JP2002185056A - Abnormality detection device of piezo actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve the abnormality detection device of a piezo actuator that can accurately detect abnormal state, such as partial and entire burnout in the piezo actuator, and to improve reliability and working efficiency in abnormality judgment. SOLUTION: A detection point 6 is provided in the middle of a conduction path 11 to piezo stacks P1 and P2 of the piezo actuator which are electrically connected in parallel and being used under the same environment conditions, and a battery 51 is connected via a switch SW. A battery voltage is applied to the piezo stack P1 via the detection point 6, voltage at the detection point 6 when charge accumulated in the piezo stack P1 is recharged to the piezo stacks P1 and P2 is detected by a voltage monitor circuit 7, and the abnormal state such as the partial and entire burnout in the piezo actuator is detected based on the detected result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormality detecting device for detecting an abnormality of a piezo actuator applied to a piezo injector of an internal combustion engine.

[0002]

2. Description of the Related Art A piezo actuator using a piezoelectric material which expands and contracts by applying a voltage has high response and excellent controllability. Therefore, it has been conventionally used for a vehicle drive device, for example, a piezo drive type injector. Is being considered. On the other hand, in recent years, it has become necessary to establish a failure diagnosis technology for on-vehicle equipment in order to respond to new vehicle regulations. Is required.

With respect to safety measures against high voltage of a piezo actuator, for example, Japanese Patent Application Laid-Open No. 1-2202177 describes that an abnormality detecting circuit is provided in a driving device of a piezo actuator. This abnormality detection circuit detects a charging current or a discharging current flowing in the driving current path during charging / discharging of the piezo actuator, and determines that an abnormality has occurred when the charging current or the discharging current has not reached a predetermined level. Occasionally, the reliability of the device is enhanced by prohibiting the operation of generating a high voltage or displaying an error.

[0004]

Here, the piezo actuator has a structure in which a plurality of piezoelectric bodies are laminated via electrodes, and a large number of capacitive elements are electrically connected in parallel. There is a failure mode (partial disconnection) in which the total capacity changes due to disconnection inside the laminate. Therefore, if this can be detected separately from the total disconnection of the piezo actuator or the disconnection of the wire, the trouble required for specifying the abnormality can be greatly reduced.

For example, when the above-described conventional detection method is applied, it is possible to set a current threshold value that is small enough to determine a partial disconnection state, and compare this set value to determine the partial disconnection state. Conceivable. However, even if the piezo actuator is not disconnected, the total capacity of the piezo actuator changes due to changes in the operating environment such as temperature and pressure. There is a problem that it is difficult to distinguish between them, and there is a possibility of erroneous determination.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a piezo actuator abnormality detecting device capable of accurately detecting an abnormal state such as partial or complete disconnection inside the piezo actuator. Another object of the present invention is to improve the reliability and workability of abnormality determination.

[0007]

According to the present invention, there is provided an apparatus for detecting an abnormality of a piezo actuator which has a structure in which a plurality of piezoelectric bodies are stacked and which expands and contracts by being charged or discharged by a driving means. A plurality of piezo actuators electrically connected in parallel and used under the same environmental conditions are provided, and connected to a detection point provided in the middle of an energization path from the driving means to the plurality of piezo actuators, and the detection point is connected. Detecting voltage applying means for applying a constant voltage for detection to one of the plurality of piezo actuators via the detecting point, and applying the detecting constant voltage to the one piezo actuator via the detecting point from the detecting voltage applying means After that, the electric charge accumulated in the one piezo actuator is transferred to the one piezo actuator and the other piezo activator. Providing a voltage monitor means for detecting a voltage of the detection point when the recharge eta. And
An abnormal state of the piezo actuator is detected based on a detection result of the voltage monitoring means.

When a predetermined amount of charge charged in the one piezo actuator from the detection voltage applying means is recharged to the plurality of piezo actuators connected in parallel, the charge is redistributed in accordance with the respective capacitances. You.
The voltage between both ends of the plurality of piezo actuators after recharging is determined according to the total capacity of the plurality of piezo actuators, and if there is a partial or complete disconnection in the piezo actuator, the total capacity changes. By detecting the voltage of the piezo actuator after charging as the voltage at the detection point, abnormalities such as partial disconnection or complete disconnection of the piezo actuator can be distinguished and detected. Further, since the plurality of piezo actuators are installed under the same environmental conditions, abnormality determination can be performed with good workability and high accuracy without being affected by environmental conditions such as temperature and pressure.

Specifically, the plurality of piezo actuators may have the same structure, and one of the piezo actuators may be used as a reference piezo actuator, and an abnormality of the other piezo actuator may be detected. it can. Then, the constant voltage for detection is +
In the case of B, if the voltage detected by the voltage monitoring means is + B / 2, it is determined that there is no disconnection, and if it is greater than + B / 2 and less than + B, it is determined that the other piezo actuator is partially disconnected, If + B, it is determined that the other piezo actuator is completely disconnected or the wiring is disconnected.

When the reference piezo actuator has the same laminated structure as the other piezo actuator,
If the other piezo actuator is normal, the voltage detected by the voltage monitoring means is １ ／ of the constant voltage. If the other piezo actuator is partially disconnected, the actual capacitance is reduced, and the detected voltage is greater than １ ／ of the constant voltage. Also,
If the other piezo actuator is completely disconnected,
The detected voltage does not change with the constant voltage. Therefore, by comparing these values with the detected voltage, the presence / absence of abnormality can be accurately determined.

Alternatively, it is possible to consider a case where there is an abnormality in both of the plurality of piezo actuators. When the plurality of piezo actuators have the same structure and the constant voltage for detection is + B, if the voltage detected by the voltage monitoring means is + B, it is determined that at least the other piezo actuator is completely disconnected or the wiring is disconnected. If it is larger than + B / 2 and smaller than + B, at least the other piezo actuator is determined to be partially disconnected, and if + B / 2, there is no disconnection or the one piezo actuator and the other piezo actuator are partially disconnected. If the disconnection amount is determined to be the same, and if it is larger than 0 and smaller than + B / 2, at least one of the piezo actuators is determined to be partially disconnected, and if it is 0, at least one of the piezo actuators is determined to be completely disconnected or wiring disconnected.

An abnormality in one of the piezo actuators,
For example, when there is a partial disconnection, the constant voltage for detection is not charged, so that the voltage detected by the voltage monitoring means is smaller than 1/2 of the constant voltage. In the case of complete disconnection or wiring disconnection, the detected voltage is zero. In addition, when the one piezoelectric actuator and the other piezoelectric actuator have the same partial cutoff, a voltage value of １ ／ of the constant voltage is detected.
If the detected voltage is larger than の of the constant voltage, it means that at least the other piezo actuator has the above-described abnormality. With this configuration, it is possible to simultaneously determine the abnormality of two equivalent piezo actuators.

Preferably, the plurality of piezo actuators are respectively incorporated in a plurality of piezo injectors provided in an internal combustion engine. Since the piezo injectors installed in the internal combustion engine are under the same environmental conditions, the above-described abnormality determination can be suitably used. Also,
By applying the present invention to a piezo injector having a large number of piezo actuators corresponding to the number of cylinders, workability such as malfunction investigation of an internal combustion engine is greatly improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment in which the present invention is applied to abnormality detection of a piezo injector provided in a common rail injection device of an engine will be described. FIG. 1 is an overall configuration diagram of a drive control system of a piezo actuator incorporated in a piezo injector, and includes a piezo actuator abnormality detection device as described later. In the drawing, P1 and P2 represent piezo stacks that constitute the main part of the piezo actuator, and since each piezo injector is connected to a common common rail (accumulation pipe), the piezo stacks P1 and P2 They are in the same environmental conditions with equal conditions such as pressure. Although the same number of piezo injectors as the number of cylinders of the engine are provided, only two of them (piezo stacks P1 and P2) are shown here for simplicity.

In FIG. 1, a drive control unit (ECU) 1 of a piezo actuator as a driving means includes a high voltage generating circuit 2 for generating a high voltage applied to the piezo stacks P1 and P2, and a high voltage generating circuit 2 for generating a high voltage. A switching circuit for charging for applying a high voltage to the piezo stacks P1 and P2 and a switching circuit for discharging for discharging electric charges accumulated in the piezo stacks P1 and P2; A control circuit 4 for controlling ON / OFF of the switching element for charging or discharging is provided. Piezo stack P1, P2
Are connected in series with selection switching elements T1 and T2, respectively.
1, the piezo stacks P1 and P2 to be driven are selected by ON-OFF control of T2.

Each of the piezo stacks P1 and P2 is formed by laminating and integrating a large number of piezoelectric bodies such as PZT formed into a circular or rectangular plate shape, and a positive electrode and a negative electrode are alternately formed between the piezoelectric bodies. You. FIG. 2 is an equivalent circuit diagram of the piezo stacks P1 and P2, and shows a large number of piezoelectric elements (C1 to C
n) has a configuration electrically connected in parallel, and expands by injecting (charging) electric charges and contracts by removing (discharging) electric charges to drive the piezo injectors to open and close. When a charge signal or a discharge signal is output from the control circuit 4,
The switching element for charging or discharging of the switching circuit 3 is turned on, and the piezo stacks P1, P2 selected by the switching elements for selection T1, T2 are charged or discharged.

For the switching, for example, a multiple switching system in which charging and discharging are performed by switching stepwise is used. In this method, the control circuit 4 starts charging when detecting the rising edge of the injection signal (for example, a 0-5 V rectangular wave signal), turns on the charging switching element of the switching circuit 3, and turns on the high voltage generation circuit 2 Is charged to the piezo stacks P1 and P2 to be driven. Thereafter, when the charging current reaches a predetermined value (for example, 20 A), the charging switching element is turned off, and after a certain OFF period (for example, 10 μs), turning on again is repeated. Then, a predetermined charging voltage (for example, 100
When V) is reached, the charging switching element is fixed to OFF, and charging is completed.

Next, when the falling edge of the control signal is detected, the discharge is started. First, the switching circuit 3
Of the piezo stacks P1 and P2 is discharged. When the discharge current reaches a predetermined value (for example, 20 A), the discharge switching element is turned off, and a certain OFF period (for example, 10 μm) is set.
s) After that, turning on the discharge switching element again is repeated. When the charging voltage reaches zero, the discharging switching element is fixed to OFF, and the discharging is completed.

In the present invention, in order to detect abnormality of the piezo stacks P1 and P2, a predetermined constant voltage (+ B) for detection is applied to one of the piezo stacks P1 and P2 in the drive control unit 1.
Is applied. The detection voltage application means 5 includes a detection point 6 provided in the middle of the energization path 11 from the switching circuit 3 to the piezo stacks P1 and P2.
And a battery 51 connected via a switch SW, and a battery voltage (+ B) is applied to one of the piezo stacks P1 and P2 via the detection point 6. In order to know the voltage between both ends of the piezo stacks P1 and P2 when the electric charge accumulated in one of the piezo stacks P1 and P2 is recharged to both of the piezo stacks P1 and P2, the detection point 6 A voltage monitoring circuit 7 is provided as voltage monitoring means for detecting the voltage of the power supply.

Next, the operation of the abnormality detecting device constituted by the detection voltage applying means 5 and the voltage monitor circuit 7 will be described. Here, the timing of performing the abnormality detection is a period during which the injection of the piezo injector is not performed (when the charging and discharging switching elements of the switching circuit 3 are turned on and off).
FF state). Here, as a temporary precondition, it is assumed that the piezo stack P1 is confirmed to be normal, and this is used as a reference piezo actuator (one piezo actuator) and a detection piezo actuator (the other piezo actuator). )
This shows a case where the presence or absence of an abnormality in the piezo stack P2 is detected.

First, the selection switching element T1 is set to O
N, switching element T2 for selection is OFF, switch S
W is turned ON, and the battery voltage (+
B) Charge. Next, the switch SW is turned off, the switching element for selection T2 is turned on (the switching element for selection T1 is kept on), and the piezo stack P
The charge stored in 1 is released to the piezo stack P2. At this time, if the piezo stack P2 is not disconnected, the capacity is doubled by the above operation, and the voltage monitored by the voltage monitor circuit 7 is + B / 2. Also,
As shown in FIG. 3, partial disconnection occurs inside the piezo stack P2 having a configuration in which capacitive elements are connected in parallel. For example, if the capacitance is reduced by half, the capacitance becomes 1.5 times by the above operation. The applied voltage is + B × ２.
If the piezo stack P2 has been completely disconnected or has been disconnected from the wiring, no charge is released, and the monitored voltage remains unchanged at + B.

Table 1 shows the correspondence between the monitor voltage and the piezo stack P2 disconnection determination. In this way, by using one of the plurality of piezo stacks (piezo stack P1) as a reference and monitoring the voltage thereof, it is possible to easily determine the abnormality of the other piezo stack P2, Partial disconnection can be detected separately from all disconnections or wiring disconnections. Further, by using the piezo stack P1 having the same environmental condition as a reference, the influence of the environmental condition can be eliminated, and a highly reliable abnormality determination device can be realized.

[0023]

[Table 1]

In the first embodiment, the case where the abnormality detection is performed on the assumption that the piezo stack P1 is normal has been described. However, in consideration of the possibility that the piezo stack P1 has an abnormality, the following will be described. The abnormality determination can be performed as shown in the second embodiment.

In the first embodiment, the selection switching element T1 is turned ON and the selection switching element T
2 is turned off, the switch SW is turned on, and when the piezo stack P1 is charged with the battery voltage (+ B), the charge Q1 charged in the piezo stack P1 is Q1 = C1 × + B
It is represented by This charge Q1 is then recharged to the combined capacitance of the piezo stack P1 and the piezo stack P2 by turning off the switch SW and turning on the selection switching element T2, so that V: monitor voltage, C
Assuming that 1: the capacity of the piezo stack P1, and C2: the capacity of the piezo stack P2, Q1 = C1 × + B = (C1 + C2) × V, and the general formula of the monitor voltage V is as follows. V = + B × (C1 / (C1 + C2))

From the above general formula, when there is no partial disconnection or the same partial disconnection in both the piezo stack P1 and the piezo stack P2, C1 = C2 and V = + B /
2. When C2 = 0 (at least the piezo stack P2 is completely disconnected or the wiring is disconnected), V = +
When B and C1 = 0 (at least the piezo stack P1 is completely disconnected or the wiring is disconnected), V = 0 and C2 <C1
(At least when the piezo stack P2 is partially broken)
It can be seen that when B / 2 <V <+ B and C1 <C2 (at least the piezo stack P1 is partially disconnected), 0 <V <+ B. Table 2 shows the correspondence between the monitor voltage and the piezo stack P1, P2 disconnection determination.

[0027]

[Table 2]

In this way, the abnormality can be detected not only for the piezo stack P2 but also for the piezo stack P1, and at least a part of the piezo stack P1 is disconnected or completely removed from the monitor voltage detected by the voltage monitor circuit 7. It is possible to accurately detect disconnection or wiring disconnection.

As described above, if the abnormality detecting device of the present invention is used for an engine malfunction investigation on the market, etc., it is possible to easily detect and replace not only the piezo injector which is completely disconnected but also at least a partially disconnected piezo injector. In addition, all the piezo injectors can be normalized by a work procedure in which a normal piezo injector after replacement is used as a reference piezo actuator and abnormality detection is performed again in combination with one of the remaining piezo injectors. Therefore, the investigation / replacement work of the piezo injector can be efficiently performed, and the number of work steps can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing the overall configuration of a piezo injector drive control system including a piezo actuator abnormality detection device according to the present invention.

FIG. 2 is an equivalent circuit diagram of a piezo stack.

FIG. 3 is a diagram showing a partially broken state of a piezo stack.

[Explanation of symbols]

 P1, P2 Piezo stack (piezo actuator) SW switch 1 Drive control section (drive means) 11 Current path 2 High voltage generation circuit 3 Switching circuit 4 Control circuit 5 Detection voltage application circuit (detection voltage application means) 51 Battery 6 Detection point 7 Voltage monitor circuit (voltage monitor means)

Claims (4)

[Claims] 1. An apparatus for detecting an abnormality of a piezo actuator which has a structure in which a plurality of piezoelectric bodies are laminated and which expands and contracts when charged or discharged by a driving means,
A plurality of piezo actuators electrically connected in parallel and used under the same environmental conditions are provided, and connected to a detection point provided in the middle of an energization path from the driving means to the plurality of piezo actuators, and connected via the detection point. Detecting voltage applying means for applying a constant voltage for detection to one of the plurality of piezo actuators; and applying the constant voltage for detection to the one piezo actuator via the detection point from the detecting voltage applying means. Thereafter, voltage monitoring means for detecting a voltage at the detection point when the electric charge accumulated in the one piezo actuator is recharged to the one piezo actuator and the other piezo actuator is provided. Detecting an abnormal state of the piezo actuator based on a detection result. Abnormality detection device of the actuator. 2. The method according to claim 1, wherein the one piezo actuator of the plurality of piezo actuators having the same structure is used as a reference piezo actuator to detect an abnormality of the other piezo actuator, and the constant voltage for detection is + B. At one time, if the voltage detected by the voltage monitoring means is + B / 2, it is determined that there is no disconnection, and + B / 2
2. The abnormality detecting device for a piezo actuator according to claim 1, wherein when it is larger than + B, it is determined that the other piezo actuator is partially disconnected, and when it is + B, it is determined that the other piezo actuator is completely disconnected or the wiring is disconnected. 3. A method for detecting an abnormality of the plurality of piezo actuators having the same structure, wherein if the voltage detected by the voltage monitoring means is + B when the constant voltage for detection is + B. It is determined that at least the other piezo actuator is completely disconnected or the wiring is disconnected,
If it is larger than + B / 2 and smaller than + B, it is determined that at least the other piezo actuator is partially disconnected, and + B
/ 2, it is determined that there is no disconnection, or that the one piezo actuator and the other piezo actuator are partially disconnected and the disconnection amount is the same, and if it is larger than 0 and smaller than + B / 2, at least a partial disconnection of the one piezo actuator. The piezo actuator abnormality detection device according to claim 1, wherein if 0, it is determined that at least one of the piezo actuators is completely disconnected or the wiring is disconnected. 4. The abnormality detecting device for a piezo actuator according to claim 1, wherein said plurality of piezo actuators are respectively built in a plurality of piezo injectors provided in an internal combustion engine.