GB2146962A - Towing bar - Google Patents

Abstract

A towing bar assembly comprises a plurality of relatively moveable members (2, 7 and 8) with a compression coil spring (81) disposed therebetween for accommodating limited relative movement therebetween, a plurality of rigid abutments (6) being provided on the relatively moveable members (2, 7 and 8) to limit the relative movement and provide a rigid force transmission point. Prior to towing, members (2) are adjustably positioned relative to members (7) to define the overall length of the towing bar assembly. During towing, compression forces applied to the towing bar assembly are absorbed by the spring (81), with the member (7) moving relative to the member (8). At each end of the towing bar assembly is a coupling hook (1) closed by a movable abutment plate (4). Means are provided for adjusting the initial compression applied to the spring (81). The towing bar assembly can be readily dismantled. <IMAGE>

Description

SPECIFICATION Towing Bar This invention relates to a towing bar and is particularly, but not exclusively, concerned with a towing bar for use with motor vehicles for road going.

For motor vehicle light-weight towing operations a towing rope or wire is commonly used and which is strung between a towing or rescue vehicle and the immobilised vehicle to form a flexible link which is tensioned during towing operations but which will slacken under braking or deceleration, allowing the towed vehicle to catch up and even overtake the towing vehicle which is under full engine and braking control, whereas the towed vehicle simply has braking control provided the brakes are still operational and there is a back-up driver in the towed vehicle.Moreover, the essentially non-rigid towing wire or cable makes dynamic towing operations somewhat precarious under normal road conditions where changes in speed, bends and irregular road surfaces impose an obligation upon the driver of the towed vehicle to exercise some skill and anticipation in relation to movement of the towing vehicle and consequent relative movement between the towing vehicle and the towed vehicle.

With a view to overcoming the disadvantages of a non-rigid link, it is known, particularly for heavy duty towing applications, to employ a rigid tow bar between the towing vehicle and the towed vehicle.

Such a rigid towing bar can accommodate both braking and acceleration towing forces in addition to providing some form of steering or guidance input to the towed vehicle which may, subject to prevailing legislation, obviate the need for a driver ofthe towed vehicle. However, the rigid nature of such known towing bars can result in transmission of shock to the towed vehicle when there is a sudden change in dynamic conditions, particularly under heavy braking of the towing vehicle and the resultant forces applied to towing points may be too extreme, particularly since deceleration under braking is normally potentially more severe than the possible acceleration in the towing configuration.Thus although the known rigid tow bar is in some respects an improvement over the known flexible tow cable, wire or rope, which suffers from slackening and jerking or even breaking under severe jerk loads imposed thereupon, the rigid tow bar known hitherto does not accommodate any relative movement between the towed and towing vehicles along the tow bar length, whereas at least the towing rope does so, albeit to an undue extreme.

According to the invention there is provided a rigid tow bar incorporating a resiliently deformable coupling element which can accommodate relative axial displacement along the length of the tow bar to accommodate or buffer shock loads therealong.

In a particular construction, a shock absorbing or cushioning but otherwise rigid tow bar incorporates a plurality of relatively slidable members with a resiliently deformable element located therebetween to allow at least limited relative displacement of the members beyond which the members revert to the action of a solid or rigid link between the ends thereof, the latter being provided with suitable coupling means.

Coveniently, the relatively displaceable members comprise a series of relatively telescopic tubular members. The resilient buffer comprises suitably a coil spring located between fixed abutments on the relatively moveable members.

Such a coil spring may comprise a compression spring mounted around one of the tubular members.

Conveniently, a series of adjustable interlocating or fixing points may be arranged between the relatively moveable members whereby to vary the overall length thereof, between the fixing ends.

Conveniently means are provided for varying the biasing or springing action of the resiliently deformable element. For example, in the case of a compression coil spring, the end reaction points of the spring may be adjustable whereby to vary the static spring length and hence the initial compression force exerted thereby in the non-deformed condition.

The fixing point at each end of the tow bar may comprise a U-shaped hook member fixedly secured at one end of a relatively moveable element provided with a relatively moveable closure plate lockable to the moveable element between an open and a closed condition to allow attachment and detachment respectively of the towing hook.

The interlinking of the various members of the towing bar may be performed by means of loating pins. The latter desirably have retaining facilities such as spring retaining clips for operational security.

There now follows a description of a particular embodiment of the invention, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows an exploded view of a rigid tow bar assembly; Figure 2 shows an assembled view of the tow bar of Figure 1; and Figure 3 shows a detailed end view of the tow bar shown in Figures 1 and 2.

Referring to the drawings, a rigid tow bar assembly comprises a plurality of interfitting tubular members and one end of the assembly with an intermediate member between the opposite ends of the assembly is essentially the same, but opposite handed is shown in Figure 1 - the complete assembly being shown in Figure 2 from which the general axial symmetry of the arrangement can be appreciated.

The key points of the tow bar assembly are a link bar 2 with a U orJ shaped towing hook rigidly secured, for example by welding, thereto at one end and slidably, telescopically interfitting with a tubular connecting bar 7 at one end thereof, the opposite end being disposed to receive a tubular buffer bar 8 around which is disposed a compression coil spring 81; a further connecting bar and link bar being provided on the other side of the buffer bar 8 in complementary fashion as shown in Figure 2.

The relative positions of the link bar 2, connecting bar 7 and buffer bar 8 may be adjusted by means of a series of locating pin and hole arrangements. Specifically, the link bar 2 incorporates a series of three diametral locating holes, 21,22 and 23 to receive a locating pin 6, one example of which is illustrated in Figure 1. Similarly, the connecting bar 7 incorporates two spaced locating holes 71 and 72 adjacent the axial ends thereof. Further, the buffer bar 8 incorporates two relatively closely spaced locating holes 82 and 83 adjacent one end thereof and at the opposite end a locating slot 84.

The relative position of the link bar 2 and the connecting bar7 may be adjusted and then secured by slidably interfitting the two bars until either the locating holes 22 or 23 become aligned with the locating hole 71, whereupon a locating pin 6 is passed therethrough.

The relative positions of the connecting bar 7 and the buffer bar 8 are adjustably secured by inserting a further locating pin 6 through the locating hole 72 and the aligned locating slot 84; location at the opposite end of the buffer bar 8 with respect to the next connecting bar 7 as shown in Figure 2 for the opposite end of the tow bar is achieved by aligning one ofthe locating holes 82 and 83 with the associated locating hole in that next connecting bar 7. According to which of the locating holes 82 and 83 is selected, so the initial biasing compression of the compression spring 81 will be adjusted, since its opposed ends will abut between spaced locating pins 6.This latter spacing will vary because a locating pin 6 at one end is axially movable in the locating slot 84 to allow the two connecting bars on either side of the buffer bar 8 to move axially relatively together and thus the two spaced ends of the tow bar overall can come together somewhat in a buffer or cushioning action under control of the compression spring 8l,which tends to revert to its original state when the compression force is removed.

Each end of the towing bar is located in position by an adjustable locking plate assembly shown in Figure 1 in exploded view and comprising an adjustable tubular bar3 secured to a stopping or abutment plate 4 with a depending side portion incorporating a locating hole 41 for alignment with the locating hole 21 at the outer end of the link bar 2.

Upon initial assembly and location of the towing bar assembly as a whole, the locking plate assembly is fitted into the end of the link bar 2 so that the adjustable bar 3 slides inside the link bar to as far as it can until the abutment plate 4 engages the end of the link bar 2, thereby allowing a clearance between the hooked end of the U or J shaped towing hook 1 and the link bar 2 - so that a towing element can be fixed therebetween, whereupon the locking plate assembly can be moved to its locking position by drawing the abutment plate 4 outwards until the locating holes 41 and 21 become aligned to receive a locating pin 6.As shown in Figure 1, each locating pin incorporates a locking arrangement so that the overall assembly is effectively a lockable pin; specificallythe head 61 of the locating pin 6 is provided with a spring retaining clip 5 whose opposite ends are received in off-set holes in the pin head 61 on opposite sides thereof, so as to form a twisting or biasing action for the length of material forming the spring which resists the turning and twisting action inherent in pulling the spring retainer over, so that its hooked of U-shaped mid-portion moves over and clips around the end of the locating pin 6 as shown in Figures 2 and 3.

Figure 3 also shows the secure locked position of the abutment plate4 and the relative location of the link bar 2 and connecting bar 7 using aligned respective locating holes 23 and 71 and a locating pin 6 with an associated locking spring clip 5.

In Figure 2, the overall length of the tow bar assembly is at a maximum with the locating hole 82 in the buffer bar 8 axially aligned with the locating hole 23 in the right hand connecting bar 7, so that the initial pre-compression force on the spring 81 is at the lower setting - providing maximum resilient cushioning displacement action and minimum resistance to such axial displacement between the remoted spaced ends of the towing bar assembly.

The cushioning action provided by the otherwise rigid tow bar assembly is advantageous in softening the dramatic effects of deceleration whilst allowing maximum accleration and towing force, positively and without the interference of the deformable cushioning spring by firm interabutment of rigid members. Without this cushioning action there may be a tendency for the towed vehicle to skid or slew under sudden deceleration with risk of possible directional instability.

The towing bar assembly as shown will operate effectively with known towing arrangements either with a towing point disposed on the vehicle center lines or with laterally off-set towing points, which are on occasion employed to promote directional stability and to dispose the towing axis at an angle to the direction of movement thereby reducing the shock forces along the towing member associated with relative axial displacement of the towing and towed vehicle.

The towing bar maintains a safe distance between the towing and towed vehicles and may readily be dismantled and assembled and positioned in situ and it is not unduly weighty, affording a degree of portability desirable for occasional towing use.

Nor is the tow bar of undue weight when assembled.

Moreover the assembled condition of the tow bar is relatively secure by use of the locking pins 6. The locking of the tow bar ends is also a safety feature.

Claims (5)

1. Atowing bar assembly comprising a plurality of relatively moveable members (2,7 and 8) with a resiliently deformable cushioning member (81) disposed therebetween for accommodating limited relative movement therebetween, a plurality of rigid abutments (6) being provided on the relatively moveable members (2, 7 and 8) to limit the relative movement and provide a rigid force transmission point.

2. A towing bar assembly, as claimed in Claim 1, wherein a plurality of telescopic, slidable, interfitting tubular members is provided.

3. A towing bar assembly, as claimed in Claim 2, wherein a compression coil spring is employed as the resiliently deformable element and is disposed around one of the tubular members.

4. A towing bar assembly as claimed in any of the preceding Claims incorporating an adjustable towing hook at each end thereof for facilitating engagement and disengagement of the respective towing bar ends.

5. A towing bar assembly substantially as herein before described with reference to, and as shown in, the accompanying drawings.