DE3915966A1 - METHOD AND DEVICE FOR REGULATING AN ACTIVE FLUID SPRING SYSTEM OF A MOTOR VEHICLE - Google Patents

Abstract

A control for a fluid suspension system having a control valve assembly (5) through which fluid is forced from a high pressure reservoir (2) into a suspension unit (1) at each vehicle wheel (w) and is exhausted from the suspension unit into a low pressure reservoir (3). A controller (6) computes a desired amount of fluid to be introduced into or withdrawn from the suspension unit in response to vehicle condition sensors via the delivery or exhaust valve of the control valve assembly (5). The amount of fluid actually introduced into or exhausted from the suspension unit (1) varies owing to fluctuations in the pressure difference across the valve assembly. The fluctuations are monitored and the computed desired amount is corrected accordingly and the control valve assembly is actuated accordingly, in order that the amount actually introduced into or withdrawn from the suspension unit may closely approximate the desired amount. <IMAGE>

Description

The invention relates to a method and a Vorrich device for regulating a fluid spring system for motor vehicles witness, in particular an active spring system for re Setting the amount of fluid in the spring units for driving witness wheels according to the requirements due to ver different vehicle conditions.

An air suspension system for the vehicle automatic level control is known, e.g. from the JP-GM-OS 58-1 67 208. The level control includes the vehicle high sensors to determine whether a relative height hen adjustment of the vehicle above or below egg takes place in a predetermined position. A direct or discharge air into and out of the spring is done according to the output signals of the Vehicle height sensors, so that the detected Relativver positions are balanced and thus the vehicle is kept at level.

JP-OS 62-1 39 709 describes a more sophisticated air Spring system proposed that as an active spring system is referred to and vehicle condition sensors for over monitoring the speed of the relative adjustments, the vertical acceleration of a mass over the Fe of each spring unit and other vehicle conditions in addition to the automatic level control device includes. The amount of air in each spring unit is released speaking of the detected vehicle conditions for the purpose of impact damping and influenced for other purposes.  

A typical active spring system has a closed one NEN air circuit with a high pressure air tank for the Ab supply of compressed air to the spring units, a low Air pressure container to catch the spring discharged air, an air compressor suck the air out of the low pressure container and again Pressurize this air for circulation through the high pressure tank, and a control valve device with both an inlet and a Exhaust valve for introducing or discharging air volumes gene in or from each spring unit.

The control valve device is a rule direction checked. Depending on the output signals the control device calculates the vehicle sensors ei ne desired or target air volume, which via the tax valve device introduced into each spring unit or should be derived from it. The control device also speaks to the air pressures in the high and never pressure tank signals to the Ver turn on and off more tightly. The compressor holds it Air pressures in both tanks within predetermined Limits.

However, with the conventional active spring systems a problem that remains unsolved from the inevitable fluctuations in the pressure difference across the Control valve device results. Through this fluctuation differences arise between that of the Re the target air volume and the deed actually introduced into or out of each spring unit their derived quantity or actual quantity, which results in a poor functioning of the spring system results.

The invention is based, the first task Difficulty described in the prior art  eliminate and a method and apparatus for Rules of the active spring system described above benen kind to improve that exact Target fluid quantities introduced into the spring units and derived from them.

According to the invention, this improvement consists in one pressure compensated control of an active fluid spring systems of the motor vehicle. According to the invention for the calculation of an in or in each spring unit from it to be derived a desired amount of fluid Vehicle conditions monitored. It will also be at the wheel valve device through which the fluid in each Fe the unit is inserted or removed from it, a Fluid pressure difference monitored. The calculated target The amount of fluid increases according to the fluid pressure difference the control valve device corrected. The latter will then according to the correction of the target fluid amount operated.

The air pressure in the spring units and the containers is subject to the actuation of the active spring systems fluctuations, for example due to a change the load on the vehicle and the load shift Exercise when cornering or with a fast vehicle acceleration or deceleration. The procedure according to the invention requires constant monitoring sol fluctuations and a corresponding appropriate Correction of the target quantity. Hence it comes through Control valve device actually in the spring unit amount of fluid introduced or derived from them close to the previously calculated target quantity. The performance of the active spring system can thus be significantly improved will.

Preferred embodiments of the invention are in  following with reference to schematic drawings tert. It shows:

Fig. 1 is a simplified illustration of an active air spring system,

Fig. 2 is a block diagram of a system for Rege lung of the spring system according to Fig. 1,

Fig. 3 is a graph for explaining the operation of the spring-control system according to Fig. 2,

Fig. 4 is a block diagram of another system for controlling the spring system shown in Fig. 1, and

Fig. 5 is a diagram for explaining the operation of the spring-control system according to Fig. 4.

The invention is described below using an example for regulating an air spring system. Is set if the same in Fig. 1, the active air suspension system in the on application to only a representative vehicle wheel W is, as will be clear that the system between each axle A and the vehicle body, not shown, having an air-spring unit 1. The air spring unit 1 is connected to both a high-pressure air tank 2 and a low-pressure air tank 3 via a control valve device 5 . The high-pressure container 2 is connected to the never-pressure container 3 via an air compressor 4 , from which it is supplied with compressed air.

The control valve device 5 is a unitary combination of an inlet and an Auslaßven valve. Compressed air is supplied from the high pressure container 2 to the air spring unit 1 when the inlet valve of the control valve device 5 opens. When the exhaust valve is opened, however, the air is discharged from the spring unit 1 and leads to the low-pressure container 3 . The air thus conducted into the low-pressure container 3 is circulated again in that it is compressed again by the compressor 4 and fed back to the high-pressure container 2 .

At the control valve device 5 , a Regeleinrich device 6 is electrically connected and receives signals from various vehicle state sensors 7 of the active air spring system as well as from the spring unit 1 and in the container 2 and 3 built-in sensors, which are described below . The inlet and the outlet valve of the control valve device 5 are opened and closed by the control device 6 as a function of the various output signals of the sensors 7 .

The block diagram in Fig. 2 illustrates how the control device 6, the control valve device 5 controls. In the spring unit 1 are usually provided a travel sensor 7 a , a sensor 7 b for vertical acceleration and a sensor 7 c for lateral or lateral acceleration. The spring travel sensor 7 a detects a relative adjustment of a mass above and below the spring part of the spring unit 1 . The sensor 7 b detects a vertical acceleration of the vehicle above the spring part of the spring unit 1 . The sensor 7 c detects a lateral acceleration of the vehicle.

Depending on the output signals of the vehicle state sensors 7 a , 7 b , 7 c ..., the control device 6 calculates an amount of air to be introduced into or derived from the spring unit 1 . Based on these calculations Be the control device 6 signals to the control valve device 5 to open or close their intake and exhaust valves, such that the required quantities of air are introduced into or removed from the spring unit 1 .

It is understood that the inlet and outlet valves of the control valve device 5 are electromagnetically actuated, normally closed valves. The inlet and the outlet valve open upon excitation when the control device 6 specifies the introduction and discharge of air into or from the spring unit 1 . Basically, the amount of air introduced into and discharged from the spring unit 1 is determined by the length of time during which the inlet and outlet valves are open. After calculating each required or abzuli tender amount of air depending on the sensor output signals, the Regelein device 6 determines the period of time during which the intake or exhaust valve must be kept open. The signals supplied by the control device 6 of the control valve device 5 represent such time spans. The control device 6 determines these time spans in accordance with time-related average air flow rates, which are determined in advance taking into account the performance data of the valves.

The areas of air pressures P _H and P _L in the high-pressure loading container 2 or low-pressure container 3 are set so that they are sufficiently higher or lower than the air pressure P _S in the spring unit 1 . The air compressor 4 works both when the pressure P _{H of} the high-pressure container 2 drops to a lower limit of the preset range, and when the pressure P _L in the low-pressure container 3 rises to an upper limit of the preset range. The compressor 4 sucks air from the low-pressure container 3 and presses the air into the high-pressure container 2 such that the container pressures P _H and P _{L are kept} within the predetermined ranges.

Thus, the container pressures P _H and P _L change at least within the predetermined ranges. The spring unit pressure P _{S also} changes within a range of considerable size depending on the load and other conditions of the vehicle.

Because such changes in the container and spring unit pressures P _H , P _L, and P _{S are} inevitable, the air flow rate per unit time through the control valve device 5 changes , although the performance data of the control valve device 5 remains the same. If the spring system was not designed according to the invention, the air quantities actually introduced into and derived from the spring unit 1 would deviate from the target quantities calculated by the control device 6 .

Based on the considerations given above, a novel method and a novel device for regulating a spring system are proposed according to the invention, in which the target air quantities calculated by the control device 6 according to the relative pressures P _S , P _H and P _{L of} the spring unit 1 and the container 2 and 3 are corrected. For this purpose, the spring system also comprises a pressure sensor 8 for the spring unit 1 , a pressure sensor 9 for the high-pressure container 2 and a pressure sensor 10 for the low-pressure container 3 for monitoring the pressures P _S , P _H and P _L of spring unit 1 and Tray 2 or 3 . These pressure sensors 8 , 9 and 10 are electrically connected to the control device 6 so that they transmit the pressures P _{S of} the spring unit 1 , P _H from the high-pressure container 2 and P _L from the low-pressure container 3 . Between the pressure sensors 8 , 9 and 10 and the control device 6 , low-pass filters 11 are interposed for filtering out interference signals from the sensor signals. After receiving the filtered sensor signals, the control device 6 is trained to control the control valve device 5 in such a way that the desired air quantities are fed exactly to and from the spring unit 1 , as explained in more detail below.

Referring to FIG. 2 6 comprising the control device for the implementing of the method according to the invention a series circuit with a circuit arrangement 61 for the Fe of control, a correction circuitry 63 and circuitry 62 tion for the Ventilsteue. The various vehicle state sensors 7 are all connected to the circuit arrangement 61 for spring control. In response to the output signals of these sensors 7 , the circuit arrangement 61 successively calculates desired or desired air quantities Q _D which are to be supplied to or removed from the spring unit 1 . The correction circuit arrangement 63 is connected to the pressure sensors 8 , 9 and 10 and calculates a correction or amplification factor K from the detected spring unit pressure P _S and the container press P _H and P _L. Then it multiplies each target quantity Q _D by the correction factor K and emits a signal representing the corrected target quantity K × Q _D. The circuit arrangement 62 for the valve control responds to this output signal of the circuit arrangement 63 in such a way that it opens the inlet or outlet valve of the control valve device 5 for a period of time which is determined by the output signal of the correction circuit arrangement 63 . To carry out the method according to the invention, the correction circuit arrangement 63 is interposed between the circuit arrangements 61 and 62 .

The mode of operation of the control device 6 is explained on the basis of the graphic representation in FIG. 3. It is assumed that the maximum air flow rate through the inlet valve of the control valve device 5 , that is to say the flow rate when the inlet valve is fully open, decreases from Q ₀ to Q ₁ if the pressure P _H in the high-pressure container 2 drops and the pressure P _S the Federein unit 1 increases. If the circuit arrangement 62 for the valve control is to influence the opening time of the inlet valve as a function of the output signal of the circuit arrangement 61 for the spring control, which represents the desired quantity Q _D , the actual or actual air quantity supplied to the spring unit 1 would not be Q _D , but Q ₁ / Q ₀ × Q _D.

The correction circuit arrangement 63 compensates for such a difference between the target air quantity and the air quantity actually supplied to the spring unit 1 . Depending on the output signals of the pressure sensor 8 assigned to the spring unit 1 and the pressure sensor 9 assigned to the high-pressure container 2 , the correction circuit arrangement 63 holds the rate of change Q ₁ / Q _{0 of} the flow rate, and a correction factor K that becomes necessary becomes the reciprocal value Q ₀ / Q ₁ derived. The correction circuit 63 thus outputs to the circuit arrangement 62 for the valve control a signal which indicates the corrected amount K × Q _D = Q ₀ / Q ₁ × Q _D. The circuit arrangement 62 for the valve control switches the inlet valve on and off accordingly, so that the air quantity Q actually introduced into the spring unit 1 comes as close as possible to the target quantity Q _D calculated by the circuit arrangement 61 for the spring control.

A similar correction is also carried out for the air discharge from the spring unit 1 . In this case, the correction circuit arrangement 63 responds to the output signals of the pressure sensor 8 of the spring unit 1 and of the pressure sensor 10 assigned to the low-pressure container 3 . Because the air flow rate through the exhaust valve of the control valve device 5 is variable depending on the relationship between the spring unit pressure P _S and the pressure P _{L of} the low pressure container 3 , the correction circuitry 63 derives the correction factor K from which these pressures P _S and P _L represent input signals. The correction factor K is used for the air supply to the spring unit 1 in order to keep the difference between the desired and actual air quantities removed from the spring unit 1 as small as possible.

The correction circuit arrangement 63 can display the pressure P _{S of} the spring unit 1 and the pressures P _H and P _{L of} the containers 2 and 3 at predetermined time intervals. Eg every three seconds, replace with new ones. In practice, such time intervals can be determined taking into account the capacity of the containers 2 and 3 , the displacement of the compressor 4 and the air quantities to be influenced.

In Fig. 4, an alternative embodiment of the Fe der control system is shown, which is characterized by a control device 6 a of modified circuit configuration. The modified control device 6 a does not have the correction circuit arrangement 63 according to FIG. 2, but only comprises the circuit arrangement 61 for the spring control and a circuit arrangement 62 a for the valve control. The spring unit 1 assigned pressure sensor 8 and the container pressure sensors 9 and 10 are connected to the circuit arrangement 62 a via associated low-pass filter 11 . The remaining components of the system are the same as described in connection with FIGS. 1 and 2.

The air flow rate through the control valve device 5 changes with a pressure change on at least one of the inlet and outlet sides of the valve, even if the valve itself is designed for a constant flow rate. In Fig. 5 is shown graphically how the relationship between the flow rate and the opening time of the intake or exhaust valve of the control valve device 5 changes with the changes in the pressure difference at the valve. Such valve features with various common pressure difference conditions can be stored digitally in the circuit arrangement 62 a for the valve control in the form of a "list".

At predetermined intervals, the circuit arrangement 62 a for the valve control can compare the sensor signals representing the air pressures on the inlet and outlet sides of the control valve device 5 with the data previously entered in the list. When supplying compressed air to the spring unit 1 , the high-pressure container 2 of the control valve device 5 is connected upstream, the Fe dereinheit 1 connected downstream. When removing air from the spring unit 1 , the latter of the control valve device 5 is connected upstream, the low-pressure container 3 is connected downstream of it.

To supply a target amount Q _D compressed air to the spring unit 1 , the circuit arrangement 62 a for the valve control relies on the pressure P _{H of} the high-pressure container 2 and the pressure P _{S of} the spring unit 1 on the previously recorded data stored in the Li. Then the circuit arrangement 62 a opens the inlet valve of the control valve device 5 for a period of time determined in accordance with the data in the list. The circuit arrangement selects one of the existing values for the upstream and downstream pressures P _H and P _S next coming value. The amount of air Q introduced into the spring unit 1 comes very close to the target amount Q _D.

For deriving a target amount Q _D air from the Fe dereinheit 1 , the circuit arrangement 62 a for the valve control similarly relates the pressure P _{S of} the spring unit 1 and the pressure P _{L of} the low-pressure container 3 to the previously recorded data in the list. Then opens the circuit arrangement 62 a the off laßventil the control valve device 5 during a time period which is determined in accordance with the list. The circuit arrangement 62 a selects one of the existing values for the upstream and downstream pressures P _S and P _L next coming value. The amount of air led out of the spring unit 1 thus comes very close to the target amount Q _D.

The above description is only for explanation and is not to be interpreted as a limitation. Various modifications or changes can be considered without further notice. For example, the spring system shown comprises a closed compressed air circuit with the spring unit 1 , the air tanks 2 and 3 and the compressor 4 ; the principles of the invention can also be applied to spring systems in which the outlet valve of the control valve device 5 is vented to the outside instead of being connected to the low-pressure air tank 3 . With such an open pressure air circuit, the air compressor 4 takes air from the atmosphere. Because in practice the atmospheric pressure can be regarded as constant, the pressure difference on the control valve device 5 can be achieved by detecting only the air pressures in the spring unit 1 and in the high-pressure container 2 both when supplying air to the spring unit 1 and when emptying of the same. The output signal of the circuit arrangement 61 for the spring control can be corrected in accordance with the pressure difference determined in this way.

It is also clear that the invention relates to active Fe dersysteme is applicable, the other as a damping medium Use gases as air. Above all, the invention on hydraulic or hydropneumatic spring systems applicable. Such hydraulic or hydropneumatic System configurations can basically be the same with the air spring system described here, with the Exception that the high pressure air tank by a Storage, the low pressure air tank through a Hy draulic fluid container is replaced. A hydraulic pump sucks the liquid from the container and releases it to the memory, in which they are under pressure until is saved to the spring unit.

The invention is also applicable to those described in JP GM application 62-1 35 138 described by the same applicant ne device. In this older application a Control valve device proposed in which the Flow rate of the liquid flowing through it con is trollable changeable. Both the flow rate as well as the opening time of the control valve device changes according to one of the control device by feeding to or removing from the spring unit amount of fluid delivered. When carrying out the invent method according to the invention with this older device the flow rate of the control valve device changes device according to one on the valve device pressure difference. The actually in the Fe fluid introduced or removed from the unit quantity then comes from the circuit arrangement for  the spring control certain target amount very close.

According to the invention, the calculation of a target Quantity of one to be introduced into each spring unit or from a series of fluids to be derived recorded values calculated for vehicle conditions. Additional Lich a fluid pressure difference on the control valve device determined by which the fluid in each Fe unit is to be initiated or removed from it, and the specified target amount is dependent on the so determined fluid pressure difference corrected such that exactly the desired amount of fluid in the spring unit can be introduced and removed from it in order to achieve a fault to achieve free working of the spring system.

Claims (5)

1. A method for controlling an active fluid spring system of a motor vehicle, which has a fluid spring unit ( 1 ) for each wheel ( W ), in which a number of states of the vehicle is detected, in order to by a control valve device ( 5 ) to calculate the spring unit ( 1 ) to be introduced and to be derived therefrom based on the determined states, and in which the control valve device ( 5 ) receives a signal representing the desired fluid amount and is actuated so that it increases the desired fluid amount and of each spring unit ( 1 ), characterized in that a fluid pressure difference is detected at the control valve device ( 5 ), and the signal representing the calculated target fluid quantity is corrected depending on the fluid pressure difference so that the actually in the spring unit ( 1 ) pressed in or derived from it amount of fluid comes close to the target amount. 2. The method according to claim 1, characterized in that the fluid pressure difference is detected by detecting fluid pressure in the spring unit ( 1 ) and fluid pressures in high and low pressure fluid containers ( 2 , 3 ). 3. Device for regulating an active fluid spring system of a motor vehicle, comprising a spring unit ( 1 ) for each vehicle wheel ( W ), a control valve device ( 5 ) through which a fluid to be introduced into the spring unit ( 1 ) and to be discharged from it is passed through, a state sensor ( 7 ) for detecting a prescribed number of vehicle states, a circuit arrangement ( 61 ) for the spring control for calculating a desired amount of fluid to be passed through the valve control device ( 5 ) and delivery of the desired Quantity representing signal, and a circuit arrangement ( 62 ; 62 a ) for the valve control for receiving the signal representing the desired amount and actuating the valve control device ( 5 ) in such a way that it passes the desired amount of fluid, characterized in that the device further pressure detection devices ( 8 , 9 , 10 ) for detecting fluid pressure difference on the Ventilsteuervor direction ( 5 ) and a e correction device ( 63 ; 62 a ) for correcting the signal representing the calculated target fluid quantity as a function of the detected fluid pressure difference, such that the quantity of the fluid actually introduced into the spring unit ( 1 ) and discharged from it is approachable to the target quantity. 4. The device according to claim 3, characterized in that the pressure detection devices a sensor ( 8 ) for detecting fluid pressure in the spring unit ( 1 ) and sensors ( 9 , 10 ) for detecting fluid pressures in high and low pressure fluid containers ( 2 , 3 ) to take, which are connected to the fluid spring unit ( 1 ) via the control valve device ( 5 ). 5. Apparatus according to claim 3 or 4, characterized in that the correction device is a correction circuit arrangement ( 63 ) which between the circuit arrangements for the spring control ( 61 ) and for the Ventilsteue tion ( 62 ) is interposed.