JPH1113583A - Fuel injection device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently ensure the fuel injection quantity at the time of starting an engine in a fuel injection device for the engine. SOLUTION: A fuel injection device for an engine is provided with a fuel pressure chamber 3 for leading pressurized fuel to a nozzle hole 1b, a piezoelectric actuator 10 contracted in response to applied voltage, a differential pressure chamber 8 partitioned between a needle valve 2 and the piezoelectric actuator 10, a throttle passage 5 communicating the fuel pressure chamber 3 with the differential pressure chamber 8, a spring 5 energizing the needle valve 2 in a closing direction, and a controller 19 for changing the contraction quantity of the piezoelectric actuator 10 with the lapse of open time of the needle valve 2 so as to maintain pressure difference generated between the differential pressure chamber 8 and fuel pressure chamber 3.

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 provided with an engine fuel injection device that operates a needle valve by changing fuel pressure before and after the needle valve via an electromagnetic strain actuator.

[0002]

2. Description of the Related Art A fuel injection valve or the like provided in an automobile engine is provided with a piezo actuator (piezoelectric element) that expands according to an applied voltage, and a needle valve (valve element) is opened via the piezo actuator. was there. By driving the needle valve by the piezo actuator, the high-speed response of the fuel injection valve is enhanced, and the ratio (dynamic range) between the maximum injection amount and the minimum injection amount is expanded, so that it is possible to cope with higher engine output. Further, since a small amount of fuel can be stably injected, the fuel efficiency of the engine can be reduced.

[0003] As this type of fuel injection valve, there is known a fuel injection valve in which a needle valve is opened based on a pressure difference between the front and rear thereof. A fuel pressure chamber and a differential pressure chamber are defined before and after the needle valve. Fuel is introduced into the fuel pressure chamber at a predetermined pressure, and the differential pressure chamber communicates with the fuel pressure chamber through an orifice. A piezo actuator is provided in the differential pressure chamber behind the needle valve,
The opening and closing operation of the needle valve is controlled by the expansion and contraction of the piezo actuator. That is, the pressure in the fuel pressure chamber and the pressure in the differential pressure chamber before and after the needle valve are equalized via the orifice in a state where a voltage is applied to the piezo actuator and expanded. At this time, the needle valve is held closed by the tension of the return spring. From this state, if both terminals of the piezo actuator are short-circuited and the piezo actuator is instantaneously contracted,
The volume of the differential pressure chamber behind the needle valve increases. At this time, since the differential pressure chamber communicates with the fuel pressure chamber in front of the needle valve via the orifice, the internal pressure of the differential pressure chamber temporarily drops, causing a pressure difference in the valve opening direction before and after the needle valve. I do. As a result, the needle valve opens against the return spring, the injection port is opened, and fuel is injected. (For a known example of this type of fuel injection valve, see, for example, JP-A-6-280711.)

[0004]

By the way, in a conventional fuel injection valve using such a piezo actuator,
When the needle valve is seated on the seat and closes the injection port, the pressure in the fuel chamber instantaneously increases, and there is a possibility that secondary injection for injecting fuel at a time other than the predetermined injection timing may occur.

Further, before starting the engine in which the fuel pressure guided to the fuel pressure chamber rises, the fuel is first guided to the fuel pressure chamber and then flows into the back pressure chamber via the orifice. Until the end of the rise, a pressure difference occurs before and after the needle valve, so that the needle valve opens against a return spring at a time other than the predetermined injection timing to cause initial fuel injection in which fuel is injected. There was a possibility.

[0006]

By the way, in the conventional fuel injection device using such a piezo actuator, the piezo actuator is driven so that the contraction amount of the piezo actuator is always changed uniformly. When the fuel pressure is low, such as when starting the engine, there is a possibility that the predetermined fuel injection amount cannot be injected.
That is, in a state where the fuel pressure is low, it is necessary to secure a predetermined fuel injection amount by lengthening the period during which the needle valve is opened, but the fuel in the fuel pressure chamber passes through the orifice while the fuel injection valve is open. As the needle valve opens for a longer period of time, the drive differential pressure generated before and after the needle valve decreases, and the needle valve is eventually held open against the spring. You lose power.

The present invention has been made in view of the above problems, and has as its object to provide a fuel injection device for an engine with a sufficient fuel injection amount at the time of starting the engine or the like.

[0008]

According to a first aspect of the present invention, there is provided a fuel injection device for an engine, wherein an electromagnetic strain actuator expands and contracts in accordance with an applied voltage or a magnetic field, and a differential pressure expands and contracts in accordance with expansion and contraction of the electromagnetic strain actuator. A chamber, a fuel pressure chamber into which the pressurized fuel is guided, a throttle passage communicating the fuel pressure chamber with the differential pressure chamber,
In an engine fuel injection device including a needle valve that is displaced in accordance with a pressure difference between a fuel pressure chamber and a differential pressure chamber, a spring that biases the needle valve in a valve closing direction, and an injection port that is opened and closed by the needle valve, Control means is provided for maintaining the pressure difference between the differential pressure chamber and the fuel pressure chamber by changing the amount of expansion and contraction of the strain actuator as the valve opening time of the needle valve elapses.

According to a second aspect of the present invention, in the fuel injection device for an engine according to the first aspect, the amount of expansion and contraction of the electromagnetic strain actuator is changed stepwise as the valve opening time of the needle valve elapses. The configuration was adopted.

According to a third aspect of the present invention, there is provided the fuel injection device for an engine according to the first aspect, wherein the amount of expansion and contraction of the electromagnetic strain actuator is continuously changed as the valve opening time of the needle valve elapses. The configuration was adopted.

According to a fourth aspect of the present invention, in the fuel injection system for an engine according to any one of the first to third aspects, the operating condition in which the required valve opening period of the needle valve is equal to or longer than a predetermined value is determined. While the control means changes the amount of expansion and contraction of the electromagnetic strain actuator as the valve opening time of the needle valve elapses under operating conditions in which the required valve opening period of the needle valve is equal to or longer than a predetermined value, Under the operating conditions in which the required valve opening period of the needle valve is shorter than a predetermined value, the amount of expansion and contraction of the electromagnetic strain actuator is uniformly changed.

According to a fifth aspect of the present invention, there is provided a fuel injection device for an engine according to any one of the first to fourth aspects, further comprising a fuel viscosity detecting means for detecting a viscosity of the fuel, and wherein the control means comprises: The configuration is such that the rate of change in the amount of expansion and contraction of the electromagnetic strain actuator is reduced as the viscosity of the fuel decreases.

According to a sixth aspect of the present invention, in the fuel injection device for an engine according to the first aspect of the present invention, the fuel injection device further includes a pressure detecting means for detecting a pressure of the differential pressure chamber, and the control means controls an amount of expansion and contraction of the electromagnetic strain actuator. Is changed as the pressure in the differential pressure chamber decreases.

[0014]

According to the first aspect of the present invention, when the electromagnetic strain actuator is extended, the pressures of the fuel pressure chamber and the differential pressure chamber generated before and after the needle valve are equalized by the throttle passage. At this time, the needle valve is held closed by the elastic restoring force of the spring.

As the electromagnetic strain actuator expands and contracts, the volume of the differential pressure chamber increases and its pressure decreases. Since a pressure drop is transmitted to the fuel pressure chamber with a delay by the throttle passage, a pressure difference is temporarily generated between the differential pressure chamber and the fuel pressure chamber. This pressure difference causes the needle valve to open the injection port against the spring, and fuel is injected from the injection port.

By the way, if the electromagnetic strain actuator is driven so that the amount of expansion and contraction changes uniformly, if the required valve opening period of the needle valve is prolonged when the fuel pressure is low, such as when starting the engine, the drive difference generated before and after the needle valve will increase. The pressure drops, and eventually the holding force required to open the needle valve against the spring may not be obtained, and the predetermined fuel injection amount may not be injected.

According to the present invention, in response to this, control is performed to change the amount of expansion and contraction of the electromagnetic strain actuator in a stepwise or continuous manner in accordance with the elapse of the valve opening time of the needle valve. By maintaining the pressure difference generated between the fuel pressure chambers, the time during which the needle valve opens against the spring is extended, and the fuel injection amount is increased. As a result, the required fuel injection amount can be ensured even when the fuel pressure is low, such as when starting the engine.

According to the second aspect of the present invention, control is performed such that the amount of expansion and contraction of the electromagnetic strain actuator is changed stepwise as the valve opening time of the needle valve elapses.
For example, when the fuel pressure is low, such as when starting the engine, the time during which the needle valve opens against the spring can be extended, and the required fuel injection amount can be secured.

According to the third aspect of the present invention, the valve opening period of the needle valve is controlled by continuously changing the amount of expansion and contraction of the electromagnetic strain actuator as the valve opening time of the needle valve elapses. Can be extended effectively.

According to the fourth aspect of the present invention, the amount of expansion and contraction of the electromagnetic strain actuator is gradually increased in accordance with the elapse of the opening time of the needle valve under the operating condition in which the required opening period of the needle valve is equal to or longer than a predetermined value. Or by performing a control to change continuously, for example, when the fuel pressure is low, such as at the time of engine start, to extend the time the needle valve opens against the spring,
The required fuel injection amount can be secured. As a result, the required fuel injection amount can be ensured even when the fuel pressure is low, such as when starting the engine.

On the other hand, by performing control to uniformly change the amount of expansion and contraction of the electromagnetic strain actuator under operating conditions in which the required valve opening period of the needle valve is shorter than a predetermined value, the pressure difference between the differential pressure chamber and the fuel pressure chamber is reduced. By increasing the maximum value, the responsiveness of the needle valve to open against the spring can be increased. As a result, the setting range of the fuel injection amount is expanded, and it is possible to cope with increasing the output of the engine.

According to the fifth aspect of the present invention, the rate of change in the amount of expansion and contraction of the electromagnetic strain actuator is changed in response to the rate of change in the fuel pressure in the differential pressure chamber increasing as the viscosity of the fuel decreases. By making the configuration smaller, the valve opening period of the needle valve can be effectively extended.

According to the sixth aspect of the present invention, the valve opening period of the needle valve can be effectively extended by changing the amount of expansion and contraction of the electromagnetic strain actuator in accordance with the decrease in the pressure of the differential pressure chamber. .

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a fuel injection valve provided in a direct 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 has a nozzle body 1 provided at the tip thereof facing a combustion chamber of an engine (not shown). The nozzle body 1 faces the combustion chamber from the combustion chamber ceiling wall of the engine, and sprays fuel spray toward the crown of the piston from an injection port 1b opened at the tip of the nozzle body 1.

The needle valve 2 is slidably housed inside the nozzle body 1. A fuel pressure chamber 3 is defined inside the nozzle body 1 around the needle valve 2. A nozzle 1b is opened at the tip of the nozzle body 1, and the nozzle 1b is opened and closed by a needle valve 2.

As shown in FIG. 2, the fuel tank 59
Is pumped up via a first fuel pump 58 driven by an electric motor 54 and is pumped to a second fuel pump 57. Usually, the discharge pressure of the second fuel pump 57 is set higher than the discharge pressure of the first fuel pump 58.

The second fuel pump 57 driven by the engine 50 sends the pressurized fuel to the pressure accumulating chamber 56, and pressurizes the fuel from the pressure accumulating chamber 56 to the fuel injection valve 7 of each cylinder.

The second fuel pump 57 driven by the engine 50 sends the pressurized fuel to the pressure accumulating chamber 56, and pressurizes the fuel from the pressure accumulating chamber 56 to the fuel injection valve 7 of each cylinder. Pressure regulator 5 is provided in fuel return passage 52.
5 is provided to return the fuel to the fuel tank 59 through the surplus fuel in the accumulator 56 so that the fuel pressure guided to the fuel injection valve 7 is maintained at a predetermined value or less.

The fuel pumped from the fuel pump 58 is introduced into the fuel pressure chamber 3 from the fuel inlet passage 6, and is injected from the injection port 1b with the lift of the needle valve 2.

The needle valve 2 has a piston portion 2c at its proximal end. A differential pressure chamber 8 is defined between the nozzle body 1 and the casing 9 and the piston portion 2c. The fuel pressure chamber 3 and the differential pressure chamber 8 communicate with each other via a throttle passage (gap) 5 formed on the outer periphery 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 piston portion 2c of the needle valve 2 and the casing 9 in a compressed state, and is arranged coaxially with the needle valve 2.

A shim 17 is interposed between the base end of the needle valve 2 and the casing 9. The maximum lift of the needle valve 2 is determined by the shim 17.

A piston 11 defining the differential pressure chamber 8 is slidably disposed inside the casing 9. Piston 11
An O-ring 12 is interposed on the outer periphery of. The differential pressure chamber 8 is hermetically sealed by the O-ring 12 slidingly contacting the cylindrical inner wall surface of the casing 9.

A piezo actuator 10 for driving the needle valve 2 to open and close via a piston 11 is provided. In the piezo actuator 10, a plurality of disk-shaped piezo elements are laminated with a disk-shaped internal electrode interposed therebetween.

An end plate 14 is connected to a fixed end of the piezo actuator 10. A plate 15 is screwed and attached to the open end of the casing 9. A disc spring 16 is interposed between the plate 15 and the piston 14.

The piezo actuator 10 expands when a voltage is applied to each piezo element from the driving amplifier 18. At this time, the pressure in the differential pressure chamber 8 is increased and the needle valve 2
Closes the valve. The piezo actuator 10 contracts when the voltage applied to each piezo element is cut off and short-circuited. At this time, the pressure in the differential pressure chamber 8 decreases with respect to the fuel pressure chamber 3, and the needle valve 2 moves in the valve opening direction against the coil spring 4.

It should be noted that a magnetostrictive actuator composed of a giant magnetostrictive element that expands and contracts according to the strength of the applied magnetic field may be used instead of the piezo actuator 10. Here, the piezo actuator and the magnetostrictive actuator are collectively referred to as an electrostrictive actuator.

In the present embodiment, the fuel is injected by the contraction operation of the piezo actuator 10, but the fuel may be injected by the extension operation of the piezo actuator 10.

The controller 19 generates a pulse signal corresponding to the calculated fuel injection amount, and applies a voltage corresponding to the pulse signal to the piezo actuator 10 via the driving amplifier 18.

The controller 19 inputs various signals for detecting engine operating conditions such as the number of revolutions of the engine 50, the amount of intake air of the engine 50, and calculates the fuel injection amount according to these engine operating conditions.

FIG. 1 shows a state before the engine is started. Each of the piezo elements of the piezo actuator 10 is extended by application of a voltage, and the piezo elements of the fuel pressure chamber 3 and the differential pressure chamber 8 generated before and after the piston portion 2c are formed. The pressure is equalized via the throttle passage 5. At this time, the needle valve 2 is seated on the seat portion of the nozzle body 1 by the elastic restoring force of the coil spring 4. In this state, the first fuel pump 58 is
And the pressures in the fuel pressure chamber 3 and the differential pressure chamber 8 are increased.

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

At the time of starting the engine and at the time of opening operation of the fuel injection valve 7 after the start, each piezo element contracts due to a short circuit of the voltage applied in synchronization with the engine rotation. When the piston 11 moves in accordance with the contraction of each piezo element, the volume of the differential pressure chamber 8 increases, and the pressure decreases. Since the pressure drop of the fuel pressure chamber 3 is transmitted via the throttle passage 5 with a delay, a pressure difference is immediately generated between the differential 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 high-pressure fuel guided to the fuel pressure chamber 3 is injected into the combustion chamber of the engine 50 through the injection port 1b.

When the fuel injection valve 7 is closed, each piezo element is extended by applying a voltage in synchronization with the rotation of the engine, and the piezo element is extended.
The needle valve 2 is moved by the pressure difference between the differential pressure chamber 8 and the fuel pressure chamber 3 and the urging force of the coil spring 4 to be seated on the seat portion of the nozzle body 1. When the needle valve 2 is seated on the seat, the injection port 1b is closed, and fuel injection is stopped.

The fuel injection valve 7 is a piezo actuator 1
Since the displacement direction of the needle valve 2 coincides with the displacement direction of 0,
The piezo actuator 10 and the needle valve 2 are arranged in series,
The structure is simplified.

When the engine is started, the electric motor 5
Although the discharge pressure of the first fuel pump 58 driven by the engine 4 increases, the second fuel pump 57 driven by the engine 50
Since the discharge pressure of the fuel does not increase and the low-pressure fuel is supplied to the fuel injection valve 7, the injection pulse width of the fuel injection valve 7 (valve opening period)
Must be increased to secure a predetermined fuel injection amount.

However, while the fuel injection valve 7 is open, the fuel in the fuel pressure chamber 3 passes through the throttle passage 2c and passes through the differential pressure chamber 8
When the injection pulse width of the fuel injection valve 7 becomes longer, the drive differential pressure generated before and after the needle valve 2 decreases, and it is necessary to open the needle valve 2 against the coil spring 4 soon. A high holding power cannot be obtained.

Conventionally, the driving voltage supplied to the piezo actuator 10 is changed from 400 V to 0 as indicated by a broken line in FIG.
V, the drive differential pressure of the needle valve 2 becomes unnecessarily large at the beginning, and if the valve opening time is long, the valve is held open as shown by a broken line in FIG. There is a possibility that it will decrease until it enters the impossible region. For this reason, even if the injection pulse width of the fuel injection valve is increased, the valve opening period does not correspond and the valve is closed, resulting in a shortage of the fuel injection amount.

To cope with this, the present invention extends the period in which the needle valve 2 can be held open by reducing the drive voltage supplied to the piezo actuator 10 stepwise or continuously when the engine is started.

In the present embodiment, as shown by the solid line in FIG. 4, it is determined whether or not the engine is started when the valve opening period of the needle valve 2 is equal to or longer than a predetermined value, and the driving voltage supplied to the piezo actuator 10 is determined in two stages. It is configured to lower.

In this manner, the drive differential pressure of the needle valve 2 is increased stepwise in two injections as shown by the solid line in FIG. 5 in one injection. That is, by changing the drive voltage from 400 V to 200 V, the piezo actuator 10 contracts by one step, the differential pressure chamber 8 expands, and the pressure decreases. Although the differential pressure decreases with the lapse of time, the drive voltage is changed from 200 V to 0 V before the differential pressure falls below the required valve holding force, whereby the piezo actuator 10 further contracts and the differential pressure chamber 8 expands. Again, a large differential pressure between the differential pressure chamber 8 and the fuel pressure chamber 3 is ensured. Since the differential pressure between the differential pressure chamber 8 and the fuel pressure chamber 3 is not proportional to the elapse of time but is secondary proportional to the passage of time, the differential pressure generated when the differential pressure is generated in two stages is larger than when a large differential pressure is generated. Better
The time during which the differential pressure drops to the predetermined value increases. As a result, the drive differential pressure generated between the differential pressure chamber 8 and the fuel pressure chamber 3 does not increase until the drive differential pressure rises twice and enters the valve opening non-holding area.
The valve opening period of the piezo actuator 10 is extended, and a sufficient fuel injection amount can be ensured even when the engine is started.

When the second fuel pump 51 functions sufficiently and the fuel pressure increases, the required valve opening period of the needle valve 2 becomes shorter than a predetermined value, so that the amount of contraction of the piezo actuator 10 is maximized in one step. Is performed. Accordingly, the maximum value of the driving differential pressure generated between the differential pressure chamber 8 and the fuel pressure chamber 3 is increased, and the responsiveness of the needle valve 2 opening against the coil spring 4 is increased. As a result, the setting range (dynamic range) of the fuel injection amount is expanded, and it is possible to cope with a high output of the engine.

FIG. 3 shows a routine for switching the fuel injection pattern, which is executed by the controller 19 at regular intervals.

To explain this, in a state where the driving voltage supplied to the piezo actuator 10 is set to 400 V and the needle valve 2 is closed, it is first determined in step 1 whether the required injection pulse width is equal to or larger than a predetermined value.

If it is determined that the required injection pulse width is equal to or larger than the predetermined value, the process proceeds to step 2 where the piezo actuator 1
The drive voltage supplied to 0 is reduced to 200V.

Then, the process proceeds to a step 3, wherein it is determined whether or not a half of the required injection pulse width has elapsed.

If it is determined that half of the required injection pulse width has elapsed, the routine proceeds to step 4, where the drive voltage supplied to the piezo actuator 10 is reduced to OV.

Then, the program proceeds to a step S5, wherein it is determined whether or not the injection is completed when the required injection pulse width has passed 2/2.

If it is determined that the injection has ended at the end of the required injection pulse width, the routine proceeds to step 6, where the drive voltage supplied to the piezo actuator 10 is increased to 400 V and the needle valve 2 is closed.

When the required injection pulse width is shorter than the predetermined value, the driving voltage supplied to the piezo actuator 10 is reduced to 0 V by another routine (not shown).

As another embodiment, as shown in FIG.
The driving voltage supplied to the piezo actuator 10 at the time of starting the engine may be reduced in four stages.

In this case, the driving differential pressure of the needle valve 2 is increased in four injections as shown in FIG. 7 by one injection. As a result, the drive differential pressure does not decrease until it enters the valve-opening impossible area, the valve-opening period of the piezo actuator 10 is extended, and a sufficient fuel injection amount can be ensured even when the engine is started.

FIG. 6 is a flowchart showing a routine for switching the fuel injection pattern, which is executed by the controller 19 at regular intervals.

To explain this, in a state where the driving voltage supplied to the piezo actuator 10 is set to 400 V and the needle valve 2 is closed, it is first determined in step 1 whether the required injection pulse width is equal to or larger than a predetermined value.

When it is determined that the required injection pulse width is equal to or larger than the predetermined value, the routine proceeds to step 2, where the piezo actuator 1
The drive voltage supplied to 0 is reduced to 300V.

Then, the process proceeds to a step 3, wherein it is determined whether or not 1/4 of the required injection pulse width has elapsed.

If it is determined that 1/4 of the required injection pulse width has elapsed, the process proceeds to step 4, where the drive voltage supplied to the piezo actuator 10 is reduced to 200V.

Then, the process proceeds to a step 5, wherein it is determined whether or not a half of the required injection pulse width has elapsed.

If it is determined that half of the required injection pulse width has elapsed, the routine proceeds to step 6, where the drive voltage supplied to the piezo actuator 10 is reduced to 100V.

Then, the process proceeds to a step 7, wherein it is determined whether or not 3/4 of the required injection pulse width has elapsed.

If it is determined that 3/4 of the required injection pulse width has elapsed, the process proceeds to step 7, where the drive voltage supplied to the piezo actuator 10 is reduced to 0V.

Then, the process proceeds to a step 9, wherein it is determined whether or not the injection is completed at the time when the required injection pulse width has elapsed.

If it is determined that the injection has ended at the end of the required injection pulse width, the routine proceeds to step 10, where the drive voltage supplied to the piezo actuator 10 is increased to 400 V and the needle valve 2 is closed.

When the required injection pulse width is shorter than the predetermined value, the driving voltage supplied to the piezo actuator 10 is reduced to 0 V by another routine (not shown).

As still another embodiment, the driving voltage supplied to the piezo actuator 10 may be reduced in multiple stages as the required ejection pulse width of the piezo actuator 10 increases.

As described above, as the required injection pulse width becomes longer, the rate of change at which the amount of contraction of the piezo actuator 10 becomes larger is reduced, so that the valve responsive period of the needle valve 2 is ensured and the valve opening period is made effective. Can be extended to

By the way, as the viscosity of the fuel decreases, the fuel in the differential pressure chamber 8 tends to leak into the fuel pressure chamber 3 and the differential pressure chamber 8
The pressure drop becomes rapid.

As still another embodiment, the driving voltage supplied to the piezo actuator 10 may be reduced in multiple stages as the viscosity of the fuel becomes lower at the time of starting the engine.

In this embodiment, the engine coolant temperature is read as a signal representative of the viscosity of the fuel, and the drive voltage supplied to the piezo actuator 10 when the engine coolant temperature is lower than a predetermined value is four levels. And the driving voltage supplied to the piezo actuator 10 is reduced in two stages when the coolant temperature of the engine is higher than the predetermined value and the fuel has a high viscosity.

The temperature of the air taken into the engine may be read as a signal representing the viscosity of the fuel.

As shown in FIG. 9, the lower the temperature of the engine cooling water, the lower the viscosity of the fuel, and while the fuel injection valve 7 is open, the fuel pressure chamber passes through the throttle passage 2c from the differential pressure chamber 8. The amount of fuel that escapes to the third side increases.

For this reason, as shown in FIG. 10, the higher the engine coolant temperature, the faster the drive differential pressure generated before and after the needle valve 2 decreases.

In response to this, the drive voltage supplied to the piezo actuator 10 is reduced in multiple stages as the viscosity of the fuel becomes lower when the engine is started, so that the drive differential pressure is reduced until the valve enters the valve-opening impossible area. Is avoided, and the fuel injection amount can be sufficiently ensured even when the engine is started.

In response to the increase in the rate of decrease in the fuel pressure in the differential pressure chamber as the viscosity of the fuel decreases, the rate of change in the amount of contraction of the piezo actuator 10 is increased. Thus, the opening period of the needle valve 2 can be effectively extended.

FIG. 8 is a flowchart showing a routine for switching the fuel injection pattern, which is executed by the controller 19 at regular intervals.

To explain this, in a state where the driving voltage supplied to the piezo actuator 10 is set to 400 V and the needle valve 2 is closed, it is first determined in step 1 whether the required injection pulse width is equal to or larger than a predetermined value.

If it is determined that the required injection pulse width is equal to or greater than the predetermined value, the routine proceeds to step 2, where it is determined whether the engine coolant temperature detected by a water temperature sensor (not shown) is equal to or greater than the predetermined value.

When it is determined that the engine coolant temperature is lower than the predetermined value and the fuel has a low viscosity, the routine proceeds to step 4, where the drive voltage supplied to the piezo actuator 10 is reduced in four steps. On the other hand, when it is determined that the engine coolant temperature is lower than the predetermined value when the fuel has a high viscosity, the process proceeds to step 3 and the drive voltage supplied to the piezo actuator 10 is reduced in two steps.

As still another embodiment, as shown in FIG. 12, the drive voltage supplied to the piezo actuator 10 when the engine is started may be gradually reduced as the valve opening time becomes longer.

In this case, the driving differential pressure of the needle valve 2 is continuously increased during one injection period. As a result, the drive differential pressure does not decrease until it enters the valve-opening impossible area, the valve-opening period of the piezo actuator 10 is extended,
A sufficient fuel injection amount can be ensured even when the engine is started.

FIG. 11 is a flowchart showing a routine for switching the fuel injection pattern.
Is executed at regular intervals.

More specifically, in a state where the driving voltage supplied to the piezo actuator 10 is set to 400 V and the needle valve 2 is closed, it is first determined in step 1 whether the required injection pulse width is equal to or larger than a predetermined value.

If it is determined that the required injection pulse width is equal to or larger than the predetermined value, the process proceeds to step 2 where the piezo actuator 1
The drive voltage supplied to 0 is reduced to 300V.

Subsequently, the process proceeds to step 3, where the voltage drop is calculated as the initial step-up / injection pulse width = 300− / injection pulse width, and the drive voltage supplied to the piezo actuator 10 becomes longer even when the valve opening time becomes longer. It is gradually reduced accordingly.

Then, the program proceeds to a step S4, wherein it is determined whether or not the injection has been completed after a lapse of 2/2 of the required injection pulse width.

If it is determined that the injection is completed at the end of 2/2 of the required injection pulse width, the routine proceeds to step 5, where the drive voltage supplied to the piezo actuator 10 is increased to 400 V and the needle valve 2 is closed. .

In the operation state where the required injection pulse width is shorter than the predetermined value, the control for reducing the drive voltage supplied to the piezo actuator 10 to 0 V is performed by another routine (not shown).

As still another embodiment, as shown in FIG. 13, a pressure sensor 20 for detecting the pressure of the differential pressure chamber 8 is provided. The configuration may be such that the drive voltage supplied to the piezo actuator 10 decreases as the pressure drops below a predetermined value.

As a result, it is possible to prevent the drive differential pressure from dropping until the valve enters the valve-opening impossible range, prolong the valve-opening period of the piezo actuator 10, and ensure a sufficient fuel injection amount even when the engine is started. Can be.

FIG. 14 is a flowchart showing a routine for switching the fuel injection pattern.
Is executed at regular intervals.

To explain this, in a state where the needle valve 2 is closed with the drive voltage supplied to the piezo actuator 10 set to 400 V, it is first determined in step 1 whether the required injection pulse width is equal to or larger than a predetermined value.

If it is determined that the required injection pulse width is equal to or larger than the predetermined value, the process proceeds to step 2 to determine whether or not an initial voltage application is performed.

If it is determined that an initial voltage is to be applied, the process proceeds to step 5, where the drive voltage supplied to the piezo actuator 10 is reduced to 300V.

If it is determined that the initial voltage application has not been performed, the routine proceeds to step 3, where it is determined whether or not the required injection pulse width has elapsed.

If it is determined that the injection has ended at the end of the required injection pulse width, the routine proceeds to step 6, where the drive voltage supplied to the piezo actuator 10 is increased to 400 V and the needle valve 2 is closed.

If it is determined that the fuel injection has not been completed for the required injection pulse width, the routine proceeds to step 4, where the pressure sensor 2
Based on the detected value from 0, it is determined whether the pressure in the differential pressure chamber 8 drops below a predetermined value.

If it is determined that the pressure in the differential pressure chamber 8 has dropped below a predetermined value, the process proceeds to step 7 in which the driving voltage supplied to the piezo actuator 10 is added to the previous driving voltage by a predetermined value. I do.

When the required injection pulse width is shorter than the predetermined value, the driving voltage supplied to the piezo actuator 10 is reduced to 0 V by another routine (not shown).

[Brief description of the drawings]

FIG. 1 is a sectional view of a fuel injection valve showing an embodiment of the present invention.

FIG. 2 is a system diagram of a fuel supply system.

FIG. 3 is a flowchart showing control contents.

FIG. 4 is a characteristic diagram showing a relationship between an ejection pulse width and a drive voltage.

FIG. 5 is a characteristic diagram showing a relationship between an injection pulse width and a needle valve driving differential pressure.

FIG. 6 is a flowchart showing control contents according to another embodiment.

FIG. 7 is a characteristic diagram showing a relationship among an injection pulse width, a drive voltage, and a needle valve drive differential pressure.

FIG. 8 is a flowchart showing control contents according to still another embodiment.

FIG. 9 is a characteristic diagram showing a relationship between fuel viscosity and engine coolant temperature.

FIG. 10 is a characteristic diagram showing the relationship between the valve opening time of the needle valve and the drive differential pressure.

FIG. 11 is a flowchart showing control contents according to still another embodiment.

FIG. 12 is a characteristic diagram showing a relationship among an injection pulse width, a drive voltage, and a needle valve drive differential pressure.

FIG. 13 is a sectional view of a fuel injection valve showing still another embodiment.

FIG. 14 is a flowchart showing control contents.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nozzle body 1b Injection port 2 Needle valve 2c Piston part 3 Fuel pressure chamber 4 Coil spring 5 Throttle passage 6 Fuel inlet 7 Fuel injection valve 8 Differential pressure chamber 9 Casing 10 Piezo actuator 11 Piston 19 Controller 20 Pressure sensor

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shunji Oki 2 Nihonsan Motor Co., Ltd. 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa

Claims (6)

[Claims] An electromagnetic strain actuator that expands and contracts in response to an applied voltage or magnetic field; a differential pressure chamber that expands and contracts in accordance with expansion and contraction of the electromagnetic strain actuator; a fuel pressure chamber into which pressurized fuel is introduced; A throttle passage communicating with the pressure chamber, a needle valve that is displaced in accordance with a pressure difference between the fuel pressure chamber and the differential pressure chamber, a spring that biases the needle valve in a valve closing direction, and an orifice that is opened and closed by the needle valve. A fuel injection device for an engine comprising: a control means for changing the amount of expansion and contraction of the electromagnetic strain actuator with the passage of the opening time of the needle valve to maintain a pressure difference generated between the differential pressure chamber and the fuel pressure chamber. A fuel injection device for an engine. 2. The engine according to claim 1, wherein said control means changes the amount of expansion and contraction of the electromagnetic strain actuator in a stepwise manner as the valve opening time of the needle valve elapses. Fuel injection device. 3. The engine according to claim 1, wherein said control means continuously changes the amount of expansion and contraction of the electromagnetic strain actuator as the valve opening time of the needle valve elapses. Fuel injection device. 4. A control device for determining an operating condition in which a required valve opening period of the needle valve is equal to or longer than a predetermined value, wherein the control unit determines whether the required valve opening period of the needle valve is longer than a predetermined value. A structure in which the amount of expansion and contraction of the strain actuator is changed as the needle valve opening time elapses, and the amount of expansion and contraction of the electromagnetic strain actuator is uniformly changed under operating conditions in which the required valve opening period of the needle valve is shorter than a predetermined value. The fuel injection device for an engine according to any one of claims 1 to 3, wherein: 5. A fuel viscosity detecting means for detecting the viscosity of the fuel, wherein the control means reduces the rate of change of the amount of expansion and contraction of the electromagnetic strain actuator as the viscosity of the fuel decreases. The fuel injection device for an engine according to any one of claims 1 to 4, wherein: 6. The apparatus according to claim 1, further comprising a pressure detecting means for detecting a pressure in the differential pressure chamber, wherein the control means changes an amount of expansion and contraction of the electromagnetic strain actuator in accordance with a decrease in the pressure in the differential pressure chamber. The fuel injection device for an engine according to claim 1, wherein: