GB2318107A - Towable vehicle - Google Patents

Abstract

A height adjustable towing device 2 fitted to a towable vehicle comprises a front support 4 and a rear support 18, the lower ends of the supports being pivoted to the forward part 6 of a towable vehicle and the upper ends being pivoted to a member 14 including a coupling head 16. Pivoting of the lower end of the front support is by means of hirth gears 8. A gas spring 22 damps movement during adjustment. The device is arranged so that up to half of the total towing force applied via the head 16 is taken up by the rear support 18.

Description

TOWABLE VEHICLE This invention relates to a towable vehicle and particularly, although not exclusively, relates to a towable vehicle incorporating an adjustable towing device, for example a height adjustable towbar.

It is well known to provide trailer towbars which are height adjustable to enable them to be safely secured to towing attachments arranged on vehicles at various heights above the ground such that the towbars extend substantially parallel to the ground. One known arrangement comprises a heavy front support member which includes large knuckle forgings incorporating a pair of hirth gears at each of its ends, one end of the support member being connected to a front support of a trailer chassis and the other end of the support being secured to a substantially horizontally extending top support member which incorporates a coupling attachment at its forward end. Adjustment of the height of the towbar of the known arrangement is achieved by disengaging the pairs of hirth gears at the ends of the front support, pivoting the front support to the desired position and then re-engaging the hirth gears.

It can, however, be relatively difficult to index and secure the two pairs of hirth gears concurrently. In addition, since the front support member is relatively heavy and cumbersome, assistance needs to be provided in order to control and facilitate its pivotal movement.

Such assistance is provided by a gas spring which is fixed between the front support member and a rear strut which extends substantially parallel to the front support member and is arranged to damp movement of the front support member when its two pairs of hirth gears are disengaged.

Nonetheless, it should be noted that the rear strut is spaced only a relatively short distance from the front support member and is relatively weak. Furthermore, its position is such that only a negligible amount of the towing force applied to the arrangement in use is transmitted to it; the vast majority of the towing force is incident upon the front support member which, as a result, must be relatively strong.

The provision of two pairs of hirth gears and a heavy front support member tend to make the arrangement described relatively expensive to manufacture.

It is an object of the present invention to address problems associated with known adjustable towing devices.

According to the invention, there is provided a towable vehicle or part thereof incorporating an adjustable towing device comprising front and rear support members arranged to form a part of a substantially parallelogram structure, each of said support members being pivotably mounted at spaced apart positions for adjusting the height of the device, wherein the device is arranged such that when in its uppermost position in use at least 10% of the towing force applied to the device can be transmitted through said rear support member.

20%, preferably 25%, more preferably 30%, especially 35% of the towing force may be transmitted through said rear support member.

By virtue of the transmission of force through said rear support member, the rear member preferably has greater tensile strength and/or the front support member may have lower tensile strength compared to prior known devices. The ratio of the tensile strength of the front support member to the rear support member may be in the range 0.5:1 to 10:1, preferably in the range 1:1 to 5:1, more preferably in the range 1:1 to 7:2, especially in the range 3:2 to 5:2.

Preferably, the front support member includes first and second spaced apart pivot arrangements which are preferably of a different type from one another.

Preferably, said first pivot arrangement is arranged at the joint of the front support members which takes maximum stress, in use. Said first pivotable arrangement is preferably pivoted relative to a chassis member of the towable vehicle. Said first pivot arrangement is preferably arranged to define a rigid connection between the chassis member and said front support member. Said first pivot arrangement preferably includes a pair of cooperable members, for example discs, which are arranged to mesh with one another such that when meshed they provide said rigid connection; and when not meshed, said first pivot arrangement is able to pivot. Means for causing the pair of cooperable members to mesh is preferably operable coaxially to the axis of the pivot axis of the first pivot arrangement. Preferably, said first pivot arrangement comprises cooperable hirth gear discs.

Said second pivot arrangement is preferably pivotable relative to a top support member which is suitably operatively connectable to a coupling member. Said second pivot arrangement preferably is of a different type compared to said first arrangement. For example, means defining the second pivot arrangement are preferably substantially translationally immovable relative to one another, whereas the preferred cooperable hirth gear discs of the first pivot arrangement are translationally movable relative to one another so that they can be selectively meshed and unmeshed. Preferably, said second arrangement includes male and female cooperable pivot members, for example a pivot pin engaging an opening or openings, which pivot members are preferably translationally fixed relative to one another. Preferably, said second arrangement has a single configuration wherein said top support member can pivot relative to said front support member provided any secondary locking means associated with said second pivot arrangement is not in operation.

Preferably, a secondary locking means is provided and is suitably associated with said second pivot arrangement but is preferably not an integral part thereof. Said secondary locking means may be arranged to restrict pivotal movement of said second pivotal arrangement. It preferably includes a locking member which is preferably axially offset (ie it is not coaxial) relative to the pivot axis of said second pivot arrangement. Said locking means may comprise an indexing means, for example comprising a male member engaging a plate having spaced apart openings.

The pivotable mounting of said rear support member may be achieved by suitable means and is preferably achieved using a pivot arrangement having any feature of said second pivot arrangement as described above.

A damping neans is preferably provided for damping movement of said front and rear support members.

Said front and/or rear support members may be pivotable through an angle of at least 250, preferably at least 350, more preferably at least 450.

Preferably in an arrangement (hereinafter referred to as a "reference arrangement") wherein the front support member defines an angle of 500 to the horizontal (or, in the event that such an angle cannot physically be achieved, reference is made to the theoretical situation calculated by extrapolating from an angle which can be achieved), a line extending through the pivot axis of the second pivot arrangement perpendicularly to a line extending between the respective pivot axes of the first and second pivot arrangements passes above pivot axes of the rear support member.

When in said reference arrangement, the ratio of the distance between the first and second pivot arrangements to the distance between the second pivot arrangement and the nearest pivot axis of said rear support member may be in the range 1 to 10, preferably 1 to 8, more preferably 2 to 6, especially 2 to 5.

The invention extends to a method of manufacturing an adjustable towing device of a towable vehicle comprising front and rear support members arranged to form a part of a substantially parallelogram structure, each of said support members being pivotably mounted at spaced apart positions for adjusting the height of the towing device, the method comprising arranging the device such that when in an uppermost position, at least 10% of the towing force applied in use is transmitted through said rear support member.

Any feature of any aspect of any invention or embodiment described herein may be combined with any feature of any aspect of any other invention or embodiment described herein.

Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which : Figure 1 is a side elevation of a height adjustable towing device shown in respective uppermost and lowermost positions; and Figure 2 is top plan view of the device of figure 1 when in an uppermost position.

The towing device 2 comprises a front support 4 having a lower end which is pivotably mounted at pivot point 8, on a forward part 6 of a trailer chassis (not shown). The pivotal mounting is achieved using a pair of hirth gears which are operable between a configuration in which they provide a rigid interconnection between front support 4 and forward part 6 and a configuration wherein the front support is freely pivotable.

At its upper end, the front support 4 is pivotably mounted by means of a pivot arrangement 10 on a downwardly extending arm 12. Pivot arrangement 10 comprises a swivel connection, for example a simple swivel pin. It should be noted that pivot arrangement 10 does not include a pair of hirth gears. A secondary clamp or index bolt may be associated with pivot arrangement 10 in order to reduce undesirable play, particularly when the towing device is in its lowermost position.

Arm 12 is rigidly connected to and extends downwardly from top support member 14. Member 14 includes a coupling head 16 at its forward end. A rear support 18 is pivotably mounted at its upper end at point 23 by means of a pin arrangement associated with the rearward end of the top support member 14. The support 18 extends downwardly, substantially parallel to the front support 4 and, at its lower end, is pivotably mounted on a bracket 20 which is fixed to the forward part of the chassis 6 behind pivot point 8.

A gas strut 22 is pivotably mounted at points 24, 26 between the front and rear supports 4, 18.

The device 2 is pivotable between the uppermost position shown in Figure 1 wherein front support 4 is inclined to the horizontal angle cr of about 500 and the lowermost position wherein support 4 extends substantially horizontally. Adjustment between the two extreme positions shown is easily achieved : the hirth gears at pivot point 8 are disengaged as is the secondary clamp or index bolt if provided; the front/rear supports are then pivoted to the desired position whereupon the hirth gears and, if necessary, the secondary clamp or index bolt, are re-engaged to rigidly secure the coupling head 16 at the desired height. The gas spring 22 damps movement during the adjustment.

The device 2 is arranged such that up to 50% of the total towing force applied to the device via head 16 in use is taken up by the rear support 18. As a result the strength and weight of the front member 4 can be reduced and, additionally, pivot point 10 need not be arranged to provide a rigid interconnection between arm 12 and front support 4 in the manner of a hirth gear but can comprise a simple pivot arrangement.

The distribution of the force between front and rear supports 4, 18 is dependent upon the arrangement of the supports and/or the positions of their respective pivot points. For example, when the front support 4 defines an angle of about 500 to the horizontal as in figure 1, a line 40 extending through pivot 10 perpendicularly to the extent of the member 4 passes above pivot point 23 and, similarly, a line 42 extending through pivot point 8 perpendicularly to the extent of member 4 extends above the pivot defined at bracket 20. In addition, when the front member defines an angle of 50 as shown and wherein the distance between pivot points 8 and 10 is about 735 mm, the distance between pivots 10 and 23 is about 195 mm.

Furthermore, the distance between pivot 23 and that defined at bracket 20 is suitably about 735 mm and the distance between pivots 8 and that defined at bracket 20 is also about 195 mm.

The ratio of the tensile strengths of the front and rear members may be 2:1.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (16)

1. A towable vehicle or part thereof incorporating an adjustable towing device comprising front and rear support members arranged to form a part of a substantially parallelogram structure, each of said support members being pivotably mounted at spaced apart positions for adjusting the height of the device, wherein the device is arranged such that when in its uppermost position in use at least 10% of the towing force applied to the device can be transmitted through said rear support member.

2. A towable vehicle or part thereof according to claim 1, wherein at least 35 of the towing force can be transmitted through said rear support member.

3. A towable vehicle or part thereof according to claim 1 or claim 2, wherein the ratio of the tensile strength of the front support member to the rear support member is in the range 0.5:1 to 10:1.

4. A towable vehicle or part thereof according to any preceding claim, wherein the front support member includes first and second spaced apart pivot arrangements which are of a different type from one another.

5. A towable vehicle or part thereof according to claim 4, wherein said first pivot arrangement is arranged at the joint of the front support members which takes maximum stress, in use.

6. A towable vehicle or part thereof according to claim 4 or claim 5, wherein said second pivot arrangement is pivotable relative to a top support member which is operatively connectable to a coupling member.

7. A towable vehicle or part thereof according to any of claims 4 to 6, wherein cooperable means defining the second pivot arrangement are substantially translationally immovable relative to one another.

8. A towable vehicle or part thereof according to any of claims 4 to 7, wherein said second pivot arrangement includes male and female cooperable pivot members.

9. A towable vehicle or part thereof according to any of claims 4 to 8, wherein a secondary locking means is provided and is associated with said second pivot arrangement.

10. A towable vehicle or part thereof according to claim 9, wherein said secondary locking means includes a locking member which is axially offset relative to the pivot axis of said second pivot arrangement.

11. A towable vehicle or part thereof according to any preceding claim, wherein a damping means is provided for damping movement of said front and rear support members.

12. A towable vehicle or part thereof according to any of claims 4 to 11, wherein, in an arrangement wherein the front support member defines an angle of 50 to the horizontal (or, in the event that such an angle cannot physically be achieved, reference is made to the theoretical situation calculated by extrapolating from an angle which can be achieved), a line extending through the pivot axis of the second pivot arrangement perpendicularly to a line extending between the respective pivot axes of the first and second pivot arrangements passes above pivot axes of the rear support member.

13. A towable vehicle or part thereof according to any of claims 4 to 12, wherein in said reference arrangement referred to in claim 12, the ratio of the distance between the first and second pivot arrangements to the distance between the second pivot arrangement and the nearest pivot axis of said rear support member is in the range 1 to 10.

14. A method of manufacturing an adjustable towing device of a towable vehicle comprising front and rear support members arranged to form a part of a substantially parallelogram structure, each of said support members being pivotably mounted at spaced apart positions for adjusting the height of the towing device, the method comprising arranging the device such that when in an uppermost position, at least 10% of the towing force applied in use is transmitted through said rear support member.

15. A towable vehicle or part thereof substantially as hereinbefore described with reference to the accompanying diagrammatic drawings.

16. A method substantially as hereinbefore described with reference to the accompanying diagrammatic drawings.