JPH07300010A - Suspension device for vehicle - Google Patents

Abstract

PURPOSE:To attain accurate attitude control by hydraulically connecting a gas spring to a hydraulic cylinder chamber, calculating a target cylinder pressure from each detection value of this,hydraulic force, springing speed and car height, and supplying/discharging pressure oil bacon a deviation from an actual pressure. CONSTITUTION:Cylinder devices 7R, 7L, hydraulically connecting gas springs 43R, 43L to hydraulic chambers 74R, 74L, are provided between suspension arms 3R, 3L and a car body 5. Further, a controller 21 inputs signals of pressures of the hydraulic chambers 74R, 74L, relative displacement (car height) in a vertical direction and signal of each sensor 23R, L, 25R, L, 27R, L of springing acceleration, and based on a springing displacement speed obtained by integrating these signals, supporting force, which must be generated in the cylinder devices 7L, 7R, is calculated. So that pressure oil, based on a deviation between a calculated value of this supporting force and actual supporting force calculated from the pressure sensors 23R, 23L, is controlled to be supplied/ discharged to/from the hydraulic chamber, oil path switching valves 11R, 11L are controlled. Accordingly, accurate control improving responsiveness and a proper steering characteristic can be maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle suspension system, and more particularly to a simple active suspension system.

[0002]

2. Description of the Related Art A suspension device for a vehicle is generally composed of a suspension spring and a damper. In such a device, the vibration characteristic of the suspension vibration system is uniquely determined in advance by the spring constant of the spring and the damping force of the damper. Therefore, by appropriately setting this vibration characteristic, the suspension characteristics such as riding comfort, wheel grounding property, vehicle body rolling or pitching are improved. However, depending on the suspension having a uniquely defined vibration characteristic, it is not possible to suitably maintain both the riding comfort and the ground contact property in the entire vibration frequency region. To further explain this point, as is well known, in a suspension vibration system, a suspension spring is sandwiched between a vehicle body side mass (sprung mass) and a wheel side mass (unsprung mass). In the forced vibration of the system, there are obtained two vibration points, that is, a sprung resonance point on the low frequency side and an unsprung resonance point on the high frequency side. In this vibration system, if the damping force is set to a large value, the grounding property will be improved, but a rugged shock will be transmitted in the vibration frequency range other than the resonance point, for example, in the frequency range beyond the unsprung resonance point, I feel extremely uncomfortable.

As described above, in a so-called passive suspension device having a spring and a damper as basic constituent elements, in which a supporting force is generated only when a relative displacement is generated, its vibration characteristic is uniquely determined. However, it has been difficult to favorably achieve both the riding comfort and the ground contact property in all frequency regions. Here, in recent years, a suspension device having a structure in which a supporting force generating mechanism such as a hydraulic cylinder is arranged between a wheel and a vehicle body has been proposed instead of the passive suspension device as described above.
As a so-called active suspension device that generates a supporting force by a force other than the supporting force by the spring or the damper, there is one disclosed in EPC application 0114757. In the disclosed active suspension device, the hydraulic cylinder is a so-called double-acting cylinder device in which hydraulic chambers are provided in front of and behind the piston, and hydraulic oil to each hydraulic chamber is obtained in order to obtain a desired supporting force. Is equipped with an actuator for controlling the flow rate.
In the control of the suspension device, the hydraulic pressure in the oil chambers before and after the piston is controlled, the drive of the piston is controlled by the pressure difference, and thereby the characteristics of the suspension device are controlled. In the suspension device of the type provided with this double-acting type cylinder, since the hydraulic oil is incompressible,
Highly responsive control is possible. However, since the hydraulic fluid is a non-compressible fluid, extremely precise control is required, so the actuator must be capable of precise flow rate control, and it is necessary to set its operating conditions. Since various sensors for detecting the behavior of the vehicle must be able to detect accurately, it is costly, and even a slight deviation will adversely affect the riding comfort and running stability. There is a problem that it is easy.

In contrast to such an active suspension system using a double-acting cylinder, a so-called single-acting cylinder device in which a hydraulic chamber is provided only on one side of a piston is used, and a gas spring is provided in the hydraulic chamber of this cylinder. A suspension device using a connected structure is disclosed in, for example, Japanese Patent Publication No. 59-14365. The disclosed suspension device is disadvantageous in responsiveness as compared with the type using the double-acting cylinder disclosed in the above-mentioned EPC application 0114757, because the cylinder works in conjunction with the gas spring, but the cylinder Since the hydraulic chamber has a structure in which a gas that is a compressible fluid is enclosed and has elasticity by itself, it does not significantly impair the riding comfort without securing relatively strict accuracy. Therefore, the one disclosed in Japanese Patent Publication No. 59-14365 can use inexpensive parts such as actuators and sensors as compared with the one disclosed in EPC Application No. 0114757, which is advantageous in terms of cost. Is. In the control of the suspension device disclosed in Japanese Patent Publication No. 59-14365, the cylinder device is controlled to give a desired vehicle height by controlling the flow rate of the hydraulic chamber of the cylinder. The following inconveniences occur in the control by the flow rate control.

That is, the vehicle has a so-called four-point support structure which is supported by four wheels, and the suspension device is mounted on each wheel. 4-point support structure is 1
Since one support point is an unstable element, it is more unstable than the three-point support structure. That is, in the four-wheeled vehicle, any one wheel constitutes an unstable support element. Therefore, when the suspension device is controlled by the flow rate as described above, the pressure balance of the supporting force of each wheel by the suspension device is lost, and rolling, pitching and the like are likely to occur. For example, when the pressure in the cylinder of the front wheels is higher than that of the rear wheels, understeer occurs, and in the opposite case, an oversteer tendency occurs, which affects the steering characteristics, which may impair running stability.
Further, the structure disclosed in Japanese Examined Patent Publication No. 59-14365 is
As described above, the gas spring, which is originally disadvantageous in terms of responsiveness, is connected to the cylinder device, and when the suspension characteristics are controlled based on the flow rate, the responsiveness is further reduced. In addition, the above-mentioned Japanese Patent Publication No. 59-143
In the suspension device disclosed in Japanese Patent No. 65, the cylinder of the suspension device is controlled based on the relative displacement between the sprung part and the unsprung part. Control based on relative displacement controls the distance between the sprung and unsprung to be constant, so if the control gain is increased, the distance between sprung and unsprung will always be constant. Therefore, the ride comfort is significantly impaired. If the gain of this relative displacement control is set so as to balance the riding comfort and the steering stability, problems of rolling or pitching occur.

The present invention has been made in view of the above points, and provides a suspension device capable of accurately controlling the posture of a vehicle and giving a good riding comfort without impairing steering stability. The purpose is to do.

[0007]

SUMMARY OF THE INVENTION The present invention is a suspension for controlling the posture of a vehicle body by supplying hydraulic pressure to a hydraulic cylinder having a single hydraulic cylinder chamber provided between a sprung portion and an unsprung portion. In the device, a gas spring hydraulically connected to the hydraulic cylinder chamber, a pressure detecting unit for detecting an oil pressure acting on the hydraulic cylinder chamber, a sprung speed detecting unit for detecting a displacement speed on the spring, and a vehicle height. A vehicle height detecting means for detecting the target cylinder pressure, and a control means for calculating a target cylinder pressure from the signal values of the respective detecting means, and for supplying and discharging a hydraulic pressure based on a deviation between the target cylinder pressure and the actual cylinder pressure to and from the cylinder chamber. It is characterized by having.

[0008]

The suspension device according to the present invention includes a single-chamber hydraulic cylinder and a gas spring communicating with the hydraulic chamber of the cylinder. The gas spring is provided with both a compressive fluid and an incompressible fluid. It is enclosed and configured. The pressure of the hydraulic chamber of the cylinder acts on the gas spring as it is. Therefore, the pressure of the hydraulic chamber of the cylinder generates a spring function due to the volume change of the compressible fluid of the gas spring corresponding to the pressure change. That is, it functions as a gas spring. In this case, the spring constant of the gas spring can be appropriately set in connection with the hydraulic flow rate control of the cylinder device of the active suspension device. In the present invention,
The target pressure in the cylinder is set based on the relative displacement between the sprung and unsprung parts and the displacement speed on the bone, and the hydraulic control is performed based on the deviation between this pressure and the actual pressure. Since the pressure change in the cylinder occurs prior to the attitude change of the vehicle, highly responsive control is possible. Further, in the present invention, control is performed based on the sprung speed so that vibration on the spring does not occur. By controlling in this way, it is possible to suppress posture changes due to bouncing such as when a wheel rides on an obstacle such as a stone, occurrence of a roll phenomenon during turning, or pitching during acceleration / deceleration. Therefore, even in such a situation, both riding comfort and steering stability can be favorably maintained.

If the control is performed by focusing only on the sprung speed, the distance between the sprung portion and the unsprung portion, that is, the absolute vehicle height may change unduly. In the present invention, the relative displacement between the sprung portion and the unsprung portion is detected and added to the control requirement, so that the vehicle height can be appropriately maintained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicle suspension device according to an embodiment of the present invention will be described below with reference to the drawings. The suspension device of the present example can be configured by, for example, a hydraulic cylinder, a hydraulic pump, and a pressure control valve arranged between them. In the following examples, the front and rear wheels will be described because the suspension devices arranged on the front and rear wheels have the same configuration. FIG. 4 is an overall configuration diagram of a vehicle suspension device according to a first embodiment of the present invention. As shown in the figure, the left and right wheels 1L, 1R are attached to the vehicle body 5 via suspension arms 3L, 3R. These suspension arms are pivotally attached to the vehicle body 5, so that the wheels 1L and 1R can swing vertically with respect to the vehicle body 5. Since the suspension mechanisms arranged for these left and right wheels have the same configuration,
The left front wheel 1L will be described below. First, between the suspension arm 3L and the vehicle body 5, a power cylinder device 7L is arranged vertically. In this cylinder device 7L, the rear end of the cylinder body 71L is fixed to the vehicle body 5 side, and a piston rod 73L fixed to a piston 72L that is vertically slidable in the cylinder body penetrates the tip of the cylinder body. And extend downwards,
It is connected to the suspension arm 3L. In this way, the support mechanism is formed by the power cylinder, and by controlling the hydraulic pressure generated in this cylinder device 7L, the support force generated by this cylinder device can be changed.

An air spring 43L communicates with a hydraulic chamber 74L of the cylinder device 7L via an orifice 41L. The spring constant Kk of the suspension vibration system is defined by the air spring 43L, and the damping constant Kc is defined by the restriction of the orifice 41L. Further, it is configured to perform only for the hydraulic pressure supply 74L. A hydraulic pressure supply system for the cylinder device 7L will be described. This supply system includes a hydraulic pump 9 and a flow passage switching valve 11L arranged in an oil passage that communicates between the hydraulic pump 9 and the cylinder device 7L connected to the air spring 43L.
Is the basic configuration. The valve 11L is an electromagnetic valve, and when the set position is the block A, oil is supplied to the hydraulic chamber 74L on the upper side of the cylinder device 7L,
The piston rod 73L extends downward.
Further, when the set position is the block B, the oil passage for the cylinder device 7L is shut off. On the other hand, when the set position is the block C, oil is supplied to the lower hydraulic chamber 75L of the cylinder device, and the piston rod 73
L contracts upward. Further, in this hydraulic pressure supply system, 13 is a relief valve, 15 is an accumulator,
It is possible to maintain a predetermined hydraulic pressure in the oil passage. In addition,
17 is an oil tank.

Next, a control system for driving and controlling the solenoid valve 11L will be described with reference to FIGS. 4 to 6.
This control system has a controller 21 and three sensors 23L, 25L, and 27L connected to its input side as basic constituent elements. The sensor 23L is a pressure sensor and detects the hydraulic pressure P in the hydraulic chamber 74L of the cylinder. Sensor 2
Reference numeral 5L is a displacement sensor, which detects a relative vertical displacement (X1-X2) between the vehicle body 5 and the wheel 1L. The sensor 27L is a vibration sensor, which is attached to the vehicle body 5 and causes a vertical vibration acceleration X ″ 2 (spring acceleration) generated there.
To detect. In the controller 21, the sensor 23
Based on the detection values of L and 25L, and the displacement speed (spring-on displacement speed) obtained by integrating the output of the sensor 27L,
As will be described later, the supporting force to be generated by the cylinder device 7L is calculated, and the cylinder device 7L is controlled so as to generate the calculated supporting force. FIG. 5 is a block diagram showing the configuration of the controller 21. As shown in the figure, this controller is composed of a calculation circuit section 33, a change circuit section 35, and a control circuit section 37. The calculation circuit unit 33 is
The piston 7 of the cylinder device against the vibration input from the wheel
The generated supporting force T of the cylinder device 7L required for the 2L to vibrate according to the preset vibration characteristic is calculated.

In this case, the calculation circuit section 33 inputs the displacement sensor output (X1 -X2) to the amplifier 331 and, on the one hand, multiplies it by a preset constant Kk to obtain Kk (X1
-X2) is calculated. On the other hand, the sensor output (X1-X2) is differentiated via the differentiator 332,
A first derivative value (X'1-X'2) is calculated. Further, this differential value is amplified by the constant value Kc via the amplifier 333 to calculate Kc (X'1-X'2). The two values thus calculated are added by the adder 334 to calculate the physical quantity Uo represented by the following equation. Uo = K * X'2 + Kc (X'1-X'2) + Kk (X
1-X2) K = correction coefficient As shown in FIG. 3, with the set frequency F near the unsprung resonance point as a boundary, it is set to a negative value K1 in a region below that and in a region above that. , Zero. X'2 = displacement speed detected by the above displacement speed detecting means (spring sprung displacement speed) Kc = constant corresponding to damping coefficient Kk = constant corresponding to spring coefficient X1-X2: body side and wheel side The relative displacement amount in the vertical direction between X'1 and X'2: the displacement velocity of the above displacement amount (X1-X2) However, the above respective values X'1, X'2, X1 and X2 are in the upward direction. The direction is positive.

Next, the control circuit section 37 takes in the pressure sensor output P, amplifies this value through the amplifier 371, and the supporting force A · P actually generated by the cylinder device.
(A: effective area of cylinder) is calculated. Next, the change circuit unit 35 will be described. The change circuit unit 35 is a circuit for changing the physical quantity Uo calculated as described above. In this circuit unit, the sprung body displacement speed X′2 is calculated by inputting the vibration sensor output X ″ 2 to the integrator 353 and integrating the value. It is amplified by the ratio K and its sign is inverted, that is, the displacement velocity in the positive direction is converted into the displacement velocity in the negative direction, and the displacement velocity in the negative direction is converted into the positive one.
The output K · X′2 of this amplifier is set to a low pass filter 352.
And supplies only the low frequency component to the adder 334 described above. In the low-pass filter 352, only the component of the vibration frequency F or lower near the unsprung resonance point is passed. Here, FIG. 6 shows a circuit configuration of the low-pass filter 352. The filter characteristic is determined by the RC time constant, and since this value is determined by the following equation in a known manner, f
If the above-mentioned frequency F is adopted as ₀ , a filter characteristic that allows frequency components below this frequency F to pass is obtained.

RC = 1 / 2πf ₀ The curve K = f (F) in FIG.
The characteristics corresponding to the filter characteristics of are shown. here,
1 shows changes in the vibration level of the vehicle body (vertical acceleration X ″ 2 on the spring) with respect to the vibration frequency at the road surface input. The vibration characteristic line I in this figure is K = 0, and the characteristic line II is 2 is obtained when the coefficient K is set to a negative value K1. Further, Fig. 2 shows the amount of displacement with respect to the vibration frequency in the input from the road surface (the vertical direction between the wheel on the unsprung side and its ground contact surface). Of the relative displacement amount X1−X0), and the characteristic line A is obtained when K = 0, while the characteristic line B changes the coefficient K to a negative value K1. Here, the quality of the riding comfort is influenced by the sprung acceleration in Fig. 1, and the lower the value, the more the riding comfort is improved. Influenced by the displacement amount (X1-X0) in Fig. 2, the lower the value, the better the ground contact. Is improved. In this case, these characteristic diagram (Fig. 1, Fig. 2) the followings can be said. From first characteristic diagram showing a ride 1, Hobobane under resonance point F
In the lower frequency range, the characteristic II shows the preferable characteristic (good riding comfort). On the other hand, from the characteristic diagram showing the grounding property of FIG. 2, the characteristic A shows a preferable property in a higher frequency range than the unsprung resonance point F (good grounding property).

Based on this point, the present invention is based on the set frequency F
Since the characteristics II and B are adopted in the following areas and the characteristics I and A are adopted in the areas further than the above, it is possible to achieve both the riding comfort and the grounding property in all frequency areas. Whether the sign of the value K1 of the coefficient K is positive or negative depends on the control direction for controlling the generated supporting force of the supporting mechanism with respect to the input of the displacement speed on the spring. In this case, K1 is a negative value, and the control direction is a direction in which the sprung displacement speed is decreased. Specifically, when the sprung displacement velocity is a positive value, that is, when the sprung displacement velocity is upward (vehicle body direction), the pressure in the hydraulic cylinder is reduced so that the oil in the cylinder is discharged. It controls. The control circuit section 37 of the controller 21 has a subtractor 374, and the actual cylinder supporting force A · P and the calculation circuit section 33 is applied to the subtractor 374.
The physical quantity Uo calculated in step 1 is supplied and the subtraction shown in the following equation is performed. T = A-P- {Kk (X1-X2) + Kc (X'1-
X′2)} This subtraction value T is supplied to the comparator 372, and the change circuit unit 3
The value is compared with the value K · X′2 calculated in step 5, and the switching valve 11L is controlled based on the comparison result, that is, the difference between the two.

That is, when K · X′2-T> 0,
The hydraulic pressure is controlled to be supplied to the hydraulic chamber 74L, and K · X ′
In the case of 2-T <0, on the contrary, control is performed so that the hydraulic pressure is released from the hydraulic chamber. When K · X′2-T = 0, the state is maintained as it is. Although the controller has an analog circuit configuration in the above example, it may have a digital circuit configuration.

[0018]

As described above, according to the present invention, the active suspension device is composed of the cylinder device connected to the gas spring and the means for supplying / discharging the hydraulic pressure to / from the cylinder device. Then, the present invention focuses on the fact that the change in the posture of the vehicle body immediately appears as the actual pressure change of the cylinder device, and when the suspension device is controlled, the displacement of the vehicle body, that is, the spring and its displacement speed, In addition, the change in the amount of displacement between the sprung and unsprung parts, that is, the change in vehicle height is detected to set the target pressure, and the pressure in the cylinder device is controlled based on the deviation between this and the actual pressure. is there. As a result, highly responsive and accurate control can be achieved. Further, in the present invention, since the control is performed so as to achieve the target hydraulic pressure in the cylinder as described above, the pressure balance of each wheel is not disturbed and the proper steering characteristic can be maintained.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing vibration characteristics of sprung acceleration,

FIG. 2 is a characteristic diagram showing relative displacement characteristics between a wheel side and a ground contact surface thereof,

FIG. 3 is a characteristic diagram showing a value of a correction coefficient with respect to a vibration frequency,

FIG. 4 is a configuration diagram showing a configuration of a first embodiment of the present invention,

5 is a block diagram showing the configuration of the controller shown in FIG. 4;

6 is a circuit diagram showing an example of a low-pass filter shown in FIG.

[Explanation of symbols]

 1L wheel 3L suspension arm 5 vehicle body 7L power cylinder device 9 hydraulic pump 11L switching valve 21 controller 23 pressure sensor 25 displacement sensor 27 vibration sensor 33 calculation circuit unit 35 change circuit unit 37 control circuit unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Haruyuki Taniguchi 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Motor Corporation

Claims (1)

[Claims] 1. A suspension device for controlling a posture of a vehicle body by supplying hydraulic pressure to a hydraulic cylinder having a single hydraulic cylinder chamber provided between a sprung portion and an unsprung portion. A connected gas spring, a pressure detecting means for detecting the hydraulic pressure acting on the hydraulic cylinder chamber, a sprung speed detecting means for detecting a displacement speed on the spring, a vehicle height detecting means for detecting a vehicle height, A suspension characterized by comprising a control means for calculating a target cylinder pressure from the signal values of the respective detection means and for supplying / discharging a hydraulic pressure based on a deviation between the target cylinder pressure and the actual cylinder pressure to / from a cylinder chamber. apparatus.