GB2227722A

GB2227722A - A method and apparatus for controlling height of a vehicle

Info

Publication number: GB2227722A
Application number: GB9002058A
Authority: GB
Inventors: Atsushi Mine; Katsuyoshi Kamimura; Yutaka Hiwatashi
Original assignee: Fuji Jukogyo KK; Fuji Heavy Industries Ltd
Current assignee: Subaru Corp
Priority date: 1989-02-03
Filing date: 1990-01-30
Publication date: 1990-08-08
Anticipated expiration: 2010-01-30
Also published as: GB9002058D0; GB2227722B

Abstract

In a motor vehicle having a vehicle height adjusting device, wherein the height of each suspension is controlled so as to attain a set reference vehicle height (H), reaction forces (PFL, PFR, PRL, PRR) of respective suspensions (1a, 1b, 1c, 1d) are detected and a difference ( DELTA P) between the detected reaction forces is calculated according to a formula, while the vehicle is stationary or is being driven straight. When the difference ( DELTA P) exceeds a predetermined value, it is determined that there are imbalances of the road surface contact loads of the wheels. Upon the determination of imbalances, the reference vehicle height (H) is increased for some suspensions and decreased for other suspensions to eliminate the imbalances. …<IMAGE>…

Description

METHOD OF AND APPARATUS FOR CONTROLLING REIGHT OF A VEHICLE The present invention relates to a method of and an apparatus for controlling height of a vehicle having a vehicle height adjusting device.

Conventionally motor vehicles are known that have a vehicle height adjusting device to control the height of a vehicle to zones such as high, medium or low. Motor vehicles are also known that monitor the vehicle height at a high resolution (such as in millimeter units, for example) and that independently adjust the height for each of the four wheels. Such vehicles are disclosed in Japanese Patent Laid-Open No. 139709/1987.

In motor vehicles provided with suspension stroke sensors to detect the up-and-down relative displacement or stroke of the suspension of each of the four wheels, suspension stroke information detected by each of the suspension sensors is used as the basis for performing vehicle height control independently for each of the suspensions. In this type of vehicles that have active suspensions, each suspension operates to achieve control of each of the suspensions to be in agreement with a reference vehicle height when there is a vehicle distortion or skewing, or when the degrees of wear of the tires are different. This causes imbalances between the contact loads of the wheels with the road surface.

As will be described later in detail with reference to the drawings, when the vehicle body is distorted, the suspensions of the left and right front wheels and the left and right rear wheels operate to cause the suspension lengths to take a set value or a reference vehicle height, so that whether the vehicle is running or stationary, the contact loads of one pair of diagonally opposite wheels are increased and the contact loads of the other pair of diagonally opposite- wheels are decreased.

If imbalances in the contact loads occur as described above, the vehicle will become unstable and will tend to tilt with respect to a line connecting the points of contact with the road surface, of the diagonally opposing pair of wheels for which the suspensions are contracted.

Such imbalances of the contact loads of the wheels not only occur when there is distortion or skewing of the vehicle body and when there is tire wear, but also occur when there is deformation in the sensor links of the suspension stroke sensors, and when the vehicle stops on a distorted road surface.

The object of the present invention is to solve these problems and to provide a method of and an apparatus for controlling the vehicle height so that a good balance is maintained between the -contact loads of the wheels in various conditions of the vehicle.

According to the present invention, in 'one aspect thereof, there is provided a method of controlling a height of a vehicle having vehicle height adjusting means, wherein strokes of wheel suspensions are detected and the height is controlled responsive to the detected strokes so as to attain a reference vehicle height independently for each suspension, said method comprising the steps of: obtaining quantities concerning the operation of the respective suspensions; calculating an amount representing a degree of imbalances among contact loads of the wheels when the condition of the vehicle is stationary or is driving straight; determining whether said amount exceeds a predetermined value; and changing the reference vehicle height for at least two of the suspensions when it is determined that said amount exceeds the predetermined value.

According to the present invention, in another aspect thereof, there is provided an apparatus for controlling height of a vehicle, having vehicle height adjusting means for each of front and rear wheels, and a controller responsive to strokes of suspensions for the wheels for controlling the height of the vehicle so as to attain a reference vehicle height independently for each suspension, said apparatus comprising: means for obtaining quantities representing states of operation of the respective suspensions; calculating means responsive to the quantities for calculating an amount representing a degree of imbalances among contact loads of the wheels while the vehicle is stationary or is being driven straight; imbalance determining means responsive to the amount for determining whether there are imbalances of the contact loads of the wheels; and reference vehicle height changing means responsive to a signal from said calculating means, indicating that there are imbalances, for changing the reference vehicle heights for at least two of the suspensions.

Preferred embodiments of the present invention will become understood from the following detailed description referring to the accompanying drawings.

FIG. 1 is a schematic perspective view showing a vehicle suspension system for a vehicle according to the present invention; FIG. 2 is a hydraulic circuit diagram showing the vehicle height adjusting system of FIG. 1; FIG. 3 is a diagrammatic perspective view for a model description of the states of extension and contraction of the suspensions when the vehicle body is distorted or skewed; FIG. 4 is a diagrammatic perspective view showing a first embodiment of the present invention; FIG. 5 is a flow chart of the control according to the first embodiment of the invention; FIG. 6 is a block diagram showing an apparatus according to the first embodiment; FIG. 7 is a flow chart of the control according to the second embodiment of the invention; and FIG. 8 is a block diagram showing an apparatus according to the second embodiment.

FIGS. 1 and 2 show an active suspension system to which the present invention may be applied. In FIG. 2, reference characters la and lb indicate suspensions of the left and right front wheels of a motor vehicle, and Ic and ld indicate suspensions of left and right rear wheels. Each of the suspensions la, lb, lc and ld is provided with a pneumatic spring portion D and a hydraulic cylinder E. The spring portion D has an oil chamber A and an air chamber B which are divided by a diaphragm C. The oil chamber A of the spring portion D and an oil chamber F of the hydraulic cylinder E are communicated through an orifice G.As shown in FIG. 1, one end of the hydraulic cylinder E (such as a bottom portion of the cylinder) is connected to a suspension arm member 14 on the vehicle wheel W, and the other end (a piston rod) of the hydraulic cylinder E is connected to a member 15 of the vehicle chassis. In accordance with the load on the cylinder E, hydraulic oil in the oil chamber F flows into and out of the oil chamber A through the orifice G so as to generate an appropriate damping force and at the same time to produce a spring action by the volumetric elasticity of the air sealed in the air chamber B. The system described above is a known hydropneumatic suspension system.

There are provided control valves 2a, 2b, 2c and 2d that supply and discharge oil to and from the oil chambers F of the hydraulic cylinders E. These control valves 2a, 2b, 2c and 2d are operated independently by a valve drive signal from a controller 3 to be described later. In FIG. 1, the control valves 2a, 2b, 2c and 2d are installed separately in two groups for the front and rear suspensions.

An oil pump 5 is driven by an engine 6 to pump up oil from an oil reservoir 4 to the system. In the system shown, an oil pump 5' for power steering and the oil pump 5 described above are driven in tandem by'the engine 6.

The oil discharged from the oil pump 5 passes through a check valve 7 and is stored in a high-pressure accumulator 8. In FIG. 1, the accumulator 8 is shown to be divided into two sections for the front and rear suspensions. When, some of the control valves 2a, 2b, 2c and 2d are switched to the intake side, high-pressure oil is supplied through the control valves that have been switched to the intake side, to the oil -chamber F of the suspensions la, lb, lc and ld. When some of the control valves 2a, 2b, 2c and 2d are switched to the discharge side, oil is discharged from the oil chambers F of the suspensions la, lb, ic and ld and the oil passes through an oil cooler 9 to flow into the oil reservoir 4.

FIG. 2 shows a relief valve 10 and a valve 11 which is switched to the unload state indicated in the figure, when signals, generated by the controller 3 responsive to signals from a pressure sensor 81, indicate that the high-pressure accumulator 8 has attained a predetermined pressure. When the valve 11 is switched to the unload side, the oil discharged from the oil pump 5 flows to the oil cooler 9 and then into the oil reservoir 4.

The suspensions la, lb, lc and ld are provided with suspension stroke sensors 13 as shown in FIGS. 1 and 2.

The sensor 13 detects up and down relative displacement for each suspension between the wheel and the vehicle body and input the information of the up and down relative displacement for each of the suspensions la, lb, lc and ld to the controller 3.

In order to detect behaviors of the vehicle, there are provided a vertical G-sensor G1 to detect vehicle vertical acceleration (vertical G), a lateral G-sensor G2 to detect vehicle lateral acceleration (lateral G) and a longitudinal G sensor G3 to detect vehicle longitudinal acceleration (longitudinal G). The positions where the G-sensors G1, G2 and G3 are installed are as indicated in FIG. 1. Signals of the sensors G1, G2 and G3 are inputted to the controller 3. Responsive to the input, the controller 3 determines control quantity for the intake and discharge of oil for each suspension, sends valve drive signals to the respective control valves 2a, 2b, 2c and 2d, and thus controls the intake and discharge of oil to each of the suspensions.

Signals from the suspension stroke sensors 13 pass through a circuit having a dead zone so that the signal within a set range in the vicinity of zero are excluded.

When the vehicle height is selected by a height switch 12 to a vehicle height between a low and a high vehicle height for running on rough roads, a signal exceeding the set range is inputted from the stroke sensors 13 to the controller 3. Then the controller 3 supplies oil to a pair of the suspensions which are more contracted than the reference vehicle height and discharges oil from the other pair of the suspensions which are more extended than the reference vehicle height, so that the vehicle height is maintained at the vehicle reference height.

The signals from the vertical G-sensor G1, the lateral G-sensor G2 and the longitudinal G-sensor G3 pass through the respective dead zone circuit, and signals in the vicinity of zero are excluded. When the signal from the vertical sensor G1 exceeds the set range, oil is discharged from the suspensions for an upward acceleration and is supplied to the suspensions for a downward acceleration. Therefore, the suspension has a soft suspension characteristic with a high degree of attenuation with respect to vibrations below the suspension, and a hard suspension characteristic for the movement of the vehicle body above the suspensions by control from the signals of the suspension stroke sensors 13.With respect to signals exceeding the set range, from the lateral G-sensor G2 and the longitudinal Gsensor G3, the controller 3 performs control for the intake and discharge of oil to and from each of the suspensions so that rolling, squating and nose-diving and other undesirable movements of the vehidle are reduced which occur accompanying turning, acceleration and/or deceleration of the vehicle.

In the active suspension system as described above, control is carried out to maintain the vehicle height at a reference height by the signal from the suspension stroke sensors 13, so that imbalances in the contact load of the tires occur when there is vehicle distortion as indicated in FIG. 3, for example.

When there is a vehicle distortion as shown in a model diagram of FIG. 3, the suspensions la and lb for the left and right front wheels, and the suspensions lc and ld for the left and right rear wheels have their suspension lengths maintained to the set values, so that regardless of whether the vehicle is stationary or running, the tires of the right front wheel and the left rear wheel have their contact load increased, and the tires of the left front wheel and the right rear wheel have their contact load reduced. In FIG. 3, elasticity of the tires is represented by the spring S, and the tires -with the larger contact load are contracted and tires with the smaller contact load are extended.

When imbalances of the contact load occur as described above, the vehicle body tends to tilt about the line X-X linking the points of contact with the road surface of tires for which the suspensions are contracted, and then the vehicle becomes unstable.

The phenomena described above likewise occur where there are differences in the wear of the tires, and deformation of the sensor links of the suspension stroke sensors, and where a deviation occurs due to sensor failure. The phenomena also occur when the vehicle is stationary on a distorted road surface.

As shown in FIG. 2, in the embodiment of the present invention, each of the suspensions la, ib, lc and ld is provided with a suspension reaction force detector 16 to detect the suspension reaction force to each of the suspensions. A pressure sensor is generally used for detecting the internal hydraulic pressure of each suspension as a suspension reaction force detector 16.

However, in the case of active suspension using the control valves 2a, 2b, 2c and 2d as pressure control valves, it is also possible to detect each suspension reaction force by a command signal to the pressure control valve.

The information of each suspension reaction force detected for each suspension is inputted to the controller 3. The controller 3 calculates a mean value of the suspension reaction force during 1 to 2 seconds (a time a little longer than the cycle time of the natural vibration of the vehicle body) when the vehicle is either stationary or being driven straight ahead. These conditions are detected by the lateral G-sensor G2.

Another method is that the signal from the detector 16 inputted to the controller 3 is passed through a low-pass filter having a cutoff frequency at a value higher than the natural frequency of the vehicle body. The mean value above or the value passed through the low-pass filter is used as basic suspension reaction force FL' PFRt Pry on PRR for the left front, right front, left rear or right rear wheels, respectively. On the basis of these reaction forces, the controller 3 calculates and determines the suspension reaction force difference AP using either one of the following formulae (1), (2) and (3) indicated below.

AP (PFR + PRL) - (PFL + PRR) ... (1) #P = (PFR + PFL) - 5PRR + PRL) ... (2) AP = (PFR + PRR) - (PFL + PRL) ... (3) The flow chart of FIG. 5 shows an example of using the formula (1).

Then, when the value of AP exceeds a set allowable value K, the controller 3 determines that there is an imbalance in the contact loads for the wheels due to an abnormality such as differences in the sensing of the suspension stroke sensors, differences in the tire wear, or skewing of the vehicle. Thereupon, the controller 3 operates to change the set reference vehicle heights indicated by HALOS HERO, HRLo and HRRO ( (same reference heights for the left front, right front, left rear and right rear wheels, respectively) so that vehicle height control (oil intake and discharge control) is performed to attain changed reference vehicle heights compensating for the imbalance.

More specifically, if AP is positive and exceeds the set allowable value K, the controller 3, as shown in FIG. 5, (A) increases the set reference vehicle height for the left front wheel by SH(EFLO Hrto +#H), (B) decreases the set reference vehicle height for the right front wheel by AH(EFRo -- > HFRO - #H), (C) decreases the set reference vehicle height for the left rear wheel by AH(HRLo + HRLO - AH), and (D) increases the set reference vehicle height for the right rear wheel by AH(HRRa + HRRO + AH).

Any two or four of the above (A), (B), (C) and (D) are performed simultaneously.

If AP is negative and exceeds -the set allowable value K, the controller 3, as shown in FIG. 5, (a) decreases the set reference vehicle height for the left front wheel by SH(HFLO -- > HFLO - #H), (b) increases the set reference vehicle height for the right front wheel by tH(HFRo Hro + AH), (c) increases the set reference vehicle height for the left rear wheel by AH(HRLo o HRLo + tH) and (d) decreases the set reference vehicle height for the right rear wheel by AE(HRRo HRRO AH) Any two or four of the above (a), (b), (c) and (d) are performed simultaneously.

When the vehicle is moving, the change of the set reference vehicle height is repeatedly performed for a certain set time. The set time is between 2 and 4 seconds when each basic suspension reaction force is determined by the mean value of the suspension reaction forces detected by the suspension reaction force detectors 16, and the set time is approximately twice the time required for taking the mean value when a low-pass filter having a cutoff frequency f is used, i.e., the set time is about 2/f seconds.

As shown in FIG. 4, even if there is a skew of the vehicle, the control described above improves the balance of the contact loads of the tires of the wheels as expressed by S, and eliminates unstable states due to the skew and at the same time greatly reduces unnecessary vehicle height control, thus allowing a reduction of the control energy.

When the vehicle stops and the engine and the vehicle height control system also stop, the set reference vehicle height of each suspension is stored in a memory backed up by a battery. When the engine is started again, the stored values of the set reference vehicle heights are used as the basis for repeating the control of the vehicle height described above. It is therefore possible to shorten the length of time required for vehicle height control after the engine has been started once again. However, if the set reference vehicle heights are not stored at the stop of the engine, the set reference vehicle height that was initially set is used as the basis for controlling the vehicle height as described above.

The present embodiment is not limited to the application to the suspension system of FIG. 2, but can also be applied to a vehicle height adjusting system that has means (such as a lateral G-sensor or a vehicle speed sensor and a steering angle sensor) for detecting whether the vehicle is either stationary or moving straight ahead. This system detects the suspension stroke of the suspension of each of the four wheels and controls vehicle height independently for each suspension so that the reference vehicle height is maintained responsive to the information for each suspension.

FIG. 6 shows a block diagram of an apparatus for carrying out the vehicle height control described above.

As shown, the vehicle height adjusting switch 12 is connected to a reference height determining means 20, which determines the reference vehicle height in response to the operation of the switch 12. The reference vehicle height determining means 20 supplies a reference vehicle height signal to a changing means 21 for changing the reference vehicle height.

The suspension reaction force detector 16 for each wheel delivers suspension reaction force signal to a calculating means 22 for calculating a difference of the suspension reaction force. It will be understood that the calculating means 22 receives signals from the suspension reaction force detectors 16 of all the wheels.

The calculating means 22, upon receiving a signal from the lateral G-sensor G2, indicating that the vehicle is stationary or is running straight ahead, calculates the difference AP by using either one of the formulae (1), (2) and (3) set forth hereinbefore. The lateral G-sensor G2 may be replaced by a combination of a vehicle speed sensor -and a steering angle sensor. The thus calculated difference AP is inputted to a determining means 23 for determining a contact load imbalance to a road surface.

The determining means determines whether the difference AP is positive or negative or whether the difference AP exceeds the set allowable value K.

The determining means 23 supplies an output signal to the reference vehicle height changing means 21 where the reference vehicle height inputted from the reference vehicle height determining means 20 is changed for any two or each of the wheels in accordance with (A), (B), (C) and (D) or with (a), (b), (c) and (d) set forth before.

The reference vehicle height changing means 21 supplies a changing signal of each of the changed reference vehicle heights to a deviation calculating means 24 for each of the wheels. The deviation calculating means 24 compares the suspension stroke signal from the suspension stroke sensor 13 with the changing signal from the changing means 21 and outputs a deviation signal to a control quantity setting means 25 for one suspension control valve 2 (2a, 2b, 2c or 2d).

It is to be understood that the reference vehicle height changing means 21 outputs the changing signal to other like deviation calculating means 24 for the other suspension control valves 2.

As described above, according to the present embodiment, it is possible to eliminate undesirable situations such as vehicle rolling due to imbalance of the tire contact loads, and therefore eliminate the energy consumption for unnecessary vehicle height adjustment due to the vehicle rolling.

A second embodiment of the present invention will be described below.

In order to eliminate the same problem as that of the first embodiment, according to the second embodiment, a means G2 (FIG. 2) is provided for detecting a vehicle straight ahead condition. The detecting means G2 is a lateral G-sensor or a combination of a vehicle speed sensor and a steering angle sensor. The detecting means G2 inputs the detected signal to a controller 3 as shown in FIG. 2.

Responsive to the signal inputted from the detecting means G2, the controller 3 determines that the vehicle is in a condition of moving straight ahead, as indicated in FIG. 7, the signal detected by each of- the suspension stroke sensors 13 (FIG. 2) are used to calculate the difference AD of the suspension stroke D from the set reference vehicle height H for each wheel when the vehicle is running straight ahead. Then, the absolute value AD for the AD of each suspension is integrated with respect to a length of time To (set to a value larger than the natural frequency of the vehicle) to obtain a value SD.

The value SD for the respective suspensions does not have a large difference when the contact loads of the tires are approximately the same. But when there is a distortion or skew of the vehicle body as shown in FIG.

3, the contact loads of two diagonally opposite tires are larger than the contact loads of the other two diagonally opposite tires, and the vehicle tends to tilt about the line X-X. As a result, the suspensions of the wheels with the smaller contact loads have a larger vibration of the suspension stroke and the value SD becomes large, while the suspensions with the larger contact loads have a smaller variation and the value SD becomes small.

In view of the above, the controller 3 determines the value ASD according to the following formula ASD = (SDFR + SDRL) - (SD,L + SDRR) where ASD is the difference between the sums of the value SD of the two diagonally opposite pairs of wheels.

That is to say, the value ASD is the difference between the sum SDFR + SDRL of the right front and the left rea2 wheels and the sum SDFL + SDRR of the left front and the right rear wheels. When the value ASD exceeds a set allowable range, the controller 3 determines that there is an imbalance in the contact loads of the wheels due to some abnormality such as differences in the -suspension stroke sensors, differences in the tire wear, or skewing of the vehicle body. As a consequence, the controller 3 operates to change the set reference vehicle heights Hrto, HFRO' HRLO and H,o for the left front, right front, left rear and right rear wheels, so that vehicle height (oil charging and discharge control) is changed to the reference vehicle height.

More specifically, when ASD is positive and exceeds a set allowable range L, the controller 3, as indicated in FIG. 7, (A') increases the set reference vehicle height for the right front wheel by AH(HFRo HFRO + AH)r (B') decreases the set reference vehicle height for the left front wheel by AH(HFLo -- > HFLO - AH), (C') decreases the set reference vehicle height for the right rear wheel by AH(HRRO -- > HRRO AH), and (D') increases the set reference vehicle height for the left rear wheel by AH(HRLo + HRLO + AH).

Any two or four operations of the above (A'), (B'), (C') and (D') are performed simultaneously.

If the value ASD is negative and exceeds the set allowable range L, the controller 3, as indicated in FIG.

7, (a') decreases the set reference vehicle height for the right front wheel by AH(HFRO + HFRO - AR), (b') increases the set reference vehicle height for the left front wheel by AH(HFLO -- > Hpto + AH), (c') increases the set reference vehicle height for the right rear wheel by /z(iRRO + HRRO + #H), and (d') decreases the set reference vehicle height for the left rear wheel by AH(HRLo -- > HRLO - AH).

Any two or four operations of the above (a'), (b'), (c') and (d') are performed simultaneously. The value AH is set to a minimum resolution unit, which is in the order of several millimeters.

When the set reference vehicle height is changed for compensation as described above, oil charging and/or discharging are coordinated with the changed reference vehicle height, and as a result, the suspensions of the wheels with the larger contact loads are contracted by the value AH and the suspensions of the wheel with the smaller contact loads are extended by the value AH so that the imbalance of the contact loads is reduced.

The change of the reference vehicle heights is repeated for every time period TH (which is approximately the time required for one vehicle height adjustment) so that the value ASD falls in the set allowable range L, the changing operation for the reference vehicle height terminates and unnecessary rocking or tilting of the vehicle is eliminated.

By the method described above, when there are a skew of the vehicle, differences in the frictions of the tires, sensor failure due to deformation of the sensor links, and similar abnormalities that result in imbalances in the tire contact loads, imbalances in the contact loads of the tires as expressed by the spring S in FIG. 3 are adjusted within a short time and tilting of the vehicle while running does not occur. Furthermore, the consumption of unnecessary energy due to repeating the vehicle height adjustment is eliminated along with other problems encountered in the conventional method.

The second embodiment described above is not limited to the vehicle height control system shown in FIG. 2, but can also be applied to a vehicle height adjusting system that detects the stroke of the suspensions of the four wheels and performs the vehicle height adjustment independently for each suspension so that the reference vehicle height is maintained responsive to the information of each suspension.

FIG. 8 is a block diagram of an apparatus for controlling the vehicle height described above. As shown, the vehicle height adjusting switch 12 is connected to a reference vehicle height determining means 20, which determines the reference vehicle height in response to the operation of the switch 12. The reference vehicle height determining means 20 supplies reference vehicle height signal to a reference vehicle height changing means 21.

The suspension stroke sensor 13 for each wheel delivers suspension stroke signal' D to a suspension stroke deviation calculating means 30 for each wheel. A reference vehicle height signal H is supplied to the stroke deviation calculating means 30, where the values of the signal H and the signal D are compared and the difference AD is calculated. The stroke deviation calculating means 30 is operated responsive to a signal from the lateral G sensor G2, indicat'ing the vehicle is driven straight or stationary. It will be understoodthat the suspension stroke deviation calculating means 30 is provided for each wheel.

The calculating means 30 computes a difference AD for each suspension. In the calculating means 30, the absolute value AD is integrated with respect to time for a predetermined time To to obtain the SD.

The thus calculated values SD for the respective suspensions are supplied to a suspension stroke deviation difference calculating means 31, where the value ASD is calculated according to the formula ASD = (SDFR + SDRn) - (SDFt + SD,) and the value ASD is inputted to a contact load imbalance determining means to determine the imbalance state of the contact load by comparing the value ASD with the allowable range L. Resulting signal of the determining means 32 is inputted to the reference vehicle height changing means 21 where the reference vehicle height H is changed as indicated in (A')(B')(C')(D') and (a')(b')(c')(d') set forth before.

The reference vehicle height changing means 21 supplies the signal of each changed reference height to a deviation calculating means 24, where each changed reference height- signal and the suspension stroke signal from the sensor 13 are compared to obtain an output signal to the control quantity setting means 25 for each control valve 2.

It will be understood from the foregoing description that the present invention has provided methods and apparatus capable of controlling the heights of the suspensions so as to maintain a good balance in which the contact loads of the wheels are equalized.

While the presently preferred embodiments of the present invention have been shown and described, it is to be understood that the disclosure is for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.

Claims

CLAIMS:

1. A method of controlling a height of a vehicle having vehicle height adjusting means, wherein strokes of wheel suspensions are detected and the height is controlled responsive to the detected strokes so as to attain a reference vehicle height independently for each suspension, characterized by the steps of: obtaining quantities (P, SD) representing states of operation of the respective suspensions; calculating an amount (AP, ASD) representing a degree of imbalances among contact loads of the wheels when the condition of the vehicle is stationary or is driving straight; determining whether said amount exceeds a predetermined value; and changing the reference vehicle height (H) for at least two of the suspensions when it is determined that said amount (AP, ASD) exceeds the predetermined value, whereby the vehicle height adjusting means controls the suspensions based on the changed reference vehicle height.

2. The method as claimed in claim 1, wherein said quantities are ones representing respective reaction forces (PFR, PFL' PRR' PRL) of the suspensions, and the reference vehicle height (H) is increased for suspensions receiving smaller reaction forces and is decreased for the other suspensions receiving larger reaction forces.

3. The method as claimed in claim 2, wherein each of the quantities (PFR' PFL' PRR' PRL) is a mean value of the reaction forces of at least two suspensions, inputted during a predetermined period of time.

4. The method as claimed in claim 2, wherein said amount representing the degree of imbalances is calculated according to a formula AP = (PFR + PRL) - (PFL + PRR) where AP is said amount; PFR a quantity representing the reaction force of the right front wheel; PRL' a quantity representing the reaction force of the left rear wheel; P I a quantity representing the reaction force of the left front wheel; and PRRZ a quantity representing the reaction force of the right rear wheel.

5. The method as claimed in claim 2, wherein said amount representing the degree of imbalances is calculated according to a formula AP = PFR + PFL) ( PRR PRL) where AP is said amount; PFR, a quantity representing the reaction force of the right front wheel; PFL, a quantity representing the reaction force of the left front wheel; a a quantity representing the reaction force of the right rear wheel; and PRL, a quantity representing the reaction force of the left rear wheel.

6. The method as claimed in claim 2, wherein said amount representing the degree of imbalances is calculated according to a formula AP = PFR + PRr ) - PFL # PRL ) where AP is said amount; PFR, a quantity representing the reaction force of the right front wheel; PRR/ a quantity representing the reaction force of the right rear wheel; PFLt a quantity representing the reaction force of the left front wheel; and PRL, a quantity representing the reaction force of the left rear wheel.

7. The method as claimed in claim 1, wherein said quantities are the strokes of the respective suspensions.

8. The method as claimed in claim 7, wherein the step of calculating comprises the step of calculating absolute values of deviations of the detected suspension strokes (DFR' DRLr DRRT DE) from the reference vehicle height (HERO HFLOI F0, Foo) and integrating the absolute values for each suspension with respect to time through a predetermined length of time (To)r and the reference vehicle height is increased for suspensions with larger integrated values and is decreased for suspensions with smaller integrated values.

9. The method as claimed in claim 8, wherein said amount representing the degree of imbalances is calculated according to a formula ASD = (SDFR + SDRL) - (SDFL + SD,) where ASD is said amount; SDFR, an integrated value for the right front wheel; SDRL, an integrated value for the left rear wheel; SDFL, an integrated value for the left front wheel; and SDRR, an integrated value for the right rear wheel.

10. An apparatus for controlling height of a vehicle, having vehicle height adjusting means for each of front and rear wheels, and a controller responsive to strokes of suspensions for the wheels for controlling the height of the vehicle so as to attain a reference vehicle height independently for each suspension, characterized by comprising: means for obtaining quantities (P, SD) representing states of operation of the respective suspensions; calculating means responsive to the quantities (P, SD) for calculating an amount (AP, ASD) representing a degree of imbalances among contact loads of the wheels while the vehicle is stationary or is being driven straight; imbalance determining means responsive to the amount for determining whether there are imbalances of the contact loads of the wheels; and reference vehicle height changing means responsive to a signal from said calculating means, indicating that there are imbalances, for changing the reference vehicle heights for at least two of the suspensions.

11. The apparatus as claimed in claim 10, wherein said means for obtaining quantities are means for detecting and outputting quantities representing reaction forces (PFL' PFR' PRL' PRR) of the respective suspensions, and said calculating means is means for calculating a difference between the reaction forces of the suspensions.

12. The apparatus as claimed in claim 11, wherein said calculating means has means to carry out a calculation according to a formula AP = (PFR + PRL) - (PFL + PRR) where AP is said amount; PFR' a quantity representing the reaction force of the right front wheel; PRL, a quantity representing the reaction force of the left rear wheel; PFL' a quantity representing the reaction force of the left front wheel; and PRR, a quantity representing the reaction force of the right rear wheel.

13. The apparatus as claimed in claim 11, wherein said calculating means has means to carry out a calculation according to a formula AP = (PFR PFL) (PRR PRL) where AP is said amount; PFR, a quantity representing the reaction force of the right front wheel; PFL, a quantity representing the reaction force of the left front wheel; PRR' a quantity representing the reaction force of the right rear wheel; and P , a quantity representing the reaction force of the left rear wheel.

14. The apparatus as claimed in claim 11, wherein said calculating means has means to carry out a calculation according to a formula AP = PFR + p,) ( PFL PRL ) where AP is said amount; PFR' a quantity representing the reaction force of the right front wheel; PRR, a quantity representing the reaction force of the right rear wheel; PFLr a quantity representing the reaction force of the left front wheel; and PE, a quantity representing the reaction force of the left rear wheel.

15. The apparatus as claimed in claim 11, wherein said reference vehicle height changing means has means for increasing the reference vehicle height (H) for suspensions with smaller reaction forces and decreasing the reference vehicle height for suspensions with larger reaction forces.

16. The apparatus as claimed in claim 10, wherein said means for obtaining quantities comprises detectors for detecting strokes of the respective suspensions, and said calculating means comprises a calculator for calculating deviations of the detected suspension strokes from the reference vehicle height (E) and an integrator for integrating the absolute values of the deviations for each suspension with respect to time through a predetermined length of time (To)r and a substractor responsive to the integrated values for calculating a difference between the integrated values.

17. The apparatus as claimed in claim 10, wherein said calculating means has means to carry out a calculation according to a formula ASD = (SDrR + SD) - (SDFL + SD,) where ASD is said amount; SDFR, an integrated value for the right front wheel; SDRL, an integrated value for the left rear wheel; SDFL, an integrated value for the left front wheel; and SDRR, an integrated value for the right rear wheel.

18. The apparatus as claimed in claim 16, wherein said reference vehicle height changing means has means for increasing the reference vehicle height (H) for suspensions with larger integrated values and decreasing the reference vehicle height for suspensions with smaller integrated values.

19. The apparatus as claimed in claim 10, wherein said changing means increases the reference vehicle heights for two of the suspensions and decreases the reference vehicle height for the rest of the suspensions.

20. A method of controlling a height of a vehicle substantially as hereinbefore described with reference to the accompanying drawings.

21. An apparatus for controlling height of a vehicle substantially as hereinbefore described with reference to and as shown in the accompanying drawings.