GB2124988A - Air or spray control screen assembly for use on a road vehicle - Google Patents

Abstract

A screen assembly for use on a road vehicle controls water spray when travelling over wet surfaces or controls airflow around the vehicle. The screen (51,52), has means (53) for mounting the screen on the vehicle so that it can be moved between an operative or lower position in which its lower edge lies adjacent to the road surface over which the vehicle is travelling and an upper, inoperative position which is disposed above its operative position, there being also provided power- actuated means, such as a fluid pressure actuated piston and cylinder unit (73) for moving the screen in at least one direction between the aforesaid positions. Preferably the said power- actuated means (73) is operatively connected to control means which is sensitive to the road speed of the vehicle. <IMAGE>

Description

SPECIFICATION Air or spray control screen assembly for use on a road vehicle This invention relates to a spray or air control screen assembly for use on a road vehicle. Such a screen when used to control spray is of course desirable, for the safety and comfort of other road users, when a vehicle is travelling in wet weather and especially if it is travelling in wet weather at high speed as may occur for example on a motorway when the vehicle tends to create a considerable amount of spray which may represent a hazard to the other road users. Alternatively, a screen assembly may be fitted to a vehicle so as in use to control the flow of air around or under the vehicle and thereby improve the aerodynamic efficiency of the vehicle's passage through the air. The object of the present invention is to provide an improved spray or air control screen assembly for a road vehicle.

In accordance with the invention there is provided a spray or air control screen assembly for a road vehicle comprising a screen, means for mounting said screen on the vehicle so that it is movable between an operative position in which its lower edge lies adjacent to the road surface and an inoperative position which is above its operative position, and power-actuated means for moving said screen in at least one direction between said operative and inoperative positions.

The power-actuated means may comprise a fluidpressure actuated piston and cylinder unit (either a pneumatically or hydraulically actuated unit) or an electric motor but preferably said power-actuated means is connected to control means sensitive to vehicle road speed arranged so that the screen can be maintained in its upper, inoperative position unless the vehicle road speed exceeds a predetermined value such as, for example, 35 m.p.h., although to avoid the problem of "hunting" (i.e. that of the screen constantly moving up and down if the vehicle speed varies frequently by small increments above and below said predetermined figure arrange ments may be made to ensure that the screen is not raised again until the vehicle speed falls to a second predetermined value (such as for example 25 m.p.h.) significantly lower than said first predetermined value.Thus said power-actuated means may be controlled by electrical signals initiated by the vehicle speedometer or by other means which are sensitive to the road speed of the vehicle, one signal being given to effect movement of the screen to its lower, operative position when (in the example mentioned above) the vehicle speed exceeds 35 m.p.h. and another signal being given to effect movement of the screen to its upper, inoperative position when (also in the above-mentioned exam ple) the vehicle speed falls again to 25 m.p.h. In addition, however, there may be provided a master swich which can be used to override the dependence of upward and downward movement of the screen upon vehicle speed as above-described.Furth ermore, such movement of the screen which is dependent upon vehicle speed can also be made subject to operation of the vehicle's windscreen wiper or wipers so that screen movement (except any movement that may be effected by use of a master switch where this is provided) between its operative and inoperative positions in accordance with vehicle road speed as above explained will also be subject to the requirement that the vehicle's windscreen wiper or wipers is or are operating.

Conveniently, the means for mounting said screen on the vehicle may be subject to spring loading which can be arranged approximately to balance the weight of the screen and its associated mechanism; or to provide a bias on the screen in an upward direction; or to permit the weight of the screen and associated mechanism to bias the screen in a downward direction. The power-actuated means for effecting movement of the screen may be arranged to effect movement in both upward and downward direction or alternatively in only one of these directions in which case either the (upward) spring loading bias or the (downward) bias exerted by the weight of the screen and associated mechanism would be used to effect screen movement in the other direction.

The invention will now be more particularly described with reference to the accompanying drawings wherein Figure lisa side view showing one example of a spray or air control screen assembly in accordance with the invention, Figure 2 is a plan view of said screen assembly, Figure 3 and 4 are respectively side and rear views of an alternative construction of a spray or air control screen assembly in accordance with the invention Figure 5 is an air and electrical circuit diagram showing one way in which a screen assembly in accordance with the invention can be used on a vehicle, Figures 6 and 7 are respectively side and plan views showing a vehicle fitted with another embodiment of a spray or air control screen in accordance with the invention, and Figure 8 is a side view of yet another embodiment of a control screen assembly in accordance with the invention.

Referring now to the drawings there is shown therein a spray-inhibiting means for a road vehicle which includes a screen 10 which when in its operative position as illustrated in full lines Figure 1 is adapted to intercept water and spray thrown rearwardly from an adjacent tyre 11 of the vehicle. In the example illustrated in the drawing said screen 10 is wide enough to extend across the width of twin tyres 11 and 12 forming part of a rear axle unit of the vehicle and there is another similar screen 13 which is similarly adapted to intercept spray thrown rearwardly from the tyres 14 and 15 of another twin tyre unit on the other side of the vehicle.As shown in Figure 2 therefore the rear axle assembly of the vehicle is protected by a pair of similar sprayinhibiting means which are conveniently interconnected by means of a bar 16 of square or rectangular cross-section which is slidably engageable with a pair of square or rectangular cross-section tubes 17 and 18 forming respectively parts of the two spray inhibiting means and extending towards each other, said bar 16 being connectable at each of its ends by means of a pin or bolt to the tubes 17 and 18so that the two screens 10 and 13 are adapted to move in unison.

The construction of each screen 10 and 13 does not form part of the present invention but as shown in Figure 1 each screen has an inlet 19 and an outlet 20, the cross-sectional area of the inlet being greater than the cross-sectional area of the outlet. Furthermore the interior of each screen is provided with a plurality of brush-like elements 21 and 22 and there may also be provided one or more imperforate baffles 23 which effectively divide the interior of the screen into two or more vertically separated regions.

Thus spray thrown rearwardly from the adjacent tyre will enter the inlet 19 of the screen and the bristles or blade-like members of the brush elements 21 and 22 will collect water from the spray whereas the smaller cross-sectional area of the outlet 20 as compared with the cross-sectional area of the inlet 19 will ensure that the water is ejected rearwardly from the screen at a velocity having a horizontal component which is greater than the forward speed of the vehicle over the ground. The water issuing from the rear of the screen 10 or 13 will thus be deposited on the road surface with a reduced velocity in a horizontal direction relative to the road surface and such an arrangement inhibits the formation of spray that might otherwise be caused by the water impinging on the road surface at an oblique angle and at a relatively high velocity.

Referring now to the screen 10, the upper part of said screen is connected to a laterally extending tubular member 24 which is itself connected to a link 25 to which is connected one end of said member 17.

Said link 25 is extended beyond the member 17 to form a portion 26 which is pivotally connected at 27 to an upwardly projecting member 28 connected to one end of a bar 29 which is secured to shackles 30 mounted on the rear axle 31. Said portion 26 is also pivotally connected at 32 to one end of a link 33 of which the other end is pivotally connected at 34 to one end of another link 35 which is itself pivotally connected at 36 to the bar 29. Furthermore a member 27 connected to said end 28 of the bar 29 is provided at its lower end with a flange 38 through which extends a screwed stop 39 which is adapted at its upper end to engage the underside of link 33.

Thus said screwed stop 39 can be adjusted to locate the linkage comprising members 25,2633 and 35 in order that the lower edge of the screen 10 is closely adjacent to the road surface when the screen is in its operative position as shown in full lines in Figure 1.

As above described this linkage is mounted on the rear axle 31 so that the screen, when in its operative position, will always maintain the same position relative to the road surface irrespective of the load carried by the vehicle concerned but in another arrangement (not shown) said linkage may itself be connected between the suspension of the vehicle and the load carrying part thereof in order that said screen will again take up a constant position relative to the road surface irrespective of the load carried by the vehicle. Such an arrangement does not however form part of the present invention.

The screen 10 or 13 mounted on the linkage as above described is also adapted to be lifted to an upper or inoperative position as indicated by chain dotted lines 40 in Figure 1 and power-actuated means are provided for moving said screen in at least one direction of movement between its operative and inoperative positions. In the example described said power-actuated means comprises a fluid-pressure actuated piston and cylinder unit 41 which is connected at one end to a downwardly projecting member 42 secured to that end of the bar 29 opposite to said end 28. The link 35 is welded to an angle plate 43 and the piston rod 44 of said unit 41 is pivotally connected to a pad 45 having a projecting rod 46 which extends through an aperture formed in the flange of the angle plate 43.A washer 47 is secured to said rod 46 and a spring 48 is located between said washer 47 and said flange of the angle plate 43. There is also provided a heavier spring 49 which bears at one end against said flange of the angle plate 43 and at the other end against an abutment 50 secured to the member 42. The spring 49 thus is arranged to exert a force on the angle plate 43 which acts on the above described linkage 25,26, 33,35, together with the attached screen 10 which is greater than the weight of said mechanism and the screen and which therefore, in the absence of any force applied by the piston and cylinder unit 41 will bias the screen 10 into its upper or inoperative position shown, as above mentioned in chain dotted lines in Figure 1.Pressurised fluid such as compressed air or hydraulic fluid can however be admitted to the appropriate end of the piston and cylinder unit 41 in order to retract the piston rod 44 so as to cause the rod 46 to compress the spring 48 thereby acting on the flange of the angle plate 43 to move the screen 10 and its associated linkage into the lower position.

Thus the full line position of the screen 10 in Figure 1 represents a position in whih the piston rod 44 has been retracted to overcome the upward biasing force exerted by the spring 49. In an alternative arrangement however the spring 49 is arranged so that it only partially counterbalances the weight of the screen 10 and the associated linkage so that the screen will then move under the influence of gravity to its lower or operative position whereas movement of the screen to its upper or inoperative position will be effected by expansion of the piston rod 44. In yet a further alternative arrangement the spring 49 is arranged approximately to counterbalance the weight of the screen 10 and the associated linkage so that the piston and cylinder unit 41 will be doubleacting and so will be used to hold the screen both in its operative and inoperative positions. The spring 48 together with the rod 46 which extends through the aperture formed in the flange of angle plate 43 provides in effect a lost motion connection which permits the screen 10 and associated linkage to ride upwardly if the screen 10 meets an obstruction on the road surface.

The power-actuated means comprising the piston and cylinder 41 is connected to control means which is sensitive to vehicle road speed and such control means may comprise for example a solenoid oper ated valve which is itself connected to the vehicle speedometer ortachograph or other means sensitive to the vehicle road speed. Conveniently, where the vehicle speedometer is used there may be provided a pair of contacts which are movable by movement of the speedometer mechanism, said pair of movable contacts being adapted to co-act with a stationary contact.Engagement between one movable contact and the stationary contact is arranged to occur at a predetermined vehicle speed (such as for example 35 m.p.h.) and such engagement in the example above described would have the effect of actuating the piston and cylinder unit 41 to act on the angle plate 43 and linkage connected thereto so as to bring the screen into its lower or operative position but if desired the connection between said speedometer contacts and the aforesaid solenoid valve can be made through a switch controlling the vehicle windscreen wiper or wipers so that said screen 10 will only be lowered when the vehicle speed exceeds 35 m.p.h. and when the windscreen wiper or wipers are operating, i.e. in wet conditions.The other contact movable by the speedometer is arranged to engage the stationary contact at a predetermined vehicle speed which is significantly lower than the first mentioned predetermined speed, for example 25 m.p.h. so that at such lower speed the solenoid valve (in the example above described) will be actuated to exhaust the piston and cylinder unit 41 and thereby permit the spring 49 to bias the screen 10 into its upper or inoperative position. Thus the screen 10 will assume its inoperative position at a speed significantly lower than that at which it will be lowered into its operative position so as to avoid the problem that might otherwise be caused by "hunting" if the vehicle speed were to vary continuously by small increments on either side of the first mentioned predetermined road speed.

In addition to the above described arrangement there may also be provided a master switch that can be arranged to actuate the aforementioned solenoid valve to pressurise the piston and cylinder unit 41 in order to lower the screen 10 irrespective of the speed of the vehicle and irrespective of whether the windscreen wipers are operating or not.

Obviously, where the piston and cylinder unit 41 is actuated to effect lifting of the screen 10 then again such actuation of the unit would be arranged to occur at a relatively low vehicle speed such as 25 m.p.h. whereas exhausting of the unit 41 to cause lowering of the screen 10 would be effected at the predetermined high speed such as 35 m.p.h. In the further alternative arrangement in which a double acting fluid pressure actuated unit is used then one end of the unit would be pressurised at speeds above say 35 m.p.h. whilst the other end would be pressurised at the lower speed such as 25 m.p.h.

As previously mentioned the power actuated means for effecting movement of the screen 10 in at least one direction between its operative and inoperative positions may comprise other means such as an electric motor which may be arranged to drive any convenient form of mechanism such as for example a screw and nut mechanism connected to the linkage associated with the screen 10 and actuation of the electric motor can be accomplished in a manner similar to that described above in connection with the fluid pressure actuated unit 41.

As above described, the screens 10 and 13 are each adapted to collect water thrown rearwardly from a twin tyre unit but it is of course to be understood that a screen which forms part of spray-inhibiting means in accordance with the invention can equally well be used to reduce spray thrown rearwardly by a single tyre. Also, as abovedescribed, the linkages supporting the two screens 10 and 13 are inter-connected by the bar 16 and this has the advantage of helping to maintain the screens in the desired position if "tramping" of the axle unit occurs.Furthermore, if the two screens are connected in this way only one power-actuated means (i.e. fluid pressure actuated unit or electric motor) need be used to effect movement of the screens although of course each screen may be movable if desired by its own fluid pressure actuated unit or electric motor, the two units or electric motors being connected to one control means sensitive to vehicle road speed. If however said two screens and associated linkages are not inter-connected, then each screen and linkage would be connected to a fluid pressure actuated unit or electric motor.

Moreover, each of said screens 10 and 13 may be connected to a spray collecting mat which would be arranged to move with the associated screen.

The assembly above described thus achieves, inter alia, the advantage that the screen 10 can always be arranged to be set in its upper or inoperative position when the vehicle is being reversed, provided that the vehicle road speed above which the screen is moved into its lower position is higher than that which would customarily be employed for reversing. On the other hand at speeds below the lower predetermined level during which the screen will be in its upper or inoperative position whilst the vehicle is travelling in a forwards as well as a rearward direction it is found that the vehicle will not create sufficient spray to be a hazard to other road users.

Referring now to the embodiment shown in Figures 3 and 4, the screen assembly shown therein comprises two portions namely a lower portion 51 and an upper portion 52, the lower portion 51 being slidable in a generally vertical direction in slides 53 and 54 which extend upwardly from a horizontally extending bar 55 rigidly connected at one end to a shackle assembly 56 mounted on the axle 57 of a wheel having a tyre 58 which is disposed just in front of the screen assembly 51 and 52. The upper screen portion 52 is secured to the chassis 59 of the vehicle so as to depend therefrom.Furthermore both of said screen portions 51 and 52 embody means which are arranged to intercept spray which in use will be flung rearwardly from the tyre 58 when the associated vehicle is travelling over a wet surface, water then being separated from said spray by the screen 51, 52 and re-deposited onto the road surface in a manner which inhibits the formation of spray. The detailed construction of the screen portions 51 and 52 does not however form any part of the present invention.

There is also provided a linkage which intercon nects said chassis 59 and the lower screen portion 51 and such linkage comprises an upper link 60 which is pivotally connected at its upper end to the underside of the chassis 59 and which is pivotally connected at its lower end to an intermediate link 61 which is connected at its lower end to a downwardly projecting plate 62. The plate 62 thus forms part of the link 61 and it is pivotally connected to one of at least two alternative pivot points (indicated by reference numerals 63 and 64) by means of which said plate can pivot relative to the bar 55. The plate 62 is also pivotally connected to a link 65 which at its upper end is pivotally connected to a peg 66 which is connected to the inner tube 67 vertically slidable in an outer tube 68. The outer tube 68 has a slot 69 in its wall through which said peg 66 projects.At its upper end the inner tube 67 has a projecting peg 70 which forms a fulcrum for a lever 71 which is pivotally connected at one end to a link 72 which is itself pivotally connected to the lower screen portion 51.

The other end of said lever 71 is pivotally connected to the upper end of a fluid pressure actuated piston and cylinder assembly 73 pivotally connected at its lower end to a bracket 74 which is mounted on the bar 55.

Considering for the moment a situation which is shown in Figure 3 i.e. a situation in which the lower screen portjon 51 is in its lowered, operative, position and assuming that an increased load is then placed on the vehicle chassis 59, the link 60 will be depressed so as to cause a downwards pivotal movement of the link 61 which thus pivots in an anti-clockwise direction relative to the bar 55 by virtue of the pivotal connection between the plate 62 and one of the pivot points 63 and 64. This pivotal movement will have the effect of lifting the link 65 and thereby similarly lifting the inner tube 67. Thus the fulcrum which is formed by said peg 70 of the lever 71 is also lifted and this in turn will lift the screen portion 51 to compensate for the downward motion of the chassis 59.At the same time the extra loading placed on the chassis 59 will have had the effect of slightly compressing the tyre 58 thus resulting in a slight downward movement of the arm 55 and this movement will also enhance the anticlockwise pivotal movement of the plate 62 relative to the arm 55, thereby adding to the upward movement of the fulcrum 70 of the lever 71. The lower edge of said lower screen portion 51 will thus be maintained at a substantially constant distance (just above the road surface 75) irrespective of the loading placed on the vehicle and the compression of the vehicle tyre 58.

In addition however the aforementioned piston and cylinder assembly is also able to effect vertical sliding movement of the lower screen portion 51. In the position shown in Figures 3 and 4 said piston and cylinder unit is in its expanded condition so that the adjacent end of the lever 71 is in a relatively raised position, thus tilting said lever 71 to a position in which the lower screen portion 51 is in its operative or lower position. Said piston and cylinder unit 73 can however be retracted in order to pivot said lever 71 in an anti-clockwise direction about its fulcrum 70, thereby lifting said lower screen portion 51 on the slides 53 and 54 in order to move it to its inoperative or upper position.Retraction of said piston and cylinder unit 73 may either be effected manually by means of a driver operable control switch which can for example be used to lift the lower screen portion 51 if the vehicle is travelling over dry road surfaces.

Alternatively if the vehicle is travelling over wet road surfaces then the piston and cylinder unit 73 can be automatically controlled by means sensitive to the vehicle road speed so that the lower screen portion 51 is set in its operative position whenever the vehicle is travelling for example at a speed above 30 m.p.h., the piston and cylinder unit 73 being retracted to lift the lower screen portion 51 when the vehicle speed falls to, say, 25 m.p.h.

Figure 5 shows in diagrammatic form an air and electrical circuit which can be used to control the piston and cylinder unit 73. Said circuit shows a mains pressurised air supply 76 which passes through a pressure regulator 77 to a changeover solenoid 78, said solenoid having pressurised air connections 79 and 80 to the piston and cylinder unit 73. Solenoid 78 is also electrically connected to a master switch 81 (which is driver-operable), a resetting delay timer 82 and means 83, such as for example a speedometer or tachograph which is sensitive to the vehicle road speed. The vehicle battery, indicated by reference numeral 84 is connected to said delay timer 82 and said speedometer ortachograph 83 to provide a power supply.The present invention is not concerned with the detailed operation of the delay timer 82 but the situation is such that when the contact arm 85 of the means 83 sensitive to the vehicle road speed is in a closed condition then the solenoid 78 will be actuated to cause pressurised air to flow into that end of the piston and cylinder unit 73 which will cause it to expand and thereby lower the lower screen portion 51. The operation of the delay timer 82 is however such that the screen portion 51 is not lowered until the end of a predetermined delay period after the vehicle has reached a pre-selected speed.Alternatively, where the means 83 comprises a speedometer, the arrangement may be such that suitable contacts are provided on the speedometer to ensure that the unit 73 will be activated to lower the screen portion 51 at a predetermined speed and again to raise it at another, lower predetermined speed in order to avoid "hunting".

Figures 6 and 7 show an alternative embodiment according to the present invention in which a load carrying vehicle 86 is provided on each of its two longitudinal sides with a screen 87 or 88 and, at its front end a further screen 89. Each of said side screens 87 and 88 is connected to a pair of similar linkages, indicated in Figure 6 by reference numerals 90 and 91 respectively which are also connected to the chassis 92 of the vehicle by means of downwardly depending links 93 and 94. Furthermore the two linkages 90 and 91 are interconnected by a link arm 95 which is arranged to transmit to the linkage 90 movement initiated by the linkage 91.The latter is connected to a piston and cylinder unit 96 which can thus be actuated either to raise or lower the associated side screens 87 or 88, such actuation of the piston and cylinder unit 96 being effected either under the control of the driver or automaticaily by means sensitive to the road'speed of the vehicle as above explained. The front screen 89 is also con nectedto a piston and cyiinder unit which is indicated by reference numeral 97 and the side screen 88 will be connected to a third piston and cylinder unit so that all three piston and cylinder units can be arranged to operate in unison.The front screen 89, which is positioned in front of the front wheels of the vehicle 86 which act, when in the lowered position, as an air dam which will help to improve the aerodynamic efficiency of the vehicle when travelling at or above a predetermined speed at which said air dam is in its lowered or operative position. The side screens 87 and 88 will also act when in their lowered positions to control the flow of air beneath the vehicle and in addition when the vehicle is travelling along a wet road surface said side screens 87 and 88 will help to control any spray which might otherwise tend to be ejected laterally from the vehicle.

Figure 8 shows a further embodiment of the present invention in which there is a vehicle screen assembly which in this case comprises two relatively pivotable parts 98 and 99, the upper part 98 being pivotally connected to the underside of the vehicle chassis 100 whereas the lower screen part 99 is pivotally connected to a link 101 which is itself pivotally connected at the point 102 to a straight link 103 and a cranked link 104. The latter is pivotally connected to the upper end of a piston and cylinder unit 105 whose lower end is pivotally connected to the link 101 and the lower end of said cranked link 104 is connected to a further link 106 which is pivotally connected to a lever 107 having a fulcrum point 108 whereby it can pivot on a bar 109 connected to the axle assembly of the wheel and tyre 110.The upper end of said lever 107 is pivotally connected to a further link 111 pivotally connected to the underside of the chassis 100. The pivot point 108 is one of the alternative fulcrum points between the lever 107 and the bar 109 a further pivot point being indicated by reference numeral 112 and these alternative pivot points, like the alternative pivot points 63 and 64 shown on Figure 3 can be used to suit tyres 110 or 58 of different characteristics.Thus the appropriate pivot point will be chosen to suit the compression characteristics of the tyre 110, the arrangement being such that a tyre which has relatively "soft" characteristics (so that increasing load on the vehicle will result in a relatively greater compression of the tyre), a pivot point will be chosen to provide a relatively greater pivotal movement of the lever 107 (in the case of the construction shown in Figure 8) or the plate 62, in the case of the construction shown in Figures 3 and 4. So far as the construction shown in Figure 8 is concerned however an increas in the load on the vehicle, accompanied by compression of the tyre 110, will result in a relative pivoting of the screen portions 98 and 99 in such a direction as to cause the lower portion 99 to be lifted in order to maintain its lower edge at a substantially constant distance from the road surface, assuming that the piston and cylinder unit 105 is in an expanded condition in order to set the screen portion 99 in its lower or operative position. Retraction of said piston and cylinder unit 105 will of course effect lifting of the screen portion 99 into an inoperative position.

Claims (17)

1. A spray or air control screen assembly for a road vehicle comprising a screen, means for mounting said screen on the vehicle so that it is movable between an operative position in which its lower edge lies adjacent to the road surface and an inoperative position which is above its operative position, and power-actuated means for moving said screen in at least one direction between said operative and inoperative positions.

2. An assembly as claimed in Claim 1 wherein said power-actuated means is operatively connected to control means which is sensitive to the road speed of the vehicle.

3. An assembly as claimed in Claim 2 wherein said control means is arranged to ensure that the screen is disposed in its operative position at a predetermined vehicle road speed and that the screen is lifted into its inoperative position at another predetermined vehicle road speed which is lower than said first-mentioned vehicle road speed.

4. An assembly as claimed in Claim 2 or Claim 3 wherein there is provided a driver-operable master control which in use is adapted to override said control means which is sensitive to the road speed of the vehicle whereby the screen can be set in its inoperative position when desired irrespective of the vehicle road speed.

5. An assembly as claimed in any one of the preceding claims wherein said screen is disposed at the front of the vehicle in front of the front wheels thereof.

6. An assembly as claimed in any one of Claims 1-5 wherein said screen extends along a side of the vehicle in a direction parallel to the longitudinal axis of the vehicle.

7. An assembly as claimed in Claim 6 when dependent upon Claim 5 wherein said front screen and said side screen are mechanically interconnected so as to be movable together between their operative and inoperative positions.

8. An assembly as claimed in any one of Claims 1-4 wherein said screen is disposed to the rear of a vehicle tyre so as to be adapted to intercept water and spray thrown rearwardly from said tyre.

9. An assembly as claimed in Claim 8 wherein said water and spray intercepting screen comprises an upper portion and a lower portion which is vertically slidable relative to the upper portion.

10. An assembly as claimed in Claim 8 wherein said water and spray intercepting screen comprises two portions which are hingedly connected together.

11. An assembly as claimed in any one of the preceding claims wherein said power-actuated means comprises a fluid-pressure actuated piston and cylinder unit.

12. An assembly as claimed in any one of the preceding claims wherein means are provided for adjusting the position of the lower edge of the screen (when the latter is in its operative position) relative to the load-carrying part of the vehicle in dependence upon the load carried by the said load-carrying part, whereby said lower edge of the screen (when the latter is in its operative position) will be maintained at a substantially constant distrance from the road surface irrespective of the weight of the load which is carried by said loadcarrying part.

13. An assembly as claimed in Claim 12 when dependent upon Claim 9 or Claim 10, wherein means are also provided for maintaining the lower edge of the lower portion of the screen (when the latter is in its operative position) at a substantially constant distance from the road surface irrespective of the compression applied to the associated tyre by the load applied to the vehicle.

14. An assembly as claimed in Claim 13wherein said means for maintaining the lower edge of the lower portion of the screen at a substantially constant distance from the road surface irrespective of the tyre compression comprises a linkage which includes a pair of pivotally connected links having two or more alternative pivot points.

15. An assembly as claimed in any one of the preceding claims wherein there is provided a vehicle windscreen wiper mechanism which is operatively connected to said power-actuated means so that the latter will always move said screen into its upper, inoperative position unless said vehicle windscreen wiper mechanism is in operation.

16. An assembly as claimed in Claim 2 wherein said control means is arranged to activate said power-actuated means to move said screen into its operative position at the end of a predetermined delay period after the associated vehicle has achieved a pre-selected speed.

17. A spray or air control screen assembly for a road vehicle substantially as hereinbefore described with reference to and as shown in Figures 1 and 2, or Figure 3 and 4, or Figure 5, or Figure 6 and 7, or Figure 8 of the accompanying drawings.