Description of Related Art Many vehicles incorporate an openable tailgate which is pivotally attached to the roof of the vehicle in order to allow access to the load area of the vehicle. Whilst the provision of a tailgate renders the load space easily accessible, because of their size, and because they incorporate the rear windscreen of the vehicle, such tailgates tend to be heavy, requiring considerable effort to open and close them. Further, if the space behind the vehicle is limited, it can be awkward or impossible to open the tailgate.

To overcome these disadvantages of tailgates, it is increasingly common for vehicle manufacturers to provide the tailgates with a rear windscreen which is openable independently of the tailgate. The rear windscreen is typically attached by a hinge or the like to the tailgate at the top of the rear windscreen.

To control movement of such openable rear windscreen, and in particular to allow the rear windscreen to be held in the open position, gas struts are typically employed, one at each of the opposite side edges of the rear windscreen, which connect to the side edges of the rear windscreen opening of the tailgate. However, such gas struts are expensive to manufacture, are highly visible and can obstruct loading of the vehicle.

Brief Summary of the Invention According to the present invention, there is provided a spring assembly for controlling movement of a closure member with respect to a body to which the closure member is attached, comprising at least one torsion rod, mounted in a housing, for coupling to the closure member, the torsion rod having a coupling portion arranged for coupling to the body.

The body may be a vehicle tailgate, and the closure member may be a separately openable rear windscreen pivotally mounted on the tailgate, although it should be understood that the present invention is not restricted to such an arrangement.

The present invention also relates to a closure member having fixed thereto a spring assembly as defined above.

The present invention further relates to a method of manufacturing the spring assembly as defined above.

Brief Description of the Drawings A spring assembly, a closure member and a method of manufacturing the spring assembly embodying the invention will now be described by way of example with reference to the accompanying schematic drawings, in which: Figure 1 is a view of the internal (in use) side of the glass pane of a vehicle tailgate with the spring assembly shown partially cut away; Figures 2A, 2B and 2C are cross sections respectively taken along lines A-A, B-B and C-C of Figure 1; Figures 3A, 3B and 3C show cross-sections corresponding to those of Figures 2A, 2B and 2C of a second embodiment of the present invention; Figure 4 shows a cut-away view of an alternative spring assembly according to a third embodiment of the present invention; Figure 5 shows a cross-section taking along the line D-D of Figure 4; and Figure 6 shows a cross-sectional view, corresponding to the cross section of Figure 5, of an alternative embodiment to that shown in Figures 4 and 5.

Figure 7 shows a perspective view of the rear of a motor car having a rear tailgate with a separately openable rear windscreen glass.

In the drawings, like elements are generally designated with the same reference numeral.

Description of the Preferred Embodiments Figure 7 shows a car body 1 to the roof 3 of which a tailgate 5 is attached by means of hinges 7.

The rear windscreen 9 of the car is openable separately from the tailgate 5, and is pivotally attached to the tailgate 5 by hinges 11. A latch mechanism 13 allows the rear windscreen 9 to be held securely closed when described.

As shown in Figure 7, the rear windscreen 9 is formed of a curved pane of glass in order to provide a pleasing visual appearance and to allow the rear windscreen 9 to conform to the general shape of the tailgate 5.

Embodiments to be described are concerned with a mechanism for allowing controlled movement of the rear windscreen 9 with respect to the tailgate 5, and in particular to a mechanism for allowing the rear windscreen 9 to be supported in its fully opened position.

Previous mechanisms for performing this function include gas struts, as described above. However, gas struts are obtrusive and expensive.

The embodiments provide a mechanism for controlling movement of the rear windscreen which is a relatively low cost, is simple to manufacture and is unobtrusive.

It should, of course, be appreciated that the invention, and the arrangements described in the embodiments, are not restricted to a mechanism for use with an openable window of a tailgate. The mechanism described could be employed to control the movement of any closure member, whether it is formed of glass or some other material. However, the embodiments to be described are particularly advantageous when used to control movement of a glass or other transparent panel because they are relatively unobtrusive.

Figure 1 shows a rear windscreen 9 to which a spring assembly 15 in accordance with the first embodiment of the invention is attached. The spring assembly 15 comprises a plastics housing 17 having an elongate main body 19 from which two limbs 21 extend generally perpendicularly with respect to the elongate portion 19.

Located within the housing 17 are two torsion rods 23A and 23A, formed in this example of resiliently deformable metal. Each of the torsion rods 23A, 23A comprises a main elongate portion 25A, 25A from which extends at one end an integral relatively short coupling portion 27A, 27A lying generally perpendicular to the main elongate portion 25A, 25A. The respective coupling portion 27a, 27b are attached to a suitable point on the inside of the upper part of the tailgate 5 of the car 1 near the hinges 11 (and/or to a suitable point on the inside of the roof 3 of the car 1 near the hinges 7). At the opposite end of the elongate portions 25A, 25A to the coupling portions 27A, 27A is an integral mounting portion 29A, 29A located within the respective limbs 21A, 21A of the housing 17.

Torsion rods are conventional devices and have previously been employed to control the movement of closure members. However, conventional torsion rods cannot be satisfactorily employed where it is desired to unobtrusively mount them on a curved closure member. If a conventional torsion rod is accommodated in a housing which follows the contour of the curved closure member, this will cause the elongate portion of the torsion rod to have the same curvature as the curvature of the closure member.

The forced curvature of the torsion rod causes lateral forces to act on the walls of the housing making movement of the closure member stiff and generating noise.

According to the first embodiment of the invention, the elongate portions 25A, 25A of the torsion rods 23A, 23A are arranged such that the elongate portions 25A, 25A cross one another at the central region thereof. The respective elongate portions 25A, 25A do not exactly follow the curvature of the rear windscreen 9. The elongate portions 25A, 25A are inclined with respect to the axis of symmetry (along which cross section B-B is taken) of the rear windscreen 9. For example, the elongate portion 25A, 25A are inclined by 80° to the axis of symmetry of the rear windscreen 9. This allows the elongate portions 25A, 25A to have a lower curvature than the curvature of the rear windscreen 9 at the point at which the housing 17 is mounted thereon.

Figure 2A shows a cross-section taken along line A-A through the limb 21A. Figure 2B is a cross-section taken along line B-B through the central region of the elongate portions 25A, 25A. Figure 2C is a cross-section taken along the line C-C at the end region of the elongate portions 25A, 25A.

In Figure 1 the outer surface of the housing 17 (that is the surface furthest from the rear windscreen 9) is shown cut away so that the torsion rods 23A, 23A can be seen.

As is clear from the cross sections of Figures 2A, 2B and 2C, the housing includes an outer surface which conceals the torsion rods 23A, 23A when viewing the spring assembly 15 from the inside surface of the rear windscreen 9, in use. When viewed from the outside surface of the rear windscreen 9, the elongate part 19 of the housing 17 will be obscured by a blackened area at the top part of the rear windscreen 9, applied in the conventional manner.

The housing 17 may be made by a suitable moulding operation. The torsion rods 23A, 23A are then located at the appropriate recesses formed by the moulding operation, and the assembled spring assembly is then fixed to the interior surface of the rear windscreen 9 by any suitable means, such as by an adhesive. When the housing 17 is fixed to the interior surface of the rear windscreen 9, movement of the torsion rods 23A, 23A, other than the twisting action, is prevented.

The physical characteristics of torsion rods are such that: 1. The spring force and the tension in the material of the torsion rods both increase in proportion to the square of the diameter of the torsion rods ; 2. the turning rate behaves in a converse manner with respect to the square of the diameter; 3. increasing the length of the elongate portion 25A, 25A of the torsion rods improves the linearity with which the torsion forces are provided by the torsion rods, but of course, the length of the elongate portions 25A, 25A is restricted by the dimensions of the rear windscreen 9; and 4. the friction between the springs and the recesses in the housing 17 dissipates some of the spring force generated by the torsion rods.

In some applications it may be advantageous to replace the single torsion rod 23A with multiple generally parallel torsion rods, and to replace the single torsion rod 23A with multiple generally parallel torsion rods. Figure 3A, 3B and 3C show cross sections corresponding to Figures 2A, 2B and 2C taken through a spring assembly where torsion rod 23A is replaced by two generally parallel torsion rods, and torsion rod 23A of Figure 1 is replaced by two generally parallel torsion rods.

With regard to point 3 above, it will also be understood by those skilled in the art that if a torsion rod is twisted beyond a predetermined amount, the torsion rod will be damaged and will no longer behave elastically. The amount of twisting that a torsion rod of a given diameter and of a given material can endure without being damaged is proportional to the length of that torsion rod (all other factors being equal).

The limitation in length of the torsion rod, due to it having to be accommodated within the dimensions of the rear windscreen 9, is a particular problem because the rear windscreen 9 may have to rotate through approximately 150° with respect to the tailgate 5 in order that a rear windscreen 9, when opened, can be held in a position where it does not cause an obstruction to a person wishing to load or unload the car 1.

Figures 4 and 5 show a third embodiment of the invention. In this embodiment torsion rod 30 comprises two generally parallel elongate portions 32A and 32A. Elongate portion 32A terminates in a coupling portion 34 similar to the coupling portion 27A of the first embodiment. The other elongate portion 32A terminates in a portion 36 corresponding to the mounting portion 29A of the first embodiment. The other ends of the elongate portions 32A, 32A each have fixed thereto a respective cogwheel 38A, 3 8A. These cog wheels 3 8A, 3 8A act such that, when a turning force is applied to one of the two elongate portions 32A, 32A, this turning force is shared substantially equally with the other of the two elongate portions 32A, 32A by the coupling action of the mated teeth of the cogs 3 8A, 3 8A. The interaction of the cogs 3 8A, 3 8A allows the two elongate portions 32A, 32A to have similar characteristics to a single elongate portion having twice the length of either of the elongate portions 32A, 32A.

Therefore, improved characteristics of the spring assembly are provided despite the constraint of the dimensions of the rear windscreen 9. A second torsion rod 39, similar to the torsion rod 30, may be provided in the housing.

Figure 6 shows a cross section corresponding to the cross section of Figure 5 of a fourth embodiment of the invention. According to the fourth embodiment, the elongate portion 32A has a crank or cam 40 fixed thereto and extending therefrom.

The cam 40 acts against a recessed surface 42 the generally C-shaped part 44 fixed to the elongate portion 32A. The action of the cam 40 on the surface 42 serves to cause twisting force applied to one of the two elongate portions 32A, 32A to be shared equally with the other of the two elongate portions 32A, 32A, in a similar manner to the third embodiment.

Other mechanical linkages between the elongate portions 32A, 32A, providing similar functionality, such as levers, could alternatively be used.