JP2634817B2 - Piezo element drive circuit - Google Patents

Description

Description: Object of the Invention [Industrial application field] The present invention relates to a piezoelectric element drive circuit that is effective for reducing the operation noise of a piezoelectric element.

2. Description of the Related Art Conventionally, an actuator using a piezoelectric element that operates quickly has been used to quickly change, for example, the damping force of a shock absorber for a vehicle in accordance with the running state of the vehicle. There are known techniques that make this possible.

For example, a "variable damping force shock absorber" (Japanese Patent Application Laid-Open No. 61-85210) has been proposed. That is, a piezoelectric member is disposed on the piston in the shock absorber, and a sliding member that changes the passage area of the communication passage between the first and second oil chambers is provided. This is a technique in which the sliding member is displaced to change the passage area to improve the responsiveness of the damping force switching control.

[Problems to be Solved by the Invention] By the way, the driving circuit of the piezoelectric body in the above-described conventional technique includes a high-voltage power supply by a DC-DC converter, a switch for turning on and off the output of the high-voltage power supply, and closing the switch for a predetermined time. A timer circuit is provided, for example, when charging the piezoelectric body, the switch is operated for a set time determined by the timer circuit in order to apply a high voltage from the high-voltage power supply to the piezoelectric body of the shock absorber. However, when the piezoelectric body is charged or discharged by such a drive circuit, the supply speed of electric energy to the piezoelectric body,
Alternatively, there has been a problem that a loud operating noise is generated when the piezoelectric body is operated due to the release speed being too fast. Such a loud operating noise is a particularly significant problem when, for example, a piezoelectric body is incorporated in a variable damping force type shock absorber of a vehicle, which gives a passenger an uncomfortable feeling.

In addition to the above problems, there is also a problem that the reliability and durability of the piezoelectric body and the variable damping force type shock absorber using the piezoelectric body are reduced.

Furthermore, since a part of the electric energy supplied or released at the time of driving the piezoelectric body is dissipated as an operation sound, there is a problem that the electric energy is wasted.

As a measure against each of the above problems, for example,
A coil or the like having a predetermined self-induction coefficient is interposed between the piezoelectric body and the drive circuit to delay the supply speed or release speed of the electric energy by the self-induction phenomenon or the electric resistance of the coil. It was thought. However, in general, when the supply speed or the discharge speed of the electric energy is delayed by a coil or the like, there is a problem that the coil becomes extremely large. For this reason, a large mounting space is required. For example, it is extremely difficult to mount the shock absorber on a vehicle with a variable damping force, and the above-described improved technology has not been sufficient.

An object of the present invention is to provide a piezoelectric element drive circuit that changes the damping force of a variable damping force shock absorber and that can reduce the operating noise of the piezoelectric element with a simple configuration.

Configuration of the Invention [Means for Solving the Problems] The present invention has been made to solve the above problems. The present invention provides a piezoelectric element for changing the damping force of a vehicle shock absorber by expansion and contraction in accordance with an applied voltage. According to the directive
A charging switch means for applying a predetermined set voltage; and a discharge switch means for discharging a voltage applied to the piezoelectric element in accordance with an external command. Means and a conductive part for charging that connects the piezoelectric element, or, at least one of the conductive part for discharging that connects the switch means for discharging and the piezoelectric element, when charging the piezoelectric element, or A piezoelectric element driving circuit, comprising: a resistor having a predetermined electric resistance determined based on the capacitance of the piezoelectric element so that a time constant at the time of discharging becomes a predetermined target time constant. It is the gist.

Here, the piezoelectric element causes a phenomenon of expansion and contraction when a voltage is applied, that is, a so-called reverse piezoelectric effect (piezo effect). For example, it can be realized by a piezoelectric ceramic such as lead zirconate titanate (PZT), crystal, Rochelle salt, or the like.

The charging switch means, according to an external command,
A predetermined set voltage is applied to the piezoelectric element via a resistor described later.

The switch means for discharging, according to an external command,
This is to discharge the voltage applied to the piezoelectric element via a resistor described later.

The charge switch means and the discharge switch means can be realized by, for example, semiconductor switch elements such as various transistors and thyristors. Further, for example, when a photosensitive SCR (LASCR) controlled by light is used, the operation reliability is improved.

The resistor is interposed in at least one of a conductive part for charging that connects the switch means for charging and the piezoelectric element, or a conductive part for discharging that connects the switch means for discharge and the piezoelectric element, and charges the piezoelectric element. It has a predetermined electric resistance determined based on the capacitance of the piezoelectric element so that the time constant at the time of discharge or the discharge becomes a predetermined target time constant. For example, when extremely high responsiveness is required in any one of charging and discharging, the configuration may be such that only the conductive portion that does not require the responsiveness is interposed. In addition, for example, when there is no adverse effect on the responsiveness in both the charging and discharging cases, the operation noise can be reduced by interposing both the charging conductive portion and the discharging conductive portion. Is extremely effective. The time constant is
For example, when a resistor is used as the resistor, it can be calculated by the product of the capacitance of the piezoelectric element and the electrical resistance of the resistor. Here, the time constant at the time of charging and the time constant at the time of discharging do not necessarily have to be the same. Therefore, when a resistor is interposed in both the conductive part for charging and the conductive part for discharging, the operating condition of the piezoelectric element May be configured so that the electrical resistance of both resistors is different.

[Operation] The piezoelectric element drive circuit of the present invention performs voltage application and discharge to a piezoelectric element that changes the damping force of a vehicle shock absorber.
A predetermined set voltage is applied to the piezoelectric element according to an external command, and the discharging switch means discharges the voltage applied to the piezoelectric element according to an external command.

Here, in particular, in the piezoelectric element drive circuit of the present invention, a charging conductive portion (that is, a charging path from the charging switch means to the piezoelectric element) connecting the charging switch means and the piezoelectric element,
Alternatively, a resistor is interposed in at least one of the conductive parts for discharging (that is, the discharge path from the piezoelectric element to the switch means for discharging) that connects the switching means for discharging and the piezoelectric element. The electric resistance of the low antibody is determined based on the capacitance of the piezoelectric element so that the time constant at the time of charging or discharging the piezoelectric element becomes a predetermined target time constant.

Therefore, according to the piezoelectric element driving circuit of the present invention, when a predetermined set voltage is applied to the piezoelectric element or when the voltage applied to the piezoelectric element is discharged in order to change the damping force of the vehicle shock absorber. In, the charging time of the piezoelectric element, or at least one of the discharging time,
It can be prevented from becoming shorter than a predetermined target time constant. Therefore, it is possible to prevent the rapid charging or the rapid discharging by suppressing the supply speed or the discharging speed of the electric energy to the piezoelectric element, thereby changing the damping force of the vehicle shock absorber. The operating noise of the piezoelectric element generated at the time can be reduced.

In addition, since rapid charging or rapid discharging of the piezoelectric element can be prevented in this way, not only can the operating noise be reduced, but also the damping force of the vehicle shock absorber can be prevented from suddenly changing. As a result, the reliability and durability of the shock absorber can be improved, and the riding comfort, maneuverability, and stability of the vehicle can be improved.

Moreover, in the piezoelectric element drive circuit of the present invention, the charging conductive section as a charging path from the charging switch means to the piezoelectric element, or the discharging conductive section as a discharging path from the piezoelectric element to the discharging switch means, By interposing a resistor, only the charging or discharging speed of the piezoelectric element is suppressed, so for the piezoelectric element,
A predetermined set voltage can be reliably applied by the charging switch means, and the voltage of the piezoelectric element can be reliably discharged by the discharging switch means. Therefore, there is no hindrance to a change in the damping force of the vehicle shock absorber.

As described above, the technical problems of the present invention are solved by the operation of each component of the present invention.

[Embodiment] Next, a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 shows a system configuration of a vehicle shock absorber control device using a piezoelectric element drive circuit according to one embodiment of the present invention.

As shown in FIG. 1, the vehicle shock absorber control device 1 includes a variable damping force type shock absorber 2, 3, 4, 5, a stop lamp switch 6 for detecting a brake operation state of the vehicle, and a running speed of the vehicle. Vehicle speed sensor 7 and an electronic control unit for controlling these (hereinafter simply referred to as ECU)
8.

The variable damping force type shock absorbers 2, 3, 4, 5 are, as described later, the variable damping force type shock absorbers 2, 3,
A piezo-type load sensor that outputs a damping force acting on 4, 5 and a piezo actuator that switches the damping force of the damping force-variable type shock absorbers 2, 3, 4, and 5 are each incorporated in a set.

In addition, the variable damping force type shock absorbers 2, 3, 4, 5
Are the suspension lower arms of the left and right front and rear wheels, respectively.
2a, 3a, 4a, 5a and a coil spring 2b, 3
b, 4b, 5b.

The detection signals of the sensors and switches are input to the ECU 8, and the ECU 8 outputs a control signal to the piezo actuator.

Since the structures of the variable damping force type shock absorbers 2, 3, 4, and 5 are all the same, the variable damping force type shock absorber 2 will be described as an example. Variable damping force type shock absorber 2
As shown in FIG. 3, a main piston 12 is slidably fitted in the cylinder 11 in the axial direction (indicated by arrows A and B in FIG. 3). The piston 12 is divided into a first hydraulic chamber 13 and a second hydraulic chamber 14. The main piston 12 is connected to one end of a piston rod 15, while the other end of the piston rod 15 is fixed to a shaft 16. The lower part (not shown) of the cylinder 11 is connected to the lower arm 2a described above, while the upper part (not shown) of the shaft 16 is connected to the vehicle body 9 described above.

The main piston 12 is provided with the first hydraulic chamber 13 and the second hydraulic chamber 13.
An extension-side fixed orifice 17 and a contraction-side fixed orifice 18 for communicating with the hydraulic chamber 14 are formed, and at the outlet side of the extension-side fixed orifice 17 and the contraction-side fixed orifice 18,
Plate valves 17a, 18 that restrict the flow direction to one direction
a is provided respectively. Therefore, the main piston 1
When the cylinder 2 slides in the cylinder 11 in the axial direction (indicated by arrows A and B in the figure), the hydraulic oil in the first hydraulic chamber 13 and the second hydraulic chamber 14 is supplied to the extension-side fixed orifice. Since they flow mutually through the contraction side fixed orifice 18 and the contraction side fixed orifice 18, the hydraulic oil has a relatively small cross-sectional area and a small flow rate. For this reason, the characteristic of the damping force of the variable damping force type shock absorber 2 at this time is as shown in FIG.
High damping (HARD) characteristics.

By the way, the piston rod 15 has a hollow portion formed in the axial direction thereof, and the hollow portion incorporates a piezo actuator 19FL which is an electrostrictive element laminate made of piezoelectric ceramics such as PZT. . A piston 20 is disposed at a position close to and opposed to a lower end surface of the piezo actuator 19FL. The piston 20 is normally urged by a leaf spring 20a in a direction indicated by an arrow A in FIG. The inside of the 15 hollow portions can slide in the axial direction. When a voltage of several hundred [V] is applied to the piezo actuator 19FL, the piston 20 moves by several tens [μm] in the direction indicated by the arrow B in FIG. On the other hand, when the voltage of several hundred [V] applied to the piezo actuator 19FL is discharged, the piston 20 moves in the direction indicated by arrow A in FIG. The charging and discharging of the piezo actuator 19FL are performed via a lead wire 19a provided in a passage formed in the shaft 16 in the axial direction thereof.

Further, the hollow portion of the piston rod 15 and the piston
An oil-tight chamber 21 is formed with the bottom surface of the piston rod 20 and the piston rod 15
A cylindrical plunger 22 is slidably fitted in a through hole that is bored in the axial direction and communicates with the bottom of the oil-tight chamber 21,
Further, the lower end of the plunger 22 is connected to an upper portion of a spool valve 24 which slidably fits into a fitting hole inside the housing 23 fixed to the piston rod 15. The spool valve 24 is normally urged by a spring 25 in a direction indicated by an arrow A in FIG. An annular groove 24a is formed in the lower part of the spool valve 24 on the outer peripheral part, and the lowermost part is shaped into a column. Therefore, when the spool valve 24 is urged by the spring 25 in the direction indicated by the arrow A in the same figure, the lowermost portion of the spool valve 24 shaped into a cylindrical shape is bored in the piston rod 15 and 1st hydraulic chamber 13
The sub flow path 26 connecting the second hydraulic chamber 14 and the second hydraulic chamber 14 is shut off. On the other hand, when a voltage is applied, the piezo actuator 19FL expands by a small amount, and the piston 20 also moves in the direction indicated by the arrow B in FIG.
And the pressure inside the oil-tight chamber 21 rises. For this reason, the plunger 22 is moved in the direction indicated by the arrow B in the same figure by a distance obtained by expanding the minute amount of extension of the piezo actuator 19FL in accordance with the ratio between the pressure receiving area of the plunger 22 and the pressure receiving area of the piston 20. , The spool valve 24 also descends by the same enlarged distance in the same direction, and the sub-flow path 26 communicates via an annular groove 24a formed in the outer periphery of the lower portion of the spool valve 24. . As described above, the first hydraulic chamber 13 and the second hydraulic chamber 14 communicate with each other through the sub-flow path 26, so that the cross-sectional area of the hydraulic oil flowing through the main piston 12 becomes relatively large. The flow rate also increases. Therefore, the characteristic of the damping force of the variable damping force type shock absorber 2 at this time is a characteristic of a small damping force (SOFT) as shown in FIG.

A piezo-type load sensor 31FL for detecting the magnitude of the damping force acting on the variable damping force-type shock absorber 2 is disposed above the shaft 16, and the piezo-type load sensor 31FL is connected to the nut 32 by the nut 32. It is fixed to the shaft 16. The piezo type load sensor 31FL is PZ
Two thin plates of piezoelectric elements made of piezoelectric ceramics such as T3
1A and 31B are overlapped, and the detection signal is a lead wire 31a disposed in a passage formed inside the shaft 16.
Is output to the ECU 8 described above.

Next, the configuration of the ECU 8 will be described with reference to FIG. As shown in the figure, the ECU 8 is configured as a logical operation circuit centering on the CPU 8a, ROM 8b, and RAM 8c, is connected to the input unit 8e and the output unit 8f via the common bus 8d, and performs input / output with the outside. Piezo type load sensor 31FL, 31FR, 31RL, 31R
The detection signal of R passes through the damping force signal detection circuit 35,
The detection signals of the stop lamp switch 6 and the vehicle speed sensor 7 are sent from the input unit 8e to the CPU 8a via the waveform shaping circuit 36, respectively.
Is input to On the other hand, the CPU 8a outputs the drive circuit 3 from the output unit 8f.
7 via piezo actuators 19FL, 19FR, 19RL, 19RR
To output a control signal.

Next, the configuration of the drive circuit 37, which is a feature of the present embodiment, will be described with reference to the circuit diagram of FIG. As shown in the figure, the drive circuit 37 includes a high voltage generation circuit 41 and four switching circuits 42FL, 42FR, 42RL, 42RL provided corresponding to the piezo actuators 19FL, 19FR, 19RL, 19RR.
It consists of 2RR.

The high voltage generation circuit 41 includes an oscillation circuit 51, a control circuit 52,
It comprises an AND circuit 53, a transistor 54 and a booster circuit 55. The above oscillation circuit mainly composed of a timer IC
Pulse signal of predetermined period output from 51 and the above control circuit
The transistor 54 is switched between a conductive state (ON) and a cut-off state (OFF) by a logical product signal obtained by inputting the control signal output from 52 to the AND circuit 53. Here, when the transistor 54 switches from the conductive state (ON) to the cut-off state (OFF), the current in the primary coil 56 of the transformer of the booster circuit 55 sharply decreases, so that the secondary coil 57a , 57b generate energy as a current due to the back electromotive force, and this energy is stored in the capacitors 59a, 59b via the diodes 58a, 58b. In this case, in order to keep the high voltage terminal at +500 [V] and the low voltage terminal at -100 [V], the control circuit 52 controls the boost circuit.
By performing feedback control for outputting a control signal to the AND circuit 53 based on the voltage of the high voltage terminal of 55, the number of times the transistor 54 is switched is adjusted.

Since the switching circuits 42FL, 42FR, 42RL, and 42RR have the same configuration, the switching circuit 42FL will be described as an example.

The switching circuit 42FL is connected to the piezo actuator 1 from the high voltage terminal (+500 [V]) of the high voltage generation circuit 41.
The charging circuit 61 for applying a voltage to the 9FL and the voltage applied to the piezo actuator 19FL
And a discharge circuit 62 for discharging the low voltage terminal (−100 [V]).

When the charging control signal Vca is input from the ECU 8, the charging circuit 61 switches the photosensitive silicon control rectifier (Light Activated SCR) 63, which is a type of thyristor, from a high-resistance cut-off state (OFF) to a low-resistance saturation state (ON). ). As a result, the high voltage terminal (+500
[V]), a voltage is applied to the piezoelectric actuator 19FL via the photosensitive silicon control rectifier 63 and the charging resistor 64, and the piezoelectric actuator 19FL expands. The following equation (1) is established between the electric resistance value R1 of the charging resistor 64, the capacitance C of the piezo actuator 19FL, and the time constant τ1 during charging.

τ1 = C × R1 (1) In this embodiment, C = 0.5 × 10 ⁻⁶ [F] R1 = 2 × 10 ³ [Ω] τ1 = 1.0 [msec].

However, it is preferable that the value of the time constant τ1 during charging be selected in the range of 1.0 to 5.0 [msec].

On the other hand, the discharge circuit 62 outputs the discharge control signal Voa from the ECU 8.
Is input, first, the transistor 65 is turned off (OF
F) switches to the conducting state (ON), and accordingly,
Transistor 66 is also turned on (ON) from the off state (OFF)
Switch to Therefore, the piezo actuator 19
The voltage applied to FL is discharged to the low voltage terminal (-100 [V]) of the high voltage generating circuit 41 via the discharging resistor 67 and the transistor 66, and the piezo actuator 19FL contracts. The electric resistance R2 of the discharging resistor 67 and the time constant τ2 at the time of discharging are the same as the electric resistance R1 of the charging resistor 64 and the time constant τ1 at the time of charging, based on the above equation (1). Was set to the value.

Next, an example of the above control will be described with reference to the timing chart of FIG. When the ECU 8 determines that it is necessary to switch the damping force of the variable damping force type shock absorber in accordance with a change in the running state of the vehicle, control as shown in FIG. First, at time T1, the ECU 8 changes the damping force variable shock absorber damping force setting characteristic from high damping force (HARD) to low damping force (SOFT). Accordingly, at the same time T1, the charge control signal Vca changes from a low level (OFF) to a high level (ON). Then, the piezoelectric actuator applied voltage starts to increase from the time T1. Here, in the present embodiment, since the charging resistor 64 is interposed in the charging circuit 61, it corresponds to the time constant τ1 (1.0 [msec] in the present embodiment) at the time of the charging from the time T1. Until the time T2 after the elapse of the delay time t1, the voltage applied to the piezo actuator does not rise sharply, and the target charging voltage becomes 63%.
The voltage is increased to about [%], and eventually reaches the target charging voltage (+500 [V]) from time T3. As described above, the piezo actuator is gradually charged according to the time constant τ1 at the time of charging.

On the other hand, at time T4, the ECU 8 changes the damping force variable shock absorber damping force setting characteristic from low damping force (SOFT) to high damping force (HARD). Accordingly, at the same time T4, the discharge control signal Voa changes from the high level (ON) to the low level (OFF). Then, the voltage applied to the piezo actuator starts to decrease from the time T4. Here, in this embodiment, since the discharge resistor 62 is interposed in the discharge circuit 62, the discharge circuit 62 corresponds to the time constant τ2 at the time of the discharge from the time T4 (1.0 [msec] in this embodiment). Until the time T5 after the delay time t1 has elapsed, the voltage applied to the piezo actuator does not drop sharply but drops to a voltage of about 63% of the target discharge voltage, and then the target voltage reaches the time T6. Discharge voltage (-
100 [V]). Thus, the piezo actuator is gradually discharged according to the time constant τ2 at the time of discharge. Thereafter, the ECU 8 continues the above-described control according to the change in the traveling state of the vehicle.

As described above, according to the present embodiment, when charging the piezo actuator, the capacitance C
And the electric resistance value R1 of the charging resistor, the rise of the applied voltage is delayed by a delay time t1 corresponding to a time constant τ1 at the time of charging corresponding to a time constant τ1 at the time of charging. It is configured to delay the drop of the applied voltage by a delay time t1 corresponding to a time constant τ2 at the time of discharge determined by the electric resistance value R2 of the resistor for use. For this reason, when the piezo actuator incorporated in the variable damping force type shock absorber of the vehicle is driven, rapid charging and rapid discharging of the piezo actuator are prevented, so that responsiveness when the damping force of the piezo actuator is changed is deteriorated. Thus, the operation noise generated when the piezo actuator is operated can be reduced appropriately, and the operation noise uncomfortable for the occupant of the vehicle can be sufficiently suppressed.

Further, with the above effect, the reliability and durability of the piezo actuator and the damping force variable shock absorber incorporating the piezo actuator as a damping force switching actuator are improved, and the vehicle equipped with the variable damping force shock absorber is improved. Ride comfort, maneuverability and stability can be maintained at a high level.

Further, since the operation noise accompanying the driving of the piezo actuator is reduced, the amount of electric energy which is dissipated as the operation sound among the electric energy supplied and released when the piezo actuator is driven is also reduced, so that the electric energy is reduced. Waste can be sufficiently suppressed, and the conversion efficiency between mechanical energy and electrical energy can be increased.

In addition, since the charging resistor and the discharging resistor have sufficient electric resistance in a small volume, the operating noise of the piezo actuator can be reduced with a small and simple drive circuit,
Since a large mounting space is not required, the mounting becomes extremely easy when the damping force switching actuator is incorporated in a variable damping force type shock absorber for a vehicle.

Furthermore, the charging circuit uses a photosensitive silicon control rectifier as a switching element, while the discharging circuit uses a transistor as a switching element, so high-voltage charging and discharging can be performed reliably and safely with a simple circuit configuration. It can be performed, and the reliability and durability of both circuits are improved.

In addition, the high voltage terminal voltage of the high voltage generating circuit is set to +500 [V].
On the other hand, since the low-voltage terminal voltage is set to -100 [V], the piezo element can be operated in a range in which the change in the amount of distortion with respect to the applied voltage of the piezo element is relatively large. In general, in a piezo element, as the applied voltage is set higher on the high voltage side, the rate of increase in the amount of distortion due to the piezo effect (inverse piezoelectric effect) is saturated, and the amount of distortion tends to hardly increase in proportion to the applied voltage. That is, the same voltage 600 [V]
Is applied, the range is, for example, low voltage 0
Rather than setting the range from [V] to high voltage +600 [V], as in the present embodiment, low voltage -100 [V] to high voltage +500.
When the voltage is set in the range of [V], the amount of distortion of the piezo element increases according to the applied voltage. As described above, since the piezo actuator is operated by applying a voltage in a range in which the piezo effect remarkably occurs, the responsiveness of the control of the variable damping force type shock absorber is also improved.

In this embodiment, the time constant τ1 at the time of charging and the time constant τ2 at the time of discharging are set to be the same, and accordingly, the electric resistance value R1 of the charging resistor and the electric resistance value R2 of the discharging resistor are set. And the same value. However, for example, the time constant τ1 at the time of charging and the time constant τ2 at the time of discharging may be set to different values according to the operating conditions of the piezo actuator. That is, the time constant for which higher responsiveness is required between the time of charging and the time of discharging is set to be short or almost without delay time, while the other time constant which may have relatively low responsiveness is set. Is set in the range of 1.0 to 5.0 [msec] in the same manner as in the above-described embodiment, and the charging resistor, the discharging resistor, and the discharging resistor are set in accordance with the thus determined time constants for charging and discharging. When the electric resistance value is determined, the quick response inherent to the piezo actuator can be sufficiently exhibited, and the operation noise can be reduced without causing the adverse effect such as a decrease in the response. .

Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments at all, and it is needless to say that the present invention can be implemented in various modes without departing from the gist of the present invention. .

Effect of the Invention As described in detail above, the piezoelectric element drive circuit of the present invention, during the operation of the piezoelectric element, the charging time of the piezoelectric element, or
A charging conductive part connecting the charging switch means and the piezoelectric element, or a discharging switch means and the piezoelectric element are connected so that at least one of the discharging times is not shortened from a predetermined target time constant. A resistor having a predetermined electrical resistance determined based on the capacitance of the piezoelectric element is interposed in at least one of the conductive parts for discharging. For this reason, when the piezoelectric element is driven, the supply speed or the discharge speed of the electric energy to the piezoelectric element is limited to a low speed to prevent a rapid charging or a rapid discharging. Can be suitably reduced without lowering the responsiveness of the piezoelectric element.

In addition, since rapid charging or rapid discharging of the piezoelectric element can be prevented in this way, not only can the operating noise be reduced, but also the damping force of the vehicle shock absorber can be prevented from suddenly changing. As a result, the reliability and durability of the shock absorber can be improved, and the riding comfort, maneuverability, and stability of the vehicle can be improved.

Further, since the operation sound accompanying the driving of the piezoelectric element is reduced, the amount of electric energy which is dissipated as the operation sound among the electric energy supplied or released at the time of driving the piezoelectric element is also reduced. Energy consumption can be minimized, and the conversion efficiency between mechanical energy and electrical energy is improved.

In addition, since a resistor having a small volume and sufficient electric resistance is used without using a large element such as a coil, the operating noise of the piezoelectric element can be reduced with a drive circuit having a small and simple configuration. For this reason, since a large mounting space is not required, there is an advantage that mounting on a variable damping force type shock absorber for a vehicle, for example, becomes extremely easy.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a driving circuit according to an embodiment of the present invention, and FIG.
FIG. 3 is a system configuration diagram of one embodiment of the present invention, FIG. 3 is a partial sectional view showing the structure of the variable damping force type shock absorber, and FIG. 4 is a diagram showing the damping force characteristic of the variable damping force type shock absorber. FIG. 5 is a block diagram showing the configuration of the electronic control device, and FIG. 6 is a timing chart showing the operation thereof. 19FL, 19FR, 19RL, 19RR ... Piezo actuator 37 ... Drive circuit 61 ... Charge circuit 62 ... Discharge circuit 64 ... Charge resistor 67 ... Discharge resistor

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yozo Majima 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (56) References JP-A-62-29410 (JP, A) JP-A-61-57630 (JP, U)

Claims (1)

(57) [Claims] 1. A charging switch means for applying a predetermined set voltage to a piezoelectric element for changing a damping force of a vehicle shock absorber by expansion and contraction according to an applied voltage in accordance with an external command, and in accordance with an external command. A discharge switch means for discharging a voltage applied to the piezoelectric element; a piezoelectric element driving circuit, comprising: a charging conductive section connecting the charging switch means and the piezoelectric element; It is interposed in at least one of the conductive parts for discharging connecting the switch means and the piezoelectric element, when charging the piezoelectric element, or so as to set the time constant at the time of discharge to a predetermined target time constant, A piezoelectric element drive circuit, comprising: a resistor having a predetermined electric resistance determined based on a capacitance of the piezoelectric element.