GB2319760A - Mechanical actuator arrangement for a vehicle suspension system - Google Patents

Abstract

A mechanical actuator arrangement comprises an input arm 50 and an output arm 52, one end of each arm pivotably connected by a shaft 54,60 to the vehicle body 64, the other ends being connected by a spring 62 located between the arms. The spring 62 may be a bending spring, a compression or tension spring in the form of a gas spring or coil spring, or a magnetic field (Fig 11). The actuator arrangement may be applied to an active suspension system for a road vehicle (Fig 10) or for a railway carriage (Fig 9), whereby command signals from sensors control a pilot actuator (not shown) which rotates the input arm 50 such that a force is transmitted through the spring 62 and output arm 52 to a link 66 (88,92, Fig 9) coupled to a wheel mechanism (82) to control cant deficiency.

Description

MECHANICA ACTUATOR ARRANGEMENT The invention concerns a mechanical actuator arrangement, and in particular, but not exclusively, a mechanical actuator arrangement as incorporated in an active vehicle suspension system, and more particularly a railway suspension system Suspension systems are known in which either an existing passive suspension arrangereent is supplemented by an auxiliary suspension system which actively controls some aspect of the static and/or dynamic characteristics of the particular vehicle involved, or else such passive arrangement is replaced by such an active system which then takes over control of all aspects of the suspension.

An example of the latter is disclosed in the German patent application DE 3707085, laid open on 17th September 1987, in which, as shown in the axial view of Figure 1 of the present application, a helical spring 10 is arranged to bear against a transverse member 12 which pivots at a point 14 on the frame 16 of the vehicle and exerts a force F at a point 18 on the member 12. In order to cater for different static loading conditions and the constantly varying dynamic conditions which obtain during a ride, the contact point 18 of the spring 10 on the member 12 is altered by moving the lower end of the spring selectively either towards the pivot point 14 or towards the wheel 20. This movement has the effect of varying the leverage aid and therefore the value of the force F' at the point 22 of the member 12.

Control is effected in response to measurements taken of, for example, relative (angular) position of the member 12 or its corresponding upper member 24 relative to the frame 16, and acceleration of the member 12 or 24. Signals may also arise from measurements in other parts of the vehicle, and in a road vehicle may include items such as driving control position.

In a rail vehicle, it is possible to use stored data about the track as part of the control input.

In both applications, additional data about anticipated events (preview) arising either from look-ahead sensors or from previous vehicles may also be incorporated. Movement of the bottom end of the spring is effected by means of a pilot actuator (not shown), for example a hydraulic cylinder or an electric servo-motor, and this together with the spring and the member 12 constitute a mechanical actuator arrangement.

A similar arrangement is described in PCT application WO 93/22150, published on 11th November 1993, in which, as illustrated in Figure 2 of the present application, the lower end of a coil spring 10 is swivellably attached to a transverse T-piece 30 arranged to swivel on a fork rnernber 32 secured to a transverse member 34. Transverse member 34 and a further such member 36 are swivellably attached at one end to one of the wheels of the vehicle concerned and at the other end to the frame 38 of the vehicle. An actuating cylinder (pilot actuator) 40 is interposed between the frame 38 and the T-piece 30 between the fork 32 and the lower end of the spring 10 so as to be able under active control to swing the lower end of the spring round in a cone whose apex lies at the top end of the spring 10. By swinging the spring round in this manner the same changes in leverage described in connection with DE 37 07 085 are achieved here also, but without the problems of the sliding connection between the lower end of the spring and the lower transverse member.

Active suspensions are of great interest in the railway industry, since it seems probable that desired improvements in running speeds and passenger comfort can be achieved more readily by improvements to vehicle suspensions than by major changes to the track. Of all the aspects of active suspension design, the actuator is often the weakest link, though it is of crucial importance. In particular, it is desirable to provide an actuator which is as close to the ideal as possible, the ideal actuator having the following features: output force independent of displacement of the moving parts of the actuator and dependent only on the input command signal; high efficiency; low cost; low weight; small size; high reliability, etc.

In accordance with a first aspect of the invention there is provided a mechanical actuator for a suspension system, the actuator comprising an input swivel-arm arrangement and an output swivel-arm arrangement, each swivel-arm arrangement at a first point thereof being swivellably mounted to a body, and a precharged energy-storage means connected between said swivel-arm arrangements at respective second points thereof, the actuator being configured such that movement of said input swivel-arm arrangement through an angle causes a moment to be imposed on said output swivel-arm arrangement by said energystorage means, a value of said moment being a function of said angle.

The input and output swivel-arm arrangements may be constituted by respective arms, the first and second points of each arm being disposed substantially at opposite ends of that arm.

A swivel axis at said first point of the input arm may be substantially parallel to a swivel axis at said first point of the output arm and, looking in the direction of said swivel axes, said energy-storage means may be disposed between said arms. Alternatively, these swivel axes may be orthogonally disposed, or indeed may assume any angle between parallelism and orthogonality. A distance between the first and second points on the input arm may be substantially equal to a distance between the first and second points on the output arm, and may also be substantially equal to a distance between the swivel axes of the input and output arms.

The swivel-arm arrangements may each be constituted by parallel arms swivellably mounted at one end to said body and swivellably connected at the other end to a crosspiece, said energy-storage means being connected between the two crosspieces. The energystorage means may be a magnetic arrangement, and in particular may comprise a permanent magnet on each crosspiece.

The actuator arrangement may be configured such that said energy-storage means is capable of imposing on said output swivel-arm arrangement a moment in either of two opposite senses, and in a neutral state of said arrangement said energy-storage means may exert substantially zero moment on said output swivel-arm arrangement. In said neutral state said first point and said second point of said input arm may be substantially aligned with said second point and said first point, respectively, of said output arm. However, where the swivel axes are orthogonal, the input arm may, in the neutral state, be substantially aligned with the swivel axis of said output arm. Alternatively, in the neutral state the energy-storage means may exert a non-zero moment on said output swivel-arm arrangement.

The input and output swivel-arm arrangements may be configured with respect to each other such that throughout a working angular range of said input swivel-arm arrangement, said energy-storage means exerts a non-zero moment of a given sense on said output swivel-arm arrangement.

A moment exerted on said output swivel-arm arrangement by said energy-storage means may be substantially directly proportional to the angle moved through by said input swivel-arm arrangement.

The energy-storage means may be a helical spring or a gas spring in the form of a compression or tension spring. Alternatively, the energy-storage means may be a bending spring.

In accordance with a second aspect of the invention, there is provided a suspension arrangement including an actuator arrangement according to any one of the preceding claims in which said body is a body of a vehicle and said output-arm moment is transmitted to a member which is movably attached to said vehicle body.

The vehicle may be a railway vehicle, with the body being a part of a waggon or carriage and the movably attached member being a bogie associated with said waggon or carriage.

Ernbodiments of the invention will now be described, by way of example only, with reference to the drawings, of which: Figure 1 is a partial longitudinal view of an automobile suspension system incorporating a first known mechanical actuator arrangement; Figure 2 is a partial general view of an automobile suspension system incorporating a second known mechanical actuator arrangement; Figure 3 is a first embodiment of a mechanical actuator according to the present invention; Figure 4 is a trigonometric representation of the actuator according to the invention during part of its operating cycle; Figure 5 is a perspective view of an actuator arrangement according to the invention incorporating a force take-off lever on the output arm; Figure 6 is a diagram showing the relationship between output force and input deflection for various output deflections for the parameters given on pages 7 and 8; Figure 7 is a diagram showing the relationship between output force and output deflection for various input deflections for the same parameters as in Figure 6; Figure 8 is a diagram showing the relationship between the required input torque and output deflection for various input deflections for the same parameters as in Figure 6; Figure 9(a) is a schematic diagram showing the application of the actuator according to the invention incorporated in a railway suspension system, Figure 9(b) is an underside view of the actuator unit of Figure 9(a), and Figure 9(c) is an internal side view of the actuator unit of Figure 9(a); Figure 10 is a schematic diagram of an automobile suspension incorporating an actuator arrangement according to the invention, and Figure 1 l(a)-(e) show various alternative configurations of the actuator arrangement according to the invention.

Referring now to Figure 3, there is illustrated one embodiment of a mechanical actuator according to the present invention, comprising an input swivel-arm arrangement and an output swivel-arm arrangement, said arrangements taking the form of respective arms 50, 52 swivellably supported by respective support shafts 54, 56 in the body 64 of a vehicle or other object in which the actuator is incorporated. At the other end of each arm there is provided a crankpin 58, 60 and between the two crankpins there is fitted a pre-stressed compression spring 62, which may take the form of, for example, a gas spring. (Spring 62 could equally well be a tension spring, as shown later in Figure 11(c)).

The mode of operation of the actuator can be seen with the aid of Figure 4, which is a view directly along the axis of the shafts and crankpins as shown by the arrow in Figure 3. In Figure 4 arm 50 is taken to be the input arm connected to a pilot actuator (not shown), and arm 52 is the output arm The pilot actuator may operate the input arm either by direct rotation thereof about point A2 or by means of appropriate levers swivellably connected to the input arm. The output arm transfers the force which will be exerted on it by the spring 62 to a member which is external to both the actuator and the body to which the actuator is attached, but which is movably connected to the body. Force transference is by way of a link 66. Figure 5 is a perspective view of such an arrangement.

It is assumed for the embodiment of Figures 3 and 4 that the distance between the shaft and crankpin on each arm is equal, this being distance r in Figure 4. The distance between points A3 on the input shaft and B3 on the output shaft is designated as s, and this will be equal to r in a neutral state of the actuator in which the arms are exactly aligned. In this neutral state the spring 62 will exert no moment on the output shaft 52 since the line of action of the spring is exactly aligned with the longitudinal axis of the output arm.

Assuming now the input arm 50 to be moved clockwise through an angle a, the line of action of the spring will move away from the longitudinal axis of the output arm, assuming an angle y with the vertical, and distance s will assume a value greater than r, assuming P to be positive. Where 9 is negative, s will be less than r. It should be borne in mind that the position of the output arm is fixed by the movement of the associated vehicle suspension via link 66 and this position is shown in Figure 4 in an arbitrary position in which P is positive. It may equally be negative, however, even though the present actuator is attempting to force the output arm into an area of positive ; this is effectively the situation with the actuator shown in Figure 5, though with angles of reverse sense. The spring in this position exerts a clockwise moment on the output arm.

Working in Cartesian co-ordinates and taking point B2 to be at position (0,0), various parameters can be defined as follows: working position of point B3 = (r.sin , r cos ) working position of point A3 = (-r.sin a, r (1-cos a)) . tan y = (sin a + sin )/(cos a + cos -1) and spring length s = [(sin cr + sin P)Z + (cos cl + cos P ly] The output moment on the output arm is given by the working force of the spring multiplied by the perpendicular distance between the line of action of the spring and the shaft pivot point B2, and has the value: P.r.sin (y-g) where the working spring force P is, for an initial compressive force C and stiffness k: P = C+k (r-s).

At the same time as the spring exerts a clockwise moment on the output arm (P positive - the moment would be anticlockwise for p negative), it exerts also a clockwise moment on the input arm, defined as the working force of the spring multiplied by the perpendicular distance between the line of action of the spring and the shaft point A2, and having the value: P.r.sin (y-a).

The output force F acts in the rightward direction and is given by the expression: F= P.r.sin (y-PYl.cos P where I is the distance between B2 and B4.

Finally, the output deflection o, also to the right, is defined as: o=l.sin .

To a first approximation, and for practical movements of an actuator incorporating a reasonably low-rate pre-compressed spring having substantial pre-compression, the output moment is proportional to the angle of rotation of the input shaft and the input moment is likewise proportional to the angle of rotation of the output shaft. In addition, movement (o) of the output arm for a particular input has relatively little effect on the moment generated at the output, and likewise movement of the input for a particular output has relatively little effect on the moment generated at the input. The actuator is therefore close to the ideal actuator in the sense that force is substantially unaffected by the relative movement of the ends of the actuator and depends almost solely on the input command signal from the pilot actuator. It is also clear that the actuator according to the invention is completely reversible in the sense that the output can be used as the input, and vice-versa.

It is apparent from the configuration shown in Figure 3 that, provided the output arm 52 is not displaced (ie. P =0), the pilot actuator is required to do virtually no work over its entire range of movement, the only losses being frictional losses in the bearings. This arises from the fact that the support-shaft and crankpin centres at the corresponding ends of the two arms are aligned when P = 0. This only applies, of course, where such alignment is possible, and in a case where the A2, B3 axes never coincided, e.g. because the distance between shaft and crankpin in the output arm was greater than the corresponding distance in the input arm, points A3 and B2 being nonetheless aligned when a =0, P = 0, the pilot actuator would always have to do work throughout the whole of its range.

In a development example of the invention the following parameter limits were assumed: peak force = 20kN, max. output displacement (o) = + 80mm and max. change in force = +10%. A set of physical parameters substantially meeting these criteria were: - shaft-to-crankpin distance = 225 mm - output arm length = 300 mm - spring load at nominal length (neutral position) = 53.3kNm - spring rate = 53.3kN1m - input arm deflection angle = + 30".

Three graphs which illustrate the action of the actuator are presented in Figures 6, 7 and 8. Figure 6 shows the relationship between output force and input angular deflection (a) for various output-arm deflections (o). It can be seen that the relationship is substantially linear, departure from linearity being most pronounced at higher input angles and higher displacements, though even then non-linearity is quite small within the limits of input angle and output displacement specified. The general effect of output displacement, then, is to increase the force when the displacement is in the opposite direction to that being urged by the actuator force, and to reduce it when the opposite applies. This corresponds to positive stiffness, which is advantageous in that it promotes stability and enhances the operation of the suspension in which the actuator is being employed.

Figure 7 shows how the output force changes with output deflection (o) for various input-arm angles (a). Only positive input angles and output forces are shown because the negative values are mirror images of the values shown. The slope of the curves reveal the effective stiffness of the actuator, and it can be seen that this falls rapidly with a reduction in the force. The stiffness of the actuator at low forces is very low, indicating that when the actuator is employed in conjunction with an existing suspension arrangement, it will not affect the normal operation of that suspension arrangement when the actuator is not active (i.e. when a = 0).

Figure 8 shows the torque required to set and maintain position of the pilot actuator under a range of ouput forces. It can be seen that the torque is dominated by the output deflection and that the position of the pilot actuator with its corresponding output force has relatively little effect.

A practical application of the present actuator is illustrated in Figure 9(a), which shows a railway carriage 80 mounted on a bogie 82 via suspension elements 84. Attached to the underside of the carriage, and possibly replacing one of the existing dampers, is an enclosure 86 containing the elements of an actuator according to the invention as illustrated in Figure 3, though without the link arm 66 connected to the output arm. The output of the actuator is taken from the support shaft 56 (see Figure 3) in the form of a link arm 88 orientated approximately parallel to the output arm 52 and teminating in a swivel connection 90 to which a link rod 92 is attached, the other end of the link rod 92 being connected to the bogie via an attachment 94 thereof. Figure 9(b) shows the enclosure, link arm and link rod in a view looking from the underside of the actuator arrangement.

Figure 9(c) illustrates the configuration of the actuator elements within the enclosure 86 and is a side view looking from the right in Figure 9(a). Input arm 50 is mounted in one wall of the enclosure by way of a bearing 96, while the output arm 52 is similarly mounted in an opposite wall in a bearing 98. A gas compression spring 62 is disposed between the other ends of the arms 50, 52. Attached to the support shaft 54 of the input arm is an actuating arm 100 which is operated by a pilot actuator (not shown) in the form of an hydraulic cylinder, and attached to the support shaft 56 of the output arm is the link arm 88.

Alternatively, an eectrical servo-motor with gearing or other means may be used to control the angular position of the input arm.

This application of the invention does not impinge upon the vertical suspension arrangement 84 of the railway vehicle, rather it is employed as part of a lateral suspension arrangement in which lateral movements of the carriage relative to the bogie are controlled.

More specifically, the actuator is used to control the phenomenon of "cant deficiency". In practice, railway tracks on a curve are set with the outer rail higher than the inner rail, the difference - in either height or angle with respect to the horizontal - being known as the "cant" (e.g. the "cant angle"). When the train is running at its rated speed for that curve, the centrifugal force of the train is exactly balanced by the force inwards due to the cant. When, however, the train runs at higher than rated speed, the cant on the rails is insufficient to provide this balancing effect, so that there is a net outward force against the rails. The train is then said to be running with "cant deficiency".

This outward force is restrained at bogie level by the action of the wheels against the rails, but is transmitted to the carriage where there is no such restraint, except a certain lateral stiffness in the vertical suspension 84. To control the effect of this transmitted force, control signals are sent to signal the pilot actuator to exert a counterforce against the bogie by way of the actuator of the invention. Assuming an anticlockwise bend, the pilot actuator achieves this by rotating the input shaft 54 of the actuator in a clockwise direction so as to move the carriage 80 leftward relative to the bogie 82.

In this scheme, one actuator is used per bogie. In addition, it would be possible to employ the actuator also in a vertical suspension arrangement, in which case the actuator configuration shown in Figure 9(c) would be turned through 90C so as to be able to exert a downwards force. Four such vertical actuator arrangements would be employed per carriage, or perhaps even three as a minimum, and therefore in a comprehensive ride control scheme there would be five or six actuators per carriage (where two bogies are employed per carriage).

When used in a vertical suspension scheme, the actuator may be required to deliver a force in one sense only, i.e. downwards. Figure 10 shows a representative automobile suspension arrangement in which an upper suspension arm 110 is attached to the vehicle body 112 by way of an actuator arrangement according to the invention. As in the rail application, the actuator in this application is housed in an enclosure 114 which is fixed to the body 112. One end of the upper arm 110 is fixed to the output support shaft 56 of the actuator, while the other is connected to the wheel and to a lower suspension arm 116. The other end of the lower suspension arm is swivellably attached to the vehicle body 112.

In the neutral position of the actuator the input and output arms are set so that a net downward force is exerted on the upper suspension arm 110, that net force being then increased or decreased either side of that neutral setting according to road conditions and the command signals that are sent to the pilot actuator (not shown) connected to the inputarm support shaft (not shown).

If required, a conventional spring may be employed in addition, as may also a damper.

Where the conventional spring provides sufficient downward force it may be possible to arrange for the actuator to back some of this force off by producing its own force of the opposite sense. Thus part at least of the actuator's duty cycle may involve the production of an upward force on the upper arm 110 (i.e. anticlockwise moment on the output shaft 56).

To achieve a non-zero output force in the neutral position of the actuator, it is necessary to ensure that the input and output arms are out of alignment in that position, in contrast to the part of the duty cycle shown in Figure 3, which corresponds to a zero-force position.

Figure 11 shows various alternative configurations of the actuator. Although it has so far been assumed that the shaft-to-crankpin distance is the same for both arms and is equal to the distance between the shaft. centres, this is by no means essential. Other arrangements are perfectly feasible, for example it is possible to use different dimensions for the shaft-crankpin pairs and for the shaft centres. It is also possible to place the input and output shafts so that their axes are not parallel. Each variant may be applied either singly or in cornbination. Each different geometry gives a different relationship between the input and output, and the designer would choose the most appropriate for his application. An example of an actuator with parallel shafts but unequal centre-to-centre distances is shown in Figure 11(a), and an example of an arrangement where the shaft axes are not parallel is shown in Figure 11(b). In Figure 11(a) non-alignment of the shafts, etc, means that the pilot actuator driving the input arm 50 will be involved in work throughout its duty cycle, in contrast to the preferred arrangement of Figure 3 in which, as already mentioned, the pilot does effectively no work when output angle is zero.

It is not essential that the shafts of the input and output arms be parallel to each other, but they may assume many different relative attitudes. Figure 11 (b) shows an arrangement in which the shafts are orthogonally disposed. The input arm 50 in the zero-moment position of the actuator may be arranged to be substantially aligned with the support shaft 56 of the output arm In this embodiment movement of the input arm alters not only the line of action of the spring for a given output angle , but also the extension of the spring, whereas the preferred embodiment of Figure 3 is essentially a lineof-action device.

Figure ll(c) shows an actuator employing a tension spring instead of a compression spring. In this case, when the input arm 50 is moved through an angle a the output shaft will experience a moment in the opposite direction to that experienced when a compression spring is employed.

It is also possible to employ a bending spring as the energy-storage means, as shown in Figure 11(d), this configuration acting in a similar manner to the compression spring arrangement.

It is possible to use any phenomenon giving a reasonably constant force over the range of movement required in place of the springs previously mentioned. An example would be the forces arising under a magnetic field. If permanent magnets were to be used to provide the locked-in energy, it would be appropriate to use another embodiment of the invention in which a more complex linkage mechanism is used to support and move the magnets. A possible arrangement is shown in Figure 11(e). In Figure 11 (e) an input arm arrangement 118 comprises two parallel arms 120, 122 and a crosspiece 124 swivellably joining the two parallel arms at one end thereof. A permanent magnet 126 is attached to the crosspiece at some point along its length and the lower ends of the two parallel arms are swivellably attached to the body of a vehicle, for example, by way of suitable shafts 128, one of the shafts being connected to a pilot actuator. A similar arrangement 130 is provided for the output arm arrangement also but in an inverted configuration, so that the two magnets face each other with a gap between them. The arrangement is set to either a compressionspring mode or a tension-spring mode in dependence on whether like poles of the magnets are facing each other, or unlike.

Where space is at a premium, it is expedient to employ a gas spring instead of a coil spring. A gas spring can store large quantities of energy and also has low stiffness which is desirable in many applications.

Claims (21)

1. A mechanical actuator for a suspension system, the actuator comprising an input swivel-arm arrangement and an output swivel-arm arrangement, each swivel-arm arrangement at a first point thereof being swivellably mounted to a body, and a precharged energy-storage means connected between said swivel-arm arrangements at respective second points thereof, the actuator being configured such that movement of said input swivel-arm arrangement through an angle causes a moment to be imposed on said output swivel-arm arrangement by said energy-storage means, a value of said moment being a function of said angle.

2. Actuator arrangement according to Claim 1, in which said input and output swivelarm arrangements are constituted by respective arms, the first and second points of each arm being disposed substantially at opposite ends of that arm.

3. Actuator arrangement according to Claim 2, in which a swivel axis at said first point of the input arm is substantially parallel to a swivel axis at said first point of the output arm and, looking in the direction of said swivel axes, said energy-storage means is disposed between said arms.

4. Actuator arrangement according to Claim 3, in which a distance between the first and second points on the input arm is substantially equal to a distance between the first and second points on the output arm.

5. Actuator arrangement according to Claim 4, in which a distance between the swivel axes of the input and output arms is substantially equal to said distance between the first and second points.

6. Actuator arrangement according to Claim 2, in which the swivel axes of the input and output arms are orthogonally disposed and said energy-storage means is disposed between the swivel axis of said input arm and said output arm.

7. Actuator arrangement according to Claim 1, in which said swivel-arm arrangements are each constituted by parallel arms swivellably mounted at one end to said body and swivellably connected at the other end to a crosspiece, said energy-storage means being connected between the two crosspieces.

8. Actuator arrangement according to any one of the preceding claims, in which said actuator arrangement is configured such that said energy-storage means is capable of imposing on said output swivel-arm arrangement a moment in either of two opposite senses.

9. Actuator arrangement according to Claim 8, in which, in a neutral state of said arrangement, said energy-storage means exerts substantially zero moment on said output swivel-arm arrangement.

10. Actuator arrangement according to Claim 9 as appendent to Claim 5, in which in said neutral state said first point and said second point of said input arm are substantially aligned with said second point and said first point, respectively, of said output arm.

11. Actuator arrangement according to Claim 9 as appendent to Claim 6, in which in said neutral state said input arm is substantially aligned with the swivel axis of said output arm.

12. Actuator arrangement according to Claim 8, in which, in a neutral state of said arrangement, said energy-storage means exerts a non-zero moment on said output swivelarm arrangement.

13. Actuator arrangement according to any one of Claims 1 to 7, in which said input and output swivel-arm arrangements are configured with respect to each other such that throughout a working angular range of said input swivel-arm arrangement, said energystorage means exerts a non-zero moment of a given sense on said output swivel-arm arrangement.

14. Actuator arrangement according to any one of the preceding claims, in which a moment exerted on said output swivel-arm arrangement by said energy-storage means is substantially directly proportional to the angle moved through by said input swivel-arm arrangement.

15. Actuator arrangement according to any one of the preceding claims, in which said energy-storage means is a helical spring or a gas spring.

16. Actuator arrangement according to Claim 15, in which said energy-storage means is a compression or tension spring.

17. Actuator arrangement according to any one of Claims 1 to 15, in which said energystorage means is a bending spring.

18. Actuator arrangement according to Claim 7, in which said energy-storage means is a magnetic arrangement disposed on said crosspieces.

19. Suspension arrangement including an actuator arrangement according to any one of the preceding claims in which said body is a body of a vehicle and said output-arm moment is transmitted to a member which is movably attached to said vehicle body.

20. Suspension arrangement according to Claim 19, in which said vehicle is a railway vehicle, said body is a part of a waggon or carriage, and said movably attached member is a bogie associated with said waggon or carriage.

21. Actuator arrangement substantially as shown in, or as hereinbefore described with reference to, Figures 3 to 8, or Figure 9, or Figure 10, or any of Figures 11 (a) to 11(e).