JPH0297739A - Damping force detecting device for shock absorber - Google Patents

Abstract

PURPOSE:To improve detecting accuracy by providing a discharge means discharging an electric charge accumulating in an accumulating means by an output signal from a damping force zero detecting means detecting zero damping force of a shock absorber. CONSTITUTION:A load detecting means 12EL generates an electric charge in accordance with force of actuating a shock absorber 1FL to be extended and contacted. While an accumulating means 42 accumulates the electric charge output by the load detecting means 12EL, outputting a signal corresponding to damping force of the shock absorber 1FL. Further a damping force zero detecting means 41 detects zero damping force of the shock absorber 1FL. By an output signal of the damping force zero detecting means 41, a discharge means 43 discharges the electric charge accumulated in the accumulating means 42. Thus eliminating a parallel resistor for the accumulating means 42 in a charge amplifier, the electric charge, accumulated in the accumulating means 42, is prevented from being discharged.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a shock absorber damping force detection device that detects the damping force of a shock absorber using the piezoelectric effect of a piezo element, and the present invention aims to improve the detection accuracy of the shock absorber damping force. A load detection means that generates an electric charge corresponding to an acting force that expands or contracts a shock absorber, and an electric storage means that stores an electric charge output from the load detection means and outputs a signal corresponding to a damping force of the shock absorber. , a zero damping force detection means for detecting zero damping force of the shock absorber, and a discharging means for discharging the electric charge stored in the electricity storage means based on an output signal of the zero damping force detection means.

[Industrial application field]

The present invention relates to a shock absorber damping force detection device,
In particular, the present invention relates to a shock absorber damping force detection device that detects the damping force of a shock absorber using the piezoelectric effect of a piezo element.

The shock absorber damping force detection device of the present invention is a device for detecting the damping force in a shock absorber installed in a vehicle such as an automobile, and is particularly used for detecting the damping force of a variable damping force type shock absorber. Ru. A variable damping force type shock absorber is used to variably control the damping force of the shock absorber depending on road surface conditions and vehicle motion conditions, thereby improving the ride comfort of an automobile.

Here, the road surface condition refers to the condition such as whether the road surface on which the vehicle is traveling is flat or uneven, and the vehicle motion condition refers to the swash phenomenon (vehicle tailing condition) when the vehicle suddenly starts, These include a nose dive phenomenon (a state in which the vehicle leans forward) during sudden braking, a roll phenomenon (a state in which the vehicle leans in the left-right direction) when the vehicle turns, and the like.

[Conventional technology]

Conventionally, to detect the damping force of a shock absorber,
For example, a device utilizing the piezoelectric effect of a piezo element as disclosed in Japanese Patent Application Laid-Open No. 63-6238 has been proposed. In this way, when detecting the damping force of a shock absorber using a piezo load sensor, a circuit is required to detect the electric charge generated by the piezo load sensor. As this detection circuit, a so-called charge amplifier has conventionally been used, which charges a capacitor with an electric charge generated by a piezo load sensor and converts it into a voltage.

FIG. 11 is a diagram schematically showing a conventional shock absorber damping force detection device, and shows a piezo load sensor and a circuit for detecting the electric charge generated by the piezo load sensor. As shown in the figure, the conventional detection circuit uses a charge amplifier, and this charge amplifier is constituted by an integrating circuit consisting of a capacitor 152 and an operational amplifier 151, and further prevents saturation of the operational amplifier 151, etc. Therefore, a resistor 153 is provided in parallel with the capacitor 152.

[Problem to be solved by the invention]

As mentioned above, the conventional shock absorber damping force detection device uses an operational amplifier 15 as shown in FIG.
A resistor 153 is provided in parallel with the capacitor 152 in order to prevent saturation of the 1st class.

By the way, since the resistor 153 is provided in parallel with the capacitor 152, the electric charge proportional to the damping force of the shock absorber stored in the capacitor 152 is discharged via the resistor 153. Therefore, the accuracy of detecting the damping force of the shock absorber decreases. This decrease in detection accuracy is particularly significant in the low frequency region.

SUMMARY OF THE INVENTION In view of the problems of the conventional shock absorber damping force detection device described above, an object of the present invention is to improve the detection accuracy of shock absorber damping force.

[Means for Solving the Problems] FIG. 1 is a block diagram showing the principle of a damping force detection device for a shock absorber according to the present invention.

According to the present invention, the load detection means 12FL generates an electric charge according to the acting force that expands and contracts the shock absorber 1FL.
and stores the charge output by the load detection means 12FL,
a power storage means 42 that outputs a signal corresponding to the damping force of the shock absorber 1FL;
Damping of a shock absorber comprising zero damping force detection means 41 for detecting zero damping force of FL, and discharging means 43 for discharging the electric charge stored in the electricity storage means 42 by the output signal of the zero damping force detection means 41. A force sensing device is provided.

A signal corresponding to the damping force of the quad absorber 1FL is output. Further, the zero damping force detection means 41 detects zero damping force of the shock absorber 1FL, and the output signal of the zero damping force detection means 41 causes the discharging means 43 to
Discharge the charge stored in 2.

Thereby, parallel resistance to the power storage means 42 in the charge amplifier can be eliminated, and discharge of the charges stored in the power storage means 42 can be prevented. Furthermore, in response to the saturation of the operational amplifier due to the elimination of the resistor, the electric charge stored in the power storage means 42 is discharged using the signal from the damping force zero detection means 41, thereby improving the detection accuracy of the damping force of the shock absorber. be able to.

(Function) According to the shock absorber damping force detection device of the present invention having the above-described configuration, the load detection means 12F generates an electric charge corresponding to the acting force that expands and contracts the shock absorber 1FL, and the electric storage means 42 Embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the shock absorber damping force detection device of the present invention. As shown in the figure, the shock absorber damping force detection device of this embodiment is as follows:
Piezo element 12 that generates electric charge according to the magnitude of damping force
The output of FL is connected to a charge amplifier circuit 42. The damping force zero detection means 41 includes two operational amplifiers 58, 59 and a logic circuit 60, 61, and includes a differential pressure sensor 30 that measures the differential pressure between the upper and lower chambers of the shock absorber, as detailed in FIG. The signal is compared with a reference voltage, and if it is within the reference voltage range, it is determined that the damping force is zero, and an output signal is supplied to the discharge means 43.

The discharge means 43 includes a resistor 53 and a transistor 54, and the switching of the transistor 54 is controlled by the output signal of the zero damping force detection means 41. That is, when the damping force zero detection means 41 determines that the damping force is zero, the transistor 54 is turned on by the output of the damping force zero detection means 41, and the output of the charge amplifier 43 (the charge stored in the capacitor 52) is turned on by the resistor 53. ) is discharged to zero, and the drift of the operational amplifier (op-amp) 51 is corrected so that the output of the operational amplifier (op-amp) 51 does not become saturated. Further, when the output of the differential pressure sensor 30 is out of the reference voltage range, that is, when a damping force is generated, the transistor 54 is in an open state, and the piezo element 12
Since the charge generated by the FL is reliably integrated by the charge amplifier circuit 42, it is possible to detect the damping force with high accuracy even in the low frequency region (lower than LH2).

Next, FIG. 3 shows a longitudinal sectional view of a variable damping force type shock absorber having a built-in damping force adjuster, which is an embodiment of the present invention.

As shown in the figure, variable damping force type shock absorber 1
In the FL, a main piston 3 is fitted into the cylinder 2 so as to be slidable in the axial direction (indicated by arrows A and B in the figure), and the main piston 3 connects the inside of the cylinder 2 to a first hydraulic chamber. 4 and a second hydraulic chamber 5. The main piston 3 is connected to one end of a piston loft 6, while the other end of the piston rod 6 is fixed to a shaft 7. The cylinder 2 is housed in an outer shell 2a, and the lower part of the outer shell 2a is attached to the lower arm 2b of the vehicle, while the shaft 16 is attached to the lower arm 2b of the vehicle.
The upper portions 7a of are fixed to the vehicle body 10 via bearings 8 and vibration isolating rubber 9, respectively.

The piston rod 6 includes a piezo actuator I1FL that switches the damping force of the variable damping force shock absorber 1FL, and a piezo actuator I1FL that switches the damping force of the variable damping force shock absorber 1FL.
Load detection means 12FL is built in, which is a piezo type damping force sensor that detects the damping force of FL. moreover,
The piston rod 6 has a first hydraulic chamber 4 (absorber lower chamber).
A differential pressure sensor 30 is built in to detect zero damping force from the differential pressure between the hydraulic pressure chamber 5 and the second hydraulic chamber 5 (the upper chamber of the absorber).

The main piston 3 is provided with a fixed orifice 13 on the extension side and a fixed orifice I4 on the contraction side that communicate the first hydraulic chamber 4 and the second hydraulic chamber 5. Plate valves 13a and 14a for restricting the flow direction to one direction are respectively disposed on the outlet side of the valves 14. Therefore, when the main piston 3 slides inside the cylinder 2 in the axial direction (indicated by arrows A and B in the figure), the hydraulic fluid inside the first hydraulic chamber 4 and the second hydraulic chamber 5 is Since the hydraulic oil flows mutually through the expansion side fixed orifice 13 and the contraction side fixed orifice 14, the flow passage cross-sectional area of the hydraulic oil is relatively small and its flow rate is also small. Therefore, the sub passage 18 is blocked. In this case, the damping force characteristic of the variable damping force type shock absorber IFL becomes a high damping force (HARD) characteristic, as shown in FIG.

By the way, as mentioned above, the piston rondro has a hollow part bored in its axial direction, and the hollow part has a P
A piezo actuator 11FL, which is an electrostrictive element laminate made of piezoelectric ceramics such as ZT, is built-in.

The piezo actuator 11FL is normally biased by the plate spring 15 in the direction indicated by arrow A in the figure.

The lower end surface of the piezo actuator I1FL has an oil-tight chamber 16.
It faces the spool valve 17 via. The spool valve 17 is slidable inside the hollow portion of the piston rod 6 in its axial direction. When a predetermined high voltage is applied to the piezo actuator I1FL, the spool valve 17
It moves a predetermined distance in the direction shown by arrow B in the figure. On the other hand, when the predetermined high voltage applied to the piezo actuator I1FL is discharged, the piezo actuator IIF
Since L moves in the direction shown by arrow A in the figure due to the urging force of the plate spring 15, the spool valve 17 also moves in the same direction.

An annular groove 17a is formed on the outer periphery of the lower part of the spool valve 17, and the upper part of the annular groove 17a is shaped into a cylindrical shape. Therefore, when the spool valve 17 moves in the direction shown by the arrow B in the figure by elongating a minute amount by applying a high voltage to the piezo actuator I1FLO, the annular groove 17a carved in the outer circumference of the lower part of the spool valve 17 A sub-flow passage 18, which is bored in the piston rod 6 and connects the first hydraulic chamber 4 and the second hydraulic chamber 5, communicates through the piston rod 6. Since the first hydraulic chamber 4 and the second hydraulic chamber 5 communicate with each other via the sub-flow passage 18 in this way, the cross-sectional area of the hydraulic oil flowing through the main piston 3 becomes relatively large. The flow rate also increases. Therefore, the damping force characteristic of the variable damping force type shock absorber 1FL at this time becomes a low damping force (SOFT) characteristic, as shown in FIG.

On the other hand, when the high voltage is discharged, the piezo actuator I1FL contracts, and the spool valve 17 also
The auxiliary flow path 18 is blocked by the cylindrical portion of the spool valve 17 which is raised a predetermined distance in the direction shown by . In this way, the first hydraulic chamber 4 and the second hydraulic chamber 5 are cut off by closing the sub-flow passage 18, so that the cross-sectional area of the hydraulic oil flowing through the main piston 3 becomes relatively small. Its flow rate also decreases. Therefore, the damping force characteristic of the variable damping type shock absorber 1FL at this time becomes a high damping force (IIARD) characteristic, as shown in FIG.

Incidentally, a load detection means 12FL consisting of a piezo type damping force sensor for detecting the magnitude of the damping force acting on the variable damping force type silicon absorber 1FL is disposed on the upper part of the piston rod 6. The damping force sensor 12FL is constructed by screwing a piezoelectric element 19FL made of piezoelectric ceramics such as PZT onto the piston rod 6 through a pressure member 20F.

FIG. 5 is an exploded view of a piezo type damping force sensor used in the shock absorber damping force detection device of the present invention.

The piezo type damping force sensor 12FL has two thin plates 19FL of piezoelectric elements made of piezoelectric ceramics such as PZT.
a, L9FLb are stacked on top of each other with an electrode 21FL in between, and the detection signal is outputted to the outside via a lead wire 21FLa disposed in a passage bored inside the piston rod 6 and connected to the ECU 3, which will be described later. Ru.

Next, the damping force zero detection sensor 30, which is disposed on the piston rod 6 and is comprised of a differential pressure sensor that detects the difference (2) between the first hydraulic chamber 4 and the second hydraulic chamber 5, will be explained.

A configuration diagram of a known differential pressure sensor using a differential transformer in the sixth (al, (b+)) is shown in (C), and its characteristic diagram is shown.

In Figure 6(a), P is connected to the first hydraulic pressure etc. (lower chamber) of the absorber, P is connected to the second hydraulic chamber (upper chamber),
When the pressure in the first hydraulic chamber (absorber lower chamber) is high, that is, when the shock absorber is moving toward the contraction side, the output voltage E0 generates a positive voltage.

This output is then output to the ECU 8, which will be described later.

Next, the configuration of the gcus will be explained based on FIG. 7. As shown in the figure, ECU3 has cpυ8a, R
OM8b.

It is configured as a logic operation circuit centered around the RAM 8c, and is connected to an input section 8e and an output section 8f via a common bus 8d, and performs input/output with the outside. Piezo type load sensor 12FL, 12PR, 12RL, 12RR detection signal and differential pressure sensor 30FL which is a damping force zero detection sensor
, 30FR, 30RL, and 30RR are input to the CPU 8a from the human power section 8e via the damping force signal detection circuit 35, and the detection signals of the stop lamp switch 6 and vehicle speed sensor 7 are input via the waveform shaping circuit 36. be done. On the other hand, the CPU 8a outputs the drive circuit 3 from the output section 8f.
7 via piezo actuator I1FL, IIP
Outputs control signals to R, IIRL, and IIRR.

Next, the structure of the shock absorber damping force signal detection circuit 35, which is a feature of this embodiment, will be explained based on the circuit diagram of FIG. As shown in the figure, the shock absorber damping force signal detection circuit 35 includes the differential pressure sensor 3 described above.
0FL, 30FR, 3QRL.

30RR and each piezo type load sensor 12F mentioned above
L.

4 detection circuits 41FL, 41FR, 41RL, 4 provided corresponding to 12FR, 12RL, 12RR
Consists of 1RR.

The above detection circuits 41FL, 41PR, 41RL, 41
Since all RRs have the same configuration, the detection circuit 41FL will be explained as an example.

The detection circuit 41FL includes a charge amplifier circuit 42 which inputs the electrostatic charge generated by the piezo type load sensor 12FL and outputs a damping force signal according to the magnitude of the damping force, and a charge amplifier circuit 42 which outputs a damping force signal according to the magnitude of the damping force, and a charge amplifier circuit 42 which detects the damping force from the voltage generated by the differential pressure sensor 30FL. is zero or -
a damping force zero detection circuit 41 for detecting a foot load or less;
a discharge circuit 43 comprising a field effect transistor 54 that discharges the charge of the charge amplifier circuit 42 in accordance with the signal;
It is composed of

When the static charge generated by the piezo type load sensor 12FL is input to the charge amplifier circuit 42, the field effect transistor 54 is in the cutoff state a (OFF), so the static charge is transferred to the capacitor 52 by the action of the operational amplifier 51. Electricity is stored in the The static charge stored in the capacitor 52 is output to the ECU 3 as a damping force signal.

The damping force zero detection circuit 41 has a comparator 58 which takes the upper limit value +Vref as the dark value, and the lower limit value -Vref as the dark value (here, the voltage widths of l-Vref and -Vref are set to be very small). The comparator 59 includes an inverter 60 and an AND circuit 61 that perform logical operations on the output signals of the comparators 58 and 59. When the signal of the differential pressure sensor exceeds the upper limit value +Vref or falls below the lower limit value -Vref, a low level (L) judgment signal is output, while the rate of change signal is the upper limit value +Vr.
When the voltage is between ef and the lower limit value -Vref, a high level (H) is output to the discharge circuit 54. Note that the field effect transistor 54 of the discharge circuit switches to a cutoff state LM (OFF) when a low level (L) pulse is input, and to a conductive state (ON) when a high level (H) pulse is input. .

Therefore, when the signal from the differential pressure sensor exceeds the upper limit value +Vref or falls below the lower limit value -Vref, a low level (L) control signal is output for a predetermined period of time, and the field effect transistor 54 enters the cutoff state 1 ( OFF), the static charge generated in the piezo type load sensor 12FL is stored in the capacitor 52 by the action of the operational amplifier 51 in the charge amplifier circuit 42, and the static charge is output to the EC 118 as a damping force signal. On the other hand, when the signal of the differential pressure sensor is between the upper limit value +Vref and the lower limit value -VrefO, the control signal is also output at a high level, so the field effect transistor 54 is in a conductive state a (ON), so the operational amplifier The static charge generated due to the drift of the zero point of 51 and stored in the capacitor 52 of the charge amplifier circuit 42 is rapidly discharged via the resistor 53 and output as a damping force signal to EC[I8. Never.

Next, an example of the operation of the damping force signal detection circuit will be explained based on the timing chart of FIG. 8. When a damping force signal begins to be output as the running condition of the vehicle changes, the operation shown in the figure starts. First, the value of the differential pressure sensor signal is up to the upper limit +Vref at time T.
Since it is within the range of lower limit value −νref, zero detection circuit 41
outputs a high level (H), and the field effect transistor 5
4 is in a conductive state. Therefore, no charge is stored in the charge amplifier circuit. Next, at the above time T1, the differential pressure sensor signal exceeds the upper limit value +Vref, so the above time T1
, -Tt, the field effect transistor 54 is in the off state (OF), and the static charge generated in the load sensor 31FL is stored in the capacitor 52 by the action of the operational amplifier 51 in the charge amplifier circuit 42, and the static charge is , is output to the ECU 3 as a damping force signal.

Furthermore, between T2 and T, the differential pressure sensor output is +Vr again.
Since the voltage is between ef and -Vref, the field effect transistor 54 becomes conductive, the charge in the charge amplifier circuit is discharged, and the output voltage of the damping force detection circuit becomes zero when the CPU
output to the input stage. Next, since T3 or T4 becomes less than -Vref, the field effect transistor 54 becomes rOFFJ, and the charge of the load sensor is stored in the charge amplifier and output as a damping force signal.

Thereafter, the damping force signal detection circuit continues to operate as described above.

As explained above, in this embodiment, the detection signal of the piezo type load sensor 12FL is stored in the charge amplifier circuit 42, and zero damping force of the absorber is detected from the differential pressure between the upper and lower chambers of the absorber, and the output of the differential pressure sensor is is the upper limit +νre
Within the range from f to the lower limit value -Vref, the damping force signal output of the charge amplifier is considered to have occurred due to the drift of the zero point of the operational amplifier 51, (where +Vref to
- Since the range of Vref is set very small, the damping force can be regarded as "i 0") Above charge amplifier circuit 4
The second field effect transistor 54 is switched on to quickly discharge the static charge stored in the capacitor 52. On the other hand, if the differential pressure sensor signal is outside the range from the upper limit value Vref to the lower limit value -Vref, The damping force signal is assumed to be due to the static charge generated by the piezo type load sensor 31FL, and the field effect transistor 54 is switched to the cut-off state to store the static charge in the capacitor 52. Therefore, the error in the damping force signal caused by the drift of the zero point of the operational amplifier 51 can be removed, so that the damping force of the shock absorber can be measured quickly and with high precision.

Furthermore, when mounted in a vehicle such as an automobile that runs under a wide range of environmental conditions, the use environment, that is, the temperature of the element,
Even if the power supply voltage fluctuates frequently, false detection due to drift of the zero point of the operational amplifier 51 can be prevented, making it possible to implement it in harsh environments such as the engine room of a vehicle, and detecting damping force signals. Improves circuit durability and reliability.

In addition, since the damping force of the shock absorber of a running vehicle can be detected with high precision, for example, if shock absorber control is performed based on the damping force signal, the control accuracy will be increased, and the ride comfort and handling of the vehicle will be improved. The properties and stability can also be improved.

In this example, the damping force zero detection sensor is a differential pressure sensor between the upper and lower chambers of the absorber that can measure the entire pressure range, but as shown in Fig. 9, the sensitivity near zero differential pressure is In order to improve the lifting strength, a stopper may be used to prevent detection of pressures above a certain level.

Furthermore, it goes without saying that the differential pressure sensor may use a semiconductor pressure conversion element or a capacitance variable sensor. As long as there is accuracy near the zero point, there is no need for accuracy in other areas, so it can be manufactured at a low cost.

Further, as the sensor for detecting zero damping force, a switch using a plate valve in the contraction side or expansion side flow path of the absorber as shown in FIG. 1O may be used. Here, 102 is an insulating piece for insulating the contact 101.

The contact 101 installed in the flow path 14 opens due to the flow of oil when the absorber contracts, so the output is rHighJ, and conversely, when the absorber extends, the contact closes rL.
Becomes OWJ. Therefore, the damping force is zero at the moment the contact changes from H to L or from L to H, that is, the moment the oil flow stops. Therefore, a well-known timer IC is used to supply a zero damping force signal (reset signal) for a short period of time (0, 1 to several digits) from this point on to the field effect transistor 54.
Alternatively, the charge amplifier circuit may be discharged by inputting it to the charge amplifier circuit. Furthermore, it is also possible to use a differential pressure switch instead of the differential pressure sensor and combine it with the processing circuit.

〔Effect of the invention〕

As described in detail above, the shock absorber damping force detection device according to the present invention eliminates the parallel resistance to the capacitor in the charge amplifier, prevents discharge of the charge stored in the capacitor, and performs calculations by eliminating the resistance. For saturation of the amplifier, the accuracy of detecting the damping force of the shock absorber can be improved by correcting the zero output with the signal of the detector that detects the zero point of the damping force.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the principle of a damping force detection device for a shock absorber according to the present invention, FIG. 2 is a circuit diagram showing an embodiment of the damping force detection device for a shock absorber according to the present invention, and FIG. Fig. 2 is a vertical cross-sectional view of a variable damping force shock absorber incorporating a built-in damping force detection device, Fig. 4 is a diagram showing the damping force characteristics of the variable damping force shock absorber of Fig. 3, and Fig. 5 is a shock absorber of the present invention. Figure 6 is an exploded view of a piezo type damping force sensor used in the damping force detection device of the shock absorber of the present invention. 7 is a diagram showing the configuration of an ECU used in the shock absorber damping force detection device of the present invention, FIG. 8 is a diagram for explaining an example of the operation of the shock absorber damping force detection device of the present invention, and FIG. 9 10 is a diagram for explaining another modification of the shock absorber damping force detection device of the present invention; FIG. 11 is a diagram for explaining another modification of the shock absorber damping force detection device of the present invention. The figure is a diagram schematically showing a conventional damping force detection device for a shock absorber. (Explanation of symbols) 1pt... Shock absorber, 12FL... Load detection means, 41... Damping force zero detection means, 42... Electricity storage means, 43... Discharging means, 30.
...Differential pressure sensor. 12EL A block diagram showing the shock absorber principle according to the present invention.A diagram of a damping force detection device.FIG. 2FL.A diagram of FIG. Diagram for explaining an example Schematic diagram 1 of a conventional shock absorber damping force detection device
This diagram shows the four bases.

Claims (1)

[Scope of Claims] 1. A load detection means (12FL) that generates a charge according to the acting force that expands and contracts the shock absorber (1FL); and a load detection means (12FL) that stores the charge output from the load detection means and attenuates the shock absorber. an electric storage means (42) that outputs a signal corresponding to the force; a damping force zero detection means (41) that detects zero damping force of the shock absorber; A damping force detecting device for a shock absorber, comprising a discharging means (43) for discharging the generated charge. 2. The power storage device according to claim 1, wherein the power storage means includes a capacitive element and an operational amplifier, and charges the electric charge generated by the load detecting means into the capacitive element and converts it into a voltage. Shock absorber damping force detection device. 3. The discharge means includes a resistance element and a switching element, the resistance element is connected in parallel with the capacitance element via the switching element, and the output signal of the zero detection means prevents saturation of the operational amplifier. A damping force detection device for a shock absorber according to claim 1. 4. The damping force zero detection means includes a differential pressure sensor that is disposed inside the piston rod member of the shock absorber and detects a differential pressure between two hydraulic chambers divided by a piston attached to the piston rod member. A damping force detection device for a shock absorber according to claim 1. 5. The load detection means is a piezo type damping force sensor that is disposed inside the piston rod member of the shock absorber at a location where the load stress changes due to the damping force of the shock absorber, and generates an electric charge in accordance with the load stress. A damping force detection device for a shock absorber according to claim 1, comprising: