl due to fuel leakage at the high-pressure fuel pump 3 in step S13 of FIG. 7, the process proceeds to step S14, and the estimated value Pest of the common rail fuel pressure is calculated by the following equation.

Pest = Pr + ΔP−Δpl
Pest: Estimated common rail fuel pressure
Pr: Actual value of common rail fuel pressure
ΔP: Common rail fuel pressure increase
Δpl: Common rail fuel pressure drop due to fuel leakage In this equation, the actual value Pr of the common rail fuel pressure is the actual value of the common rail fuel pressure at the rising timing (injection timing calculation timing) of the current REF signal.

After calculating the estimated value Pest of the common rail fuel pressure in step S14, the process proceeds to step S5 in FIG.
In step S5 of FIG. 6, it is determined whether or not the estimated value Pest of the common rail fuel pressure is equal to or higher than the injection permission fuel pressure Ps. When the estimated value Pest of the common rail fuel pressure is less than the injection permission fuel pressure Ps, the process returns to step S2.

  On the other hand, when the estimated value Pest of the common rail fuel pressure is equal to or higher than the injection permission fuel pressure Ps, the process proceeds to step S6, fuel injection is permitted at the next injection timing, and compression stroke injection is executed in step S7.

  According to this embodiment, the predetermined timing (injection timing calculation timings T1, T3, T5, T7, T9, T11) before the fuel injection timing (T2, T4, T6, T8, T10, T12) in the compression stroke is reached. ), An estimated value of fuel pressure (estimated value of common rail fuel pressure Pest) acting on the fuel injectors 5A to 5D at the fuel injection timing (T2, T4, T6, T8, T10, T12) is calculated in advance. (Step S4). Further, when the engine is started, the fuel pressure estimated value Pest at the fuel injection timing (T2, T4, T6, T8, T10, T12) is compared with a predetermined injection permission fuel pressure (injection permission fuel pressure Ps) to obtain the fuel. Fuel injection is prohibited while the estimated pressure value Pest is less than the permitted injection fuel pressure Ps, and the compression stroke injection is permitted when the estimated fuel pressure value Pest becomes equal to or higher than the permitted injection fuel pressure Ps (step S5). . Further, the fuel leakage amount ΔL in the high-pressure fuel pump 3 (corresponding to the fuel pressure drop Δpl due to the fuel leakage in the high-pressure fuel pump 3) corresponding to the engine operating condition is calculated. The estimated value of the fuel pressure at the fuel injection timing (T2, T4, T6, T8, T10, T12) corrected by the amount ΔL (corresponding to this, the fuel pressure drop Δpl due to fuel leakage at the high-pressure fuel pump 3) Pest is calculated (steps S13 and S14). Thereby, the deviation between the estimated value and the actual value of the fuel pressure at the fuel injection timing can be suppressed, so that the compression stroke injection can be reliably performed at a fuel pressure equal to or higher than the injection permission fuel pressure.

  Further, according to the present embodiment, the cylinder (the second cylinder or the third cylinder) having the fuel injection timing in the compression stroke during the stroke in which the pump plunger 12a of the high-pressure fuel pump 3 is raised is the cylinder (the second cylinder). Or the third cylinder) at a predetermined timing (injection timing calculation timing T1, T5, T9) before the fuel injection timing (T2, T6, T10), that cylinder (second cylinder or third cylinder) The estimated value of fuel pressure (estimated value of common rail fuel pressure Pest) acting on the fuel injection valves 5A to 5D at the fuel injection timings (T2, T6, T10) is calculated in advance (step S4). Further, when the engine is started, the estimated value Pest of the fuel pressure at the fuel injection timing (T2, T6, T10) of the cylinder (second cylinder or third cylinder) and a predetermined injection permission fuel pressure (injection permission fuel pressure Ps) As a result of comparison with the above, while the estimated value Pest of the fuel pressure is less than the injection permitted fuel pressure Ps, fuel injection of the cylinder (second cylinder or third cylinder) is prohibited, and the estimated value Pest of the fuel pressure is the injection permitted fuel. When the pressure becomes equal to or higher than Ps, the compression stroke injection of the cylinder (the second cylinder or the third cylinder) is permitted (step S5). Further, the fuel leakage amount ΔL in the high-pressure fuel pump 3 (corresponding to the fuel pressure drop Δpl due to the fuel leakage in the high-pressure fuel pump 3) corresponding to the engine operating condition is calculated. The estimated value Pest of the fuel pressure at the fuel injection timing (T2, T6, T10) is calculated by correcting by the amount ΔL (corresponding to the fuel pressure drop Δpl due to fuel leakage in the high-pressure fuel pump 3 corresponding to this) (step) S13, S14). As a result, the estimated value of the fuel pressure at the fuel injection timing and the actual value are likely to deviate from each other, and the compression is surely performed at the fuel pressure higher than the injection-permitted fuel pressure in the upward stroke (discharge stroke) of the pump plunger of the high-pressure fuel pump. Stroke injection can be performed.

  Further, according to the present embodiment, the fuel pressure from the predetermined timing (injection timing calculation timings T1, T3, T5, T7, T9, T11) to the fuel injection timing (T2, T4, T6, T8, T10, T12). The amount of increase ΔP is calculated (steps S12 and S22), and the fuel at the fuel injection timing is calculated based on the calculated value and the correction value based on the fuel leakage amount ΔL (fuel pressure decrease Δpl due to fuel leakage in the high-pressure fuel pump 3). An estimated pressure value Pest is calculated (step S14). Thereby, the estimated value Pest of the optimal fuel pressure can be calculated for each injection timing.

  Further, according to the present embodiment, the estimated value Pest of the fuel pressure at the fuel injection timing acts on the fuel injection valves 5A to 5D at a predetermined timing (injection timing calculation timings T1, T3, T5, T7, T9, T11). A value obtained by subtracting the fuel pressure decrease Δpl due to fuel leakage in the high-pressure fuel pump 3 from the sum of the fuel pressure (actual value Pr of the common rail fuel pressure) and the fuel pressure increase ΔP. Therefore, the estimated value Pest of the fuel pressure can be accurately calculated using a simple calculation formula.

  Further, according to the present embodiment, by calculating the fuel leakage amount ΔL (the corresponding fuel pressure decrease Δpl due to the fuel leakage) according to the engine speed, the fuel leakage amount ΔL (this corresponding to the variation in the engine speed) Variation in fuel pressure drop Δpl) due to fuel leakage corresponding to the above can be suppressed. As a result, the robustness of the fuel pressure is improved, so that variation in exhaust emission can be suppressed.

  In addition, according to the present embodiment, the higher the engine speed, the smaller the fuel leak amount ΔL (the corresponding fuel pressure drop Δpl due to fuel leak) is calculated, so that good startability can be obtained when the engine speed is high. Can be secured.

  Further, according to the present embodiment, by calculating the fuel leakage amount ΔL (the corresponding fuel pressure drop Δpl due to fuel leakage) according to the engine coolant temperature, the fuel leakage due to the engine coolant temperature variation is calculated. Variations in the amount ΔL (the corresponding fuel pressure drop Δpl due to fuel leakage) can be suppressed. As a result, the robustness of the fuel pressure is improved, so that variation in exhaust emission can be suppressed.

  Further, according to the present embodiment, the lower the engine coolant temperature, the smaller the fuel leak amount ΔL (the corresponding fuel pressure drop Δpl due to fuel leak) is calculated. Therefore, when the engine coolant temperature is low Good startability can be ensured.

  In the present embodiment, the case where the injection timing calculation timing is set to the rising timing of the REF signal has been described. However, the injection timing calculation timing may be set to be the falling timing of the REF signal. Furthermore, it is not limited to the timing of the REF signal. In short, the present invention can be applied to the case where a predetermined crank angle temporally before the injection timing is provided as the injection timing calculation timing.

  In the present embodiment, the pump drive cam 13 is connected to the intake valve camshaft and the high-pressure fuel pump is driven by the pump drive cam. However, the present invention is not limited to this configuration. For example, the pump drive cam 13 may be connected to the exhaust valve camshaft. Furthermore, the pump drive cam can be provided on a shaft other than the camshaft. It is not essential to provide a common rail.

1 is a schematic configuration diagram of an engine fuel supply device showing an embodiment of the present invention. Diagram showing suction / discharge operation of high-pressure fuel pump Change waveform diagram of common rail fuel pressure at engine startup when using conventional technology Waveform diagram for explaining the relationship between plunger lift, injection timing, and rise timing of the REF signal Change waveform diagram of common rail fuel pressure at engine start in this embodiment Flow chart of fuel injection control in this embodiment Calculation flowchart of estimated value of fuel pressure in this embodiment The figure which shows the relationship between an engine speed and fuel leak amount (DELTA) L (fuel pressure fall amount (DELTA) pl by fuel leak). The figure which shows the relationship between engine coolant temperature and fuel leak amount ΔL (fuel pressure drop Δpl due to fuel leak)

Explanation of symbols

1 Fuel tank 2 Low pressure fuel pump (feed pump)
3 High-pressure fuel pump 4 Common rail (Fuel Gallery)
5A to 5D Fuel injection valve 6 Electric motor 7 Fuel supply passage 8 Fuel filter 9 Return passage 10 Low pressure pressure regulator 11 Damper 12 Plunger pump 12a Plunger 12b High pressure chamber (pump chamber)
12c Cylinder 13 Pump drive cam 14 Suction check valve 15 Discharge check valve 16 Control solenoid 17 Leakage fuel passage 18 Orifice 19 Safety valve 20 Engine control unit (ECU)
21 Fuel pressure sensor

Claims (6)

A high-pressure fuel pump that discharges the fuel at a high pressure;
A fuel injection valve that directly supplies high-pressure fuel from the high-pressure fuel pump to a combustion chamber of the engine,
In an engine fuel supply device that performs fuel injection in a compression stroke at the start of the engine,
A fuel pressure estimated value calculating means for calculating in advance an estimated value of the fuel pressure acting on the fuel injection valve at the fuel injection timing at a predetermined timing before the fuel injection timing in the compression stroke;
By comparing the estimated value of the fuel pressure at the fuel injection timing with a predetermined injection permitted fuel pressure when the engine is started, fuel injection is prohibited while the estimated fuel pressure value is less than the permitted injection fuel pressure. Fuel injection prohibition / compression stroke injection permission determination means for permitting compression stroke injection when the estimated value of the fuel pressure is equal to or higher than the injection permitted fuel pressure,
The fuel pressure estimated value calculating means has means for calculating the amount of fuel leakage in the high-pressure fuel pump in accordance with engine operating conditions,
The means for calculating the fuel leakage amount includes a map showing a relationship among the engine speed, the engine coolant temperature, and the fuel leakage amount, and calculates the fuel leakage amount smaller as the engine speed is higher. In addition, the lower the coolant temperature of the engine, the smaller the amount of fuel leakage,
And corrected by the fuel leakage quantity, the fuel supply device for an engine, and calculates the estimated value of the fuel pressure at the fuel injection timing. The volume of the pump chamber is changed by the reciprocating motion of the pump plunger, the fuel is sucked into the pump chamber in the stroke in which the pump plunger is lowered, and the fuel in the pump chamber is increased in pressure and discharged in the stroke in which the pump plunger is raised. A high-pressure fuel pump;
A fuel injection valve that directly supplies high-pressure fuel from the high-pressure fuel pump to a combustion chamber of the engine,
In an engine fuel supply device that performs fuel injection in a compression stroke at the start of the engine,
For a cylinder that has fuel injection timing in the compression stroke during the stroke in which the pump plunger ascends, when the fuel injection timing of the cylinder reaches a predetermined timing, the fuel injection timing is the same as that of the cylinder. Fuel pressure estimated value calculating means for calculating in advance an estimated value of the fuel pressure acting on the valve;
By comparing the estimated value of the fuel pressure at the fuel injection timing of the cylinder with the predetermined injection permission fuel pressure at the time of starting the engine, the fuel injection of the cylinder is performed while the estimated value of the fuel pressure is less than the injection permission fuel pressure. A fuel injection prohibition / compression stroke injection permission determining means for prohibiting and permitting the compression stroke injection of the cylinder when the estimated value of the fuel pressure becomes equal to or higher than the fuel pressure permitted for injection;
The fuel pressure estimated value calculating means includes means for calculating a fuel leakage amount in the high-pressure fuel pump according to an engine operating condition, and the means for calculating the fuel leakage amount includes an engine speed, an engine A map showing the relationship between the coolant temperature and the amount of fuel leakage is provided, and the higher the engine speed, the smaller the fuel leak amount is calculated, and the lower the engine coolant temperature is, the lower the fuel leak amount is. A fuel supply device for an engine, wherein the estimated value of the fuel pressure at the fuel injection timing is calculated by calculating a smaller value and correcting the fuel leakage amount.   An increase in fuel pressure from the predetermined timing to the fuel injection timing is calculated, and an estimated value of the fuel pressure at the fuel injection timing is calculated based on the calculated value and a correction value based on the fuel leakage amount. The engine fuel supply device according to claim 1.   The estimated value of the fuel pressure at the fuel injection timing is obtained by adding the fuel pressure actually acting on the fuel injection valve at the predetermined timing and the increase in the fuel pressure. 4. The fuel supply device for an engine according to claim 3, wherein the value is a value corrected by subtracting a decrease in fuel pressure due to fuel leakage at the pump.   An increase in fuel pressure from a predetermined timing before the fuel injection timing of the cylinder to a fuel injection timing of the cylinder is calculated, and the fuel injection timing is calculated based on the calculated value and a correction value based on the fuel leakage amount. 3. The fuel supply device for an engine according to claim 2, wherein an estimated value of the fuel pressure at is calculated.   The estimated value of the fuel pressure at the fuel injection timing of the cylinder is the fuel pressure actually acting on the fuel injection valve of the cylinder at a predetermined timing before the fuel injection timing of the cylinder, and the fuel of the cylinder 6. The engine according to claim 5, wherein the corrected value is obtained by subtracting a decrease in fuel pressure due to fuel leakage at the high-pressure fuel pump from a value obtained by adding the increase in fuel pressure until the injection timing. Fuel supply system.

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