GB2294554A - Suspension system - Google Patents
Suspension system Download PDFInfo
- Publication number
- GB2294554A GB2294554A GB9421683A GB9421683A GB2294554A GB 2294554 A GB2294554 A GB 2294554A GB 9421683 A GB9421683 A GB 9421683A GB 9421683 A GB9421683 A GB 9421683A GB 2294554 A GB2294554 A GB 2294554A
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- GB
- United Kingdom
- Prior art keywords
- valve
- fluid
- flow
- suspension
- signal
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60G—VEHICLE SUSPENSION ARRANGEMENTS
- B60G17/00—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load
- B60G17/015—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements
- B60G17/018—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements characterised by the use of a specific signal treatment or control method
- B60G17/0182—Resilient suspensions having means for adjusting the spring or vibration-damper characteristics, for regulating the distance between a supporting surface and a sprung part of vehicle or for locking suspension during use to meet varying vehicular or surface conditions, e.g. due to speed or load the regulating means comprising electric or electronic elements characterised by the use of a specific signal treatment or control method involving parameter estimation, e.g. observer, Kalman filter
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Vehicle Body Suspensions (AREA)
Abstract
In an active or semi-active vehicle suspension system, control means 17 controls a valve 15 regulating the flow of fluid to or from fluid struts of the suspension system in accordance with inputs 17a representing a number of suspension characteristics. The controller operates on the inputs 17a in accordance with the formula qd = SIGMA Knxn, where qd is the required flow rate Kn is a series of operating states and Xn is a series of predetermined gains selected to reproduce the dynamics of an equivalent analogue system. A Kalman filter KF may be used to estimate some of the inputs 17a from measured quantities 21, 23 and 25. Also disclosed is a flow controller which operates on the valve control signals in a manner dependent on the pressure drop across the valve thus taking account of the non-linearity of the operation of the control valve. <IMAGE>
Description
SUSPENSION SYSTEMS AND FLOW CONTROLLERS
This invention relates to suspension systems and in particular to active or semi-active vehicle suspension systems of the type in which a vehicle body is stabilised to meet current vehicle operating conditions by the flow of fluid within the system under the control of valve means.
In a typical active suspension the vehicle body is suspended from the unsprung portion of the vehicle via a plurality of fluid struts and fluid is pumped into or exhausted from these struts via a plurality of control valves (one for each strut) from an external fluid pressure source/sink carried on the vehicle in order to control the motion of the body relative to the unsprung portion of the vehicle.
Typically in semi-active suspension systems the vehicle body is suspended from the unsprung portion of the vehicle via conventional springing and plurality of fluid struts, each of which comprises a double-acting ram, are connected between the body and unsprung portion of the vehicle, these rams functioning as dampers with fluid being allowed to pass from one end of the ram to the other via individual ram control valves.
Semi-active self energising self-levelling suspension systems are also known in which the vehicle body is supported from the unsprung portion of the vehicle via a plurality of fluid struts each of which includes a plurality of chambers between which fluid is allowed to flow under the control of valves, flow of fluid between a first pair of chambers providing a damping function and flow of fluid between a second pair of chambers providing a self-levelling function.
In all the suspension systems described above the quality of ride provided is dependent on the appropriate control of the valves which control the flow of fluid within the system.
Traditionally such valves have been controlled using continuous system control theory using continuous controller hardware (i.e. analogue electronics) which is expensive to implement.
It is an object of the present invention to provide an improved form of active or semi-active vehicle suspension which is cheaper to implement.
Thus according to the present invention there is provided an active or semi-active vehicle suspension system comprising:
a plurality of fluid struts each disposed between a
vehicle body and the llnsprung portion of the vehicle,
each strut including one or more chambers into and out
of which fluid is allowed to flow under the control of valve means in order to provide a force to stabilise the motion of the body, digital control means which receives inputs representative of various suspension operating states at one or more predetermined sampling frequencies and operates thereon to provide output signals for the control of said valve means and which are representative of the required rate of flow of fluid into and out of said strut chambers to provide the necessary forces to stabilise the body to meet current vehicle operating conditions, the control means operating on the inputs in accordance with the formula
Where
is the required flow rate,
is a series of operating states and
is a series of predetermined
gains which are selected to reproduce the dynamics of an
equivalent analogue controlled system without any
significant loss of performance.
When analysing the performance of suspension systems it is common to consider the behaviour of one wheel (a so-called quarter suspension). If the present invention is analysed in this way the operating states
considered will include:1. Vertical vehicle body velocity 2. Vertical Wheel velocity 3. Suspension deflection 4. Tyre deflection 5. Suspension strut force 6. Flow rate through valve means.
Typically vertical body velocity and vertical wheel velocity are obtained by integrating the output form vertical body and wheel accelerometers. Suspension deflection can be measured directly using any one of a wide range of suitable sensors. The other states 4,5 and 6 referred to above can be derived from states 1,2 and 3 using Kalman filtering techniques.
Conventionally in continuous (analogue) control theory the gains (gain vector)
are selected using established multi-variable control techniques namely the formulation of a linear quadratic regulator (LQR). Such an implementation is inefficient if digital methods of control are used.
Digital control achieving the same standard of performance can be achieved by ensuring the eigenvalues of the digital system match those of the equivalent continuous (analogue) system.
The system of equations describing a digital system can be found from the differential equations describing the continuous system and the digital systems sample time.
The equations describing the continuous system are of the form x =
Ax + Bu where A is a matrix describing the continuous dynamics of the system and B is a matrix describing the effect of the control input u.
Thus u(i) = -K x(i) ----- equ (i)
where u(i) - is output from the digital control means
at instant i
K - is the gain vector
x(i) - is the operating state at instant i also u t) = u(iT) ----- equ (ii)
where u(#) is the output from the digital control means at an instant # part way through a sample period and iT # # # iT+T where i = 1,2,3 ---
and T is the sample period.
and also x(i+l) = + x (i) + F u(i) ----- equ (iii) where x(i+l) is the state at the start of the next
instant after instant i
and x(i) is the state at the start of instant
and u(i) is the output from the digital control means
at the end of instant i.
AT and + and C are matrices 4t = and 1 a where1=iT'T-"C The selection of gains to give a certain set of eigenvalues for a digital system is a standard procedure using, for example, Ackermann's formula:
where K is the gain vector
is the transpose of the
unit vector X is the controllability matrix and
is formed by the substitution of + for Z in
the system characteristic equation.
The invention also provides a flow controller comprising a fluid flow control valve for providing a required volume flow rate of fluid through a valve opening which is varied in response to a valve driving signal and digital control means which:a) measures/estimates the current valve opening; b) measures/estimates the current pressure drop across the
current valve opening; c) receives a demand signal corresponding to the required
volume flow rate, and d) calculates the valve driving signal using a) and b) and
modifies this signal to take into account the pressure
drop across the opening so that the required flow rate
is achieved.
In practice in a solenoid-operated spool valve the above control is achieved by multiplying the flow demand signal
by the operator
where W is the gradient of the variation of the solenoid valve opening with valve spool displacement
is the discharge efficient of the fluid)
is the density of the fluid
is the pressure drop across the valve opening (this may be measured or estimated)
This type of flow controller has many applications other than for the control of fluid control valves used in suspension systems.
Several embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 shows diagrammatically part of a semi-active vehicle suspension according to the present invention;
Figure 2 shows diagrammatically part of an active vehicle suspension according to the present invention, and
Figure 3 shows diagrammatically part of a semi-active self- energising self-levelling vehicle suspension according to the present invention.
Referring to Figure 1 this shows diagrammatically one quarter of a semi-active vehicle suspension for a four wheeled vehicle. The body mass of the vehicle is represented by the block 10, the mass of the wheel and other unsprung portions of the vehicle by the block 11, and the tyre springing by diagrammatic spring representation 12. The body 10 is suspended from the unsprung portion at 11 of the vehicle by any form of conventional springing diagrammatic illustrated at 13.
Between the vehicle body 10 and unsprung portion 11 a cylinder assembly or ram 14 is provided. The motion of the body 10 relative to the unsprung portion of the vehicle is controlled by a solenoid operated valve 15 which controls the flow of fluid from one side of the ram piston 14a to the other 14b.
It will be understood that in a complete vehicle installation there is a double-acting ram 14 associated with each wheel and each ram has its own solenoid control valve 15. These control valves are connected with a digital control means 16 which forms the basis of the present invention.
Digital control means 16 basically comprises 3 elements. A state estimating element, such as a Kalman Filtering element KF, an optimal suspension controller 17 and a flow controller 18.
Body mass 10 is provided with a vertical accelerometer 19 whose output is fed to an integrator 20 via line 21. Similarly the output of the vertical accelerometer 22 provided on wheel mass 11 is also fed into integrator 20 via line 23. Integrator 20, which forms part of the initial signal processing capability of digital control means 16, thus provides at lines 21a and 23a signals representative of the vertical velocity of body mass 10 and wheel mass 11. These signals are fed into Kalman Filter KF. It will be appreciated that the integration process carried out in separate integrator 20 could be carried out with Kalman filtering element
KF for a more efficient implementation.
A sensor 24 is provided between the body mass 10 and wheel mass 11 to directly measure the deflection of the suspension number 13. The deflection signal is fed into digital control means 16 via line 25 which enters the Kalman Filter KF.
Solenoid operated valve 15 is provided with a valve spool position sensor 26 whose output is fed into flow controller 18 via line 27. The output from flow controller 18 is fed to solenoid 15a of control valve 15 to establish the required valve opening.
Basically the suspension system operates as follows. The optimal suspension controller 17 determines the flow rate required to control the motion of the vehicle body in response to the current vehicle operating conditions (more details as to how this is achieved will be given below).
This flow demand signal is then fed to flow controller 18 together with the valve spool position signal from sensor 26.
Within flow controller 18 the flow demand signal
is operated on, in a manner to be described in more detail below, by a non-linear gain device 30 in response to the pressure drop across valve 15 which is measured using pressure sensors 15c and 15d (or a differential pressure sensor). Gain device 30 modifies the flow demand signal to take into account the non-linearity of the operation of the solenoid valve 15.The modified flow demand signal
(which corresponds to a desired valve spool position) is fed into a summing junction 31 in which it is compared with the actual spool valve position on line 27 to generate an error signal which is then fed into a conventional PID controller 32 which issues the final valve spool position JCv which is relayed to solenoid 15a via line 28.
Turning now to a more detailed description of the operation of the optimal suspension controller 17 and associated estimating means such as Kalman Filter KF these operate as follows:
Kalman Filter KF receives the body and wheel velocity signals on lines 21a and 23a and the suspension deflection signal on line 25. Using standard Kalman Filtering techniques these three operating state signals are processed to provide three further suspension operating state signals indicative of wheel tyre deflection, the force applied to the body by strut 14, and the flow rate of fluid through the associated valve 15 respectively.
These six operating state signals are fed into optimal suspension controller 17 as indicated at 17a. Controller 17 operates on these signals to produce the output representative of the fluid flow rate required through valve 15 to stabilise the vehicle body to meet the current vehicle operating conditions using the previously stated general formula
For the six states fed into controller 17 this formula becomes::
The gains
are obtained using the previously quoted
Ackermans formula
Turning now to the flow controller aspect of the invention in more detail the non-linear gain device 30 operates on the flow demand signal
to take account of the non-linearity of the operation of the solenoid valve 15 as described above this is achieved by multiplying the signal
by the operator
where W is the gradient of the variation of the solenoid
valve opening with valve spool displacementv
is the discharge coefficient of the fluid (typically 0.62))
is the density of the fluid
is the pressure drop across the valve (this may be
measured, e.g. using sensors 15c and 15d lor estimated)
The use of non-linear gain device 30 enables the system to use a simple and therefore relatively cheap solenoid operated control valve 15 and still achieve an acceptable quality of control and to provide more accurate control at low pressure drops across the valve.
This control technique using the operator
is applicable to a wide variety of control situations other than suspension systems where it is desired to provide a control valve which responds linearly to the applied solenoid voltage.
The above operator is derived from the realisation that the flow (F) through a valve at a given opening is given by the equation:
Figure 2 shows diagrammatically one quarter of an active vehicle suspension for a four wheeled vehicle. Components of a similar function to those previously described with reference to figure 1 have been similarly numbered. In this arrangement the vehicle body 10 is suspended from the unsprung portion 11 of the vehicle via double acting ram 14 which is supplied with fluid under pressure via a three position solenoid valve 30 from an accumulator 31 charged by a pump 32 which draws fluid from a sump 33.
As previously, the position of solenoid valve 30 is communicated to the digital control means 16 by a sensor 26 and the solenoid valve 30 is controlled by a solenoid 30a in response to signal provided on line 28 from digital control means 16. Pressure sensors 30c,30d & 30e (or an appropriate differential pressure sensor) are provided to measure the pressure drop across the valve 30.
As will be appreciated, depending on which of the three states is currently occupied by valve 30, double acting ram 14 is either locked in a fixed length condition or is extended or retracted to adjust the position of the body mass 10 relative to the unsprung mass 11.
The constructional and operational details of digital control means 16 are identical to those previously described with reference to figure 1 and will not therefore be repeated.
Figure 3 shows diagrammatically one quarter of a semi-active self-energising self-levelling suspension in which a SESLSA (Self-Energising Self-Levelling Semi-Active) strut 40 acts between the vehicle body 10 and unsprung portion 11 of the vehicle. Strut 40, as described in PCT patent application no. PCT/GB91/01160has three chambers 40a,40b,40c. Change in volume of chambers 40a,40b provide the self levelling function whilst changing relative volume of chambers 40b,40c provide the damping of the suspension.
As can be seen from figure 3, chamber 40a is connected with accumulator 41 and chamber 40c with accumulator 42.
Chambers 40c and 40b are interconnected via solenoid operated valve 50 connection to chamber to 40b being down the centre of tube 43. Valve 50 is a two positioned valve controlled by a solenoid 50a which is connected by line 28 to digital control means 16. Pressure sensors 50c and 50d measure the pressure drop across valve 50.
Again the construction and operation of digital control means 16 is identical to that previously described with reference to figure 1.
Claims (10)
1. Vertical vehicle body velocity
2. Vertical wheel velocity
3. Suspension deflection
4. Tyre deflection
5. Suspension strut force
6. Flow rate through valve means.
3. A system according to claim 2 in which vertical body
velocity and vertical wheel velocity are obtained by
integrating the output from vertical body and wheel
accelerometers respectively and suspension deflections
are measured directly using suspension deflection
sensing means.
4. A system according to claim 2 or 3 in which operating
states 4, 5 and 6 are derived from operating states 1,
2 and 3 using Kalman filtering techniques.
5. A system according to claim 2 in which = K, (tyre deflection) + K L (suspension deflection)
+ Kss (vertical wheel velocity)
+ K+ (vertical body velocity)
+ KS (suspension strut force)
+ K6 (flow rate through valve) where the gains K1 to K6 are obtained from Ackermans formula
in which:
is the transpose of the
unit vector
is the controllability matrix and
is formed by the substitution of # for in in the system controllability equation.
6. A system according to any one of claims 1 to 5 in which the operating states
are fed via a Kalman filter to an optimal suspension controller which determines the required rate of flow of fluid into and out of said strut chambers and issues a corresponding rate signal, this flow rate signal is fed via a flow controller to a solenoid-operated flow control valve which controls the flow of fluid into and out of said strut chambers to stabilise the body to meet current vehicle operating conditions, the flow controller operating on the flow rate signal in a non-linear manner responsive to the pressure drop across the solenoid-operated flow control valve to take into account the non-linearity of the
operation of the solenoid-operated flow control valve
to produce a modified flow rate signal which
corresponds to a desired flow control valve opening,
this desired flow control valve opening being compared
with a current actual control valve opening signal to
produce an error signal which is used as a basis for a
final control valve opening signal which is fed to the
solenoid of the flow control valve.
7. A system according to claim 6 in which the
non-linearity of the operation of the flow control
valve is taken into account by multiplying the flow rate signal by the operator
wnere w is the gradient of the variation of the solenoid valve opening with valve spool displacement,
Cd is the discharge efficient of the fluid, P is the density of the fluid, and
is the pressure drop across the valve opening.
8. A flow control system comprising a fluid flow control
valve for providing a required volume flow rate of
fluid through an opening of the valve which is varied
in response to a valve driving signal supplied by a
digital control means which:
a) measures/estimates the current valve opening;
b) measures/estimates the current pressure drop
across the current valve opening;
c) receives a demand signal corresponding to the
required volume flow rate, and
d) calculates the valve driving signal using a) and
b) and modifies this signal to provide a final
valve driving signal which takes into account the
pressure drop across the opening so that the
required flow rate is achieved.
9. A system according to claim 8 in which the valve
driving signal is multiplied by the operator
to give the final valve driving signal where: W is the gradient of the variticn cf the solenoid valve opening with valve spool displacement,
is the discharge efficient of the fluid, is the density of the fluid, and is the pressure drop across the valve opening
10. An active or semi-active vehicle suspension system
constructed and arranged substantially as hereinbefore
described with reference to and as shown in Figure 1 or
Figure 2 or Figure 3 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9421683A GB2294554A (en) | 1994-10-27 | 1994-10-27 | Suspension system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9421683A GB2294554A (en) | 1994-10-27 | 1994-10-27 | Suspension system |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9421683D0 GB9421683D0 (en) | 1994-12-14 |
| GB2294554A true GB2294554A (en) | 1996-05-01 |
Family
ID=10763502
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9421683A Withdrawn GB2294554A (en) | 1994-10-27 | 1994-10-27 | Suspension system |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2294554A (en) |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4967361A (en) * | 1987-04-17 | 1990-10-30 | Fuji Jukogyo Kabushiki Kaisha | Active-suspension controlling system of vehicles |
| EP0426338A1 (en) * | 1989-11-02 | 1991-05-08 | General Motors Corporation | Vehicle suspension apparatus |
-
1994
- 1994-10-27 GB GB9421683A patent/GB2294554A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4967361A (en) * | 1987-04-17 | 1990-10-30 | Fuji Jukogyo Kabushiki Kaisha | Active-suspension controlling system of vehicles |
| EP0426338A1 (en) * | 1989-11-02 | 1991-05-08 | General Motors Corporation | Vehicle suspension apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9421683D0 (en) | 1994-12-14 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |