JP4239401B2 - Fuel injection 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 are deteriorated, variable shock, noise, etc. are 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 when the engine is restarted immediately after the engine is stopped, the fuel injection is stopped and no fuel is consumed, so the common rail pressure decreases 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]
[Problems to be solved by the invention]
However, it has been difficult to perform pressure reduction control by “empty driving” as in the above-described conventional apparatus using a piezoelectric drive type injector for the following reason. That is, the solenoid-driven injector has a long invalid injection period of about 400 μm, and the solenoid valve may be driven to open and close within the range of this invalid injection period, for example, 300 μm, whereas the piezo-driven injector Because of its high responsiveness, the ineffective injection period is much shorter than that of solenoid-driven injectors. 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.
[0006]
Therefore, pressure reduction control in a piezo-driven fuel injection device is usually performed by a dedicated pressure reducing valve provided on the common rail. By opening and closing the pressure reducing valve as necessary, the common rail pressure becomes higher than the target value. I try not to become too much. However, this system requires a dedicated pressure reducing valve and a control circuit for controlling the valve, and there is a problem of increase in size and cost of the apparatus due to an increase in the number of parts.
[0007]
The present invention has been made in view of the above circumstances, and in a fuel injection device using a piezo injector, it enables decompression control by idle driving, and has both high response during normal injection and controllability during decompression. The object is to achieve both compatibility without increasing the size and cost of the apparatus.
[0008]
[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 rising speed of the voltage applied to the piezo drive unit is made slower than the normal injection driving, or the rising of the applied voltage By slowing down the speed and the falling speed when discharging the charged voltage, the ineffective injection period from the driving of the control valve to the opening of the nozzle needle is made longer than that during normal injection driving. Invalid injection period variable means;
When the invalid injection period varying means is operated, the control valve is driven to open with a shorter time width than the extended invalid injection period, and the high pressure fuel in the pressure accumulating chamber is supplied to the leak flow path by performing idle driving. And a pressure reducing means for reducing the fuel pressure in the pressure accumulating chamber.
[0009]
As in the present invention, even in the configuration employing the piezo-driven injector having excellent responsiveness, the control valve can be controlled within the invalid injection period by adjusting the invalid injection period to be longer only during idle driving. Valve opening drive is possible. Specifically, the invalid injection period varying means slows the voltage rising speed when applied to the piezo drive unit, and shortens the time during which the control valve is actually opened compared to normal injection drive. By doing so, it is possible to prevent the pressure in the control chamber from dropping to the injection start pressure. Similarly, when the rising speed of the voltage during charging and the falling speed during discharging are slowed, the invalid injection period can be lengthened. Therefore, during normal injection driving, it exhibits excellent responsiveness in a short invalid injection period, and when decompression is necessary, the invalid injection period is lengthened, and pressure reduction control by idle driving is performed to prevent the occurrence of noise, etc. be able to. Moreover, a pressure reducing valve as a separate member is unnecessary, and the increase in size and cost of the apparatus can be suppressed.
[0010]
In the configuration of claim 2, the invalid injection period varying means is configured such that the magnitude of the energization current to the piezo drive unit is smaller than that during normal injection drive, or the energization interval is changed to be greater than during normal injection drive. By doing so, the rising speed or falling speed of the applied voltage of the piezo drive section is slowed down.
[0011]
For example, in a multi-switching system, if the current that is energized at a time is less than that during normal injection driving, the expansion speed or contraction speed of the piezo drive section is slowed down, and the voltage rising speed or falling speed is slowed down. . The same applies to the case where the energization current is made the same and the interval for energizing the piezo drive unit is increased.Since the expansion rate or contraction of the piezo drive unit is slow, the voltage rise rate or fall rate is slowed down. can do.
[0012]
In the configuration of claim 3, in the injector, the nozzle needle receives pressure in the valve opening direction by the fuel supplied from the pressure accumulating chamber and pressure in the valve closing direction by the fuel in the control chamber, When the control valve is driven to open and communicates between the control chamber and the leak flow path, the nozzle needle opens as the pressure in the control chamber decreases.
[0013]
Specifically, the control chamber applies a back pressure to the nozzle needle in this way. In the above configuration, in a state where the control valve is closed, the communication between the control chamber and the leak channel is cut off, and the nozzle needle is closed by the pressure in the control chamber. Next, when the control valve is opened, the pressure in the control chamber decreases, and when the pressure falls below the injection start pressure, the nozzle needle starts to lift and fuel is injected. At this time, if the control unit adjusts the expansion / contraction speed of the piezo drive unit to be slow, the time from when the control valve opens until the control chamber becomes equal to or lower than the injection start pressure becomes longer, and the invalid injection The period can be lengthened.
[0014]
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.
[0015]
FIG. 1 (b) 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 passage 33 connected to the high-pressure pipe 31 so that fuel is supplied to the nozzle hole 14.
[0016]
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 passage 43 connected to the leak pipe 41, and the high pressure port 82 communicates with the high pressure passage 33. By switching the seat position of the valve body 84, the control chamber 15 is connected to the low pressure passage 43 or the high pressure passage. It communicates with the passage 33. That is, when the valve body 84 is seated on the upper low-pressure seat 81a 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 passage 33 through the valve chamber 83, and the valve body 84 is When the high pressure port 82 is closed by sitting on the lower high pressure seat 82a, the fuel overflows from the control chamber 15 to the low pressure passage 43 and the pressure is reduced.
[0017]
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. 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).
[0018]
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, common rail pressure, etc., and operates the engine based on the signals from these sensors. Detect state. 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.
[0019]
On the other hand, the ECU 5 controls the fuel injection to the engine by driving the injector 1 at a predetermined timing on the basis of the detected operating state, and controls the pressure reduction of the common rail pressure by the idle driving of the injector 1. A control block for driving the injector 1 is shown in FIG. Whether 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, and a predetermined pressure reduction condition for reducing the common rail pressure A depressurization determination circuit is provided as depressurization determination means for determining whether or not, and outputting a blank shot signal when the depressurization condition is satisfied. 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.
[0020]
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. The variable voltage rise / fall time circuit of the controller sets the time until the piezoelectric actuator 2 of the injector 1 is charged to a predetermined voltage and the time for discharging from the predetermined voltage. These rise / fall times are set as short as possible so that the ineffective injection period from the drive of the actuator 2 to the opening of the nozzle needle 13 is shortened and the fuel is quickly injected. The injection valve energization processing circuit starts charging / discharging in accordance with the injection signal, and controls energization to the piezo actuator 2 so that charging or discharging is completed within the time set by the voltage rise / fall time variable circuit. The injector 1 is driven to inject.
[0021]
On the other hand, when a blanking signal is output from the decompression determination circuit, the voltage rising / falling time variable circuit of the controller causes the charging voltage of the piezo actuator 2 to rise up to a predetermined voltage or the rising of the charging voltage. Both the time and the fall time when discharging the applied voltage are made slower than during normal injection driving. As a result, the invalid injection period from the driving of the piezo actuator 2 to the opening of the nozzle needle 13 becomes longer than that during normal injection driving, and the injector 1 is energized and driven with a shorter time width than this invalid injection period. It is possible to perform driving. The injection valve energization processing circuit starts charging / discharging in accordance with the idle driving signal, and controls the energization to the piezo actuator 2 so that the charging or discharging is completed with the changed start / fall time. Drive idle. At this time, the voltage rise / fall time variable circuit constitutes an invalid injection period variable means for making the invalid injection period longer than that at the time of normal injection driving, and the injection valve energization processing circuit is more than the extended invalid injection period. The pressure reducing means is configured to perform idle driving in a short time width to overflow the high pressure fuel in the common rail 3 to the leak flow path 43 and to reduce the common rail pressure. Details of this control will be described later.
[0022]
The failure detection circuit of the controller is for detecting an abnormality of the piezo actuator 2. For example, the controller detects the charging voltage of the piezo actuator 2, and the applied voltage of the piezo actuator 2 is predetermined even after a predetermined time has elapsed since charging. When the voltage does not reach, or when the applied voltage does not become zero even after a lapse of a certain time from the discharge, an abnormal signal is output.
[0023]
The operation during normal injection driving of the injector 1 having the configuration shown in FIG. 1 will be described with reference to FIG. 3 (dashed line). 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 (for example, before the time point 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). (The state shown in FIG. 5B), 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 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.
[0024]
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 passage 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 the spring 16 is exceeded, the nozzle needle 13 starts to lift (time B 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.
[0025]
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.
[0026]
Thus, the injector 1 having the above-described configuration requires a predetermined invalid injection period (t) from the start of voltage application until the nozzle needle 37 actually starts to lift. Therefore, if idle driving is performed in which the valve body 84 is driven with a time width shorter than the invalid injection period (t), high pressure fuel from the common rail 3 overflows through the control chamber 15 so that fuel is not injected. It is possible to reduce the common rail 3 pressure. However, since the piezo-driven injector 1 has good response, the invalid injection period (t) is shorter than that of the conventional electromagnetic-driven injector under the normal injection drive control conditions indicated by the one-dot chain line in FIG. In the range of the invalid injection period (t), it is difficult to perform the idle driving by causing the valve body 84 to reciprocate at two positions.
[0027]
Therefore, in the present invention, by controlling the energization of the piezo actuator 2 by the ECU 5, the injection characteristic of the injector 1 is changed between the normal injection driving and the idle driving, and the invalid injection period ( t _k ) Is the invalid injection period (t _f ) To be longer. Specifically, by using the voltage rise / fall time variable circuit and the injection valve energization processing circuit of the ECU 5 described above, the rising speed of the voltage when charging the piezoelectric actuator 2 and the falling speed of the voltage when discharging it. It is possible to adjust the invalid injection period (t) by adjusting. This will be described in detail below.
[0028]
As shown by the solid line in FIG. 3, when the pulse width of the idle driving signal is the same as the pulse width at the time of injection driving, the voltage rise is performed so that the voltage rise speed when charging the piezo actuator 2 is slow. If the time is increased, the extension speed of the piezo stack 21, that is, the lowering speed of the piezo piston 22 becomes slower, so that the timing at which the valve body 84 of the three-way valve 8 moves away from the upper low-pressure seat 81 a is delayed. For this reason, the timing at which the pressure in the control chamber 15 begins to decrease is delayed (at the time point C in FIG. 3), and the pressure drop is also moderated. Accordingly, when the valve body 84 is seated on the lower high-pressure seat 82a, the discharge start (at the time point D in FIG. 3) almost coincides, and the valve body 84 rises again and high-pressure fuel flows from the high-pressure port 82. Therefore, the pressure in the control chamber 15 is the pressure (injection start pressure) P at which the nozzle needle 13 starts to lift. ₀ The fuel injection is not performed. In the meantime, the fuel overflows from the high pressure port 82 to the low pressure port 81, so the common rail 3 pressure decreases.
[0029]
As described above, even if the pulse width of the idle driving signal is as long as the pulse width at the time of injection driving, the valve element 84 is actually opened by increasing the time until the voltage rises to the predetermined voltage (charging time). Time (time when the low pressure port 82a is opened) T _k Is the valve opening time T of the valve body 84 at the time of injection driving. _f It becomes shorter than that, and idle driving is possible. FIG. 4 illustrates the relationship between the injection pulse width that drives the injector 1 and the injection amount. In the injector 1 having the configuration of the present embodiment, when normal injection driving is performed, the injection pulse width (= invalid injection period (t _f ) Is about 100 μm, but when the charging time is extended as described in FIG. 3, the invalid injection period (t) _k1 ) Is about 330 μm, and approaches about 400 μm, which is the invalid injection period (t) of the conventional solenoid-driven injector 1 indicated by (4) in the figure. Therefore, this invalid injection period (t _k1 If the valve body 84 of the three-way valve 8 is reciprocally driven in two positions within the range of), the idle driving that reduces the pressure of the common rail 3 without injecting fuel is possible.
[0030]
In addition, the rising speed of the voltage at the time of charging and the falling speed of the voltage at the time of discharging may be slowed. In this case, the invalid injection period (t _k2 ) Can be lengthened. However, in this case, since the falling speed of the piezo voltage from the start of discharge (at time D in FIG. 3) becomes slow and the voltage falling time becomes long, the valve body 84 leaves the high pressure port 82 and becomes low pressure. It takes time to close the port 81. In the meantime, since the pressure in the control chamber 15 is lowered and started to rise, the invalid injection period (t) when both the charging time and the discharging time are delayed as shown by (3) in the figure. _k2 ) Is shorter (about 220 μm) than when only the charging time (2) in the figure is increased.
[0031]
Next, an example of injector control when the present invention is applied to a four-cylinder engine will be described with reference to the timing chart of FIG. FIG. 6 is a diagram illustrating a circuit configuration for driving the injector 1. For the switching, a multiple switching method is used in which charging and discharging are performed stepwise during charging and discharging. INJ1 to INJ4 represent the piezoelectric actuators 2 built in the four injectors 1 (# 1 to # 4) provided in each cylinder, and select the corresponding cylinder control switching elements T111 to T114 and the separation control switching elements T112 and T132. Thus, charging / discharging the predetermined INJ1 to INJ4 (here, a case where the INJ1 corresponding to the injector 1 of # 1 is driven will be described as an example). The coil L151, the switching element T151, and the diode D151 constitute a voltage booster circuit (DC-DC), and boosts the battery voltage to a predetermined voltage. C151 is a capacitor for storing energy converted into a high voltage by a voltage booster circuit, T152 is a charging switching element, T153 is a discharging switching element, L152 is a charging / discharging coil, and R111 and R112 are detection resistors for detecting a charging current. is there.
[0032]
In FIG. 5, first, when the injection signal is output at a predetermined time based on the calculation result of the injection amount / timing calculation circuit of the CPU at the time of normal injection driving, the injection valve energization processing circuit of the controller The cylinder control switching element T111 corresponding to 1 and the separation control switching element T112 are turned on. The capacitor C151 is charged with sufficient energy to charge the piezo actuator 2 by a voltage booster circuit (DC-DC) constituted by L151, T151, and D151. Further, when a gate signal for driving charging switching element T152 is output from the CPU via the controller, charging switching element T152 is turned on in accordance with this signal, and charging to INJ1 is started.
[0033]
At this time, the charging current I11 (for example, 10 A) is supplied from the capacitor C151 to the charging switching element T152-charging / discharging coil L152-disconnection control switching element T112-COMA-INJ1- # 1-cylinder control switching element T111-detection resistor R111-GND. The piezo voltage of INJ1 rises. By repeating this operation, the piezo voltage can be charged up to a target predetermined voltage (for example, 150 V). In this embodiment, charging is performed with four pulses such as I11-I12-I13-I14, and the injector 1 is driven to open at a charging time T1 set in advance by a voltage rise / fall time variable circuit. Control drive is performed so as to reach the predetermined voltage required for the above.
[0034]
Next, discharge control starts when the injection signal falls. At the time of discharging, contrary to charging, charging switching element T152 is turned off, and a gate signal for driving discharging switching element T153 is output. As a result, the discharge current I21 flows through the path of GND-detection resistor R111-cylinder control switching element T111- # 1-INJ1-COMA-disengagement control switching element T112-charging / discharging coil L152-discharging switching element T153, and flows into INJ1. The charged energy is discharged and the piezo voltage decreases by a predetermined voltage. By repeating this operation, the piezoelectric voltage is discharged to 0V. In this embodiment, discharge is performed with four pulses such as I21-I22-I23-I24, and the injector 1 is driven to close at a discharge time T2 set in advance by a voltage rise / fall time variable circuit. Control drive to the voltage required for
[0035]
On the other hand, when a decompression determination is made by the decompression determination means of the ECU 5 and a blank shot signal is output, blank shot drive control is executed. Even during the idling driving, the injector 1 can be driven in the same driving sequence as in the injection driving. However, by the voltage rise / fall time variable circuit, the charging time T1 ′ is made longer than that during the injection control, the invalid injection time is made longer, and the injector 1 is driven idle by a shorter time width. Specifically, a single piezoelectric charging current I31 by the injection valve energization processing circuit is set to about half (for example, 5A) of the charging current I11 at the time of injection driving, and the number of times of charging is set to eight pulses I31 to I38. . Since the charging current at one time is half, the charging time T1 ′ is twice the charging time T1 at the time of injection control, and it is possible to slow the charging start-up speed. The charging time T1 ′ during idle driving is determined by the required value of the system with respect to the charging time T1 during injection.
[0036]
As in the case of charging, the piezo discharge current I41 for one discharge is set to about half (for example, 5A) during the injection driving, and the number of discharges is eight pulses from I41 to I48 at the discharge time T2 ′. Control drive. Since the discharge current at one time is half, as a result, the discharge time T2 ′ becomes twice the discharge time T2 during the injection control, and the discharge falling speed can be slowed down. The discharge time 21 ′ when idle is determined by the required value of the system with respect to the discharge time T 2 during injection.
[0037]
As described above, the invalid injection period (t) can be adjusted by adjusting the charging times T1, T1 ′ and the discharging times T2, T2 ′. Therefore, during the normal injection driving, the invalid injection period (t) is shortened to ensure high responsiveness, and during the idle driving, the invalid injection period (t) is lengthened, and the range of the invalid injection period (t). The common rail 3 can be controlled to be depressurized.
[0038]
FIG. 7 is a timing chart showing another example of injector control. In the embodiment of FIG. 5, the charging current value and discharging current value per time are adjusted, and the charging time and discharging time are adjusted by increasing the number of energizations. In the example of FIG. Is the same as in normal injection driving, and the intervals of charging (I31 to I34) and discharging (I41 to I44) are lengthened. In this way, the charging time T1 ′ and the discharging time T2 ′ can be adjusted instead of adjusting the current value, and the same effect can be obtained.
[0039]
In the example shown in the timing charts of FIGS. 5 and 7, the time adjustment is performed both during charging and discharging. However, as shown in FIG. 3, the time adjustment may be performed only during charging. . Further, in these examples, the case where idle driving is performed using one of the multiple cylinders is shown, but half of the multiple cylinders, or all cylinders can be equally idle. If it does in this way, more suitable pressure reduction control can be performed and it can control to the optimal common rail pressure.
[0040]
Further, the timing of the idle driving may be performed before each injection among the multi-stage injections per cylinder, or may be performed only before the main injection and only before and after the main injection. Thus, the controllability of the common rail pressure can be further improved by optimally setting the number of cylinders to be idled, the timing, and the like.
[0041]
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 the starter switch is changed from the on state to the off state. Thus, the pressure in the common rail 3 can be efficiently reduced.
[0042]
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 an injector during injection driving, idle driving, and injector operation.
FIG. 4 is a diagram showing a relationship between an injection pulse width and an injection amount.
FIG. 5 is a timing chart showing an example of control by the ECU.
FIG. 6 is a circuit configuration diagram for driving an injector.
FIG. 7 is a timing chart showing another example of control by the ECU.
[Explanation of symbols]
1 Injector
13 Nozzle needle
14 injection hole
15 Control room
2 Piezo actuator (piezo drive unit)
3 Common rail (pressure accumulation chamber)
33 High pressure flow path
43 Leakage channel
5 ECU (control unit)
6 High pressure pump
7 Fuel tank
8 3-way valve (control valve)

Claims (3)

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 between the control chamber and the leak flow path, a nozzle needle that opens the nozzle hole, a control chamber that causes the pressure of fuel supplied from the pressure accumulating chamber to act on the nozzle needle, and 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,
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 rising speed of the voltage applied to the piezo drive unit is made slower than the normal injection driving, or the rising of the applied voltage By slowing down the speed and the falling speed when discharging the charged voltage, the ineffective injection period from the driving of the control valve to the opening of the nozzle needle is made longer than that during normal injection driving. Invalid injection period variable means;
When the invalid injection period varying means is operated, the control valve is driven to open with a shorter time width than the extended invalid injection period, and the high pressure fuel in the pressure accumulating chamber is supplied to the leak flow path by performing idle driving. A fuel injection device for an internal combustion engine, comprising pressure reducing means for overflowing the fuel and reducing the fuel pressure in the pressure accumulating chamber. The ineffective injection period varying means reduces the magnitude of the energization current to the piezo drive unit from that during normal injection drive, or changes the energization interval to be greater than during normal injection drive. 2. The fuel injection device for an internal combustion engine according to claim 1, wherein the rising speed or falling speed of the applied voltage of the section is slowed. In the injector, the nozzle needle receives a pressure in the valve opening direction by the fuel supplied from the pressure accumulating chamber and a pressure in the valve closing direction by the fuel in the control chamber, and drives the control valve to open. 3. The fuel injection device for an internal combustion engine according to claim 1, wherein the nozzle needle opens when the pressure in the control chamber decreases when the control chamber communicates with the leak flow path. .

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