JPS6341214Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a suspension device used in vehicles such as automobiles.

In recent years, in addition to coil springs that absorb shocks caused by the vertical movement of wheels and shock absorbers that quickly remove bounce caused by expansion and contraction of the coil springs and stabilize the vehicle body by applying damping force, suspension devices that have air springs have been developed. It is considered. The main purpose of providing an air spring is to maintain a constant vehicle height regardless of the load by increasing or decreasing the internal pressure of the air chamber depending on the number of passengers or the load.

FIG. 1 is a side view schematically showing a mechanical part (hereinafter referred to as a suspension body) of a conventional suspension device. The illustrated suspension device includes a strut type damping force switching type shock absorber 11, a coil spring 12, and a rolling diaphragm type air spring 13. The air spring 13 is adapted to adjust the amount of compressed air in its air chamber 16 via a communication passage 15 formed in a piston rod 14 connected to the piston of the shock absorber 11. Through this adjustment, the internal pressure of the air chamber 16 can be adjusted, and the vehicle height can be kept constant.

Coil spring 12 and air spring 13 as described above
In the case of a suspension device with
In addition to the spring constant of the air spring 13, the spring constant of the air spring 13 is also relevant.

According to the conventional suspension -wine device, the shock due to the up and down movement of the wheels increases when the coil spring 12 grows, and when the coil spring 12 shrinks, it shrinks air springs 13. The expansion and contraction operations of No. 13 are the same. Therefore, there was a problem in that the composite spring constant of the two springs 12 and 13 could not be made smaller than the spring constant of the coil spring 12 alone.

This idea was made in order to deal with the above situation, and it is possible to make the composite spring constant of the two springs, the coil spring and the air spring, less than the spring constant of the coil spring alone, and it also makes it possible to reduce the load during driving etc. An object of the present invention is to provide a suspension device that can set a spring constant having a different value according to the fluctuation frequency of the suspension device.

Hereinafter, one embodiment of this invention will be described in detail with reference to the drawings.

FIG. 2 is a side view showing the suspension main body portion of one embodiment.

In the figure, 21 is a strut type damping force switching type shock absorber. This shock absorber 21 is a cylinder 21 attached to the wheel side.
1 and a piston (not shown) slidably inserted into the cylinder 211. A piston rod 22 is connected to this piston.
The upper end of the piston rod 22 in the figure is supported by a body frame 25 via a bearing 23 and a mount rubber 24. Incidentally, the movement of the piston rod 22 up and down in the figure is restricted by a nut or the like, but rotation is allowed by a bearing 23.

26 is a drive pin disposed within the piston rod 22 coaxially with the piston rod 22.
An actuator (not shown) for switching the absorber is connected to the upper end of the drive pin 26. By controlling the supply of compressed air to the actuator and the discharge of compressed air from the actuator, the drive pin 26 can be rotated in different directions. By controlling the rotational direction of the drive pin 26, the shock absorber 21
The hard state and soft state are switched.

A coil spring 27 is disposed substantially coaxially with the piston rod 22. The upper end of the coil spring 27 in the figure is fixed to a spring receiver 28 attached to the piston rod 22. The lower end in the figure is fixed to a spring receiver 29 attached to the cylinder 211.

Reference numeral 30 denotes a bellows type air spring, which is disposed approximately coaxially with the piston rod 22. The upper end of the air spring 30 in the figure is fixed to a spring receiver 31 attached to a cylinder 211, contrary to the coil spring 27. The lower end of the air spring 30 in the figure is also fixed to a spring receiver 32 attached to the piston rod 22, contrary to the coil spring 27. An air seal 33 is interposed between the upper end of the air spring 30, the spring receiver 31, and the piston rod 22. Therefore, the upper end of the air spring 30 and the spring receiver 3
1 is capable of sliding along the piston rod 22 following the vertical movement of the cylinder 211.

The air chamber 34 of the air spring 30 is connected to the piston rod 2.
2 and the drive pin 26, and is connected to the reserve tank and the exhaust pipe via a communication path 35 and an air inlet 36.

Such an air spring 30 can adjust the amount of air in the air chamber 34 to increase or decrease its internal pressure, thereby moving the cylinder 211 up and down to adjust the vehicle height. In this case, the expansion and contraction of the air spring 30 with respect to the vertical movement of the cylinder 211 is performed by the coil spring 27.
It is the opposite of that of . That is, when the cylinder 211 moves upward in the drawing relative to the piston rod 22, the air spring 30 expands while the coil spring 27 contracts. Conversely, when moving downward in the figure, the coil spring 27 expands while the air spring 30 contracts. Therefore, when raising the vehicle height, compressed air is discharged from the air chamber 34 to lower the internal pressure, and when lowering the vehicle height, compressed air is supplied to the air chamber 34 to increase the internal pressure. .

According to the above configuration, the coil spring 27 responds to changes in load such as changes in static load and load fluctuations during running.
The expansion and contraction operations of the air spring 30 and the expansion and contraction operations of the air spring 30 are reversed. Therefore, the combined spring constant of the coil spring 27 and the air spring 30 can be set to a value equal to or smaller than the spring constant of the coil spring 27 alone. In other words, making the composite spring constant equal to the spring constant of the coil spring 27 alone is as follows:
This is possible by keeping the internal pressure of the air spring 30 at a constant value regardless of the load applied to the suspension body. That is, by doing so, the spring constant of the air spring 30 can be made zero. The reason why the composite spring constant can be made smaller than the spring constant of the coil spring 27 alone is as follows. That is, in response to a contraction displacement of the coil spring 27, the compression stroke of the coil spring 27 can be assisted by increasing the internal pressure of the air chamber 34 and stretching the air spring 30;
By lowering the internal pressure of the air spring 30 and compressing the air spring 30, the extension stroke of the coil spring 27 can be assisted.

Further, according to the above configuration, even if the compressed air at the pneumatic pressure 34 escapes for some reason and the air spring 30 contracts, the vehicle height will not be lowered, so safety can be improved.

Here, a method of setting the internal pressure of the air chamber 34 of the air spring 30 when the composite spring constant is made smaller than the spring constant of the coil spring 27 alone will be explained. In FIG. 3a, a characteristic curve Ca shows the spring characteristics of the coil spring 27 alone. This spring characteristic is expressed by the characteristic curve Cb
If it is desired to change the spring characteristics to have a spring constant (inclination) as shown in , it is sufficient to cause the air spring 30 to bear the load shown by diagonal lines.

Now, if the load W is _W1 on the characteristic curve Cb, the stroke S is _S1 . This stroke S ₁
The load borne by the air spring 30 to obtain W is W _A.
If this burden load W _A is converted into load/pressure, the internal pressure P ₁ of the air spring 30 for obtaining the stroke S ₁ can be obtained. By performing such conversion for each load W, it is possible to determine the spring characteristics of the air spring 30 to obtain the composite spring characteristics shown by the characteristic curve Cb. This is shown in FIG. 3b as a characteristic curve Cc. From FIGS. 3a and 3b, the relationship between the load W and the internal pressure P for obtaining preset composite spring characteristics can be determined, and the characteristics shown in FIG. 4 can be obtained.

Therefore, if the internal pressure P is memorized in accordance with the characteristics shown in FIG. 4, the composite spring characteristics having a predetermined spring constant can be reproduced by simply detecting the load W. In this case, by appropriately setting the load borne by the air spring 30 for each stroke S, it is possible to set a composite spring constant having a smaller value than the spring constant of the coil spring 27 alone.

In addition, in Fig. 3a, W ₀ is coil spring 2
When the coil spring 27 receives the load W alone, the coil spring 27
This is the load for setting the to the neutral position. Also,
X ₁ is a stop point that restricts the position of the coil spring 27 in the direction of contraction, and X ₂ is a full bound point in the direction of extension.

FIG. 5 is a diagram showing the configuration of the control system of the suspension main body described above.

41 is a wheel, and 42 is an actuator for switching the shock absorber 21 between hardware and software. 43 is the vehicle height sensor,
44 is an internal pressure sensor that detects the internal pressure of the air chamber 34;
45 is a load sensor that detects the load W applied to the suspension body. This load sensor 45 is provided, for example, at the upper end of the piston rod 22. Since this portion is not easily affected by the impact caused by the vertical movement of the wheels 41, a substantially stationary load can be detected as long as the vehicle body does not move vertically.

Here, a configuration for obtaining a composite spring constant smaller than the spring constant of the coil spring 27 alone will be described.

51 indicates the air spring 3 from the load/internal pressure map 52 according to the load W detected by the load sensor 45.
This is an internal pressure setting circuit that reads data indicating a set internal pressure P of 0. The load/internal pressure map 52 includes the fourth
Data indicating the set internal pressure P according to the characteristic diagram shown in the figure is stored corresponding to each load W. 53 is a solenoid valve drive circuit that outputs the set internal pressure P read out by the internal pressure setting circuit 51 and the internal pressure sensor 44.
Compare the magnitude with the internal pressure Pa detected by
According to the comparison result, the air supply solenoid valve 54
and controls the opening and closing of the exhaust solenoid valve 55.
The air supply solenoid valve 54 is inserted into a communication path that communicates with the air inlet 36 and a reserve tank 56 in which compressed air is stored. The exhaust solenoid valve 55 is connected to an exhaust pipe 57 for discharging compressed air from the air chamber 34 of the air spring 30 and an air inlet 36.
It is inserted into a communication path that communicates and connects the Note that 58 is an internal pressure detection circuit that converts the internal pressure detected by the internal pressure sensor 44 into a signal that can be supplied to the solenoid valve drive circuit 53. Also, 59
A pressure switch detects the internal pressure of the reserve tank 56 and maintains it at a predetermined internal pressure, 60 is an engine, 61 is a compressor, and 62 is a dryer.

The operation of the above configuration will be explained with reference to the flowchart of FIG. In step _S1 , the internal pressure setting circuit 51 sets the load/internal pressure map 52 according to the load W detected by the load sensor 45.
Data indicating the set internal pressure P is read out from. (See step _S2 ) The internal pressure setting circuit 51 further converts this read data into a signal that can be supplied to the solenoid valve drive circuit 53. The solenoid valve drive circuit 53 compares the set internal pressure P and the actual internal pressure Pa of the air spring 30 based on the set internal pressure signal supplied from the internal pressure setting circuit 51 and the internal pressure signal supplied from the internal pressure detection circuit 58. (See step _S3 ) If the internal pressure Pa is smaller than the set internal pressure P, only the air supply solenoid valve 54 is opened. As a result, compressed air is sent from the reserve tank 56 to the air chamber 34, and the internal pressure Pa of the air chamber 34 is increased.
(See step _S4 ) If the internal pressure Pa is greater than the set internal pressure P, only the exhaust solenoid valve 55 is opened. As a result, the compressed air in the air chamber 34 is discharged from the exhaust pipe 57, and the internal pressure Pa of the air chamber 34 is lowered. (Refer to step S ₅ ) And the internal pressure Pa
When becomes equal to the set internal pressure P, both the air supply solenoid valve 54 and the exhaust solenoid valve 55 are closed. (See step _S6 ) After this, if the set internal pressure P does not change, the internal pressure Pa is always maintained at the set internal pressure P under the monitoring of the internal pressure sensor 44.
When the static load changes or the detected load W changes due to load fluctuations during driving, the set internal pressure P corresponding to the new load W is read out from the load/internal pressure map 52 according to the above-mentioned operation, and the internal pressure Pa Control is performed to make P equal to the new set internal pressure P.
Therefore, the suspension body exerts a damping force in accordance with the spring characteristics having a preset spring constant.

Note that regardless of the load W, the solenoid valve drive circuit 53 always sends a signal indicating the same set internal pressure P.
, the spring constant of the air spring 30 becomes zero, and the same composite spring constant as the spring constant of the coil spring 27 can be obtained. However, in this case, the spring characteristics are obtained by translating the spring characteristics of the coil spring 27 along the vertical axis (the axis indicating the load W). Here, a configuration for setting spring constants having different values in accordance with the fluctuation frequency of load fluctuations during driving etc., which is a feature of this invention, will be explained.

The load W detected by the load sensor 45 is
It goes without saying that it changes due to changes in the static load, but even if the static load is the same, it changes around the static load due to deterioration of road conditions while driving. The fluctuation frequency identification circuit 63 shown in FIG. 5 detects the fluctuation frequency of the detected load W as described above. Further, as shown in FIG. 7, the variation range (0 to ₀ ) of this fluctuating frequency is divided into, for example, three identification frequency bands F ₁ , F ₂ , and F ₃ . Then, the detected fluctuation frequency Δ is in three identification frequency bands F ₁ ,
Identify which identification frequency band of F ₂ or F ₃ it exists in. Note that ₁ and ₂ are the respective identification frequency bands F ₁ , F ₂ ,
This is the threshold value for setting _F3 .

Further, the load/internal pressure map 52 has three storage areas M ₁ , M ₂ , M ₃ corresponding to the three identification frequency bands F ₁ , F ₂ , F ₃ . Each storage area M ₁ ,
M ₂ and M ₃ each have air springs 30 in order to obtain three composite spring constants with different preset values.
Data indicating the set internal pressure P of is stored. In this case, the storage area M ₁ corresponding to the identification frequency band F ₁
, data indicating the set internal pressure P for the smallest composite spring constant is stored, and data indicating the set internal pressure P for the intermediate composite spring constant is stored in the storage area _M2 corresponding to the identification frequency band _F2 . , identification frequency band
Data indicating the set internal pressure P for the largest composite spring constant is stored in the storage area _M3 corresponding to _F3 . The internal pressure setting circuit 51 is a fluctuation frequency identification circuit 6
A corresponding storage area is specified according to the identification result of step 3, and data indicating the set internal pressure P stored in this storage area is read out according to the detected load W.

The operation of the above configuration will be explained with reference to the flowchart of FIG. The fluctuating frequency identification circuit 63 detects the fluctuating frequency in step _S1 , and identifies in which identification frequency band _F1 , _F2 , _F3 the fluctuating frequency exists in step _S2 . If the fluctuating frequency exists in the identification frequency band _F1 , the process moves to step _S3 , and the internal pressure setting circuit 51 stores the memory area.
M ₁ is specified. Similarly, if it exists in the identification frequency band _F2 or _F3 , the process moves to step _S4 or _S5 , and the storage area _M2 or _M3 is specified.

When the storage area is specified, data indicating the set internal pressure P corresponding to the detected load W is read out from this storage area as explained in the flowchart of FIG. 6 earlier, and the internal pressure Pa of the air spring 30 is It is made equal to the read set internal pressure P.

From the above, if the fluctuation frequency is small, a small composite spring constant is set, and a soft ride can be obtained. On the other hand, as the fluctuation frequency increases, the riding comfort becomes harder, but the steering stability improves.

In the above description, the case where three identification frequency bands are provided has been described, but any number may be used as long as there are two or more identification frequency bands.

Further, by providing hysteresis to the threshold value for setting the identification frequency band, the responsiveness of the switching operation of the composite spring constant may be made slow, making it less sensitive to instantaneous fluctuations.

Next, the configuration of the part that adjusts the vehicle height to obtain the target vehicle height will be explained.

71 is a vehicle height manual switch for selecting the vehicle height, "LOW", "MIDDLE", "HIGH",
You can select from four modes: ``AUTO.'' 72 is the target vehicle height setting circuit, "LOW",
When either "MIDDLE" or "HIGH" mode is selected, a vehicle height signal indicating the target vehicle height corresponding to that mode is output. A vehicle height signal comparison circuit 73 compares the target vehicle height with the actual vehicle height based on the target vehicle height signal and the vehicle height signal indicating the actual vehicle height supplied from the vehicle height sensor 43. 74 is an internal pressure correction signal generation circuit. This internal pressure correction signal generation circuit 74 generates a signal indicating a correction internal pressure for correcting the difference between the vehicle height set by the set internal pressure P and the target vehicle height according to the comparison result of the vehicle height signal comparison circuit 73. This is generated and supplied to the internal pressure setting circuit 51.
The internal pressure setting circuit 51 synthesizes this internal pressure correction signal and the set internal pressure signal and supplies it to the solenoid valve drive circuit 53 as a target internal pressure signal indicating the target internal pressure for obtaining the target vehicle height.

The operation in the above configuration will be explained. Set vehicle height manual switch 71 to ``LOW'', ``MIDDLE'',
When one of the “HIGH” modes is selected,
A target vehicle height signal corresponding to the selected mode is output from the target vehicle height setting circuit 72, and a vehicle height signal comparison circuit 73 compares the target vehicle height with the actual vehicle height. Then, according to the comparison result, an internal pressure correction signal is output from the internal pressure correction signal generation circuit 74,
A target internal pressure signal obtained by combining the internal pressure correction signal and the set internal pressure signal is supplied from the internal pressure setting circuit 51 to the solenoid valve drive circuit 53. Thereby, the internal pressure Pa of the air chamber 34 is set to the target internal pressure, and the target vehicle height is obtained. .

Even in this case, if the detected load W fluctuates due to load fluctuations during driving, for example, the load/internal pressure map 5
Since the set internal pressure P read from 2 is changed, the target internal pressure is changed. Therefore, the suspension body has a spring constant according to the characteristic curve Cb shown in FIG. 3a. However, in this case, the load borne by the air spring 30 changes by the corrected internal pressure indicated by the internal pressure correction signal, so the spring characteristics are obtained by translating the characteristic curve Cb along the vertical axis (the axis indicating the load W).

Set vehicle height manual switch 71 to “AUTO”
When mode is selected, the target vehicle height setting circuit 72 does not output a target vehicle height signal, so the internal pressure correction signal generating circuit 74 also does not output an internal pressure correction signal. Therefore, in this case, the set internal pressure P
A vehicle height determined according to the characteristic curve Cb of FIG. 3a is obtained.

Note that the corrected internal pressure may be determined in the following manner instead of by comparing the vehicle height determined by the set internal pressure P with the target vehicle height. In other words, the set internal pressure when the detected load W is _W2
P ₂ (see Figure 3 a, b) sets the vehicle height to "MIDDLE".Then, set the vehicle height manual switch 7.
When one of the modes "LOW", "MIDDLE", and "HIGH" is selected in step 1, the internal pressure correction signal generation circuit 74 first outputs the target vehicle height and "MIDDLE".
Corrected internal pressure is output according to the difference between the vehicle height and the vehicle height. Thereafter, the vehicle height determined by the composite internal pressure of this corrected internal pressure and the set internal pressure P is detected by the vehicle height sensor 43, and a correction is output in advance according to the difference between this vehicle height and the target vehicle height. Change the internal pressure value. That is, when the load W is _W2 in advance, the grain correction internal pressure is generated, and then the value of the correction internal pressure is changed according to the actual load.

In this way, the time required to obtain the target vehicle height can be shortened. That is, the air chamber 34
Due to its nature, it takes a certain amount of time to take in and out the compressed air. Therefore, in the former method, in which the vehicle height cannot be adjusted until the vehicle height is determined by the set internal pressure P, it takes a considerable amount of time to obtain the target vehicle height. On the other hand, in the latter method, when the vehicle height manual switch 71 is operated, the vehicle height is adjusted directly, so the actual load W is equal to the load W ₂
As long as the vehicle height does not deviate significantly from the target vehicle height, it is possible to directly obtain a vehicle height close to the target vehicle height.

The vehicle height signal comparison circuit 73 has a function of changing the already output correction internal pressure value by the difference when the vehicle height differs from the target vehicle height for a certain period of time after the vehicle height adjustment has been completed. has.

Next, the configuration of the portion of the shock absorber 21 that performs hardware/software switching will be explained.

81 is shock absorber 21 “HARD”,
This is a suspension manual switch for selecting three modes: ``SOFT'' and ``AUTO.''
When each mode is selected, “H” is output from the corresponding terminal.
A level signal is output.

82 is a speed sensor that detects vehicle speed. The output signal of this speed sensor 82 is supplied to a threshold value determination circuit 83 which outputs an "H" level signal when the vehicle speed exceeds a certain speed.

A handle angle sensor 84 detects the rotation angle and angular velocity of the handle. The output signal of the steering wheel angle sensor 84 is supplied to a threshold value determining circuit 85 which outputs an "H" level signal when the rotation angle or angular velocity of the steering wheel exceeds a certain angle or a certain angular velocity.

Reference numeral 86 denotes an acceleration sensor as a vehicle body attitude sensor that detects changes in the attitude of the vehicle body. This acceleration sensor 86 is designed to detect changes in the pitch, roll, and yaw of the vehicle body posture on the vehicle springs using a weight or the like. When acceleration acts forward and backward, left and right, or up and down, the weight tilts,
The acceleration of the vehicle body is detected using the movement of the vehicle. The output signal of the acceleration sensor 86 is supplied to a threshold value determination circuit 87 which outputs an "H" level signal when the acceleration of the vehicle body exceeds a certain value.

88 is an accelerator opening/closing speed sensor that detects the opening/closing speed of the accelerator. The output signal of the accelerator opening/closing speed sensor 88 is supplied to a threshold value determining circuit 89 which outputs an "H" level signal when the accelerator opening/closing speed exceeds a certain value.

90 is a brake pressure sensor that detects the degree of depression of the brake. The output signal of this brake pressure sensor 90 is supplied to a threshold value determination circuit 91 which outputs an "H" level signal when the degree of depression of the brake exceeds a certain value.

The threshold value determination circuits 83, 85, 87, 8
The output signals of 9 and 91 are each supplied to one input terminal of an AND circuit 93 via an OR circuit 92. The other input terminal of this AND circuit 93 has
An "H" level signal that is output when the "SOFT" mode is selected in the suspension manual switch 81 is supplied via an inverter circuit 94. The output signal of the AND circuit 93 and the "H" level signal that is output when the "HARD" mode is selected in the suspension manual switch 81 are passed through the OR circuit 95 to a solenoid valve for damping force switching. Drive circuit 9
6.

The output signal of the solenoid valve drive circuit 96 is supplied to an air supply/exhaust solenoid valve 97 for switching damping force. This supply/exhaust solenoid valve 9
7 is the actuator 42 and the reservoir tank 5
6 and an exhaust pipe 98.

The operation in the above configuration will be explained. When the "HARD" mode is selected by the suspension manual switch 81, an "H" level signal is supplied to the solenoid valve drive circuit 96 via the OR circuit 95. . As a result, the solenoid valve drive circuit 96 drives the air supply/exhaust solenoid valve 97 so that compressed air is supplied from the reserve tank 56 to the actuator 42 . As a result, the drive pin 26 (see FIG. 2) rotates in a direction that puts the shock absorber 21 in the hard state.

Further, the shock absorber 21 is configured such that when the "AUTO" mode is selected by the suspension manual switch 81, the levels of the output signals of the various sensors 82, 84, 86, 88, and 90 reach the corresponding threshold values. Discrimination circuit 83, 85, 8
Even when the thresholds 7, 89, and 91 are exceeded, "H" level signals are output from these circuits 83, 85, 87, 89, and 91, so that the hard state is set.

On the other hand, suspension manual switch 81
When the "SOFT" mode is selected, the AND circuit 93 closes the gate. Therefore, the input signal to the solenoid valve drive circuit 96 is at the "L" level regardless of the driving state. The solenoid valve drive circuit 96 drives the solenoid valve 97 so that the compressed air of the actuator 42 is discharged from the exhaust pipe 98 when the input signal is at the "L" level. As a result, the drive pin 26 rotates in the opposite direction to the case where the shock absorber 21 is in the hard state, and the shock absorber 21 is set in the soft state.

Note that the air spring is not limited to the bellows type air spring, and of course, for example, a rolling diaphragm type air spring may be used.

Furthermore, to control the amount of air in the air chamber 34, an electropneumatic proportional valve 101 may be used instead of the solenoid valve, as shown in FIG. In this case, an electropneumatic proportional valve drive circuit 102 is provided in place of the solenoid valve drive circuit 53, and the internal pressure sensor 44 and internal pressure detection circuit 58 are not required. 10th
The figure shows a flowchart of the control operation. step
The load W is detected in step S ₁ , and the set internal pressure P is set in step S ₂ .
is loaded. Then, in step _S3 , a control voltage V corresponding to the set internal pressure P is output from the electro-pneumatic proportional valve drive circuit 102 and supplied to the control terminal of the electro-pneumatic proportional valve 101. As a result, the internal pressure Pa of the air chamber 34
is made equal to the set internal pressure P.

In this way, according to this invention, it is possible to set the composite spring constant of the coil spring and the air spring to a value less than or equal to the composite spring constant of the coil spring alone, and also to set the composite spring constant to a value that differs according to the frequency of load fluctuation. A configurable suspension device can be provided.

[Brief explanation of drawings]

FIG. 1 is a side view showing the suspension body of a conventional suspension device, FIG. 2 is a side view showing the suspension body of an embodiment of the suspension device according to this invention, and FIGS. 3 and 4 are Figure 5 is a characteristic diagram to explain how to determine the set internal pressure of the air spring in order to obtain preset composite spring characteristics. Figure 6 is a flowchart for explaining the operation to obtain preset composite spring characteristics, Figure 7 is a diagram for explaining the operation of the variable frequency identification circuit shown in Figure 5, and Figure 8. is a flowchart for explaining the switching operation of the composite spring constant, No. 9
This figure shows the configuration of the main part of another embodiment of this invention, and FIG. 10 is a flowchart for explaining the operation of FIG. 9. 21...Shock absorber, 22...Piston rod, 23...Bearing, 24...Mount rubber, 25...Body frame, 26...Drive pin, 27...Coil spring, 28...Spring receiver,
29... Spring receiver, 30... Air spring, 31...
Spring receiver, 32... Spring receiver, 33... Air seal, 34... Air chamber, 35... Communication path, 36...
Air inlet, 44... Internal pressure sensor, 45... Load sensor, 51... Internal pressure setting circuit, 52... Load/
Internal pressure map, 53... Solenoid valve drive circuit, 54... Air supply solenoid valve, 55... Exhaust solenoid valve, 56... Reserve tank,
57... Exhaust pipe, 58... Internal pressure detection circuit, 63...
...Fluctuating frequency identification circuit, 101...Electro-pneumatic proportional valve,
102...Electro-pneumatic proportional valve drive circuit.

Claims (1)

[Claims for Utility Model Registration] A suspension body having a coil spring that expands and contracts according to a change in load, and an air spring whose expansion and contraction action is opposite to that of the coil spring with respect to the change in load, and for the air spring. a servo valve inserted in a communication path for supplying compressed air and a communication path for discharging compressed air from the air spring; and a plurality of composite springs having predetermined values of the coil spring and the air spring. a set internal pressure storage means for storing data indicating a set internal pressure of the air spring for obtaining a constant; a load sensor for detecting the load applied to the suspension body; and a fluctuation frequency of the load detected by the load sensor. a set internal pressure reading means for reading out data indicating a set internal pressure according to a composite spring constant from the set internal pressure storage means, the higher the fluctuating frequency is according to the identification result of the fluctuating frequency identifying means; and servo valve control means for controlling opening and closing of the servo valve so that the internal pressure of the air spring is equal to the set internal pressure indicated by the data read by the set internal pressure reading means.