JP4154857B2 - Fuel injection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to pressure reduction control of fuel pressure in a como rail of a fuel injection device.
[0002]
[Prior art]
A common rail type fuel injection device stores fuel boosted 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 configurations of the injector, the needle that opens and closes the nozzle hole of the nozzle portion is raised and lowered by increasing or decreasing the back pressure to switch between injection and stop, and the back pressure is obtained from the fuel from the common rail There is something. The back pressure is increased or decreased by the following means. That is, a valve body is provided between a back pressure chamber in which fuel is introduced from a common rail and generates a back pressure and a low pressure source such as a fuel tank, and a valve body for opening and closing a port on the low pressure source side in the valve chamber When the valve body is lifted, the back pressure chamber communicates with the low pressure source to reduce 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 body, a two-way valve or a three-way valve can be used.
[0004]
As an actuator for driving a valve body, a piezo actuator using a piezoelectric action of a piezoelectric material such as PZT has recently 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 extends by charging, and the port is closed to drive the valve body to lift it from the valve seat. Switching of the operation of the piezo actuator is performed by a control means such as a microcomputer controlling energization means for charging and discharging the piezo stack.
[0005]
[Problems to be solved by the invention]
By the way, in the common rail type fuel injection device, the fuel pressure in the common rail is controlled by adjusting the pumping amount of the fuel to the common rail so as to obtain the optimal injection pressure corresponding to the operation condition together with the fuel injection control. However, if the operating condition suddenly changes from a condition requiring high injection pressure (high pressure and high load) to a condition requiring relatively low pressure injection pressure (low pressure and low load), the fuel pressure in the common rail cannot be reduced. If fuel is injected in this pressure state, noise may be generated or exhaust may be deteriorated. Therefore, it is necessary not only to reduce the pumping amount of the common rail, but also to actively flow out high-pressure fuel from the common rail.
[0006]
As described above, in the configuration in which the injector uses the fuel from the common rail as the control oil, the valve body is lifted with the needle seated to reduce the fuel pressure in the common rail, and the fuel in the back pressure chamber is released. (JP 2000-161170 A). The back pressure of the needle in the closed state is sufficiently higher than the pressure at which the needle can be opened, 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 brought into a lift state (half lift) that does not reach the full lift as in the needle opening / closing control, the amount of decrease in the pressure in the back pressure chamber is small. Therefore, the fuel in the common rail is returned to the fuel tank through the injector and the fuel pressure in the common rail is reduced by setting the valve body to a half lift within the range where the back pressure of the needle does not fall below the needle openable pressure. become.
[0007]
In order to realize the half lift of the valve body when the injector is mounted with the piezo actuator, it is charged to a charge level that can withstand the fuel pressure in the valve chamber equal to the fuel pressure in the common rail in order to lift the valve body from the seated state. On the other hand, it is necessary not to exceed a charge amount (injection start charge amount) at which the needle lifts and fuel injection starts.
[0008]
However, when the valve body is in the seated state, 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 approximately equal to the fuel pressure in the common rail, so it acts in the seating direction. The unbalanced pressure is overwhelmingly dominant. On the other hand, once the valve body is lifted, the fuel pressure in the valve chamber decreases and the pressure receiving surface of the valve body where the fuel pressure acts in the lift direction increases, so that the force acting in the seating direction acts in the lift direction. The unbalanced pressure state is relieved.
[0009]
This relaxation of the unbalanced pressure state acts in a direction that promotes the extension of the piezo stack, so the charge amount that the valve body lifts and the fuel starts to return from the back pressure chamber to the fuel tank (leak start charge amount) By slightly exceeding the value, the lift amount of the valve body is relatively large, and there is not much difference between the leakage start charge amount and the injection start charge amount.
[0010]
Further, since the urging force acting on the valve body in the seating direction is weakened as the pressure is reduced, the injection start charge amount is also reduced.
[0011]
For this reason, it is not always easy to set the charge amount of the piezo stack when the common rail is decompressed by the half lift of the valve body.
[0012]
The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a fuel injection device capable of satisfactorily depressurizing a common rail by a half lift of a valve body by setting a charge amount of a piezo stack to an appropriate value. And
[0013]
[Means for Solving the Problems]
According to the first aspect of the present invention, the nozzle has a needle for opening and closing the nozzle hole, the high-pressure fuel stored in the common rail is supplied, and the fuel is introduced from the common rail. A back pressure chamber for generating back pressure of the needle; 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 lowering the pressure of the back pressure chamber as the body lift amount increases, and a piezo stack that presses and drives the valve body, the larger the charge amount of the piezo stack, An injector having a piezo actuator that increases the lift amount;
Energizing means for energizing the piezo stack to charge and discharge the piezo stack;
Pressure detecting means for detecting the fuel pressure in the common rail;
The energization means controls the energization, and in response to a fuel injection command, the valve body is switched between a seating state and a full lift state to open and close the needle, and in response to a fuel pressure reduction command in the common rail. And a control means for setting a target charge amount according to the detected fuel pressure, and for setting the valve body in a lift state while the needle is in a seated state,
In the energization control for the depressurization command, the detected fuel is detected so that the piezo stack rises to a charged state with a target charge amount set according to the detected fuel pressure at a predetermined cycle. It sets so that the length of the period when the said piezo stack is in a charge state may become short, so that a pressure is high.
[0014]
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 pressure reduction speed is high, the injection start charge amount is also quickly reduced. In the present invention, as the fuel pressure is higher, the length of the period in which the piezo stack is in the charged state is shortened, and it is possible to avoid the injection start charge amount being lower than the actual charge amount of the piezo stack.
[0015]
In a second aspect of the present invention, the nozzle has a needle for opening and closing the nozzle hole, and a high-pressure fuel stored in the common rail is supplied to inject the fuel from the nozzle hole, and the fuel is introduced from the common rail. A back pressure chamber for generating back pressure of the needle; 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 lowering the pressure of the back pressure chamber as the body lift amount increases, and a piezo stack that presses and drives the valve body, the larger the charge amount of the piezo stack, An injector having a piezo actuator that increases the lift amount;
Energizing means for energizing the piezo stack to charge and discharge the piezo stack;
Pressure detecting means for detecting the fuel pressure in the common rail;
The energization means controls the energization, and in response to a fuel injection command, the valve body is switched between a seating state and a full lift state to open and close the needle, and in response to a fuel pressure reduction command in the common rail. And a control means for setting a target charge amount according to the detected fuel pressure, and for setting the valve body in a lift state while the needle is in a seated state,
In the energization control with respect to the decompression command, the control means is configured to charge the piezo stack in a charged state with a target charge amount set according to the detected fuel pressure in a predetermined cycle. The charging amount during the period in the state is set so as to gradually decrease with the target charging amount as an initial value.
[0016]
The charge amount of the piezo stack gradually decreases as the common rail pressure decreases, so that there is a margin up to the injection start charge amount. In addition, since the leak start charge amount also falls because the force acting on the valve body in the valve closing direction is weakened, a margin for the leak start charge amount is secured.
[0017]
According to a third aspect of the present invention, in the configuration of the first or second aspect of the invention, in the energization control with respect to the pressure reduction command, the target charge amount decreases as the pressure reduction speed of the fuel pressure in the common rail increases. Set as follows.
[0018]
If the pressure reduction rate of the fuel pressure in the common rail varies due to factors such as fluctuations in fuel properties and individual differences among injectors, the time until the injection start charge falls below the charge of the piezo stack even if the fuel pressure in the common rail is the same. The margin is small. In the present invention, the target charge amount is set smaller as the pressure reduction speed of the fuel pressure in the common rail is larger. Therefore, even if the correspondence between the charge amount that can be half-lifted and the common rail pressure varies, the injection start charge amount is the piezo stack. It is possible to secure a time margin until the amount of charge falls below.
[0019]
According to a fourth aspect of the present invention, the nozzle has a needle that opens and closes the nozzle hole, the high-pressure fuel stored in the common rail is supplied and the nozzle is injected from the nozzle hole, and the fuel is introduced from the common rail. A back pressure chamber for generating back pressure of the needle; 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 lowering the pressure of the back pressure chamber as the body lift amount increases, and a piezo stack that presses and drives the valve body, the larger the charge amount of the piezo stack, An injector having a piezo actuator that increases the lift amount;
Energizing means for energizing the piezo stack to charge and discharge the piezo stack;
Pressure detecting means for detecting the fuel pressure in the common rail;
The amount of charge of the piezo stack is adjusted by controlling energization by the energization means, and in response to the fuel injection command, the valve body is switched between a seating state and a full lift state to open and close the needle, A fuel having a control means for setting a target charge amount according to the detected fuel pressure and setting the valve body in a lifted state while the needle is seated in response to a command to reduce the fuel pressure in the common rail An injection device,
In the energization control with respect to the pressure reducing command, the control means estimates a charge amount of the piezo stack that can bring the valve body into a lifted state (half lift) based on the detected fuel pressure while the needle is in a seated state, A charge amount lower than the estimated charge amount is set as an initial value so that the target charge amount gradually increases until the detected fuel pressure starts to decrease.
[0020]
By gradually increasing the target charge amount from a charge amount that is lower than the estimated charge amount that can be a half lift, even if the injection start charge amount fluctuates due to factors such as fluctuations in fuel properties or individual differences in the injector, an error will occur. It is possible to set the charge amount that can be half lifted while avoiding injection.
[0021]
According to a fifth aspect of the present invention, in the configuration of the fourth aspect of the present invention, in the energization control for the pressure reducing command, the control means is configured such that the period of the charging state is shorter as the fuel pressure in the common rail is higher. Set as follows.
[0022]
The higher the fuel pressure in the common rail when starting decompression, the higher the decompression speed at the start of decompression, and the faster the injection start charge amount decreases. In the present invention, as the fuel pressure is higher, the length of the period in which the piezo stack is in the charged state is shortened, and it is possible to avoid the injection start charge amount being lower than the actual charge amount of the piezo stack.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 2 shows the configuration of a common rail fuel injection device for a diesel engine to which the present invention is applied. The number of injectors 1 corresponding to the number of cylinders of the diesel engine is provided corresponding to each cylinder (only one injector 1 is shown in the figure), and fuel is supplied from a common common rail 54 communicated via a supply line 55. The 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 pumped to the common rail 54 by the high-pressure supply pump 53 and stored at a high pressure.
[0024]
The fuel supplied from the common rail 54 to the injector 1 is used not only for injection into the combustion chamber, but also as control hydraulic pressure of the injector 1 and returns to the fuel tank 51 from the injector 1 via a low-pressure drain line 56. It is supposed to be.
[0025]
The CPU 31 calculates a fuel injection timing and an injection amount based on a detection signal such as a crank angle, and a piezo actuator drive for driving a piezo actuator mounted on each injector 1 according to an injection command corresponding to the fuel injection timing. Output to circuit 2. The injection signal is a binary signal composed of “H” and “L”, and fuel is injected from the injector 1 for a predetermined period.
[0026]
Further, the CPU 31 performs control so as to obtain an appropriate injection pressure according to the operating conditions known from other sensor inputs. A pressure sensor 4 as pressure detecting means is provided on the common rail 54, and a common rail pressure detection signal 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 pumped to the common rail 54. In addition, when the common rail pressure needs to be suddenly reduced, the CPU 31 generates a pressure reduction command internally, performs energization control different from that at the time of fuel injection on the piezo actuator drive circuit 2, and controls the injector 1 as will be described later. The fuel as oil is returned to the fuel tank 51 to reduce the common rail pressure.
[0027]
FIG. 1 shows the structure of the injector 1. The injector 1 is a rod-like body, and is attached so that a lower portion in the drawing penetrates a combustion chamber wall (not shown) of the engine and protrudes into the combustion chamber. The injector 1 includes a nozzle portion 1a, a back pressure control portion 1b, and a piezo actuator 1c in order from the bottom.
[0028]
A needle 121 is slidably held at its rear end in a sleeve-like body 104 of the nozzle portion 1a, and the needle 121 is seated on or separated from an annular sheet 1041 formed at the tip of the nozzle body 104. . High pressure fuel is introduced from the common rail 54 into the outer peripheral space 105 at the tip of the needle 121 through the high pressure passage 101, and fuel is injected from the injection hole 103 when the needle 121 is lifted. Fuel pressure from the high-pressure passage 101 acts on the annular step surface 1211 of the needle 121 in the lift direction (upward).
[0029]
Fuel as control oil is introduced from the high-pressure passage 101 through the in-orifice 107 behind the needle 121, and a back pressure chamber 106 that generates the back pressure of the needle 121 is formed. This back pressure acts on the rear end surface 1212 of the needle 121 together with the spring 122 disposed in the back pressure chamber 106 in the seating direction (downward).
[0030]
The back pressure is increased or decreased by a back pressure control unit 1 b, and the back pressure control unit 1 b is driven by a piezo actuator 1 c including the piezo stack 127.
[0031]
The back pressure chamber 106 is always in communication with the valve chamber 110 of the back pressure control unit 1b through an out orifice 109. The valve chamber 110 has a conical shape with the ceiling surface 1101 facing upward, and a low pressure port 110 a communicating with the low pressure chamber 111 is opened at the top of the ceiling surface 1101, and the low pressure chamber 111 communicates with the drain line 56. It communicates with the low pressure passage 102. A high-pressure port 110 b communicating with the high-pressure passage 101 through the high-pressure control passage 108 is opened at the bottom surface of the valve chamber 110.
[0032]
In the valve chamber 110, a ball 123 whose lower portion is cut horizontally is disposed. The ball 123 is a vertically movable valve body. When the ball 123 is lowered, the ball 123 is seated on a valve chamber bottom surface (hereinafter, referred to as a high pressure side seat) 1102 as a valve seat with the cut surface, thereby closing the high pressure port 110b. Is shut off from the low pressure chamber 111 by being seated on the ceiling surface (hereinafter referred to as a low pressure side seat) 1101 as a valve seat and closing the low pressure port 110a. . As a result, when the ball 123 is lowered, the back pressure chamber 106 communicates with the low pressure chamber 111 via the out orifice 109 and the valve chamber 110, the back pressure of the needle 121 decreases, and the needle 121 is separated. On the other hand, when the ball 123 is raised, the back pressure chamber 106 is cut off from the low pressure chamber 111 and communicates only with the high pressure passage 101, the back pressure of the needle 121 rises and the needle 121 is seated.
[0033]
The ball 123 is pressed and driven by the piezo actuator 1c. In the piezo actuator 1c, two pistons 124 and 125 having different diameters are slidably held in a vertical hole 112 formed in the vertical direction above the low pressure chamber 111, and the piezo stack 127 is disposed above the large-diameter piston 125 on the upper side. Are arranged with the up-down direction as the expansion / contraction direction.
[0034]
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 and is displaced in the vertical direction by the same amount as the amount of expansion and contraction of the piezo stack 127.
[0035]
A space defined by the lower small-diameter piston 124, the large-diameter piston 125, and the vertical hole 112 facing the ball 123 is filled with fuel to form a displacement expansion chamber 113. The expansion of the piezo stack 127 increases the diameter. When the piston 125 is displaced downward to press the fuel in the displacement expansion chamber 113, the pressing force is transmitted to the small diameter piston 124 through 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 extension amount of the piezo stack 127 is expanded and converted into the displacement of the small-diameter piston 124.
[0036]
At the time of fuel injection, first, the piezo stack 127 is charged and the piezo stack 127 is extended, whereby the small-diameter piston 124 is lowered to push down the ball 123. As a result, the ball 123 lifts from the low pressure side seat 1101 and is seated 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 seating direction becomes more dominant than the force acting on the seating direction, and the needle 121 is seated and fuel injection is started.
[0037]
On the contrary, when the injection is stopped, the piezo stack 127 is reduced by the discharge of the piezo stack 127 and the pushing force to the ball 123 is released. At this time, the inside of the valve chamber 110 is at a low pressure, and high pressure fuel pressure is applied to the bottom surface of the ball 123 from the high pressure control passage 108, so that upward fuel pressure is applied to the ball 123 as a whole. is doing. Then, by releasing the pushing force to the ball 123, the ball 123 is separated from the high pressure side seat 1102 and is seated again on the low pressure side seat 1101, and the fuel pressure in the valve chamber 110 is increased. Stops.
[0038]
Further, as will be described later, the injector 1 lifts the ball 123 while the needle 121 is seated to return the fuel to the fuel tank 51, and is also used for sudden pressure reduction of the common rail pressure.
[0039]
FIG. 3 shows the configuration of a piezo actuator drive circuit 2 that is an energizing means for charging and discharging the piezo stack 127. For convenience of explanation, the piezo stack 127 is appropriately represented as piezo stack 127A, piezo stack 127B, piezo stack 127C, and piezo stack 127D corresponding to the four cylinders. The piezo actuator drive circuit 2 supplies a DC power source 21 by a DC-DC converter 211 that generates a DC voltage of several tens to several hundreds V by power supply (+ B) of an in-vehicle battery, and a buffer capacitor 212 connected in parallel to the output terminal. 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, and generates a back electromotive force when the switching element 2112 is turned off via the diode 2113. Thus, the buffer capacitor 212 is charged. The buffer capacitor 212 has a sufficiently large capacitance, and maintains a substantially constant voltage value even when the piezo stacks 127A to 127D are charged.
[0040]
A first energization path 22a for energizing the piezo stacks 127A to 127D from the buffer capacitor 212 of the DC power supply 21 via the inductor 23 is provided. In the energization path 22a, these are connected in series between the buffer capacitor 212 and the inductor 23. A first switching element 24a is interposed. The first switching element 24 a is configured by a MOSFET, and the parasitic diode (hereinafter referred to as the first parasitic diode) 241 a is connected so as to be reverse-biased with respect to the voltage across the buffer capacitor 212. Further, the inductor 23 and the piezo stacks 127A to 127D form a second energization path 22b. The energization path 22b includes a second switching element 24b connected to a midpoint of connection between the inductor 23 and the first switching element 24a, and includes the inductor 23, the piezo stacks 127A to 127D, and the second switching element 24b. A closed circuit is formed. The second switching element 24b is also composed of a MOSFET, and the parasitic diode (hereinafter referred to as second parasitic diode) 241b is connected so as to be reverse-biased with respect to the voltage across the buffer capacitor 212.
[0041]
The energization paths 22a and 22b are common to each of the piezo stacks 127A to 127D, and the piezo stacks 127A to 127D as driving objects can be selected as follows. Each of the piezo stacks 127A to 127D is connected in series with switching elements (hereinafter referred to as selective switching elements as appropriate) 25A, 25B, 25C, 25D, 25E, and 25F, of which the first type of selective switching elements. 25A to 25D are connected to the piezo stacks 127A to 127D in a one-to-one correspondence, 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.
[0042]
In the second type of selective switching elements 25E and 25F, the selective switching element 25E is commonly connected to the piezo stack 127A and the piezo stack 127B, and the selective switching element 25F is commonly connected to the piezo stack 127C and the piezo stack 127D. Is done. The second type of selective switching elements 25E and 25F have two piezo stacks including the piezo stacks 127A to 127D even if any of the piezo stacks 127A to 127D can be controlled by the selective switching elements 25A to 25D. 127A, 127B or piezo stacks 127C, 127D are separated from the piezo actuator drive circuit 2 to ensure the operation of the remaining two piezo stacks 127C, 127D or piezo stacks 127A, 127B (Limp form).
[0043]
MOSFETs are used for the selection switching elements 25A to 25F, and the parasitic diodes (hereinafter referred to as selection parasitic diodes) 251A, 251B, 251C, 251D, 251E, and 251F are reversely biased with respect to the buffer capacitor 212. It is connected to the.
[0044]
Control signals are input from the controller 29 to the gates of the switching elements 24a, 24b, and 25A to 25F. As described above, any of the selective switching elements 25A to 25D is turned on to drive the piezo stacks 127A to 127D to be driven. Is selected, and a pulsed control signal is input to the gates of the switching elements 24a and 24b to turn on and off the switching elements 24a and 24b, thereby performing charge control and discharge control of the piezo stacks 127A to 127D. Yes.
[0045]
Also, a relatively low resistance resistor 27E is provided in series with the piezo stack 127A and the piezo stack 127B, and a resistor 27F that is the same as the resistor 27E is provided in series with the piezo stack 127C and the piezo stack 127D. is there. The voltage between both ends is input to the controller 29, and the charging currents of the piezo stacks 127A to 127D are detected.
[0046]
The second switching element 24b is provided with a resistor 28 having a relatively low resistance in series. The voltage between both ends is input to the controller 29, and the discharge currents of the piezo stacks 127A to 127D are detected.
[0047]
The controller 29 is input with voltages at both ends of each of the piezo stacks 127A to 127D (hereinafter referred to as piezo stack voltage), which is a charge amount.
[0048]
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 is caused to flow through the first energization path 22a. When the charging current reaches the preset upper limit current value, the switching element 24a is turned off and the off period starts. At this time, since the back electromotive force generated in the inductor 23 is forward biased with respect to the parasitic diode 241b of the second switching element 24b, the flywheel gradually decreases to the second energization path 22b by the energy accumulated in the inductor 23. Current flows and charging of the piezo stacks 127A to 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 off, and charging is completed. By charging the piezo stacks 127 </ b> A to 127 </ b> D in this way, the piezo stacks 127 </ b> A to 127 </ b> D are extended to press and lift the ball 123 through the displacement expansion chamber 113.
[0049]
In 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 to allow a gradually increasing discharge current to flow through the second energization 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 and an off period starts. 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 energization path 22 a by the energy accumulated in the inductor 23 and the energy is recovered in the buffer capacitor 212. When the discharge current reaches the lower limit current value (approximately 0), the second switching element 24b is turned on again, and this is repeated. When the piezo stack voltage reaches 0, the switching element 24b is fixed off, and the discharge is completed. By discharging the piezo stacks 127A to 127D in this way, the piezo stacks 127A to 127D are contracted, the pressing force to the ball 123 by the fuel pressure in the displacement expansion chamber 113 is released, and the ball 123 is seated.
[0050]
If the piezo stacks 127A to 127D are unable to discharge due to disconnection of a line connecting the piezo stacks 127A to 127D and the piezo actuator driving circuit 2, the fuel injection period specified by the injection signal of the injector 1 is ended. Although the fuel continues to be injected, the injector 1 shown in FIG. 1 includes a mechanical fail-safe mechanism that closes the valve when the piezo stack 127 is in a charged state for 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 generates a pressing force that presses the ball 123. When the ball 123 is in the lifted state, the fuel pressure is The pressure can resist the upward biasing force acting on the ball 123. For this reason, the pressurized fuel in the displacement expansion chamber 113 leaks little by little from the sliding portions of the pistons 124 and 125 to the low pressure portion such as the low pressure chamber 111 and the lift amount of the ball 123 decreases, and the back pressure chamber 106 The flow rate of the fuel that flows into the low pressure chamber 111 decreases, and as a result, the back pressure gradually increases. Finally, the needle 121 is seated and the fuel injection stops.
[0051]
The controller 29 charges and discharges the piezo stacks 127 </ b> A to 127 </ b> D at a predetermined time according to various control signals from the CPU 31 that controls the entire fuel injection control. As such a control signal, a charge / discharge timing setting signal for defining a charging timing and a discharging timing is input. The charge / discharge timing setting signal is a binary signal composed of “L” and “H”, and charging of the piezo stacks 127A to 127D is started at the rising edge, and the piezo stacks 127A to 127D are discharged at the falling edge. The charge / discharge timing setting signal defines the injection period for the injection command.
[0052]
Further, a target voltage setting signal proportional to a target piezo stack voltage (hereinafter referred to as target voltage) that is a target charge amount is input as a control signal, and the controller 29 switches the switching element when the piezo stack voltage reaches the target voltage. 24a is fixed off as described above. The target voltage setting signal is set so that a sufficient piezo stack voltage that allows the ball 123 to be fully lifted is applied to the injection command.
[0053]
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.
[0054]
A control signal for selecting a cylinder to be controlled is also output from the CPU 31, and among the selection switching elements 25A to 25F, the piezo stacks 127A to 127D corresponding to the selected cylinder are turned on.
[0055]
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 a half lift is estimated based on the detected common rail pressure (step S101). The CPU 31 stores in advance a half-liftable voltage estimation map in which the common rail pressure and the piezo stack voltage are associated with each other, and estimates based on this map. The map data shows that the piezo stack voltage (leak start voltage) and fuel injection are started when the ball 123 starts to lift and the fuel starts to return from the injector 1 to the fuel tank 51 at each common rail pressure in advance through experiments or the like. The piezo stack voltage (injection start voltage) is calculated and the estimated voltage falls within the voltage range between the two voltages. As shown in FIG. 5, this voltage range is a band-like range that rises to the right. Needless to say, the estimated voltage may be given by a function expression corresponding to the piezo stack voltage with respect to the common rail pressure, instead of the map.
[0056]
Next, a target voltage of the piezo stack voltage as a target charge amount of the piezo stacks 127A to 127D is obtained by subtracting a preset downward correction value from the estimated piezo stack voltage (hereinafter referred to as a half-liftable estimated voltage) (step). S102). The downward correction value is 20V in the illustrated example. The piezo stacks 127A to 127D are charged until the target voltage is reached by turning on / off the switching element 24a (step S103). Here, a 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), and is once discharged to be in a non-charged state. The battery is repeatedly charged in the control cycle. The target voltage of the piezo stack voltage at that time is calculated and updated in steps S106 to S109 described later. Further, 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.
[0057]
The control cycle is, for example, 4 ms, and is set shorter than the time during which the ball 123 can maintain the lifted state by the fail-safe mechanism.
[0058]
In step S104, it is determined whether or not the common rail pressure has been reduced. This is done based on the difference from the previously acquired common rail pressure. If the pressure is not reduced, the target voltage is updated by adding a predetermined step value to the target voltage (step S105), and the process returns to step S103.
[0059]
As described above, since the initial value of the target voltage is set lower than the estimated voltage, it can be considered that the target voltage is lower than the leakage start voltage. However, the voltage range in which half lift is possible is shifted up and down depending on conditions such as fuel properties. However, it is difficult to exceed the injection start voltage. Whether or not such a condition can be satisfied depends on a downward correction value for lowering the target voltage, but if the height deviation width of the voltage range in which half lift is possible is obtained in advance by changing the conditions such as fuel properties, The downward correction value that can satisfy this condition can be obtained.
[0060]
Even if the piezo stack voltage is lower than the leak start voltage in the first charge (step S103), the piezo stack voltage is placed in a voltage range that can be half-lifted by executing steps S104 and S105 once or a plurality of times. Thus, the common rail pressure can be reduced while avoiding erroneous fuel injection.
[0061]
If the common rail pressure has started to be reduced (step S104), it is determined whether or not 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 pressure reduction, is set to the common rail pressure in one control cycle. Estimate based on the amount of decompression (step S107). In this case, a voltage reduction amount estimation map in which the decompression amount and the piezo stack voltage reduction amount are associated in advance is stored in the ROM of the CPU, and estimation is performed based on this map. The map data is created in advance by determining the amount of decrease in the piezo stack voltage that can be half lifted with respect to the amount of decrease in the common rail pressure through experiments or the like. The amount of decrease in the piezo stack voltage tends to increase to the right as shown in FIG. 6 because the piezo stack voltage soon falls below the injection start voltage as the pressure reduction speed of the common rail pressure increases.
[0062]
In subsequent step S108, the target voltage is updated by subtracting the estimated decrease amount from the target voltage.
[0063]
Further, the ON duty is set based on the target voltage (step S109). This is presumed on the basis of the ON duty setting map in which the ON duty and the target voltage are previously associated with each other in the ROM of the CPU 31. Map data is created based on the time required for the injection start voltage to fall below the piezo stack voltage when the piezo stack voltage is set to a half-liftable voltage at each target voltage in advance by experiments. . As the common rail pressure is higher and the target voltage is higher, the ON duty shows a tendency of lowering to the right as shown in FIG. 7 because the piezo stack voltage soon falls below the injection start voltage.
[0064]
After updating the target voltage and the ON duty (steps S108 and 109), the process returns to step S103, and the piezo stacks 127A to 127D are charged.
[0065]
The CPU 31 outputs a charge / discharge timing setting signal to the controller 29 in a length obtained by multiplying the ON duty by a control cycle in synchronization with the control cycle. Further, the common rail pressure is reduced by outputting a target voltage setting signal having a magnitude proportional to the target voltage.
[0066]
Thus, after the common rail pressure starts to be reduced, the piezo stacks 127A to 127D rise to the charged state every 4 ms until the target value is reached, and maintain the charged state for the time specified by the ON duty. Each time the piezo stack voltage rises to the charged state, steps S107 and S108 are executed and gradually decrease stepwise, while the ON duty gradually increases. FIG. 8 shows an example of the change over time of the piezo stack voltage. The first half is for the injection command, and the second half is for the pressure reduction command.
[0067]
According to this fuel injection device, the following effects are produced. FIG. 9 shows the change over time of the common rail pressure during the pressure reduction control. In the figure, the case where the ON duty is constant is indicated by a broken line as a comparative example. The pressure is reduced only during the period in which the piezo stacks 127A to 127D are in the charged state. Specifically, the pressure reduction period and the constant pressure period 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 rapidly decreases at the beginning of the reduced pressure when the common rail pressure is high, and finally becomes gentle.
[0068]
On the other hand, in the present invention, since the ON duty is set to be small at the beginning of pressure reduction when the common rail pressure is high, the pressure reduction speed of the common rail pressure is averaged.
[0069]
In the pressure reduction control, if the set target voltage is lower than the leakage start voltage, the process proceeds from step S104 to step S105. Therefore, the target voltage that can be half-lifted is reset again, so that the pressure reduction is delayed. Done without.
[0070]
FIG. 10 shows a path followed by the piezo stack voltage as the common rail pressure is reduced during the pressure reduction control, and shows the case of the present invention and the comparative example together. 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 rate of decrease is high as described above. Since the duty is kept small, it is avoided that the injection start voltage falls below the piezo stack voltage, and the half lift state can be realized stably.
[0071]
In the comparative example in which the ON duty is constant, if the ON duty is reduced, it is possible to avoid the injection start voltage exceeding the piezo stack voltage. However, when the common rail pressure approaches the target pressure and the pressure reduction speed becomes low, it is 1 There is a problem that the pressure reduction amount per control cycle is not sufficient, and the pressure reduction control is prolonged. In the present invention, the ON duty increases as the common rail pressure approaches the target pressure, so that a sufficient amount of pressure reduction can be obtained during one control cycle.
[0072]
It should be noted that the ON duty setting map may be applied to the detected common rail pressure instead of the target voltage.
[0073]
(Second Embodiment)
FIG. 11 shows a configuration diagram centering on a piezoelectric 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 contents executed by the CPU. In the figure, parts that operate substantially the same as in the first embodiment will be described with the same numbers as in the first embodiment.
[0074]
Although the ON duty is variable in the first embodiment, it is fixed in this embodiment, and is set to 75%, for example. Then, as shown in FIG. 13, in the piezo stack charging state period, the controller 29A rises to the target voltage at the beginning of each control cycle, and then repeatedly turns on and off the switching element 14b at the time of injection stop to discharge with a low discharge current. Thus, the piezo stack voltage is gradually reduced. In the controller 29A, the current upper limit value of the discharge current that defines the timing of switching the switching element 14b from on to off is variable, and the discharge current is lowered by lowering the current upper limit value. A current upper limit setting signal proportional to the current upper limit value is input from the CPU 31A.
[0075]
In step S110 instead of step S109, in order to further optimize the target voltage with respect to the common rail pressure that gradually decreases even during the piezo stack charging state period, the difference between the first and last piezo stack voltage in the piezo stack charging state period (hereinafter referred to as the piezo stack charging state period). , Discharge amount) is set based on the target voltage (step S109). In this case, 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 CPU 31A, and is set based on this map. The map data is created based on the change over time in which the voltage range in which half lift is possible shifts to the low voltage side as the common rail pressure decreases, based on the above-described experiment. As can be seen from FIG. 9, the higher the common rail pressure, the larger the common rail pressure reduction speed. Therefore, the amount of shift of the voltage range to the low voltage side is also large. Therefore, the discharge amount tends to rise to the right as shown in FIG.
[0076]
Since the piezo stack 127 is a capacitive element, the CPU 31A calculates the discharge rate of the piezo stack 127, and thus the current upper limit value, based on this discharge amount.
[0077]
Thus, the piezo stack voltage gradually decreases at a rate defined by the discharge amount during the piezo stack charge state period. As a result, 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 common rail pressure, a margin to the injection start voltage is ensured, and stable half lift A state is obtained.
[0078]
FIG. 15 shows a path followed by the piezo stack voltage as the common rail pressure is reduced in this fuel injection device. Since the piezo stack voltage gradually decreases during the piezo stack charging state, the margin of the piezo stack voltage with the injection start voltage is shown. The common rail pressure decreases while maintaining
[0079]
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 through experiments or the like.
[0080]
In addition, since the discharge amount is increased in the early stage of pressure reduction where the common rail pressure is high and the injection start voltage is rapidly reduced, a sufficient margin for the injection start voltage can be obtained, but the discharge amount can be fixed. Good. In this case, it is preferable that 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 the ON duty is gradually decreased as in the first embodiment. Since the discharge amount is fixed, the current upper limit value may be configured so that two types of output can be output, one for discharging when the injection is stopped and one for discharging when the common rail pressure is reduced.
[0081]
In addition, the ON duty until the pressure reduction of the common rail pressure is also set to be smaller as the piezo stack target voltage is higher to avoid erroneous injection when the pressure reduction is started, but the pressure reduction starts. The ON duty may be fixed to such an extent that it is known whether or not it has been done.
[0082]
Also, at the start of decompression control, the piezo stack target voltage is set to a voltage lower than the voltage that is estimated to be capable of half-lift, and if the decompression is not started, it is gradually increased to prevent erroneous injection due to fluctuations in fuel properties, etc. If it is avoided (steps S101 to S105) that the fluctuation in the voltage range of the piezo stack voltage that can be half-lifted is small, steps S102, S104, and S105 are omitted, and it is estimated that half-lifting is possible from a map or the like. The decompression control may be started with the piezo stack voltage.
[0083]
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.
[0084]
Further, the charge amount of the piezo stack may be determined by using not the piezo stack voltage but the amount of power supplied to the piezo stack as an index.
[0085]
The injector is configured such that the driving force generated by the piezo stack is transmitted to the ball via the fuel pressure in the displacement expansion chamber. However, the present invention has a single piston that is pressed by the piezo stack without the displacement expansion chamber. The present invention can also be applied to a fuel injection device including an injector configured to directly press and drive a 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 drive 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 the 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]
1 Injector
1a Nozzle part
1b Back pressure control unit (back pressure increasing / decreasing means)
1c Piezo actuator
110 Valve chamber
110a Low pressure port
123 Ball (valve)
127, 127A, 127B, 127C, 127D Piezo stack
2 Piezo actuator drive circuit
31, 31A CPU (control means)
4 Pressure sensor (pressure detection means)

Claims (5)

A nozzle having a needle that opens and closes the nozzle hole, is supplied with high-pressure fuel stored in a common rail, and injects the fuel from the nozzle hole, and fuel is introduced from the common rail to generate a back pressure of the needle The valve body is disposed in a back pressure chamber and 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, and the lift amount of the valve body is increased. And a back pressure increasing / decreasing means for decreasing the pressure of the back pressure chamber according to the present invention, and a piezo actuator having a piezo stack that presses and drives the valve body and increasing the lift amount of the valve body as the charge amount of the piezo stack increases. An injector with
Energizing means for energizing the piezo stack to charge and discharge the piezo stack;
Pressure detecting means for detecting the fuel pressure in the common rail;
The energization means controls the energization, and in response to a fuel injection command, the valve body is switched between a seating state and a full lift state to open and close the needle, and in response to a fuel pressure reduction command in the common rail. And a control means for setting a target charge amount according to the detected fuel pressure, and for setting the valve body in a lift state while the needle is in a seated state,
In the energization control for the depressurization command, the detected fuel is detected so that the piezo stack rises to a charged state with a target charge amount set according to the detected fuel pressure at a predetermined cycle. The fuel injection device, wherein the length of the period in which the piezo stack is in a charged state is shortened as the pressure is increased. A nozzle having a needle that opens and closes the nozzle hole, is supplied with high-pressure fuel stored in a common rail, and injects the fuel from the nozzle hole, and fuel is introduced from the common rail to generate a back pressure of the needle The valve body is disposed in a back pressure chamber and 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, and the lift amount of the valve body is increased. And a back pressure increasing / decreasing means for decreasing the pressure of the back pressure chamber according to the present invention, and a piezo actuator having a piezo stack that presses and drives the valve body and increasing the lift amount of the valve body as the charge amount of the piezo stack increases. An injector with
Energizing means for energizing the piezo stack to charge and discharge the piezo stack;
Pressure detecting means for detecting the fuel pressure in the common rail;
The energization means controls the energization, and in response to a fuel injection command, the valve body is switched between a seating state and a full lift state to open and close the needle, and in response to a fuel pressure reduction command in the common rail. And a control means for setting a target charge amount according to the detected fuel pressure, and for setting the valve body in a lift state while the needle is in a seated state,
In the energization control with respect to the decompression command, the control means is configured to charge the piezo stack in a charged state with a target charge amount set according to the detected fuel pressure in a predetermined cycle. A fuel injection device characterized in that a charge amount during a period in a state is set to gradually decrease with a target charge amount as an initial value. 3. The fuel injection device according to claim 1, wherein, in the energization control with respect to the pressure reduction command, the control means is set so that the target charge amount decreases as the pressure reduction speed of the fuel pressure in the common rail increases. Fuel injection device. A nozzle having a needle that opens and closes the nozzle hole, is supplied with high-pressure fuel stored in a common rail, and injects the fuel from the nozzle hole, and fuel is introduced from the common rail to generate a back pressure of the needle The valve body is disposed in a back pressure chamber and 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, and the lift amount of the valve body is increased. And a back pressure increasing / decreasing means for decreasing the pressure of the back pressure chamber according to the present invention, and a piezo actuator having a piezo stack that presses and drives the valve body and increasing the lift amount of the valve body as the charge amount of the piezo stack increases. An injector with
Energizing means for energizing the piezo stack to charge and discharge the piezo stack;
Pressure detecting means for detecting the fuel pressure in the common rail;
The amount of charge of the piezo stack is adjusted by controlling energization by the energization means, and in response to the fuel injection command, the valve body is switched between a seating state and a full lift state to open and close the needle, A fuel having a control means for setting a target charge amount according to the detected fuel pressure and setting the valve body in a lifted state while the needle is seated in response to a command to reduce the fuel pressure in the common rail An injection device,
In the energization control with respect to the depressurization command, the control means estimates the amount of charge of the piezo stack that can bring the valve body into a lift state while the needle is seated based on the detected fuel pressure, and the estimated charge A fuel injection device characterized in that a target charge amount is set to gradually increase until a detected fuel pressure starts to decrease, with a charge amount lower than the amount being an initial value. 5. The fuel injection device according to claim 4, wherein in the energization control with respect to the pressure reduction command, the control means sets the length of the period in the charged state to be shorter as the fuel pressure in the common rail is higher. apparatus.

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