GB2117725A - Anti jack-knifing devices for articulated vehicles - Google Patents

Abstract

Rams 30, 32 are connected between a trailer and a tractor unit to control relative pivoting. They are in parallel with a conventional steering ram 24 in a hydraulic system 34, 36, 38, 40 which provides servo assistance to the steering in the tractor unit. Thus, relative pivoting is allowed when the steering column 42 is turned, but not otherwise. <IMAGE>

Description

SPECIFICATION Anti jack-knifing devices for articulated vehicles This invention relates to articulated vehicles, and more particularly to devices for reducing the dangerous tendency of articulated vehicles to jack-knife, for example during emergency braking of the vehicle.

There have been a number of prior proposals to try to solve this problem. For example, it has been sugested to provide a brake on the turntable pivot itself. However, this approach merely dampens any tendency of the tractor and trailer to pivot out of line with each other, and has not proved adequate to prevent jack-knifing. Accordingly, much effort is currently being expended on the development of control systems for the brakes on the wheels of the articulared vehicle, to detect any tendency to jack-knife during braking and apply the brakes in such a manner as to compensate for the tendency. However, this requires sophisticated electronic and mechanical systems, in addition to a hydraulic system, and is therefore very expensive. Moreover, these control systems have still not attained a practical, commercial level.

The present invention provides an articulated vehicle comprising a trailer pivotably connected to a tractor unit provided with steering means, and means for controlling relative pivoting between the trailer and the tractor unit, wherein the control means is connected to control pivoting in response to the steering means so as to allow or cause the trailer and tractor unit to pivot relative to each other in response to the steering of the tractor unit but to resist other relative pivoting between the trailer and tractor unit.

Preferably the pivoting control means comprises one or more hydraulic rams connected between the trailer and the tractor unit, off the axis of the pivoting connection. Preferably the ram or rams are double acting. Where the steering means has hydraulic servo assistance, the ram or rams may be connected directly to that. Alternatively, they may be connected to their own hydraulic servo arrangement, suitably controlled by the steering wheel of the steering means in the tractor unit.

The invention also encompasses anti jackknifing devices arranged for fitting to an articulated vehicle to provide a vehicle as defined above.

Examples of the invention will now be described, referring to the accompanying diagrammatic drawings, in which: Figure 1 shows in plan view the general arrangement of an articulated vehicle fitted with an anti jack-knifing device, Figure 2 shows schematically the hydraulic arrangement of the vehicle of Fig. 1, and Figures 3A to 3Fshow various alternative hydraulic ram arrangements for anti jack-knifing devices according to the invention.

The vehicle shown in Fig. 1 comprises a tractor unit 10 and a trailer 1 2. The tractor unit 10 has steerable front wheels 14, with kingpins 16, steering arms 18, 20 and a connecting track rod 22 as is conventional.

The steering is hydraulically servo assisted, by means of a double-acting steering ram 24 acting on the steering arm 18; again this is a well known arrangement.

Adjacent its rear wheels 26, the tractor unit 10 has the usual turntable 27, on which is pivotably connected to the front of the trailer 1 2. The trailer is thus supported by the wheels 26 of the tractor unit and its own rear wheels 28.

To help prevent jack-knifing, two dubleacting hydraulic rams 30, 32 are provided, extending between conections points on the chassis of the tractor unit 10 and the front of the chassis of the trailer 1 2. There is one of these rams on each side of the pivot axis of the turntable 27, and forward of the turntable 27. The connections to the tractor unit and trailer are provided by universal Hooke's joints, so that they pivot freely. The connections to the trailer are provided with quick release pins, so that when the trailer is deteached from the turntable 27, the rams 30, 32 are easily detached from th trailer and stowed on the chassis of the tractor unit.

The hydraulic connections to the rams 30, 32 can be seen from Fig. 2. The servoassisted steering system has a conventional hydraulic circuit including the steering ram 24, a reservoir 34 for hydraulic fluid, a pump 36, an accumulator 38, and a servo steering valve 40. The latter is acted on by a steering column 42 and the driver's steering wheel in the cab of the tractor unit. It acts to divert hydraulic fluid under pressure through pipes 45, to either a side A or a side B of the piston 44 in the steering ram 24, reinforcing the driver's effort on the steering wheel in order to turn the front wheels 1 4 to steer the vehicle. Once the wheels 14 are in the required position (set by the position of the driver's steering wheel) fluid is diverted directly back from the valve 40 to the reservoir 34, and hydraulic pressure in the ram 24 keeps the wheels 14 steady.

Unlike a conventional steering system, however, pipes 46 lead to the rams 30, 32, connecting them in parallel with the ram 24 and in back-to back parallel with each other, as indicated by the reference letters A and B.

Although Fig. 2 shows these pipes 46 directly connected to the sides A and B of the ram 24, it will be appreciated that in practice they are likely to be connected to the respective pipes 45.

The effect of these hydraulic connections is that when the driver turns his steering wheel during normal driving, not only does the ram 24 turn the front wheels 14, but also fluid flows to the rams 30, 32 to accommodate the pivoting between the tractor unit and the trailer about the turntable 27, which will naturally occur as a result of road influences, e.g.

during negotiation of a bend or corner. However, the rams will only allow such pivoting to the extent dictated by the steering wheel position, and will tend to resist greater or lesser amounts of pivoting. The relative crosssections of the rams 30, 32 and the steering ram 24, and the mounting positions of the rams 30, 32 relative to the turntable 27, should be chosen such that the amount of pivoting of the tractor and trailer thus provided corresponds to that which would occur naturally when steering the vehicle during normal driving. Furthermore, depending on factors such as the geometry of mounting of the rams, the ratio of the extent of travel of their pistons to the angle between the tractor and trailer may not be linear. A proportional valve may be included in the hydraulic circuit to vary the fluid flow to the rams to compensate for this.

If while driving an emergency occurs at which there is a tendency to jack-knife, the hydraulic pressure in the rams 30, 32 will act against this tendency. They will act to try to keep the tractor and trailer in the pivoted position relative to each other appropriate to the current setting of the driver's steering wheel. Moreover, in a very serious case, the driver has the ability to exercise control over the tendency to jack-knife by appropriate turning of the steering wheel, which will drive the rams 30, 32 accordingly.

The rams 30, 32 have the added advantage that during manoeuvring of the vehicle in confined spaces, they cause pivoting between the tractor and trailer, which makes the vehicle much easier to handle. If desired, shut-off valves 48 may be provided in the pipes 46. When closed, these leave the rams 30, 32 in a closed circa, and effectively lock the turntable against pivoting. This may be desirable when the vehicle is parked. A further, normally closed valve 50 may also be provided for use when the valves 48 are closed to connect the pipes 46 together. The rams 30, 32 will then "float", i.e. they will offer no appreciable resistance to relative pivoting of the trailer and tractor, since such pivoting will merely cause displacement of fluid from one side of each ram to the other through the valve 50.The valves 48, 50 are suitably arranged so that they can be controlled manually from the driver's cab. Alternatively or additionally, they may be arranged to operate automatically when the angle between the trailer and tractor is greater than a given amount, say + 45 , so that the rams "float" to facilitate maneouvring and reversing. Although in the above example, the rams 30, 32 are driven from the steering hydraulic system, it is possible for it to have its own separate hydraulic system if desired. Such a system would have a separate spool valve to control the servo action of the rams 30, 32, which would be mechanically controlled from the steering column 42.The steering system would then be separately mechanically controlled from the steering column, and may even be purely mechanical if desired (though this would be unusual in a modern vehicle).

However, the arrangement of Fig. 2 is preferable, since obviously it is more economic for the ram 24 and the rams 30, 32 to have a common hydraulic supply and valve 40.

The ram positions shown in Figs. 1 and 2 are exemplary only, and many other arrangments are possible. Figs. 3A to 3F show some other possibilities. In Figs. 3A and 3B, there is only one ram 30, connected to the trailer 1 2 by a detachable Hooke's joint 52 and to the tractor 10 by a Hooke's joint 54. The pipes 46 of Fig. 2 would connect this single ram in parallel to the ram 24. Figs 3C to 3F show various arrangements of two rams 30, 32. Hydraulically, these would be connected similarly to those in Fig. 2. Again, their Hooke's joint connections to the trailer and tractor are designated, by reference numbers 52 and 54 respectively. In all these cases, the Hooke's joint 52 may have a quick release pin, as previously, to facilitate disconnection of the trailer from the tractor, and the ram can then be stowed on the tractor unit.

Claims (12)

1. An articulated vehicle comprising a trailer pivotably connected to a tractor unit provided with steering means, and means for controlling relative pivoting between the trailer and the tractor unit, wherein the control means is connected to control pivoting in response to the steering means so as to allow or cause the trailer and tractor unit to pivot relative to each other in response to the steering of the tractor unit but to resist other relative pivoting between the trailer and tractor unit.

2. An articulated vehicle according to claim 1, wherein the pivoting control means comprises one or more hydraulic rams connected between the trailer and the tractor unit, off the axis of the pivoting connection.

3. An articulated vehicle according to claim 2 wherein the ram or rams are double acting.

4. An articulated vehicle according to claim 2 or claim 3 wherein the steering means includes a hydraulic system providing servo assistance thereto, and the hydraulic ram or rams of the control means is/are connected to that hydraulic system.

5. An articulated vehicle according to claim 4 wherein the ram or rams of the control means is/are connected in parallel with a ram providing the servo assistance to the steering means.

6. An articulated vehicle according to claim 5 in which the control means has two said rams which are double-acting, connected in back-to-back parallel with each other.

7. An articulated vehicle according to any one of claims 4, 5 and 6 including valve means arranged so that the ram or rams in the control means may be disconnected from the hydraulic system of the steering means.

8. An articulated vehicle according to any one of claims 4 to 7 including valve means arranged to vary the fluid flow to the ram or rams in the control means to compensate for non-linearity in the relation between the extent of travel of said ram or rams and the angle of pivoting between the trailer and the tractor unit.

9. An articulated vehicle according to any one of claims 2 to 8 including valve means operable to allow the ram or rams in the control means to float so as to permit relative pivoting when desired between the trailer and tractor unit independently of the steering means.

10. An articulated vehicle according to claim 9 wherein said valve means is arranged to operate automatically to allow the ram or rams in the control to float when the trailer and tractor unit have pivoted relative to each other by more than a given amount.

11. An articulated vehicle according to claim 2 or claim 3 wherein the hydraulic ram or rams of the control means is/are connected in a hydraulic system which is independent of a hydraulic system (if any) associated with the steering means, and which is controlled by the steering wheel of the steering means in the tractor unit.

12. An articulated vehicle having an anti jack-knifing device substantially as any described herein with reference to the accompanying drawings.

1 3. An anti jack-knifing device arranged for fitting to an articulated vehicle and for connection to steering means thereof so as to produce an articulated vehicle according to any one of the preceding claims.