JP2000179427A - Fuel injection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently operate an electrically driven pump which is used for accumulating high pressure fuel in a common rail, and adjust fluctuation of the fuel pressure inside the common rail at the time of abrupt fluctuation of an injection quantity. SOLUTION: In this fuel injection device 1, high pressure fuel is accumulated in a common rail 7 by means of a high pressure pump 5. Rotational speed of the high pressure pump 5 is feedback-controlled for keeping fuel pressure in the common rail 7 at a specified value. A solenoid valve 21 is arranged on a fuel return passage 16 from the common rail 7 to a fuel tank 2. The solenoid valve 21 is opened when the rotational speed of the high pressure pump 5 is lower than a speed value N1, while it is closed when the rotational speed of the high pressure pump 5 is higher than a speed value N2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection device which uses an electric pump to directly supply high-pressure fuel stored in a common rail to each cylinder of an internal combustion engine via an injector.

[0002]

2. Description of the Related Art In an internal combustion engine system in which fuel is directly injected into a cylinder, a fuel pressure of about 4 to 10 MPa, which is 20 times higher than that of a conventional manifold injection type internal combustion engine, is required. You. For this reason, in an internal combustion engine system in which fuel is directly injected into a cylinder, a ratio of power consumption required for increasing the pressure of the fuel to engine power consumption is increased, so that a minimum necessary high-pressure fuel is supplied. A fuel-based system is needed.

As a solution to this, a system using an electric pump driven by an electric motor has been proposed. For example, a pressure-accumulation type fuel injection device as disclosed in Japanese Patent Application Laid-Open No. 9-209870 is known. It is.

This accumulator type fuel injection device is provided with a fuel return passage from the common rail to the fuel tank in order to reduce the fuel pressure fluctuation in the common rail caused by injecting fuel from the injector and to obtain stable fuel injection characteristics. By providing an electromagnetic valve and controlling the opening and closing of this electromagnetic valve in response to a control signal to the injector, by superimposing the pressure fluctuation in the common rail and the pressure fluctuation in the common rail in response to fuel injection from the injector In addition, the pressure fluctuation in the common rail due to the fuel injection from the injector is absorbed, and the fuel pressure in the common rail is suppressed within a predetermined fluctuation range.

[0005]

However, in a fuel injection device that stores high-pressure fuel in a common rail by using the above-described electric pump driven by an electric motor, the orifice is always rotated while the electric motor is rotated. Since the fuel in the common rail is maintained at a predetermined pressure while the fuel is appropriately circulated through the fuel tank, (1) wasteful electric power for the fuel circulated into the fuel tank through the orifice is wasted in the electric motor. However, the efficiency of the fuel supply system is low, and the size of the motor is increased, which hinders miniaturization of the device. (2) When the electric pump is operated at a low speed, the pump volume efficiency is reduced. There are problems such as a decrease in motor efficiency and a decrease in motor efficiency.

[0006] It is therefore an object of the present invention to provide a fuel injection device which can solve the above-mentioned problems in the prior art.

[0007]

In the present invention, attention is paid to the fact that the discharge flow rate of the electric pump is equal to the sum of the orifice recirculation flow rate and the injection quantity, and the discharge flow rate of the electric pump is proportional to its rotation speed. If it is determined that the rotation speed of the electric pump is high and the injection amount is large, the fuel return passage is closed by an electromagnetic valve to reduce the orifice recirculation flow rate to zero, thereby reducing the electric pump discharge amount and reducing its power consumption. On the other hand, when it is determined that the rotation speed of the electric pump is small and the injection amount is small, the fuel return passage is opened by an electromagnetic valve to increase the discharge amount of the electric pump, that is, the rotation speed of the electric pump is increased. The object of the present invention is to solve the above problem by avoiding use in a low efficiency area.

According to the first aspect of the present invention, the fuel supplied from the fuel tank is pressurized by the electric pump to accumulate the fuel in the common rail, and the high pressure fuel accumulated in the common rail is injected from the injector. In, a rotation speed control means for controlling the rotation speed of the electric pump so as to maintain the fuel pressure in the common rail at a required value, and a fuel return passage for recirculating fuel from the common rail to the fuel tank, A solenoid valve for opening and closing the fuel return passage; and a first for determining whether a rotation speed of the electric pump is lower than a first reference value.
Determining means for determining whether the rotation speed of the electric pump is higher than a second reference value greater than the first reference value; and responding to the first and second determining means. When the rotation speed of the electric pump is lower than the first reference value, the electromagnetic valve is opened, and when the rotation speed of the electric pump is higher than the second reference value, the electromagnetic valve is closed. There has been proposed a fuel injection device including electromagnetic valve control means for controlling opening and closing of an electromagnetic valve.

The rotation speed of the electric pump is controlled by a rotation speed control means so that the pressure in the common rail becomes a predetermined value, and the fuel pressurized by the electric pump is sent into the common rail. As the fuel injection amount decreases, the rotation speed of the electric pump decreases, and when the rotation speed of the electric pump becomes lower than the first reference value, the fuel return passage is opened. As a result, the amount of fuel recirculated through the fuel return passage increases, thereby increasing the rotation speed of the electric pump and operating efficiently.

On the other hand, when the rotation speed of the electric pump increases due to the increase in the fuel injection amount, and when the rotation speed of the electric pump becomes higher than the second reference value, the fuel return passage is closed and the fuel return passage is closed. The amount of recirculated fuel becomes zero, the rotational speed of the electric pump decreases, and the power consumption of the electric pump is reduced.

Further, according to the above-mentioned structure, the opening and closing of the solenoid valve is provided with a hysteresis characteristic, the opening and closing control of the solenoid valve is stably performed, and the fuel pressure in the common rail is more preferably controlled to a predetermined value. it can.

According to a second aspect of the present invention, in the fuel injection device according to the first aspect, a difference between the first reference value and the second reference value is determined in accordance with an increase in fuel pressure in the common rail. A fuel injection device modified to be larger is proposed.

Since the fuel is incompressible, the rotation speed of the electric pump after the solenoid valve is closed will be substantially the same even if the pressure in the common rail changes if the injection amount is the same. That is, when the rotation speed of the electric pump is high in the high injection amount state, the injection amount decreases, whereby the injection amount when the rotation speed of the electric pump reaches the rotation speed at which the solenoid valve is opened is: Since the amount of reflux from the common rail is zero, it is substantially the same regardless of the pressure in the common rail at that time. However, if the solenoid valve is open and fuel is recirculating from the common rail in proportion to the square root of the pressure, the higher the pressure in the common rail, the greater the rotation speed of the electric pump will increase with a smaller injection amount. Become. As a result, if the second reference value is fixed at a constant value irrespective of the pressure in the common rail, when the pressure in the common rail increases, the solenoid valve is temporarily switched from closed to open, and then the injection is performed. When the amount increases, the value immediately exceeds the second reference value, and a phenomenon occurs in which the solenoid valve immediately returns to the closed state. This means that the width of the hysteresis given for the opening / closing control of the electromagnetic valve is narrowed, and the opening / closing of the electromagnetic valve is frequently controlled, so that stable control may not be performed. To prevent this, the first reference value and the second reference value are not fixed to fixed values, but are set according to the set value of the target fuel pressure at each time. Is constantly changed to an appropriate value, and the frequent opening and closing operation of the solenoid valve can be prevented.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of a pressure-accumulation type fuel injection device according to the present invention. The fuel injection device 1 shown in FIG.
And a low-pressure pump 3 and its drive motor 4, a high-pressure pump 5 and its drive motor 6, a common rail 7 as a pressure accumulator for storing pressurized fuel, and an injector 8 and its control circuit 9.

The low-pressure pump 3 draws fuel from the fuel tank 2 through the fuel filter 11 and supplies it to the high-pressure pump 5 as low-pressure fuel. High pressure pump 5 which is an electric pump
The high-pressure fuel is further pressurized from the low-pressure fuel and supplied to the common rail 7 through a fuel supply passage 12 formed by a high-pressure pipe.

The fuel pressure in the common rail 7 is detected by a pressure sensor 13, a detection signal from the pressure sensor 13 is input to a control unit 14, and the rotation speed of the drive motor 6 of the high-pressure pump 5 is responsive to the detection signal. By controlling, the fuel pressure in the common rail 7 can be set to a predetermined target pressure. Here, the control unit 14 is configured as a microcomputer system having a known configuration, and the control of the rotational speed of the high-pressure pump 5 is executed according to a control program for controlling the rotational speed described later.

The high-pressure fuel (for example, high-pressure gasoline) in the common rail 7 controls the high-pressure fuel injection pipe 15 by sequentially opening and closing the injectors 8 according to a control signal from a control circuit 9 in accordance with the rotation speed and load of the engine. The fuel is injected directly from the injector 8 into a cylinder (not shown) of the engine.

An orifice 17 is provided in a fuel return passage 16 formed by a return pipe from the common rail 7 to the fuel tank 2. Excess high-pressure fuel in the common rail 7 is returned to the fuel tank 2 through the orifice 17. It has a configuration that can be used. In the drawings, a single line indicates a low-pressure portion, and a double line indicates a high-pressure portion, among lines indicating a fuel pipe.

In the fuel injection device 1, an electromagnetic valve 21 is provided upstream of the orifice 17 in the fuel return passage 16.
Is provided, and the opening and closing of the electromagnetic valve 21 is controlled by the control unit 14. Note that the solenoid valve 21 may be provided downstream of the orifice 17. The electromagnetic valve 21 is opened and closed by the control unit 14 so as to be opened when the rotation speed of the high-pressure pump 5 is low and closed when the rotation speed of the high-pressure pump 5 is high. This opening and closing control also
The control is executed in accordance with a control program described later for the solenoid valve opening / closing control, and details thereof will be described later.

FIG. 2 shows the common rail 7 executed in the microcomputer system in the control unit 14.
4 is a flowchart showing a program for controlling the fuel pressure in the inside. First, at step S1, the actual fuel pressure Pa in the common rail 7 detected by the pressure sensor 13 is determined.
The value ΔP of the deviation Pt−Pa from the target fuel pressure Pt is calculated as the deviation value. Here, the actual fuel pressure Pa
Is calculated based on data obtained from an output signal from the pressure sensor 13 by an interface circuit (not shown) of the microcomputer system in the control unit 14.

In the next step S2, a value obtained by multiplying the deviation value ΔP by a proportional constant Kp is set as a proportional output. In step S3, the sum of the value obtained by multiplying the deviation value ΔP by the integration constant Ki and the previous integrated output is set as the current integrated output.

In step S4, the sum of the proportional output obtained in step S2 and the integral output obtained in step S3 is calculated as a motor output. Step S shown in FIG.
1 to S4 are repeatedly executed at appropriate time intervals, so that the rotational speed of the drive motor 6 is feedback-controlled by PI control, and the actual fuel pressure P
a is maintained at the target fuel pressure Pt.

FIG. 3 is a flowchart showing a program for controlling the opening and closing of the solenoid valve 21 which is executed in the microcomputer system in the control unit 14. First, in step S11, it is determined whether or not the solenoid valve 21 is currently open. If it is determined that the solenoid valve 21 is currently in the closed state, the determination result of step S11 is NO, and the process proceeds to step S12.

In step S12, it is determined whether the rotation speed of the high-pressure pump 5 is lower than a predetermined speed N1. It is generally known that the high-pressure pump 5 has a low pump volume efficiency in a low rotation range. If the high-pressure pump 5 is operated while avoiding the low rotation range, the high-pressure pump 5 can be operated efficiently. . The predetermined speed N1 indicates a lower limit value of the rotation speed of the high-pressure pump 5 necessary to secure a desired operation efficiency of the high-pressure pump 5. When the rotation speed of the high-pressure pump 5 decreases due to the decrease in the fuel injection amount, and it is determined that the rotation speed of the high-pressure pump 5 is lower than the predetermined speed N1, the determination result of step S12 is YES, and the process proceeds to step S13. Here, an opening command for the solenoid valve 21 is issued, and the processing for opening and closing control of the solenoid valve 21 ends.

As described above, when the high-pressure pump 5 enters an inefficient operation range below the predetermined speed N1 due to a decrease in the rotation speed of the high-pressure pump 5, the solenoid valve 21 is opened and the common rail 7 is opened.
A part of the fuel inside the fuel tank is recirculated from the fuel return passage 16 into the fuel tank 2. The amount of fuel discharged from the high-pressure pump 5 is
Since it is equal to the sum of the injection amount and the recirculation amount, the solenoid valve 21
Is opened, the rotation speed of the high-pressure pump 5 increases, the rotation speed of the high-pressure pump 5 becomes higher than the predetermined speed N1, and the high-pressure pump 5 is operated in an efficient operating state for controlling the fuel pressure in the common rail 7. Can operate.

If it is determined in step S12 that the rotation speed of the high-pressure pump 5 is equal to or higher than the predetermined speed N1, the determination result in step S12 is NO, and the process ends.

If it is determined in step S11 that the solenoid valve 21 is currently open, the determination result in step S11 is YES, and the process proceeds to step S14.

In step S14, it is determined whether the rotation speed of the high-pressure pump 5 is higher than a predetermined speed N2. When it is determined that the rotation speed of the high-pressure pump 5 is higher than the predetermined speed N2, the determination result of step S14 is YES,
In step S15, a command to close the solenoid valve 21 is issued, and the process for opening and closing control of the solenoid valve 21 ends.

When the solenoid valve 21 is closed, the recirculation flow rate of the fuel recirculated to the fuel tank 2 through the fuel return passage 16 becomes zero, and the rotation speed of the high-pressure pump 5 decreases, thereby reducing the system as a system. The power corresponding to the recirculation amount, which has been lost, becomes zero. As a result, the overall efficiency of the fuel injection device 1 is improved.

If it is determined in step S14 that the rotation speed of the high-pressure pump 5 is equal to or lower than the predetermined speed N2, the result of the determination in step S14 is NO, and the process for opening / closing the electromagnetic valve 21 is terminated.

In the fuel injection device 1, since the solenoid valve 21 is controlled to open and close according to the flowchart shown in FIG. 3, when the injection amount decreases and the rotation speed of the high-pressure pump 5 becomes lower than the predetermined speed N1, the solenoid valve 21 The fuel is recirculated through the fuel return passage 16 by opening 21 to thereby increase the rotation speed of the high-pressure pump 5 (see FIG. 2). on the other hand,
When the rotation speed of the high-pressure pump 5 becomes higher than the predetermined speed N2 due to the increase in the injection amount, the solenoid valve 21 is closed to reduce the amount of fuel recirculated through the fuel return passage 16 to zero, thereby reducing the rotation speed of the high-pressure pump 5. Lower the efficiency as a system.

As described above, the increase / decrease of the injection amount is determined by the high pressure pump 5
Control the amount of fuel recirculation by opening and closing the solenoid valve 21 according to the rotation speed of the high-pressure pump 5,
Thereby, the fuel injection device 1 is operated in a highly efficient state as a whole.

FIG. 4 is a diagram for explaining how the power consumption of the high-pressure pump 5 is improved by the above-described opening / closing control of the solenoid valve 21. FIG. 4A is a power line diagram showing a relationship between the fuel injection amount according to the opening and closing of the solenoid valve 21 and the power consumption of the high-pressure pump 5, and a characteristic line (a) indicates that the solenoid valve 21 is closed. In this case, the characteristic line (b) shows the characteristic when the solenoid valve 21 is open. FIG. 4B is a diagram showing the opening / closing operation of the electromagnetic valve 21 according to the rotation speed of the high-pressure pump 5.

Now, when the solenoid valve 21 is closed and the fuel injection amount decreases, the rotation speed of the high-pressure pump 5 correspondingly decreases and becomes smaller than the first reference value N1 corresponding to the injection amount Q1. Then, since the solenoid valve 21 is opened, the operation follows the characteristic line (b). On the other hand, the solenoid valve 21
Is open and the operation according to the characteristic line (b) is being performed, the fuel injection amount is increased, whereby the rotation speed of the high-pressure pump 5 is increased, and the second fuel injection amount corresponding to the injection amount Q2 is increased.
Is higher than the reference value N2, the electromagnetic valve 21 is closed, and thereafter, the operation follows the characteristic line (a).

As described above, when the opening / closing of the electromagnetic valve 21 is controlled to be opened / closed at the rotation speed set in accordance with the fuel injection amount and the operation is performed in accordance with the characteristic line (a) or (b), the electric motor in the high rotation region is driven. Consumption can be reduced.

When a normally open type electromagnetic valve 21 is used, the difference between the characteristics (a) and (b) in FIG. Therefore, even if about 10 W of power is consumed to open and close the electromagnetic valve 21 in accordance with the rotation speed of the high-pressure pump 5, about 60 W of power can be saved, and the drive motor 6 has a small rating. This is good, and downsizing is possible. In addition,
By using a self-holding type solenoid valve as the solenoid valve 21, power consumption can be further reduced.

As a matter of course, a normally closed type solenoid valve may be used. However, the use of the normally open type is preferable in terms of fail-safe because if the power supply of the high-pressure pump driver is cut off, the pressure in the common rail 7 is already released. Regarding the lack of pressure in the common rail 7 at the time of starting the engine, within 1 second at the latest after the power of the high-pressure pump driver is turned on,
There is no problem because the pressure rises to 0 MPa.

Next, with reference to FIG. 5, the operation of the above-described embodiment when the injection amount changes suddenly will be described. As shown in FIG. 7A, when the injection amount increases rapidly at time T1, the actual fuel pressure Pa in the common rail 7 starts to decrease suddenly as shown in FIG. Therefore, as shown in FIG. 3C, the rotation speed of the high-pressure pump 5 increases, the actual fuel pressure Pa increases, and the pressure in the common rail 7 is reduced to the target fuel pressure Pt.
(See FIG. 2).

At time T2 when the rotation speed of the high-pressure pump 5 reaches the predetermined speed N2, the solenoid valve 21 is closed, and the fuel returning to the fuel tank 2 through the fuel return passage 16 becomes zero. It increases sharply and reaches the target fuel pressure Pt at time T3. However, when the control of the solenoid valve 21 is not performed, the operation is performed as shown by a dotted line in FIG. That is, since the solenoid valve 21 is not closed, a part of the fuel in the common rail 7 is always returned to the fuel tank 2 through the fuel return passage 16, and at time T4 after time T3, Pa = Pt Becomes

On the other hand, when the fuel injection amount decreases at the time T5, the actual fuel pressure Pa sharply increases, so that the rotation speed of the high-pressure pump 5 rapidly decreases. When the rotation speed of the high-pressure pump 5 becomes lower than the predetermined speed N1 at time T6, the solenoid valve 21 is switched from the closed state to the open state. As a result, a part of the high-pressure fuel in the common rail 7 starts to recirculate into the fuel tank 2 through the fuel return passage 16, so that the actual fuel pressure Pa rapidly decreases, and Pa = Pt at time T7. . If the opening and closing control of the solenoid valve 21 is not performed, the fuel pressure Pa can be reduced only by the fuel injection amount.
Is increased as shown by the dotted line, and Pa = Pt at time T8.

As described above, by controlling the opening and closing of the solenoid valve 21, when the injection amount changes suddenly, the actual fuel pressure Pa
Can be quickly matched with the target fuel pressure Pt.

As described with reference to the embodiment shown in FIG. 1, the control of the recirculation by the solenoid valve 21 is performed based on the rotation speed of the high-pressure pump 5. Since the operating pressure range of the system is variable from about 5 to 10 MPa, the amount of recirculation by the orifice 17 changes according to the pressure. Therefore, even with the same injection amount, the higher the actual fuel pressure Pa, the higher the rotation speed of the high-pressure pump 5. That is, the higher the injection pressure, the more the small amount of injection is performed, the more the solenoid valve 21 is closed, and the more frequently the solenoid valve 21 is controlled to open and close, making it impossible to secure control stability. There is.

This will be described with reference to FIG. FIG.
Is a diagram corresponding to (A) of FIG.
The power diagram shown in (b) is an example in the case where the fuel pressure is constant at P1, and the power increases when the fuel pressure becomes P2 which is larger than P1, so that the power diagram moves upward in FIG. FIG. 6 is a power diagram including the characteristic lines indicated by reference numerals (c) and (d). Accordingly, the hysteresis width as viewed from the injection amount is reduced. Therefore, in order to secure a required hysteresis width, it is necessary to change the values of N1 and N2.

That is, since the fuel is incompressible, the rotational speed of the high-pressure pump 5 after the solenoid valve 21 is closed becomes substantially the same even if the pressure in the common rail 7 changes, if the injection amount is the same. That is, when the rotation speed of the high-pressure pump 5 is high in the high injection amount state, the injection amount decreases, whereby the injection when the rotation speed of the high-pressure pump 5 reaches the rotation speed at which the solenoid valve 21 is opened is performed. Since the amount of reflux from the common rail 7 is zero, the amount is substantially the same regardless of the pressure in the common rail 7 at that time. However, solenoid valve 2
1 is open, and when the fuel is recirculated from the common rail 7 in proportion to the square root of the pressure, the higher the pressure in the common rail 7 is, the smaller the injection amount becomes and the higher the rotation speed of the high-pressure pump 5 becomes. Become. As a result, if the second reference value N2 is fixed to a constant value irrespective of the pressure in the common rail 7, when the pressure in the common rail 7 increases, the solenoid valve 21 is temporarily switched from closed to open. After that, when the injection amount increases, the phenomenon immediately exceeds the second reference value N2, and the solenoid valve 21 immediately returns to the closed state. This means that the width of the hysteresis given for the opening / closing control of the electromagnetic valve 21 is narrowed, and the electromagnetic valve 21 is frequently opened / closed, and there is a possibility that stable control cannot be performed.

In order to solve the above-mentioned problem in the embodiment shown in FIG. 1, the values of the first reference value N1 and the second reference value N2 are not fixed to fixed values, but the target values at each time are set. The first reference value N1 according to the set value of the fuel pressure Pt
And / or setting the second reference value N2 to prevent the value of N2-N1 from always becoming an appropriate value and preventing the solenoid valve 21 from frequently opening and closing.

FIG. 7 is a flowchart showing a program for controlling the opening and closing of the solenoid valve 21 based on such a concept. The solenoid valve control program based on FIG. 7 can be used in place of the solenoid valve control program shown in FIG.

First, in step S21, the solenoid valve 2
It is determined whether or not 1 is currently open. Solenoid valve 21
Is determined to be currently closed, the determination result in step S21 is NO, and the process proceeds to step S22.

In step S22, a predetermined speed N1A is calculated by a map calculation determined from the target fuel pressure Pt based on the map shown in FIG.
to go into.

In step S23, it is determined whether the rotation speed of the high-pressure pump 5 is lower than a predetermined speed N1A.
If it is determined that the rotation speed of the high-pressure pump 5 is lower than the predetermined speed N1A, the determination result of step S23 is YES, and the process proceeds to step S24, where an opening command for the electromagnetic valve 21 is issued, and the opening and closing of the electromagnetic valve 21 is performed. The processing for control ends.

When it is determined in step S13 that the rotation speed of the high-pressure pump 5 is equal to or higher than the predetermined speed N1A,
The decision result in the step S23 is NO, and the process for opening / closing control of the solenoid valve 21 is ended as it is.

If it is determined in step S21 that the solenoid valve 21 is currently open, the determination result in step S21 is YES, and the process proceeds to step S25.

In step S25, a predetermined speed N2A is calculated by a map calculation determined from the target fuel pressure Pt based on the map shown in FIG.
to go into.

Here, the graph shown in FIG. 8 shows a high-pressure pump corresponding to the value of the target fuel pressure Pt and the fuel injection amount (corresponding to Q1 in FIG. 4) for switching the solenoid valve 21 from the closed state to the open state. 5, a characteristic line (e) showing the relationship between the rotation speed N1A and the target fuel pressure Pt and the fuel injection amount to switch the solenoid valve 21 from the open state to the closed state (corresponding to Q2 in FIG. 4). Speed N2A of high pressure pump 5 corresponding to
And a characteristic line (f) indicating the relationship between. As is clear from the above description, the value of the rotation speed N1A is constant regardless of the value of the target fuel pressure Pt, whereas the value of the rotation speed N2A is the value of the target fuel pressure Pt. N2A is proportional to Pt ² , increasing with increasing temperature. Therefore, if the predetermined speed N2A is calculated based on the map shown in FIG. 8 and the electromagnetic valve 21 is switched from the open state to the closed state at the rotation speed N2A obtained thereby, the opening and closing control of the electromagnetic valve 21 is controlled. For this purpose can be made substantially constant irrespective of the value of the target fuel pressure Pt. Here, the characteristic line for the N2A calculation shown in FIG. 8 is an example, and is not intended to be limited to the one shown in FIG.

In step S26, it is determined whether or not the rotation speed of the high-pressure pump 5 is higher than a predetermined speed N2A.
If it is determined that the rotation speed of the high-pressure pump 5 is higher than the predetermined speed N2A, the determination result in step S26 is YES, and the process proceeds to step S27, where a command to close the electromagnetic valve 21 is issued, and the opening and closing of the electromagnetic valve 21 is performed. The processing for control ends.

If it is determined in step S26 that the rotation speed of the high-pressure pump 5 is equal to or lower than the predetermined speed N2A,
The decision result in the step S26 is NO, and the process for opening / closing control of the solenoid valve 21 is ended as it is.

[0057]

According to the present invention, as described above, the rotation speed of the electric pump is controlled by the rotation speed control means so that the pressure in the common rail becomes a predetermined value, and the solenoid valve provided in the return passage is provided. Is opened when the rotation speed of the electric pump is lower than the first reference value, and is closed when the rotation speed of the electric pump is higher than the second reference value that is higher than the first reference value. The hysteresis characteristic is given to the opening and closing of the solenoid valve, the opening and closing control of the solenoid valve is performed stably, and the electric pump is prevented from operating in the inefficient low rotation range, and the fuel injection is small and the electric pump is rotated at high speed. In the case where the operation is apt to occur, the reflux loss can be reduced, and thereby the overall operation efficiency can be greatly improved.

Further, the difference between the first reference value and the second reference value, which is the hysteresis width for controlling the opening and closing of the solenoid valve, is changed according to the fuel pressure in the common rail.
It is possible to prevent the solenoid valve from being frequently turned on and off.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of an embodiment of a fuel injection device according to the present invention.

FIG. 2 is a flowchart showing a control program for controlling fuel pressure in a common rail shown in FIG.

FIG. 3 is a flowchart showing a control program for opening and closing control of the solenoid valve shown in FIG. 1;

4 is a power diagram for explaining improvement in power consumption of the high-pressure pump by opening and closing control of the solenoid valve shown in FIG. 3;

FIG. 5 is a graph for explaining the operation of the fuel injection device shown in FIG. 1;

FIG. 6 is an explanatory diagram for explaining that a change in fuel injection pressure affects a hysteresis width of electromagnetic valve opening / closing control.

FIG. 7 is a flowchart showing another control program for controlling the solenoid valve shown in FIG. 1;

FIG. 8 is a diagram showing map calculation characteristics for map calculation of a predetermined speed for opening and closing the solenoid valve based on a target fuel pressure.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 fuel injection device 2 fuel tank 3 low pressure pump 4, 6 drive motor 5 high pressure pump 7 common rail 8 injector 9 control circuit 11 fuel filter 12 fuel supply passage 13 pressure sensor 14 control unit 15 fuel injection pipe 16 fuel return passage 17 orifice 21 electromagnetic Valve Pa Actual fuel pressure Pt Target fuel pressure

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 37/08 F02M 37/08 B 47/00 47/00 P 55/00 55/00 B (72) Invention Person Tsuneo Adachi 3-13-26 Yayumi-cho, Higashimatsuyama-shi, Saitama F-term (reference) in Zexel Higashimatsuyama Plant 3G066 AA02 AB02 AD12 BA12 BA17 BA19 BA46 BA67 CB01 CB07U CB11 CB12 CB16 CC01 CD03 CD26 CE21 CE22 DB01 DB16 DC17 DC18 3G301 HA01 HA04 HA06 JA02 JA03 KA01 KA11 LB13 LC03 MA28 NA03 NA04 NA06 NA08 ND02 NE27 PB08A PB08Z PG00Z

Claims (2)

[Claims] 1. A pressure-accumulation type fuel injection device in which fuel supplied from a fuel tank is pressurized by an electric pump to accumulate pressure on a common rail, and high-pressure fuel accumulated on the common rail is injected from an injector. Rotation speed control means for controlling the rotation speed of the electric pump so as to keep the pressure at a required value, a fuel return passage for recirculating fuel from the common rail to the fuel tank, and opening and closing the fuel return passage. An electromagnetic valve for performing the operation, first determining means for determining whether or not the rotation speed of the electric pump is lower than a first reference value, and a second determination unit for determining whether the rotation speed of the electric pump is higher than the first reference value. A second determining means for determining whether or not the rotation speed is higher than a reference value of 2; Solenoid valve control means for opening and closing the solenoid valve so as to open the solenoid valve when the rotation speed of the electric pump is higher than the second reference value when the rotation speed is higher than the second reference value; A fuel injection device comprising: 2. The fuel injection device according to claim 1, wherein a difference between the first reference value and the second reference value is changed so as to increase as a fuel pressure in the common rail increases.