JP2002161832A - Fuel injection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized fuel injection device having excellent controllability capable of providing half lift control of a nozzle needle in a system for controlling back pressure of the nozzle needle by a hydraulic control valve. SOLUTION: A control chamber 4 for providing the back pressure to the nozzle needle 12 for opening and closing an injection hole 11 is provided. A three-way valve 5 for opening and closing between the control chamber 4 and a drain passage 2 is controlled by an ECU 9. The ECU 9 adjusts an applied voltage of a piezoactuator 14 for driving the three-way valve 5, repeatedly drives the three-way valve 5 to open and close, and maintains pressure of the control chamber 4 higher than the pressure which the nozzle needle 12 is lifted fully so that lift of the nozzle needle 12 during a period of injection is maintained in a half lift position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel injection device for an internal combustion engine such as a diesel engine, and more particularly, to a fuel injection device capable of variably controlling a lift amount.

[0002]

2. Description of the Related Art In order to inject high-pressure fuel into a diesel engine or the like, a common rail type fuel injection device has conventionally been used. In this device, fuel is supplied to the fuel injectors of each cylinder from a common common rail, and generally, solenoid-operated fuel injectors are widely used. In recent years, a piezo-driven fuel injection valve using a piezo actuator that expands and contracts according to an applied voltage has been proposed. This transmits the displacement of the piezo actuator to the nozzle needle directly or via hydraulic pressure, and has an advantage of excellent responsiveness.

[0003] In these conventional fuel injection devices, the fuel injection amount is controlled by the valve opening time of the nozzle needle. However, since a certain time is required for the valve opening and closing operations of the nozzle needle, the fuel injection amount is controlled. When is small (or when the fuel injection period is short), the behavior of the nozzle needle becomes unstable, and it is difficult to control the fuel injection amount stably. Therefore, it has been studied to variably control the lift amount of the nozzle needle to perform a small amount of fuel injection with good controllability. A device that performs variable control using a piezo-driven fuel injection valve is known, for example, from US Pat. No. 5,803,370, in which a piezo actuator is driven by an integral rod by controlling an applied voltage to the piezo actuator. It is described that the lift amount of the nozzle needle is changed to hold the nozzle needle at an intermediate position (half lift position) from the valve seat contact position to the full lift.

[0004]

However, the apparatus disclosed in the above-mentioned U.S. Pat. No. 5,803,370 has a structure in which a rod integrated with a piezo actuator directly drives a nozzle needle, and the piezo actuator has a structure corresponding to the displacement of the nozzle needle. Displacement and generated force are required. For this reason, there is a problem that the physical size of the piezo actuator must be increased, and the energy required for driving also increases. In addition, in order to stop the nozzle needle at a predetermined half-lift position, it is necessary to provide a damper member.Specifically, a damper piston is slidably provided around a rod for driving the nozzle needle, and is provided above the damper piston. A damper room is located. Further, a fuel chamber communicating with the damper chamber is provided below the damper piston so as not to prevent the rod and the nozzle needle from rising during contraction of the piezo actuator, and the structure is complicated.

On the other hand, there is a fuel injection device that controls the back pressure of a nozzle needle by a hydraulic control valve driven by a piezo actuator. The hydraulic control valve is configured to open and close between a control chamber that applies a back pressure to the nozzle needle and a drain passage, and raises and lowers the nozzle needle as the pressure in the control chamber increases and decreases as the drain passage opens and closes. In this device, the piezo actuator only needs to generate a displacement necessary for driving the hydraulic control valve, so that the size can be reduced. However, half lift control has not been studied so far.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to realize a small-sized fuel injection device excellent in controllability by enabling a half lift control of a nozzle needle in a system for controlling a back pressure of a nozzle needle by a hydraulic control valve. I do. It is another object of the present invention to enable a piezo actuator to perform a half-lift control with smaller energy, thereby further saving labor.

[0007]

According to a first aspect of the present invention, there is provided a fuel injection device comprising: a control chamber for applying a pressure in a valve closing direction to a nozzle needle for opening and closing an injection hole; And a control valve for increasing or decreasing the pressure, so that the nozzle needle opens as the pressure in the control chamber decreases. Then, by controlling the opening and closing of the control valve, the pressure of the control chamber is maintained higher than the pressure at which the nozzle needle is fully lifted, and the lift position of the nozzle needle during the injection period is controlled to a predetermined position lower than the full lift position. A control unit is provided.

In the apparatus having the above-described structure in which the pressure in the control chamber for applying the back pressure to the nozzle needle is controlled by the control valve, the pressure in the control chamber is maintained within a predetermined range by repeatedly opening and closing the control valve. It is possible to Therefore, it is possible to control the pressure in the control chamber to control the nozzle needle to an arbitrary position that does not reach the full lift position, for example, to a half lift position. Therefore, the controllability of fuel injection can be improved without increasing the size of the device or complicating the structure, and a small-sized fuel injection device having excellent controllability can be realized.

More specifically, the control valve is configured to be opened by being supplied with energy to connect the control chamber to the drain passage. The pressure in the control chamber is controlled by repeating the opening and closing operation of the control valve. That is, in the normal state, the control valve is closed to hold the control chamber at a high pressure, and the control unit is driven to open to reduce the pressure in the control chamber. The pressure in the control chamber can be increased or decreased to control the nozzle needle to maintain a desired lift position.

[0010] In the invention of claim 3, the control unit includes:
Energy is supplied so that the control valve repeats valve opening for a predetermined time at a predetermined cycle. At this time, the control valve repeats a constant valve opening operation, so that the pressure in the control chamber repeatedly increases and decreases within a certain range. Accordingly, the control is performed such that the lift position of the nozzle needle maintains a certain range. can do.

In the invention according to claim 4, the control section includes:
When the control valve repeats the valve opening at a predetermined cycle, the control valve is repeatedly opened and closed so that the initial valve opening time is longer than the subsequent valve opening time. When the nozzle needle is lifted, a large force is first required to lift the nozzle needle from the nozzle seat. Therefore, the initial valve opening operation of the control valve is lengthened, and the pressure in the control chamber is further reduced. Good.

According to a fifth aspect of the present invention, a lift amount detecting means for directly or indirectly detecting the lift amount of the nozzle needle is provided. The control unit opens and closes the control valve based on a detection signal from the lift amount detection unit.For example, when the lift amount of the nozzle needle exceeds a predetermined value, the control valve is closed. On the other hand, when the lift amount falls below a predetermined value, the control valve is opened to control the pressure in the control chamber to decrease. In this way, the nozzle needle can be held in a predetermined lift range with better controllability.

According to a sixth aspect of the present invention, the control unit performs half-lift control for controlling the nozzle needle to a predetermined half-lift position when a target fuel injection amount or fuel injection time is smaller than a predetermined value. . By making the lift amount smaller than at the time of the full lift, the opening area around the nozzle needle can be reduced to lower the injection rate (injection amount per unit time), and the time required for opening and closing the nozzle needle can be shortened. Therefore, the half-lift control of the present invention is effective when the fuel injection amount is small or when the fuel injection time is short, and the injection amount control can be performed with high accuracy.

[0014] In the invention of claim 7, the control section includes:
When the fuel injection timing of the internal combustion engine largely deviates from the top dead center of the compression, half-lift control for controlling the nozzle needle to a predetermined half-lift position is performed. Injection at the point when the pressure inside the cylinder deviates from the top dead center where the pressure in the cylinder is not high enough needs to reduce the injection rate to prevent colliding with the cylinder wall and impairing lubricity. A small amount of fuel injection is often required, as in the case where pilot injection is performed before the fuel injection. In such a case, the half-lift control of the present invention is effective, and controllability of fuel injection is greatly improved.

In the invention of claim 8, the total opening area of the injection hole is changed by the lift position of the nozzle needle. For example, if a plurality of the injection holes are provided, and the number of the injection holes opened when the lift position of the nozzle needle is fully lifted and when the nozzle needle is half-lifted is changed, the lift position is changed. The adjustment of the injection amount is facilitated, and the controllability of the fuel injection is further improved.

According to the ninth aspect of the present invention, the control valve is driven by a piezo actuator, and the control section repeatedly applies a predetermined high voltage and a lower voltage to the piezo actuator, thereby controlling the nozzle needle. Control to a predetermined half-lift position. Preferably, the use of a responsive piezo actuator makes it possible to control the opening and closing of the control valve with good controllability. At this time, the control unit alternately applies a predetermined high voltage required for opening the control valve and a lower voltage necessary for closing or almost closing the valve, thereby controlling the control valve. Opening and closing can be repeated to perform half-lift control.

According to a tenth aspect of the present invention, the control section controls the control valve to repeatedly open and close to control the nozzle needle to a predetermined half-lift position. When the valve is operated, the control valve is controlled so as not to completely seat on the valve seat.
When the control valve is closed from the open state, the pressure change in the control chamber is not completely seated on the valve seat, and even when the valve is slightly lifted from the valve seat, the pressure change in the control chamber is the same as when the control valve is completely seated. The energy to make little change and lift slightly is much less than the energy to get a complete seat. Therefore, the required energy can be greatly reduced without changing the injection performance.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a fuel injection valve which is a main part of a fuel injection device of the present invention, and is suitably used, for example, in a common rail injection system of a diesel engine. The fuel injection valve has a piezo drive unit 1 at the upper end and an injection nozzle unit 10 at the lower end, between which a control valve 3 is driven by the piezo drive unit 1.
There is provided a control valve 4 for increasing and decreasing the pressure as the three-way valve 5 is driven. The nozzle needle 12 of the injection nozzle unit 10 moves up and down according to the pressure of the control chamber 4, and opens or closes the injection hole 11 at the tip of the nozzle body B1 to start or stop fuel injection. The injection hole 11 is fully opened when the nozzle needle 12 is at the upper end position, and fuel is supplied from a fuel pool 31 following the high-pressure passage 3 through a gap around the nozzle needle 12. On the other hand, when the nozzle needle 12 is at the lower end position, the nozzle needle 12 is fully closed, the conduction with the fuel reservoir 31 is cut off, and the supply of fuel is stopped. The lower end position of the nozzle needle 12 corresponds to the nozzle seat 1 on which the nozzle needle 12 is seated.
3 and the upper end position is determined by the orifice plate P1 above the nozzle body B1.

Here, as the injection nozzle section 10, in addition to the general-purpose type shown in FIG. 1, an injection nozzle section 10 of a variable injection hole type as shown in FIG. 2 may be used. In the injection nozzle unit 10 of FIG. 2, a plurality of injection holes 11a and 11b are provided at the tip of the nozzle body B1 at different heights in the axial direction, respectively. The nozzle needle 12 has a hollow interior as a high pressure passage 34 communicating with the fuel reservoir 31, and the nozzle needle 12 lifts the injection hole 1 through the high pressure passage 34.
Fuel is supplied to 1a and 11b. By doing so, the number of injection holes that are opened (that is, the total opening area of the injection holes) changes according to the lift position of the nozzle needle 12, so that half-lift control (which will be described in detail later), which is a feature of the present invention, is performed. It can be performed more effectively.

The nozzle body B1 is disposed at the lower end of the housing H of the piezo drive unit 1 via orifice plates P1 and P2, and is fixed oil-tight by a cylindrical nozzle holder B2. The high-pressure passage 3 extends upward from the fuel reservoir 31 and includes the orifice plates P1, P2 and the housing H.
It communicates with the outside common rail (not shown) through the inside.
Inside the housing H, an external fuel tank (not shown)
Is formed with a drain passage 2 for returning fuel. A control chamber 4 is formed between the upper end of the nozzle needle 12 and the orifice plate P1.
2 is constantly urged in the closing direction (downward) by the spring force of a spring 41 disposed in the control chamber 4 and the hydraulic pressure of the control chamber 4.

The hydraulic pressure in the control chamber 4 is controlled by a three-way valve 5 as a control valve. The three-way valve 5 includes a substantially conical valve chamber 51 and a substantially spherical valve body 52 formed at the lower end of the housing H. The valve chamber 51 has a passage penetrating the orifice plates P1 and P2 and a main passage provided at the lower end thereof. It is always in communication with the control room 4 via the orifice 42. The valve chamber 51 has two ports, a drain port 21 and a high-pressure port 32. When the valve body 52 in the valve chamber 51 moves upward or downward to close one of the two ports, the other is opened. To the control room 4. The drain port 21 is a valve chamber 51
The high-pressure port 32 which communicates with the drain passage 2 via the spill chamber 22 provided above and penetrates vertically through the orifice plate P2 is connected to the high-pressure passage 3 via a groove 33 provided in the lower end face of the orifice plate P2 in the radial direction. Communicating.

Therefore, when the valve chamber 51 communicates with the drain port 21, the pressure in the control chamber 4 becomes low, and the nozzle needle 1
2 rises away from the nozzle sheet 13. On the other hand, when the valve chamber 51 communicates with the high-pressure port 32, the pressure in the control chamber 4 becomes high, the nozzle needle 12 descends, and the nozzle seat 13
To sit down. Here, the control chamber 4 is connected to the lower end of the high-pressure port 32 by a sub-orifice 43 provided in the orifice plate P1 without passing through the three-way valve 5 without passing through the high-pressure passage 3.
Always in communication with The sub-orifice 43 allows the fuel to flow from the high-pressure passage 3 to the control chamber 4 through the sub-orifice 43, thereby alleviating the pressure drop in the control chamber 4 at the start of injection, opening the nozzle needle 7 gently. At the end of the operation, there is an effect that the pressure increase is promoted to quickly close the nozzle needle 7.

The opening of the drain port 21 to the valve chamber 51 is provided with a drain seat 53 as a conical valve seat.
The opening of the high-pressure port 32 to the valve chamber 51 forms a high-pressure sheet 54 having a flat shape. The reason for making one of the flat shapes is to allow the axial displacement of the valve body 52. The valve body 52 closes the corresponding port by sitting on one of the seats 53, 54, but the pressure of the valve chamber 51 always keeps the drain port 21.
, The valve body 52 is normally seated on the drain seat 53. The seating force on the high-pressure seat 54 is given by the small-diameter piston 18 of the piezo drive unit 1. Next, details of the piezo drive unit 1 will be described.

The piezo drive section 1 has a piezo actuator 14 housed in the upper end of the housing H, and a piezo piston 15 that is integrally displaced in contact with the lower end thereof. And, it transmits to the small diameter piston 18 via the displacement expansion chamber 6. The piezo actuator 14 has a known configuration, and is formed by laminating a piezoelectric body that expands by injection of electric charge and contracts by release of electric charge, and expands and contracts according to an applied voltage to drive the piezo piston 15. The application of the voltage to the piezo actuator 14 is controlled by the ECU 9 as control means. The piezo piston 15 is slidably disposed in the piezo cylinder H1 and connected to a large-diameter piston 17 by a small-diameter rod 16. The large-diameter piston 17 and the small-diameter piston 18 are slidably disposed in a large-diameter cylinder H3 and a small-diameter cylinder H4 formed coaxially with the cylinder forming member H2, respectively.
7 extends above the upper surface of the piezo piston 7 and is fixedly driven into the lower surface of the piezo piston 15.

A space formed below the piezo piston 15 and around the rod 16 forms an oil sump chamber 7 communicating with the drain passage 2, and accommodates a spring 71 to urge the piezo piston 15 upward. I have. At the same time, the large-diameter piston 17 integrally connected to the piezo piston 15 is also urged upward by the spring 71. As a result, the piezo piston 15 and the large-diameter piston 17 move up and down integrally according to the expansion and contraction of the piezo actuator 14. An O-ring 73 is provided on the outer periphery of the piezo piston 15 to prevent the working oil in the oil reservoir 62 from contaminating the piezo actuator 14. Also,
A passage for connecting the oil sump chamber 7 to the drain passage 2 is formed by forming a through hole in the oil sump chamber 7 in the radial direction from the side wall of the housing H and then closing the hole with the blind plug 74.

The cylinder forming member H2 includes a small-diameter piston 1
8 has a reduced diameter portion, and forms a stopper 61 for restricting the upward movement of the small diameter piston 18. The large and small cylinders H3 and H4 communicate with each other through this reduced diameter portion.
The displacement expansion chamber 6 is formed by a hydraulic chamber formed between the reduced diameter portion and the small diameter piston 18 and a hydraulic chamber formed between the reduced diameter portion and the large diameter piston 17. The displacement expansion chamber 6 hydraulically converts the displacement of the piezo actuator 14 and amplifies it according to the diameter difference between the large and small pistons 17 and 18 (for example, two to three times the displacement of the large diameter piston 17). introduce. The lower end of the small-diameter piston 18 is located in the spill chamber 22 formed below the cylinder forming member H2, and the small-diameter distal end is inserted into the drain port 21 so that the valve body 52 is closed.
Is in contact with

The large-diameter piston 18 has an axial passage 7 therein.
2, the upper end of the passage 72 extends into the base end of the rod 16, branches into a T shape, and opens to the oil sump chamber 7. The lower end of the passage 72 opens at the lower end surface of the large-diameter piston 18 and communicates with the displacement expansion chamber 6 via the check valve 8 mounted on the lower end of the large-diameter piston 18. The check valve 8 is for replenishing the fuel from the oil reservoir chamber 7 to the displacement expansion chamber 6 when the fuel in the displacement expansion chamber 6 decreases due to leakage or the like, and is a flat valve 81 that closes the lower end opening of the passage 72. And a disc spring 82 for urging the flat valve 81 upward. The flat valve 81 is a thin disk-shaped plate (thickness: 0.1 mm).
1 to 0.2 mm) and has a pinhole 84 (diameter: 0.02 to 0.5 mm) at the center.

The disc spring 82 has an extremely thin ring shape (thickness: 0.01 to 0.05 mm) and a biasing force of 0.5 to 2 N.
It is made small. These flat valve 81 and disc spring 82
The holder 83 for accommodating and holding is shaped like a cylinder with a bottom and is driven and fixed to the outer periphery of the lower end of the large-diameter piston 18. When the pressure in the displacement expansion chamber 6 decreases due to a fuel leak or the like, the flat valve 81 descends against the urging force of the disc spring 82, and the passage 7
Fuel flows from 2. The holder 83 has a through hole 85 that is sufficiently larger than the pinhole 84 on the bottom surface.
Since the fuel flows freely between the internal space 3 and the displacement expansion chamber 6, the fuel is quickly supplied to the displacement expansion chamber 6.

The pinhole 84 of the flat valve 81 is for leaking the fuel in the displacement expansion chamber 6 to the oil sump chamber 7. For example, when some abnormality occurs during the fuel injection, the electric charge of the piezo actuator 14 is released. Even if the fuel injection cannot be performed, the fuel can be leaked through the pinhole 84, so that the pressure in the displacement expansion chamber 6 can be reduced to stop the fuel injection. Further, after assembling the fuel injection device, vacuuming when filling the displacement expansion chamber 6 with fuel is facilitated, the fuel is quickly charged, and troubles due to remaining air are prevented. Furthermore, when the engine is stopped and left for a long time, the small-diameter piston 18 may drop by its own weight and replenish the fuel into the displacement expansion chamber 6 via the check valve 8. 84
Can be drained from the drain passage 2 to the drain passage 2, so that the small-diameter piston 18 and the valve body 52 can be lifted, and can be prepared for starting the engine. The size of the pinhole 84 is
It is set appropriately so that these effects can be achieved within a range that does not affect the fuel injection characteristics.

Next, a method of controlling the fuel injection valve by the ECU 9 will be described with reference to a time chart of FIG. FIG.
The dotted lines indicate the behavior of each part when the normal control for fully lifting the nozzle needle 12 is performed. In the full lift control, first, when starting the fuel injection (time t1), a predetermined high voltage (for example, 100 V) is applied to the piezo actuator 14 in accordance with the injection signal from the ECU 9.
Is applied. The piezo actuator 14 generates a displacement proportional to the applied voltage (a), and the piezo piston 15
The large-diameter piston 17 is moved downward by the same displacement amount, and the hydraulic pressure in the displacement enlargement chamber 6 is increased. The small-diameter piston 18 is lowered by the increase in the hydraulic pressure of the displacement expansion chamber 6, and the valve body 52 is pushed down from the drain seat 53. The lift (b) of the valve body 52 increases with an increase in the applied voltage (a) (moving downward in FIG. 1 is defined as positive).
Sit at 4. At this time, the lift (b) of the valve body 52 is moved by the large-diameter piston 1 with respect to the displacement of the piezoelectric actuator 14.
7 and the small-diameter piston 18 are enlarged by an area ratio (for example, twice).

With the lift (b) of the valve body 52, the valve chamber 51
And the drain port 21 conducts, and then the high pressure port 32
Is cut off, the pressure in the valve chamber 51 decreases, and the hydraulic pressure (c) in the control chamber 4 communicating with the valve chamber 51 decreases. When the hydraulic pressure (c) of the control chamber 4 decreases and the hydraulic pressure of the fuel reservoir 31 acting upward on the nozzle needle 12 exceeds the hydraulic pressure of the control chamber 4 and the spring force of the spring 41, the nozzle from the nozzle seat 13 The lift (d) of the needle 12 is started, and the injection of fuel from the injection hole 11 is started (time t2). After the time t2, the hydraulic pressure of the control room 4 (c)
Is lowered, and the lift (d) of the nozzle needle 12 is raised to the full lift position. This state is maintained until a predetermined injection stop timing.

When the fuel injection is stopped, the applied voltage (a) is reduced to zero by discharging the electric charge of the piezo actuator 14 (time t4). During this time, the piezo actuator 14 contracts by the amount of displacement when voltage is applied and returns to its original length, and the piezo piston 15
It is energized by 1 and rises. The large-diameter piston 17 connected to the piezo piston 15 by the rod 16 also rises together with the piezo piston 15 and reduces the oil pressure in the displacement expansion chamber 6. Small-diameter piston 1 due to a decrease in oil pressure in displacement expansion chamber 6
8 loses the force of pressing the valve body 52 against the high pressure sheet 54 against the high pressure of the high pressure port 32, and rises together with the valve body 52.

When the valve body 52 is seated again on the drain seat 53 and the lift position (b) returns to the initial state, the valve chamber 5
1 is connected to the high-pressure port 32, and the connection to the drain port 21 is cut off, so that the hydraulic pressure (c) of the valve chamber 51 and the control chamber 4 is restored. The hydraulic pressure (c) of the control room 4 rises,
When the force acting downward on the nozzle needle 12 exceeds the oil pressure of the fuel reservoir 31, the nozzle needle 12 descends from the full lift position and sits on the nozzle seat 13 again,
The fuel injection is stopped (time t6).

In the full lift control, the ECU 9
Controls the voltage application start time and the discharge start time to the piezo actuator 14 according to the target fuel injection amount. The fuel injection amount generally increases in proportion to the valve opening period (fuel injection time) of the nozzle needle 12, but a certain time is required until the nozzle needle 12 fully lifts and sits on the nozzle seat 13 from the full lift position. For this reason, if the target fuel injection amount is small, it is necessary to start descent before full lift. For example, variation tends to occur between injections, and accurate injection amount control is difficult.

Therefore, in the present invention, in such a case,
The lift position at the time of opening the nozzle needle 12 is controlled to an arbitrary position having a smaller lift amount than the full lift, for example, a predetermined half lift position. The solid line in FIG. 3 shows an example of half-lift control (half-lift control).
The start of fuel injection is the same as at the time of the full lift control,
The ECU 9 applies a predetermined high voltage to the piezo actuator 14 equal to the required voltage at the time of full lift (time t).
1). As a result, the piezo actuator 14 generates a displacement corresponding to the applied voltage (a), and the piezo piston 15
Large diameter piston 17, displacement expansion chamber 6, and small diameter piston 1
The valve element 52 is driven via 8. When the hydraulic pressure (c) of the control chamber 4 decreases to a predetermined pressure with the lift (b) of the valve body 52, the lift (d) of the nozzle needle 12 is started (time t2).

At the time of the full lift control, the applied voltage (a) is kept constant until the time t4 after the time t2. However, in order to perform the half lift control, the application of the voltage to the piezo actuator 14 is performed at a predetermined time. The process is repeated so that a high positive voltage (for example, 100 V) and a potential of zero alternate. Specifically, immediately after the time t2 when the nozzle needle 12 starts lifting, the electric charge of the piezo actuator 14 is released to make the applied voltage (a) zero (time t3).
). At the time of the full lift control, since the applied voltage (a) is maintained at a predetermined high voltage, the hydraulic pressure (c) of the control chamber 4 that is in communication with the drain port 21 is reduced until the nozzle needle 12 is fully lifted. In the half-lift control, when the applied voltage (a) becomes zero, the valve body 52
Is seated again on the drain seat 53, and the hydraulic pressure (c) in the control chamber 4 starts to increase without reaching the minimum pressure (dotted line) at the time of full lift. The nozzle needle 12 continues to lift for a while after that, but the rising speed is slow and starts lowering again without reaching the full lift.

Then, when a predetermined high voltage is applied again and then discharge is repeated, the lift (b) of the valve body 52 is increased.
Alternately repeat the state of sitting on the drain seat 53 and the state of sitting on the high-pressure seat 54. In response, the hydraulic pressure (c) of the control chamber 4 rises and falls, and the nozzle needle 1
No. 2 repeats the vibration in a certain range sandwiching the half lift position. Here, four times of high voltage application ((2) to (5)) are repeated at regular intervals from time t2 to time t4. After (5), if the potential remains zero, the nozzle The needle 12 is lowered to the position where it is seated on the nozzle seat 13, and the fuel injection is completed (time t5). At this time, since the nozzle needle 12 descends from the half-lift position, the fuel injection end time t5 is earlier than the fuel injection end time t6 at full lift.

Here, when performing the half-lift control, as shown in FIG.
, The time width of the high voltage application is made longer than (2) to (5) after the second time. This is because when the nozzle needle 12 is lifted, the nozzle sheet 13 is
This is because a greater pressure drop must be applied to the control chamber 4 when lifting from the state of sitting on the nozzle seat 13 than when lifting from above. From the second time (2) to (5), a high voltage is applied so that the hydraulic pressure (c) of the control chamber 4 substantially changes within a range of pressure corresponding to a preset lowering limit and a rising limit of the nozzle needle 12. , And the time interval of each time may be set.

Alternatively, in order to hold the nozzle needle 12 at a predetermined half-lift position, the nozzle needle 1
Means for directly or indirectly detecting the lift amount of No. 2 may be provided, and the opening and closing of the three-way valve 5 may be controlled based on the detection result so that the lift amount of the nozzle needle 12 is within a predetermined range. For example, a well-known capacitive or eddy-current type gap sensor is arranged near the nozzle needle 12 so as to directly detect the lift amount of the nozzle needle 12, or a known pressure sensor for detecting the pressure of the control chamber 4 is provided. The lift amount of the nozzle needle 12 can be indirectly detected from the pressure in the control chamber 4 by providing the control unit 4. Then, the applied voltage (a) is controlled so that the lift amount of the nozzle needle 12 does not fall below the lower limit or does not exceed the upward limit so that the lift position of the nozzle needle 12 falls within a certain range.

Thus, the nozzle needle 12 is
It can be maintained at a predetermined half-lift position with good controllability. In the half-lift control, the opening area around the nozzle needle 12 is smaller than at the time of the full lift, the injection rate (injection amount per unit time) is low, and the time required for opening and closing is short, so that a small amount of fuel is injected stably. be able to. Therefore, when the target fuel injection amount or the fuel injection time is smaller than the predetermined value, the injection control can be performed with high accuracy by performing the half-lift control. In particular, when the injection nozzle portion 10 of FIG. 2 in which the number of injection holes is variable is used and only the lower injection hole 11a is opened at the time of half-lift and the total opening area of the injection holes is made smaller than at the time of full lift, more It is effective and a desired injection amount can be easily realized. For example, in order to reduce the noise of a diesel engine, it is effective to perform pilot injection for injecting a small amount of fuel before a predetermined period of time for performing main injection, but it is not easy to accurately meter a small amount of fuel. Further, when the injection timing deviates significantly from the top dead center of the compression, if the injection rate is large, it may collide with the cylinder wall and dilute the lubricating oil. In such a case, the half-lift control of the present invention is effective, and by performing stable fuel injection amount control, the combustion performance of the internal combustion engine can be greatly improved. Also, by lowering the injection rate, it is possible to prevent collision with the cylinder wall.

The two-dot broken line in FIG. 3 shows another example of the control of the applied voltage (a) of the piezo actuator 14 in the case of the half-lift control (half-lift control), and the first (1) high voltage application. After (for example, 100 V), the application voltage (a) is not dropped to zero, a predetermined low positive voltage is maintained, and the application of the high voltage again is repeated. At this time, the predetermined low positive voltage is the minimum voltage (for example, 6) for maintaining the valve body 52 open with respect to the drain port 52.
0V), and the lift amount of the valve body 52 is
3 may be small enough not to be seated. As a result, the lift (b) of the valve body 52 is
And a state in which the user does not completely sit on the drain seat 53 and lifts very slightly is alternately repeated. In addition,
The rise of the hydraulic pressure in the control chamber 4 is caused by the valve body 52 being seated on the drain seat 53 as in the above-described half-lift control or being slightly lifted from the drain seat 53 as in the present embodiment. Since the inflow of high-pressure fuel from the port 32 is dominant, it hardly changes.

Accordingly, the lift (d) of the nozzle needle 12 is almost the same as in the case of the above-described half-lift control, and the same half-lift control can be performed. Such control is possible when the applied voltage is reduced from the applied voltage (required voltage for full lift) of the piezo actuator for seating the valve body 52 of the three-way valve 5 on the high-pressure seat 54. Without being lowered to zero, a state is obtained in which the seat is almost seated on the drain seat 53 (the seat is lifted slightly without completely seated).

In FIG. 4, point A shows the displacement and generated force of the piezo actuator 14 for starting the lift of the valve body 52 from the drain seat 53.
Since the high pressure in 1 acts in the valve closing direction, this point A has the highest demand for the generated force to the piezo actuator 14, and requires 90V. Once lifted from the drain seat 53, the hydraulic pressure in the valve chamber 51 also acts in the valve opening direction, so the demand for the generated force on the piezo actuator 14 is reduced, and the valve body 52 is fully lifted and sits on the high pressure seat 54. At point B, a voltage slightly higher than point A, 100V, is required. When the lift amount is reduced from the point B, when the voltage is reduced to 60 V, the point reaches the point C where the drain seat 53 is almost seated, and the oil pressure in the control chamber 4 rises almost in the same manner as when the valve body 52 is completely seated. I do.

Therefore, when the operation of seating on the drain seat 53 and decreasing the lift amount from the point B and repeating the full lift operation is repeated, it is not necessary to completely sit on the drain seat 53, and it is necessary to move back and forth between the points C and B. I just need. That is, similar half-lift control is achieved by applying a voltage from 100 V to 60 V and from 60 V to 100 V. By such control, 100V → 0V →
The required energy is 60% compared to 100V
Can be reduced. Therefore, half-lift control can be performed with less energy.

In the above embodiment, a three-way valve is used as the control valve. However, a two-way valve may be used instead of the three-way valve. Although the control chamber is provided facing the upper end of the nozzle needle, a piston member that moves in cooperation with the nozzle needle is provided, and the piston is configured to act as a back pressure on the control chamber. Of course you can.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the overall configuration of a fuel injection device according to the present invention.

FIG. 2 is a partial sectional view of a fuel injection device showing another example of the injection hole shape.

FIG. 3 is a time chart for explaining the operation of the present invention.

FIG. 4 is a diagram showing a relationship between generated force and displacement in open / close control of a three-way valve.

[Explanation of symbols]

 H housing H housing B1 Valve body 1 Piezo drive unit 10 Injection nozzle unit 11 Injection hole 12 Nozzle needle 13 Nozzle seat 14 Piezo actuator 15 Piezo piston 16 Rod 17 Large diameter piston 18 Small diameter piston 2 Drain passage 21 Drain port 22 Spill chamber 3 High pressure Passage 31 fuel pool 32 high pressure port 4 control chamber 5 three-way valve (control valve) 51 valve chamber 52 valve body 53 drain seat (valve seat) 54 high pressure seat 6 displacement expansion chamber 7 oil sump chamber 8 check valve 9 ECU (control) Part)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 51/06 F02M 51/06 N 61/18 320 61/18 320D F-term (Reference) 3G066 AA07 AB02 AC09 AD07 BA51 BA67 CC01 CC08T CC14 CC28 CC30 CC52 CE27 DA01 DA12 DC06

Claims (10)

[Claims] 1. A control chamber for applying pressure in a valve closing direction to a nozzle needle for opening and closing an injection hole, and a control valve for driving the opening and closing of the control chamber to increase or decrease the pressure in the control chamber. In the fuel injector in which the nozzle needle opens, the pressure in the control chamber is maintained higher than the pressure at which the nozzle needle fully lifts by controlling the opening and closing of the control valve, and the lift position of the nozzle needle during the injection period is maintained. And a control unit for controlling a predetermined position lower than a full lift position. 2. The control valve opens when energy is supplied to open the control chamber in communication with a drain passage. The control unit repeats the opening and closing operation of the control valve to open and close the control chamber. 2. The fuel injection device according to claim 1, wherein the pressure in the control chamber is controlled. 3. The fuel injection device according to claim 2, wherein the control unit supplies energy so that the control valve repeats opening for a predetermined time at a predetermined cycle. 4. The fuel injection device according to claim 2, wherein the control section repeatedly opens and closes the control valve such that the initial valve opening time is longer than the subsequent valve opening time. 5. A lift amount detecting means for directly or indirectly detecting a lift amount of the nozzle needle, wherein the control section opens and closes the control valve based on a detection signal from the lift amount detecting means. The fuel injection device according to any one of claims 1 to 4, wherein: 6. The controller according to claim 1, wherein said controller performs half-lift control for controlling said nozzle needle to a predetermined half-lift position when a target fuel injection amount or fuel injection time is smaller than a predetermined value. The fuel injection device according to any one of the above. 7. The controller according to claim 1, wherein the control unit controls the nozzle needle to a predetermined half-lift position when the fuel injection timing of the internal combustion engine deviates significantly from the top dead center of the compression. The fuel injection device according to any one of the above. 8. The fuel injection device according to claim 1, wherein a total opening area of the injection hole changes according to a lift position of the nozzle needle. 9. The control valve is driven by a piezo actuator, and the control unit repeatedly applies a predetermined high voltage and a lower voltage to the piezo actuator, thereby setting the nozzle needle in advance. 9. The fuel injection device according to claim 1, wherein the fuel injection device is controlled to a predetermined half-lift position. 10. The control unit controls the nozzle needle to a predetermined half-lift position by repeatedly opening and closing the control valve. In the series of opening and closing operations, the controller controls the nozzle needle during the valve closing operation. 10. The fuel injection device according to claim 1, wherein the control valve is controlled so as not to completely seat on the valve seat.