JPH0634598Y2 - Fuel injection valve drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a fuel injection valve drive device for controlling expansion and contraction of a piezoelectric element to adjust the fuel injection amount and fuel injection timing from the fuel injection valve. .

[Prior Art] In recent years, a piezoelectric element has been widely used as an actuator in a field where high-speed response is required, paying attention to its high extension response. An example of such a field is a fuel injection device that injects fuel with high response in response to high-speed rotation of an internal combustion engine, and proposals for applying a piezoelectric element to a fuel injection valve have already been made (for example, Japanese Patent Laid-Open Publication No. 2003-242242). "Fuel injection device" of Sho 58-210357). In this type of fuel injection device, at the time of fuel injection, the piezoelectric element is charged and extended to directly or indirectly lift the valve element in the valve opening direction to perform the valve opening. On the other hand, at the end of fuel injection, The electric charge of the piezoelectric element is removed and shortened to eliminate the bias of the valve element in the valve opening direction, thereby closing the valve. That is, the fuel injection valve driving device is configured to charge the piezoelectric element to extend the piezoelectric element and discharge the piezoelectric element to shorten the piezoelectric element.

Conventionally, the discharge of the piezoelectric element consumes electric charge by short-circuiting both ends of the piezoelectric element, while the charge of the piezoelectric element newly accumulates electric charge by applying a voltage to both ends of the piezoelectric element. It was

Furthermore, by connecting a capacitor in parallel with the power supply circuit for charging the piezoelectric element, the charge discharged from the piezoelectric element is stored in the capacitor, and the stored charge is charged again in the piezoelectric element. A fuel injection valve drive device that avoids wasteful power consumption has also been considered.

In the fuel injection valve driving device as described above, a coil that forms a series resonance circuit together with the capacitance component of the piezoelectric element between the piezoelectric element and the capacitor, and a switching element that opens and closes the series resonance circuit (for example, Thyristor), and when the switching element is closed, the electric charge stored in the capacitor is instantly transferred to the piezoelectric element.
On the other hand, in addition to the series resonance circuit, a coil that forms a series resonance circuit together with the capacitor and a switching element that opens and closes the series resonance circuit are provided between the piezoelectric element and the capacitor. When the switching element is closed, the electric charge stored in the piezoelectric element is instantly transferred to the capacitor.

[Problems to be Solved by the Invention] However, such a fuel injection valve drive device has the following problems, and further improvement has been desired.

When transferring the charge from the piezoelectric element to the capacitor, the charge of the piezoelectric element is transferred through the series resonance circuit of the capacitor and the coil, but not all the charges are transferred to the piezoelectric element. This is because it is necessary to shorten the time required to charge the capacitor from the power supply circuit when considering the response of the expansion and contraction drive of the piezoelectric element. Therefore, it is necessary to use a capacitor with as large a capacitance as possible. Is good. As a result, a small amount of electric charge remains in the piezoelectric element without being completely discharged, and the amount of residual electric charge increases as the piezoelectric element is repeatedly charged and discharged.

As a result of the above, the potential difference between the piezoelectric element and the capacitor gradually approaches the equilibrium state, the displacement amount of the expansion and contraction drive of the piezoelectric element decreases, and in the worst case, the drive of the piezoelectric element stops and the fuel injection valve does not operate. There was a problem.

Therefore, the present invention has been made in view of the above problems,
While increasing the responsiveness of expansion / contraction drive of the piezoelectric element, stable control of expansion / contraction drive of the piezoelectric element is realized without reducing the displacement amount of expansion / contraction drive of the piezoelectric element, and the fuel injection amount and fuel injection injected into the cylinder are performed. An object of the present invention is to provide a fuel injection valve drive device capable of adjusting the timing as expected.

Configuration of the Invention [Means for Solving the Problems] In order to achieve the above object, the present invention has the following configurations as means for solving the problems. That is, the present invention provides a casing, a fuel passage formed so as to penetrate through the casing, a valve body disposed at a tip portion of the fuel passage to open and close a tip opening of the fuel passage, and the fuel passage. And a piezoelectric element that is disposed in a cylinder independent of that and that opens and closes the valve body by being supplied with an electric charge to expand or shorten, and from a pressure accumulating means that stores fuel of a predetermined pressure to a cylinder of the internal combustion engine. In a fuel injection valve attached to the tip of a fuel passage that guides the fuel injection valve, a fuel injection valve drive device for controlling the expansion and contraction operation of the piezoelectric element to adjust the fuel injection amount and the fuel injection timing injected into the cylinder. A power supply circuit, a capacitor that is connected in parallel with the power supply circuit and stores the electric charge supplied from the power supply circuit, and has a predetermined inductance, and between the piezoelectric element and the capacitor. A first element connected in series to form a first series resonance circuit together with the piezoelectric element, and opening and closing the first series resonance circuit, and when the first series resonance circuit is closed, A first switching means for supplying an electric charge to the piezoelectric element; and a second switching element having a predetermined inductance and connected in series between the piezoelectric element and the capacitor to form a second series resonance circuit together with the capacitor. An element, a second switching unit that opens and closes the second series resonant circuit, and discharges electric charges from the piezoelectric element to the capacitor when the second series resonant circuit is closed; and short-circuits both ends of the piezoelectric element. And a short circuit that temporarily closes each time the piezoelectric element discharges electric charge to the capacitor and completes a single fuel injection. In is a fuel injector driving apparatus characterized by comprising and a third switching means for opening when the supply or discharge of charges have been made as a summary.

Here, the piezoelectric element may be any crystal as long as it has a property of generating mechanical strain by applying a voltage, for example, piezoelectric ceramics such as ceramics formed by stacking PZT, polymer This is the case with piezoelectric materials such as quartz and quartz.

The first element having an inductance is, for example, a coil or the like, and forms a first series resonance circuit having a predetermined resonance frequency together with the capacitance component of the piezoelectric element. Next, the second element having an inductance is a coil or the like, and forms a second series resonance circuit having a predetermined resonance frequency together with the capacitor.

When the first switching means and the second switching means are closed, the electric charges are instantaneously transferred in the series resonance circuits, so that the first switching means and the second switching means have a similar responsiveness to each resonance frequency and a small ionic resistance. Any switching means can be used regardless of semiconductor switching elements such as FET, thyristor, triac and the like.

The short circuit shorts both ends of the piezoelectric element, and there is a third switching element for opening and closing on the circuit.
The third switching means uses a semiconductor switching element such as a FET, a thyristor or a triac, like the first and second switching means. The above third
The switching means is normally in the open state, but is closed temporarily each time the piezoelectric element discharges and one fuel injection is completed.

[Operation] In the fuel injection valve drive device of the present invention having the above-described configuration, first, the first switching means is closed (the second switching means and the third switching means are opened) to close the first series resonance circuit. , Electric charges stored in the capacitor in advance are transferred to the piezoelectric element (charging of the piezoelectric element). Then, the piezoelectric element expands (or shortens), and the valve body opens the tip opening of the fuel passage, so that the fuel guided from the pressure accumulating means through the fuel passage is injected into the cylinder of the internal combustion engine.

Next, when the second switching means is closed (the first switching means and the third switching means are opened) to close the second series resonance circuit, the electric charge stored in the piezoelectric element is transferred to the capacitor (piezoelectric element). (Discharging of the element), the piezoelectric element is shortened (or extended) and the valve body closes the tip opening of the fuel passage, so that one fuel injection is completed. At this time, not all the electric charge of the piezoelectric element is transferred to the capacitor, and a small amount of electric charge is not completely discharged and remains in the piezoelectric element. Then, the fourth switching means is closed. Then, the electric charge remaining in the piezoelectric element is short-circuited, becomes zero, and the piezoelectric element is completely shortened (or expanded).

[Embodiment] An embodiment of the present invention will be described in order to further clarify the configuration of the present invention described above.

A fuel injection device for a diesel engine as an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a piezoelectric element drive circuit together with a block diagram of an electronic control device, FIG. 2 is a schematic block diagram of a four-cylinder diesel engine, and FIG. 3 (a) is a structure of a fuel injection valve having a piezoelectric element. FIG. 3 (B) is an enlarged sectional view showing the structure of the hydraulic piston portion of the fuel injection valve.

As shown in FIG. 2, reference numeral 1 denotes a diesel engine, which is a fuel injection valve 8 for direct injection into the combustion chamber for each diesel cylinder.
Is provided. The intake of the diesel engine 1 is performed by the supercharger T via the intake manifold 9.

The fuel injection valve 8 is connected via a fuel supply pipe 10 to a fuel pressure accumulation pipe 11 common to each cylinder. The fuel pressure accumulating pipe 11 has a pressure accumulating chamber 12 having a constant volume therein, and the fuel in the pressure accumulating chamber 12 is supplied to the fuel injection valve 8 via the fuel supply pipe 10. On the other hand, the pressure accumulating chamber 12 is connected via a fuel supply pipe 13 to a discharge port of a fuel supply pump 14 whose discharge pressure can be controlled. The suction port of the fuel supply pump 14 is connected to the discharge port of the fuel pump 15, and the suction port of the fuel pump 15 is connected to the fuel reservoir tank 16.
Further, each fuel injection valve 8 is connected to a fuel reservoir tank 16 via a fuel return conduit 17. The fuel pump 15 is provided to feed the fuel in the fuel reservoir tank 16 into the fuel supply pump 14, and if the fuel can be sucked into the fuel supply pump 14 without the fuel pump 15, It is not necessary to provide the pump 15 in particular. On the other hand, the fuel supply pump 14 is provided for discharging high-pressure fuel, and the high-pressure fuel discharged from the fuel supply pump 14 is accumulated in the pressure accumulating chamber 12. This pressure is also called rail pressure.

Further, in order to detect the operating state of the engine 1, the diesel engine 1 has two crank angle sensors 21, 22,
Cooling water temperature sensor 24, boost pressure sensor 26 and fuel pressure sensor 28
Etc. are provided. The electronic control device 30 uses the piezoelectric element drive circuit 40 and the pump drive device 45 to drive the diesel engine 1 based on the outputs of the above-described sensors and the amount of depression of the accelerator pedal 32, that is, the output of the accelerator sensor 34 that detects a load. The fuel injection amount and the fuel injection timing are controlled to control the output of the diesel engine 1. The configuration of the electronic control unit 30 and the processing performed by the electronic control unit 30 will be described later.

Next, the structure of the fuel injection valve 8 will be described. As shown in FIG. 3A, the fuel injection valve 8 includes a fuel injection valve main body 50 having a fuel inlet 48 assembled therein, and a nozzle fixed to the fuel injection valve main body 50 by a nozzle holder 51 via a spacer 52.
53 and an actuator 54 using a piezoelectric element are provided. A control rod 56, a pressurizing pin 57 and a needle 58, which are arranged in series with each other, are slidably inserted into the fuel injection valve main body 50, the spacer 52, and the nozzle 53. A fuel chamber 59 is formed above the control rod 56, and the fuel chamber 59 is connected to the pressure accumulating chamber 12 (FIG. 2) via the inflow port 48 and the fuel supply pipe 10. Therefore, the fuel pressure in the pressure accumulating chamber 12 is applied in the fuel chamber 59, and the fuel pressure in the fuel chamber 59 acts on the upper surface of the control rod 56. The needle 58 has a conical pressure receiving surface 60, and a needle pressurizing chamber 61 is formed around the pressure receiving surface 60. The needle pressurizing chamber 61 is connected to the fuel chamber 59 via the fuel passage 62 on the one hand.
On the other hand, it is connected to the nozzle hole 53a formed at the tip of the nozzle hole 53a via the annular fuel passage 63 formed around the needle 58 on the other hand. A biasing spring 64 that biases the pressure pin 57 downward is inserted into the fuel injection valve main body 50, and the needle 58 is also pressed downward by the biasing spring 64. The control rod 56 has a pressure receiving surface 65 having a conical shape in the middle thereof, and the control rod pressurizing chamber 66 is provided around the pressure receiving surface 65.
Is formed. The control rod pressurizing chamber 66 is the fuel injection valve main body 50.
It is made to communicate with a cylinder 67 formed therein, and a hydraulic piston 68 is slidably inserted into this cylinder 67. An O-ring 69 is attached to the hydraulic piston 68.

Next, the structure of the actuator 54 that drives the control rod 56 via the control rod pressurizing chamber 66 will be described. The actuator 54 includes a casing 71 fixed to the fuel injection valve main body 50, a hydraulic piston 68 and a piezoelectric element 72 inserted between the casing 71. The piezoelectric element 72 has a laminated structure in which a large number of thin plate piezoelectric elements are laminated, and when piezoelectric is applied to the piezoelectric element 72, the piezoelectric element 72 causes longitudinal strain due to an electrostrictive effect, that is, in the longitudinal direction. extend.
The amount of extension is small, for example, about 50 μ, but the response is extremely good, and the response time from application of voltage to extension is about 80 μsec. When the voltage application is stopped, the voltage element 72 contracts immediately. As shown in FIG. 3 (a), a disc spring 73 is inserted between the hydraulic piston 68 and the fuel injection valve main body 50, and the spring force of the disc spring 73 causes the hydraulic piston 68 to move.
68 is pressed toward the piezoelectric element 72. A fuel passage 74 is formed in the hydraulic piston 68 as shown in FIG.
A check valve 75 is inserted in the fuel passage 74. Fuel is circulated between the casing 71 and the piezoelectric element 72 by a device (not shown) for cooling the piezoelectric element 72, and when the fuel in the control rod pressurizing chamber 66, that is, the control oil leaks, the fuel in the casing 71 becomes the fuel. It is replenished into the control rod pressurizing chamber 66 via the passage 74 and the check valve 75.

The fuel in the control rod pressurizing chamber 66, that is, the downward force acting on the upper surface of the control rod 56 on the needle 58 when the control oil is not pressurized, and the downward force by the compression spring 64,
An upward force acting on the pressure receiving surface 60 of the needle 58 is applied.
At this time, the diameter of the control rod 56, the spring force of the compression spring 64, and the area of the pressure receiving surface 60 of the needle 58 are set so that the total of the downward force is slightly larger than the upward force.
Therefore, a downward force is normally applied to the needle 58,
Thus, the normal needle 58 closes the nozzle hole 53a. Next, when a voltage is applied to the piezoelectric element 72, the piezoelectric element 72
Is increased, the hydraulic piston 68 moves to the left, and as a result, the control hydraulic pressure in the control rod pressurizing chamber 66 rises. At this time, since the upward force acts on the bearing surface pressure 65 of the control rod 56, the control rod 56 rises, and thus the needle 58 rises, so that fuel is injected from the nozzle hole 53a. The response at this time is about 80 μsec, which is extremely fast, as described above. On the other hand, when the voltage application to the piezoelectric element 72 is stopped, the piezoelectric element 72 contracts, and as a result, the control rod pressurizing chamber 66
Since the control oil pressure inside is lowered, the control rod 66 and the needle 58 are lowered and the fuel injection is stopped. At this time, the response is about 80 μsec, which is extremely fast.

Next, the configurations and functions of the electronic control unit 30 in this embodiment and the piezoelectric element drive circuit 40 which is the main part of one embodiment of the present invention will be described. As shown in FIG. 1, an electronic control unit 30 that operates by receiving power from a battery 101 via an ignition switch 100 is a known CPU 110, ROM111, RA.
Mainly on M112, timer 115, input port 117, output port 11
It is configured as a logical operation circuit in which 8 and the like are connected to each other by a bus 119. At the input port 117, the crank angle sensors 21, 22, the cooling water temperature sensor 24, the boost pressure sensor 26,
A fuel pressure sensor 28 and an accelerator sensor 34 are connected, and the CPU 110 outputs a crank angle (hence the rotation speed N of the diesel engine 1), a cylinder discrimination signal, a cooling water temperature Thw, and a supercharging pressure B via the input port 117. Fuel pressure P and load L
It is possible to read the operating state of the diesel engine 1 such as. On the other hand, the output port 118 is connected to the piezoelectric element drive circuit 40 that drives the piezoelectric elements of the four fuel injection valves 8 and the pump drive device 45 that drives the fuel supply pump 14, and the CPU 110 outputs the output port 118. The opening and closing of the fuel injection piece 8 and the control of fuel supply are performed via the. Since the control of the fuel supply pump 14 is not directly related to the gist of the present invention, the fuel pressure P is controlled in proportion to the rotational speed N of the diesel engine 1, and the description thereof will be omitted. Further, in FIG. 1, other than the circuit for driving the piezoelectric element included in one fuel injection valve 8 of the piezoelectric element drive circuit 40, the others are omitted. Piezoelectric elements included in the fuel injection valves 8 of the other three cylinders are also controlled via the output port 118 with the same circuit configuration.

The piezoelectric element drive circuit 40 is supplied with a voltage of about 250 V that the drive voltage generation circuit 120 boosts and outputs the battery voltage, and the thyristors SCR1, SCR2, SCR3, and the transistor TR.
The piezoelectric element 72 is configured to be exclusively driven by switching. Drive voltage generation circuit
A capacitor C is connected in parallel to 120, and a thyristor SCR1 is connected between the positive side output of the drive voltage generating circuit 120 and the capacitor C. The thyristor SCR1 is connected to the drive voltage generating circuit 120 on the anode side and to the capacitor C on the cathode side. On the other hand, the cathode side of thyristor SCR1 is connected to the other thyristor via coil L1.
The anode side of SCR2 is also connected, and the cathode side of thyristor SCR2 is connected to the piezoelectric element 72 of actuator 54.

The cathode side of the thyristor SCR2 is connected to the anode side of another thyristor SCR3 via the coil L2, and the cathode side of the thyristor SCR3 is connected to the thyristor SCR1 side of the capacitor C.

On the other hand, as a short circuit of the charge stored in the piezoelectric element 72,
Both ends of the piezoelectric element 72 are short-circuited via the NPN type transistor TR. That is, the collector of the transistor TR is on the thyristor SCR2 side of the piezoelectric element 72, the emitter is on the minus side output of the drive voltage generating circuit 120, and the base is on the output port 118.
The open / close of the short circuit is controlled.

The gates of thyristors SCR1, SCR2, SCR3 are also output ports.
Driven directly connected to 118. Where thyristor S
CR2 and SCR3 correspond to the first switching means and the second switching means, respectively, and the transistor TR corresponds to the third switching means.

Therefore, the processing performed by the electronic control unit 30 will be described next with reference to the flow charts shown in FIGS. 4 to 8 and, at the same time, the thyristors SCR1, SCR2, SCR3, and the transistors driven through the output port 118, and the transistors. The TR on / off operation and the opening / closing of the fuel injection valve in response to the expansion / contraction of the piezoelectric element will be described.

The electronic control unit 30 starts its operation when the ignition switch 100 is turned on, and executes the main control routine shown in FIG. First, in step 200, so-called initialization processing is performed. Here, initial settings such as a clear flag of an internal register of the CPU 110 are performed. In the following step 210, the initial voltage supply control routine for the capacitor C is executed. This routine will be described later with reference to FIG.

In step 220 following step 210, the number of revolutions N of the diesel engine 1 from each sensor is input via the input port 117.
A process of reading operating states such as the load L, the cooling water temperature Thw, the supercharging pressure B and the fuel pressure P is performed. In the following step 230,
Fuel injection amount τ based on load L and other operating conditions
Further, in step 240, a process of calculating the start and end times of fuel injection is performed.

In response to these results, the CPU 110 determines the fuel injection start timing and end timing with the timer 115 in step 250.
Set to. As a result, the timer 115 starts self-propelled, and outputs an interrupt signal to the CPU 110 at the fuel injection start timing and fuel injection start timing.

In the following step 260, the fuel supply pump 14 is controlled from the output port 118 via the pump drive device 45, and the fuel pressure P is controlled. However, since this is not directly related to the present invention, description of this control is omitted. . The following step 270 is
An initialization control routine for short-circuiting the residual charge of the piezoelectric element 72 and replenishing the capacitor C with electric power is executed.
This routine will be described later with reference to FIG. After the processing of step 270 ends, the processing returns to step 220, and the above-described processing for fuel injection is repeated.

The process of step 210 described above will be described in detail with reference to the flowchart of FIG. When the process is started, in step 310, a process of outputting a pulse signal to the gate of the thyristor SCR1 via the output port 118 is performed. As a result, the thyristor SCR1 becomes conductive and the drive voltage generating circuit 120 charges the capacitor C. At this time, the terminal voltage of the capacitor C becomes equal to that of the drive voltage generating circuit 120. After the above processing is completed, the process exits to "RTN" and this routine is once completed. The capacitor C has a large capacitance of about 50 μF in order to reduce the time required for the above-mentioned charging.

When the fuel injection start timing set in the process of step 250 described above is reached, an interrupt is generated from the timer 115, and the CPU 110 executes the fuel injection valve opening control interrupt routine shown in FIG. In this interrupt routine,
At 410, a process of outputting a pulse signal to the gate of thyristor SCR2 via output port 118 is performed. As a result, when the thyristor SCR2 becomes conductive, this circuit turns on the coil L1.
Since it is a series resonance circuit consisting of the inductance of the capacitor and the capacitance of the piezoelectric element 72, the capacitor C
Part of the electric charge stored in the piezoelectric element 72 moves to the piezoelectric element 72.
As a result, the piezoelectric element 72 expands, the control rod 56 of the fuel injection valve 8 is pushed upward and the fuel injection valve 8 is opened, and fuel is injected from the nozzle hole 53a at the tip of the nozzle 53. If the charge moves from the capacitor C to the piezoelectric element 72, the thyristor SC
Since R2 has no holding current, it turns off and the piezoelectric element 72
The charge stored on the battery is not discharged anywhere. Of course, a part of the electric power is used to drive the control rod 56 upward, but the energy (charge) stored in the piezoelectric element 72 is several times larger than the consumed electric power. Even after the drive of 56, the piezoelectric element 72 is in a state in which a marginal charge is stored. If the piezoelectric element 72 expands and becomes a valve open state, the piezoelectric element 72 does almost no work, and thus the electric charge is hardly lost.

Next, when the fuel injection end timing set in the process of step 250 described above is reached, an interrupt is generated from the timer 115, and the CPU 110 executes the fuel injection valve closing control interrupt routine shown in FIG. In this interrupt routine,
In step 510, thyristor SCR3 via output port 118.
A process of outputting a pulse signal to the gate of is performed. As a result, when the thyristor SCR3 becomes conductive, this circuit is a series resonance circuit formed by the inductance of the coil L2 and the capacitance of the capacitor C. Therefore, the electric charge stored in the piezoelectric element 72 within several tens of microseconds is stored in the capacitor. Move to C. As a result, the piezoelectric element 72 is shortened, and as a result, the control oil pressure in the control rod pressurizing chamber 66 is reduced, so that the control rod is reduced.
56 and needle 58 are lowered to reduce fuel injection.
At this time, not all the electric charge of the piezoelectric element 72 is transferred to the capacitor C, and a small amount of electric charge is not completely exhausted.
Remains in. After the above processing is completed, the process exits to "RTN" and this routine is once completed.

Next, the process of step 270 described above will be described in detail based on the flowchart of FIG. When the process starts
In step 610, the transistor is output through output port 118.
Processing for outputting a control signal to the base terminal of TR is performed. As a result, the emitter-collector of the transistor TR becomes conductive, both ends of the piezoelectric element 72 are short-circuited, and the above-mentioned residual charge is completely eliminated and becomes zero. Note that the piezoelectric element 72 is further shortened and the fuel injection valve 8 is operated closer to the closing side in accordance with this electric charge short-circuiting process.

Thus, the fuel injection valve 8 performs the fuel injection operation (open / close valve operation) once, but the capacitor C stores a considerable amount of electric charge. Therefore, this power can be used for the next on-off valve operation, and power saving can be achieved. However, due to the power consumption accompanying the opening / closing operation of the fuel injection valve 8 and a partial short circuit of the power, the electric charge stored in the capacitor C naturally lowers compared to the initial state, and it becomes necessary to replenish the energy. . This is followed by step 620,
Make up for lost energy. That is, step 62
At 0, a control signal is output to the gate of thyristor SCR1,
Processing for turning this on is performed. Since this process is performed at the timing when the fuel injection valve 8 is closed, the drive voltage is generated in the capacitor C as in the case where the thyristor SCR1 is turned on in the initialization process (process of step 200 in FIG. 4). Electric power is supplied from the circuit 120, and charges lost due to opening / closing of the fuel injection valve 8 are replenished. After the processing of step 620, the control routine ends by exiting to "RTN".

In addition, the piezoelectric element by the operation of thyristors SCR2, SCR3, SCR4
The timing chart of FIG. 9 shows the state of extension of 72 and the state of the above-described power replenishing operation by the operation of the thyristor SCR1. In the figure, when the thyristor SCR1 becomes conductive, the terminal voltage of the capacitor C indicated by the one-dot chain line 710 becomes equal to the output voltage Vo of the drive voltage generation circuit. Next, when the thyristor SCR2 is turned on, the terminal voltage of the piezoelectric element 72 indicated by the solid line 720 rises and doubles to about V0. Next, when the thyristor CR3 becomes conductive, the terminal voltage of the piezoelectric element 72 drops and becomes the predetermined voltage V1. After that, the transistor TR becomes conductive and the terminal voltage of the piezoelectric element 72 becomes zero. After that, the above processing is repeatedly executed.

In the present embodiment configured as described above, the piezoelectric element
The terminal voltage between the piezoelectric elements 72 after one expansion and contraction operation of 72 is 9th
As shown in the figure, since it becomes completely zero, the displacement amount of expansion and contraction drive of the piezoelectric element decreases like the fuel injection valve drive device using the conventional piezoelectric element, and in the worst case, the drive of the piezoelectric element stops. Therefore, the fuel injection valve does not stop operating.

In this embodiment, a large amount of the electric charge discharged from the piezoelectric element 72 is stored in the capacitor C, and the stored electric charge is charged again in the piezoelectric element 72, thereby preventing waste of electric power. There is.

Further, in the present embodiment, the expansion action of the piezoelectric element 72 is used, and the capacitance of the capacitor is set large in order to further shorten the charging time of the capacitor. Therefore, the response of opening and closing the fuel injection valve 8 is about several tens of μsec. And is extremely fast. As a result, it is possible to accurately control the fuel injection amount and the fuel injection timing, and it is possible to achieve improvement in fuel consumption and exhaust gas purification.

Although one embodiment of the present invention has been described above, the present invention is not limited to such an embodiment, and it is needless to say that the present invention can be implemented in various modes without departing from the scope of the present invention. is there.

Effects of the Invention As described in detail above, in the fuel injection valve driving device according to the present invention, the third switching means is provided so that the charge of the piezoelectric element is transferred to the capacitor and the piezoelectric element is shortened (or expanded). Each time the valve body closes the tip opening of the fuel passage and completes one fuel injection, the short circuit is closed to short-circuit both ends of the piezoelectric element. Therefore, even when a capacitor having a large electrostatic capacity is used to improve the responsiveness, the residual charge is not stored in the piezoelectric element every time fuel injection is repeated. Therefore, the expansion / contraction operation of the piezoelectric element can be stably controlled, and the fuel injection valve can be driven based on the control to adjust the desired fuel injection amount and fuel injection timing.

Further, in the present invention, since a considerable amount of electric charge once stored in the piezoelectric element is transferred to the capacitor and this electric power is used for driving the piezoelectric element in time, it is possible to save the electric power.

[Brief description of drawings]

FIG. 1 is a block diagram of a drive circuit for a piezoelectric element 72 together with a block diagram of an electronic control device, FIG. 2 is a schematic block diagram of a 4-cylinder diesel engine, and FIG. 3 (a) is a sectional view showing the structure of a fuel injection valve 8. FIG. 3 (b) is an enlarged sectional view showing the structure of a hydraulic piston 68 forming a part of the fuel injection valve 8, and FIGS. 4 to 8
FIG. 9 is a flow chart showing various control routines executed by the electronic control unit 30, and FIG. 9 is a time chart showing control in this embodiment. 1 …… Diesel engine 8 …… Fuel injection valve 12 …… Accumulator 14 …… Fuel supply pump 40 …… Piezoelectric element drive circuit 50 …… Fuel injection valve body 53 …… Nozzle 58 …… Needle 72 …… Piezoelectric element 120 ...... Drive voltage generation circuit SCR1, SCR2, SCR3 …… Thyristor C …… Capacitor L1, L2 …… Coil TR …… Transistor

Claims (1)

[Scope of utility model registration request] 1. A casing, a fuel passage formed so as to penetrate through the casing, a valve body arranged at a tip end portion of the fuel passage for opening and closing a tip opening of the fuel passage, and the fuel passage. Is provided in a separate and independent cylinder and is provided with a piezoelectric element that opens and closes the valve body by being supplied with an electric charge to extend or shorten, and supplies fuel to a cylinder of the internal combustion engine from a pressure accumulating means that stores fuel at a predetermined pressure. A fuel injection valve driving device for adjusting a fuel injection amount and a fuel injection timing to be injected into the cylinder by controlling expansion and contraction operation of the piezoelectric element in a fuel injection valve attached to a leading end of a fuel path to be guided. A power supply circuit, a capacitor connected in parallel with the power supply circuit for storing electric charge supplied from the power supply circuit, having a predetermined inductance, and connected in series between the piezoelectric element and the capacitor. A first element connected to the piezoelectric element to form a first series resonant circuit together with the first series resonant circuit, and the first series resonant circuit is opened and closed; and when the first series resonant circuit is closed, the piezoelectric element is removed from the capacitor. First switching means for supplying electric charge to the element, and a second element having a predetermined inductance and connected in series between the piezoelectric element and the capacitor to form a second series resonance circuit together with the capacitor A second switching unit that opens and closes the second series resonant circuit and discharges electric charges from the piezoelectric element to the capacitor when the second series resonant circuit is closed; and a short circuit that short-circuits both ends of the piezoelectric element. The circuit and the short circuit are temporarily closed each time the piezoelectric element discharges electric charge to the capacitor and completes a single fuel injection, and an electric circuit is formed between the piezoelectric element and the capacitor. A fuel injection valve drive device, comprising: a third switching means that opens when a load is supplied or discharged.