JP2002202019A - Fuel injector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably reduce the common rail pressure using an injector operated by a piezo-actuator in a common rail type fuel injector. SOLUTION: A valve element 123 for relieving back pressure of a needle 121 of the injector 1 to a low pressure source is pressed to be driven by a piezo-stack 127 to achieve half-lift, whereby with the needle 121 still in the seated state, fuel is relieved from a back pressure chamber 106 to reduce the common rail pressure. In pressure reduction, piezo-stack voltage is raised to a half-lift enabling value in a designated control cycle, and the higher the common rail pressure is, and the higher the lowering speed of injection start voltage is, the percentage of the charging state period in the control cycle can be decreased, whereby even if the lowering speed of the injection start voltage is high, the injection start voltage is not below the actual piezo-stack voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to pressure reduction control of a fuel pressure in a coma rail of a fuel injection device.

[0002]

2. Description of the Related Art A common rail type fuel injection device stores fuel pressurized by a high pressure supply pump in a common rail, and supplies the fuel from the common rail to an injector for fuel injection.

[0003] Although there are various types of injector configurations, the needle for opening and closing the injection hole of the nozzle portion is moved up and down by increasing and decreasing the back pressure to switch between injection and stop, and the back pressure is obtained by the fuel from the common rail. Some have been configured. The back pressure is increased or decreased by the following means. That is, a valve chamber is interposed between a back pressure chamber in which fuel is introduced from a common rail to generate back pressure and a low pressure source such as a fuel tank, and a valve body that opens and closes a port on the low pressure source side in the valve chamber. Is arranged, and the back pressure chamber communicates with the low pressure source by lifting the valve body, thereby reducing the back pressure. As a result, the needle is lifted and fuel injection is started. As the back pressure increasing / decreasing means having the valve chamber and the valve element, a two-way valve or a three-way valve can be used.

[0004] As an actuator for driving the valve element,
In recent years, a piezo actuator utilizing a piezoelectric action of a piezoelectric material such as PZT has been considered. In the piezo actuator, a piezo stack that expands and contracts due to charging and discharging generates a pressing force. For example, the piezo stack is extended by charging, and the port is pressed to drive the valve body in the closed state to lift it from the valve seat. The switching of the operation of the piezo actuator is performed by controlling the energizing means for charging and discharging the piezo stack by a control means such as a microcomputer.

[0005]

By the way, in the common rail type fuel injection device, the fuel injection control and the amount of fuel fed to the common rail are adjusted so as to obtain an optimum injection pressure according to the operating conditions. Control the internal fuel pressure. However, when the operating condition suddenly changes from a condition requiring a high injection pressure (high pressure and high load) to a condition requiring a relatively low pressure (low pressure and low load), the fuel pressure in the common rail cannot be reduced. However, if the fuel is injected in this pressure state, noise may be generated or exhaust gas may be deteriorated. Therefore, it is necessary not only to reduce the amount of the common rail to be pumped but also to positively discharge high-pressure fuel from the common rail.

In the configuration in which the injector uses the fuel from the common rail as control oil as described above, the valve is lifted while the needle is seated to release the fuel in the back pressure chamber in order to reduce the fuel pressure in the common rail. (Japanese Patent Laid-Open No. 2000-161170). The back pressure of the needle in the closed state is sufficiently higher than the pressure at which the needle can open, and the seating state is maintained even if the back pressure is reduced to some extent. On the other hand, if the valve body is set in a lift state (half lift) that does not reach the full lift as in the needle opening / closing control, the pressure drop in the back pressure chamber is small. Therefore, by setting the valve body to a half-lift within a range in which the back pressure of the needle does not fall below the pressure at which the needle can be opened, the fuel in the common rail returns to the fuel tank via the injector, and the fuel pressure in the common rail decreases. become.

In the case where the injector is equipped with the piezo actuator, in order to realize a half-lift of the valve body, the valve body is lifted from a seated state by a charge that can withstand the fuel pressure in the valve chamber equal to the fuel pressure in the common rail. While charging to the amount, it is necessary not to exceed the charged amount (injection start charged amount) at which the needle lifts and fuel injection starts.

However, when the valve body is seated, the area of the pressure receiving surface of the valve body where the fuel pressure in the valve chamber acts in the lift direction is small, and the fuel pressure in the valve chamber is substantially equal to the fuel pressure in the common rail. An unbalanced pressure state in which the force acting in the direction is overwhelmingly dominant. On the other hand, once the valve element is lifted, the fuel pressure in the valve chamber decreases and the pressure receiving surface of the valve element on which the fuel pressure acts in the lift direction increases, so that the force acting in the seating direction acts in the lift direction. And the unbalanced pressure state is alleviated.

The relief of the unbalanced pressure state is as follows.
Acting in the direction that encourages the piezo stack to elongate, the valve body lifts and the fuel from the back pressure chamber starts returning to the fuel tank (leak start charge amount). The lift amount is relatively large, and there is not much difference between the leak start charge amount and the injection start charge amount.

In addition, as the pressure is reduced, the urging force acting on the valve body in the seating direction is weakened, so that the injection start charge is also reduced.

For this reason, it is not always easy to set the charge amount of the piezo stack when the common rail is depressurized by the valve body half-lift.

The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a fuel injection device that can set a charge amount of a piezo stack to an appropriate value and satisfactorily reduce the pressure of a common rail by a half-lift of a valve body.

[0013]

According to the first aspect of the present invention, there is provided a nozzle having a needle for opening and closing an injection hole, and supplying high-pressure fuel stored in a common rail to inject the fuel from the injection hole. And a back pressure chamber in which fuel is introduced from the common rail to generate back pressure of the needle; and a valve body in a valve chamber interposed between the back pressure chamber and the low pressure source, and a port on the low pressure source side is closed. Back pressure increasing / decreasing means arranged to reduce the pressure of the back pressure chamber as the lift amount of the valve body increases, and a piezo stack for pressing and driving the valve body. An injector having a piezo actuator for increasing the lift amount of the valve body as the charge amount increases, an energizing means for energizing the piezo stack to charge and discharge the piezo stack, and a fuel pressure in the common rail. Pressure detecting means for detecting the pressure, and controlling the energization by the energizing means, for the fuel injection command, switching the valve body between the seated state and the full lift state to open and close the needle, and Control means for setting a target charge amount in accordance with the detected fuel pressure and setting the valve body in a lift state while the needle is in a seated state. The control means is controlled so that the piezo stack rises to a charged state in a predetermined cycle at a target charge amount set in accordance with the detected fuel pressure, and in the energization control with respect to the pressure reduction command, The period during which the piezo stack is in a charged state is set to be shorter as the fuel pressure is higher.

When the fuel pressure in the common rail decreases,
The force acting on the valve body in the seating direction is reduced, and the lift amount of the valve body increases. Therefore, when the fuel pressure is high and the decompression speed is high, the injection start charge amount quickly decreases.
In the present invention, as the fuel pressure increases, the length of the period during which the piezo stack is in the charged state is shortened, and it is possible to prevent the injection start charge amount from falling below the actual piezo stack charge amount.

According to the second aspect of the present invention, there is provided a nozzle portion which has a needle for opening and closing the injection hole, is supplied with high-pressure fuel stored in a common rail, and injects the fuel from the injection hole; Is introduced, a back pressure chamber for generating a back pressure of the needle, and a valve body disposed in the valve chamber interposed between the back pressure chamber and the low pressure source so that the port on the low pressure source side can be closed. Back pressure increasing / decreasing means for reducing the pressure in the back pressure chamber as the lift amount of the valve body increases, and a piezo stack for pressing and driving the valve body. An injector having a piezo actuator for increasing the lift amount of the valve body, an energizing means for energizing the piezo stack to charge and discharge the piezo stack, and a pressure for detecting a fuel pressure in the common rail Control means for controlling the energization by the energizing means, and in response to a fuel injection command, switching the valve body between a seated state and a full lift state to open and close the needle, thereby controlling the fuel pressure in the common rail. Control means for setting a target charge amount in accordance with the detected fuel pressure for the pressure reduction command and setting the valve body in a lift state while the needle is in a seated state, In the power supply control in response to the pressure-reducing command, the control unit controls the piezo stack to be in a charged state at a predetermined cycle at a target charge amount set according to the detected fuel pressure, and the piezo stack is in a charged state. Is set so that the charge amount in a certain period gradually decreases with the target charge amount as an initial value.

By gradually decreasing the charge amount of the piezo stack with a decrease in the common rail pressure, it is possible to provide a margin until the injection start charge amount. In addition, since the amount of charge at the start of leakage decreases as the force acting on the valve body in the valve closing direction decreases, a margin for the amount of charge at the start of leakage is secured.

According to a third aspect of the present invention, in the configuration of the first or second aspect of the present invention, in the energization control in response to the pressure reduction command, the target charging is performed as the fuel pressure reduction speed in the common rail increases. Set the volume to be low.

If the rate of pressure reduction of the fuel pressure in the common rail fluctuates due to factors such as fluctuations in fuel properties, individual differences in injectors, etc., the injection start charge becomes less than the charge in the piezo stack even if the fuel pressure in the common rail is the same. The time margin of the time is small. In the present invention, since the target charge amount is set to be smaller as the pressure reduction rate of the fuel pressure in the common rail is higher, the injection start charge amount is reduced even if the correspondence between the half-liftable charge amount and the common rail pressure fluctuates. , It is possible to secure a time margin until the charge amount falls below the charge amount.

According to the fourth aspect of the present invention, there is provided a nozzle having a needle for opening and closing the injection hole, a high-pressure fuel stored in a common rail being supplied, and injecting the fuel from the injection hole, and a fuel from the common rail. Is introduced, a back pressure chamber for generating a back pressure of the needle, and a valve body disposed in the valve chamber interposed between the back pressure chamber and the low pressure source so that the port on the low pressure source side can be closed. Back pressure increasing / decreasing means for reducing the pressure in the back pressure chamber as the lift amount of the valve body increases, and a piezo stack for pressing and driving the valve body. An injector having a piezo actuator for increasing the lift amount of the valve body, an energizing means for energizing the piezo stack to charge and discharge the piezo stack, and a pressure for detecting a fuel pressure in the common rail The charging amount of the piezo stack is adjusted by controlling the energization by the discharge means and the energizing means, and the needle is switched by switching the valve body between a seated state and a full lift state in response to a fuel injection command. Control means for opening and closing the valve, setting a target charge amount in accordance with the detected fuel pressure in response to a command to reduce the fuel pressure in the common rail, and setting the valve body to a lift state while the needle is seated. A fuel injection device having:
The control means estimates an amount of charge of a piezo stack that can bring the valve body into a lift state (half-lift) while the needle is in a seated state, based on the detected fuel pressure in the energization control for the pressure-reducing command, With the charge amount lower than the estimated charge amount as an initial value, the target charge amount is set to gradually increase until the detected fuel pressure starts to decrease.

By gradually increasing the target charge amount from a charge amount lower than the estimated charge amount that can be a half-lift, the injection start charge amount varies due to factors such as fluctuations in fuel properties and individual differences of injectors. In addition, it is possible to set a charge amount that can be half-lifted while avoiding erroneous injection.

According to a fifth aspect of the present invention, in the configuration according to the fourth aspect of the present invention, in the energization control in response to the pressure-reducing command, the control unit controls the length of the charge state as the fuel pressure in the common rail increases. Is set to be short.

The higher the fuel pressure in the common rail at the start of pressure reduction, the higher the pressure reduction speed at the start of pressure reduction and the faster the injection start charge decreases. In the present invention, as the fuel pressure increases, the length of the period during which the piezo stack is in the charged state is shortened, and it is possible to prevent the injection start charge amount from falling below the actual piezo stack charge amount.

[0023]

(First Embodiment) FIG. 2 shows the configuration of a common rail type fuel injection device for a diesel engine to which the present invention is applied. As many injectors 1 as the number of cylinders of the diesel engine are provided for each cylinder (only one injector 1 is shown in the figure), and the fuel is supplied from a common common rail 54 that communicates via a supply line 55. Fuel is injected from the injector 1 into the combustion chamber of each cylinder at an injection pressure substantially equal to the fuel pressure in the common rail 54 (hereinafter referred to as the common rail pressure). The fuel in the fuel tank 51 is fed to the common rail 54 by the high-pressure supply pump 53 and stored at a high pressure.

The fuel supplied to the injector 1 from the common rail 54 is used not only for injection into the combustion chamber, but also as a control oil pressure for the injector 1 and the like, and is supplied from the injector 1 through a low-pressure drain line 56 to a fuel tank. Reflux to 51.

The CPU 31 calculates a fuel injection timing and an injection amount based on a detection signal such as a crank angle and the like, and outputs an injection signal corresponding to the calculation to drive a piezo actuator mounted on each injector 1. Output to the piezo actuator drive circuit 2. The injection signal is a binary signal consisting of “H” and “L”, and causes the injector 1 to inject fuel for a predetermined period.

The CPU 31 controls the injection pressure so as to be appropriate according to the operating conditions known from other sensor inputs or the like. The pressure sensor 4 as a pressure detecting means is provided on the common rail 54, and a detection signal of the common rail pressure is digitized by the AD converter 32 and input to the CPU 31. The CPU 31 controls the metering valve 52 based on the common rail pressure to adjust the amount of fuel fed to the common rail 54. When the common rail pressure needs to be rapidly reduced, the CPU 31 internally generates a pressure reduction command to perform a current supply control to the piezo actuator drive circuit 2 different from that during fuel injection, and to control the injector 1 as described later. The fuel as oil is returned to the fuel tank 51 to reduce the common rail pressure.

FIG. 1 shows the structure of the injector 1.
The injector 1 is a rod-shaped body, and is attached so that a lower part in the figure penetrates a combustion chamber wall (not shown) of the engine and protrudes into the combustion chamber. The injector 1 includes a nozzle unit 1a, a back pressure control unit 1b, and a piezo actuator 1c in this order from the bottom.
It has become.

A needle 121 is slidably held at its rear end in a sleeve-shaped main body 104 of the nozzle portion 1a. The needle 121 is seated on an annular seat 1041 formed at the front end of the nozzle main body 104 or Leave.
High-pressure fuel is introduced into the outer peripheral space 105 at the distal end of the needle 121 from the common rail 54 via the high-pressure passage 101, and fuel is injected from the injection holes 103 when the needle 121 is lifted. The needle 121 has an annular step surface 1211
The fuel pressure from the high pressure passage 101 acts in the lift direction (upward).

Behind the needle 121, the high pressure passage 101
A fuel as a control oil is introduced from the through an in orifice 107 to form a back pressure chamber 106 for generating a back pressure of the needle 121. This back pressure acts on the rear end surface 1212 of the needle 121 together with the spring 122 provided in the back pressure chamber 106 in a seating direction (downward).

The back pressure is increased or decreased by a back pressure control unit 1b, and the back pressure control unit 1b is driven by a piezo actuator 1c having the piezo stack 127.

The back pressure chamber 106 has an out orifice 10
9 and is always in communication with the valve chamber 110 of the back pressure control unit 1b. The valve chamber 110 has a ceiling surface 1101 formed in an upwardly conical shape, and a low-pressure port 110 a communicating with the low-pressure chamber 111 is opened at the top of the ceiling surface 1101.
The low pressure chamber 111 is a low pressure passage 1 leading to the drain line 56.
02. A high-pressure port 110b communicating with the high-pressure passage 101 via the high-pressure control passage 108 is opened on the bottom surface of the valve chamber 110.

A ball 123 having a lower portion cut horizontally is provided in the valve chamber 110. The ball 123 is a valve body that can move up and down. When the ball 123 descends, the cut surface serves as a valve seat bottom (hereinafter, referred to as a high-pressure side seat) 1 as a valve seat.
By closing the high pressure port 110b while sitting on the valve 102, the valve chamber 110 is isolated from the high pressure control passage 108, and when ascending, the valve chamber 110 is seated on the ceiling surface (hereinafter, referred to as a low pressure side seat) 1101 as the valve seat and the low pressure port 110a. Is closed to shut off the valve chamber 110 from the low-pressure chamber 111. Thereby, when the ball 123 descends, the back pressure chamber 106
Is the low pressure chamber 1 through the out orifice 109 and the valve chamber 110
11, the back pressure of the needle 121 is reduced, and the needle 121 is separated. On the other hand, when the ball 123 rises, the back pressure chamber 106 is isolated from the low pressure chamber 111 and the high pressure passage 10 is closed.
1, the back pressure of the needle 121 increases, and the needle 121 is seated.

The ball 123 is a piezo actuator 1c
Is pressed and driven. The piezo actuator 1c
A vertical hole 112 formed vertically above the low-pressure chamber 111.
Two pistons 124 and 125 having different diameters are slidably held, and a piezo stack 127 is disposed above the large-diameter piston 125 on the upper side with the vertical direction extending and contracting.

The large-diameter piston 125 is kept in contact with the piezo stack 127 by a spring 126 provided below the large-diameter piston 125, so that the large-diameter piston 125 is vertically displaced by the amount of expansion and contraction of the piezo stack 127.

The space defined by the lower small-diameter piston 124 facing the ball 123, the large-diameter piston 125, and the vertical hole 112 is filled with fuel to form a displacement expansion chamber 113, and the piezo stack 127 extends. When the large-diameter piston 125 is displaced downward and presses the fuel in the displacement expansion chamber 113, the pressing force is transmitted to the small-diameter piston 124 via the fuel in the displacement expansion chamber 113. Here, since the small-diameter piston 124 has a smaller diameter than the large-diameter piston 125, the amount of extension of the piezo stack 127 is expanded and converted to the displacement of the small-diameter piston 124.

At the time of fuel injection, first, the piezo stack 1
27 is charged and the piezo stack 127 expands, whereby the small-diameter piston 124 descends and pushes down the ball 123. As a result, the ball 123 moves to the low-pressure side seat 1.
The lifter 101 lifts the seat and sits on the high-pressure side seat 1102 so that the back pressure chamber 106 communicates with the low pressure passage 102, so that the fuel pressure in the back pressure chamber 106 decreases. As a result, the force acting on the needle 121 in the unseating direction is more dominant than the force acting on the needle 121 in the seating direction, and the needle 121 is unseated and fuel injection is started.

On the contrary, when the injection is stopped, the piezo stack 127 is contracted by the discharge of the piezo stack 127 and the ball 12
Release the pushing force to 3. At this time, the pressure in the valve chamber 110 is low, and the high pressure fuel pressure acts on the bottom surface of the ball 123 from the high pressure control passage 108.
An upward fuel pressure acts on the ball 123 as a whole. When the pressing force on the ball 123 is released, the ball 123 separates from the high-pressure seat 1102 and sits on the low-pressure seat 1101 again, and the fuel pressure in the valve chamber 110 rises. Stops.

Further, as will be described later, the injector 1 lifts the ball 123 with the needle 121 in a seated state and returns the fuel to the fuel tank 51, and is also used for suddenly reducing the common rail pressure.

FIG. 3 shows the configuration of a piezo actuator drive circuit 2 which is a current supply means for charging and discharging the piezo stack 127. For convenience of description, the piezo stack 127 is appropriately represented as a piezo stack 127A, a piezo stack 127B, a piezo stack 127C, and a piezo stack 127D corresponding to four cylinders.
The piezo actuator driving circuit 2 is a DC-D that generates a DC voltage of several tens to several hundreds of volts by power supply (+ B) of a vehicle-mounted battery.
The DC power supply 21 is constituted by the C converter 211 and the buffer capacitor 212 connected in parallel to the output terminal thereof, and outputs a voltage for charging the piezo stacks 127A to 127D. The DC-DC converter 211 is a general step-down chopper type circuit, and stores energy in the inductor 2111 when the switching element 2112 is turned on.
When the switching element 2112 is turned off, the buffer capacitor 212 is charged via the diode 2113 from the inductor 2111 which generates the back electromotive force. The buffer capacitor 212 has a sufficiently large capacitance,
A substantially constant voltage value is maintained even when the piezo stacks 127A to 127D are charged.

Buffer capacitor 212 of DC power supply 21
2 to piezo stacks 127A to 127D
3 is provided, and a first switching element 24a is interposed between the buffer capacitor 212 and the inductor 23 in series with the first power supply path 22a. The first switching element 24a is formed of a MOSFET, and a parasitic diode (hereinafter, referred to as a first parasitic diode) 241a is connected so as to be reversely biased with respect to a voltage between both ends of the buffer capacitor 212. Further, the inductor 23 and the piezo stacks 127A to 127D are connected to the second current path 22b.
Is formed. The current path 22b is connected to the inductor 2
3 and a second switching element 24b connected to a connection midpoint between the first switching element 24a and a closed circuit including the inductor 23, the piezo stacks 127A to 127D and the second switching element 24b. .
The second switching element 24b is also formed of a MOSFET, and a parasitic diode (hereinafter, referred to as a second parasitic diode) 241b is connected so as to be reverse biased with respect to a voltage between both ends of the buffer capacitor 212.

The energization paths 22a and 22b are common to the piezo stacks 127A to 127D, respectively, and the piezo stacks 127A to 127D to be driven are as follows.
27D can be selected. Piezo stack 127A-127
D is connected in series with a switching element (hereinafter, appropriately referred to as a selective switching element) 25A, 25B, 2
5C, 25D, 25E, and 25F, of which the first type of selective switching elements 25A to 25D are connected.
Are one-to-one with piezo stacks 127A-127D respectively
And the selection switching elements 25A to 25D corresponding to the piezo stacks 127A to 127D of the injectors of the injection cylinders are turned on.

The selection switching elements 25E and 25F of the second type are such that the selection switching element 25E is common to the piezo stack 127A and the piezo stack 127B, and the selection switching element 25F is the piezo stack 127C and the piezo stack 127D. Connected in common. Second type selection switching element 25E, 25
F indicates that even if the selection switching elements 25A to 25D cause an uncontrollable state in any of the piezo stacks 127A to 127D, the piezo stacks 127A to 127D do not operate.
Two piezo stacks 127A and 127 including the 127D
B or the piezo stacks 127C and 127D are separated from the piezo actuator drive circuit 2 to ensure the operation of the remaining two piezo stacks 127C and 127D or the piezo stacks 127A and 127B (limp form).

MOSFETs are used for the selection switching elements 25A to 25F, and their parasitic diodes (hereinafter, referred to as selective parasitic diodes) 251A, 251
B, 251C, 251D, 251E, and 251F are connected to the buffer capacitor 212 so as to be reverse biased.

Switching elements 24a, 24b, 25A
Control signals are input to the gates of the to 25F from the controller 29, and as described above, any one of the selection switching elements 25A to 25D is turned on to select the piezo stack 127A to 127D to be driven, and A pulse-like control signal is input to the gates of the elements 24a and 24b, and the switching elements 24a and
4b on and off, and the piezo stacks 127A to 127D
, And charge control and discharge control.

Also, a resistor 27E having a relatively low resistance is connected in series to the piezo stack 127A and the piezo stack 127B, and the piezo stack 127C and the piezo stack 1 are connected in series.
The same resistor 27F as the resistor 27E is provided in series with the resistor 27D. The voltage between both ends of the controller 2
9, the charging current of the piezo stacks 127A to 127D is detected.

A resistor 28 having a relatively low resistance is provided in series with the second switching element 24b. The voltage between both ends is inputted to the controller 29, and the discharge current of the piezo stacks 127A to 127D is detected.

The controller 29 is supplied with the voltage at both ends of the piezo stacks 127A to 127D (hereinafter referred to as the piezo stack voltage), which is the amount of charge.

At the time of charge control, the controller 29 sets the ON period and the OFF period of the first switching element 24a as follows, and outputs a control signal for the first switching element 24a. That is, the first switching element 24a is turned on and a gradually increasing charging current flows through the first current path 22a. When the charging current reaches a preset upper limit current value, the switching element 24a is turned off and the off period starts. At this time, the back electromotive force generated in the inductor 23 is the second
Is forward biased with respect to the parasitic diode 241b of the switching element 24b, the flywheel current that gradually decreases in the second current path 22b flows due to the energy accumulated in the inductor 23, and the piezo stacks 127A to 127A.
The charging of 127D proceeds. When the charging current reaches the lower limit current value (approximately 0), the first switching element 24a is turned on again to enter the ON period, and this is repeated (multiple switching method). When the piezo stack voltage reaches a preset voltage, the switching element 24a is fixed to off, and the charging is completed. Thus, the piezo stack 1
By charging 27A to 127D, the piezo stack 1
27A to 127D extend to press and lift the ball 123 via the displacement expansion chamber 113.

During the discharge control, the ON period and the OFF period of the second switching element 24b are set as follows, and a control signal for the second switching element 24b is output. That is, the second switching element 24b is turned on, and a gradually increasing discharge current flows through the second current path 22b. When the discharge current reaches a preset current value (hereinafter, referred to as an upper limit current value), the switching element 24b is turned off to enter an off period. At this time, a large back electromotive force is generated in the inductor 23, and the flywheel current is caused to flow through the first current path 22 a by the energy stored in the inductor 23, and the energy is recovered by the buffer capacitor 212. When the discharge current reaches the lower limit current value (substantially 0), the second switching element 24b is turned on again, and this is repeated. And
When the piezo stack voltage reaches 0, the switching element 2
4b is fixed off, and the discharge is completed. By discharging the piezo stacks 127A to 127D in this manner, the piezo stacks 127A to 127D are contracted and the pressing force of the displacement expansion chamber 113 on the ball 123 due to the fuel pressure is released, and the ball 123 is seated.

The piezo stacks 127A to 127D
When the piezo stacks 127A to 127D cannot be discharged due to a disconnection of a line connecting the piezo actuator drive circuit 2 to the piezo actuator drive circuit 2, the fuel continues to be injected by the injector 1 even when the fuel injection period specified by the injection signal ends. However, the injector 1 shown in FIG. 1 has a mechanical fail-safe mechanism that closes the valve when the time during which the piezo stack 127 is in a charged state exceeds a certain time. That is, the injector 1 compresses and pressurizes the fuel in the displacement expansion chamber 113 by the extension of the piezo stack 127, and pressurizes the ball 1.
When the ball 123 is in the lift state, the fuel pressure is a pressure that can withstand the upward urging force acting on the ball 123. For this reason, the pressurized fuel in the displacement expansion chamber 113 is
Leakage from the sliding portions 24 and 125 little by little into low-pressure chambers such as the low-pressure chamber 111, the lift of the ball 123 is reduced, and the flow rate of fuel flowing from the back-pressure chamber 106 to the low-pressure chamber 111 is reduced. The pressure gradually increases until the needle 12
1 is seated and fuel injection is stopped.

The controller 29 charges and discharges the piezo stacks 127A to 127D at predetermined times according to various control signals from the CPU 31 which controls the entire fuel injection control. As such a control signal, a charge / discharge timing setting signal that defines a charging timing and a discharging timing is input. The charge / discharge timing setting signal is a binary signal consisting of “L” and “H”.
The charging of A to 127D is started, and the piezo stacks 127A to 127D are discharged at the fall. The charge / discharge timing setting signal defines the injection period for the injection command.

Also, a target voltage setting signal proportional to a target piezo stack voltage (hereinafter, referred to as a target voltage), which is a target charge amount, is input as a control signal, and the controller 29 causes the piezo stack voltage to reach the target voltage. Then, the switching element 24a is fixed off as described above. The target voltage setting signal corresponds to the ball 123 in response to the injection command.
Is set such that a sufficient piezo stack voltage capable of full lift is provided.

In response to the pressure reduction command, the CPU 31 determines the charging timing and discharging timing of the piezo stacks 127A to 127D and the target voltage as follows, and reduces the common rail pressure to the target pressure.

A control signal for selecting a cylinder to be controlled is also output from the CPU 31, and among the selected switching elements 25A to 25F, those of the piezo stacks 127A to 127D corresponding to the selected cylinder are turned on.

FIG. 4 is a flowchart at the time of pressure reduction control executed by the CPU 31. First, a piezo stack voltage that can be used as a half lift is estimated based on the detected common rail pressure (step S101). For this, a half-liftable voltage estimation map in which the common rail pressure and the piezo stack voltage are associated in advance is stored in the ROM of the CPU 31, and the estimation is performed based on this map. The map data indicates that the piezo stack voltage (leak start voltage) and the fuel injection at the time when the ball 123 starts to lift and the fuel starts to flow back to the fuel tank 51 from the injector 1 at each common rail pressure in an experiment or the like in advance are started. And a piezo stack voltage (injection start voltage) at the same time, and an estimated voltage is created so as to fall within a voltage range sandwiched by these two voltages.
This voltage range is a band-like range that rises to the right as shown in FIG. It is a matter of course that the estimated voltage may be given by a function formula in which the piezo stack voltage corresponds to the common rail pressure instead of the map.

Next, the piezo stacks 127A to 127D
The target voltage of the piezo stack voltage as the target charge amount is obtained by subtracting a preset downward correction value from the estimated piezo stack voltage (hereinafter, referred to as a half-lift capable estimated voltage) (step S102). The downward correction value is 20 V in the example shown. And the switching element 24
piezo stack 127A-127D
Is charged until the target voltage is reached (step S103).
Here, the period during which the piezo stacks 127A to 127D are in a charged state (hereinafter, referred to as a piezo stack charged state period) is shorter than a common rail pressure take-in period (hereinafter, referred to as a control period). In the control cycle, the charge state is repeatedly raised. The target voltage of the piezo stack voltage at that time is calculated and updated in steps S106 to S109 described later. The ratio of the piezo stack charging state period to the length of the control cycle (hereinafter referred to as ON duty) is set based on a duty setting map described later, and a smaller value is given as the target voltage is higher.

The control cycle is, for example, 4 ms, and is set shorter than the time during which the ball 123 can maintain the lift state by the fail-safe mechanism.

In step S104, it is determined whether the common rail pressure has been reduced. This is performed based on the difference from the previously taken common rail pressure. If the pressure has not been reduced, the target voltage is updated by adding a predetermined step value to the target voltage (step S105), and step S10 is performed.
Return to 3.

As described above, since the initial value of the target voltage is set lower than the estimated voltage, it is conceivable that the initial value is lower than the leak start voltage. Even if
It is difficult to exceed the injection start voltage. Whether or not such a condition can be achieved depends on the downward correction value that lowers the target voltage.However, if the conditions such as fuel properties are changed in advance to obtain the height deviation width of the half-liftable voltage range, The lower correction value that can satisfy the condition can be obtained.

Then, the first charging (step S103)
Even if the piezo stack voltage is lower than the leak start voltage, the steps S104 and S105 can be performed once or a plurality of times so that the piezo stack voltage can be set within a voltage range in which the half-lift can be performed, thereby preventing erroneous fuel injection. In this way, it is possible to start reducing the common rail pressure.

If the common rail pressure has started decreasing (step S104), it is determined whether the common rail pressure has reached the target pressure (step S106). If a negative determination is made in step S106, the amount of decrease in the piezo stack voltage, which is an appropriate correction value for setting the piezo stack voltage to a value commensurate with the decrease in the injection start voltage due to the decrease in pressure, is set to the value of the common rail pressure in one control cycle. Estimation is performed based on the reduced pressure amount (step S107). For this, a voltage reduction amount estimation map in which the pressure reduction amount and the piezo stack voltage reduction amount are stored in advance in the ROM of the CPU, and estimation is performed based on this map. The map data is created in advance by obtaining the amount of decrease in the half-liftable piezo stack voltage with respect to the amount of decrease in the common rail pressure by experiments or the like. The amount of decrease in the piezo stack voltage tends to rise to the right as shown in FIG. 6 since the piezo stack voltage falls below the injection start voltage as the common rail pressure decreasing speed increases.

In the following step S108, the target voltage is
The target voltage is updated by subtracting the estimated decrease amount.

The ON duty is set based on the target voltage (step S109). This is performed by storing an ON duty setting map in which the ON duty and the target voltage correspond to each other in advance in the ROM of the CPU 31 and estimating based on this map. The map data is created based on the time required before the injection start voltage falls below the piezo stack voltage when the piezo stack voltage is set to the half-liftable voltage at each target voltage in an experiment or the like in advance. . The ON duty has a tendency to decrease to the right as shown in FIG. 7 because the higher the common rail pressure and the higher the target voltage, the earlier the piezo stack voltage falls below the injection start voltage.

After updating the target voltage and the ON duty (steps S108 and S109), the process returns to step S103, and the piezo stacks 127A to 127D are charged.

The CPU 31 sends the O
A charge / discharge timing setting signal is output in synchronization with the control cycle at a length obtained by multiplying the N duty by the control cycle. Also, by outputting a target voltage setting signal having a magnitude proportional to the target voltage, the common rail pressure is reduced.

As a result, after the common rail pressure starts to decrease, the piezo stack 127A is maintained until the common rail pressure reaches the target value.
~ 127D rises to charge state every 4ms and turns ON
The state of charge is maintained for a time defined by the duty. Each time the piezo stack voltage rises to the charged state, steps S107 and S108 are executed, and the piezo stack voltage gradually decreases in a stepwise manner, while the ON duty gradually increases. FIG. 8 shows an example of the change over time of the piezo stack voltage. The first half corresponds to the injection command, and the second half corresponds to the pressure reduction command.

According to the present fuel injection device, the following effects can be obtained. FIG. 9 shows the change over time of the common rail pressure during the pressure reduction control. In the figure, the broken line also shows the case where the ON duty is constant as a comparative example. The pressure is reduced only during the period in which the piezo stacks 127A to 127D are in a charged state. Specifically, the period during which the pressure is reduced and the period at a constant pressure are alternately repeated, but the figure shows a general tendency. . In the comparative example, since the length of the charging state period is constant, the common rail pressure decreases rapidly at the beginning of the depressurization when the common rail pressure is high, and gradually decreases at the end.

On the other hand, in the present invention, the ON duty is set to be small in the initial stage of the depressurization when the common rail pressure is high, so that the deceleration speed of the common rail pressure is averaged.

In the pressure reduction control, if the set target voltage is lower than the leak start voltage, the process proceeds from step S104 to step S105.
Since the target voltage capable of half-lift is reset again, the pressure reduction is performed without delay.

FIG. 10 shows the path followed by the piezo stack voltage along with the reduction of the common rail pressure during the pressure reduction control, and shows both the case of the present invention and the comparative example.
In the comparative example in which the ON duty is constant, the injection start voltage may fall below the piezo stack voltage when the common rail pressure is high and the decrease speed is high as described above.
Since the N duty is suppressed to a small value, the injection start voltage is prevented from being lower than the piezo stack voltage,
The half-lift state can be stably realized.

In the comparative example where the ON duty is constant, it is possible to prevent the injection start voltage from exceeding the piezo stack voltage by reducing the ON duty.
When the common rail pressure approaches the target pressure and the pressure reduction speed decreases, the pressure reduction amount per control cycle cannot be said to be sufficient, and there is a problem that the pressure reduction control is prolonged. In the present invention, since the ON duty increases as the common rail pressure approaches the target pressure, a sufficient pressure reduction amount can be obtained during one control cycle.

The ON duty setting map may be provided for the detected common rail pressure instead of the target voltage.

(Second Embodiment) FIG. 11 is a block diagram mainly showing a piezo actuator drive circuit of a fuel injection device according to a second embodiment of the present invention. In the first embodiment, the control program executed by the CPU is replaced with another setting, and FIG. 12 shows the control executed by the CPU. In the figure, portions that operate substantially the same as in the first embodiment will be described with the same reference numerals as in the first embodiment.

Although the ON duty is variable in the first embodiment, it is fixed in this embodiment, and is set to, for example, 75%. Then, as shown in FIG. 13, during the piezo stack charging state period, the controller 29A repeatedly turns on and off the switching element 14b as in the case of the injection stop after discharging to the target voltage at the beginning of each control cycle, and discharges with a low discharge current. To gradually reduce the piezo stack voltage. The controller 29A includes the switching element 1
The upper limit value of the discharge current that defines the timing at which the switch 4b is switched from on to off is variable. The lower the upper limit value of the discharge current, the lower the discharge current.
A current upper limit setting signal proportional to the current upper limit is input from the CPU 31A.

In step S110 instead of step S109, the first and last piezo stack voltages in the piezo stack charging state period are adjusted to further optimize the target voltage with respect to the common rail pressure gradually decreasing during the piezo stack charging state period. A difference (hereinafter, referred to as a discharge amount) is set based on the target voltage (step S109). This is C
A discharge amount setting map in which the discharge amount and the target voltage are associated with each other is stored in advance in the ROM of the PU 31A, and setting is performed based on this map. Map data is
A temporal change in which the voltage range in which the half-lift can be performed shifts to the low voltage side with a decrease in the common rail pressure is obtained in advance from the above experiments and the like, and is created based on this. As is known from FIG. 9, the rate of decrease of the common rail pressure is higher as the common rail pressure is higher, so that the shift amount of the voltage range to the lower voltage side is larger. Therefore, the discharge amount tends to rise to the right as shown in FIG.

Since the piezo stack 127 is a capacitive element, the CPU 31A calculates the discharge speed of the piezo stack 127, that is, the current upper limit value based on the amount of discharge.

Thus, during the piezo stack charging state, the piezo stack voltage gradually decreases at a rate defined by the discharge amount. Thereby, during the piezo stack charging state period, even if the injection start voltage falls below the piezo stack voltage given at the beginning of the control cycle due to a decrease in the common rail pressure, a margin to the injection start voltage is secured, and a stable half lift The state is obtained.

FIG. 15 shows the path followed by the piezo stack voltage along with the reduction of the common rail pressure in the present fuel injection device. Since the piezo stack voltage gradually decreases during the piezo stack charging state, the piezo stack voltage becomes lower than the injection start voltage. The common rail pressure decreases while maintaining the margin.

In the present embodiment, the discharge amount is set based on the piezo stack target voltage, but may be set based on the detected common rail pressure. In this case, the discharge amount is set to increase as the common rail pressure increases. The correspondence between the common rail pressure and the discharge amount may be obtained in advance by experiments or the like.

Further, since the discharge amount is increased in the initial stage of the pressure reduction in which the common rail pressure is high and the injection start voltage decreases rapidly, the margin for the injection start voltage can be sufficiently increased. It is good to do. In this case, the piezo stack charging state period is set to be short so that the piezo stack voltage does not exceed the injection start voltage on the side where the common rail pressure is high, or as in the first embodiment, O
It is preferable to gradually decrease the N duty. In addition, since the discharge amount is fixed, the current upper limit value may be configured to be capable of outputting two types of values, one for discharge when injection is stopped and the other for discharge when the common rail pressure is reduced.

Also, the ON duty until the common rail pressure reduction is started is set to be smaller as the piezo stack target voltage is higher, thereby avoiding erroneous injection when the pressure reduction is started. The ON duty may be fixed to such an extent that it is known whether or not the pressure reduction has started.

When the pressure reduction control is started, the target voltage of the piezo stack is set to a voltage lower than the voltage estimated to be capable of half-lift, and if the pressure reduction is not started, the voltage is gradually increased. Although the erroneous injection is avoided (steps S101 to S105), if the variation in the voltage range of the piezo stack voltage capable of half-lifting is small, steps S102, S104, and S10 are performed.
5 may be omitted, and the pressure reduction control may be started at the piezo stack voltage estimated to be half-liftable from a map or the like.

In this case, instead of setting the piezo stack target voltage based on the common rail pressure reduction amount, the piezo stack target voltage may be set based on the common rail pressure according to the map shown in step S101.

The amount of charge of the piezo stack may be determined not by the piezo stack voltage but by the amount of electric power supplied to the piezo stack.

Further, the injector has a structure in which the driving force generated by the piezo stack is transmitted to the ball via the fuel pressure in the displacement expansion chamber. The present invention can also be applied to a fuel injection device provided with an injector having a configuration in which the piston directly drives the ball.

[Brief description of the drawings]

FIG. 1 is a configuration diagram centering on an injector of a fuel injection device to which the present invention is applied.

FIG. 2 is an overall configuration diagram of the fuel injection device.

FIG. 3 is a circuit diagram of a piezo actuator driving circuit that drives a piezo actuator mounted on the injector.

FIG. 4 is a flowchart showing control in a CPU constituting the fuel injection device.

FIG. 5 is a first graph showing control in a CPU constituting the fuel injection device.

FIG. 6 is a second graph showing control in a CPU constituting the fuel injection device.

FIG. 7 is a third graph showing control in a CPU constituting the fuel injection device.

FIG. 8 is a timing chart showing the operation of the fuel injection device.

FIG. 9 is a first graph showing an operation of the fuel injection device.

FIG. 10 is a second graph showing the operation of the fuel injection device.

FIG. 11 is a circuit diagram of a piezo actuator driving circuit for driving a piezo actuator mounted on an injector of another fuel injection device to which the present invention is applied.

FIG. 12 is a flowchart showing control in a CPU constituting the fuel injection device.

FIG. 13 is a timing chart showing the operation of the fuel injection device.

FIG. 14 is a graph showing control in a CPU constituting the fuel injection device.

FIG. 15 is a graph showing the operation of the fuel injection device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Injector 1a Nozzle part 1b Back pressure control part (back pressure increasing / decreasing means) 1c Piezo actuator 110 Valve room 110a Low pressure port 123 Ball (valve element) 127, 127A, 127B, 127C, 127D Piezo stack 2 Piezo actuator drive circuit 31, 31A CPU (control means) 4 Pressure sensor (pressure detecting means)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F02M 51/06 F02M 51/06 N 55/02 350 55/02 350E 61/10 61/10 DS F16K 31/02 F16K 31/02 A 37/00 37/00 J F term (reference) 3G066 AA07 AB02 AC09 AD07 BA00 BA12 BA22 CC01 CC05T CC08T CC08U CC14 CC53 CC64U CC67 CC68U CC70 CE13 CE27 CE34 CE35 DA06 DC06 DC18 3G301 HA02 JA11 JA37 KA17 LB11 LC05 LC06 LC10 MA28 PB08Z PG02Z 3H062 AA02 AA16 BB10 BB33 CC07 DD01 EE06 FF41 HH10 3H065 AA01 BA01 CA01 CA03 CA07

Claims (5)

[Claims] A high-pressure fuel stored in a common rail is supplied to inject the fuel from the injection hole; and a needle is provided to introduce the fuel from the common rail. A back pressure chamber for generating back pressure, and a valve body disposed in a valve chamber interposed between the back pressure chamber and the low pressure source so that the port on the low pressure source side can be closed. Back pressure increasing / decreasing means for reducing the pressure in the back pressure chamber as the amount increases, and a piezo stack for pressing and driving the valve element, the lift amount of the valve element increases as the charge amount of the piezo stack increases. An injector having a piezo actuator for increasing the current; an energizing means for energizing the piezo stack to charge and discharge the piezo stack; a pressure detecting means for detecting a fuel pressure in a common rail; In response to a fuel injection command, the valve body is switched between a seated state and a full lift state to open and close the needle, and a fuel pressure reduction command in the common rail is controlled. A control means for setting a target charge amount in accordance with the detected fuel pressure, and for setting the valve body to a lift state while the needle is in a seated state, wherein the control means comprises: In a cycle, the piezo stack rises to a charged state at a target charge amount set according to the detected fuel pressure, and in the energization control for the pressure reduction command, the higher the detected fuel pressure, the higher the piezo stack The fuel injection device is set so that the length of the period during which the battery is in a charged state is shortened. 2. A nozzle portion having a needle for opening and closing an injection hole, wherein a high-pressure fuel stored in a common rail is supplied, and the fuel is injected from the injection hole. A back pressure chamber for generating back pressure, and a valve body disposed in a valve chamber interposed between the back pressure chamber and the low pressure source so that the port on the low pressure source side can be closed. Back pressure increasing / decreasing means for reducing the pressure in the back pressure chamber as the amount increases, and a piezo stack for pressing and driving the valve element, the lift amount of the valve element increases as the charge amount of the piezo stack increases. An injector having a piezo actuator for increasing the current; an energizing means for energizing the piezo stack to charge and discharge the piezo stack; a pressure detecting means for detecting a fuel pressure in a common rail; In response to a fuel injection command, the valve body is switched between a seated state and a full lift state to open and close the needle, and a fuel pressure reduction command in the common rail is controlled. A control means for setting a target charge amount in accordance with the detected fuel pressure and for setting the valve body in a lift state while the needle is in a seated state, wherein the control means comprises: In the energization control in response to the command, the charge amount during a period in which the piezo stack rises to a charged state at a predetermined cycle at a target charge amount set according to the detected fuel pressure, and the piezo stack is in a charged state. Is set so as to gradually decrease the target charge amount as an initial value. 3. The fuel injection device according to claim 1, wherein, in the energization control in response to the pressure reduction command, the target charging amount decreases as the pressure reduction speed of the fuel pressure in the common rail increases. Fuel injection device set to be. 4. A nozzle portion having a needle for opening and closing an injection hole, wherein a high-pressure fuel stored in a common rail is supplied to inject the fuel from the injection hole, A back pressure chamber for generating back pressure, and a valve body disposed in a valve chamber interposed between the back pressure chamber and the low pressure source so that the port on the low pressure source side can be closed. Back pressure increasing / decreasing means for reducing the pressure in the back pressure chamber as the amount increases, and a piezo stack for pressing and driving the valve element, the lift amount of the valve element increases as the charge amount of the piezo stack increases. An injector having a piezo actuator for increasing the current; an energizing means for energizing the piezo stack to charge and discharge the piezo stack; a pressure detecting means for detecting a fuel pressure in a common rail; The amount of charge of the piezo stack is adjusted by controlling the energization by the step, and in response to a fuel injection command, the valve is switched between a seated state and a full lift state to open and close the needle, and the common rail Control means for setting a target charge amount in accordance with the detected fuel pressure in response to a command to reduce the fuel pressure inside, and for setting the valve body to a lift state while the needle is in a seated state. The control means, in the energization control for the pressure reduction command, the charge amount of the piezo stack that can put the valve body in the lift state while the needle is in the seated state based on the detected fuel pressure, The charge amount lower than the estimated charge amount is set as an initial value, and the target charge amount is set so as to gradually increase until the detected fuel pressure starts to decrease. Fuel injector. 5. The fuel injection device according to claim 4, wherein
A fuel injection device, wherein the control means is set such that, in energization control in response to the pressure reduction command, the longer the fuel pressure in the common rail is, the shorter the period of the state of charge is.