GB2575854A

GB2575854A - Trailer towing-control apparatus

Info

Publication number: GB2575854A
Application number: GB1812183.0A
Authority: GB
Inventors: Walton Abel John
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-07-26
Filing date: 2018-07-26
Publication date: 2020-01-29
Also published as: GB201812183D0

Abstract

Trailer towing-control apparatus 10 comprising drawbar 12 with connector 16 at its front and articulated connection 22 at its rear. Connector 16 is pivotally connectable to towing vehicle 18, and connection 22 is attachable to trailer body 24 such that trailer body 24 pivots horizontally relative to drawbar 12. Apparatus 10 further comprises a powered actuator for pivoting trailer body 24 horizontally about connection 22. Apparatus 10 further comprises a servo-controller that controls the pivoting of connection 22 such that, when towing vehicle 18 and trailer 100 are reversing, articulated connection 22 points in the direction in which towing vehicle 18 is being steered so that drawbar 12 lies along the front-back axis of vehicle 18, or to the side of the axis in which vehicle 18 is being steered.

Description

TRAILER TOWING-CONTROL APPARATUS

This invention relates to trailer towing-control apparatus for the directional control of a trailer when connected to a towing vehicle, and more particularly, which assists in steering the trailer in the reverse mode of travel.

It is well known that it is difficult to reverse (back up”) a towing vehicle and trailer. This is due to the articulation point of the trailer coupling being between the towing vehicle’s rear wheels and the wheels of the trailer. The trailer is thus pushed from behind its wheels so that it turns in the opposite direction to that in which the towing vehicle turns. WO2006/129284 discloses a trailer drawbar which is pivotally connectable at a forward end to the towing vehicle. To address the reversing problem, a rearward end of the drawbar is pivotally connected to the body of the trailer at a position rearward of the trailer’s axle. (Forward” and rearward” are used here and elsewhere in this specification in the sense of the towing vehicle’s directions of forward and rearward motion). During forward travel of the towing vehicle and trailer, the pivotable connection at the drawbar rearward end is locked, to hold the drawbar in the straight ahead direction relative to the trailer body. When it is desired to manoeuvre the towing vehicle and trailer in reverse, articulation of the drawbar’s forward end relative to the towing vehicle is restrained in the horizontal plane, so that the drawbar is held to extend straight backwards from the towing vehicle. At the same time, the pivotable connection at the drawbar’s rearward end is unlocked, so that the trailer body is free to pivot relative to the drawbar. As this pivotable connection is rearward of the trailer axle, the rolling resistance forces acting on the trailer wheels cause the trailer body to pivot relative to the drawbar with a castor action. The trailer body therefore follows” the manoeuvres of the drawbar in a stable way, easily apparent and predictable even to an unskilled vehicle driver.

This arrangement generally works well for small, lightweight trailers. However, larger, heavier trailers (e.g. heavy trailers with spaced, fixed, twin axles which have a higher rolling resistance due to tyre scrub on cornering) can generate unacceptably high bending forces at the constrained forward end of the drawbar when manoeuvred in reverse. The problem can arise when reversing even lightweight trailers around a sharp and/or steeply uphill turn. A long, steeply downhill reverse manoeuvre can also be difficult, as when the towing vehicle is braked, the trailer body may tend to overrun the rearward pivot and begin to jack-knife under the castor action. If the trailer is parked at the end of a reversing manoeuvre with the drawbar at an angle, the trailer body may need to be manhandled into alignment with the drawbar before the drawbar can be locked relative to the trailer body so that the vehicle and trailer can be driven off in the forward direction again. In the case of a large, heavy trailer, such manhandling may be difficult or impossible.

Arrangements are known in which the trailer wheels are steerable so as to mitigate the bending forces on the drawbar to some extent. However, excessive bending forces may still arise. Also, a trailer which uses such a steerable wheel method of reverse steering will in many situations move crabwise”, in directions which are not readily foreseeable by the novice towing vehicle driver. This problem may be exacerbated where rearward visibility is restricted, so that the direction of the trailer wheels cannot readily be seen. There is therefore scope for improvement of trailer towingcontrol apparatus used to steer trailers in the reverse mode of travel.

The present invention provides a trailer towing-control apparatus comprising a drawbar having a connector at its operative forward end, the connector being pivotally connectable to a towing vehicle, the drawbar having an articulated connection at its operatively rearward end, the articulated connection being attachable to the trailer body or chassis; the towing-control apparatus further comprising a powered actuator operatively arranged to move the articulated connection whereby the connected trailer body or chassis pivots relative to the drawbar in a horizontal plane; the towingcontrol apparatus further comprising a servo-controller which controls the powered actuator to move the articulated connection in the same angular direction that the towing vehicle is being steered in during reverse travel of the towing vehicle and trailer, to thereby bring the drawbar to an equilibrium position in the horizontal plane in which it is in alignment with the fore and aft axis of the towing vehicle, or lies to the same side of that axis in the horizontal plane as the towing vehicle is being steered in.

Because the direction of the drawbar relative to the towing vehicle is controlled during reversing manoeuvres through the powered actuator varying the angle of the vehicle body or chassis relative to the drawbar in the horizontal plane, there is no need to lock the connector at the drawbar’s operative forward end against angular movement, which means that no bending stresses need to be (or can be) imposed on the drawbar to produce reverse steering movements of the trailer. The position and current direction of motion of the trailer are also easily visible to the towing vehicle driver, even when their rearward vision is limited, e.g. restricted to wing mirrors. Because the drawbar achieves an equilibrium position which is at least in alignment with the towing vehicle’s fore and aft axis, or even lies to the same side of that axis in the horizontal plane as the towing vehicle is being steered in, the pushing force of the towing vehicle is applied to the trailer during reverse travel with greater mechanical advantage than is possible with some known trailer towing-controls.

Because the steering of the trailer does not rely on a castor action, the articulated connection is attachable to the trailer body or chassis at any suitable point, including forward of the trailer axle(s). This gives greater freedom in designing the trailer body and chassis; where desired, permits the use of a shorter drawbar, saving trailer weight and expense of materials; and where desired permits tighter trailer turning circles (because a drawbar articulated to the trailer body/chassis suitably forward of the trailer axle(s) does not interfere with the trailer wheels as much as a drawbar articulated further back).

The drawbar may be made quite short, for example mounted to the A-frame of a trailer or caravan so as to form a part of the trailer tongue/tow hitch assembly. Thus it may be fitted or retrofitted to the trailer as part of a trailer tongue/tow hitch assembly, whereby no or very little structural alteration is needed to the remainder of the trailer in order to achieve the benefits of the present invention.

When the towing vehicle and trailer are moving in the forward direction, the powered actuator and servo-controller may be used to move the articulated connection so that the drawbar is aligned along the trailer’s fore and aft axis; whereupon the powered actuator may be used or controlled so as to hold or lock the drawbar in this position.

The servo controller may comprise a control rod or cable connectable to the rear of the towing vehicle, offset from the drawbar connector so as to operate a servo control valve in response to angular movement of the drawbar relative to the towing vehicle in the horizontal plane; the control valve regulating the supply of power fluid to the powered actuator.

The control rod or cable may operate a lever mounted on the drawbar; the vehicle, drawbar, control rod/cable and lever forming a parallelogram mechanism.

A piston and cylinder may be connected between the control rod and the drawbar. Fluid pressure in the cylinder may be arranged to operate the servo control valve.

A solenoid valve may be provided to fluidically lock the piston and cylinder to provide jack-knifing control under braking, during forward motion of the towing vehicle and trailer.

An opposed pair of such control rods/cables may be provided, one each on either side of the drawbar connector. An opposed pair of such pistons and cylinders may be provided.

The control rod or cable may operate the servo control valve via a belt drive, chain drive, gearing or a connecting rod.

The servo control valve may be operated by a Bowden cable having a sheath anchored to the drawbar and an end couplable to the rear of the vehicle, offset from the drawbar connector so as to operate the control valve in response to angular movement of the drawbar relative to the towing vehicle in the horizontal plane.

The powered actuator may be pressurised fluid powered; the servo controller comprising an an electrically powered pump (e.g. powered from the towing vehicle’s electrics). The powered actuator may comprise a piston and cylinder, for example an opposed pair of pistons and cylinders. Alternatively, a single, double acting piston and cylinder may be used.

A solenoid valve may be used to fluidically lock the piston and cylinder so as to hold the drawbar in the fore and aft alignment with the trailer body/chassis during forward motion of the vehicle. For example, the solenoid valve may be reversing light switch operated, with 0V input = valve closed.

Alternatively, the powered actuator may be electrically powered, e.g. from the towing vehicle electrics.

The angle between drawbar and towing vehicle and/or changes in this angle is determined by a rotary sensor or encoder, a linear movement or distance sensor or encoder, or a non-contact proximity sensor. The determined angle may be used to provide an error value used by the servo controller or used to operate the servo control valve.

The invention and some of its lurther advantages and optional features may be better understood from the following description of illustrative embodiments, made by way of non-limiting example and with reference to the drawings, in which:

Figure 1 is a diagrammatic plan view of a trailer embodying the present invention, shown connected to a towing vehicle;

Figure 2 is a diagrammatic plan view of another trailer embodying the present invention, shown connected to a towing vehicle;

Figures 3 and 4 are diagrammatic plan and side views of one example of servoactuated drawbar and its pivotal connection to a trailer body or chassis, which may be used in implementing the present invention; and

Figure 5 is a further diagrammatic plan view of a trailer, drawbar and towing vehicle embodying the present invention.

Figure 1 shows towing-control apparatus 10 for a trailer 100. The towing control apparatus 10 comprises a drawbar 12 formed as a structural framework fabricated from steel tubes 14. The drawbar 12 has a connector or hitch 16 fixed to its operative forward end, the connector being pivotally connectable to a towing vehicle 18. The connector may be any suitable articulated coupling for attaching a trailer to a towing vehicle; for example a conventional cup for receiving a towing ball 20 fixed to the back of the towing vehicle, or a conventional ring coupling for reception in a towing pintle fixed to the back of the towing vehicle.

The drawbar 12 has an articulated connection at its operatively rearward end, by which it is connected to the chassis of the trailer 100 so as to allow relative pivoting of the trailer body 24 and the drawbar 12 about a generally vertical axis passing through the drawbar rearward end. For example, the articulated connection may comprise a generally vertically arranged hinge pin 22 pivotally interconnecting the drawbar 12 and a cross-beam 26 of the trailer chassis. However, the exact form of the articulated connection is not essential to the invention and any suitable connection may be used, that allows the drawbar to be coupled to the trailer body 24 or chassis at its rearward end, for relative pivoting movement in the horizontal plane. Moreover, because (as further explained below) movement of the drawbar relative to the body 24 of the trailer 100 is servo-assisted and controlled, the trailer 100 does not rely on a castor action for control of its steering movement in the reverse mode of travel. Therefore the articulated connection of the operatively rearward end of the drawbar 12 may be at any suitable point on the trailer chassis or body 24, and is not confined to regions rearward of the trailer axle(s). By way of illustrative example, Figure 1 schematically shows a large, heavy, twin axled trailer 100 in which pivoting movement of the trailer body 24 relative to the drawbar 12 is servo-actuated and controlled, and in which the articulated connection between these components still happens to be rearward of both trailer axles, as taught by WO2006/129284. However, in other examples (some of which are described later on in this specification), the articulated connection between the trailer chassis or body 24 and the operatively rearward end of the drawbar 12 may be positioned close to, at, (between,) or forward of the trailer axle(s). To provide for evenly balanced forces when towing the trailer 100 straight ahead or reversing it straight backwards, the articulated connection 2 2 is usually (but need not be) provided at a suitable point along the fore-and-aft centreline of the trailer body or chassis 24.

To pivot the trailer body or chassis 24 in the horizontal plane relative to the drawbar 12 about the articulated connection 22, so as to ensure thatthe trailer 100 is steered in the desired direction during reverse travel, the towing-control apparatus 10 further comprises a powered actuator operatively arranged to pivot the articulated connection

22. As shown in Figure 1, the powered actuator takes the form of an opposed pair of hydraulic cylinders and pistons 28a, 28b, each pivotally connected between a respective end of a crossmember 14a of the drawbar framework, and a cross-beam 26a of the trailer chassis. For contraction, the cylinders 28a and 28b are selectively supplied with pressurised hydraulic fluid over hydraulic lines 30a and 30b, by a high pressure pump 32, which draws hydraulic fluid from a reservoir 34. The pump 32 may be electrically operated, e.g. from the towing vehicle 18’s power supply. The illustrated cylinders 28a and 28b are double-acting, with their ends opposite to the supply lines 30a and 30b are interconnected by a lockup line 36 containing a solenoid valve 38. The solenoid valve 38 is opened for reverse travel of the trailer 100, thereby unlocking the articulated connection 22 for pivoting movement of the trailer body 24 relative to the drawbar 12. For example, the solenoid valve may be electrically connected to the towing vehicle 18’s reversing light circuit, thereby opening automatically to unlock the drawbar 12 for pivoting movement relative to the trailer body 24, when the towing vehicle 18 is put into reverse gear. When the vehicle 18 is driven in the forward direction the solenoid valve 38 initially remains open if required, so as to allow the pistons and cylinders 28a, 28b to bring the drawbar 12 into the straight-ahead position relative to the trailer body 24. When in this position, the solenoid valve 38 may be closed, locking the drawbar 12 against pivoting movement about the articulated connection 22, for continued forward movement of the trailer 100 and towing vehicle 18. Instead of the opposed piston and cylinders 28a, 28b, any other suitable powered actuators may be used to apply bi-directional torque between the trailer body or chassis 24 and the drawbar 12 about the articulated connection 22, to cause the required relative pivoting movement of these components about the articulated connection 22. For example, a single double acting piston and cylinder actuator or an opposed pair of single acting pistons and cylinders may be provided in place of the opposed pair of double acting piston and cylinder actuators 28a, 28b shown in Figure 1. Still other arrangements of such actuators are within the competence of the skilled person, to ensure the required torque application and relative movement about the articulated connection 22. For example other actuators may be pneumatically operated, e.g. from the towing vehicle’s pneumatic system. Alternatively or additionally, electrically operated, reversible (bi-directional) actuators may be used, e.g. an electric motor connected to: a worm and wheel drive, a screw and nut drive, a ball screw drive, a rack and pinion drive (curved or straight), etc; or one or more electrically powered linear motors.

The towing-control apparatus 10 further comprises a servo-controller which controls the powered actuator 28a, 28b to move the articulated connection 22 in the same angular direction that the towing vehicle 18 is being steered in during reverse travel of the towing vehicle 18 and trailer 100, to thereby bring the drawbar 12 to an equilibrium position in the horizontal plane in which it is in alignment with the fore and aft axis of the towing vehicle 18, or lies to the same side of that axis in the horizontal plane as the vehicle 18 is being steered in. The towing control apparatus 10 shown in Figure 1 comprises an anti-jack knifing mechanism similar to that described in WO2006/129284. This mechanism operates to lock up the towing connector 16 against pivoting movement relative to the towing vehicle 18 in the horizontal plane, when the trailer 100 and towing vehicle 18 are moving forward and the towing vehicle’s driver operates the service brake (footbrake). To that end, the anti-jack knifing mechanism comprises a pair of parallel control rods 40a, 40b, removably pivotably connectable at their forward ends to the back of the towing vehicle 18, on either side of, and equidistant from, the towing ball 20 and drawbar connector 16. The rearward ends of the control rods 40a, 40b are pivotally coupled to a lever 42, which is pivotally mounted at its centre 44 to the structure of the drawbar

12. The control rods 40a, 40b, lever 42 and towing vehicle 18 thereby form a parallelogram linkage. Outer ends of the lever 42 are connected to a crossbar 14b or other suitable structural part of the drawbar 12, via respective hydraulic piston and cylinder units 46a, 46b. Corresponding cylinders of each unit respectively sealed by their pistons, are interconnected by a crossover line 48. This line may be blocked by a solenoid valve 50, which may be connected into the towing vehicle’s brake light circuit. Thus, when the driver operates the towing vehicle’s service brake, the solenoid valve closes and locks the parallelogram linkage 42, 40a, 40b, 18. Pivoting movement about the towing ball 20 and towing connector 16 is thereby resisted, providing an anti-jack knifing function.

The control rods 40a, 40b and hydraulic cylinders 46a and 46b may be used as the error signal sensor for the servo-controller of the trailer towing-control apparatus 10, when the trailer 100 and towing vehicle 18 are travelling in reverse. For this purpose, the solenoid valve 50 (if used) is closed. When the reversing towing vehicle 18 begins to turn to the left as shown in Fig. 1, the piston and cylinder unit 46b is compressed via the control rod 40b and lever 42. This causes a rise in pressure in the hydraulic fluid contained in the piston and cylinder unit 46b. This pressure rise is communicated via a pilot line L2 having a connection (not shown) to a pilot valve in a servo control valve 52. The pressure rise in the pilot line L2 causes the pilot valve in servo-control valve 52 to connect a line 54a from the high pressure side of the pump 32 to line 30b leading to the contraction port of the piston and cylinder 28b. The low pressure side of the pump 32 is supplied with hydraulic fluid from the reservoir 34 via a line 54b. The pressure rise in the pilot line L2 also causes the pilot valve in servo-control valve 52 to connect line 30a leading from the contraction port of the piston and cylinder 28a, to a drain line 58a leading to the reservoir 34. Thus, piston and cylinder 28b is caused to contract, and piston and cylinder 28a is permitted to expand. This applies a torque about the articulated connection 22, causing the trailer body 24 to swing anticlockwise relative to the drawbar 12, and follow the towing vehicle’s turn to the left. The rise in pressure in the piston and cylinder unit 46b is thereby counteracted and the resulting pressure drop is communicated to the servo-control valve 52 via the line L2, to eventually close the connections between the lines 54a and 30b on the one hand and between the lines 30a and 58a on the other hand. The drawbar 12 is thereby maintained in an equilibrium position in which it extends substantially straight rearward of the towing vehicle 18. In a modification, the solenoid valve 38 (if present) is closed, and the extension port of the piston and cylinder 28b is connected to the line L2 via a line L.4 (this connection being omitted in Fig. 1 for simplicity). As the piston and cylinder 28b contracts, hydraulic fluid from its extension port is fed into the piston and cylinder unit 46b via the lines L2 and L4, thereby shifting the equilibrium position of the drawbar 12 to lie to the same side of vehicle’s fore and aft axis in the horizontal plane as the vehicle is being steered in, at an angle which is a proportion of the displacement angle of the trailer body 24 relative to the drawbar, about the articulated connection 22. This proportion is a function, inter alia, of the relative cross-sectional sizes of the piston and cylinder 28b and the piston and cylinder unit 46b. The crosssection of the former should not be too large relative to the cross-section of the latter, as this can result in positive feedback in the servo-control loop, and unstable operation of the powered actuator formed by the pistons and cylinders 28a, 28b. When the drawbar achieves an equilibrium position which lies to the same side of the towing vehicle’s fore and aft axis in the horizontal plane as the vehicle is being steered in, the pushing force of the towing vehicle can be applied to the trailer during reverse travel with greater mechanical advantage. The optimum displacement angle at the drawbar connector will depend on the trailer and towing vehicle geometries (e.g. the length of the drawbar and the perpendicular distances of the articulated connection from the trailer axle(s) and the drawbar connector from the towing vehicle rear axle), as well as the abilities for the trailer and towing vehicle wheels and tyres to withstand sideways forces. However a drawbar connector displacement angle which is a fraction of or equal to the trailer body/drawbar displacement angle, will usually be beneficial.

Operation of the servo-control system shown in Fig. 1 as the towing vehicle performs a reverse right turn is similar to that described above for a reverse left turn. When the reversing towing vehicle 18 begins to turn to the right, the piston and cylinder unit 46a is compressed via the control rod 40a and lever 42. The resulting hydraulic pressure rise in the piston and cylinder unit 46a is communicated via a pilot line Li having a connection (not shown) to a pilot valve in the servo control valve 52. The pressure rise in the pilot line Li causes the pilot valve in servo-control valve 52 to connect line 54a from the high pressure side of the pump 32 to line 30a leading to the contraction port of the piston and cylinder 28a. The pressure rise in the pilot line Li also causes the pilot valve in servo-control valve 52 to connect line 30b leading from the contraction port of the piston and cylinder 28b, to a drain line 58b leading to the reservoir 34. Thus, piston and cylinder 28a is caused to contract, and piston and cylinder 28b is permitted to expand. This applies a torque about the articulated connection 22, causing the trailer body 24 to swing clockwise relative to the drawbar 12, and follow the towing vehicle’s turn to the right. The rise in pressure in the piston and cylinder unit 46a is thereby counteracted and the resulting pressure drop is communicated to the servo-control valve 52 via the line Li, to eventually close the connections between the lines 54a and 30a on the one hand and between the lines 30b and 58b on the other hand. The drawbar 12 is thereby maintained in an equilibrium position in which it extends substantially straight rearward of the towing vehicle 18. If the modification described above is used, the solenoid valve 38 (if present) is closed, and the extension port of the piston and cylinder 28a is connected to the line Li via a line Ls (this connection being omitted in Fig. 1 for simplicity). As the piston and cylinder 28a contracts, hydraulic fluid from its extension port is fed into the piston and cylinder unit 46a via the lines Li and L3, thereby shifting the equilibrium position of the drawbar 12 to lie to the same side of vehicle’s fore and aft axis in the horizontal plane as the vehicle is being steered in, at an angle which is a proportion of the displacement angle of the trailer body 24 relative to the drawbar, about the articulated connection 22. A return spring 70 may be provided, acting between the trailer body 24 or chassis and the structure of the drawbar 12, to bias the drawbar towards alignment with the trailer’s fore and aft axis.

A small sprocket 152a with an attached hand-wheel or rotary handle (not shown) may be provided, linked to a large sprocket 60a, which in turn is coupled to the control rods 40a and 40b via a diametrically extending, pivoting lever 43. This mechanism can be used to bring the control rods into a position, when the connector or hitch 16 is not connected to the towing vehicle, that allows spherical bearings 216 or other suitable coupling means at the forward ends of the control rods to mate with the towing vehicle connection. When the trailer is un-hitched after use, if the vehicle and trailer are not in perfect line, the control rods will not be aligned with the vehicle’s fore and aft axis. When the towing vehicle is re-presented to the trailer, the push-rods will probably have to be adjusted. This would be difficult for an operator, without an aid, against the resistance of the hydraulics.

Figure 2 is a schematic plan view showing the general layout of another trailer 200 and drawbar 12 embodying the present invention, connected to a towing vehicle 18. Like parts are given like reference numbers throughout the various Figures. The drawbar 12 of the trailer 200 has its operatively rearward end connected to the trailer body by an articulated connection 22 which is coupled to a cross-beam 226 of the trailer body 24 or chassis at a point forward of the trailer axle 210.

Referring now to Figures 3 and 4, the drawbar articulated connection 22 comprises a hinge pin 224 received through upper and lower interleaved sets of bearing eyes 222, attached respectively to the crossbeam 226 and framework tubes 14 of the drawbar

12. A powered actuator in the form of an opposed pair of double acting hydraulic pistons and cylinders 28a, 28b is mounted symmetrically to either side of the articulated connection 22; one end of each piston or cylinder being pivotally coupled to the cross-beam 226 and the other end of each piston or cylinder being pivotally coupled to mountings 228 on the structural framework of the drawbar 12.

The error signal for servo-control of the powered actuator 28a, 28b is obtained from an actuating mechanism 60. This comprises a toothed drive belt or chain 208 passing around a large sprocket wheel 210 and a small sprocket wheel 212. The large sprocket wheel 210 is rotatably mounted to a framework tube 14 of the drawbar 12. The control rods 40a, 40b are coupled by pivot pins 244a, 244b respectively, at diametrically opposed positions on the large sprocket wheel 210. The small sprocket wheel 212 is fixed to the operating shaft of the servo-control valve 152 and operates to rotate the shaft anticlockwise from a neutral position to a first operating position, and clockwise from the neutral position to a second operating position. The control rods 40a, 40b may also be pivotally connected respectively to opposite ends of a lever 242, centrally pivotally mounted to a frame member 14 of the drawbar 12. In this way, the control rods 40a, 40b are maintained parallel to one another even when spherical bearings 216 at their operative forward ends are disconnected from the towing vehicle. The small sprocket wheel 212 may be provided with a hand-wheel or rotary handle in similar manner to the small sprocket 152a described with reference to Figure 1, for adjustment of the control rods 40a, 40b during hitching of the trailer to the towing vehicle.

The control rods 40a, 40b may be pivotally connected at their operative rearward ends to ends of respective piston and cylinder units 46a, 46b. The other ends of these piston and cylinder units, if used, are pivotally mounted to a bed plate 214 or another suitable structural part of the drawbar 12. The piston and cylinder units 46a, 46b may be interconnected e.g. at their extension ports, by a line 48 and solenoid valve 50, thereby to provide anti-jack knifing functionality in the same way as the corresponding components described above with reference to Figure 1. The piston and cylinder units may be double acting, with one set of their extension or retraction ports connected to the line 48 and solenoid valve 50, and the other set of their extension or retraction ports connected to a crossover line which is of suitably narrow diameter or is otherwise provided with an (e.g. adjustable) choke. The crossover line therefore can be used to provide hydraulic damping of trailer snaking, which might otherwise arise during high speed forward towing of the trailer. In the arrangement shown in Figures 3 and 4, the bed plate also provides a secure mounting for the servo-control valve 152, and a high pressure electric pump 32 and hydraulic reservoir 34 similar to those described with reference to Figure 1; although many other suitable mounting arrangements for these components are also possible.

During reversing of the trailer, if the towing vehicle begins to turn to the left, control rod 40a begins to move in the forward direction and control rod 40b begins to move in the rearward direction. The large sprocket wheel 210 is thus turned slightly anticlockwise. The belt or chain 208 thereby moves the small sprocket wheel through a larger angle anticlockwise; from the neutral position in which the hydraulic fluid supply line 54a from the high pressure side of the pump 32 is connected to neither line 30a nor line 30b; to the first operative position in which the hydraulic fluid supply line 54a is connected to the line 30b, leading to the extension port of the piston and cylinder 28b. The operating shaft of the servo-control valve 152 may reach a limiting position in which further turning of the small sprocket wheel 212 of the actuating mechanism 60 in the same direction, is taken up by lost motion (slippage) at a friction clutch (not shown) acting between the small sprocket wheel 212 and the operating shaft of the servo-control valve 152. Alternatively, a toothless belt 208 may be used in the actuating mechanism 60, with the small sprocket wheel replaced by a small pulley; whereby the belt 208 is designed to slip on the pulley when the limiting position is reached. Yet alternatively, relative rotation between the small sprocket wheel and the operating shaft of the servo-control valve 152 can be resiliently resisted; the stiffness of the resilient connection being selected so as not to yield as the servo control valve is moved from the neutral position to the first or second operative position, and to yield when the small sprocket wheel continues to move and the servo-control valve has reached its limiting positions. Such a yielding resilient link or frictional slip connection could be provided elsewhere in the kinematic chain of the actuating mechanism 60, e.g. in the push rods 40a, 40b; or in their connection to the large sprocket wheel 210 or in their connection to the spherical bearings or other coupling means 216.

Also in this first operative position, the line 30a from the extension port of the piston and cylinder 28a is connected to the drain line 58b, leading to the hydraulic reservoir 34. The piston and cylinder 28b therefore begins to extend, and the piston and cylinder 28a is allowed to retract, thereby applying torque to the articulated connection 22 so as to move the beam 226 and the attached trailer body 24 (Fig. 2) in the anticlockwise direction relative to the drawbar 12. The trailer body therefore begins to follow the turning of the towing vehicle, until the control rod 40a moves rearwardly and the control rod 40b moves forwardly again. This turns the large sprocket wheel 210 slightly clockwise, restoring the small sprocket wheel and the servo-control valve 152 to their neutral positions. The drawbar is thereby maintained in an equilibrium position in which it extends substantially straight backwards from the towing vehicle. In the neutral position of the servo-control valve 152, excess hydraulic fluid from the pump 32 may be returned to the reservoir 34 via a line 58a and a pressure relief valve 258.

Operation of the servo-control valve 152 as the towing vehicle performs a reverse right turn is similar to that described above for a reverse left turn. Control rod 40a begins to move in the rearward direction and control rod 40b begins to move in the forward direction. The large sprocket wheel 210 is thus turned slightly clockwise. The belt or chain 208 thereby moves the small sprocket wheel through a larger angle clockwise; from the neutral position in which the hydraulic fluid supply line 54a from the high pressure side of the pump 32 is connected to neither line 30a nor line 30b; to the second operative position in which the hydraulic fluid supply line 54a is connected to the line 30a, leading to the extension port of the piston and cylinder 28a. Lost motion may again be provided between the actuating mechanism 60 and the operating shaft of the servo-control valve 152 in a limiting position, as described above. Also in this second operative position, the line 30b from the extension port of the piston and cylinder 28b is connected to the drain line 58b. The piston and cylinder 28a therefore begins to extend, and the piston and cylinder 28b is allowed to retract, thereby applying torque to the articulated connection 22 so as to move the beam 226 and the attached trailer body 24 (Fig. 2) in the clockwise direction relative to the drawbar 12. The trailer body therefore begins to follow the right turn of the towing vehicle, until the control rod 40b moves rearwardly and the control rod 40a moves forwardly again. This turns the large sprocket wheel 210 slightly anticlockwise, restoring the small sprocket wheel and the servo-control valve 152 to their neutral positions. The drawbar is thereby again maintained in an equilibrium position in which it extends substantially straight backwards from the towing vehicle.

Although the illustrative examples of trailers described above comprise specific deflection or angle sensing arrangements at the drawbar connector 16 (i.e. at the connector or hitch attachable to the towing vehicle), used to derive an error signal used in particularly described servo-control arrangements for specific types of powered actuators used to set a required angle between the drawbar and a trailer chassis or body, any suitable deflection or angle sensing arrangements, servo-control arrangements and powered actuators may be used. Moreover, the specifically described deflection and angle sensing arrangements, drawbar-to-trailer attachment configurations, servo-controllers and powered actuators may be used in any suitable combinations. For example, the fluid pressure in the piston and cylinder units 46a, 46b shown in Figures 2-14 may be used to provide an error signal for the servo controller in the same way as described with reference to figure 1. Likewise, an actuating mechanism 60 as described with reference to Figures 2-4 may be used to actuate the servo-control valve 52 of the trailer shown in Figure 1, rather than the piston and cylinder units 46a, 46b shown in Figure 1. Thus, Figure 5 is a conceptual diagram showing more generic angle or deflection measurement and powered actuator components. Furthermore, although the towing vehicle 18 shown in Figure 5 is illustrated to have a single pair of steerable front wheels 312 and a pair of fixeddirection rear wheels 314, other wheel arrangements are also possible; such as steerable front and/or rear wheels, additional axles, multiple wheels and tyres on some or all of the axle ends, caterpillar tracks etc. Likewise, although the trailer 300 is shown with a single wheel at each end of a single (notional) axle, other arrangements are also possible, such as multiple axles and multiple wheels per axle end. The drawbar 12 shown in Figure 5 is relatively short, and mounted via the articulated connection 22 to the front of an A-frame 310 of the trailer 300. Thus it may comprise a part of a tow hitch or tongue assembly for the trailer 300, either fitted as original equipment or as a replacement for a standard tow hitch. However, as already described above, the articulated connection 22 may be provided at any suitable location on the trailer body or chassis 24; usually (but not necessarily) at some point along the trailer’s central fore and aft axis 320. Any suitable sensor 360 may be used to measure or determine the angle or a change in the angle 0 between the longitudinal axis of the drawbar 12 and the intersecting fore and aft axis 318 of the towing vehicle

18. For example, the sensor may comprise an optical rotary encoder, potentiometer, giant magnetoresistance sensor and rotating magnet, or the like; mechanically connected between the drawbar 12 or drawbar connector 16 on the one hand and the rear of the towing vehicle or its towhook, towball, towing pintle or the like on the other hand. The mechanical connections are such that corresponding parts of the sensor are relatively rotatable about the pivot axis of the drawbar connector 16, so as to measure changes in the angle Θ. Alternatively the angle θ or changes therein may be determined by distance measuring apparatus connected between the rear of the towing vehicle 18 and the drawbar 12; such as one or more of the earlier described control rods, or one or more tensioned cables or Bowden cables; in each case connected to a suitable force or pressure or distance transducer or used for direct mechanical and/or hydraulic feedback control of the servo control system. Yet alternatively, suitable non-contact distance measuring apparatus mounted on one or other of the drawbar or rear of the towing vehicle or its tow hook etc., and aimed at a suitable target on the other of the drawbar or towing vehicle etc., can be used to determine the angle θ or changes therein. For example, ultrasonic sonar sensors (e.g. of the type used as parking sensors) or laser interferometers may be used.

As previously mentioned, the powered actuator 28 may be of any suitable type. The powered actuator 28 is mechanically connected between (a) the trailer body or chassis 24 (including, but not limited to, A-frame 310, as shown in Fig. 5) and (b) the drawbar 12; to set the angle φ between the drawbar 12 and the intersecting trailer fore and aft axis 320. The determined change, ΔΘ, in the angle 0 is used as a negative feedback error signal in a servo-control loop, whereby powered actuator 28 is driven in a direction which tends to reduce the magnitude of the error signal Δ0.

In a modification, once the error has been substantially eliminated (ΔΘ « 0), the actuator 28 continues to be operated in the same direction, until 0 overshoots” the 180 degrees, straight behind position by a predetermined proportion (e.g. 0.5) of the change in the angle φ, Δφ, used to achieve Δ0 « 0. Thereafter Δ0 and Δφ are maintained in the same proportion to one another, either until the reversing manoeuvre has been completed, or until both Δ0 and Δφ are substantially zero, whereupon the trailer is being reversed straight backwards and the whole control cycle can be repeated until the reversing manoeuvre has been completed. Still other control regimes are possible, within the scope of the claims.

Claims

CLAIMS:

1. A trailer towing-control apparatus comprising a drawbar having a connector at its operative forward end, the connector being pivotally connectable to a towing vehicle, the drawbar having an articulated connection at its operatively rearward end, the articulated connection being attachable to the trailer body or chassis; the towingcontrol apparatus further comprising a powered actuator operatively arranged to move the articulated connection whereby the connected trailer body or chassis pivots relative to the drawbar in a horizontal plane; the towing-control apparatus further comprising a servo-controller which controls the powered actuator to move the articulated connection in the same angular direction that the towing vehicle is being steered in during reverse travel of the towing vehicle and trailer, to thereby bring the drawbar to an equilibrium position in the horizontal plane in which it is in alignment with the fore and aft axis of the towing vehicle, or lies to the same side of that axis in the horizontal plane as the towing vehicle is being steered in.

2. A trailer towing-control apparatus as defined in claim 1, in which the articulated connection is attached to the trailer body or chassis forward of the trailer axle(s).

3. A trailer towing-control apparatus as defined in claim 2, in which the drawbar is mounted to an A-frame of the trailer so as to form a part of the trailer tongue/tow hitch assembly.

4. A trailer towing-control apparatus as defined in any preceding claim in which, when the towing vehicle and trailer are moving in the forward direction, the powered actuator and servo-controller are used to move the articulated connection so that the drawbar is aligned along the trailer’s fore and aft axis.

5. A trailer towing-control apparatus as defined in any preceding claim, in which the servo controller comprises control rod or cable connectable to the rear of the towing vehicle offset from the drawbar connector so as to operate a servo control valve in response to angular movement of the drawbar relative to the towing vehicle in the horizontal plane; the servo control valve regulating a supply of power fluid to the powered actuator.

6. A trailer towing-control apparatus as defined in claim 5, in which the control rod or cable operates a lever mounted on the drawbar; the vehicle, drawbar, control rod/cable and lever forming a parallelogram mechanism.

7. A trailer towing-control apparatus as defined in claim 5 or 6, in which a piston and cylinder unit is connected between the control rod or cable and the drawbar.

8. A trailer towing-control apparatus as defined in claim 7, in which an opposed pair of such pistons and cylinder units is provided.

9. A trailer towing-control apparatus as defined in claim 7 or 8, in which fluid pressure in the piston and cylinder unit(s) is arranged to operate the servo control valve.

10. A trailer towing-control apparatus as defined in any of claims 7- 9, in which a solenoid valve is provided to fluidically lock the piston and cylinder unit(s) to provide jack-knifing control under braking, during forward motion of the towing vehicle and trailer.

11. A trailer towing-control apparatus as defined in any of claims 5-10, in which an opposed pair of such control rods/cables is provided, one each on either side of the drawbar connector.

12. A trailer towing-control apparatus as defined in any of claims 5-11, in which the control rod(s) or cable(s) operate(s) the control valve via a belt drive, chain drive, gearing or a connecting rod.

13. A trailer towing-control apparatus as defined in any of claims 5-12, in which the servo control valve is operated by a Bowden cable having a sheath anchored to the drawbar and an end couplable to the rear of the vehicle, offset from the drawbar connector.

14. A trailer towing-control apparatus as defined in any preceding claim, in which the powered actuator is pressurised fluid powered and the servo controller comprises an electrically powered pump.

15. A trailer towing-control apparatus as defined in claim 14, in which the powered actuator comprises a piston and cylinder.

16. A trailer towing-control apparatus as defined in claim 14, in which the powered actuator comprises an opposed pair of pistons and cylinders.

17. A trailer towing-control apparatus as defined in claim 15 or 16, in which a solenoid valve is used to fluidically lock the piston(s) and cylinder(s) so as to hold the drawbar in the fore and aft alignment with the trailer body or chassis during forward motion of the vehicle.

18. A trailer towing-control apparatus as defined in any of claims 1-4, in which the angle between drawbar and towing vehicle and/or changes in this angle is determined by a rotary sensor or encoder, a linear movement or distance sensor or encoder, or a non-contact proximity sensor.

19. A trailer towing-control apparatus as defined in claim 18, in which the determined angle or determined change in angle is used to provide an error value used by the servo controller.

20. A trailer towing-control apparatus as defined in claim 18 or 19, in which the powered actuator is electrically powered.

21. A trailer towing-control apparatus as defined in claim 18 or 19, in which the determined angle is used to operate a servo control valve which regulates a supply of power fluid to the powered actuator.