JP4389411B2 - Injection control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a common rail fuel injection device for an internal combustion engine, and more particularly to a pressure reducing mechanism for a fuel injection device using a piezo injector.
[0002]
[Prior art]
In a common rail fuel injection device of a diesel engine, a common pressure accumulating chamber (common rail) is provided in each cylinder to accumulate high pressure fuel pumped from a high pressure pump. In this device, the pumping amount from the high-pressure pump to the common rail is adjusted according to the operating state of the engine such as the common rail pressure, water temperature, and engine speed, and the fuel pressure of the common rail is controlled to the target pressure. Thus, the fuel injection amount is calculated, and the fuel is injected and supplied from the injector to each cylinder at a predetermined timing. At this time, if the fuel injection pressure (the fuel pressure of the common rail) is not appropriate, the fuel consumption and the exhaust purification performance will be reduced, and noise will be generated. In order to prevent this, for example, an apparatus provided with a fuel injection pressure adjusting means as described in JP-A-2-191865 has been proposed.
[0003]
The adjustment of the common rail pressure is normally performed by increasing the pumping amount to the common rail from the fuel injection amount when increasing the pressure, and decreasing the fuel injection amount or stopping the pumping when decreasing the pressure. However, for example, when the accelerator is operated again after a sudden deceleration or restarted immediately after the engine is stopped, the fuel injection is stopped and the fuel is not consumed, so the common rail pressure does not decrease to the target pressure. In the next operation, fuel having a pressure higher than the target pressure is injected. Since this causes the above problem, in the device disclosed in Japanese Patent Laid-Open No. 2-191865, the electromagnetic valve that opens and closes the injector is set to a delay time from the opening of the electromagnetic valve until the nozzle needle actually opens the nozzle hole (invalid The pressure is reduced by performing “empty driving” that is driven in a shorter time width than the injection period). Since the high-pressure fuel in the common rail overflows to the low-pressure side by opening the solenoid valve, the common rail pressure can be quickly reduced without performing fuel injection.
[0004]
On the other hand, as the injector, a solenoid-driven injector as used in the apparatus of Japanese Patent Laid-Open No. 2-191865 has been used, but in recent years, instead of this, a piezo-driven type that is more responsive. The use of this type of injector is under consideration. A piezo-driven injector is a piezo valve that uses a piezoelectric element that expands and contracts when a voltage is applied. The piezo-driven injector can quickly generate an expansion / contraction amount corresponding to the applied voltage to drive the valve element. Therefore, it is expected to improve the controllability of fuel injection.
[0005]
However, due to the high response characteristic of the piezoelectric drive injector, the invalid injection period is much shorter than that of the solenoid drive injector. For this reason, it has been difficult to realize “blank driving” driving that opens and closes the piezo valve in a time width shorter than the invalid injection period. In addition, because it is difficult to perform a large amount of leakage with the “blank drive” drive, it is also known to install a fuel relief valve in the high-pressure part such as a common rail. However, it is necessary to install a new fuel relief valve. It was disadvantageous.
[0006]
Therefore, as a means to adjust the common rail pressure by using a piezo-driven injector, the electric energy injected into the piezo actuator is set lower than that during normal injection, and the opening of the valve body that displaces as the piezo actuator expands A method of generating a fuel leak without generating an injection by adjusting to a half-open position has been studied. According to this method, it can be expected that sufficient pressure reduction is obtained without installing a fuel relief valve.
[0007]
[Problems to be solved by the invention]
However, in the above method, in order to adjust the valve body to a predetermined opening, it is required to adjust the extension amount of the piezoelectric actuator in units of several μm. In addition, the position of the valve body is determined by the balance between the generated force of the piezo actuator and the hydraulic pressure acting on the valve body, that is, the common rail pressure, so if the common rail pressure decreases due to fuel leakage, the balance of the force acting on the valve body There was a risk of mis-injection due to a change in.
[0008]
The present invention has been made in view of the above circumstances, and in a fuel injection device using a piezo injector, when the common rail pressure is required to be reduced, the opening degree of the valve body can be appropriately adjusted to ensure a necessary amount of leakage. Further, it is an object of the present invention to provide a fuel injection device that can perform accurate pressure reduction without causing erroneous injection due to a change in common rail pressure or the like.
[0009]
[Means for Solving the Problems]
A fuel injection device for an internal combustion engine according to claim 1 is a pressure accumulator that stores high-pressure fuel pumped from a high-pressure pump, a piezo-drive injector that injects high-pressure fuel in the accumulator into a cylinder of the internal combustion engine, and operation of the engine. A control unit for controlling the driving of the high-pressure pump and the injector according to the state is provided.
The injector includes a nozzle needle that opens a nozzle hole, a control chamber that causes the pressure of fuel supplied from the pressure accumulating chamber to act on the nozzle needle, and the control that is performed by opening and closing between the control chamber and the leak channel. A control valve for increasing / decreasing the pressure in the chamber, and a piezo that extends by applying a predetermined voltage to open the control valve, and contracts by discharging the charged voltage to close the control valve. A drive unit, the nozzle needle is opened as the control valve is driven, and fuel supplied from the pressure accumulating chamber is injected,
The controller is configured to determine whether or not a decompression condition for reducing the fuel pressure in the pressure accumulating chamber is satisfied based on an operating state of the internal combustion engine;
When the decompression determination means determines that the decompression condition is satisfied, the control valve is half-opened by applying a voltage lower than that during normal injection to the piezoelectric drive unit, and the fuel supplied from the pressure accumulating chamber is A pressure reducing means for reducing the fuel pressure in the pressure accumulating chamber by overflowing to the leak flow path, and a voltage applied to the piezo drive by the pressure reducing means, the control valve leaves the seat position and the nozzle needle is closed. Is set based on the fuel pressure in the pressure accumulating chamber, and an applied voltage adjusting means for changing the setting voltage according to a change in the fuel pressure in the pressure accumulating chamber is provided.
[0010]
In the present invention, the applied voltage adjusting means sets the voltage applied to the piezo drive unit at the time of a pressure reduction request based on the fuel pressure in the pressure accumulating chamber, and the timely setting is changed according to the pressure change. Even if the fuel pressure in the pressure accumulating chamber decreases with the operation of the pressure reducing means, the control valve can always be held at a predetermined half-open position. Therefore, it is possible to secure a necessary leak amount and perform highly accurate decompression control without causing erroneous injection or the like.
[0011]
According to a second aspect of the present invention, pressure detecting means for detecting the fuel pressure in the pressure accumulating chamber is provided at a predetermined time, and the setting change of the applied voltage to the piezo drive unit by the applied voltage adjusting means is performed by the pressure detecting means. It shall be implemented in synchronization with the detection time of the fuel pressure.
[0012]
For example, if the fuel pressure is detected at a predetermined timing based on a crank angle signal of the internal combustion engine, and the setting value of the voltage applied to the piezo drive unit is changed in synchronization with this, the control valve is It can always be adjusted to an optimum position according to the fuel pressure in the pressure accumulating chamber, and the pressure reduction by the pressure reducing means can be effectively performed.
[0013]
Alternatively, as described in claim 3, the setting change of the applied voltage to the piezo drive unit by the applied voltage adjusting means can be carried out every predetermined time. Thus, when the position of the control valve is adjusted with time, there is an advantage that the pressure reduction speed can be made constant regardless of the rotational speed of the internal combustion engine.
[0014]
According to a fourth aspect of the present invention, the applied voltage adjusting means has means for lowering the value of the current flowing to the piezo drive section when applying a voltage to the piezo drive section than during normal injection.
[0015]
For example, when a voltage is applied to the piezo drive unit by a multiple switching method, energization is performed in several times, but in order to reach a predetermined set voltage with high accuracy, the voltage increase amount per time is smaller. Good. Therefore, when a pressure reduction is required, the applied voltage can be controlled with higher accuracy by setting the current energized at a time lower than that during normal injection by the applied voltage adjusting means.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to a common rail fuel injection device of a multi-cylinder diesel engine (hereinafter referred to as an engine) will be described. FIG. 1A is an overall configuration diagram of a common rail fuel injection device. A plurality of piezo drive injectors 1 (one of which is shown in the figure) for supplying fuel to each cylinder of an engine, and each injector 1 A common rail 3 as a pressure accumulation chamber for accumulating fuel supplied to the engine, a high-pressure pump 6 for pumping high-pressure fuel to the common rail 3, and an electronic control device (hereinafter referred to as a control unit) for controlling these according to the operating state of the engine. (Referred to as ECU) 5. The injector 1 is connected to the common rail 3 by a high-pressure pipe 31 and to the fuel tank 7 by a leak pipe 41. The common rail 3 is connected to the high-pressure pump 6 by a high-pressure pipe 32 and to the fuel tank 7 by a leak pipe 42.
[0017]
FIG. 1B is a diagram showing a detailed configuration of the injector 1. A housing 11 of the injector 1 is provided with a cylinder 12 in a lower half portion and slidably accommodates a nozzle needle 13. When it moves upward, the nozzle hole 14 at the lower end of the housing 11 is opened and fuel is injected. A control chamber 15 that applies pressure in the valve closing direction to the nozzle needle 13 is formed at the upper end of the cylinder 12. The nozzle needle 13 moves up and down in the cylinder 12 as the pressure in the control chamber 15 increases and decreases. To do. A spring 17 that urges the nozzle needle 13 in the valve closing direction is disposed in the control chamber 15. The nozzle needle 13 has a slightly smaller diameter at the lower half and forms an annular space that becomes the fuel reservoir 16 between the nozzle needle 13 and receives the pressure in the valve opening direction by the fuel in the fuel reservoir 16. The fuel reservoir 16 communicates with a high-pressure channel 33 connected to the high-pressure pipe 31 and supplies fuel to the nozzle hole 14.
[0018]
A three-way valve 8 serving as a control valve for increasing or decreasing the hydraulic pressure in the control chamber 15 is provided in an intermediate portion of the housing 11. The three-way valve 8 includes a ball-shaped valve body 84 disposed in a valve chamber 83 having a low pressure port 81 at the upper end and a high pressure port 82 at the lower end. The valve chamber 83 is connected via a communication passage 85. It always communicates with the control room 15. The low pressure port 81 communicates with the low pressure flow path 43 connected to the leak pipe 41, and the high pressure port 82 communicates with the high pressure flow path 33. By switching the seat position of the valve body 84, the control chamber 15 is connected to the low pressure flow path. 43 or the high-pressure channel 33. That is, when the valve body 84 is seated on the upper low-pressure seat 81 a and the low-pressure port 81 is closed, the pressure in the control chamber 15 is increased by the high-pressure fuel flowing from the high-pressure flow path 33 through the valve chamber 83, and the valve body 84. Is seated on the lower high-pressure seat 82a and the high-pressure port 82 is closed, the fuel overflows from the control chamber 15 to the low-pressure flow path 43 and the pressure is reduced.
[0019]
The three-way valve 8 is driven by a piezo actuator 2 serving as a piezo drive unit housed in the upper half of the housing 11. The piezo actuator 2 includes a piezo stack 21 formed by laminating a large number of flat piezoelectric bodies, and a piezo piston 22 that abuts on the lower end surface thereof and slides in a cylinder 25. The piezo stack 21 expands by injection of electric charge and contracts by removal of electric charge, and is connected to the ECU 5 via a lead wire 26 extending from the upper end. The piezo piston 22 has a rod 23 protruding from the lower end surface. When the piezo piston 22 moves up and down integrally with expansion and contraction of the piezo stack 21, the rod 23 drives the valve body 84 of the three-way valve 8. Since the extension amount of the piezo stack 21 is proportional to the applied voltage, the position of the valve body 84 can be adjusted by adjusting the applied voltage.
[0020]
FIG. 1B shows an initial state in which the piezo stack 21 contracts, the valve body 84 rises together with the piezo piston 22 and closes the low pressure port 81, and the pressure in the control chamber 15 and the biasing force of the spring 16 are shown. The nozzle needle 13 is lowered and the injector 1 is closed. A disc spring 24 is disposed around the rod 23 in the lower end portion of the cylinder 25 to urge the piezo piston 22 and the piezo stack 21 upward (in the contraction direction).
[0021]
As shown in FIG. 1A, the ECU 5 serving as a control unit includes a CPU that executes a program for controlling the engine, and the piezo actuator 2 and the high-pressure pump 6 of each injector 1 in accordance with commands from the CPU. It has a controller (control circuit) for driving. The CPU receives signals from various sensors (not shown) that detect the crankshaft rotation angle, engine speed, accelerator opening, cooling water temperature, and the like, and a pressure sensor S that is a pressure detection means that detects common rail pressure. Based on the signals from these sensors, the operating state of the engine is detected. Then, the target pressure of the common rail 3 is calculated so that the engine is in an optimal combustion state, and a pumping command signal is output to the high pressure pump 6 so that the target value and the actual common rail pressure coincide with each other. Perform pressure feedback control.
[0022]
On the other hand, the ECU 5 controls the fuel injection to the engine by driving the injector 1 at a predetermined timing based on the detected operating state. FIG. 2 is a control block diagram for driving the injector 1. The CPU has an injection amount / timing calculation circuit that calculates a target fuel injection amount and injection timing during normal injection driving and outputs an injection signal. Is provided. When an injection signal is output from the CPU at a predetermined time, the predetermined injector 1 is energized and driven through the injection valve energization processing circuit of the controller to inject fuel into the engine cylinder. At this time, the charge voltage / charge current variable circuit of the controller sets a voltage value charged to the piezo actuator 2 of the injector 1 and further adjusts the time until the set voltage value is reached. The value of the current flowing from the drive circuit to the piezo actuator 2 during operation is set.
[0023]
At the time of normal injection driving, the ineffective injection period from the driving of the piezo actuator 2 to the opening of the nozzle needle 13 is made as short as possible so that fuel injection is performed promptly and the injection stability is ensured. The charging voltage value is sufficiently high, and the charging current value is set high enough not to cause a problem due to circuit heat generation. The injection valve energization processing circuit starts charging the piezo actuator 2 according to the injection signal, charges with the current set by the charge voltage / charge current variable circuit, and energizes so that the charging is completed at the set voltage. The injector 1 is driven to perform injection.
[0024]
Furthermore, the ECU 5 controls the common rail pressure by reducing the amount of fuel via the three-way valve 8 of the injector 1 based on the detected operating state. In the pressure reduction control of the common rail pressure, the voltage applied to the piezo actuator 2 is adjusted so that the extension amount of the piezo stack 21 is changed to a position where the valve body 84 half-opens the low pressure port 81, that is, an intermediate position between the low pressure seat 81a and the high pressure seat 82a. Adjust so that At this time, both the low pressure port 81 and the high pressure port 82 are opened, and the high pressure flow path 33 and the low pressure flow path 43 communicate with each other so that the fuel in the common rail 3 overflows into the low pressure flow path 43. It can be reduced.
[0025]
In the control block diagram of FIG. 2, the CPU determines whether or not a predetermined pressure reduction condition for reducing the common rail pressure is satisfied, and adjusts the voltage applied to the piezo actuator 2 when the pressure reduction condition is satisfied. Thus, a decompression determination circuit is provided as decompression determination means for outputting a decompression signal in order to execute decompression. For example, in the case of sudden deceleration, the pressure reduction determination is made based on the target fuel injection amount and the actual common rail pressure, and the target fuel injection amount calculated by the injection amount / timing calculation circuit is zero or less, and When the actual common rail pressure is higher than the target common rail pressure, it is determined that the pressure reducing condition is satisfied.
[0026]
When a decompression signal is output from the decompression determination circuit, the charging voltage and charging current variable circuit of the controller serving as the applied voltage adjusting means charges the piezo actuator 2 so that the valve body 84 of the three-way valve 8 is in the intermediate position. And the current flowing from the drive circuit to the piezoelectric actuator 2 are set. When the charging voltage of the piezo actuator 2 is gradually increased from 0, the valve body 84 of the three-way valve 8 leaves the low-pressure seat 81a at a certain voltage, a fuel leak occurs, and then is seated on the high-pressure seat 82a for control. When the pressure in the chamber 15 is sufficiently reduced, injection is started. Therefore, at the time of pressure reduction control, the charging voltage is set lower than that at the time of normal injection so that the three-way valve 8 leaves the low-pressure seat 81a and the nozzle needle 1 is kept closed and only fuel leakage occurs. This voltage is set based on the common rail pressure, and is set and changed in a timely manner according to the change in the common rail pressure.
[0027]
The injection valve energization processing circuit serving as the pressure reducing means starts charging the piezo actuator 2 in accordance with the pressure reducing signal, charges with the current set by the charge voltage / charge current variable circuit, and completes charging at the set voltage. As such, the energization is controlled. As a result, the extension amount of the piezo stack 21 is adjusted, the three-way valve 8 is held at the intermediate position, the high-pressure fuel in the common rail 3 overflows into the leak passage 43, and the common rail pressure decreases. Details of this control will be described later.
[0028]
The operation of the injector 1 having the configuration of FIG. 1 will be described with reference to the timing chart of FIG. A one-dot chain line in FIG. 3 indicates an operation at the time of normal injection driving, and a solid line indicates an operation at the time of a pressure reduction request. In FIG. 1A, the high-pressure fuel supplied from the common rail 3 to the piezo injector 1 via the high-pressure pipe 31 flows into the fuel reservoir 16 through the high-pressure channel 33. At the same time, the high-pressure fuel flows into the high-pressure port 82 of the three-way valve 8 communicating with the high-pressure channel 33. When no voltage is applied to the piezo actuator 2 (before time A in FIG. 3), the valve body 84 of the three-way valve 8 contacts the low-pressure seat 81a and the high-pressure port 82 is opened (FIG. 1 ( b)), high-pressure fuel flows into the control chamber 15 from the high-pressure port 82 through the valve chamber 83 and the communication passage 85, and the control chamber 15 is at a high pressure. In this state, the force in the valve closing direction (the pressure in the control chamber 15 and the urging force of the spring 16) is greater than the force in the valve opening direction (fuel pressure in the fuel reservoir 16) applied to the nozzle needle 13, so the nozzle needle Since 13 does not lift and the injection hole 14 is closed and the valve is closed, fuel is not injected into the cylinder of the engine.
[0029]
Next, when application of voltage to the piezo actuator 2 is started by an injection signal (for example, a rectangular pulse signal) from the ECU 5 (time A in FIG. 3), the piezo stack 21 expands as the piezo voltage increases, The piezo piston 22 descends and moves the valve body 84 of the three-way valve 8 downward. At this time, as indicated by the alternate long and short dash line in FIG. 3, as the piezo voltage rises, the valve body 84 first separates from the upper low-pressure seat 81a and opens the low-pressure port 81, and then opens to the lower high-pressure seat 82a. Sit down and close the high pressure port 82. As the high-pressure fuel in the control chamber 15 overflows from the low-pressure port 81 to the low-pressure flow path 43, the pressure in the control chamber 15 gradually decreases, and the fuel pressure in the valve opening direction of the fuel reservoir 16 changes. When the force in the valve closing direction by 15 and the spring 16 is exceeded, the nozzle needle 13 starts to lift (at the time point C in FIG. 3). That is, the injector 1 is opened, and the fuel reservoir 16 and the injection hole 14 communicate with each other to inject fuel into the engine cylinder.
[0030]
Thereafter, when the voltage applied to the piezo actuator 2 is released by the ECU 5 (at the time point D in FIG. 3), the piezo stack 21 contracts, and the piezo piston 22 and the valve body 84 of the three-way valve 8 rise. Then, the valve body 84 moves away from the lower high-pressure seat 82a, opens the high-pressure port 81, and then sits on the upper low-pressure seat 81a to close the low-pressure port 81, whereby high-pressure fuel flows into the control chamber 15 again. The pressure gradually increases. When the force in the valve closing direction by the control chamber 15 and the spring 16 exceeds the fuel pressure in the valve opening direction of the fuel reservoir 16, the nozzle needle 13 starts to descend, the nozzle hole 14 is closed, and the injector 1 is closed. Return to valve status.
[0031]
Here, in the injector 1 configuration, when the valve body 84 starts to lift (at the time point B in FIG. 3), the pressure in the control chamber 15 starts to decrease, but the nozzle needle 37 reaches the pressure at which the lift starts. In order to achieve this (at time C in FIG. 3), it is necessary to further increase the piezo voltage. In other words, by adjusting the piezo voltage, it is possible to adjust the lift position of the valve body 84 and hold the control chamber 15 higher than the pressure at which the nozzle needle 37 starts to lift, that is, the injection start pressure.
[0032]
Therefore, in the present invention, as indicated by a solid line in FIG. 3, the charging voltage of the ECU 5 and the charging voltage to the piezo actuator 2 set by the charging current variable circuit (the maximum value of the piezo voltage) are set lower than those during normal injection. To do. When voltage application is started by the decompression signal from the ECU 5 (at the time point A in FIG. 3), the piezo stack 21 expands as the piezo voltage rises, but the extension amount of the piezo stack 21, that is, the piezo piston 22 descends. The valve body 84 of the three-way valve 8 is held at an intermediate position between the upper low-pressure seat 81a and the lower high-pressure seat 82a to be smaller than that during normal injection.
[0033]
At this time, the high-pressure fuel flowing into the valve chamber 83 from the high-pressure port 82 overflows directly to the low-pressure flow path 43 via the low-pressure port 81, so that the pressure of the common rail 3 can be reduced. On the other hand, the distance between the valve body 84 of the three-way valve 8 and the low-pressure seat 81a becomes narrower than that during normal injection, and overflow of high-pressure fuel from the control chamber 15 is limited. Therefore, the pressure in the control chamber 15 does not drop to the injection start pressure, and the nozzle needle 37 does not lift, so that no injection occurs.
[0034]
Here, in FIG. 1B, the valve body 84 of the three-way valve 8 receives a downward force from the piezoelectric stack 21 via the piezoelectric piston 22 and an upward force from the high-pressure fuel in the valve chamber 83. The position is determined by the balance of these forces. Since the pressure of the high-pressure fuel flowing into the valve chamber 83 is equal to the pressure of the common rail 3, the force acting upward on the valve body 84 varies depending on the common rail pressure, and accordingly, the valve body 84 is held at an intermediate position. The charging voltage of the piezo actuator 2 also changes. This relationship is shown in FIG.
[0035]
FIG. 4 shows the charging voltage (leak start voltage) necessary for the valve body 84 to leave the low pressure seat 81a and the maximum voltage (no injection limit voltage) at which the nozzle needle 37 can keep the valve closed. Also rises in proportion to the common rail pressure. Therefore, when a pressure reduction is requested, first, the common rail pressure is detected by the pressure sensor S, and the charging voltage of the piezo actuator 2 is set so as to be between the leakage start voltage and the non-injection limit voltage at the detected common rail pressure. Furthermore, as the common rail pressure decreases, the leak start voltage and the non-injection limit voltage also decrease. Therefore, the force acting upward on the valve body 84 decreases with the set voltage of the piezo actuator 2 kept constant. In addition, the balance of power changes. For this reason, the valve body 84 moves downward, and finally comes into contact with the high-pressure sheet 82a, resulting in erroneous injection.
[0036]
Therefore, in the present invention, the common rail pressure is detected in a timely manner, and the setting voltage of the piezo actuator 2 is changed as shown by Δ in FIG. 4 according to the detection result. Thereby, the valve body 84 is always positioned between the low pressure seat 81a and the high pressure seat 82a, and the common rail pressure can be controlled to be reduced without causing erroneous injection.
[0037]
FIG. 5 is a timing chart showing an example of a method for changing the setting of the charging voltage implemented by the charging voltage / charging current variable circuit of the ECU 5, and shows the relationship between the common rail pressure and the charging voltage before and after the start of the pressure reduction control. During normal injection control, the charging voltage for the piezo actuator 2 is set to a voltage V0 sufficient for the valve body 84 to securely contact the high-pressure seat 82a. The injection valve energization processing circuit charges and discharges the piezo stack 21 in accordance with the injection signal output at a predetermined time from the injection amount / time calculation circuit. This is repeated for each injection. Meanwhile, a necessary amount of high-pressure fuel is pumped to the common rail 3 from the high-pressure pump 6, and the common rail pressure (solid line in the figure) is maintained at a predetermined target pressure (two-dot chain line in the figure).
[0038]
Next, when a decompression signal is output by the decompression determination means (arrow in the figure), first, the common rail pressure is detected by the pressure sensor S, and the relationship between the common rail pressure and the charging voltage determined in advance from the detected value ( For example, based on the characteristic diagram of FIG. 4, the charging voltage of the piezo actuator 2 optimum for pressure reduction is determined. The injection valve energization processing circuit charges and discharges the piezo stack 21 accordingly. The pressure reduction control is performed in synchronization with the rotation of the engine, for example, similarly to the normal injection interval. When the next decompression signal is output, the common rail pressure is detected again, and the charging voltage of the piezo actuator 2 is changed based on this detected value, and the piezo stack 21 is charged / discharged. This is repeated until the common rail pressure reaches the target pressure.
[0039]
Here, the interval of the pressure reduction control has been described as being synchronized with the rotation of the engine in the same manner as the normal injection interval, but it may of course be performed at regular time intervals. In this case, the pressure reduction speed of the common rail 3 can be made constant regardless of the operating state of the engine.
[0040]
Further, the actual pressure of the common rail 3 is detected by the pressure sensor S, and the charging voltage of the piezo actuator 2 is set based on the detected pressure. In practice, however, static leakage occurs from the sliding portion of the injector 1 or the like. Therefore, the pressure can be corrected by the amount of decompression obtained by calculation from the amount of fuel leak at the time of decompression control. As a result, the acting force of the high-pressure fuel applied upward to the valve body 84 can be estimated with higher accuracy, erroneous injection can be reliably prevented, and controllability can be improved.
[0041]
FIG. 6 illustrates a method for setting the charging current in the charging voltage / charging current variable circuit of the ECU 5. The solid line indicates the injection pulse at the time of normal injection, the charging voltage for the piezo actuator 2, and the charging current for applying the voltage. Show the relationship. The piezo actuator 2 is normally energized by a multi-switching system in which charging and discharging are performed in multiple steps by a voltage booster circuit (DC-DC) and a drive circuit including a charging switching element and a discharging switching element. Will be implemented. The voltage booster circuit (DC-DC) boosts the voltage of the battery to a predetermined voltage, and the energy converted into a high voltage by the voltage booster circuit is stored in a capacitor. Then, the piezo stack 21 is charged from the capacitor via the charging switching element by repeating ON / OFF of the charging switching element a predetermined number of times.
[0042]
At this time, each time the charging switching element is turned on / off, a predetermined charging current flows, and the charging voltage of the piezoelectric actuator 2 increases stepwise to reach a predetermined setting voltage. Here, the charging voltage of the piezo actuator 2 is the product of the charge amount per charge and the number of times of charge, and the resolution of the charge voltage is determined by the charge amount per time. In order to control the charging voltage with high accuracy, it is better that the resolution of the charging voltage is high. To achieve this, it is only necessary to reduce the charging current to reduce the charging amount per time. In particular, at the time of pressure reduction control, as shown in FIG. 4, since the setting range of the charging voltage is narrower than that at the time of normal injection, it is necessary to increase this resolution. However, during normal injection, the number of times of charging is increased by lowering the amount of charge, and the time required to reach the set voltage is increased. Therefore, the rise of the injection pulse and the time when the piezo stack 21 reaches the expansion amount that can actually be injected The difference (invalid injection period) becomes large and there is a problem that the injection performance (responsiveness) is impaired.
[0043]
In order to avoid this, in the present invention, as shown in FIG. 6, only during the decompression control, the charging current is lowered to lower the charge amount per time, and the resolution of the charging voltage is increased. At the time of normal injection, the charging current is increased to increase the amount of charge per time so that the invalid injection period is shortened. Thereby, while ensuring the injection performance at the time of normal injection, the resolution at the time of pressure reduction control can be increased to prevent erroneous injection and the like, and the controllability of the common rail pressure can be further improved.
[0044]
In the above-described embodiment, the decompression determination condition is, for example, the case where the fuel injection amount is <0 and the actual common rail pressure> the target common rail pressure due to rapid deceleration, but the engine is restarted after high load operation, Of course, the present invention may be applied when the pressure in the common rail 3 becomes higher than necessary by repeatedly turning on and off the starter switch. In this case, as a depressurization condition for reducing the fuel pressure in the common rail 3, for example, it is only necessary to confirm that the ignition switch or starter switch has changed from the on state to the off state. Thus, the pressure in the common rail 3 can be efficiently reduced.
[0045]
In the above embodiment, a three-way valve is used as a control valve.
[Brief description of the drawings]
FIG. 1A is an overall configuration diagram of a fuel injection device according to a first embodiment, and FIG. 1B is a cross-sectional view showing a schematic configuration of an injector.
FIG. 2 is a block diagram of control by an ECU.
FIG. 3 is a timing chart for explaining the operation of the injector during injection driving, during pressure reduction control, and injector operation.
FIG. 4 is a diagram showing a relationship between common rail pressure and charging voltage.
FIG. 5 is a timing chart showing an example of charging voltage control by an ECU.
FIG. 6 is a diagram showing a relationship between a charging current and a charging voltage.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Injector 13 Nozzle needle 14 Injection hole 15 Control chamber 2 Piezo actuator (piezo drive part)
3 Common rail (pressure accumulation chamber)
33 High-pressure channel 43 Low-pressure channel (leakage channel)
5 ECU (control unit)
6 High pressure pump 7 Fuel tank 8 3-way valve (control valve)

Claims (4)

An accumulator that stores high-pressure fuel pumped from a high-pressure pump, a piezo-drive injector that injects high-pressure fuel in the accumulator into a cylinder of the internal combustion engine, and driving of the high-pressure pump and the injector according to the operating state of the engine A control unit for controlling
The injector controls the control by opening and closing a nozzle needle for opening and closing the nozzle hole, a control chamber for causing the pressure of fuel supplied from the pressure accumulating chamber to act on the nozzle needle, and opening and closing between the control chamber and the leak passage. A control valve that increases or decreases the pressure in the chamber, and a piezo drive that expands by applying a voltage and opens the control valve, and contracts and discharges the charged voltage to close and drive the control valve And the nozzle needle is opened as the control valve is driven to inject fuel supplied from the pressure accumulating chamber,
A depressurization determining means for determining whether or not a depressurization condition for lowering the fuel pressure in the pressure accumulating chamber is satisfied based on the operating state of the internal combustion engine;
When the decompression determination means determines that the decompression condition is satisfied, the control valve is half-opened by applying a voltage lower than that during normal injection to the piezoelectric drive unit, and the fuel supplied from the pressure accumulating chamber is Pressure reducing means for reducing the fuel pressure in the pressure accumulating chamber by overflowing to the leak flow path;
The voltage applied to the piezo drive unit by the pressure reducing means is set based on the fuel pressure in the pressure accumulating chamber so that the control valve leaves the seat position and the nozzle needle remains closed, and this set voltage An injection control device for an internal combustion engine, comprising: an applied voltage adjusting means for changing the setting according to a change in fuel pressure in the pressure accumulating chamber. Pressure detecting means for detecting the fuel pressure in the pressure accumulating chamber at a predetermined time is provided, and the setting change of the applied voltage to the piezo drive unit by the applied voltage adjusting means is synchronized with the detection time of the fuel pressure by the pressure detecting means. An injection control device for an internal combustion engine according to claim 1 implemented as described above. 2. An injection control device for an internal combustion engine according to claim 1, wherein the setting change of the applied voltage to the piezo drive unit by the applied voltage adjusting means is carried out every predetermined time. 2. An injection control apparatus for an internal combustion engine according to claim 1, wherein said applied voltage adjusting means includes means for lowering the value of a current flowing to said piezo drive unit when a voltage is applied to said piezo drive unit than during normal injection.

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