JPH0814270B2 - Fuel injection device for internal combustion engine - Google Patents

Description

The present invention relates to a fuel injection device for an internal combustion engine.

[Conventional technology]

Japanese Patent Application No. 63-9584 is provided with a pressure chamber to which fuel is supplied through a throttle passage, and the piezoelectric element extends to increase the fuel pressure in the pressure chamber, whereby the needle closes the injection hole. At the same time, there is disclosed a fuel injection valve in which the piezoelectric element contracts to reduce the fuel pressure in the pressure chamber, and the needle causes the injection hole to open.

The conventional drive circuit that expands and contracts this piezoelectric element is
As shown in the figure, it includes a power supply 52, thyristors 53 and 56, and charging side and discharging side coils 54 and 55. This drive circuit 5
The piezoelectric element 27 is alternately charged and discharged by 1 and expanded and contracted. As a result, the fuel pressure in the pressure chamber is increased or decreased, and the fuel injection valve is opened or closed.

[Problems to be Solved by the Invention]

However, in such a fuel injection device, immediately after the engine is stopped, the piezoelectric element is in the expanded state with the electric charge being charged. Therefore, the volume of the pressure chamber is minimized and the amount of fuel held in the pressure chamber is also minimal. After the engine is stopped, the piezoelectric element gradually spontaneously discharges with the lapse of time, and the volume of the pressure chamber increases accordingly. However, the discharge of the piezoelectric element is slow, and the fuel supply pressure decreases and the pressure is balanced before the piezoelectric element finishes discharging. Therefore, it becomes difficult to introduce the fuel into the pressure chamber through the throttle passage, and bubbles may be generated in the pressure chamber as the volume of the pressure chamber increases.

On the other hand, when the engine is started, the piezoelectric element is charged and extended to increase the fuel pressure in the pressure chamber, so that the needle closes the injection hole. However, as described above, the pressure chamber is not filled with fuel, so that the fuel pressure in the pressure chamber cannot be increased to a desired pressure, and a sufficient valve closing force cannot be obtained. Therefore, there is a problem that erroneous injection occurs in the initial stage of engine start.

[Means for solving the problem]

According to the present invention, the pressure chamber to which fuel is supplied through the throttle passage is provided, and the piezoelectric element extends to increase the fuel pressure in the pressure chamber, whereby the needle opens the injection hole, and A fuel injection device having a fuel injection valve in which the piezoelectric element contracts to reduce the fuel pressure in the pressure chamber, whereby the needle opens the injection hole, and the piezoelectric element is provided after the internal combustion engine is stopped. A discharge means for discharging the electric charge charged in the above, and a discharge current from the piezoelectric element by the discharge means at a speed at which the needle does not open the injection hole, and the fuel pressure is reduced to be in a pressure equilibrium state. A fuel injection device for an internal combustion engine, comprising: a discharge current control unit that limits a current range in which the piezoelectric element contracts at a faster speed.

[Work]

Since the discharge current control means limits the discharge current from the piezoelectric element after the internal combustion engine is stopped to a predetermined range, the piezoelectric element does not cause the needle to open the injection hole and the fuel pressure in the pressure chamber decreases after the internal combustion engine is stopped. Contracts at a faster rate than the pressure equilibrium. Therefore, as the piezoelectric element contracts, fuel is introduced into the pressure chamber through the throttle passage, and the amount of fuel held in the pressure chamber increases, so that the valve closing force at the time of starting is secured.

〔Example〕

FIG. 2 shows an electrostrictive fuel injection valve. In FIG. 1, reference numeral 1 denotes a nozzle body having an injection hole 2 at its tip, and a needle 3 is inserted into the nozzle body 1 so that the injection hole 2 can be opened and closed.

The nozzle body 1 is fitted into the body 4, and the fuel is injected from the injection hole 2 through the fuel inlet 5, the fuel passage 7 having the sealing plug 6 mounted therein, the fuel passage 8, the fuel storage chamber 9, and the pressure accumulating chamber 10. To be done. The fuel injection control by opening / closing the needle 3 is directly performed by the seat portion 11 immediately upstream of the injection hole 2.
The needle 3 has a tapered pressure receiving surface 12, and the needle 3 receives the fuel pressure from the pressure receiving surface 12.
Moves in the valve opening direction. A fuel storage chamber 9 is formed around the pressure receiving surface 12. The pressure accumulating chamber 10 includes the fuel accumulating chamber 9 and the injection hole 2.
Is formed between the injection holes 2 and 3, and extends to the vicinity of the injection hole 2. The passage cross-sectional area of the pressure accumulating chamber 10 is formed larger than the cross-sectional area of the fuel passage 8 reaching the fuel storage chamber 9. Also,
The cross-sectional area of the pressure accumulating chamber 10 is preferably 10 times or more the total area of the injection holes 2, and the volume of the pressure accumulating chamber 10 is 0.5c.
It is preferable to secure at least c.

The upper end of the needle 3 is connected to the body 4 via a distance piece 13 and a knock pin 14, and a compression spring 15 is interposed in this portion. The nozzle body 1 is connected to the body 4 by a retaining nut 16.
A slight clearance 17, which is a throttle passage, is formed between the upper portion of the needle 3 and the inner peripheral surface of the nozzle body 1, and the fuel is formed above the fuel reservoir chamber 9 through the clearance 17. The pressure chamber 18 is filled.

The pressure chamber 18 is formed between the lower end of the piston 19 and the upper end of the body 4, and the fuel pressure in the pressure chamber 18 can act as a force in the opening / closing direction of the needle 3. The piston 19 is slidably fitted in the case 20 and is biased upward by a disc spring 21. Case 20 has knock pin 22
The pressure chamber 18 positioned by is sealed by an O ring 23 and a backup ring 24 provided on the outer circumference of the piston 19. The case 20 is fixed to the body 4 via a nut 25.

Electrostrictive actuator 26 that can expand and contract in case 20
Is provided. Reference numeral 27 denotes a piezo-piezoelectric element portion in which a large number of piezo-piezoelectric elements are laminated, and ceramic plates 28, 29 and metal plates 30, 31 are provided on both sides thereof. Reference numeral 32 indicates an adjustment shim. The electrostrictive actuator 26 is expanded and contracted by a drive control circuit 80 connected via a lead wire 33.

The fuel inlet 5 has a reservoir tank 35 and a fuel pump 36.
Is connected to the fuel tank 37 via.

In the fuel injection valve configured as described above, the supplied fuel is sent to the fuel reservoir chamber 9 through the fuel introduction port 5 and the fuel passages 7 and 8, and further through the clearance 17 into the pressure chamber. 18, the pressure accumulating chamber 10 on the injection hole side is filled. When the piezoelectric element 27 contracts, the needle 3 is lifted and opened by the fuel pressure received by the pressure receiving surface 12, and the fuel is injected from the injection hole 2. When the piezoelectric element 27 expands, the pressure in the pressure chamber 18 increases, and the needle 3 is pushed downward by the pressure to close the valve, and the injection ends.

The drive control circuit 80 shown in FIG. 1 is an electronic control unit.
50 and a drive circuit 51. Drive circuit 51 is power supply
52, a thyristor 53, a charging side coil 54, a discharging side coil 55, and a thyristor 56. Piezo piezoelectric element 27
One terminal is connected to the negative terminal of the power supply 52.
The other terminal of the piezoelectric element 27 is a charging coil on the one hand.
54 and the thyristor 53, and is connected to the positive side terminal of the power supply 52, and on the other hand, the discharge coil 55 and the thyristor 56.
Is connected to the negative terminal of the power source 52 via. Also,
A resistor 57 is connected in parallel with the piezoelectric element 27.

The electronic control unit 50 includes a load sensor that indicates the output pulse of the crank angle sensor 60 and the depression amount of the accelerator pedal.
Water temperature sensor showing 61 output signal and engine cooling water temperature
The output signal of 62 is input. In addition, the electronic control unit 50
Is connected to the gate terminal of each thyristor 53, 56, and further includes an ignition switch 63 and a starter switch.
Connected to 64.

FIG. 3 shows a time chart of drive control of the piezoelectric element 27 during normal engine operation.

In FIG. 3, in A, the control signal of the thyristor 56 is output from the electronic control unit 50, and the thyristor 56 is turned on. When the thyristor 56 is turned on, the electric charge charged in the piezoelectric element 27 is discharged via the discharging coil 55 and the thyristor 56, and thus the terminal voltage of the piezoelectric element 27 decreases. At this time, the terminal voltage of the piezoelectric element 27 becomes -200V by the oscillation circuit composed of the discharging coil 55 and the piezoelectric element 27. When the charge charged in the piezoelectric element 27 is discharged, the piezoelectric element 27 contracts. As a result, the fuel pressure in the pressure chamber 18 decreases, and the needle 3 is lifted by the fuel pressure received by the pressure receiving surface 12 to open the valve (see FIG. 2).

Next, in B, when the thyristor 53 is turned on by the control signal of the thyristor 53, the piezo piezoelectric element 27 is charged with electric charges from the power source 52 via the thyristor 53 and the charging coil 54. At this time, the terminal voltage of the piezoelectric element 27 becomes 600V, which is higher than the voltage of 300V of the power source 52, by the oscillation circuit including the charging coil 54 and the piezoelectric element 32 (which can be regarded as a capacitor of the capacitance C). Next, when a reverse voltage is applied to the thyristor 53, the thyristor 53 turns off.
As a result, the fuel pressure in the pressure chamber 18 increases, and this pressure pushes the needle 3 downward to close the valve (see FIG. 2).

Further, in C, the thyristor 56 is turned on, the fuel injection valve is opened, as in the case of A, and the same operation is repeated thereafter.

The electric charges charged in the piezoelectric element 27 in (b) are gradually discharged through the resistor 57. Piezo piezoelectric element
When the electrostatic capacity of 27 is C and the resistance value of the resistor 57 is R, the discharge time constant τ is represented by τ = CR. τ is set to 1 second or more, preferably 10 seconds. As a result, even in c, the piezo-piezoelectric element 27 is sufficiently charged to close the fuel injection valve, and under any operating condition, the fuel injection valve is discharged by the discharge through the resistor 57. It never opens.

The valve opening period (between the air and the air) and the valve opening timing (a) are calculated from the output signals of the crank angle sensor 60, the load sensor 61 and the water temperature sensor 62.

FIG. 4 shows changes in the internal pressure of the reservoir tank 35 and the terminal voltage of the piezoelectric element 27 when the engine is stopped.

In FIG. 4, the fuel injection valve is opened between the two hoses to execute fuel injection, and the ignition switch is turned on.
63 is turned off and the engine is stopped. When the ignition switch 63 is turned off, the fuel pump 36 stops and the reservoir tank
The internal pressure of 35 gradually decreases. On the other hand, the piezoelectric element 27 discharges through the resistor 57 with a time constant τ. The time constant τ is determined so that, regardless of the timing of turning off the ignition switch, the piezoelectric element 27 finishes discharging before the pressure in the reservoir tank 35 drops and reaches equilibrium. Furthermore, the time constant τ is such that the piezoelectric element 27 contracts due to the discharge of the piezoelectric element 27 and the pressure inside the pressure chamber 18 decreases, but the needle 3 does not open the injection hole 2 due to the discharge of the piezoelectric element 27. Is decided.

Due to the discharge of the piezoelectric element 27, the volume of the pressure chamber 18 increases and the pressure decreases, and the pressure in the reservoir tank 35 causes the fuel to be introduced into the pressure chamber 18 through the clearance 17. When the piezoelectric element 27 has finished discharging, the pressure chamber 18
Has the maximum volume, and the pressure in the reservoir tank 35 fills the pressure chamber 18 with fuel.

FIG. 5 shows changes in the internal pressure of the reservoir tank 35, the terminal voltage of the piezoelectric element 27 and the internal pressure of the pressure chamber 18 when the engine is started.

In FIG. 5, the ignition switch 63 is turned on at G and the starter switch 64 is turned on at H.
As soon as the starter switch 64 is turned on, the fuel pump
36 is driven and the pressure in the reservoir tank 35 starts to increase. Furthermore, the piezoelectric element 27 is charged with electric charge,
The piezoelectric element 27 extends. Since the pressure chamber 18 is filled with a sufficient amount of fuel when the engine is stopped as described above, the expansion of the piezoelectric element 27 causes a high pressure to be generated in the pressure chamber 18. The valve closing force due to this pressure is
Since it is larger than the thrust force that urges the needle 3 acting in the direction of valve opening, the needle 3 can reliably close the injection hole 2. Further, since the charge charging timing of the piezoelectric element 27 is synchronized with the pressure boosting timing in the reservoir tank 35, it is possible to suppress the leakage of the high pressure fuel in the pressure chamber 18 through the clearance 17, which is sufficient. The valve closing force can be maintained.

As described above, according to this embodiment, it is possible to reliably prevent erroneous injection when the engine is started.

FIG. 6 shows a drive circuit 51 in which the collector and the emitter of the transistor 58 are connected in parallel to the piezoelectric element 27 instead of the discharge resistor 57. The base of the transistor 58 is connected to the electronic control unit 50. At engine start-up and normal operation, the base current is set to 0 and the transistor 5 is turned off. Therefore, the piezoelectric element 27
Does not discharge through transistor 58. When the engine stop is detected by turning off the ignition switch 63, the pulse signal output from the electronic control unit 50 causes a pulsed base current to flow, and the transistor 58 is on / off controlled. As a result, the piezoelectric element 27 is discharged.
This state is shown in FIG. Similar to the first embodiment, this discharge rate is set to be faster than the decrease in the pressure in the reservoir tank 35, and is optimally controlled by the electronic control unit 50 so that the fuel injection valve will not open.

According to this embodiment, the same effect as that of the first embodiment can be obtained. Further, since the piezoelectric element 27 is not discharged during engine start-up and normal operation, the valve closing force hardly decreases, and more reliable valve closing can be performed. Further, it is possible to arbitrarily and easily change the discharge characteristic of the piezoelectric element 27 after the engine is stopped.

Other elements such as a thyristor may be used to discharge the piezoelectric element.

〔The invention's effect〕

As described above, according to the present invention, it is possible to reliably prevent erroneous injection when the internal combustion engine is started.

[Brief description of drawings]

FIG. 1 is a diagram showing a drive control circuit of a fuel injection valve, FIG. 2 is an overall configuration diagram of a fuel injection device, FIG. 3 is an operation explanatory diagram during normal engine operation, and FIG. 4 is an operational explanation when the engine is stopped. 5 and 5 are diagrams for explaining the operation at the time of starting the engine, FIG. 6 is a diagram showing the drive circuit of the second embodiment, FIG. 7 is a diagram for explaining the operation of the second embodiment, and FIG. It is a figure which shows a drive circuit. 2 ... Injection hole, 3 ... Needle, 17 ... Clearance, 18 ... Pressure chamber, 27 ... Piezoelectric element, 51 ... Drive circuit.

Claims (1)

[Claims] 1. A pressure chamber to which fuel is supplied via a throttle passage is provided, and a piezoelectric element extends to increase a fuel pressure in the pressure chamber, whereby a needle opens an injection hole and the piezoelectric element is provided. A fuel injection device having a fuel injection valve in which an element contracts to reduce the fuel pressure in the pressure chamber, thereby causing the needle to open the injection hole, wherein the piezoelectric element is provided after the internal combustion engine is stopped. The discharging means for discharging the charged electric charge, and the discharging current from the piezoelectric element by the discharging means are supplied to the pressure equilibrium state at a speed at which the needle does not open the injection hole and the fuel pressure decreases. A fuel injection device for an internal combustion engine, comprising: a discharge current control unit that limits a current range in which the piezoelectric element contracts at a high speed.