JP4635352B2 - Piezo actuator driving circuit and fuel injection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric actuator drive circuit and a fuel injection device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an injector for fuel injection of an internal combustion engine is equipped with a solenoid that drives a needle, and switching between opening and closing of the injector is performed by controlling energization of the solenoid. The drive circuit for energization control is provided with switch means for switching between energization and shutoff of the solenoid mounted for each injector, and the solenoid corresponding to the switch means that is turned on is selectively energized. The injector of the cylinder will open.
[0003]
The number of fuel injections is enormous, although it depends on the engine speed. In the case of an internal combustion engine having a large number of cylinders or an internal combustion engine that performs multi-stage injection in which fuel injection is divided into a plurality of times in one combustion cycle, the number is further increased. Since the solenoid is energized once for each fuel injection, the power consumption becomes large. In order to reduce power consumption, if the surge energy is recovered from the solenoid when the switch means is turned off and is to be reused, it is necessary to recover the positive surge. It will be connected to the capacitor. For this reason, the switch means is provided on the ground side with respect to the solenoid.
[0004]
By the way, in recent years, piezo actuators have been studied as means for opening and closing an injector because higher response than a solenoid can be expected. The piezo actuator uses a piezoelectric action of a piezoelectric material such as PZT, and a piezo stack, which is a capacitive element, expands or contracts due to charge / discharge, thereby displacing a drive target. In the case of a fuel injection device for an internal combustion engine, at the injection timing, the piezo stack is charged to open the needle, and after a predetermined time, the piezo stack is discharged to close the needle.
[0005]
FIG. 3 shows the configuration of a piezo actuator drive circuit for driving the piezo actuator, which is an application of the solenoid drive circuit. The piezo actuator drive circuit can charge and discharge the four piezo stacks 91A, 91B, 91C and 91D by the charge / discharge circuit portions 92a and 92b, and is used for an internal combustion engine for four cylinders, for example. Two systems of charge / discharge circuit units 92a and 92b are provided, and the first charge / discharge circuit unit 92a is in charge of charging and discharging of the group including the first and second piezo stacks 91A and 91B. The discharge circuit unit 92b is in charge of charging and discharging of the group including the third and fourth piezo stacks 91C and 91D. Each of the charge / discharge circuit units 92a and 92b includes an inductor 922 and switching elements 923 and 924, and has a so-called multiple switching system circuit configuration. When the first switching element 923 is turned on / off, each of the charge / discharge circuit units 92a and 92b is charged from the capacitor 921 common to both the charge / discharge circuit units 92a and 92b to the piezo stacks 91A to 91D of the group in charge. When 924 is turned on / off, the piezo stacks 91A to 91D in a charged state are discharged.
[0006]
Lines 93A and 93B connecting the connection terminals 95A, 95B, 95C, and 95D to which the cables 96A, 96B, 96C, and 96D reaching the ground side terminals of the piezo stacks 91A to 91D are connected to the charge / discharge circuit units 92a and 92b. , 93C, 93D are provided with switch means 94A, 94B, 94C, 94D in a one-to-one correspondence with the piezo stacks 91A-91D, and by selecting one corresponding to the injection cylinder, a cylinder is selected. Is made.
[0007]
Further, in this circuit configuration, if an abnormality is detected in the connection between the connection terminals 95A to 95D and the piezo stacks 91A to 91D, the charge / discharge circuit unit 92a (92b) responsible for charging / discharging the piezo stacks 91A to 91D is not used. As the operation, the operations of the piezo stacks 91C and 91D (91A and 91B) of the group not including the piezo stacks 91A to 91D are ensured. For example, the ground side of one of the piezo stacks 91A to 91D is grounded without passing through the switch means 94A to 94D due to a short circuit of the cables 96A to 96D, and falls into the same state as when the switch means 94A to 94D is turned on. However, when the piezo stacks 91C and 91D (91A and 91B) of a group not including the piezo stacks 91A and 91B (91C and 91D) are charged, the piezo stacks 91A and 91B (91C and 91D) are also charged. In addition, simultaneous injection in two cylinders can be avoided (Limp Home) (first conventional example).
[0008]
In the first conventional example, the piezo stacks 91C and 91D (91A and 91B) of the other group can be charged while the discharge of the piezo stacks 91A and 91B (91C and 91D) of one group is not completed. There is an advantage that multistage injection including post injection for activating the catalyst can be easily performed. However, post-injection is not used for combustion, so the degree of freedom in injection timing is wide, and it is not always necessary to perform multiple injections in which the injection state overlaps among a plurality of cylinders. Also, it has been studied to provide an injector specially for post injection in the exhaust passage.
[0009]
For this reason, a piezoelectric actuator drive circuit having the configuration shown in FIG. 4 has been studied. In this configuration, in the configuration shown in FIG. 3, the charge / discharge circuit portion is shared by all the piezo stacks, and the circuit configuration is simplified. This piezo actuator drive circuit includes a line 97a for connecting a charging terminal 92a and a connection terminal 98a to which a common non-grounded cable 99a is connected to one group of piezo stacks 91A and 91B, and the other group. Either one of the groups is charged in one-to-one correspondence with the connection terminal 98b to which the common non-grounded cable 99b is connected to the piezo stacks 91C and 91D and the line 97b connecting the charge / discharge circuit unit 92. Switch means 94a and 94b are provided so as to be cut off from the discharge circuit section 92. As described above, even if any one of the piezo stacks 91A to 91D is grounded without using the cylinder selecting switch means 94A to 94D, the switch means 94a (94b) corresponding to the group to which the piezo stacks 91A to 91D belong. Is turned off and the group is cut off from the charge / discharge circuit unit 92 to realize limp home (second conventional example).
[0010]
By the way, in the second conventional example, the charging / discharging circuit unit including the inductor and the two switching elements is reduced by one as compared with the first conventional example. Additional switch means 94a and 94b for shutting off the piezo stacks 91A and 91B (91C and 91D) of the group from the charge / discharge circuit unit 92 are added. For this reason, only the effect of simplifying the configuration of one inductor can be obtained.
[0011]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a piezo actuator driving circuit and a fuel injection device capable of realizing a limp home with a simple configuration.
[0012]
[Means for Solving the Problems]
According to the first aspect of the present invention , each of the fuel injection devices is equipped with a piezo actuator, a plurality of injectors that are opened and closed by the piezo actuator to switch between fuel injection and stop, and a piezo actuator drive that drives the piezo actuator. And a circuit.
The piezo actuator drive circuit includes a charge / discharge circuit unit common to a plurality of injectors that charge and discharge a piezo stack mounted on the piezo actuator, a connection terminal to which an energizing cable reaching the piezo stack terminal is connected, and it has a switch means for selecting the piezo stack for receiving the output of the charge and discharge circuit from among the plurality of the piezo stack,
A non-ground side connection terminal for an energized cable reaching a non-ground side terminal of each piezo stack, and a wire end connected to the non-ground side connection terminal, and the output of the charge / discharge circuit unit is connected to the non-ground side An ungrounded line for transmission to the connection terminal is provided in one-to-one correspondence with the piezo stack,
The switch means is provided in the middle of the line on the non-grounded side so that conduction and disconnection of each line can be switched.
[0013]
To select a piezo stack for charging and discharging, only the switch means corresponding to the piezo stack needs to be turned on. Also, if normal charging / discharging is impossible in any of the piezo stacks, the switch means corresponding to the piezo stack is turned off to shut off the piezo stack from the charging / discharging circuit unit, and the remaining charge / discharge circuit unit It is possible not to affect the charging / discharging of the piezo stack.
[0014]
Since only the same number of switch means as the piezo stack is required, the configuration is simple.
[0016]
Even if normal charging / discharging is not possible in the piezo stack of any injector, normal operation of the remaining injectors can be ensured with a simple configuration with few switch means.
[0017]
According to a second aspect of the present invention, in the configuration of the first aspect of the invention, there is provided control means for determining an injection period of the injector and outputting a piezo stack charge command and a discharge command corresponding to the injection period to the piezo actuator drive circuit. Equipping,
The control means is set so that the charge holding period of the piezo stack defined by the determined injection period is in succession between the injectors.
[0018]
Appropriate injection control suitable for the configuration of the piezoelectric actuator drive circuit of the present invention can be realized.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
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, common rail pressure). The injector 1 is configured to switch between opening and closing by a piezo actuator 1a. 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.
[0020]
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.
[0021]
The CPU 61, which is a control means, controls the entire internal combustion engine, calculates the fuel injection timing and injection amount based on the detection signal such as the crank angle, that is, the injection period, specifies the injection cylinder, It outputs to the piezo actuator drive circuit 2 for driving the piezo actuator mounted on the injector 1.
[0022]
Further, the CPU 61 performs control so as to obtain an appropriate injection pressure according to the operating conditions known by other sensors. As such sensors, a pressure sensor 62 is provided on the common rail 54, and the CPU 61 controls the metering valve 52 based on the common rail pressure to adjust the amount of fuel pumped to the common rail 54.
[0023]
FIG. 1 shows a configuration of a piezo actuator driving circuit 2 that charges and discharges a piezo stack of a piezo actuator 1 a mounted on each injector 1. The piezo stacks 11A, 11B, 11C, and 11D driven by the piezo actuator drive circuit 2 correspond one-to-one with the injectors 1 mounted in the respective cylinders. The piezo actuator drive circuit 2 is unitized and provided with connection terminals 201A, 201B, 201C, 201D, 202a and 202b for energizing the piezo stacks 11A to 11D. The connection terminals 201A to 201D are on the power supply side which is the non-ground side, and the connection terminals 202a and 202b are on the ground side. The connection terminals 201A to 202b are connected to the piezo stacks 11A to 11D by the wire harness 3.
[0024]
The wire harness 3 includes power-side cables 31A, 31B, 31C, and 31D and ground-side cables 32a and 32b. Each of the power supply side cables 31A to 31D is provided for each of the piezo stacks 11A to 11D, and one end thereof is connected to the ground side terminals of the piezo stacks 11A to 11D in a one-to-one correspondence. The other end is connected to the power supply side connection terminals 201A to 201D in a one-to-one correspondence.
[0025]
The cables 32a and 32b on the ground side are divided into two forks on the piezoelectric stacks 11A to 11D. The cable 32a has two fork ends connected to the ground-side terminals of the piezo stacks 11A and 11B, and includes an injector group (hereinafter referred to as a bank) including an injector 1 having the piezo stack 11A and an injector 1 having the piezo stack 11B. Common). On the other hand, the cable 32b has a bifurcated end connected to the ground-side terminal of the piezo stacks 11C and 11D, and is common to the bank including the injector 1 having the piezo stack 11C and the injector 1 having the piezo stack 11D. is there. The other ends of the ground-side cables 32a and 32b are connected to the ground-side connection terminals 202a and 202b in a one-to-one correspondence.
[0026]
The piezo actuator drive circuit 2 includes a DC power supply 21 by a DC-DC converter 211 that generates a DC voltage of several tens to several hundreds V by power supply (+ B) of a vehicle-mounted battery, and a buffer capacitor 212 connected in parallel to the output terminal thereof. And the energy for charging the piezo stacks 11 </ b> A to 11 </ b> D is stored in the buffer capacitor 212. The DC-DC converter 211 is a general step-up 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 11A to 11D are charged.
[0027]
A first energization path 22a for energizing the piezo stacks 11A to 11D from the buffer capacitor 212 of the DC power source 21 via the connection terminals 202A to 202D is formed. In the middle of the first energization path 22a, a first switching element 24a and an inductor 23 are provided in series from the buffer capacitor 212 side. 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.
[0028]
A second energization path 22b that bypasses the buffer capacitor 212 and the first switching element 24a is formed. The energization path 22b includes a second switching element 24b connected to a connection midpoint between the inductor 23 and the first switching element 24a, and includes the inductor 23, the piezo stacks 11A to 11D, and the second switching element 24b. Form a closed circuit. The second switching element 24b is also composed of a MOSFET, and the parasitic diode (hereinafter referred to as a second parasitic diode) 241b is connected so as to be reverse-biased with respect to the voltage across the buffer capacitor 212. The inductor 23 and the switching elements 24a and 24b constitute a charge / discharge circuit unit 20 together with the DC power source 21, and an output for charging from the inductor 23 to the piezo stacks 11A to 11D is obtained.
[0029]
The energization paths 22a and 22b are branched into four from the output end of the inductor 23. The branched lines 221A to 221D correspond to the four power supply side connection terminals 201A to 201D on a one-to-one basis. Are connected to the piezo stacks 11A to 11D via the cables 31A to 31D from the power supply side connection terminals 201A to 201D.
[0030]
Further, switching elements 25A to 25D for selecting a cylinder, which are switch means, are provided in the middle of the branch lines 221A to 221D, respectively, and a selective switching element 25A corresponding to the piezo stacks 11A to 11D of the injector 1 of the injection cylinder. ~ 25D is turned on.
[0031]
MOSFETs are used for the selection switching elements 25A to 25D, and the parasitic diodes (hereinafter referred to as selection parasitic diodes) 251A, 251B, 251C, and 251D are connected to the buffer capacitor 212 so as to be reverse-biased. Yes.
[0032]
A control signal is input from the controller 29 to each gate of the switching elements 24a, 24b, 25A to 25D.
[0033]
In addition, a resistor 27E having a relatively low resistance is provided in series with the piezo stack 11A and the piezo stack 11B, and a resistor 27F that is the same as the resistor 27E is provided in series with the piezo stack 11C and the piezo stack 11D. is there. The voltage between both ends is input to the controller 29, and the charging currents of the piezo stacks 11A to 11D are detected.
[0034]
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 11A to 11D are detected.
[0035]
A cylinder selection signal for selecting a cylinder for each cylinder is input to the piezo actuator drive circuit 2 as an injection command input from the CPU 61 to the controller 29. Moreover, the injection signal which prescribes | regulates the charge time and discharge time of the piezo stacks 11A-11D is input. The cylinder selection signal and the injection signal are binary signals composed of “H” and “L”.
[0036]
The CPU 61 outputs a cylinder selection signal prior to the injection signal. When any of the cylinder selection signals rises, the controller 29 turns on the cylinder selection switching elements 25A to 25D corresponding to the cylinder, and only the branch lines 221A to 221D provided with the switching elements 25A to 25D are turned on. To do. Then, charging control is executed at the rise of the injection signal that is a charging command. At the time of charge control, the ON period and OFF period of the first switching element 24a are set as follows, and a control signal for the first switching element 24a is output. 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 11A to 11D 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 11A to 11D in this way, the piezo stacks 11A to 11D extend to open the injector 1.
[0037]
Further, the discharge control is executed at the falling edge of the injection signal which is a discharge command. For example, the cylinder selection signal falls together at this time. During the discharge control, the controller 29 sets the ON period and the OFF period of the second switching element 24b as follows, and outputs a control signal for the second switching element 24b. 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 11A to 11D in this way, the piezo stacks 11A to 11D are contracted and the injector 1 is closed.
[0038]
Note that the CPU 61 sets a control program so that the charge holding periods of the piezo stacks 11 </ b> A to 11 </ b> D defined by the determined injection period are changed between the injectors 1 when setting the injection period. Appropriate injection control suitable for the configuration of the piezo actuator drive circuit 2 having only one charge / discharge circuit section can be realized.
[0039]
Further, if there is an abnormality in the connection between the connection terminals 201A to 202b and the piezo stacks 11A to 11D, the controller 29 prohibits the corresponding selection switching elements 25A to 25D from being turned on, and the corresponding piezo stacks 11A to 11D are charged / discharged. What is necessary is just to take the measure cut off from part 20, and limp home is realizable. Moreover, the charging / discharging circuit unit 20 is only one system, and in addition to the selection switching elements 25A to 25D corresponding to the number of cylinders, other piezo stacks, for example, the piezo stacks 11A to 11D in an abnormal state are charged and discharged. Therefore, the number of switching elements can be reduced. The detection of abnormality can be determined from the charging current, discharging current, piezo stack voltage and engine operating state.
[0040]
In addition, although this embodiment showed what was applied to the fuel-injection apparatus of an internal combustion engine, it can be applied if it is an apparatus provided with the several piezoelectric actuator.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a piezo actuator driving circuit of the present invention that drives a piezo actuator mounted on an injector of a fuel injection device of the present invention.
FIG. 2 is an overall configuration diagram of the fuel injection device.
FIG. 3 is a circuit diagram of a conventional piezo actuator driving circuit.
FIG. 4 is a circuit diagram of another conventional piezoelectric actuator drive circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Injector 11A, 11B, 11C, 11D Piezo stack 2 Piezo actuator drive circuit 20 Charging / discharging circuit part 201A, 201B, 201C, 201D, 202a, 202b Connection terminal 221A, 221B, 221C, 221D Line 25A, 25B on the ungrounded side 25C, 25D selection switching element (switching means)
3 Wire harness 31A, 31B, 31C, 31D, 32a, 32b Cable 61 CPU (control means)

Claims (2)

In a fuel injection apparatus, each of which is equipped with a piezo actuator, and includes a plurality of injectors that are opened and closed by the piezo actuator to switch between fuel injection and stop, and a piezo actuator drive circuit that drives the piezo actuator.
The piezoelectric actuator drive circuit is
A common charging and discharging circuit part to a plurality of injectors for performing charging and discharging of the piezo stack, which is mounted on the piezoelectric actuator, and a connection terminal to which a leading energizing cable to the terminals of the piezo stack are connected, a plurality of piezoelectric stacks and it has a switch means for selecting the piezo stack for receiving the output of the charge and discharge circuit from among,
A non-ground side connection terminal for an energized cable reaching a non-ground side terminal of each piezo stack, and a wire end connected to the non-ground side connection terminal, and the output of the charge / discharge circuit unit is connected to the non-ground side An ungrounded line for transmission to the connection terminal is provided in one-to-one correspondence with the piezo stack,
The fuel injection device according to claim 1, wherein the switch means is provided in the middle of the line on the non-grounded side to switch between conduction and disconnection of each line. The fuel injection device according to claim 1, further comprising a control unit that determines an injection period of the injector and outputs a charge command and a discharge command of the piezo stack corresponding to the injection period to the piezo actuator drive circuit,
A fuel injection device in which the control means is set so that the charge holding period of the piezo stack specified by the determined injection period is in succession between the injectors .

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