U.S. patent application number 08/981711 was filed with the patent office on 2001-08-30 for control method for vehicle suspension system.
Invention is credited to HESLEWOOD, RAY, HEYRING, CHRISTOPHER BRIAN, LONGMAN, MICHAEL.
Application Number | 20010018629 08/981711 |
Document ID | / |
Family ID | 3788181 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010018629 |
Kind Code |
A1 |
HEYRING, CHRISTOPHER BRIAN ;
et al. |
August 30, 2001 |
CONTROL METHOD FOR VEHICLE SUSPENSION SYSTEM
Abstract
A method of controlling a vehicle suspension system for a
vehicle body supported by a plurality of spaced apart support means
arranged in at least generally diagonally opposite pairs, the
vehicle suspension system including adjustment means for adjusting
the position of each of the support means relative to the vehicle
body, sensor means adapted to generate a signal indicative of the
position of each of the support means, and control means arranged
to receive said signals, wherein the required position for each
support means is determined as a function of the diagonal average
of the positions of each pair of diagonally opposite support means,
the position of each support means being adjusted on the basis of
the said diagonal averages. A method includes determining the
difference between the diagonal average of the positions of each
pair of diagonally opposite support means of the vehicle.
Inventors: |
HEYRING, CHRISTOPHER BRIAN;
(EAGLE BAY, AU) ; HESLEWOOD, RAY; (BUSSELTON,
AU) ; LONGMAN, MICHAEL; (DUNSBOROUGH, AU) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
3788181 |
Appl. No.: |
08/981711 |
Filed: |
April 23, 1998 |
PCT Filed: |
June 27, 1996 |
PCT NO: |
PCT/AU96/00397 |
Current U.S.
Class: |
701/37 ;
280/5.508; 280/5.512; 701/38 |
Current CPC
Class: |
B60G 17/056 20130101;
B60G 2204/80 20130101; B60G 17/052 20130101; B60G 17/018 20130101;
B60G 21/06 20130101; B60G 2600/12 20130101 |
Class at
Publication: |
701/37 ; 701/38;
280/5.512; 280/5.508 |
International
Class: |
B60G 017/01 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 27, 1995 |
AU |
PN 3843 |
Claims
The claims defining the invention are as follows:
1. A method of controlling a vehicle suspension system for a
vehicle body supported by a plurality of spaced apart support means
arranged in at least generally diagonally opposite pairs, the
vehicle suspension system including adjustment means for adjusting
the position of each of the support means relative to the vehicle
body, sensor means adapted to generate a signal indicative of the
position of each of the support means, and control means arranged
to receive said signals, the method including determining the
position of each support means, determining a diagonal average for
each pair of diagonally opposite support means, the diagonal
average being the average of the position of one support means and
the position of the diagonally opposite support means, wherein the
required position for each support means is a function of at least
two said diagonal averages, the position of each support means
being adjusted on the basis of the said at least two diagonal
averages.
2. A method according to claim 1 including determining the
difference between said diagonal averages.
3. A method according to claim 2 wherein the required position for
each support means is further determined as a function of a desired
vehicle height.
4. A method according to claim 3, the method including obtaining a
desired front vehicle height and a desired back vehicle height.
5. A method according to claim 3 or 4 wherein the desired vehicle
height(s) is manually selected by the driver of the vehicle.
6. A method according to claim 3 or 4 wherein the desired vehicle
height(s) is automatically selected by the control means in
dependence on predetermined conditions.
7. A method according to claim 6 wherein the desired vehicle
height(s) is adjusted as a function of the vehicle speed.
8. A method according to claim 7 wherein the desired vehicle
height(s) is lowered when the vehicle is above a predetermined
speed.
9. A method according to any one of the preceding claims wherein
the required position for each wheel is further determined as a
function of the Roll Split constant for the vehicle.
10. A method according to claim 9 wherein the required position of
each support means are determined as follows:
FWSP=FSP.+-.(1.0-RS).times.(D1-D- 2) BWSP=BSP.+-.RS.times.(D1-D2)
where FWSP is the required position for the front support means,
BWSP is the required position for the back support means, FSP is
the desired overall front vehicle height, BSP is the desired
overall back vehicle height, RS is the Roll Split constant for the
vehicle, and D1, D2 are the respective diagonal averages of each
pair of diagonally opposite wheels.
11. A method according to any one of the preceding claims wherein
the method includes continually adjusting the required position for
each support means.
12. A method according to any one of claims 1 to 10 wherein the
method includes initiating the control method at intervals and
adjusting the required positions of each support means at that
time.
13. A method according to any one of claims 1 to 10 wherein the
method includes determining the average position of each support
means over a preset period and determining the required position of
each support means on the basis of the average positions
thereof.
14. A method according to any one of claims 1 to 10 wherein the
method includes conducting a series of required position
determinations for each support means over a preset period to
thereby obtain the average required position of each support means
over that period, determining the average position of each support
means over that period and adjusting the position of each support
means on the basis of the obtained average required position of
each support means and the average position of each of the support
means.
15. A method according to claim 14 wherein, during start-up of the
vehicle, the actual instantaneous required position of each support
means determined by the control method is used to adjust the
positions of each support means.
16. A method according to any one of the preceding claims wherein
the method includes determining the rate of change of the speed of
the vehicle and adjusting the position of each support means only
when the rate of change is below a predetermined rate.
17. A method according to any one of the preceding claims including
providing a door sensor to sense the closing of the door so that
the control method will only be actuated after the door is
closed.
18. A method according to any one of the preceding claims wherein
the vehicle suspension system includes individual fluid rams
arranged between each support means and the vehicle body.
19. A method according to claim 18 wherein each fluid ram means
includes a double acting ram having a first and second chamber, and
conduit means individually communicating the first chamber of the
respective rams with the second chamber of the respectively
diagonally opposite ram to provide fluid circuits therebetween, the
adjustment means varying the quantity of fluid in said fluid
circuits to thereby adjust the position of each said support
means.
20. A method according to claim 19 wherein the suspension system
includes a load distribution unit for equalising the fluid
pressures between the fluid circuits to thereby at least
substantially distribute the load between the support means of the
vehicle, the load distribution unit including two separate
displaceable piston assemblies each slideably mounted in a
respective housing, and separating the housing into two chambers,
each of the chambers being in communication with one of the
conduits connecting the fluid rams, and at least one sensor means
for sensing the position of each piston assembly, the control
method further including controlling the position of the piston
assemblies of the load distribution unit.
21. A method according to claim 20 wherein the position of each
piston assembly is centred such that, when measured on the basis of
a calibrated scale between 0 and 1, the position of each piston
satisfies the following equation; 5 PAV = P1 + P2 2 = 0.5 where PAV
is the average position of the piston assemblies, and P1,P2 are the
respective positions of each piston assembly.
22. A method according to claim 20 or 21 wherein the required
position of each piston assembly is determined on the basis of the
following equation; 6 LDUSP = 0.5 D1 - D2 2 where LDUSP is the
required position of each piston assembly of the load distribution
unit, and D1,D2 are the respective diagonal average of each pair of
diagonally opposite support means, the diagonal averages being
expressed on a scale between 0 and 1.
23. A method according to claim 22 including displacing the piston
assemblies by adding and removing fluid respectively from each said
two chambers.
24. A method according to any one of the preceding claims wherein
each support means is in the form of at least one wheel.
Description
[0001] The present invention is generally directed to vehicle
suspension systems, and in particular, to a control method for
controlling vehicle suspension systems. The present invention is
described with respect to suspension systems developed by the
applicant. It is however to be appreciated that the control method
is also applicable for other vehicle suspension systems.
[0002] The Applicant has developed a suspension system disclosed in
Australian Patent Application No. 23664/92, details of which are
incorporated herein by reference. This suspension system
incorporates double acting rams for each vehicle wheel. The upper
and lower chambers of each front wheel ram is respectively
interconnected with the lower and upper chambers of the diagonally
opposite rear wheel ram to provide a fluid circuit thereof. A
corresponding fluid circuit is provided with the other front wheel
ram and rear wheel ram. The two fluid circuits are interconnected
by a load distribution unit which is arranged to maintain at least
substantially equal pressure in the two fluid circuits.
[0003] In the Applicant's International Application No.
PCT/AU94/00646, there is disclosed a control arrangement for the
above described suspension system incorporating a control
arrangement for maintaining the vehicle in a position at least
substantially parallel to the plane of the ground upon which the
vehicle is traversing, details of which are also incorporated
herein by reference. The control arrangement includes sensor means
adapted for generating a signal indicative of the extension of each
wheel ram, and therefore the position of each of the wheels
relative to the vehicle body. The control arrangement then
determines the average height of the vehicle body at selected
locations between respective pairs of orthogonally adjacent wheels.
Adjustment means are provided to adjust the quantity of fluid in
the fluid circuits communicating with the rams of the said
orthogonally adjacent wheels to establish the preset datum height
between the orthogonally adjacent wheels and the vehicle body at
the said selected locations.
[0004] The wheel rams are described as being adjusted in orthogonal
pairs to avoid disturbing the position of the load distribution
unit as the fluid quantity in each circuit is adjusted in the above
application. However, because of the interconnection between the
wheel rams, adjustment of the average height between one orthogonal
wheel pair can produce a change in the average height between other
orthogonal wheel pairs which can result in the overshooting of the
average height between the other orthogonal wheel pairs past the
desired height. The control arrangement must therefore adjust the
average height between each of the orthogonal wheel pairs over a
number of steps in an iterative process to progressively minimise
this height error until the required average height is reached
between each pair. This means that the fluid must be pumped and
released from each of the fluid circuits over a number of steps to
bring the vehicle body to a position parallel to the plane of the
ground.
[0005] The primary problem of such an iterative process is that a
large amount of fluid must be cycled to and from the circuits with
fluid being pumped into and removed from each fluid circuit over a
number of cycles until the vehicle reaches its final position.
Therefore, much energy and time is wasted in this iterative
process.
[0006] It is therefore advantageous to have a control method which
allows for faster adjustment of the vehicle body position.
[0007] With this in mind, the present invention provides a method
of controlling a vehicle suspension system for a vehicle body
supported by a plurality of spaced apart support means arranged in
at least generally diagonally opposite pairs, the vehicle
suspension system including adjustment means for adjusting the
position of each of the support means relative to the vehicle body,
sensor means adapted to generate a signal indicative of the
position of each of the support means, and control means arranged
to receive said signals, the method including determining the
position of each support means, determining a diagonal average for
each pair of diagonally opposite support means, the diagonal
average being the average of the position of one support means and
the position of the diagonally opposite support means, wherein the
required position for each support means is a function of at least
two said diagonal averages, the position of each support means
being adjusted on the basis of the said at least two diagonal
averages.
[0008] As the control method determines the required position of
each wheel individually, this provides for a faster adjustment of
the vehicle position.
[0009] The control method preferably includes determining the
diagonal average of the front left and back right wheels of the
vehicle, and the diagonal average of the front right and back left
wheels of the vehicle. The control method may then determine the
difference between the diagonal averages to provide the "total
articulation" of the vehicle. The term "articulation" refers to the
situation where the first pair of the diagonally opposite wheels
moves together in a common direction and the position of the second
pair of wheels remains unchanged or moves together in an opposing
common direction to the first pair thereof such that there is
relative displacement between each pair of diagonally opposite
wheels. As well as providing an indication of the degree of
articulation of the wheels of the vehicle, the determination of the
total articulation of the vehicle also indicates the flatness of
the terrain upon which the vehicle is supported. When the vehicle
position is on a flat surface, then the respective diagonal
averages would be the same showing that the vehicle is not in
articulation. When the vehicle is resting on or travelling over an
undulating surface, the respective diagonal averages can differ
showing that the vehicle is in articulation.
[0010] A "height set point" may be selected, this height set point
being the desired height of the vehicle. A single overall height
set point may be selected. Alternatively, the height set point may
consist of a front height set point and a back height set point to
allow pitch attitude adjustment of the system. These height set
points may be manually selected by the driver of the vehicle and/or
may be automatically selected by the control means in dependence on
predetermined conditions. The height set points of the vehicle may
for example be adjusted as a function of the vehicle speed. The
height set points may be lowered when the vehicle is above a
predetermined speed. The vehicle will generally only be moving at
high speeds when the vehicle is not in an off road location where a
lower height set point is desired.
[0011] The control method may also take into account any difference
in the roll stiffness between the front and back of a vehicle which
will vary between different models of vehicles. The ratio of the
roll stiffness of the front of the vehicle and the total roll
stiffness of the vehicle is referred to as the "Roll Split" or
"Roll Couple Distribution" of the vehicle which will be a constant
value for that vehicle. When the roll stiffness of the front and
rear of the vehicle is the same, the Roll Split constant would be
0.5.
[0012] The wheel positions may preferably be measured on the basis
of a calibrated scale to take into account differences such as in
the relative degree of extension between the front and rear wheels.
Each wheel position may for example be measured on a scale between
0 and 1. A wheel position may be designated to be at 0 when the
wheel is fully retracted, i.e at or near the bump stop, and may be
designated to be at 1 when at or near full extension. The other
wheels may be calibrated on the same scale taking into account
possible different wheel travel positions. It is alternatively
possible to measure the actual extension of the wheels for the
determination.
[0013] The control method may therefore determine the required
position or the wheel set points of each wheel as follows:
FWSP=FSP .+-.(1.0-RS).times.(D1-D2)
BWSP=BSP.+-.RS.times.(D1-D2)
[0014] where
[0015] FWSP is the wheel set point for the front wheels,
[0016] BWSP is the wheel set point for the back wheels,
[0017] FSP is the front height set point of the vehicle,
[0018] BSP is the back height set point of the vehicle,
[0019] RS is the Roll Split constant for the vehicle, and
[0020] D1, D2 are the respective diagonal averages for each pair of
diagonally opposite wheels.
[0021] The position of each wheel relative to the vehicle body may
be continuously adjusted on the basis of the above noted control
method. Alternatively, the control method can be initiated at
regular or irregular intervals, and the wheels adjusted at that
time. The periods between initiation of the control method could
for example be as little as 10 milliseconds which provides
sufficient time for the valves controlling the fluid flow to and
from the fluid circuits to open and close.
[0022] When the vehicle is moving, it may not be necessary to
continually adjust the position of each wheel to wheel set points
determined by the control method. For example, the average wheel
position of each wheel over a preset period could be determined and
the wheel set points determined on the basis of the average wheel
positions. It is alternatively possible to do a series of wheel set
point determinations over a preset period to thereby obtain the
average wheel set points over that preset period. The average wheel
positions will also be determined over that period and the wheel
positions adjusted on the basis of the average wheel set points and
average wheel positions. However, at start up, where significant
changes in the load distribution in the vehicle can arise as a
result of people and other loads being placed within the vehicle,
the actual instantaneous wheel set point of each wheel determined
by the control method can be used to adjust the wheel positions to
thereby quickly position the vehicle in response to those load
changes.
[0023] The control means may also determine the rate of change of
the vehicle speed. Therefore, if the rate of change of the speed is
above a certain rate, then the control method will not adjust the
wheel positions. This will take into account when the vehicle is
braking or accelerating when such adjustment of the wheel positions
are not required or desired.
[0024] In another arrangement a door sensor may be provided to
sense the closing of the door so that the control method will only
be actuated after the occupants are within the vehicle.
[0025] In the vehicle suspension system described in international
application no. PCT/AU94/00646, a load distribution unit is
provided to equalise the fluid pressures between the two fluid
circuits to thereby at least substantially distribute the load
between the wheels of the vehicle. One of the described embodiments
of the load distribution unit includes two separate displaceable
piston assemblies mounted in a series arrangement and moveable
along a common axis, each piston assembly including a piston rod
and a piston supported thereon. It is however to be understood that
although the following description will refer to the above noted
arrangement, the housings are in practice located adjacent to each
other such that the piston assemblies move along adjacent parallel
axes. Each piston is slideably mounted within a respective housing
and separates the chamber into inner and outer chambers, these
chambers being in communication with the conduits connecting the
wheel rams. A "front bump" chamber is also provided between the
housings for accommodating an inner end of each piston rod.
Respective "back bump" chambers are also provided on the opposing
side of each housing, each back bump chamber accommodating a
respective outer end of one of the piston rods. Fluid accommodated
within the front bump chamber is compressed when both the front
wheels of the vehicle go over a bump whereas the fluid in the back
bump chambers are compressed when both the back vehicle wheels goes
over a bump. It is noted that this arrangement can be reversed by
changing the interconnection of the load distribution unit with the
wheel rams. Addition or removal of fluid from the front bump and
back bump chambers control the position of each piston relative to
its respective housing. It should be noted that in alternative
embodiments of the load distribution unit, the pistons are
supported on a single piston rod. Alternatively, a solid resilient
member can be provided between the two piston rods. In both of
these embodiments, there is little to no relative displacement
between the pistons, and the pistons move together as a unit.
[0026] When the wheels are in articulation, the piston assemblies
move in tandem and there is no relative movement between them.
However, when a load is placed in the back or the front of the
vehicle, the piston assemblies will move respectively closer or
further apart so that there is relative movement between the piston
assemblies.
[0027] Each piston assembly is ideally located at an intermediate
position when the wheels are not in articulation, and move away
from that intermediate position when a load is placed on one end of
the vehicle and/or when the wheels are in articulation. At this
intermediate position, the pistons may be located approximately
half way between the end walls of each housing to provide maximum
clearance therebetween to thereby provide unimpeded movement of the
pistons. The pistons will move away from their intermediate
position when the wheels are in articulation but should ideally
return to that intermediate position when the wheels are not in
articulation. However, due to non-linearities in the sensor means
and so on resulting in an error in the position of, the piston
assemblies from the intermediate position even when the wheels are
not in articulation which can possibly adversely affect the
operation of the load distribution unit. Sensor means are therefore
also provided to determine the position of each of the piston
assemblies and thereby enable adjustment of the position of the
piston assemblies, for example by controlling the fluid flow into
and out of that load distribution unit. It is to be noted that in
the alternative embodiments of the load distribution unit where the
pistons move as a unit, only one sensor means is required.
[0028] The control method according to the present invention
therefore also preferably includes controlling the position of the
piston assemblies of the load distribution unit. The position of
each piston may be measured on the basis of a calibrated scale
between 0 and 1. The wheels of the vehicle may be articulated in
one direction physically or in a computer model of the suspension
system until the difference between the respective diagonal
averages is equal to 1.0 (i.e D1-D2=1.0) showing that the wheels
are fully articulated in one direction. The position of the piston
at full articulation is designated to be at 0. The wheels are then
articulated in the opposing direction until the difference between
the respective diagonal averages is equal to -1.0 (i.e D1-D2=-1.0)
showing that the wheels of the vehicle are fully articulated in the
opposing direction. The piston position may therefore be measured
and determined on the basis of a scale from 0 to 1.
[0029] The load distribution unit will preferably need to be
"centred" such that the pistons will be at the required
intermediate positions when the vehicle is not in articulation. To
this end, the position of each piston will preferably be displaced
to satisfy the following equation; 1 PAV = P1 + P2 2 = 0.5
[0030] where
[0031] PAV is the average position of the pistons, and
[0032] P1,P2 are the respective positions of each piston.
[0033] The pistons of the load distribution unit are preferably
initially centred to the required position during, for example
periodic servicing of the vehicle. This may be achieved by adding
or removing fluid from the front bump chamber of the load
distribution unit to maintain a predetermined regulating pressure
therein. At the same time, the pistons of the load distribution
unit may be centred by adding or removing fluid from the back bump
chambers of the load distribution unit so that the average position
of the pistons relative to the end walls of their respective
housing is 0.5. This will allow correction of the positioning of
the pistons even when the wheels are in articulation during the
centring procedure because the average position of the pistons are
corrected.
[0034] Once the load distribution unit is adjusted as above, a
fixed amount of fluid may be maintained within the front bump
chamber. During subsequent operation of the vehicle, the load
distribution unit can be centred by adding or removing fluid from
the back bump chambers only.
[0035] The set points of each of the pistons can be determined on
the basis of the following equation; 2 LDUSP = 0.5 D1 - D2 2
[0036] where
[0037] LDUSP is the set point of each piston of the load
distribution unit, and
[0038] D1,D2 are the respective diagonal average of each pair of
diagonally opposite wheels, the diagonal averages being expressed
on a scale between 0 and 1.
[0039] This determination takes into account the total articulation
of the wheels and determines when the pistons are not in the
required position.
[0040] The pistons may then be displaced to the required position
by adding fluid to the inner chamber and removing fluid from the
outer chamber of one housing and adding fluid to the outer chamber
and removing fluid from the inner chamber of the opposing housing
to move the pistons in tandem in one direction while maintaining
the relative distance between them. The pistons can be moved in
tandem in the other direction by reversing the fluid flow.
[0041] It should be noted that the above determination of the load
distribution unit set points is only required for one piston in the
alternative embodiments where the pistons move together as a
unit.
[0042] The control means may be an electronic control unit. It is
however also possible for the control means to comprise analogue or
mechanical means.
[0043] It will be convenient to further describe the invention by
reference to the accompanying drawings which illustrates possible
control methods of the invention. Other embodiments of the control
method of the invention are possible, and consequently the
particularity of the accompanying drawing is not to be understood
as superseding the generality of the preceding description of the
invention.
[0044] FIG. 1 is a schematic view of a vehicle suspension
system;
[0045] FIG. 2 is a flow chart showing the basic control method for
determining the wheel set points according to the present
invention; and
[0046] FIG. 3 is a flow chart showing the control method for
determining the load distribution unit set points according to the
present invention.
[0047] FIG. 1 shows a vehicle suspension system comprising four
wheel rams, 1, 2, 3, 4. Each wheel ram has an upper chamber 1a, 2a,
3a, 4a and a lower chamber 1b, 2b, 3b, 4b, with conduits 5, 6, 7, 8
interconnecting the upper chamber of each wheel ram with the lower
chamber of the diagonally opposite wheel ram to thereby provide a
fluid circuit between each diagonally opposite wheel ram.
[0048] A load distribution unit is in communication in each of the
conduits 5, 6, 7, 8 to ensure at least substantially uniform
pressure between the two fluid circuits. The load distribution unit
9 includes two housings 14, 15, each respectively accommodating a
piston assembly 14a, 15a. Each piston assembly includes a piston
rod 10, 11 supporting a respective piston 12, 13. Each piston
divides its respective housing into an inner chamber 18, 19 and an
opposing outer chamber 16, 17. A front bump chamber 20 is provided
between the housings 14, 15 to accommodate an inner end of the
piston rods 10, 11. Back bump chambers 21, 22 are provided on the
opposing side of each housing 14, 15 to accommodate an outer end of
the respective piston rods 10, 11. The position of the piston
assemblies 14a, 15a can initially be centred by adding or removing
fluid from the back bump chambers 21, 22 while regulating the
pressure within the front bump chamber 20 to set the load
distribution unit 9 prior to operation of the vehicle. The position
of the piston assemblies 14a, 15a can be controlled during
operation of the vehicle by the addition or removal of fluid from
the inner chambers 18, 19 and the outer chambers 16, 17.
[0049] Referring to FIG. 2, the sequence of the control method when
used to determine the wheel position set points is shown as a flow
chart. The position of the front left wheel (FL), back right wheel
(BR), front right wheel (FR) and back wheel (BL) are initially
measured. The diagonal average (D1, D2) of each diagonally opposite
pair of wheels is then determined. The difference (D1-D2) between
the diagonal averages (D1, D2) is then determined to provide an
indication of the total articulation of the wheels of the
vehicle.
[0050] Each vehicle model has a specific roll split constant (RS),
also known as the "roll couple distribution", which is the ratio of
the roll stiffness of the front of the vehicle and the total roll
stiffness of the vehicle. The portion of the articulation required
for the front of the vehicle is therefore determined by multiplying
the difference between the diagonal averages (D1-D2) with a figure
equal to the roll split constant (RS) subtracted from 1.0. The
portion of articulation required at the back of the vehicle is
determined by multiplying the difference between the diagonal
averages (D1-D2) with the roll split constant (RS). A height set
point (SP), which is the required average height of the vehicle,
can be set manually by the driver. Alternatively, the height set
point (SP) may be automatically selected. Therefore, to obtain the
required wheel position set points, the portion of articulation
previously determined can be respectively added or subtracted from
the height set point (SP) to determine the set points of the front
right wheel (FRSP), front left wheel (FLSP), back left wheel
(BLSP), and back right wheel (BRSP). Alternatively an individual
front height set point (FSP) and back set point (BSP) can be
used.
[0051] The procedure of determining the wheel set points for each
wheel can be shown as equations as follows: 3 Front Right Wheel
FRSP = FSP - ( 1.0 - RS ) .times. ( D1 - D2 ) Front Left Wheel FLSP
= FSP + ( 1.0 - RS ) .times. ( D1 - D2 ) Back Left Wheel BLSP = BSP
- RS .times. ( D1 - D2 ) Back Right Wheel BRSP = BSP + RS .times. (
D1 - D2 )
[0052] The wheels can be set to the required wheel set points by
adding or removing fluid from the chambers of each wheel ram. It
should be noted that this procedure for determining the wheel
setpoints could be used on any vehicle suspension system.
[0053] The control method can also control the position of the
piston assemblies 14a, 15a of the load distribution unit 9 as shown
in FIG. 3. The difference between the diagonal averages (D1-D2) is
then divided by two and then added or subtracted from 0.5 to
respectively obtain the set point of each piston assembly (LDUSP1,
LDUSP2).
[0054] This control method for determining the set point of each
piston of the load distribution unit can be shown as an equation as
follows: 4 LDUSP1 = 0.5 + D1 - D2 2 LDUSP2 = 0.5 - D1 - D2 2
[0055] In this equation, the diagonal means D1, D2 are expressed on
a scale between 0 and 1.
[0056] The control method according to the present method provides
a procedure for determining the required position of each wheel to
thereby allow rapid adjustment of the height of the vehicle. The
control method also preferably allows the wheel positions to be
correctly adjusted even when the wheels are in articulation.
Although this control method has been described with respect to the
Applicants' vehicle suspension system, the control method can also
be used on other passive or active suspension systems where the
wheel positions can be adjusted.
* * * * *