JPH0571438A - Fuel injector - Google Patents

Abstract

PURPOSE:To obtain the optimum injection rate for combustion such that even in the case of using high pressure fuel, in the initial stage of injection, the injection rate is low, and in the later stae, the injection rate is high by providing a control valve on the low pressure side of a directional control valve of a fuel injection valve to control the pressure of a back pressure chamber related to a nozzle needle. CONSTITUTION:An injector 3 disposed in every cylinder of an engine includes an injection hole opened and closed by the vertical motion of a nozzle needle 9, and a throttle member 8 having an orifice acting on the pressure reducing side and a back pressure chamber 7 are disposed above the nozzle needle 9. Fuel injection is controlled by turning on and off an injection control three-way solenoid valve 6 which is a directional control valve in the injector 3. In this case, in order to attain a designated injection rate, a back pressure control valve 4 which is a control valve is connected to the low pressure side of the three-way solenoid valve 6. In the no-injection state, the valve 4 closes the low pressure side of the three-way solenoid valve 6, and in the injection state, a spool valve 11 is operated by applying designated voltage to a piezo electric element 12 to control fuel flow.

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 for injecting high pressure fuel into a diesel engine.

[0002]

2. Description of the Related Art Conventionally, as disclosed in Japanese Unexamined Patent Publication No. 59-165858, "Electromagnetically controlled injection system for diesel engine", high pressure fuel is accumulated in a kind of surge tank called a common rail, There is known a pressure accumulating fuel injection device which injects fuel into a diesel engine by opening and closing an injection valve.

[0003]

By the way, in the above pressure accumulating fuel injection device, NO _X (nitrogen oxide) in exhaust gas
As a method of reducing the fuel consumption, injection timing delay control, injection rate control, or the like can be considered. In other words, the back pressure acting on the nozzle needle that opens and closes the injection hole of the fuel injection valve is controlled by the throttle to gradually increase the injection rate from the initial injection and immediately cut the injection at the end of injection. Is the way to get. Further, it is known that the higher the injection pressure of the fuel injection valve is, the finer the fuel supplied to the engine is, resulting in the reduction of smoke and HC in the exhaust gas. The demand is increasing. However, when the required injection pressure becomes higher than the conventional one, there is a problem that it is difficult to obtain an optimum injection rate for combustion because the effect of the throttle for controlling the back pressure is weakened.

The present invention has been made to solve the above problems, and its object is to achieve a low injection rate in the initial stage of injection and a high injection rate in the latter stage of injection even if high-pressure fuel is used. It is an object of the present invention to provide a fuel injection device capable of obtaining a so-called boot-type injection rate that is optimum for such combustion.

[0005]

SUMMARY OF THE INVENTION According to the structure of the invention for solving the above problems, the pressure of a back pressure chamber for holding a back pressure acting on a nozzle needle for opening and closing an injection hole of a fuel injection valve is controlled by a switching valve. In the fuel injection device configured to inject the fuel from the injection hole by switching control between the high pressure side that is the supply path side and the low pressure side that is the fuel return path side, and the low pressure side of the switching valve. A first state in which the low-pressure side fuel flow is cut off, a second state in which a part of the low-pressure side fuel is released, and a third state in which the low-pressure side fuel is completely released are arranged in series. Of at least three states, the control valve is set to the high pressure side and the control valve is set to the first state at the time of no injection, and the control valve is switched to the low pressure side at the initial stage of injection and at the same time. In the second state, in the latter stage of injection Characterized by comprising a control device for a serial switching valve to remain switched to the low-pressure side of the control valve the third state.

[0006]

When there is no injection, the control device sets the switching valve of the fuel injection valve to the high pressure side and sets the control valve to the first state to shut off the fuel flow on the low pressure side of the switching valve.
Next, in the initial stage of injection, the switching device of the fuel injection valve is switched to the low pressure side by the control device, and at the same time, the control valve is set to the second state so that part of the fuel on the low pressure side of the switching valve is released.
Then, the pressure in the back pressure chamber is slightly released by the amount of the fuel in the back pressure chamber flowing into the control valve side, and the nozzle needle of the fuel injection valve is slightly raised to achieve a low injection rate. Then, in the latter stage of the injection, the control valve keeps the switching valve of the fuel injection valve switched to the low pressure side to bring the control valve into the third state, and the fuel on the low pressure side of the switching valve is completely released. Then, the fuel in the back pressure chamber is completely escaped to the control valve side, the pressure in the back pressure chamber is completely released, and the nozzle needle of the fuel injection valve is completely raised to achieve a high injection rate.
As described above, in the fuel injection device of the present invention, the control valve is provided on the low pressure side of the switching valve of the fuel injection valve to control the pressure in the back pressure chamber, so that low injection is performed at the initial stage of injection even when high pressure fuel is used. Rate, and it is possible to obtain an optimum injection rate for combustion that has a high injection rate in the latter stage of injection.

[0007]

EXAMPLES The present invention will be described below based on specific examples. FIG. 1 is an overall configuration diagram showing a fuel injection device according to the present invention. A fuel injection valve (hereinafter referred to as an injector) 3 is arranged in the combustion chamber of each cylinder of the engine. The injection hole of this injector 3 is opened and closed by the vertical movement of the nozzle needle 9. Above the nozzle needle 9, a throttle member 8 having an orifice acting on the pressure reducing side and a back pressure chamber 7 are arranged. The injector 3 is connected to a high pressure accumulating pipe common to all cylinders, a so-called common rail 2. Supply fuel is accumulated in the common rail 2 continuously at a high predetermined pressure. Therefore, the high-pressure pump 1 boosts the fuel sucked from the fuel tank 18 to the predetermined pressure required by the system, and the pressure is increased to the pump control solenoid valve 1.
Maintained by turning on and off 7. Fuel injection from the injector 3 to the engine is controlled by turning on / off a three-way solenoid valve 6 for injection control, which is a switching valve provided in the injector 3. A back pressure control valve 4, which is a control valve, is connected and arranged on the low pressure side of the three-way solenoid valve 6 in order to achieve a predetermined injection rate. The spool valve 11 is biased by the spring to the back pressure control valve 4, and the low pressure side of the three-way solenoid valve 6 of the injector 3 is closed in the non-injection state (first state). In the injection state, application of a predetermined voltage to the piezo element 12 operates the spool valve 11 to control the flow of fuel (first and second states). Further, the back pressure control valve 4 has a decompression chamber 10 having a predetermined capacity for releasing a part of the fuel on the low pressure side of the three-way solenoid valve 6 and the fuel on the low pressure side of the three-way solenoid valve 6 to completely escape the fuel tank 18. A decompression passage 13, which is a passage for returning to, is formed. An ECU (Electronic C) that is an electronic control unit that constitutes a control device
The ontrol unit 5 has a rotation sensor 14 that outputs a signal based on the number of revolutions of the engine, an accelerator sensor 15 that outputs a signal based on the accelerator opening that is information on the load, and a signal based on the fuel pressure supplied from the high-pressure pump 1. Each signal line from the pressure sensor 16 that outputs is connected.

Next, the EC used in the apparatus of this embodiment
Based on the flowcharts of FIGS. 2 and 3 showing the processing procedure of U5, description will be made with reference to various maps of FIG. 4 and a time chart of FIG. The programs of FIGS. 2 and 3 are repeatedly executed at predetermined time intervals. First, in step 100 of the main program of FIG. 2, the accelerator sensor 1
The signal from 5 is read to calculate the accelerator opening A _CCP and stored in a RAM (not shown) in the ECU 5. Next, the routine proceeds to step 102, where the signal from the rotation sensor 14 is read, the engine speed N _E is calculated and stored in the RAM. Next, the process proceeds to step 104 and the above-mentioned step 1
Accelerator opening A _CCP obtained at 00 and step 10
The command injection amount Q based on the engine speed N _E obtained in 2
_FIN is calculated and stored in RAM. In step 106, the accelerator opening A _CCP and the engine speed N _{E are also the same.}
Then, the command injection timing T _FIN is calculated and stored in the RAM. In step 108, the accelerator opening A is also set.
Command injection pressure P _{FIN based on CCP} and engine speed N _E
Is calculated and stored in the RAM.

After the above-mentioned command values and the like are calculated and stored, FIG.
The interrupt program, which is the reference pulse synchronization process of, is executed. In step 200, the command injection amount Q _FIN obtained in step 104 is read from the RAM. Next, in step 202, the fuel supply pressure P _C which is a signal from the pressure sensor 16 is read. Then, the process proceeds to step 204, and the engine speed N _E obtained in step 102 is read from the RAM. Next, the routine proceeds to step 206, where the initial injection amount ratio coefficient α is set to the command injection amount Q _FIN stored in advance in the ROM (not shown) in the ECU 5.
It is obtained from the map based on (see Fig. 4 (a)). Initial This map represents the basis the relationship between α engine speed N _E and the initial injection quantity ratio coefficient to the command injection quantity Q _FIN, curve and the engine rotational speed N _E corresponding to the command injection quantity Q _FIN The injection amount ratio coefficient α is obtained. Then step 20
8, the initial injection amount Q _FINI is calculated by the following equation. Q _FINI = Q _FIN · α Next, move to step 210, where the initial injection time T _QI is R
It is obtained from a map (see FIG. 4 (b)) based on the fuel supply pressure P _C stored in the OM in advance. This map shows the relationship between the initial injection time T _QI and the initial injection amount Q _FINI as the fuel supply pressure P
_The initial injection time T _QI is obtained from the curve corresponding to the fuel supply pressure P _C and the initial injection amount Q _FINI calculated in step 208. Next step 21
A map based on the fuel supply pressure P _C stored in advance in the ROM for the second injection time T _QF (see FIG. 4 (c)).
Ask more. This map is obtained by subtracting the initial injection amount Q _FINI from the late injection time T _QF and the command injection amount Q _FIN
FIN -Q _FINI) represents on the basis of the fuel supply pressure P _C of the relationship between the curve and the injection amount corresponding to the fuel supply pressure P _C (Q _FIN -Q _FINI) from the later injection time T _QF is calculated Be done. Next, in step 214, the total injection time T _Q is calculated by the following equation. T _Q = T _QI + T _QF That is, the total time of the initial injection time T _QI and the late injection time T _QF is the total injection time T _Q. Next, in step 216, the command injection timing T _FIN obtained in step 106 is read from the RAM. Then, the process proceeds to step 218, and the injection timing T _T is calculated by the following equation. T _T = f (T _FIN, N _E ) That is, the injection timing T _T is the command injection timing T _FIN
And the engine speed N _E as a parameter.

After the above-mentioned processing, the process returns to the program of FIG. 2 and, in step 110, injector control, step 1
In step 12, back pressure control valve control is executed, and in step 114, high pressure pump control processing is executed. Here, before the injector control, as shown in FIG. 6 (a) when there is no injection ... (I), the ports XY of the three-way solenoid valve 6 of the injector 3 are communicated with each other, and the nozzle needle 9 is It is held down by pressure. In the injector control process, the cylinder # 1 (first cylinder) is discriminated by the cylinder discriminating pulse from the non-injection state shown in FIG. 6 (a). Then, in order to achieve the injection initial stage (II) state of FIG. 6 (b) and the injection late stage (III) state of FIG. 6 (c), the above step 21 is performed.
After the injection timing T _T calculated in 8, the three-way solenoid valve 6 of the injector 3 is switched from the high pressure side to the low pressure side (TWV
Pulse # 1 output). The black-painted portions and arrows in FIGS. 6 (a), (b), and (c) show the fuel and its flow. That is, in the initial injection (II) state of FIG. 6 (b) and the late injection period (III) of FIG. 6 (c), the three-way solenoid valve 6 is excited, the ports YZ are communicated, and the back pressure chamber 7 is communicated. High pressure fuel is back pressure control valve 4
Get out to the side.

As for the back pressure control valve control process, before the injector control, the back pressure control valve 4 is in the first state in which the flow of fuel on the low pressure side is shut off.
The non-injection state is maintained together with the control state of the three-way solenoid valve 6. Then, in step 110 described above, the three-way solenoid valve 6 of the injector 3 is switched from the high pressure side to the low pressure side, and at the same time, a predetermined voltage is applied to the piezo element 12 of the back pressure control valve 4 to slightly raise the spool valve 11. (Back pressure control valve pulse # 1 output). At this time, the back pressure control valve 4 is in a second state where a part of the fuel on the low pressure side is released, and the back pressure chamber 7 of the injector 3 and the decompression chamber 10 of the back pressure control valve 4 are in communication (port Y).
-Z-> A-B). Then, the high-pressure fuel in the back pressure chamber 7 flows in by the volume of the decompression chamber 10, so that the pressure in the back pressure chamber 7 is slightly released and the nozzle needle 9 of the injector 3 is slightly raised. Then, the above-mentioned state of the back pressure control valve 4 is held for the initial injection time T _QI calculated in step 208, whereby the low injection rate at the initial stage of injection is achieved. Next, after the initial injection time T _QI , a predetermined voltage is applied to the piezo element 12 of the back pressure control valve 4 to further raise the spool valve 11 (back pressure control valve pulse # 1 output). At this time, the back pressure control valve 4 is in a third state in which the low pressure side fuel is completely released, and the back pressure chamber 7 of the injector 3 and the depressurization path 13 of the back pressure control valve 4 are in communication (ports YZ → A). -C). Then, the high-pressure fuel in the back pressure chamber 7 passes through the pressure reducing passage 13 and is returned to the fuel tank 18, so that the nozzle needle 9 of the injector 3 is moved up to the maximum. Then, the above-mentioned state of the back pressure control valve 4 is held for the latter-stage injection time T _QF calculated in step 208, whereby the high injection rate in the latter-stage injection is achieved.

In the high-pressure pump control process, the pressure sensor 16 provided on the common rail 2 monitors the fluctuating pressure of the fuel supplied to the injector 3, and the pump control electromagnetic pressure is adjusted to the required predetermined pressure. The valve 17 is on / off controlled. In this manner, the high injection rate is reliably controlled using the high-pressure fuel at a low injection rate in the initial stage of injection and a high injection rate in the latter stage of injection, and an injection rate optimal for combustion is realized. With the above-described operation, the fuel injection device of the present invention enables so-called boot-type injection similar to delta-type injection. Further, in addition to the boot-type injection described above, injection rate control such as so-called pilot-type injection in which the timings of the low injection rate and the high injection rate are shifted is also possible. Further, by providing a proportional control valve instead of the back pressure control valve 4, delta type injection using high pressure fuel becomes possible.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing a processing procedure of an ECU used in the apparatus of the embodiment.

FIG. 3 is a flowchart showing a processing procedure of an ECU used in the apparatus of the embodiment.

FIG. 4 is an explanatory diagram showing various maps used in the processes of FIGS. 2 and 3;

FIG. 5 is an explanatory view showing a time chart according to the apparatus of the embodiment.

FIG. 6 is an explanatory diagram showing a flow of fuel in a non-injection state, an initial stage of injection, and a latter stage of injection according to the apparatus of the embodiment.

[Explanation of symbols]

1-High-pressure pump 2-Common rail 3-Injector (fuel injection valve) 4-Back pressure control valve (control valve) 5-ECU (control device) 6- (Injection control) 3-way solenoid valve (switching valve) 7-Back pressure Chamber 8-Throttle member 9-Nozzle needle 10-Decompression chamber 11-Spool valve 12-Piezo element 13-Decompression path 14-Rotation sensor 15-Accelerator sensor 16-Pressure sensor 17-
Solenoid valve for pump control

Claims (1)

[Claims] 1. A pressure in a back pressure chamber for holding a back pressure acting on a nozzle needle for opening and closing an injection hole of a fuel injection valve is controlled by a switching valve between a high pressure side which is a fuel supply path side and a fuel return path side. In a fuel injection device which is controlled to switch to a certain low pressure side and injects the fuel from the injection hole, it is arranged in series with the low pressure side of the switching valve and shuts off the fuel flow on the low pressure side. A control valve having at least three states of a first state, a second state in which a portion of the low-pressure side fuel is released, and a third state in which the low-pressure side fuel is completely released, and the switching when no injection is performed. The valve is on the high pressure side and the control valve is in the first state, the switching valve is switched to the low pressure side at the initial stage of injection, and at the same time the control valve is in the second state, and the switching valve is set to the low pressure side in the latter stage of injection. The control valve is set to the third position while being switched. A fuel injection apparatus characterized by comprising a control device for the state.