GB2260299A

GB2260299A - System for determining signals for use in vehicle suspension control or regulation

Info

Publication number: GB2260299A
Application number: GB9221309A
Authority: GB
Inventors: Udo Neumann
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1991-10-11
Filing date: 1992-10-09
Publication date: 1993-04-14
Also published as: GB9221309D0; JPH05201226A; DE4133666C2; DE4133666A1

Abstract

A vehicle suspension regulating or control system comprises means to determine actual wheel load fluctuation (P) starting from signal values which represent the relative movements (Xar) between the vehicle wheel units (2) and the vehicle body (1) and from signal values which represent the movement (Xa) of the vehicle body, in addition, possible changes (P') in the actual wheel load fluctuation can be computed as a function of possible changes in the suspension characteristics, whereupon it is ascertained through interrogation of certain criteria whether a situation critical for travel safety is present and whether the suspension characteristics are to be reset for minimising the wheel load fluctuations in the case of a situation critical for travel safety. <IMAGE>

Description

2,1)-,2 1' SYSTEM FOR DETERMINING SIGNALS FOR USE IN VEHICLE SUSPENSION

CONTROL OR REGULATION The present invention relates to a system for determining signal values for use in suspension regulation or control in a vehicle, such as a passenger or goods vehicle or other land vehicle.

A powerful springing and/or damping arrangement is essential for the wheel suspension of a motor vehicle. In this case, on the one hand travel safety is to be taken into account and on the other hand it is desirable to provide a highest possible travel comfort for the vehicle occupants or shock-sensitive vehicle loads. These are conflicting objectives from the aspect of the springing and/or damping system. A high travel comfort is to be achieved by softest possible suspension settings, whereas relatively hard settings are desired with a view to high travel safety.

In order to resolve this conflict of design objectives, passive suspensions are discarded in favour of regulable (active) suspensions.

A passive suspension is designed, according to the intended use of the vehicle, to have either a hard tendency (sports) or a soft tendency (comfort) as installed. Influencing of the suspension characteristics is not possible in these systems during travel. In the case of active suspensions, thereagainst, the characteristics of the springing and/or damping system can be influenced according to the travel state during travel itself.

In DE-OS 38 27 737, the afore-mentioned conflict of objectives between travel safety and travel comfort is solved by control or regulation on the basis that an active or adjustable suspension is, in the case of changing operating conditions such as changing road surface properties, so controlled that change in the travel comfort is carried out while still ensuring travel safety. The effective value of the wheel load fluctuations during the travel operation is utilised as a weighting criterion for travel safety. Wheel load fluctuation signifies the deviation of the wheel load (normal force between tyre and road surface) from its static value. The wheel load fluctuation, as well as the wheel load itself,, is, however, amenable to direct measurement only with great difficulty, since measurement value sensors would have to be mounted between the road surface and the wheel or tyre. By contrast, measurement of spring travel can be realised in a relatively simple manner and economically. Spring travel signifies displacement of the vehicle body relative to the wheel. In DE- OS 38 27 737, the spring travel is measured as a substitute magnitude for wheel load fluctuation. The sliding effective value and the sliding mean value for the substitute magnitude, as well as their difference, are formed from these measurement val ues. After this difference has been compared with a preset target value, an electrical indicating and/or control signal for control or regulation of the suspension is delivered when the target value is exceeded.

In German patent application P 41 07 090.9, the actual wheel load fluctuation is deduced starting from signals which represent the relative movements between the vehicle wheel units and the vehicle body. In addition, possible changes in the actual wheel load fluctuation are computed preliminarily as function of possible changes in the suspension characteristics, whereupon it is ascertained through interrogation of certain criteria whether a situation critical for travel safety is present and whether the suspension characteristics are to be reset for minimising wheel load fluctuation in the case of a situation critical for travel safety.

There remains scope for simplifying the determination of the actual wheel load fluctuation and thus for simplifying a system such as that in the above-mentioned German application.

According to the present invention there is provided a system for determining signal values for use in suspension regulation or control in a vehicle with at least two wheel units connected to the vehicle body by regulable or controllable suspension systems influencing relative movement of the wheel units and body, comprising means to determine first signal values representing movement of the wheel units relative to the vehicle body, means to determine second signal values representing movements of the vehicle body, and means to determine, in dependence on the first and second signal values, third signal values representing wheel load fluctuation.

By means of a system embodying the present invention, the wheel load fluctuations are deduced starting from signals which represent the relative movements between the wheel units and the body of the vehicle and signals which represent the movements of the vehicle body.

4 - Moreover, as described in German patent application P 41 07 090.9, possible changes in the wheel load fluctuation can be computed preliminarily as a function of a possible change in the suspension characteristics. Through interrogation of certain criteria, in particular through logical interlinking of the determined wheel load fluctuation with the preliminarily computed possible changes in the wheel load fluctuation, it can be ascertained whether a situation critical for the travel safety is present and whether the suspension characteristics are to be reset for minimising wheel load fluctuation 10 in the case of a situation critical for the travel safety.

Thus, not only a substitute magnitude for the wheel load fluctuation is ascertained in a system embodying the invention, but also in simple manner the wheel load fluctuation itself.

By contrast to the subject of German application P 41 07 090.9, a system embodying the present invention is of advantage in respect of the determination effort whenever, for example, body acceleration sensors are provided in a wheel frame regulation system. The determination of the actual wheel load fluctuations c an be substantially simplified through the use of signals from the body acceleration sensors. This has the consequence of the simplification of the total system.

In addition to use of acceleration measurement value detectors which, for measurement of vertical acceleration, are mounted at each wheel contact point of the vehicle body, it can be of advantage to use at least three measurement value detectors which detect the vertical acceleration of the vehicle body at at least three points of the vehicle body, in particular at three points which do not lie on a straight line.

is Preferably, the ascertained actual wheel load fluctuations are logically interlinked, in consequence of a modification of the suspension setting, with the changes in the wheel load fluctuations, whereby there can be obtained a differentiated decision as to whether a change in the suspension characteristics does justice to the objective of optimisation of travel safety with best possible comfort at the same time. In this case, travel safety is accorded a higher priority than travel comfort. Through the differentiated decision in respect of the modification of the suspension setting, fewer switching pulses are applied to the regulable or controllable springing and/or damping systems. This increases the service life of the systems and also improves travel safety and travel comfort, since a different characteristic is set only when this contributes to or is absolutely necessary for increasing the travel safety.

An embodiment of the present invention will now be more particularly described with reference to the accompanying drawings, in which:

Fig. 1 is a model diagram illustrating forces present in a wheel suspension unit of a vehicle, in conjunction with a system for regulation or control of an adjustable damper and/or adjustable spring of the suspension unit; Figs. 2a and 2b are, together, a flow chart illustrating control or regulating value determination steps in a system embodying the invention, when a soft suspension setting is present; and Figs. 3a and 3b are, together, a flow chart illustrating control or regulating value determination steps in a system embodying the invention, when a hard suspension setting is present.

Referring now to the drawings, there is shown in Fig. 1 a control or regulation system for a wheel unit in a motor vehicle. The vehicle comprises a body 1 with a participating mass Ma, and a wheel 2, with a participating mass Mr. The tyre of the wheel acts as a spring 5, with a spring constant Cr, on a road surface 4. The wheel is connected to the body by a suspension system comprising a shock absorber 3 with a damping constant d and a parallelly arranged spring 6 with a spring constant C, the shock absorber and spring representing the suspension to be controlled or regulated. At least one of the shock absorber 3 and the spring 6 is designed to be regulable or controllable. The overall system includes a measurement value detector 7 for the spring stroke movement, a measurement value detector 11 for the body movement, means 8 for the ascertaining of values, means 9 for the weighting of the values and an output stage 10. Magnitudes, such as Pgr, k, V, AI, Aq, T, N1, N2 and Tr, which are expl ained further below, are fed to the means 9 for the weighting of the values.

The items 1 to 6 in Fig. 1 thus represent a two-body model for a wheel unit, in which the tyre stiffness is described as the spring 5 with the spring constant Cr. In this embodiment, the shock absorber 3 is assumed to be regulable, whilst the properties of the spring 6 are described by the constant value C. However, the dashed line in Fig. 1 shows that the spring 6 can also be designed to be regulable. In that case, the combination of the spring 6 and the shock absorber 3 would represent a springing and damping system which is to be controlled or regulated.

i The displacement of the vehicle body and the displacement of the wheel are denoted by, respectively, Xa and Xr, namely the displacement from the equilibrium position when the vehicle is stationary in the unloaded state. The road surface unevennesses are described by Xe. The detector 7 detects the spring stroke movements of the wheel unit, whilst the detector 11 detects the movements of the body 1, preferably the vertical absolute body acceleration Xa" at the wheel contact point of the body. In this embodiment, the spring stroke travel Xa-Xr is assumed as the measurement magnitude for the spring stroke movement, but the relative velocity Xa'-Xr' or the relative acceleration Xa"-Xr" can equally well be detected or otherwise ascertained through differentiation and/or low-pass filtering. The dashes beside the symbols thus denote time derivatives. First signals, representing the spring stroke movement, and second signals, representing body movement, are fed to the means 8, which at its output provides signals indicative of wheel load fluctuation P and its sensitivity P'. These magnitudes are explained more precisely further below in connection with Figs 2a and 2b. in the means 9, the magnitudes P and P' are logically interlinked and compared with each other and/or with the other entered magnitudes, and the results of the comparisons are fed to counting units. The entered magnitudes can be suspension setting parameters such as Pgr and k, travel state magnitudes such as travel velocity V, longitudinal acceleration A] and transverse acceleration Aq of the vehicle, ambient temperature T, counter setting parameters such as target values N1 and N2, "reset" time Tr, and any other appropriate magnitudes. A control - 8 signal, as output signal of the means 9, is fed to the output stage 10, where the switching-over of the springing and/or damping characteristics of the springing and/or damping system to be controlled or regulated is effected by drive of an appropriate setting 5 member.

In Figs. 2a and b and 3a and b the mode of operation of the means 8 and 9 is shown in more detail. A significant difference in relation to German patent application P 41 07 090.9 is evident particularly from the stages 211 and 311 described in the following, whilst the manner of function of the remaining stages substantially corresponds to that described in P 41 07 090.9.

is In Figs. 2a, b and 3a, b, electronic filter units and/or computer units are denoted by 211, 311, 212 and 312, multiplier units by 214, 314, 215 and 315, parameter input units by 213 and 313, discriminators by 216, 316, 217, 317, 218 and 318, means for the preparation of counting signals by 219, 319, 220 and 320, counting units by 221, 321, 222 and 322, adding units by 223 and 323 and discriminators by items 224, 324, 225 and 325. Output units 226, 326, 227 and 327 produce control signals whtch are passed on to the output stage 10 (Fig. 1). Items 228 and 328 represent a unit for the determining of the next computing cycle.

Within the scope of the description of Figs. 2a, b and 3a, b, the means 8 and 9 of Fig. 1 and the physical background of the system shall now be described. As already indicated, the deviation of the wheel load (normal force between tyre and road surface) from its static value is denoted as wheel load fluctuation P. Whilst this and possibly also the tyre spring stroke travel, which is related directly to the 1 load fluctuation, is capable of measurement only with difficulty, the spring stroke travel Xa-Xr or the spring stroke velocity (Xa-Xr)', for example, can be detected by measurement value detectors which can be realised in relatively simple manner and thus economically. In the case of vehicles with a ride height or level regulation, an already present detector may be able to be utilised for detecting spring stroke travel or velocity. With the aid of the two-body model discussed above, it can be established that the desired magnitude P Cands in the accel erati on:

following relationship to the spring stroke P = C(MaMr)Xa''] - FMrXar''], wherein the spring stroke acceleration is denoted by Xar'' Furthermore, as described in German patent application P 41 07 090.9, wheel fluctuation sensitivity P' (with respect to the damping constant d) can be ascertained by the relationship P, = b P/b d = -F(MaCrs 3)/D(s)l Xar, (4) in which Xar is the 1'de-averaged" spring stroke travel, s is the Laplace variable, and D(s)=CCr+Crds+(CMr+(C+Cr)iMa)s 2+ (Ma+Mr)ds 3 +Ma+Mrs 4 (5) 1 The de-averaged spring stroke travel Xar is obtained from the measurement magnitude Xa-Xr through subtraction of its running mean val ue t l/Tm j [Xa(r)-Xr(r)]dr, t-TM (2) thus:

t l/Tm j Xa(r)-Xr(r)]dr t-Tm Xar(t) Xa(t)-Xr(t) (3) In this case, Tm is a setting parameter and t is the actual instant. Through this "de-averaging" of the spring stroke travel Xa-Xr, the influence of loading of the vehicle, which means a change in the static spring travel, as well as the influence of asymmetric (in respect of the compression and tension range) spring characteristics and/or shock absorber characteristics (change in the mean dynamic spring travel) on the computation of the wheel load fluctuation, are eliminated.

The value P' is a measure of the change in the wheel load fluctuation P when the damping constant d of the shock absorber to be controlled or regulated is modified. In Darticular, the sign of P' provides data about whether the wheel load fluctuation P is increased 5 or reduced on a change in the damping constant d. Since the optimisation of the travel safety is associated with the minimisation of the magnitude JP], the equation (4) for determination of the sensitivity P' of the magnitude P is an important decision criterion in respect of control or regulation of a damping system. In the general case, the sensitivity P' is defined as the derivative of the wheel load fluctuation P according to a "characteristic" suspension parameter. This is characteri sed by different parameter values describing different suspension settings. This parameter could, for example, have the physical significance of spring stiffness in a spring such as the spring 6. In this case, the sensitivity P' (with respect to spring stiffness C) is P' = aP/ bC = -C(MaCrs 2)/D(s)l Xar wherein D(s) has the same meaning as for equation (5).

The val ues of the model parameters (Ma, Mr, C, Cr and d) are either known or can be ascertained for a particular vehicle by, for example, parameter identification procedures.

The signal values indicative of the Me-averaged" spring stroke travel Xar are present at the input of the means 8 or the electronic filter units and/or computing units 212 and 312. The computation of the running mean value according to the equation (2) as well as its 5 subtraction from the measurement magnitude Xa-Xr according to equation (3) can take place in, for example, the electronic evaluating system of the detector 7. In addition, the signals Xa' ' of the detector 11 are present at the input of the means 8 or the filter units and/or computer units 211 and 311.

The units 211 and 311 have the transmission behaviour illustrated with the aid of the equation (1). The si nal value Xar'' which was used in the equation (1) and represents the spring stroke acceleration, can be ascertained from the signal of a suitably mounted spring stroke travel or velocity detector 7 at least approximately through differentiation and, optionally through low-pass filtering. The signal value Xa'', which was also used in the equation (1) and represents the vertical acceleration of the body at the wheel support point, is ascertained by an appropriately mounted detector 11. If such a detector is not present, but there are used, for example, at least three vertical acceleration sensors (with output signals Xal'', XaP'. Xa3'') at different points, which do not lie on a straight line, of the vehicle body, the body acceleration measurement necessary for the equation (1) can be ascertained as weighted linear combinations according to the equation :1 5 Xa'' = blXal'' + b2XaP' + HXaY' 13 The co-efficients bl, b2 and b3 are obtained in simple manner from the position of the acceleration sensors and the wheel contact points.

The units 211, 212, 311 and 312 can be realised electronically in digital form, for example through processing of a differential equation representing the transmission properties (equation (1), (4) or (6)) in computer units, or electronically in analog form, for example through replication of a differential equation representing the transmission properties (equation (1), (4) or (6)) by electronic components.

If a detector which detects the relative spring velocity Xa'-Xr' or relative spring acceleration Xa',-Xr'' is used in place of a spring travel sensor, then the expressions in the square brackets on the righthand side of the equation sign in equations (4) and (6) are to be divided by the Laplace variable s (in the case of relative velocity Xa'- Xr') and s 2 (in the case of relative acceleration Xa''-Xr''). The "de-averaging" of the measurement magnitudes W-Xr' or W'-Xr'' is effected analogously to the equation (3), wherein Xar becomes either Xar' or Xar'' and the measurement magnitude Xa-Xr becomes either Xa'- Xr' or Xa''-Xr" The signals of the wheel load fluctuation P and its sensitivity P' are thus present at the output of the filter units and/or computing units 211, 212, 311 and 312.

For a more exact description of the means 9, a possible regulation law, which is described in German application P 41 07 090.9, for the control or regulation of the springing and/or damping system is initially discussed in the following:

A change in the suspension characteristics for minimisation of wheel load fluctuation is generally sensible only when a travel situation critical in terms of safety is present. This can possibly be detected when the wheel load fluctuation in amplitude exceeds a 5 threshold value Pgr, thus when the condition 1P1 > Pgr (7) is fulfilled. If the condition is infringed, which means that a situation critical in terms of safety is not present, the suspension characteristics can remain unchanged, for example in the setting "soft" or "hard". In the case of infringement of the condition (7), the actually present suspension characteristics could, however, be varied with a view to other regulation objectives, such as in the sense of maximising of travel comfort.

During a travel situation which is critical in terms of safety, 15 i.e. when condition (7) is fulfilled, a modification of the suspension setting recommends itself particularly when the condition JP' 1 > kIPI (8) is fulfilled. Moreover, a modification of the suspension characteristics in the direction "hard" is expedient when additionally the condition PP 1 < 0 (9a) is fulfilled. If, thereagainst, PP 1 > 0 (9b) applies, a modification in the direction "soft" is sensibl The magnitudes Pgr and k are to be considered as suspension setting parameters and are fed to the input units 213 and 313. The setting parameters can either assume constant values for the suspension system to be controlled or regulated or are dependent on magnitudes influencing the travel state, such as vehicle velocity V, longitudinal acceleration A] or the transverse acceleration Aq and/or the ambient temperature T.

The significance of the afore-mentioned inequalities (7), (8), (9a) and (9b) can be described plainly. If the conditions are fulfilled, the significance is as follows:

Condition (7):

Resetting of the spring and/or damping characteristic when the wheel load fluctuation exceeds a certain magnitude Pgr, which means that the vehicle is in a critical travel situation.

Conditions (9a) and (9b):

Resetting of the spring and/or damping characteristic only when this change causes a reduction in the momentary wheel load fluctuation P. When P is,for example positive (and according to condition (7) greater than Pgr) and the instantaneous characteristic is possibly "soft", then it is only reset in the direction "hard" when the sensitivity P' is negative, which means that the wheel load fluctuation P is reduced for an increase in the characteristic parameter, for example the damping constant (harder setting). In case the sensitivity P' is positive at the considered instant (instantaneous characteristic "soft"), a variation of the setting in the direction "hard" would have the consequence of an increase in the wheel load fluctuation P.

Condition (8):

Resetting of the spring and/or damping characteristic only when this is worthwhile with a view to improvement in the travel safety, whi ch means that the change i n the wheel 1 oad fluctuation, which is achieved through the modification, with respect to the instantaneous wheel load fluctuation must reach a value determinable by the value k.

The manner of function of the means 8 and 9 shown in Fig. 1 is explained more closely with the aid of Figs. 2a, b and 3a, b. The case in which the setting "soft" is the instantaneous suspension frame setting is illustrated in Figs. 2a and b. Figs. 3a and b shows the case, in which the setting "hard" is the instantaneous suspension setting. In the following, Figs. 2a, b and 3a, b are described together.

Parameters, such as suspension setting parameters Pgr and k, the travel velocity P, longitudinal accel erati on A] and transverse acceleration Aq of the vehicle, the ambient temperature T, numerical target values N1 and N2 and the "reset" time Tr, are entered into the input units 213 and 313.

The magnitudes PP' and k1P1 needed for the regulation law are formed in the multiplier units 214, 314, 215 and 315.

is The discriminator units 216, 316, 217, 317, 218 and 318 have the following function:

The discriminator units 216 and 316 compare the magnitude 1P1 with the magitude Pgr and generate a "Y" signal if 1P1 is greater than the magnitude Pgr and a signal " N " if 1P1 is smaller than the magnitude Pgr.

The discriminator units 217 and 317 compare the magnitude PP' with the magnitude 0. The unit 217 generates a "Y'I signal if PP' is smaller than the magnitude 0 and a 'IN" signal if PPI is greater than the magnitude 0. The unit 317 generates a "N" signal if PP' is smaller than the magnitude 0 and a "V signal if PP' is greater than the magnitude 0.

The discriminator units 218 and 318 compare the amount of the magnitude P' with the magnitude klPI. The units 218 and 318 generate a Yll signal if IP'I% is greater than the magnitude kiPi and a signal IN" if 1P11 is smaller than the magnitude kPI.

When the output signals of the discriminators 216, 217 and 218 (Fig. 2a) or 316, 317 and 318 (Fig. 3a) have the value Y at the same time, a signal is fed to the unit 219 (Fig. 2b) or 319 (Fig. 3b) for the preparation of a counting signal, at the output of which the signal Z1 is then counted in the counting unit 221 or 321. When the value N is present as output signal at at least one of the discriminators 216, 217 and 218 or 316, 317 and 318, a signal is fed to the unit 220 (Fig. 2b) or 320 (Fig. 3b) for the preparation of a counting signal, at the output of which the signal Z2 is then counted in the counting unit 222 or 322.

The counter states Z1ges and Z2ges respectively of the counting units 221 and 222 or 321 and 322 are fed as output signals to the discriminators 224 and 225 or 324 and 325, where the counter states are compared with target values N1 and N2. In particular, the counter states Z1tot and Z2tot are compared with the sum Z1tot and+Z2tot as target value, which is formed by the adding unit 223 or 323 and fed to the discriminators 224 and 225 or 324 and 325. Moreover, it is advantageous to compare the counter states Z1tot and Z2tot with each other as target values in the discriminators 224 and 225 or 324 and 325. The counter states can also be compared with target magnitudes which are ascertained in dependence on magnitudes influencing the travel state, such as for example travel velocity V, longitudinal acceleration Al and transverse acceleration Aq of the vehicle and/or the ambient temperature T, which are entered into the input unit 213 or 313 as described above. The resetting of the counter states occurs through the input of reset signals into the counting units 224 and 225 or 324 and 325. The reset signals are, for example, fed to the counting units 224 and 225 or 324 and 325 after each switchover operation of the damping and/or springing characteristics and/or at certain time intervals Tr and/or in dependence on the counter states and/or on magnitudes influencing the travel state.

When the counter states M0tand Z2tot exceed the ascertained and/or preset target values N1 and N2, the signals Y are present at the output of the discriminators 224 and 225 or 324 and 325. If the counter states Mot and Z2tot fall below the ascertained and/or preset target values, the signals N are present at the output of these discriminators.

One possibility, which is relatively simple to realise, for the function of the discriminators 224 and 225 or 324 and 325 is the comparison of the counter states Mot and Z2tot with numerical target values N1 and N2 for each sum Zltot+Z2tot. It is avoided by the manner of function of the discriminators that a switchover to a different damping and/or springing characteristic takes place in travel situations in which the wheel load fluctuation is increased only for a short time without endangering the travel safety (for example, driving over a manhole cover). Consequently, travel comfort is increased without impairing travel safety, and the service life of the regulable or controllable springing and/or damping system is prolonged, since the setting members utilised areinvariably mechanical and thus susceptible to wear. Merely a single sensor is necessary for this realisation of the system.

The output signals Y of the discriminators 224 and 225 or 324 and 325 are fed to the output units 226 and 227 or 326 and 327, where control signals are produced which are passed on to the output stage (Fig. 1). If a signal Y is present at the input of the output unit 226 or 327, a control signal for switching over to a harder damping and/or springing characteristic is passed to the output stage 10. If a signal Y is present at the input of the output unit 227 or 326, a control signal for switchingover to a softer damping and/or springing characteristic is conducted to the output stage 10.

is Moreover, the output units 226 and 227 or 326 and 327 provide a drivingsignal for the unit 228 or 328 for determination of the next computing cycle. The N-signals present at the output of the discriminators 224 and 225 or 324 and 325 are equally fed to the unit 228 or 328 for determination of the next computing cycle. Here, the next detection of the "de-averaged" spring travel Xar in the filter units and/or computer units 211 and 212 or 311 and 312 is determined. This occurs in dependence on time and/or magnitudes influencing the travel state, such as travel velocity V, and/or transverse acceleration Aq of temperature T. In this manner, time longitudinal acceleration A] the vehicle and/or ambient intervals are formed, at the beginning of each of which the control or regulation cycle is run through. This can, for example, be so structured that the cycle is run through at greater intervals for slower travel velocity, for example during parking, than for higher velocities.

A particularly simple design of the system can be achieved in that, wi th bypassing of the unit 228 or 328 for determination of the next computing cycle, a new regulation cycle is started on each occasion as soon as the preceding one has terminated. In this case, the computing cycle indicated in Figs. 2a, b or Figs. 3a, b is run through constantly, which means that the interval lengths are only dependent on the computing time.

The system embodying the invention is preferably arranged for each wheel unit of the suspension to be controlled or regulated. The switchings of the damping and/orspringing characteristics preferably take place independently of each other for the individual wheel units.

In a further variant, which is particularly simple to realise, the springing and/or damping system to be controlled or regulated has only two setting stages, which differ by different values of the characteristic parameters. If the units and discriminators denoted by the items 219 to 225 (Figs. 2a, b) or 319 to 325 (Figs. 3a, b) are bypassed (dashed line), then when at least one of the three conditions interrogated in the units 216, 217 and 218 or 316, 317 and 318 is not fulfilled (signal N at the input of unit 220 or 320), a switching signal is fed to the unit 227 or 327, in consequence of which a switchover to characteristic takes place.

the softer or harder damping and/or springing A switchover to the harder or softer characteristic takes place when each of the threeconditions interrogated in the units 216, 217 and 218 or 316, 317 and 318 is fulfilled (signal Y at the input of unit 219 or 319) through the feeding of a switching signal to the unit 226 or 327. This variant is distinguished by reduced complication, since the units 219 to 225 or 319 to 325 are superfluous; the springing and/or damping system need have only two setting stages and merely a single sensor is necessary for picking up the spring stroke movement.

It is advantageous to integrate a system embodying the invention entirely or partially into the springing and/or damping system to be controlled or regulated. In this manner, a problem-free modification is possible of hitherto conventional, i.e. passive, suspensions in that, for example, the passive shock absorber elements are replaced by active ones, into which the system is integrated. Such a shock absorber element has merely a connection to the electrical on-board mains in compact mode of construction by contrast to the conventional element.

Furthermore, a system embodying the invention can be utilised for the generation of an indicating signal representative of the travel safety. This indicating signal, for example, provides information about whether a situation, which is unsafe for travel is present. Then measures going beyond the control or regulation of the suspension can perhaps be undertaken in order to increase travel safety.

1. A system for determining signal values for use in suspension regulation or control in a vehicle with at least two wheel units connected to the vehicle body by regulable or controllable suspension systems influencing relative movement of the wheel units and body, comprising means to determine first signal values representing movement of the wheel units relative to the vehicle body, means to determine second signal values representing movements of the vehicle body, and means to determine, in dependence on the first and second signal values, third signal values representing wheel load 10 f 1 uctuati on.

2. A system as claimed in claim 1, wherein the first signal values represent the relative acceleration Xar" of the vehicle body and each wheel unit, the second signal values represent the acceleration X&' of the vehicle body at a contact point of the respective wheel and the means to determine the third signal values comprises at least one of filtering means and computing means to obtain the wheel load fluctuation by logically interlinking the first and signal values according to the equation [(Ma+Mr)Xa''] - MrXar''], wherein Ma is the vehicle body mass and Mr the wheel mass.

24 - 3. A system as claimed in claim 1 or claim 2, further comprising means to calculate fourth signal values representing possible changes in wheel load fluctuation as a function of change in the vehicle suspension characteristics, interrogation means to interrogate the fourth values with respect to predetermined criteria, and recognition means response to the interrogation result to recognise a vehicle travel state requiring resetting of the suspension characteristics to reduce wheel load fluctuation.

4. A system as claimed in any one of the preceding claims, wherein the suspension systems are each adjustable in at least two stages for resetting of the vehicle suspension characteristics and each have at least two spring rate characteristics.

5. A system as claimed in any one of the preceding claims, wherein the suspension systems are each adjustable in at least two stages for resetting of the vehicle suspension characteristics and each have at least two damping characteristics.

6. A system as claimed in any one of the preceding claims, the means for determining the first signal values comprising at least one detector associated with each wheel unit and arranged to detect at least one of travel, velocity and acceleration of the stroke of springing or damping means of the suspension system for that wheel uni t, and the means for determining the second signal values comprising at least three detectors arranged to detect vertical acceleration of the vehicle body at at least three points disposed otherwise than on a straight line.

7. A system as claimed in any one of claims 1 to 5, the means for determining the second signal values being arranged to form the values as weighted linear combinations of measurements of the vertical acceleration of the vehicle body.

8. A system as claimed in claim 1, further comprising means to calculate fourth signal values representing possible changes in wheel load fluctuation as a function of change in the vehicle suspension characteristics, means to perform at least one of analysis of the amounts of the third and fourth values and logical linking of the third values and the fourth values with each other or with further values, means to perform at least one of comparison of the analysed amounts with each other or with further amounts and comparison of the linked values with each other or with further values, and means to provide regulating or control values for the suspension systems in dependence on the comparison result or results.

9. A system as claimed in claim 1, further comprising means to calculate fourth signal values representing possible changes in wheel load fluctuation as a function of change in the vehicle suspension characteristics, means to so logically interlink for at least one wheel unit the third signal value P, the fourth signal value P' and a suspension setting parameter value k as to provide the linked values PP and klPI, first comparison means to compare the linked values and a further suspension setting parameter value Pgr with the values 05 IPI and 1P1 at selectable time interv first-set of equations als in accordance with a IPI > Pgr, PP 1 < 0 and 1P'I > kIPI in the case of a softer vehicle suspension setting at the comparison instant and in accordance with a second set of equations IPI > Pgr, PP 1 > 0 and IP.1 > kIPI in the case of a harder vehicle suspension setting at the comparison instant and to provide a first indicator value in the case of a positive result of all of the equations in either set and a second indicator value in the case of a negative result of any one of the equations in either set, means to count the first indicator values, and the second indicator values, second comparison means to compare the count totals of the indicator values with target values, and means to provide a regulating or control value for the respective suspension system in dependence on the result of the comparison with the target values.

10. A system as claimed in claim 9, wherein the target values are the 20 sum of the count totals of the indicator values, the count totals themselves, values derived from the count totals, or any combination thereof.

11. A system as claimed in claim 8 or claim 9, wherein the second comparison means is arranged to carry out the count totals comparison with consideration of values influencing the vehicle travel state.

12. A system as claimed in claim 1, comprising means to determine setting parameters for the suspension systems in dependence on the third values, the setting parameters having values which are constant.

13. A system as claimed in claim 1 or 12, comprising means to determine setting parameters for the suspension systems in dependence on the third values, the setting parameters having values dependent on at least one value influencing the vehicle travel state.

14. A system as claimed in claim 13, wherein said at least one influencing value is selected from values indicative of vehicle speed of travel, vehicle longitudinal acceleration, vehicle transverse acceleration and ambient temperature.

15. A system as claimed in claim 1, wherein the means to determine the signal v a] ues are arranged to determine a de-averaged value indicative of a stroke travel at each suspension system by subtraction, from a value Xa(t)-Xr(t) indicative of that travel, of the running mean value of the travel by way of the equation t Xa(t)-Xr(t)} - 71/Tm j FXa(r)-Xr(r)]dr t-Tm 28 - wherein Xa i s vehi cl e body travel, Xr i s the respecti ve wheel uni t travel, t is the actual instant and Tm is a setting parameter, to determine the first signal values by at least one of differentiation and low-pass filtering of the de-averaged travel val ues, and to determine, in dependence on the first signal values, at least one of the sensitivity of the wheel load fluctuation with respect to a constant of suspension system damping by way of the transfer function - (MaCrs3 VD(S) and the sensitivity of the wheel load fluctuation with respect to stiffness of suspension system springing by way of the transfer function -(MaCrs 2)ID(s), wherein s is the Laplace variable, D(s) = CCr+Crds+(CMr+(C+Cr)Ma)s2 +(Ma+ Mr)ds 3 +MaMrs 4, C is suspension spring stiffness, Cr is tyre stiffness, Ma is vehicle body mass, Mr is wheel mass and d is the damping constant.

16. A system as claimed in claim 1 or claim 15, wherein the means to determine the signal values are arranged to determine a de-averaged value indicative of stroke velocity at each suspension system by substraction, from a value W(t)-Xr(t) indicative of that velocity, of the running mean value of the velocity by way of the equation t Xa'(t)-Xr'(t)j - t(l/Tm 1 [Xal(r)-Xr'(r)]dr t-Tm wherein Xa' is vehicle body velocity, Xr' is the respective wheel unit velocity, t is the actual instant and Tm is a setting parameter, to determine wheel load fluctuation from the de-averaged velocity values by way of the transfer function [I/s][(]+Mr/Ma)C + (I+Mr/Ma)ds+Mrs 2 11 and to determine, from the first signal values, at least one of the sensitivity of wheel load fluctuation with respect to a constant of suspension system damping by way of the transfer function -[(MaCrs 2)/D(s)] and the sensitivity of the wheel load fluctuation with respect to stiffness of suspension system springing by way of the transfer function -[(MaCrs)/0(s)], wherein s is the Laplace variable, 2 3 4 D(s) = CCr+Crds+(CMr+(C+Cr)Ma)s +(Ma+Mr)ds +MaMrs C is suspension spring stiffness, Cr is tyre stiffness, Ma is vehicle body mass, Mr is wheel mass and d is the damping constant.

17. A systen as claimed in any one of claims 1, 15 and 16, wherein the means to determine the signal values are arranged to determine a deaveraged value indicative of stroke acceleration at each suspension system by subtraction, from a value X&'(t)-Xr"(t) indicative of that acceleration, of the running mean value of the acceleration by way of the equation t tXa" (t)-Xr" (t - tl /TM f EX&'(r)-Xr"M]dr t-Tm 3 wherein X&' is vehicle body acceleration, Xrl' is the respective wheel unit acceleration, t is the actual instant and Tm is a setting parameter, to determine wheel load fluctuation from the de-averaged acceleration values by way of the transfer function -El/S 2 1 C(IMr/Ma)C + (1+Mr/Ma)ds + Mrs 2 1, and to determine, from the first signal values, at least one of the sensitivity of wheel load fluctuation with respect to a constant of 15 suspension system damping by way of the transfer function E(MaCrs)/D(s)3 and the sensitivity of the wheel load fluctuation with respect to stiffness of system springing by way of the transfer function -E(MaCr)/0(s)l, wherein s is the Laplace variable, D(s) = CCr+Crds+(CMr+(C+Cr)Ma)s 2 +(Ma+ Mr)ds 3 +MaMrs 4 C is suspension spring stiffness, Cr is tyre stiffness, Ma is vehicle body mass, Mr is wheel mass and d is the damping constant.

18. A system substantially as hereinbefore described with reference to the accompanying drawings.

19. A vehicle comprising at least two wheel units connected to the vehicle body by regulable or controllable suspension systems influencing relative movement of the wheel units and body, and a system as claimed in any one of the preceding claims for determining signals for use in regulation or control of the suspension system.