JPH09209870A - Accumulator fuel injector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To loosen fluctuation of fuel pressure in a common rail, and provide stable fuel injection characteristics, by providing a solenoid valve in a fuel return passage from the common rail in which pressure of fuel supplied by a fuel pump is accumulated to a fuel tank, and controlling the solenoid valve to be opened/closed corresponding to a control signal to an injector. SOLUTION: In an accumulator fuel injector 20 in which pressure of fuel supplied from a fuel pump is accumulated in a common rail 7 and ejected from an injector 8, a solenoid valve 21 is arranged on the upstream side of an orifice 17 in a fuel return passage 16, and controlled together with the injector 8 by a control circuit 22. That is, phase is shifted from the control pulse of the injector 8, the control pulse of the solenoid valve 21 is outputted to the solenoid valve 21, and thereby pressure fluctuation by the injector 8 on a pressure side lower than a target pressure in the common rail 7 and pressure fluctuation by the solenoid valve 21 on a pressure side higher than the target pressure are superposed, therefore fluctuation of fuel pressure in the common rail 7 is loosened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure accumulation type fuel injection device, and in particular, a pressure accumulation type fuel injection device capable of injecting high-pressure gasoline or the like into an engine cylinder and mitigating pressure fluctuations in a common rail. It is about.

[0002]

2. Description of the Related Art Generally, a pressure-accumulation type fuel injection device is applied to a high-pressure gasoline in-cylinder injection system. FIG.
The outline will be described with reference to FIG. FIG. 4 is a schematic configuration diagram of the pressure-accumulation type fuel injection device 1.
Is a fuel tank 2, a low pressure pump 3 and its drive motor 4, a high pressure pump 5 and its drive motor 6,
It has a common rail 7 as a pressure accumulator that stores pressurized fuel, an injector 8 and its control circuit 9, and a low pressure regulator 10.

The low-pressure pump 3 sucks up fuel through a fuel filter 11 and supplies it to the high-pressure pump 5 as low-pressure fuel.

The high-pressure pump 5 further pressurizes the low-pressure fuel into high-pressure fuel, which is supplied to the common rail 7 via a fuel supply passage 12 formed by a high-pressure pipe. The high-pressure pump 5 can also be a radial piston pump, which is driven by an engine.

The pressure in the common rail 7 is detected by the pressure sensor 13, the detection signal is input to the pump drive unit 14, and the drive motor 6 of the high-pressure pump 5 is controlled, whereby the pressure in the common rail 7 is set to a predetermined value. The target pressure of can be set.

The high-pressure fuel (for example, high-pressure gasoline) in the common rail 7 is controlled by the control signal from the control circuit 9 in order to open and close the injector 8 in accordance with the engine speed and load. And is directly injected into the cylinder (not shown) of the engine from the injector 8 via.

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, and excess high-pressure fuel in the common rail 7 is returned to the fuel tank 2 through the orifice 17.
In the figure, of the lines showing the fuel pipe, the single line shows the low-pressure portion, and the double line shows the high-pressure portion.

FIG. 5 is a graph showing the control signal (control pulse) of the injector 8 and the fuel pressure in the common rail 7. As shown in the figure, the fuel pressure in the common rail 7 varies depending on the fuel injection of the injector 8. There is a problem of doing.

For example, when the control pulse of the injector 8 is changed from "OFF" to "ON", the injector 8 is opened from "closed" to "open", fuel injection is performed, and the fuel pressure in the common rail 7 becomes the target pressure. Lower. However, the fuel injection pipe 15 from the common rail 7 to the injector 8 requires an absolute length,
There is a slight timing delay (delay in fuel pressure decrease in the common rail 7) between the control pulse and the fuel pressure. Conversely, the control pulse is "ON"
When the injector 8 is changed from “open” to “closed” by changing from “OFF” to “OFF”, fuel accumulation starts in the common rail 7 and the fuel pressure rises. However, the fuel injection pipe 15
At the same time, the fuel supply passage 12 also needs to have an absolute length, and there is a delay in the mutual timing (a delay in the fuel pressure increase in the common rail 7).

The fluctuation of the fuel pressure in the common rail 7 as described above causes the fluctuation of the fuel injection amount for each cycle of each injector 8 or the fluctuation of the fuel injection amount between the cylinders. Further, if the variation of the fuel injection amount exceeds the allowable limit, there is a problem that stable engine operation cannot be desired.

Such fuel pressure fluctuation is caused by the common rail 7
It is possible to mitigate this by increasing the amount of fuel supplied to the fuel tank 2 and increasing the amount of fuel that recirculates in the fuel tank 2, that is, by circulating more fuel through the common rail 7, it is heated by the engine. There is a problem that the temperature of the fuel in the fuel tank 2 rises due to the recirculating fuel, which causes bubbles in the fuel tank 2. Further, as the amount of recirculated fuel increases, the drive motor 4 of the low-pressure pump 3 and the drive motor 6 of the high-pressure pump 5 require useless power consumption, resulting in energy loss.

Known techniques for controlling the pressure in the common rail include Japanese Patent Laid-Open Nos. 4-234562 and 6-26.
-323220 and JP-A-6-346818.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and reduces the fuel pressure fluctuation in the common rail caused by the fuel injection from the injector to obtain a stable fuel injection characteristic. An object of the present invention is to provide a pressure-accumulation type fuel injection device that can perform the operation.

It is another object of the present invention to provide a pressure accumulating fuel injection device capable of reducing the pressure fluctuation in the common rail which causes the fuel injection amount from the injector to fluctuate.

Further, according to the present invention, by reducing the amount of fuel recirculated to the fuel tank, it is possible to suppress the temperature rise of the fuel in the fuel tank and to reduce the energy loss of the drive motor of the pump and the like. An object is to provide an injection device.

That is, according to the present invention, a solenoid valve is provided in a fuel return passage from a common rail to a fuel tank, and the solenoid valve is turned on / off at a timing corresponding to a control signal of an injector. Focusing on mitigating fluctuations in the common rail, a pressure-accumulation fuel injection device that accumulates fuel supplied from a fuel tank by a fuel pump in the common rail and injects it from an injector, from the common rail to the fuel tank. An electromagnetic valve is provided in the fuel return passage, and the electromagnetic valve is controlled to open / close in response to a control signal to the injector.

An orifice may be provided in the fuel return passage. The mounting position of the solenoid valve may be either upstream or downstream of the orifice.

Further, the manner of connecting the solenoid valve to the fuel return passage may be of a series type or a parallel type.

The level of vertical fluctuation of the fuel pressure in the common rail due to opening / closing of the solenoid valve may be any level that can moderate the level of vertical fluctuation of fuel pressure due to opening / closing of the injector.

The control signal from the control circuit to the solenoid valve is
Create this based on the control signal to each injector. That is, since the fuel pressure fluctuation in the common rail occurs due to the on-off valve (not shown) built into the injector, the fluctuation cycle and fluctuation waveform of the pressure depend on the control signal to the injector on-off valve. Determine according to the cycle and width.

Therefore, based on the control signal of the injector, a pressure wave up to the solenoid valve due to the pipe length and volume of the fuel supply passage to the common rail, the fuel injection pipe to the injector, and the fuel return passage to the fuel tank. ON / OFF of the solenoid valve considering the delay of
The control circuit outputs a signal for controlling the. Solenoid valve ON
The OFF duty (duty cycle) is a function of the injector injection period and duration, and can be finally determined experimentally.

In the pressure-accumulation fuel injection device according to the present invention, an electromagnetic valve is provided on the fuel return passage side from the common rail to the fuel tank, and the electromagnetic valve is controlled to open and close in response to the control signal from the injector. Therefore, the fuel pressure in the common rail can be controlled by superimposing the pressure fluctuation in the common rail corresponding to the fuel injection from the injector, and the pressure fluctuation in the common rail due to the fuel injection from the injector is absorbed. Therefore, the fuel pressure in the common rail can be suppressed within a predetermined fluctuation range.

Therefore, the pressure in the common rail can be stabilized as much as possible and the operation of the engine can be stabilized.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a pressure accumulation type fuel injection device 20 according to an embodiment of the present invention will be described with reference to FIGS. However, the same parts as those in FIGS. 4 and 5 are designated by the same reference numerals, and the detailed description thereof will be omitted. FIG. 1 is a schematic configuration diagram of the pressure-accumulation fuel injection device 20. The pressure-accumulation fuel injection device 20 is provided with an electromagnetic valve 21 upstream of an orifice 17 in the fuel return passage 16, and a control circuit 9 is provided.
The solenoid valve 21 is controlled together with the injector 8 by the control circuit 22 corresponding to. Other configurations are substantially the same as those of the pressure accumulation type fuel injection device 1 of FIG.

FIG. 2 is a graph showing the fuel pressure in the common rail 7 with respect to the control signal (control pulse) of the solenoid valve 21 when the injector 8 is not operated. As shown, the control pulse of the injector 8 is The control pulse of the solenoid valve 21 is output to the solenoid valve 21 by shifting the phase.

For example, when the control pulse is changed from "ON" to "OFF" and the solenoid valve 21 is changed from "open" to "closed", fuel accumulation starts in the common rail 7 and the fuel pressure exceeds the target pressure. To rise. However, there is a slight timing delay between this control pulse and the fuel pressure (delay in fuel pressure rise in the common rail 7).
There is. . On the contrary, when the control pulse of the solenoid valve 21 is changed from "OFF" to "ON", the solenoid valve 21 is opened from "closed" to "open", and the fuel pressure in the common rail 7 is reduced. However, there is a delay in the timing of each other (delay in the fuel pressure decrease in the common rail 7).

In the pressure-accumulation type fuel injection device 20 having such a structure, as shown in FIG. 3, the pressure fluctuation by the injector 8 on the low pressure side of the target pressure in the common rail 7 and the pressure by the solenoid valve 21 on the high pressure side of the target pressure. The fuel pressure in the common rail 7 can be kept within a very limited predetermined range including the target pressure by superimposing the fluctuation on the fuel pressure.

The phases of the control signal to the injector 8 and the control signal to the solenoid valve 21 and the respective duty (duty cycle) are appropriately controlled so that this superposition alleviates the pressure fluctuation as much as possible.

Since the solenoid valve 21 is turned on / off in response to the pressure fluctuation in the common rail 7, the pressure fluctuation in the common rail 7 is relaxed as compared with the case where the solenoid valve 21 is not provided. be able to.

Further, since the pressure fluctuation is reduced, the amount of fuel recirculated to the fuel tank 2 can be reduced, the efficiency of the pressure accumulating fuel injection device 20 as a whole can be increased, and the risk of bubbles occurring in the fuel tank 2 can be increased. Sex can be reduced.

If the solenoid valve 21 is "closed" at the time of starting the engine, the pressure in the common rail 7 rises faster and the startability can be improved. Further, if the electromagnetic valve 21 is closed when the engine is stopped, the pressure drop in the common rail 7 is delayed, so that the startability at the time of restart within a short time can be improved.

[0031]

As described above, according to the present invention, the solenoid valve is provided in the fuel return passage from the common rail to the fuel tank, and the solenoid valve is controlled in response to the control signal from the injector. It is possible to mitigate the fuel pressure fluctuations in the common rail due to.

[0032]

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a pressure accumulation type fuel injection device 20 according to an embodiment of the present invention.

FIG. 2 is a graph showing a fuel pressure in the common rail 7 with respect to a control signal (control pulse) of the solenoid valve 21 when the injector 8 is not operated.

FIG. 3 is a graph showing the fuel pressure in the common rail 7 in which the pressure fluctuations due to the injector 8 and the pressure fluctuations due to the solenoid valve 21 are superimposed.

FIG. 4 is a schematic configuration diagram of a conventional pressure accumulation type fuel injection device 1.

FIG. 5 is a graph showing a control signal (control pulse) of the injector 8 and fuel pressure in the common rail 7 in the same manner.

[Explanation of symbols]

 1 Fuel Storage Fuel Injection Device (Fig. 4) 2 Fuel Tank 3 Low Pressure Pump 4 Drive Motor for Low Pressure Pump 5 High Pressure Pump 6 Drive Motor for High Pressure Pump 7 Common Rail (Accumulator) 8 Injector 9 Control Circuit for Injector 8 10 Low Pressure Regulator 11 Fuel Filter 12 Fuel Supply Passage with High-Pressure Pipe 13 Pressure Sensor 14 Pump Drive Unit 15 High-Pressure Fuel Injection Pipe 16 Fuel Return Passage with Return Pipe 17 Orifice 20 Accumulation Fuel Injection Device (FIG. 1) 21 Solenoid Valve 22 Injector 8 and Electromagnetic Control circuit of valve 21

Claims (2)

[Claims] 1. A pressure-accumulation fuel injection device for accumulating fuel supplied from a fuel tank by a fuel pump in a common rail and injecting it from an injector, wherein a solenoid valve is provided in a fuel return passage from the common rail to the fuel tank. At the same time, the pressure-accumulation fuel injection device is characterized in that the electromagnetic valve is controlled to open and close in response to a control signal to the injector. 2. The pressure-accumulation fuel injection device according to claim 1, wherein an orifice is provided in the fuel return passage.