Vehicle suspension systems

A vehicle suspension system includes a vehicle body, a plurality of wheels arranged in lateral and longitudinal spaced relation to support the vehicle body. Two hydraulic rams are between each wheel and the vehicle body, with one ram of each wheel connected by a fluid circuit with a ram of the laterally adjacent wheel and the other ram of each wheel connected by a fluid circuit to the ram of the longitudinally adjacent wheel. A respective sensor for each wheel is adapted to generate a signal indicative of the positional relation of that wheel relative to the vehicle body. A programmed controller is arranged to receive the signals from each sensor and compare the positional relation of the body with respect to a preset datum position, and a fluid adjustment device is operable in respect to a detected variation of the positional relation from the datum position to adjust the volume of fluid in the relevant fluid circuit to correct the positional relation if required.

This invention relates to improvements in the suspension system for a 
vehicle, and is specifically related to controlling the disposition of the 
vehicle body relative to the vehicle wheels when the vehicle is subject to 
load distribution variation. 
In recent times there has been a trend towards resilient sprung suspension 
systems incorporating variable damping and spring rates in an attempt to 
improve vehicle stability and reduce movement of the vehicle body relative 
to the surface being traversed. Some other more advanced suspension 
systems, commonly referred to as active and semi-active suspensions, 
incorporate a number of electronic sensors which monitor information such 
as vertical wheel travel and body roll, as well as speed, acceleration, 
steering and braking commands. This and other data is processed by a 
computer which instructs hydraulic or pneumatic actuators to override the 
normal function of resilient springs in order to interpret, compensate and 
adjust the suspensions performance to suit speed, terrain and other 
factors in order to maintain a level ride and controlled distribution of 
weight onto all wheels. These suspension systems require an external 
intelligent back-up system, and call for substantial input of external 
energy, drawn from the vehicle engine, to operate the actuators that 
affect the adjustment to the suspension system. 
A range of constructions of `active` and `semi-active` suspensions for 
vehicles have been proposed including systems operating on the basis of 
compression and/or displacement of fluids and such systems currently in 
use incorporate a pump to maintain the working fluid at the required 
pressure and effect the high speed distribution thereof, and sophisticated 
control mechanisms to regulate the operation of the suspension system in 
accordance with sensed road and/or vehicle operating conditions. These 
known systems incorporating pumps and electronic control systems, which 
are both required to operate substantially continuously while the vehicle 
is in operation, are comparatively expensive to construct and maintain, 
and require energy input, and therefore have limited acceptability in the 
vehicle industry. 
There is disclosed in International Patent Application No. WO91/04877, a 
vehicle having a load support body, and a pair of front ground engaging 
wheels and a pair of rear ground engaging wheels connected to the body to 
support the body and wherein each wheel is displaceable relative to the 
body in a generally vertical direction. 
Interconnected between each wheel and the body is a fluid ram including 
first and second fluid filled chambers that varies in volume in response 
to vertical movement between the respective wheel and the body. 
The first chambers of the front and rear wheels on each side of the vehicle 
are in communication by respective individual first fluid circuits. 
Similarly the second chambers of the front wheels and of the rear wheels 
respectively are in communication by respective individual second fluid 
circuits. This construction provides, when the vehicle is in use, 
substantially the same fluid pressure in the two chambers of any 
individual fluid circuit thereby inducing all wheels to maintain tractive 
ground engagement. 
In practice at least one and preferably each of said individual fluid 
circuits include at least one pressure accumulator, and preferably also a 
damping device operable to at least partially dissipate pressure shock in 
the fluid circuit. The vehicle suspension above described differs greatly 
from all the known systems in that the wheel travel is not dependent upon 
progressive resilient suspension mechanisms which require variable 
reactions to the many ever changing conditions experienced by the vehicle. 
This allows free vertical travel of the individual wheels with respect to 
the vehicle body or chassis without having to first overcome the 
resistance of the conventional springing mechanisms normally incorporated 
between the wheels and the vehicle body. Thus, the wheels are individually 
unrestrained and free to move to follow the undulations of the surface 
being travelled without continually changing the vehicle weight 
distribution between the individual wheels. This reduction or elimination 
of changes in weight distribution significantly improves the traction 
between the wheels and the surface being traversed and the handling 
characteristics of the vehicle. 
A further development of the above described suspension system is disclosed 
in International Patent Application No. WO 93/01063. 
It will be appreciated, that in order for the hydraulic system, as 
disclosed in the previously referred to prior patent application, to 
function correctly, the relative pressures and fluid volumes of the 
individual circuits must be correlated, so that each circuit can perform 
its specific functions, without interference from circuits which share the 
weight supporting function of the same wheel. In this regard it will be 
appreciated that if the front and rear fluid circuits are each initially 
supplied with too much fluid these circuits will become over pressurised 
relatively to the two side circuits. The side circuits will thereby be 
relieved of some of the vehicles weight and the vehicle is principally 
supported by the front and rear circuits. A typical consequence of this 
will be that the gas volumes in the side circuits accumulators become 
expanded beyond their optimum working sizes and this in turn permits 
excessive roll motions to occur when cornering. 
Alternatively the side circuits may be provided with too much fluid with 
reference to the front and back circuits and the resultant pressure/volume 
imbalance leads to the side circuits carrying more of the vehicles weight 
than intended and consequentially excessive pitch motion would result. Not 
only does such imbalance affect the ride quality but it would also render 
the vehicle less safe as the wheels would not all be carrying the correct 
proportion of the total loads and not reacting to different driving 
conditions properly. 
Additionally most vehicles are non-symmetrically loaded for a large portion 
of the operating time, and indeed, an engine mounted at the front usually 
makes the front wheels carry more weight than the back. If the side 
circuits of such an eccentrically loaded vehicle are permitted to carry 
too much of the total weight then the vehicle will tend to pivot on the 
support of the side circuits and will pitch forwards onto the front wheels 
thereby further reducing the optimum weight being born on the rear wheels. 
Similarly, in a vehicle that may be subjected to a large load being 
suddenly applied at the rear, this can disturb the equilibrium of the 
relative pressures and volumes so that the front circuit may even become 
negatively loaded when the side circuits carry more than their share of 
weight. 
It is therefore the object of this invention to provide a vehicle 
suspension system which determines changes in the vehicular height and 
inclination and adjusts the fluid in appropriate circuits to reinstate or 
rectify the optimum relative heights, while providing the optimum load 
distribution to the wheels. 
With this object in view, there is provided a vehicle suspension system 
comprising a plurality of wheel assemblies arranged in longitudinal and 
lateral spaced relation to a vehicle body, each wheel assembly including a 
wheel and two fluid rams each operably connecting the wheel to the vehicle 
body to support the vehicle body, one fluid ram of each two laterally 
spaced wheel assemblies being in direct fluid communication by a fluid 
conduit, and the other fluid ram of each said two laterally spaced wheel 
assemblies being in direct fluid communication with a respective fluid ram 
of a wheel assembly longitudinally spaced therefrom on the same side of 
the vehicle, sensor means adapted to generate signals indicative of the 
positional relations of each of said laterally and longitudinally spaced 
wheels relative to the vehicle body, control means arranged to receive 
said signals and compare said positional relations with a respective 
preset datum position, and adjustment means operable in response to 
variation of the positional relation of each wheel from the respective 
datum position beyond a preset limit to adjust the volume of fluid in the 
fluid circuits to establish a positional relation within said preset 
limit. 
In one form of the suspension system, each of the fluid ram means between 
the wheels and the vehicle body includes two single acting fluid rams 
arranged to expand and contract together as a result of relative movement 
between the wheel and the vehicle body. One fluid ram of each of the two 
front wheels are in direct communication by a fluid conduit and one 
cylinder of each of the two rear wheels are similarly in direct 
communication by a further fluid conduit. The remaining fluid rams at the 
front and rear wheels on each side of the vehicle are in direct 
communication by a respective fluid conduit. Thus, if the vehicle body 
moves down with respect to the wheel at the front left hand corner, fluid 
is displaced from each fluid ram of that wheel to the cylinder of the 
right front wheel and the left rear wheel respectively, to effect an equal 
and opposite movement of the vehicle body relative to the wheels. 
Preferably, the fluid ram of each two wheel assemblies which are 
longitudinally spaced are double acting fluid rams, each having upper and 
lower chambers, said double acting fluid rams having the respective upper 
chambers thereof in direct fluid communication and the respective lower 
chambers thereof in direct fluid communication by respective upper and 
lower longitudinal conduits, the upper conduits on the respective sides of 
the vehicle being in direct fluid comunication with the lower conduit on 
the opposite side of the vehicle. 
Alternatively, or in addition, the fluid ram of each two wheel assemblies 
which are laterally spaced are double acting fluid rams having upper and 
lower chambers, said double acting rams of the laterally spaced wheel 
assemblies having the respective upper chambers thereof in direct fluid 
communication and the respective lower chambers thereof in direct fluid 
communication by respective upper and lower lateral conduits, said upper 
lateral conduits on the respective ends of the vehicle being in direct 
fluid communication with the lower conduit at the opposite end of the 
vehicle. 
In yet a further alternative construction, the fluid rams of each two 
longitudinally spaced wheel assemblies are each double acting fluid rams 
having respective upper and lower fluid chambers, the upper and lower 
chambers of the two longitudinally spaced fluid rams on one side of the 
vehicle being in fluid communication upper chamber to upper chamber and 
lower chamber to lower chamber, and the upper and lower chambers of the 
two longitudinally spaced fluid rams on the opposite side of the vehicle 
are correspondingly in fluid communication. 
In the absence of pressure accumulators in the circuits, the volume of 
fluid in each of the conduits and the two fluid rams connected thereto 
remains the same under all operating conditions, barring leakage. 
Accordingly, if there is a difference in the extent of movement of one 
fluid ram in relation to the other fluid ram connected thereto by a fluid 
conduit, this indicates a change in the volume of fluid in the total 
assembly comprising the two cylinders and the connecting conduit. 
However, in prior art suspension systems of the general type previously 
referred to, it is conventional practice to provide in each fluid conduit 
a pressure accumulator to establish a degree of resilience within the 
fluid circuit, and hence in the suspension system. Accordingly, as the 
total weight of the vehicle body varies, such as, as a result of adding or 
removing people or load from the vehicle body, the pressure in the fluid 
circuits will vary resulting in a variation in the volume of hydraulic 
fluid in the accumulators. 
Thus, if accumulators are similarly incorporated in the suspension system 
as presently proposed, the quantity of the fluid in the accumulator may 
vary with variations in operating conditions thus resulting in a variation 
in the actual amount of fluid in the circuit, excluding the amount of 
fluid in the accumulator, resulting in a lowering of the body with respect 
to the wheels. This will result in the signals from the positional sensor 
communicating to the control means, a lowering of the operating height of 
the vehicle body. When such conditions are detected by the control means, 
the latter initiates operation of a pump and actuates the appropriate 
valves to supply further fluid to that circuit to return the vehicle body 
to its normal operating height. Upon subsequent removal of the additional 
load, the resulting reduction in pressure in the fluid system will result 
in the return of fluid from the accumulator to the fluid circuit and 
necessitate the draining of fluid from the circuit to a reservoir to again 
establish the nominal correct height of the vehicle body with respect to 
the wheels. 
In the alternative form of the suspension, as previously referred to 
wherein the two single acting cylinders provided between each wheel and 
the vehicle body, are replaced by two double acting fluid cylinders, the 
fluid in the upper chamber of each cylinder supports the vehicle weight. 
Further, only one position sensing means for each wheel assembly is 
required and the signals therefrom received by the control means will 
control the volume of fluid in the circuit connecting these upper 
chambers. 
The invention will be more readily understood from the following 
description of a number of specific constructions of vehicle suspension 
systems incorporating the feature of the invention, and as illustrated in 
the accompanying drawings.

Referring now to FIG. 1 of the drawings, which illustrates the suspension 
system in a fundamentally diagrammatic form. In this drawing, each of the 
wheels, is mounted on the chassis in the same manner as now described with 
reference to the front left wheel. The wheel 1, is connected to the 
chassis by a wishbone type structure 120 which is pivotally connected to 
the chassis 125 by respective co-axial pivot connections 121 and 122. For 
the sake of clarity the wishbone type suspension arm 120 and associated 
pivot connections are identified by reference numeral only in respect of 
wheel 1 and the remaining three wheels 2, 3 and 4 are identically 
connected to the chassis 125. 
Between the vehicle chassis 125 and each wheel there is provided two single 
acting cylinders as indicated at 5 and 12, with respect to wheel 1, each 
pivotally connected to the chassis 125 at 127 and 128 and to the wishbone 
arm 120 at 129 and 130. The pivot connections at the respective ends of 
the cylinders 5 and 12 are aligned in the generally longitudinal direction 
of the chassis 125 whereby as the wheel 1 and the wishbone arm 120 
carrying the wheel pivots relative to the chassis 125, each of the 
cylinders 5 and 12 expand or retract. 
The above description with respect to the mounting of the wheel 1 and the 
interacting pair of cylinders 5 and 12 also applies to the connection of 
each of the other three wheels of the vehicle, however, for the sake of 
clarity individual reference numerals for the corresponding components are 
not shown for each wheel mounting although the respective cylinders on 
each wheel have been individually identified. 
The cylinders 5 and 6, interacting respectively with the front wheels 1 and 
2 of the vehicle, are interconnected by the fluid line 13 whilst the 
cylinders 9 and 10, associated with rear wheels 3 and 4, are 
interconnected by the fluid line 15. Similarly the cylinders 12 and 11 
associated with the front and rear wheels 1 and 4 respectively, are 
interconnected by the fluid line 16, whilst the front and rear wheels 7 
and 8 on the opposite side of the vehicle are interconnected by the fluid 
line 14. 
With the pairs of cylinders arranged as above described between each wheel 
and the vehicle chassis and interconnected as above described by fluid 
lines 13, 14, 15 and 16 respectively, a vehicle suspension system is 
created whereby relative movement in a vertical direction between any one 
wheel and the chassis 125 will result in a corresponding opposite movement 
between the transversely opposite wheel and the chassis 125, and between 
the longitudinally spaced wheel and the vehicle on the same side of the 
vehicle. 
The result of this configuration of inter-communicating hydraulic cylinders 
is that the vehicle chassis 125 will remain substantially level although 
its average height thereof with respect to a selected ground datum may 
vary while all wheels remain in ground contact. It is also important to 
note that in view of the interconnection of the hydraulic cylinders by the 
respective hydraulic lines, the pressures in all the cylinders and lines 
will be substantially the same. Thus the weight transferred from the 
chassis through the cylinders to each of the wheels will cause effective 
tractive engagement with the surface upon which the vehicle is supported 
or moving over. 
Each of the fluid lines 13, 14, 15, and 16 are in communication with 
respective hydraulic accumulators 73, 74, 75 and 76 with respective 
damping valve 83, 84, 85 and 86 interposed between the respective fluid 
line and accumulators. Each accumulator is divided in the known manner 
into two chambers by a movable internal wall. The hydraulic accumulators 
as illustrated are the common flexible diaphragm type, however, 
accumulators of other constructions may be used, including piston type, 
and accumulators using springs or other resilient mechanisms as a 
substitute for the compressed gas are also acceptable. 
The suspension system as described with respect to FIG. 1 of the drawings 
is the basic suspension system as disclosed in PCT Application AU90/00474 
which was laid open to public inspection under International Patent 
Application No. WO91/04877 and the present invention relates to a further 
development of that suspension system as will now be described with 
reference to FIGS. 2 and 3 of the accompanying drawings. 
Referring now to FIG. 2, there is shown the hydraulic circuit layout 
whereby the present invention would be applied to the suspension system as 
shown in FIG. 1, however, for the sake of clarity, the majority of the 
mechanical componentary of the vehicle and suspension system has been 
removed and the hydraulic suspension system and control thereof is shown 
diagrammatically independent of the mechanical parts. It is however, to be 
noted that hydraulic components as shown in FIG. 1 and represented in 
diagrammatic form in FIG. 2, carry the same reference numerals. As 
described with reference to FIG. 1, each of the wheels 1, 2, 3 and 4 are 
connected to the vehicle chassis by a respective pair of single acting 
hydraulic cylinders such as indicated at 5 and 12 in resect of wheel 1. 
Hydraulic cylinders 5 and 6 of front wheels 1 and 2 are interconnected by 
the hydraulic line 13 and the rear cylinders 9 and 10 connected to wheels 
3 and 4 respectively are interconnected by the rear hydraulic line 15. 
Similarly, the hydraulic cylinders 11 and 12 of left hand wheels 4 and 1 
are interconnected by the hydraulic line 16 and the hydraulic cylinders 7 
and 8 of the right hand wheels 2 and 3 are interconnected by hydraulic 
line 14. 
Each of the hydraulic lines has two spaced hydraulic accumulators 
communicating therewith, such as accumulators 17 and 18 connected to 
hydraulic line 13; accumulators 19 and 20 connected to hydraulic line 14; 
accumulators 21 and 22 connected to hydraulic line 15 and accumulators 23 
and 24 connected to hydraulic line 16. These accumulators are of the 
conventional liquid-gas formed with an internal flexible dividing wall 
whereby the displacement of liquid from any one of the hydraulic circuits 
into an accumulator will result in compression of the gas in the gas 
portion of the accumulator. Such accumulators and the construction and 
operation thereof are well known and will not be further described herein. 
Interconnected between the vehicle chassis 125 (not shown in FIG. 2) and 
the respective wheels 1,2,3 and 4 are individual position sensors 25, 26, 
27 and 28 which are arranged to issue a processable signal indicative of 
the positional relationship in the vertical plane of the wheel with 
respect to the vehicle chassis. Each of the position sensors 25, 26, 27 
and 28 are connected to the programmed controller 29 to respectively 
supply a signal to the controller indicative of the position of the 
respective wheel in relation to the vehicle chassis. Alternatively, 
inclinometers may be attached to each axle as the inclination is directly 
related to the relative position of the respective wheels. 
In addition, each of the hydraulic lines 13, 14, 15 and 16 incorporates a 
pressure sensor 35, 36, 37 and 38 respectively, each of which supply a 
signal to the programmable controller 29 indicative of the pressure in the 
respective hydraulic lines. 
The hydraulic pump 30 draws hydraulic fluid from the hydraulic fluid 
reservoir 39 and may selectively deliver hydraulic fluid to any one of the 
hydraulic lines 13, 14, 15 and 16 via respective supply lines 13a, 14a, 
15a and 16a, each of which incorporates a three position solenoid actuated 
valve 31, 32, 33 and 34 respectively. Each such solenoid actuated valve is 
also connected to a respective fluid return line 13b, 14b, 15b and 16b 
that each terminate at the hydraulic fluid reservoir 39. Accordingly, by 
actuation of the relevant solenoid valve 13a, 14a, 15a and 16a, fluid can 
either be delivered by the pump 30 to the respective hydraulic lines 13, 
14, 15 and 16, or fluid can be returned from those respective lines to the 
reservoir 39 or each hydraulic line can be isolated from both the pump 30 
and reservoir 39. 
It will be appreciated that each of the hydraulic lines 13, 14, 15 and 16 
and the respective hydraulic cylinders at each end thereof constitute a 
closed circuit, that contains a fixed volume of hydraulic fluid. 
Accordingly if one wheel moves a particular distance in one direction, the 
wheel at the opposite end of that particular circuit must move an equal 
distance in the opposite direction, assuming the three way valve in the 
fluid line to that circuit is closed. Thus, the total of the movement of 
the two wheels on the one circuit, measured from a common datum will 
always be the same. Thus, by programming the controller 29 to continually 
monitor the sum of the position signals from the two position sensors on 
the respective wheels on the same hydraulic circuit, the controller can 
determine whether there has been a change in the total amount of fluid in 
that circuit. Where such a change has been determined by the controller 
29, the controller will initiate the operation of the pump 30 of the 
vehicle is too low, and the opening of the appropriate solenoid valves in 
the relevant supply lines from the pump to the respective fluid circuits, 
to add fluid to re-establish the correct total reading from the two 
position sensors on that one circuit. If the vehicle is too high the 
appropriate solenoid valve is operated to return fluid to the reservoir 
39. 
The above discussed operation of the suspension system under the control of 
the programmed controller 29, ensures that each of the four hydraulic 
circuits 13, 14, 15 and 16 always contain the correct spacial amount of 
hydraulic fluid to thereby maintain the correct relationship of each of 
the wheels with respect to the vehicle body 25. 
The above discussed mode of operation of the suspension system as 
illustrated in FIG. 2 is based on the assumption that there are no 
pressure accumulators in the respective circuits 13, 14, 15 and 16, 
however, in an actual vehicle as would be commercially acceptable, 
pressure accumulators as indicated at 17, 18, 19, 20, 21, 22, 23 and 24 
must be provided. The pressure accumulators provide resilience in the 
suspension system. In view of the basic nature of such accumulators, 
variations in the load supported by the respective hydraulic circuits 13, 
14, 15 and 16 will result in variations in the volume of hydraulic fluid 
displaced from the circuit into the accumulators coupled to that circuit. 
This displacement of fluid into the accumulator is equivalent to a 
temporary loss or leakage of fluid from the circuit, and will result in a 
lowering of the vehicle chassis relative to the wheels. This change in 
relative position of the chassis 125 will be detected by the controller 29 
from the input signals from the position sensors, such as for example 
sensors 25 and 26, and the solenoid valve 31 will be activated to allow 
the pump 30 to deliver hydraulic fluid to the circuit 13 to correct the 
positional relation of the chassis 125 to the wheels 1 and 2. 
It is to be understood that the control system described herein to correct 
the positional relation between the vehicle chassis and the supporting 
wheels does not operate continuously as the vehicle is in motion. The 
control system proposed is for the purpose of correcting the chassis to 
wheels positional relationship following a change in the load on the 
vehicle and/or the distribution of that load. The position sensors and/or 
the controller normally remain inactive for relatively long periods of 
time. Typically, the controller and sensors are activated for a short 
period following each instance of starting the vehicle engine, as 
typically there is the possibility that while the vehicle was stationary a 
change in load or load distribution in or/on the vehicle occurred. 
However, the controller and sensors may be activated at regular time 
intervals of the order of 5 to 10 minutes while the vehicle is in motion. 
The above discussed operation of the controller in processing the 
information provided by the position sensors enables the controller to 
correlate the heights of adjacent wheels in both orthogonal direction thus 
establishes whether the average height of each side or each end of the 
vehicle is above or below a predetermined prescribed height. This 
information can optionally be further processed or cross referenced by the 
controller to determine and confirm whether the front of the vehicle is 
too high relatively to the back or vice versa and/or whether the vehicle 
is leaning to the left or right about its longitudinal axis. 
If, for example, it is determined that the back end of the vehicle has 
become too low relative to the front, this change in trim can be a result 
of various factors and each require a different appropriate response. For 
example, a heavy load may have been placed at the back of the vehicle and 
this can easily be determined by measuring the relative pressures in the 
front and back circuits by way of the pressure sensors 35, 36, 37 and 38 
as shown in FIG. 2. If the pressure at the back has increased while the 
pressure at the front has diminished this would indicate that the load had 
either shifted from the front towards the rear or that a weight had been 
added at the back. If a heavy load has been placed towards the rear of the 
vehicle, the pressure in the rear circuit 15 will increase along with a 
lesser increase in pressure of the side circuits 14, 16. If the two side 
circuits 14, 16 have not experienced an increase of pressure this would 
indicate that the net load had not increased although the centre of 
gravity of the existing load may have moved backwards on the vehicle. 
Also, it is to be understood that the preferred position of the wheels with 
respect to the vehicle can be different for different operating conditions 
of the vehicle. Thus, the vehicle chassis would normally be preferably 
higher when the vehicle is operating off-road or unsealed roads than when 
operating on sealed roads or highways. Accordingly, the controller can be 
programmed to permit the operator to select from a range of preset chassis 
heights which is appropriate to use in the prevailing operating 
conditions. 
In order to determine the optimum relative working volumes and hence 
pressure of each circuit computer models or empirical experience can 
define the extreme parameters of loads in different positions and this 
information is stored be used as a reference. 
The parameters can be established as follows: 
1. Prescribed ground height of the vehicle in determined with a selected 
average load, for example, two persons, and with the suspension hydraulic 
cylinders half extended, that is in the centre of the stroke thereof. In 
this state, the accumulators should have optimum operating gas volumes to 
produce a level of resilience for best occupant comfort. 
2. The maximum allowable load is placed on the vehicle and in sequence 
located in the respective extreme position on the vehicle is both the 
lateral and longitudinal directions. With the weight located in each 
extreme position, the gas in the associated accumulators will become 
further compressed and in order to maintain the vehicles at the prescribed 
attitude, an amount of fluid must be introduced into each hydraulic 
circuit equal to the change in volume of the gas in the accumulator in 
that circuit. 
3. It is to be noted that dynamic forces resulting from changes of speed or 
direction are not included in the considerations as the present proposal 
is only concerned with changes resulting from a change in the static 
weight distribution or level change. 
4. Various level checking and level re-establishment operations or 
procedures can be adopted but for convenience are described as follows: 
a. If four position sensors are used, the information received from the 
front pair is first added and divided by two to establish the average 
front height of the vehicle. 
b. The information from the two rear position sensors is similarly then 
added and averaged to establish the average rear height of the vehicle. 
c. A comparison is made of the average height of the front versus the rear 
to establish if one end has gone up or down relative to the other and/or 
whether there is a net increase or decrease in vehicle height. 
d. If the net height remains correct but for example the back has subsided 
and the front has gone up, the pump 30 is activated while the three way 
solenoid valve 33 is opened between the pump and rear circuit 15, so that 
fluid is introduced into the rear hydraulic circuit to raise the rear of 
the vehicle. 
e. The three way solenoid valve 31 between the front circuit 13 and the 
tank 39 is opened to release some fluid from the front circuit so that as 
the back is pumped up the front is allowed to lower. 
f. When the fore and aft attitude is approximately correct, the pressures 
of the two side circuits 14 and 16 is monitored from the pressure sensors 
36, 38 to establish how much weight is being borne on the side circuits. 
g. This is then compared with data relating to pressure received from the 
front and rear pressure sensors 35,37 so that if the transverse pair are 
over or under pressurised fluid can be introduced or removed from the 
appropriate circuit. 
h. The information from the height sensors is then compared to establish 
whether the average height of the left side relative to the right side is 
within the predetermined parameters, and if any adjustment is necessary, 
this is achieved by returning fluid to the tank 39 from the vehicles high 
side and introducing a similar amount of fluid to the low side via the 
pump 30 until the level lateral attitude is reached. 
i. If any adjustments such as described in h. were made, then the entire 
sequence a. to h. should be rechecked in the event that the other initial 
heights and pressures have become modified during the process. 
It should be noted that while the above has been described as a sequence of 
events all these steps may occur more or less concurrently so that the 
attitude change is seen to be a single operation with various solenoids 
opening and closing while the pump is in action. 
If the attitude can not be corrected within the normally permitted 
parameters or pressures in the various circuits, because for example an 
extreme load has been applied asymmetrically, then new references are 
progressively selected and the process is repeated until a satisfactory 
relationship of heights and pressures is achieved. 
The general rule is that if one end is heavily laden and shows a 
significant pressure increase relative to the other end then the two side 
circuits between the front and rear should both adopt a pressure roughly 
equivalent to the average of the two extreme circuits. This ensures that 
the weight distribution is as uniform as possible in the two cylinders of 
each wheel. Similarly the average of the front and rear circuits pressure 
should be roughly equivalent to the average pressure of the two side 
circuits. This rule is only approximate as each vehicle has its own weight 
distribution parameters such as the hydraulic cylinders may have different 
bore sizes leading to different pressure differentials and fluid 
capacities. 
Referring now to FIG. 3 of the drawings, there is shown the same basic 
vehicle and hydraulic system as previously described with respect of FIGS. 
1 and 2 and corresponding components in FIG. 3 carry the same reference 
numeral as in FIGS. 1 and 2. However, in the constructions shown in FIG. 
3, each of the hydraulic cylinders connected between the respective wheels 
and the vehicle chassis, are double acting cylinders. The upper chambers 
of each of the double acting cylinders are interconnected in the manner as 
previously described with reference to FIG. 2 and the relevant 
interconnecting hydraulic circuits carry the same reference numeral as in 
FIG. 2, namely 13, 14, 15 and 16. In addition, the lower end chambers of 
each of the double acting hydraulic cylinders is interconnected in the 
identical manner to the upper chambers and are respectively identified by 
reference numerals 13c, 14c, 15c and 16c. 
The other principle difference between the construction shown respectively 
in FIGS. 2 and 3 is that hydraulic circuit 13 at the front of the vehicle 
is connected by the hydraulic line 51 to hydraulic circuit 15c at the rear 
of the vehicle, whilst hydraulic circuit 13c at the front is connected by 
hydraulic line 52 to the hydraulic circuit 15 at the rear of the vehicle. 
Similarly, the hydraulic circuits on the respective sides of the vehicle 
chassis are similarly interconnected in that the left side hydraulic 
circuit 16 is connected to the right side hydraulic circuit 14c by the 
hydraulic line 53 and the lower hydraulic circuit 16c at the left hand 
side of the vehicle is connected to the upper hydraulic circuit 14 on the 
right hand side of the vehicle by the hydraulic line 54. 
The construction of the suspension system as shown in FIG. 3 is described 
in greater detail in the Applicant's PCT Application constituting 
International Patent Application No. WO93/01063, the disclosure of which 
is incorporated herein by reference. Further, the hydraulic circuits 13, 
14, 15 and 16 are connected to a pump and reservoir of the same 
construction and in the same manner as previously described with respect 
to FIG. 2. That is, a pump and tank such as pump 30 and tank 39 in FIG. 2 
are incorporated into the suspension system in FIG. 3 with the same 
configuration of three way solenoid valves and fluid conduits 13a, 14a, 
15a and 16a in FIG. 2 incorporated into FIG. 3. This arrangement of the 
pump, fluid tank, solenoid valves and conduits operates in the identical 
manner to that previously described with respect to FIG. 2 and the 
description shall not be repeated here with respect to FIG. 3. 
It is to be noted that although the circuits 13, 14, 15 and 16 connected 
between the upper chambers of the respective double acting cylinders, are 
in constant communication with the lower line on the opposite side or end 
of the vehicle as above described, this does not adversely affect the 
height adjustment of the vehicle chassis by way of supplying or 
withdrawing fluid from the circuits 13, 14, 15 and 16 since the upper 
chambers of the respective double acting cylinders have the dominant 
influence on the trim of the vehicle chassis with respect to the ground 
engaging wheels. 
In the preceding descriptions of the respective embodiments of the 
invention, as illustrated in the accompanying drawing, specific reference 
has been made to hydraulic systems providing the supporting connection 
between the wheels and the vehicle body or chassis and it is to be 
understood that pneumatic or other fluid systems can equally be used 
within the scope of the invention as herein described. 
FIG. 4 depicts diagrammatically the internal operations of the programmed 
controller illustrating the processing of the information received from 
the wheel position sensors and the pressure sensors to trigger the 
operation of solenoid valves to achieve the desired predetermined fluid 
condition in the respective fluid circuits. 
In order for the controller 29 to be universal in its fitment it is 
equipped with a power supply adaptor 40 that converts the vehicles power 
supply to a voltage acceptable to the controller. 
The information from the wheel position and pressure sensors is received 
into the input buffers for each wheel 41a front left, 41b front right, 41c 
back right and 41d back left where the information is stored. At this 
point there is an adjustment for setting a zero reading of each system so 
as to gain a datum point from where to work. Items 42a, 42b, 42c and 42d 
are span adjusters to set the width of field of operation to either side 
of the set zero. The information is then passed to summers where it is 
added and divided in pairs to get an average of two wheels to indicate the 
average wheel height and/or pressure of each circuit. Item 43 averages 
front left and front right wheels to obtain the front system as 44 does 
front right and back right for the right system, 45 back right and back 
left for the back system and 46 back left and front left for the left 
system. 
At this point there is an allowance for a take off (47, 48, 49, 50) to 
supply other equipment (indicators, data logger, memory storage etc) with 
the information thus far gained. 
The sequencing device 51 allows information to be processed in a 
predetermined order (or simultaneously) as specified for the particular 
vehicles requirements. 
The information is then compared (via selector 52) to one of any number of 
pre-set values. The comparators do an `if greater than then` or `if less 
than then` scenario to each system at 53a and 53b, 54a and 54b, 55a and 
55b and 56a and 56b respectively. An adjustable time delay (57, 58, 59, 
60) is used to control the delay before acting and the length of time 
acted upon for each of the solenoids to rectify the difference in the 
fluid volume and/or pressure in the particular circuit. For systems fitted 
with pressure regulators on the side circuits, a reset button 65 is 
incorporated with a time equalisation adjustment to give the regulators 
time to supply enough fluid volume to reach their pre-set pressure before 
the solenoids are turned off by the time delay. 
Each circuit supply and return solenoids or other fluid valving devices are 
then switched via a driver or other electrical or mechanical device; 61a 
front down, 61b front up, 62a right down, 62b right up, 63a back down, 63b 
back up, 64a left down and 64b left up. 
It will be appreciated that the controller can take many forms and be 
programmed to receive inputs relating to other areas of the vehicle 
operation. However, it is to be understood that the controller does not 
function in a manner analogist to an active suspension. More particularly, 
the present invention is directed to adjusting the suspension system to 
correct the changes in the load and/or load distribution and not changes 
in the road or terrain being traversed.