JP4613920B2 - Fuel injection device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection device for an internal combustion engine including a pressure accumulator for storing high-pressure fuel.

  A conventional fuel injection device for an internal combustion engine includes a fuel pump including a high-pressure pump that pressurizes sucked fuel and pumps high-pressure fuel to an accumulator, and an adjustment valve that adjusts the fuel pumping amount of the high-pressure pump. . The fuel pressure from the fuel pump to the pressure accumulator is controlled to control the fuel pressure in the pressure accumulator to the target pressure. At this time, the operation amount of the fuel pump is set based on a predetermined gain, so that the fuel pressure in the accumulator follows the change in the target fuel pressure with good response.

This gain is set for each engine speed and pressure deviation, for example. Further, when the pressure or temperature of the fuel pumped by the fuel pump changes, the amount of change in the fuel pressure in the accumulator changes, so that the gain is corrected by the bulk elastic coefficient in order to cancel it in advance (for example, , See Patent Document 1).
JP 2000-234543 A

  Here, in the high-pressure fuel injection system, there are a dynamic leak and a static leak of the injector, and further an internal leak of the fuel pump. The amount of leakage varies depending on the fuel temperature, fuel pressure, and engine speed. Due to the influence of this leak, the rate of change of the fuel pressure in the accumulator with respect to a predetermined operation amount of the fuel pump becomes different. In the above-described conventional device, the leak amount increases in a region where the fuel temperature and the fuel pressure are high. Therefore, the change rate of the fuel pressure in the pressure accumulator is reduced and the control responsiveness of the fuel pressure in the pressure accumulator is reduced. On the other hand, the amount of leak is reduced in the region where the fuel temperature and the fuel pressure are low. There is a problem that the rate of change of the pressure increases and the fuel pressure in the pressure accumulator easily causes overshoot.

  The present invention has been made in view of the above points, and it is an object of the present invention to prevent or suppress an overshoot of fuel pressure in the accumulator and a decrease in control response due to the influence of a leak.

In order to achieve the above object, according to the first aspect of the present invention, the operation of the regulating valve (53) for adjusting the fuel pumping amount of the high-pressure pump (52) is feedback-controlled by the pressure control means (3), thereby (1) A fuel injection device for an internal combustion engine that controls the pressure of the high-pressure fuel in the internal combustion engine to a target pressure, wherein the pressure control means (3) increases the feedback control gain as the pressure of the high-pressure fuel increases. It is characterized by being enlarged.

In this way, it is possible to change the speed of the pressure accumulator in the fuel pressure even if the pressure changes in the high-pressure fuel to a substantially constant, preventing a decrease in overshoot and control response of the accumulator in the fuel pressure or Can be suppressed.

According to the second aspect of the present invention, the operation of the regulating valve (53) for adjusting the fuel pumping amount of the high-pressure pump (52) is feedback-controlled by the pressure control means (3), and the high-pressure fuel in the pressure accumulator (1). The pressure control means (3) increases the gain of feedback control as at least one of the temperature and pressure of the high-pressure fuel increases. Further, the pressure control means (3) executes feedback control by PID control, and increases the gain of the proportional term and the gain of the integral term as the pressure of the high-pressure fuel increases. Features.
In this way, even if the pressure of the high-pressure fuel changes, the rate of change of the fuel pressure in the accumulator can be made substantially constant. Can be suppressed.

  In addition, if the gain of the proportional term and the gain of the integral term are increased in a quadratic curve as the pressure of the high-pressure fuel increases, the rate of change of the fuel pressure in the accumulator even if the pressure of the high-pressure fuel changes Therefore, it is possible to reliably prevent or suppress an overshoot of the fuel pressure in the accumulator and a decrease in control responsiveness.

  The pressure control means (3) executes feedback control by PID control. If the gain of the proportional term and the gain of the integral term are increased as the temperature of the high pressure fuel increases, the high pressure fuel is increased. Since the rate of change of the fuel pressure in the accumulator can be made substantially constant even if the temperature of the accumulator changes, overshoot of the fuel pressure in the accumulator and a decrease in control response can be prevented or suppressed.

In the invention according to claim 5, the operation of the regulating valve (53) for adjusting the fuel pumping amount of the high-pressure pump (52) is feedback-controlled by the pressure control means (3), and the high-pressure fuel in the accumulator (1) is controlled. The pressure control means (3) increases the gain of feedback control as at least one of the temperature and pressure of the high-pressure fuel increases. Further, the pressure control means (3) executes feedback control by PID control, and in the region where the temperature of the high pressure fuel is lower than the set temperature, the proportional term increases as the temperature of the high pressure fuel decreases. The gain is reduced, and the gain of the proportional term is made constant in a region where the temperature of the high-pressure fuel exceeds the set temperature.
In this way, when the temperature of the high pressure fuel is low, the rate of change of the fuel pressure in the accumulator is reduced, so that overshoot of the fuel pressure in the accumulator can be reliably prevented or suppressed.

  Also, in the region where the temperature of the high-pressure fuel exceeds the set temperature, if the gain of the integral term is increased as the temperature of the high-pressure fuel increases, the steady-state deviation when the temperature of the high-pressure fuel is high decreases, and the rail pressure Can be accurately controlled to the target rail pressure.

  In addition, the code | symbol in the bracket | parenthesis of each means described in a claim and this column shows the correspondence with the specific means as described in embodiment mentioned later.

  An embodiment of the present invention will be described. FIG. 1 is a diagram illustrating an overall configuration of a fuel injection device for an internal combustion engine according to an embodiment.

  As shown in FIG. 1, the fuel injection device includes a pressure accumulator 1 in which high-pressure fuel is stored. A plurality of injectors 2 are connected to the pressure accumulator 1, and the injector 2 is controlled by an electronic control unit (hereinafter referred to as ECU) 3 to open a valve for a predetermined period at a predetermined time and is stored in the pressure accumulator 1. High pressure fuel is injected into each cylinder of an internal combustion engine (more specifically, a diesel engine, not shown).

  Specifically, the injector 2 is controlled to open and close by controlling the fuel pressure in the back pressure chamber formed therein. An injection system leak pipe L1 is connected to the injector 2, and surplus fuel in the injector 2 and fuel discharged from the back pressure chamber are supplied to the fuel tank 4 via the injection system leak pipe L1 and the common leak pipe L2. Returned.

  The fuel pump 5 sucks fuel from the fuel tank 4, pressurizes the sucked fuel to a high pressure, and pumps the fuel to the pressure accumulator 1. The fuel pump 5 includes a feed pump 51 that sucks fuel from the fuel tank 4, and a high-pressure pump that pressurizes the fuel sent from the feed pump 51 based on the reciprocation of a plunger (not shown) and pumps the fuel to the accumulator 1. 52 and an adjustment valve 53 that adjusts the opening area of the fuel passage from the feed pump 51 to the high-pressure pump 52.

  The feed pump 51 and the high-pressure pump 52 are driven by an internal combustion engine and are driven at a rotational speed proportional to the engine rotational speed. The adjustment valve 53 is configured by an electromagnetic valve and is controlled by the ECU 3. More specifically, the adjustment valve 53 continuously changes the position of the valve body (not shown) according to the magnitude of the current supplied to the coil (not shown), thereby reducing the opening area of the fuel passage. It is continuously adjustable. Then, by changing the opening area of the fuel passage by the adjustment valve 53, the fuel intake amount of the high-pressure pump 52 is adjusted, and consequently the fuel pumping amount is adjusted.

  A pump system leak pipe L3 is connected to the fuel pump 5, and the fuel discharged from the high pressure pump 52 is returned to the fuel tank 4 via the pump system leak pipe L3 and the common leak pipe L2.

  The accumulator 1 is provided with a pressure sensor 61 that detects fuel pressure in the accumulator 1 (hereinafter referred to as rail pressure) and a temperature sensor 62 that detects fuel temperature in the accumulator 1. Further, the internal combustion engine is provided with a rotation speed sensor 63 for detecting the engine rotation speed.

  The ECU 3 includes a well-known microcomputer including a CPU, ROM, RAM, EEPROM, etc. (not shown), and performs arithmetic processing according to a program stored in the microcomputer. The ECU 3 receives signals from the pressure sensor 61, the temperature sensor 62, and the rotation speed sensor 63, and various information such as the accelerator opening from various sensors (not shown) as needed.

  Then, the ECU 3 calculates the optimal injection timing and injection amount (injection period) according to the operating state of the internal combustion engine and the vehicle, and controls the valve opening timing and valve opening period of each injector 2.

  In addition, the ECU 3 controls the adjustment valve 53 to adjust the amount of fuel sucked into the high-pressure pump 52, thereby adjusting the fuel pumping amount of the high-pressure pump 52 and controlling the rail pressure to match the target pressure. To do. In the present embodiment, the ECU 3 performs feedback control of the operation of the adjustment valve 53 by PID control.

  Next, rail pressure control executed by the ECU 3 as pressure control means will be described. FIG. 2 is a flowchart showing a procedure for matching the rail pressure with a target pressure (hereinafter referred to as a target rail pressure). The ECU 3 executes this processing routine as an interrupt process for each predetermined crank angle of the internal combustion engine.

  First, the target rail pressure is calculated based on the fuel injection amount and the engine speed NE detected by the engine speed sensor 63 (step S100). The relationship between the fuel injection amount and the engine speed NE and the target rail pressure is stored in the memory of the ECU 3 as function data. The ECU 3 refers to this function data to calculate the target rail pressure. The fuel injection amount is a value that is calculated based on the accelerator pedal depression amount and the engine speed NE in a routine different from this routine and stored in the memory of the ECU 3.

  Subsequently, the current rail pressure is detected by the pressure sensor 61 (step S101), and a difference ΔP (hereinafter referred to as a pressure deviation) between the target rail pressure and the current rail pressure is obtained (step S102).

  Subsequently, based on the pressure deviation ΔP and the engine speed NE obtained in step S102, a basic proportional term gain MKP, integral term gain MKI, and differential term gain MKD in the PID control equation are calculated (step S103). The relationship between the pressure deviation ΔP and the engine speed NE and the respective gains MKP, MKI, and MKD is obtained in advance by experiment, and is stored in the memory of the ECU 3 as function data. The ECU 3 refers to the function data and determines each gain. MKP, MKI, and MKD are calculated.

  Subsequently, when the engine speed NE is equal to or higher than a predetermined value (for example, 1000 rpm), that is, when step S104 is YES, in steps S105 and 106, the gains MKP, MKI, and MKD obtained in step S103 are corrected. .

  Specifically, based on the fuel temperature in the pressure accumulator 1 detected by the temperature sensor 62, the proportional term temperature gain coefficient KPT, the integral term temperature gain coefficient KIT, and the differential term temperature gain coefficient KDT are calculated, and the rail pressure is calculated. Based on this, a proportional term pressure gain coefficient KPP, an integral term pressure gain coefficient KIP, and a derivative term pressure gain coefficient KDP are calculated (step S105).

  Here, FIG. 3 shows the relationship between the fuel temperature and the leak amount. 3 is the total amount of dynamic leak and static leak of the injector 2, and further the internal leak of the fuel pump 5. In FIG. As shown in FIG. 3, the amount of leak increases in proportion to the increase in fuel temperature.

  In the memory of the ECU 3, the relationship between the proportional term temperature gain coefficient KPT and the differential term temperature gain coefficient KDT and the fuel temperature as shown in FIG. 4 is stored as function data. As shown in FIG. 4, in the region where the temperature of the high pressure fuel is equal to or lower than the set temperature Tb (for example, 40 ° C.), the proportional term temperature gain coefficient KPT and the differential term temperature gain coefficient KDT as the temperature of the high pressure fuel decreases. (However, KPT ≦ 1, KDT ≦ 1). In the region where the temperature of the high-pressure fuel exceeds the set temperature Tb, KPT = 1 and KDT = 1 are set so that no substantial correction is made. Then, the ECU 3 calculates the proportional term temperature gain coefficient KPT and the differential term temperature gain coefficient KDT by referring to the function data shown in FIG.

  Further, the memory of the ECU 3 stores the relation between the integral term temperature gain coefficient KIT and the fuel temperature as function data as shown in FIG. As shown in FIG. 5, in the region where the temperature of the high-pressure fuel is equal to or lower than the set temperature Tb, KIT = 1 is set so that no substantial correction is made. Further, in the region where the temperature of the high pressure fuel exceeds the set temperature Tb, the integral term temperature gain coefficient KIT is increased as the temperature of the high pressure fuel becomes higher (where KIT ≧ 1). Then, the ECU 3 calculates the integral term temperature gain coefficient KIT by referring to the function data shown in FIG.

  FIG. 6 shows the relationship between rail pressure and leak amount for each fuel temperature. Note that the leak amount in FIG. 6 is the total amount of dynamic leak, static leak, and internal leak of the fuel pump 5 of the injector 2. As shown in FIG. 6, the leak amount increases as the rail pressure increases, and more specifically, there is little change in the leak amount in the region where the rail pressure is approximately 80 MPa or less, and the rail pressure exceeds approximately 80 MPa. In the region, the leak amount increases in a quadratic curve.

  In the memory of the ECU 3, the relationship between the proportional term pressure gain coefficient KPP, the integral term pressure gain coefficient KIP, the differential term pressure gain coefficient KDP and the rail pressure as shown in FIG. 7 is stored as function data. As shown in FIG. 7, in a region where the pressure of the high-pressure fuel is equal to or lower than the set pressure Pb (for example, 80 MPa), KPP = 1, KIP = 1, and KDP = 1 are set so that no substantial correction is made. In the region where the pressure of the high pressure fuel exceeds the set pressure Pb, each pressure gain coefficient KPP, KIP, KDP increases in a quadratic curve as the pressure of the high pressure fuel increases (provided that KPP ≧ 1, KIP ≧ 1, KDP ≧ 1). Then, the ECU 3 calculates each pressure gain coefficient KPP, KIP, KDP by referring to the function data shown in FIG.

  Then, based on the basic gains MKP, MKI, MKD obtained in step S103 and the gain coefficients KPT, KIT, KDT, KPP, KIP, KDP obtained in step S105, the final proportional term gain KP (Where KP = MKP * KPT * KPP), final integral term gain KI (where KI = MKI * KIT * KIP), final differential term gain KD (where KD = MKD * KDT * KDP) Calculate (step S106).

  Subsequently, after calculating the proportional term QFP (where QFP = KP * ΔP), the integral term QFI (where QFI = KI * ∫ΔPdt), and the differential term QFD (where QFD = KD * dΔP / dt) Is added to calculate the basic required discharge amount QFB (QFB = QFP + QFI + QFD) (step S107). Incidentally, the required discharge amount corresponds to the fuel pumping amount of the high-pressure pump 52 necessary for making the rail pressure coincide with the target rail pressure.

  Subsequently, based on the fuel temperature in the pressure accumulator 1 and the rail pressure, the volume elastic modulus PCREF of the fuel is calculated from the characteristic equation stored in the memory of the ECU 3 (step S108). The bulk modulus of elasticity PCREF decreases as the fuel temperature and rail pressure increase.

  Subsequently, the final required discharge amount QPMP is calculated by the following equation (1) based on the basic required discharge amount QFB obtained in step S107 and the bulk elastic modulus PCREF obtained in step S108 (step S109). ).

QPMP = QFB * PCREF / KVOL (1)
KVOL is the volume of the high pressure part. More specifically, KVOL is the sum of the volume of the fuel passage between the high pressure pump 52 and the accumulator 1 and the volume in the accumulator 1.

  Subsequently, based on the final required discharge amount QPMP obtained in step S109, a current value to be supplied to the regulating valve 53 is calculated, and a drive signal for operating the regulating valve 53 is output (step S110). The relationship between the final required discharge amount QPMP and the current value to be supplied to the regulating valve 53 is obtained in advance by experiment and is stored in the memory of the ECU 3 as function data. The ECU 3 refers to this function data and determines the current value. calculate.

  By controlling the current value supplied to the regulating valve 53 in step S110, the fuel suction amount of the high-pressure pump 52 is adjusted, the fuel pumping amount is adjusted, and the rail pressure is controlled to the target rail pressure. And after performing the process of step S110, ECU3 once complete | finishes this process routine.

  FIG. 8 shows the relationship between the engine speed NE and the leak amount. In a region where the engine speed NE is low (approximately 1000 rpm or less), the rate of change of the leak amount is extremely large, and the engine speed is low. The amount of leak in the region where NE is low is dominated by the rotational speed dependency. Therefore, when the engine speed NE is less than the predetermined value, that is, when step S104 is NO, KP = MKP, KI = MKI, KD = MKD, and each gain MKP, MKI, MKD obtained in step S103 is corrected. This is not performed (step S111).

  In this embodiment, since the gain of feedback control is increased as the temperature and pressure of the high-pressure fuel increase, the rate of change of the rail pressure even if the amount of leak changes due to a change in the temperature or pressure of the high-pressure fuel. Can be made substantially constant, and rail pressure overshoot and control response degradation can be prevented or suppressed.

  In addition, as the pressure of the high-pressure fuel increases, the gain of the proportional term and the gain of the integral term are increased in a quadratic curve, so the change speed of the rail pressure can be made substantially constant with high accuracy. Rail pressure overshoot and control responsiveness can be reliably prevented or suppressed.

  Further, in the region where the temperature of the high-pressure fuel is equal to or lower than the set temperature Tb, the gain of the proportional term is reduced as the temperature of the high-pressure fuel decreases. As a result, the rail pressure overshoot can be reliably prevented or suppressed.

  Furthermore, in the region where the temperature of the high pressure fuel exceeds the set temperature Tb, the gain of the integral term is increased as the temperature of the high pressure fuel increases, so that the steady-state deviation when the temperature of the high pressure fuel is high is small. Thus, the rail pressure can be accurately controlled to the target rail pressure.

(Other embodiments)
In the above embodiment, the adjustment valve 53 is a valve that continuously adjusts the opening area of the fuel passage according to the magnitude of the current. However, the adjustment valve 53 is of a type that opens and closes the fuel passage from the feed pump 51 to the high-pressure pump 52. A regulating valve may be used. When this type of regulating valve is used, the regulating valve 53 is opened during the intake stroke of the high-pressure pump 52 and fuel suction of the high-pressure pump 52 is started, and the regulating valve 53 is closed during the intake stroke. As a result, the fuel intake is terminated. All of the fuel sucked into the high-pressure pump 52 during the valve opening period of the regulating valve 53 is pressurized and pumped to the pressure accumulator 1 in the pumping stroke following the suction stroke. Therefore, the fuel pumping amount of the high-pressure pump 52 is adjusted by changing the valve opening period of the adjusting valve 53.

It is a figure showing the whole fuel injection device for internal-combustion engines concerning one embodiment of the present invention. It is a flowchart which showed the control procedure of the rail pressure in one Embodiment. It is a figure which shows the relationship between fuel temperature and the amount of leaks. It is a figure which shows the relationship between the proportional term temperature gain coefficient KPT and the differential term temperature gain coefficient KDT, and fuel temperature. It is a figure which shows the relationship between integral term temperature gain coefficient KIT and fuel temperature. It is a figure which shows the relationship between rail pressure and leak amount. It is a figure which shows the relationship between a proportional term pressure gain coefficient KPP, an integral term pressure gain coefficient KIP, a differential term pressure gain coefficient KDP, and rail pressure. FIG. 8 is a graph showing the relationship between the engine speed NE and the leak amount.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Accumulator, 2 ... Injector, 3 ... Electronic control unit, 52 ... High pressure pump, 53 ... Adjusting valve.

Claims (7)

A pressure accumulator (1) for storing high-pressure fuel;
An injector (2) for injecting high-pressure fuel stored in the pressure accumulator (1) into the internal combustion engine;
A high pressure pump (52) for pressurizing the sucked fuel and pumping high pressure fuel to the accumulator (1);
An adjustment valve (53) for adjusting the fuel pumping amount of the high-pressure pump (52);
Pressure control means (3) for feedback-controlling the operation of the regulating valve (53) to control the pressure of the high-pressure fuel in the accumulator (1) to a target pressure,
The internal combustion engine fuel injection device, wherein the pressure control means (3) increases the gain of feedback control as the pressure of the high-pressure fuel increases. A pressure accumulator (1) for storing high-pressure fuel;
An injector (2) for injecting high-pressure fuel stored in the pressure accumulator (1) into the internal combustion engine;
A high pressure pump (52) for pressurizing the sucked fuel and pumping high pressure fuel to the accumulator (1);
An adjustment valve (53) for adjusting the fuel pumping amount of the high-pressure pump (52);
Pressure control means (3) for feedback-controlling the operation of the regulating valve (53) to control the pressure of the high-pressure fuel in the accumulator (1) to a target pressure,
The pressure control means (3) increases the feedback control gain as at least one of the temperature and pressure of the high-pressure fuel increases.
Further, the pressure control means (3) performs feedback control by PID control, and increases the gain of the proportional term and the gain of the integral term as the pressure of the high pressure fuel increases. A fuel injection device for an internal combustion engine.   The pressure control means (3) increases the gain of the proportional term and the gain of the integral term in a quadratic curve as the pressure of the high-pressure fuel increases. Fuel injection device for internal combustion engine.   The pressure control means (3) executes feedback control by PID control, and increases the gain of the proportional term and the gain of the integral term as the temperature of the high-pressure fuel increases. The fuel injection device for an internal combustion engine according to any one of claims 1 to 3. A pressure accumulator (1) for storing high-pressure fuel;
An injector (2) for injecting high-pressure fuel stored in the pressure accumulator (1) into the internal combustion engine;
A high pressure pump (52) for pressurizing the sucked fuel and pumping high pressure fuel to the accumulator (1);
An adjustment valve (53) for adjusting the fuel pumping amount of the high-pressure pump (52);
Pressure control means (3) for feedback-controlling the operation of the regulating valve (53) to control the pressure of the high-pressure fuel in the accumulator (1) to a target pressure,
The pressure control means (3) increases the feedback control gain as at least one of the temperature and pressure of the high-pressure fuel increases.
Further, the pressure control means (3) executes feedback control by PID control, and in a region where the temperature of the high pressure fuel is lower than the set temperature, the gain of the proportional term is increased as the temperature of the high pressure fuel becomes lower. And the gain of the proportional term is made constant in a region where the temperature of the high-pressure fuel exceeds the set temperature.   The pressure control means (3) makes the gain of the integral term constant in a region where the temperature of the high pressure fuel is lower than or equal to a preset temperature, and in the region where the temperature of the high pressure fuel exceeds the preset temperature, 6. The fuel injection device for an internal combustion engine according to claim 4, wherein the gain of the integral term is increased as the value increases. The high-pressure pump (52) is driven by the internal combustion engine,
The pressure control means (3) does not change the gain based on changes in temperature and pressure of the high-pressure fuel in a region where the rotational speed of the internal combustion engine is 1000 rpm or less. The fuel injection device for an internal combustion engine according to any one of the above.

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