JP3444120B2 - Fuel injection device - Google Patents

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 equipped with a fuel injection valve that operates a needle valve by changing a fuel pressure before and after the needle valve via a piezoelectric element.

[0002]

2. Description of the Related Art A fuel injection valve or the like provided in an automobile engine is provided with a piezoelectric element (piezo element) that expands in response to an applied voltage, and a needle valve (valve body) is opened through the piezoelectric element. was there. By driving the needle valve with the piezoelectric element, the high-speed response of the fuel injection valve is enhanced, the injectable range is expanded, and high output of the engine can be dealt with. In addition, it becomes possible to stably inject a small amount of fuel, thereby reducing the fuel consumption of the engine.

As this type of fuel injection valve, there is known one in which a needle valve is opened based on the differential pressure across the needle valve. A fuel pressure chamber and a back pressure chamber are defined before and after the needle valve, fuel is introduced into the fuel pressure chamber at a predetermined pressure, and the back pressure chamber communicates with the fuel pressure chamber by an orifice. A piezoelectric element is provided in the back pressure chamber behind the needle valve, and the opening / closing operation of the needle valve is controlled by expansion and contraction of the piezoelectric element. That is, in the state where the piezoelectric element is extended by applying a voltage, the fuel pressure chamber and the back pressure chamber before and after the needle valve are equalized by the orifice. At this time, the needle valve is held closed by the tension of the spring. When the voltage is lowered from this state to contract the pressure element, the volume of the back pressure chamber behind the needle valve increases and the internal pressure decreases. Since the pressure drop is transmitted to the fuel pressure chamber in front of the needle valve with a delay, a pressure difference is temporarily generated in the valve opening direction before and after the needle valve. As a result, the needle valve opens against the spring, the injection port opens, and fuel is injected. (For a known example of this type of fuel injection device, see, for example, Japanese Patent No. 2500684.)

[0004]

By the way, in the conventional fuel injection device using such a piezoelectric element, the piezoelectric element is driven so that the expansion / contraction amount of the piezoelectric element is always kept constant. Therefore, there is a problem that the injection control may not be normally performed when the fuel pressure is low such as when the load is low. That is, when the fuel pressure is low, the internal pressure of the back pressure chamber is too low when the piezoelectric element contracts, and thereby bubbles are generated in the fuel pressure chamber. The bubbles absorb the volume change of the back pressure chamber due to the expansion and contraction of the piezoelectric element, and as a result, the needle valve may not normally open and close.

An object of the present invention is to solve the above problems by controlling the driving voltage of the piezoelectric element according to the fuel pressure.

[0006]

A fuel injection device according to a first aspect of the present invention includes an injection port that is opened and closed by a needle valve, a fuel pressure chamber that guides pressurized fuel to the injection port, and a piezoelectric element that expands according to an applied voltage. , A back pressure chamber defined between the needle valve and the piezoelectric element, a throttle passage that connects the fuel pressure chamber and the back pressure chamber, a spring that urges the needle valve in the closing direction, and a back pressure chamber The control means reduces the drive voltage Vp applied to the piezoelectric element as the fuel pressure decreases.

The fuel injection device described in claim 2 is, as the control means of the invention described in claim 1, an initial injection pulse width calculation means for calculating an initial injection pulse width Ti in accordance with the operating state of the engine, and a fuel pressure. A fuel pressure sensor for detecting a fuel pressure Pf introduced into the chamber, a drive voltage calculating means for calculating a drive voltage Vp applied to the piezoelectric element according to the fuel pressure Pf, and an initial injection pulse width Ti for correcting the drive voltage Vp. An injection pulse width correction amount calculating means for calculating a final injection pulse width Ti ′, an injection pulse generator for generating a pulse signal corresponding to the calculated injection pulse width Ti ′, and a pulse signal for generation. And a drive circuit for applying the applied voltage to the piezoelectric element.

According to a third aspect of the fuel injection device, the control means of the first or second aspect of the invention controls the drive voltage Vp applied to the piezoelectric element so that the back pressure chamber does not become a negative pressure. It was configured.

[0009]

In the fuel injection device according to the first aspect of the present invention, the pressures in the fuel pressure chamber and the back pressure chamber generated before and after the needle valve are equalized by the throttle passage when the piezoelectric element is extended by applying a voltage. Has been converted. At this time, the needle valve is held closed by the elastic restoring force of the spring.

As the voltage applied to the piezoelectric element is cut off and the piezoelectric element contracts, the volume of the back pressure chamber increases and its pressure decreases. Since the pressure drop is delayed and transmitted to the fuel pressure chamber through the throttle passage, a pressure difference is temporarily generated between the back pressure chamber and the fuel pressure chamber. Due to this pressure difference, the needle valve opens the injection port against the spring, and fuel is injected from the injection port.

According to the present invention, the drive voltage Vp applied to the piezoelectric element is controlled so as to decrease as the fuel pressure introduced to the back pressure chamber decreases, thereby suppressing the volume change of the back pressure chamber. , It is possible to prevent the pressure in the back pressure chamber from being excessively lowered to generate bubbles in the back pressure chamber.

As a result, the volume change of the back pressure chamber due to the expansion and contraction of the piezoelectric element is not absorbed by the bubbles, and the needle valve normally opens and closes, so that the fuel injection amount can be adjusted accurately.

In the fuel injection device according to claim 2,
The initial injection pulse width calculation means calculates the initial injection pulse width Ti according to the engine operating state.

The drive voltage calculating means calculates the drive voltage Vp applied to the piezoelectric element according to the fuel pressure Pf introduced into the fuel pressure chamber. As the fuel pressure Pf decreases, the drive voltage Vp of the piezoelectric element is controlled to decrease to suppress the volume change of the back pressure chamber, so that the pressure in the back pressure chamber excessively decreases and the back pressure is reduced. Prevents the generation of air bubbles in the room.

The injection pulse width correction amount calculation means calculates the final injection pulse width Ti 'according to the drive voltage Vp.
The injection pulse width correction amount is set so that the final injection pulse width Ti ′ increases as the drive voltage Vp decreases, and the fuel injection amount is not affected by changes in the drive voltage Vp. Try to fit the desired value.

A pulse signal corresponding to the thus calculated injection pulse width Ti 'is produced by the injection pulse generator, and a voltage corresponding to this pulse signal is applied to the piezoelectric element via the injection valve drive circuit.

In the fuel injection device according to claim 3,
By controlling the drive voltage Vp applied to the piezoelectric element so that the back pressure chamber does not become a negative pressure, it is possible to prevent bubbles from being generated in the back pressure chamber.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a fuel injection device provided in a cylinder injection type spark ignition engine will be described below with reference to the accompanying drawings.

As shown in FIG. 1, the fuel injection valve 7 faces the cylinder 64 from the ceiling wall of the combustion chamber, and the fuel is directly injected from the fuel injection valve 7 into the cylinder 64.

In the intake stroke in which the piston 65 descends, air is sucked into the cylinder 64 from each intake passage 71 as the intake valve is opened.

In the compression stroke in which the piston 65 rises, the air sucked into the cylinder 4 through each intake passage 71 is compressed by the piston 65.

When the piston 65 reaches the vicinity of the top dead center in the compression stroke, the fuel is ignited and burned via the spark plug 66.

The timing of fuel injection differs depending on the operating state. For example, by setting the compression stroke at low rotation and low load, the air-fuel mixture is burned around the spark plug 66 so that combustion can be performed with a lean air-fuel ratio. Collective stratified combustion is performed. On the other hand, at the time of high rotation and high load, the fuel injection timing is set to the intake stroke, so that homogeneous combustion that forms a homogeneous air-fuel mixture in the cylinder 4 is performed.

In the expansion stroke in which the piston 65 descends, the burned gas causes the piston 65 to rotate the crankshaft via the connecting rod.

In the exhaust stroke in which the piston 65 rises, the exhaust gas in the cylinder 64 is exhausted from the exhaust passage 72 as the exhaust valve is opened. Each of these steps is continuously repeated.

A throttle valve 70 is provided in the middle of the intake passage 71. The throttle valve 70 is opened and closed by an accelerator pedal to adjust the intake air amount.

As shown in FIG. 3, the fuel tank 59
The fuel stored in is sucked up by the low pressure fuel pump 58 and sent to the high pressure fuel pump 57. The high-pressure fuel pump 57 sends the pressurized fuel to the pressure accumulation chamber 56, and pressure-feeds the fuel from the pressure accumulation chamber 56 to the fuel injection valve 7 of each cylinder. Excess fuel sent from the high-pressure fuel pump 57 to the accumulator chamber 56 is returned to the fuel tank 59 through the fuel return passage 52.

The fuel pressure introduced to the fuel injection valve 7 is variably controlled in accordance with the operating state and regulated via the pressure regulator 55, as will be described later. That is, although various modes of controlling the fuel pressure can be considered, for example, when the high pressure fuel pump 57 is mechanically driven by the camshaft of the engine, the electric motor is used until the discharge pressure of the high pressure fuel pump 57 rises at the time of starting. The operation is performed with the discharge pressure of the driven low-pressure fuel pump 58 as the fuel injection pressure. Since the fuel injection pressure is low at this start, the fuel injection timing is set to the intake stroke. After that, it is conceivable that the fuel pressure is switched to a high fuel pressure to shift to normal operation. It is also possible to increase the fuel pressure as the engine speed increases during normal operation. This is different from the conventional engine that injects fuel into the intake passage. In an engine that directly injects fuel into the combustion chamber, the required amount of fuel must be injected during a limited period (during stroke). Therefore, when the engine speed is high, the injection time must be set short. Therefore, if the fuel pressure is increased as the engine speed increases,
It is possible to inject the required fuel in a short injection time.

The control unit 33 controls the intake air amount Qa detected by the intake air amount sensor 36, the engine speed Ne detected by the crank angle sensor 35, and the cooling water temperature Tw detected by the cooling water temperature sensor 37. A signal corresponding to the oxygen concentration in the exhaust gas detected by an O ₂ sensor (not shown), a signal corresponding to the fuel pressure Pf detected by the fuel pressure sensor 34, and the like are input as will be described later.

The control unit 33 calculates the basic injection amount Tp by the following equation based on the detected intake air amount Qa and the engine speed Ne.

Tp = K · Qa / Ne (1) However, K; constant and, during homogeneous combustion, the air-fuel ratio falls within a narrow range around the stoichiometric air-fuel ratio, or stratified charge combustion is performed. The initial injection pulse width Ti is calculated by the following equation so as to obtain the air-fuel ratio for realization, and the fuel injection amount is feedback-controlled.

Ti = Tp × α × COEF + Ts (2) where α is the air-fuel ratio feedback correction coefficient, COEF
Is the sum of various correction coefficients using parameters such as the correction coefficient for the cooling water temperature and the correction coefficient for lean combustion, and Ts is the invalid injection pulse width.

A drive voltage corresponding to the calculated initial injection pulse width Ti is output to the fuel injection valve 7 described later to perform fuel injection control.

As shown in FIG. 2, in the fuel injection valve 7, the needle valve 2 is slidably housed inside the nozzle body 1 and the casing 9. A fuel pressure chamber 3 is defined around the needle valve 2 inside the nozzle body 1 and the casing 9. An injection port 1b opens at the tip of the nozzle body 1, and the injection port 1b is opened and closed by a needle valve 2.

The fuel pumped from the fuel injection pump 57 is introduced into the fuel pressure chamber 3 from the fuel inlet 13 through the fuel passage 12, and is injected from the injection port 1b as the needle valve 2 is lifted.

Inside the nozzle body 1, a seat surface 1a is recessed in a conical shape around the injection port 1b. On the other hand, at the tip of the needle valve 2, the seat portion 2a projects in a conical surface shape. When the seat portion 2a is seated on the seat surface 1a, the injection port 1b is closed. When the seat portion 2a is separated from the seat surface 1a, the injection port 1b is opened.

The support portion 2b protrudes from the middle of the needle valve 2 in the outer diameter direction, and the support portion 2b is brought into sliding contact with the cylindrical inner wall surface of the nozzle body 1 so that the seat portion 2a is coaxial with the seat surface 1a. I will guide you to. The support portion 2b is provided with a notch portion (not shown), and the fuel flows through the notch.

The needle valve 2 has a piston portion 2 on its proximal end side.
c is formed to project in an annular shape. A back pressure chamber 8 is defined between the casing 9 and the piston portion 2c. The fuel pressure chamber 3 and the back pressure chamber 8 are communicated with each other via a throttle passage 5 formed on the outer circumference of the piston portion 2c. The throttle passage 5 is formed as a gap of, for example, about 6 μm between the casing 9 and the outer circumference of the piston portion 2c.

A coil spring 4 for urging the needle valve 2 in the valve closing direction is provided. The coil spring 4 is interposed between the recess formed in the needle valve 2 and the casing 9 in a compressed state, and is arranged coaxially with the needle valve 2.

A back pressure piston 11 which defines a back pressure chamber 8 is slidably disposed inside the casing 9. An O-ring 12 is provided on the outer circumference of the back pressure piston 11. The back pressure chamber 8 is sealed by the O-ring 12 slidingly contacting the cylindrical inner wall surface of the casing 9.

A piezoelectric element 10 for driving the needle valve 2 in the valve opening direction via a back pressure piston 11 is provided. A plurality of disk-shaped piezoelectric elements 10 are laminated with the disk-shaped internal electrode plates sandwiched therebetween, and an actuator that expands and contracts in the axial direction of the needle valve 2 when a voltage is applied through each internal electrode plate is used. Constitute.

A flat spring 16 for pressing the piezoelectric element 10 is provided. The flat spring 16 is interposed between the casing 9 and the back pressure piston 11 in a compressed state, and presses the piezoelectric element 10 in the compression direction by its elastic restoring force.

The casing end 14 is joined to the fixed end of the piezoelectric element 10. The casing end 14 is arranged so that the compression amount of the flat spring 16 becomes a predetermined value, and is joined to the casing 9 by welding.

The piezoelectric element 10 expands when a voltage is applied via the lead wires 18 and 19 to increase the pressure in the back pressure chamber 8 and close the needle valve 2. The piezoelectric element 10 contracts when the voltage applied thereto is cut off, lowers the pressure in the back pressure chamber 8 and compresses the coil spring 4, and drives the needle valve 2 in the valve opening direction.

Base end face 2d of needle valve 2 and casing 9
A disc-shaped shim 15 is interposed between them. The needle valve 2 comes into contact with the shim 15 when the valve is opened, so that the axial movement of the needle valve 2 is restricted. That is, the plate thickness of the shim 15 determines the full lift amount of the needle valve 2.

Lead wires 18 and 19 are injection valve drive circuit 31.
Extending to. A pulse signal corresponding to the fuel injection amount calculated by the engine control unit 33 is generated by the injection pulse generator 32, and a voltage corresponding to this pulse signal is applied to the piezoelectric element 10 via the injection valve drive circuit 31.

FIG. 2 shows a state before the engine is started. A voltage is applied to the piezoelectric element 10 to expand the piezoelectric element 10, and the pressures of the fuel pressure chamber 3 and the back pressure chamber 8 generated before and after the piston portion 2c are restricted. It is equalized by the passage 5. At this time, the needle valve 2 is seated on the seat portion 1 a of the nozzle body 1 by the elastic restoring force of the coil spring 4. Piezoelectric element 1
By applying a voltage of, for example, 500 V to 0 for about 0.5 seconds, the preparation before engine start is completed.

Even when the engine is stopped, the needle valve 2 is seated on the seat portion 1a of the nozzle body 1 by the elastic restoring force of the coil spring 4 to prevent fuel leakage.

When the fuel injection valve 7 is opened at the start of the engine and after the start of the engine, the piezoelectric element 10 contracts because the voltage applied in synchronization with the engine rotation is cut off. As the back pressure piston 11 moves at a speed of about 0.1 m / s as the piezoelectric element 10 contracts, the back pressure chamber 8 expands in volume and its pressure drops to about 2 MPa. Since the pressure drop is transmitted to the fuel pressure chamber 3 through the throttle passage 5 with a delay, a pressure difference is temporarily generated between the back pressure chamber 8 and the fuel pressure chamber 3. Due to this pressure difference, the needle valve 2 opens the injection port 1b against the coil spring 4, and the high-pressure fuel guided to the fuel pressure chamber 3 is injected into the cylinder 64 through the injection port 1b.

When the fuel injection valve 7 is closed, the piezoelectric element 1
0 expands when a voltage is applied in synchronization with the engine rotation, and the pressure in the back pressure chamber 8 temporarily rises as the back pressure piston 11 moves, and the pressure in the back pressure chamber 8 and the fuel pressure chamber 3 increases. The needle valve 2 is moved by the difference and the biasing force of the coil spring 4 and is seated on the seat portion 1 a of the nozzle body 1. When the needle valve 2 is seated on the seat portion 1a, the injection port 1b is closed and the fuel injection is stopped.

Since the displacement direction of the piezoelectric element 10 and the displacement direction of the needle valve 2 are the same in the fuel injection valve 7, the piezoelectric element 10 and the needle valve 2 can be arranged in series, and the structure can be simplified. Be peeled off.

By the way, when the fuel pressure introduced into the back pressure chamber 8 is low at the time of starting the engine, the piezoelectric element 1
At the time of contraction of 0, the pressure of the back pressure chamber 8 may drop too much, and bubbles are generated in the back pressure chamber 8 at this time. The bubbles absorb the volume change of the back pressure chamber 8 due to the expansion and contraction of the piezoelectric element 10, and as a result, the needle valve 2 may not normally open and close.

FIG. 8 shows the relationship between the voltage applied to the piezoelectric element 10, the lift amount of the needle valve 2 and the pressure of the back pressure chamber 8. Bubbles are generated in the back pressure chamber 8 in the negative pressure region where the pressure in the back pressure chamber 8 is lower than 0 Pa. In FIG. 8, (b) shows the characteristic at the time of normal operation in which the fuel pressure Pf guided to the fuel pressure chamber 3 becomes a prescribed 5 MPa, and the applied voltage at which bubbles are generated in the back pressure chamber 8 is X2. On the other hand, FIG. 7A shows the characteristic during operation in which the fuel pressure Pf introduced to the fuel pressure chamber 3 decreases to 0.3 MPa, and the applied voltage at which bubbles are generated in the back pressure chamber 8 is X1 at low fuel pressure. It is lower than X2 during normal operation. This is because when the fuel pressure is low, the back pressure chamber 8 is more likely to be negative pressure due to the pressure drop in the back pressure chamber 8 due to the contraction of the piezoelectric element 10. Here, the piezoelectric element 10 is 500 V
When the voltage is applied, it extends about 50 μm,
As the drive voltage Vp decreases, the amount of expansion gradually decreases.

FIG. 5 shows the relationship between the fuel pressure Pf and the drive voltage Vp of the piezoelectric element 10 for keeping the fuel pressure chamber 3 at a positive pressure. In order to keep the back pressure chamber 8 at a positive pressure, the driving voltage Vp of the piezoelectric element 10 is gradually reduced from the maximum voltage (500V) as the fuel pressure Pf introduced into the fuel pressure chamber 3 is lowered, and the needle It is necessary to suppress the lift amount of the valve 2.

The present invention copes with this, and as the fuel pressure Pf introduced into the fuel pressure chamber 3 decreases, the piezoelectric element 10 is reduced.
By controlling the drive voltage Vp of the back pressure chamber 8 to suppress the volume change of the back pressure chamber 8 to prevent the fuel pressure in the back pressure chamber 8 from excessively decreasing, and to prevent bubbles in the back pressure chamber 8. To prevent the occurrence of.

FIG. 4 shows a routine for controlling the drive voltage Vp of the piezoelectric element 10. Control unit 33
Is the initial injection pulse width Ti depending on the operating state of the engine.
Initial injection pulse width calculating means 41, driving voltage calculating means 43 for calculating the driving voltage Vp applied to the piezoelectric element 10 according to the fuel pressure Pf, and the calculated driving voltage V
An injection pulse width correction amount calculation means 42 for calculating the final injection pulse width Ti ′ by correcting the initial injection pulse width Ti according to p.

The initial injection pulse width calculating means 41 inputs the detected values of the intake air amount Qa and the engine speed Ne, and
The initial injection pulse width Ti corresponding to these detected values is searched based on the map shown in FIG.

The drive voltage calculation means 43 inputs the detected value of the fuel pressure Pf, and searches the drive voltage Vp applied to the piezoelectric element 10 according to the fuel pressure Pf based on FIG. By decreasing the drive voltage Vp as the fuel pressure Pf guided to the fuel pressure chamber 3 decreases, the lift amount of the needle valve 2 decreases, and the back pressure chamber 8 is maintained at a positive pressure. It is possible to prevent air bubbles from being generated inside 8.

The injection pulse width correction amount calculation means 42 is shown in FIG.
The injection pulse width correction amount is searched according to the drive voltage Vp based on the table shown in FIG. 3 to calculate the final injection pulse width Ti ′. The injection pulse width correction amount is set so that the final injection pulse width Ti ′ increases as the drive voltage Vp decreases, and the fuel injection amount from the injection port 1b influences the change in the drive voltage Vp. It is designed to be within the expected value without being disregarded.

In this way, the pulse signal corresponding to the injection pulse width Ti 'calculated by the control unit 33 is generated by the injection pulse generator 32, and the voltage corresponding to this pulse signal is transmitted via the injection valve drive circuit 31 to the piezoelectric element. 10 is applied.

The piezoelectric element 10 contracts when the voltage applied in synchronization with the engine rotation is cut off, and the back pressure chamber 8
Due to the pressure difference generated in the fuel pressure chamber 3, the needle valve 2 opens the injection port 1b against the coil spring 4, and the high-pressure fuel guided to the fuel pressure chamber 3 is injected into the cylinder 64 through the injection port 1b.

Since the drive voltage Vp applied to the piezoelectric element 10 is controlled according to the fuel pressure Pf so that the back pressure chamber 8 is maintained at a positive pressure, the back pressure chamber 8 becomes a negative pressure and the back pressure is reduced. It is possible to prevent bubbles from being generated in the fuel in the chamber 8. As a result, the volume change of the back pressure chamber 8 due to the expansion and contraction of the piezoelectric element 10 is not absorbed by the bubbles, the needle valve 2 is normally opened and closed, and the fuel injection amount can be accurately adjusted.

As another embodiment, as described above, the fuel pressure Pf introduced into the fuel pressure chamber 3 may be changed according to the operating state of the engine, for example, the number of revolutions. In this case also, the piezoelectric element 10 is used. The drive voltage Vp applied to the back pressure chamber 8 is adjusted according to the fuel pressure Pf.
Can be prevented from becoming a negative pressure and bubbles are generated in the fuel in the back pressure chamber 8, and the fuel injection amount can be accurately adjusted.

[Brief description of drawings]

FIG. 1 is a system diagram of an engine showing an embodiment of the present invention.

FIG. 2 is a sectional view of the fuel injection valve.

FIG. 3 is a system diagram of a fuel supply system.

FIG. 4 is a block diagram showing the configuration of a control system of the same.

FIG. 5 is a characteristic diagram showing the relationship between fuel pressure and piezoelectric element drive voltage.

FIG. 6 is a characteristic diagram showing the relationship between engine speed and intake air amount.

FIG. 7 is a characteristic diagram showing the relationship between fuel pressure and injection pulse width correction amount.

FIG. 8 is a characteristic diagram similarly showing a bubble generation region.

[Explanation of symbols]

1 nozzle body 1b nozzle 2 needle valve 2c Piston part 3 Fuel pressure chamber 4 coil spring 5 throttle passage 7 Fuel injection valve 8 back pressure chamber 9 casing 10 Piezoelectric element 11 Back pressure piston 13 Fuel inlet 18 lead wire 19 lead wire 31 Injection valve drive circuit 32 injection pulse generator 33 Engine control unit 34 Fuel pressure sensor 35 crank angle sensor 36 Intake air amount sensor 41 means for calculating initial injection pulse width 42 injection pulse width correction amount calculation means 43 Drive Voltage Calculation Means

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H02N 2/00 H01L 41/08 C (56) Reference JP-A 64-80751 (JP, A) JP-A 62-7969 ( JP, A) Actual development Sho 63-143760 (JP, U) Tokuheihei 8-506883 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02M 51/06 F02D 41/20 330 F02M 37/20 F02M 51/00

Claims (3)

(57) [Claims] 1. An injection port opened and closed by a needle valve, a fuel pressure chamber for introducing pressurized fuel to the injection port, a piezoelectric element extending by an applied voltage, and a back pressure defined between the needle valve and the piezoelectric element. In a fuel injection device that includes a chamber, a throttle passage that connects the fuel pressure chamber and the back pressure chamber, and a spring that biases the needle valve in the valve closing direction, as the fuel pressure introduced into the back pressure chamber decreases. A fuel injection device comprising a control means for reducing the drive voltage Vp applied to the piezoelectric element. 2. The control means, an initial injection pulse width calculation means for calculating an initial injection pulse width Ti according to the operating state of the engine, a fuel pressure sensor for detecting a fuel pressure Pf introduced into the fuel pressure chamber, and a fuel pressure. Drive voltage Vp applied to the piezoelectric element according to Pf
Drive voltage calculation means for calculating, and an injection pulse width correction amount calculation means for calculating the final injection pulse width Ti ′ by correcting the initial injection pulse width Ti according to the drive voltage Vp, and the calculated injection pulse width The fuel injection device according to claim 1, further comprising: an injection pulse generator that generates a pulse signal corresponding to Ti ′; and a drive circuit that applies a voltage according to the generated pulse signal to the piezoelectric element. . 3. The fuel injection device according to claim 1, wherein the control means controls the drive voltage Vp applied to the piezoelectric element so that the back pressure chamber does not become a negative pressure.