JPH035223A - Fluid type suspension for vehicle - Google Patents

Abstract

PURPOSE:To avoid rapid change of car height when a spring constant is changed-over by providing a spring constant selector valve functioning also as a throttle valve capable of controlling the opening degree of the valve at the portion where a plurality of pressure accumulating means to each other in a suspension provided with a plurality of independent pressure accumulating means. CONSTITUTION:This suspension 10 comprises a cylinder mechanism 11 having a cylinder 16 and hollow rod 17 slidably fitted to the cylinder 16 and accumulators 12 and 12' as pressure accumulating means. The accumulators 12 and 12' comprise housings 31 and 31' as vessels, internal cylinders 32 and 32' provided in the housings, and bellows-like separating members 33 and 33' respectively, and the inside of the separating members 33 and 33' are oil chambers 35 and 35'. In addition, the oil chamber 35 is communicated to the flow section 27 of the rod 17 through an oil passage 36, and an electro-magnetic type spring constant selector valve 39 is provided to the portion connecting both oil chambers 35 and 35'. The valve 39 is constituted so as to have a function as a throttle valve capable of controlling the opening degree other than the function to open and close oil passages.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic suspension system for a vehicle that is capable of changing a spring constant.

[Prior Art] A gas spring type vehicle suspension system includes a cylinder, a wood inserted into the cylinder, and an air chamber filled with compressed gas. The load of the vehicle is supported by acting on the rod. Spring constant (static spring constant) of this type of suspension system
K is determined by the following formula.

K-(k-P-A2)/V P: Gas pressure A2: Rod cross-sectional area V: Gas volume: As can be seen from the polytropic exponential equation, the spring constant is inversely proportional to the gas volume V, that is, the capacity of the air chamber. . That is, the larger ■ is, the lower the spring constant K is, so that a softer ride can be obtained.

If (2) becomes smaller, the spring constant K becomes higher, resulting in a harder ride, but the performance on curves and the like improves.

Among such hydraulic suspension systems, one in which the spring constant K can be changed has been proposed.

For example, the suspension system 1 of the prior art shown in FIG. is configured to act in a direction to push out the rod 7 of the cylinder mechanism 6, and a spring constant switching valve 8 is provided in a flow section connecting these accumulators 4 and 5. Hydraulic unit 9 connected to cylinder mechanism 6
The vehicle height can be adjusted by adjusting the protrusion amount of the rod 7, that is, the axial length H of the cylinder mechanism tR6, by supplying or discharging a desired amount of oil into the cylinder mechanism 6 as necessary. It's Toshide.

In the suspension system 1 of the prior art described above, when the switching valve 8 is in the closed state, only the gas volume of the first air chamber 2 functions as a gas spring, so that the spring constant becomes high. On the other hand, when the switching valve 8 is in the open state, the combined gas volume of the first air chamber 2 and the second air chamber 3 works together as a gas spring.
The spring constant will be lower. Therefore, when switching the spring constant from "low to high", the switching valve 8 is closed, and when switching from "high to low", the switching valve 8 is opened. In this specification, a state where the spring constant is relatively high is called a hard mode, and a state where the spring constant is relatively low is called a soft mode.

[Problems to be Solved by the Invention] In the suspension system 1, immediately after switching from the soft mode to the hard mode, that is, immediately after the switching valve 8 is closed, the pressures in the two air chambers 2 and 3 are equal to each other. However, if the load applied to the cylinder mechanism 6 changes after that due to a change in the load of the vehicle or a change in the driving conditions, the air chamber 2 of one of the accumulators 4 communicating with the cylinder mechanism 6 changes. While the pressure changes,
Since the other accumulator 5 is shut off by the switching valve 8, the pressure in this accumulator 5 remains the same. Therefore, a difference occurs between the pressures of the two air chambers 2 and 3. When the switching valve 8 is fully opened to switch from hard mode to soft mode when such a pressure difference is occurring,
A fluid flow occurs between the accumulators 4 and 5 so that the pressures in both air chambers 2.3 are equalized. For this reason, it has been found that the axial length H of the cylinder mechanism 6 suddenly changes at the moment the hard mode is switched to the soft mode, causing the vehicle body to become unstable and the ride to be uncomfortable.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a hydraulic suspension device that can switch the spring constant in at least two stages and that can solve the above-mentioned problems when switching the spring constant. ′ [Means for Solving the Problems] A fluid suspension system developed by the present inventor to achieve the above object is equipped with a plurality of pressure accumulating means each having independent air chambers. In a hydraulic suspension system for a vehicle that utilizes the repulsive force of enclosed compressed gas as a force to support the load of the vehicle, it is possible to provide communication and isolation between the plurality of pressure accumulating means at a portion connecting the plurality of pressure accumulating means to each other. This invention is characterized by the provision of a spring constant switching valve which also functions as a throttle valve that can control the opening degree per unit time. As a means for controlling the spring constant switching valve, for example, duty control is employed in which the frequency of opening and closing of the electromagnetic valve is changed depending on the required flow rate per unit time.

[Operation] In the above suspension system, when opening the spring constant switching valve to switch from the hard mode to the soft mode, the spring constant switching valve is temporarily kept in a throttled state for a predetermined period of time. By doing this, even if there is a pressure difference between the multiple pressure accumulating means before switching, the situation where the pressure difference suddenly disappears when switching modes is avoided, and the vehicle height gradually returns to normal. state. In addition, if the spring constant switching valve is not fully opened but is throttled to a certain extent and functions as a throttle valve, the flow path resistance between the pressure accumulating means will change, so the dynamic spring constant will change according to the degree of throttle. can be done.

[Example] The first example of the present invention will be described below with reference to Figures 1 to 5.
This will be explained with reference to the figures.

As shown in FIG. 1, a total of four suspension systems 10 are provided for each of the front, rear, left and right wheels.

As illustrated in FIG.
The cylinder mechanism 11 includes a plurality of accumulators 12 and 12' as an example of pressure accumulating means. The cylinder mechanism 11 includes a cylinder 16 having an oil chamber 15 therein, and a hollow rod 17 inserted movably in the axial direction of the cylinder 16. A shaft seal portion 18 is provided on the upper end side of the cylinder 16 in the drawing. A mounting portion 20 provided at the bottom of the cylinder 16 is connected to a member on the wheel side.

Damping force generation mechanism 2 provided at the lower end side of the rod 17 in the drawing
2 includes a piston-like portion 23 and a variable orifice 24. The variable orifice 24 can change the cross-sectional area of the flow path, that is, the damping force, by changing the rotational position of a valve 26 rotated by a motor 25 with a speed reducer.

An oil circulation section 27 along the axial direction is provided inside the rod 17, and this circulation section 27 can communicate with the oil chamber 15 via the variable orifice 24. A mounting portion 28 provided at the upper end of the rod 17 is connected to a member on the vehicle body side (not shown).

The accumulators 12.12' each have a sealed housing 31.31' as a pressure vessel and an inner cylinder 32.32 provided inside the housing 31.31'.
', a bellows-like partition member 33.33', etc., and the inside of the partition member 33°33' is an oil chamber 35.35.
' is used as

One oil chamber 35 communicates with the circulation portion 27 of the rod 17 via an oil passage 36. The outer surfaces of the partition members 33° 33' are used as air chambers 37, 37'.
' is filled with an inert gas such as nitrogen. The bellows-shaped partition member 33° 33' expands and contracts in the axial direction in response to changes in the volume of the air chambers 37, 37'. 38.38' is a bellows cap.

An electromagnetic spring constant switching valve 39 using a solenoid is provided at a portion connecting the oil chambers 35, 35'. This switching valve 39 is normally closed, that is, in a non-energized state, it is closed. When this switching valve 39 is in the open state, the pressure of the gas sealed in both air chambers 37, 37 is applied to the oil chamber 35.
, 35' and the oil passage 36 to act on the oil chamber 15 of the cylinder mechanism 11. Then, the rod 17 is moved by the pressure of the gas.
is urged in the direction of protruding from the cylinder 16.

The gas in the air chambers 37, 37' is sealed at a pressure high enough to support the load of the vehicle body. When the rod 17 moves relative to the cylinder 16 in the axial direction, oil according to the pushing amount of the rod 17 flows through the oil passage 36 into the oil chambers 35, 35'.
The volume of the air chambers 37, 37' changes accordingly. When the two air chambers 37, 37' cooperate as a gas spring in this manner, a relatively low spring constant can be obtained. When the spring constant switching valve 39 is closed, only one air chamber 37 acts as a gas spring, so the spring constant becomes high. The spring constant switching valve 39 can change the ratio of valve opening/valve closing frequency per unit time by a duty control logic circuit of a control device 62 which will be described later.

As shown in FIG. 1, vehicle height adjustment valve assemblies 46, 47, 48, 49 and a hydraulic pump 51 are connected to each cylinder mechanism 11 via hydraulic piping 41, 42, 43, 44. . These valve assemblies 46 to 49, hydraulic pump 51, etc. constitute a fluid drive system 52. 53 is a drain pipe, and this drain pipe 53 collects oil leaking from the shaft seal portion 18 of the cylinder mechanism 11 and the like into the tank 54 on a daily basis. The valve assemblies 46 to 49 have the same configuration and each includes a solenoid valve 55 for raising the vehicle height and a solenoid valve 56 for lowering the vehicle height. A solenoid valve 55 for raising the vehicle height is provided between the discharge side of the pump 51 and the cylinder mechanism 11. A lowering solenoid valve 56 is provided between the cylinder mechanism 11 and the tank 54. An oil passage 57 connecting the discharge side of the pump 51 and the solenoid valve 55 is provided with an accumulator 58 and a pressure switch 59 as an example of pressure detection means.
is provided. The accumulator 58 is filled with an inert gas such as nitrogen, and when the oil discharged from the pump 51 flows into the accumulator 58, the gas in the accumulator 58 is compressed. .

The vehicle height value for each wheel is determined by the vehicle height sensor 61 (see Figure 4).
detected by. This vehicle height sensor 61 is connected to a control device 62 using a microprocessor or the like. The control device 62 is configured to send opening/closing control signals to the above-mentioned spring constant switching valve 39 and the solenoid valves 55, 56 of the valve assemblies 46 to 49. The desired vehicle height value is determined by the vehicle height setting device 65.
can be entered by

Next, the operation of the suspension system having the above configuration will be explained.

When the spring constant switching valve 39 is in the open state, the gas volume, which is the sum of the capacities of both air chambers 37 and 37', acts as a gas spring, resulting in a soft mode. On the other hand,
When the spring constant switching valve 39 is in the closed state, only the capacity of one of the air chambers 37 acts as a gas spring, resulting in a hard mode. The opening and closing operations of the spring constant switching valve 39 are controlled by a control device 62. - For example, as shown in FIG. 5, when switching from soft mode to hard mode, the spring constant switching valve 39 is immediately fully opened, but when switching from hard mode to soft mode, a predetermined time t has elapsed. The duty ratio control is performed so that the opening degree of the switching valve 39 is narrowed until then, and after a period of time has elapsed, the switching valve 39 is fully opened. The duty control in this embodiment is performed by arbitrarily changing the valve opening frequency per unit time at a frequency of, for example, several 11 Hz to several tens of Hz, thereby controlling the actual opening degree, that is, the flow path. Control the resistance value. Note that since the spring constant switching valve 39 inevitably causes a delay in operation, depending on the specifications of the switching valve 39, it is also possible to change the substantial opening degree by changing the frequency. Therefore, the duty control referred to in this specification includes adjustment of the opening degree by such frequency control.

In this embodiment, when switching from hard mode to soft mode, the spring constant switching valve 39 is temporarily turned off for a predetermined period of time t.
Therefore, even if there is a pressure difference between the accumulators 12 and 12' in the hard mode before switching, the pressure difference is prevented from being suddenly eliminated when the mode is switched.

[As time passes, the differential pressure is gradually eliminated and the vehicle height finally reaches the normal vehicle height, so the spring constant can be switched smoothly without causing problems such as sudden changes in vehicle height. In this case, duty control may be performed to gradually increase the degree of opening of the valve at the time of mode switching, as shown by the two-dot chain line m in FIG. Since the spring constant switching valve 39 of the above-mentioned embodiment is a normally closed solenoid valve, even if a problem occurs in the valve operation due to an electrical failure, etc., there is no possibility that it will be inadvertently switched from the hard mode to the soft mode. It is safer because there is no

As shown in FIG. 6, when switching from the hard mode to the soft mode, the spring constant switching valve 39 is kept closed for a predetermined time t according to the first duty ratio, and after the lapse of the second duty ratio. The opening degree of the spring constant switching valve 39 may be controlled by the duty ratio. If the switching valve 39 is always duty-controlled in this way, the cumulative time of energizing the solenoid for operating the switching valve 39 can be shortened, and the amount of heat generated by the solenoid can be suppressed and power can be saved. In this case, the first duty ratio and the second duty ratio may be the same. As in this control example, the spring constant switching valve 39
By changing the opening degree of accumulator 1
By changing the channel resistance between 2.12', it is possible to change the dynamic spring constant according to the magnitude of the channel resistance.

In the suspension system 10, the vehicle height value detected by the vehicle height sensor 61 is sent to the control device 62 at predetermined intervals.
At the same time, the detected vehicle height value is compared with the vehicle height target value. When the vehicle height value exceeds the allowable range of the target value, the control device 62 sends a vehicle height adjustment output signal to the drive system 52, and when the vehicle height is too high, the lowering solenoid valve 56 is opened. A portion of the oil is drained from the cylinder mechanism 11. When the vehicle height is too low, the rising electromagnetic valve 55 is opened, and the high-pressure pressure stored in the accumulator 58 is supplied to the cylinder mechanism 11. In this way, the vehicle height adjustment output is continued in each cylinder mechanism 11 until the vehicle height value matches the target value. When the pressure in the accumulator 58 falls below a predetermined value, the pressure switch 59 is turned on, thereby starting the pump 51, and oil is supplied to the accumulator 58 until the internal pressure of the accumulator 58 reaches a predetermined value or higher.

FIG. 7 shows a second embodiment of the present invention, in which valve assemblies 46 to 49 are integrally assembled to each cylinder mechanism 11.

In each of the embodiments described above, the actual opening degree of the spring constant switching valve 39 is changed by duty control, frequency control, or a combination thereof, but when carrying out the present invention, the amount of throttling is changed in multiple stages. Even if a solenoid valve with a plurality of boats capable of controlling the flow rate is adopted and the flow rate per unit time is changed in multiple stages as in the case of duty control, the intended purpose of the present invention can be achieved. can.

Also, by connecting three or more accumulators,
The spring/constant may be changed over in three or more stages. Furthermore, the cylinder mechanism 11 may include both an air chamber and an oil chamber as pressure accumulating means.

[Effects of the Invention] According to the present invention, it is possible to prevent the vehicle height from suddenly changing when switching the spring constant, and it is also possible to change the dynamic spring constant according to the degree to which the spring constant switching valve is tightened. be. Therefore, by selecting the optimum spring constant according to the driving situation, it is possible to further improve driving stability, and it is possible to prevent the ride from feeling uncomfortable when changing the spring constant.

[Brief explanation of the drawing]

1 to 5 show a first embodiment of the present invention.
The figure is a hydraulic system diagram showing the structure of the suspension system and fluid drive system, Figure 2 is a vertical cross-sectional view of the cylinder mechanism and accumulator, and Figure 3
Figure 4 is a plan view of the accumulator and valve assembly, Figure 4 is a diagram showing the relationship between the control device and the drive system, Figure 5 is a diagram showing the operating state of the spring constant switching valve during mode switching, and Figure 6 is a diagram showing the operating state of the spring constant switching valve when switching modes.
7 is a hydraulic system diagram showing a second embodiment of the present invention, and FIG. 8 is a hydraulic system diagram showing a conventional suspension system. 10... Suspension device, 11... Cylinder mechanism, 12°12'... Accumulator (pressure accumulating means), 15...
Oil chamber, 16... Cylinder, 17... Rod, 37° 37'... Air chamber, 39... Spring constant switching valve, 62...
··Control device.

Claims (2)

[Claims] (1) In a hydraulic vehicle suspension system that is equipped with a plurality of pressure accumulating means having independent air chambers and uses the repulsive force of the compressed gas sealed in the air chambers of these pressure accumulating means as a force to support the load of the vehicle. , a spring constant switching element is provided at the part connecting the plurality of pressure accumulating means to each other, which functions as a throttle valve that can communicate and disconnect each of the pressure accumulating means and control the degree of opening per unit time. A fluid suspension system for a vehicle characterized by being provided with a valve. (2) The fluid-operated vehicle according to claim 1, wherein the spring constant switching valve is controlled to be in the open state after narrowing the opening for a predetermined time when transitioning from the closed state to the open state. Suspension system.