Tightening devices with grip-hooks are used on vehicle wheels in order to improve the vehicle's grip in slippery driving conditions, such as on icy and snow-covered roads.

Norwegian patent no. 116 148 describes a tightening device with radial arms which are integral with grip-hooks in the form of clamps. An operating body on a central tightening mechanism is locked to one of the arms after the gripping clamps are mounted on the wheel.

Norwegian patent no. 130 387 and US patent 4 549 591 describe tightening devices with radial arms which are integral with gripping clamps in the same way as in the above-mentioned patent publication. The radial arms are provided with teeth which are engaged with a cogwheel in a housing at the hub of the wheel, the tightening being performed by turning the cogwheel with a spring handle which, after the radial arms have been pulled a sufficient distance towards the hub, is locked in one of the radial arms.

Norwegian patent 143 870 describes a gripping device for mounting on vehicle wheels, comprising at least three coplanar arms, one end of which is bent so as to lie along the tread of the vehicle tyre, and the other is kept under tension by means of a tightening mechanism. Two of the arms are rigidly connected with each other and with a part of the tightening mechanism which slidably receives the last-mentioned end of at least a third arm for tightening of the gripping device around the tread of the tyre.

The tightening devices involved in these known gripping devices have the disadvantage that the forces which are exerted by the grip-hooks on the tyre are relatively small, with the result that the grip-hooks easily work loose.

The object of the invention is to provide a tightening device for claw arms with grip-hooks which is not encumbered with the above-mentioned drawback. Moreover, the tightening device should be simple to operate.

These objects are achieved according to the invention with a tightening device for claw arms with grip-hooks of the type mentioned in the introduction, characterized by the features which are stated in the claims.

The tightening device can be employed with any type of grip-hook which can be arranged on the tyre's tread, such as grip-hooks in the form of clamps as described in one of the above-mentioned patent publications, or grip-hooks as described in the applicant's cop enduing Norwegian patent application no.

965392.

The terms "radial" and "axial" should be understood on the basis of the wheel's geometry. Similarly, the wheel's "inside", "outside" and "underside" should be understood on the basis of the position of the wheel on a vehicle, thus being understood as facing towards the vehicle, away from the vehicle and down towards the ground respectively. Similarly, "the inner bracket" and "the outer bracket" should be understood as being located closest to the wheel and furthest from the wheel respectively.

The invention will now be explained in more detail in connection with a description of individual embodiments, and with reference to the drawing, in which fig. 1 is a perspective view of a tightening device for claw arms with grip- hooks according to the invention, fitted on a vehicle wheel, figs. 2a and b illustrate cross sections through an embodiment of the tightening device according to the invention, viewed along the section line X-X in fig. 1, figs. 3a, b and c illustrate cross sections through a second embodiment of the tightening device according to the invention, figs. 4a and b illustrate cross sections through a third embodiment of the tightening device according to the invention, figs. 5a and b illustrate cross sections through a fourth embodiment of the tightening device according to the invention.

The same reference numerals are used for corresponding parts in all the figures.

Fig. 1 is a perspective view of a tightening device for claw arms 5 with grip- hooks 1 according to the invention, fitted on a vehicle wheel 2. The wheel 2, only about half of which is shown, comprises a tyre 3 with a tread 4 in which the grip-hooks 1 are placed. The tightening device is placed at the wheel's centre 8 on the wheel's outside 9, the wheel's outside being the side which faces away from the vehicle (not shown). The claw arms 5 extend radially from the tightening device to the grip-hooks 1.

When the tightening device is activated, the claw arms 5 with the grip-hooks 1 are pulled towards the wheel's centre 8, with the result that the grip-hooks are securely clamped to the tyre's tread 4. The tyre's tread thereby obtains an uneven surface which increases the friction between the tyre's tread and the ground, thus improving the vehicle's grip.

Figs. 2a and b show cross sections through an embodiment of the tightening device according to the invention, viewed along the section line X-X in fig.

1. The tightening device comprises link arms which are connected to claw arms and are arranged between an inner bracket 30 and an outer bracket 31 which are axially movable relative to each other, axial direction being indicated by the arrow P 1. A centre axis 61 forms the centre line in the tightening device.

In the embodiment in figs. 2a and b two link arms 34, 35 are connected to their claw arm 5 at first ends closest to the centre axis 61 via a rotating joint 36, and at second ends furthest from the centre axis 61 via rotating joints 37 and 38 respectively connected to lugs 41 and 42 respectively on the inner bracket 30 and the outer bracket 31 respectively.

The inner bracket 30 and the outer bracket 3 1 are further provided with corresponding centrally located threaded portions or elements 32 and 33 respectively, of which at least one threaded portion or element is secured with regard to rotation in its bracket. In the embodiment in figs. 2a and b the inner bracket 30 has a centrally located threaded element 32 in the form of a screw, which is freely rotatable, but axially immovably secured in the inner bracket by means of a lock nut 40, while the outer bracket 3 1 has a centrally located threaded portion 33 in the form of a securely fixed internally threaded casing.

When mounting the tightening device with the grip-hooks, the grip-hooks are placed loosely on the tyre's tread, the brackets thus being located apart from each other in a loosened position, as illustrated in fig. 2a. The tightening device is activated by inducing a relative rotation of the threaded portions, which with reference to fig. 2a is caused by turning the screw 32 by means of a gripping portion 46 to be gripped by a spanner. The screw 32 will thereby be pulled into the casing 33, pressing the inner bracket 30 against the outer bracket 31, into a tightened position where the brackets are located near each other, as illustrated in fig. 2b. The first ends of the link arms in the rotating joint 36 are thereby moved towards the brackets, and the link arms are forced to rotate about their second ends in the rotating joints 37, 38 on the brackets.

The rotation causes the first ends of the link arms with the claw arm to be moved towards the centre axis 61, opposite the direction indicated by the arrow P2, thereby clamping the grip-hook which is attached to the claw arm securely against the tyre's tread.

The claw arm 5 is securely clamped between the brackets' lugs 41, 42 when the brackets in the tightened position are moved as close as possible to each other, as illustrated in fig. 2b. The claw arm thus obtains a secure and stable position, holding the grip-hook firmly against the tyre's tread. The claw arm can thereby be given a radial orientation, but to prevent the grip-hook from being twisted in its position on the tyre's tread, it is preferred that the claw arm should be designed with a slight curvature, thus giving it an angle v2 in relation to the wheel's radial direction, directed away from the wheel. This angle should preferably be between 2 and 10", and most preferred approximately 5".

The inner bracket and/or the outer bracket may be integrated with a housing for the tightening device, for protection thereof. The housing may be provided as an enveloping surface in extension of one or both of the brackets.

There are a number of obvious ways of doing this, and no further description will be given.

Figs. 3a, b correspond to figs. 2a, b, similarly showing cross sections through a second embodiment of the tightening device according to the invention, where the brackets 30, 31 do not have lugs for attaching the link arms as in the embodiment in figs. 2a and b, but instead consist of flat plates 30, 31 with cut-outs for attaching the link arms 43 and 44 respectively in rotating

joints 37, 38. Fig. 3c illustrates a cross section viewed in the section line Y-Y in fig. 3a, through the rotating joint 38, showing how the link arm 44 by means of a bolt 45 is rotatably secured in a cut-out between two protrusions 54, 55 in the bracket 31. Here the link arms have been given a bend 56 at a substantially right angle, with the result that in the position in fig. 3b, where the brackets are located in the tightened position, they extend axially out from the brackets and at their bend 56 change direction to extend towards the centre axis 61. In this embodiment the claw arms are provided with support portions 60, which project from the claw arms in the direction towards the brackets, and which, when the brackets are located in the tightened position, abut against the brackets, with the result that, in the same way as in the explanation with reference to fig. 2b, the claw arms are held securely clamped between the brackets.

In the embodiment in figs. 3a, b the centrally located threaded portions are furthermore designed differently from those in the embodiment in figs. 2a, b, the claw arms 32 in figs. 3a, b being composed of a securely fixed screw, while the threaded portion 33 is composed of a rotatable, but axially immovable internally threaded casing. The axial movement between the brackets 30, 31 is generated by turning the casing 33 by means of the gripping portion 46.

Figs. 4a and b illustrate cross sections through a third embodiment of the tightening device according to the invention, where spring rods 47, 48 at first ends closest to the centre axis 61 are attached by means of rivets to the claw arm 5 at attachment points 49, and at second ends furthest from the centre axis 61 are each correspondingly attached to a bracket 30 and 31 respectively at attachment points 50 and 5 1 respectively.

In this embodiment the function is in principle the same as in the above- mentioned embodiments, the difference being that in this case the link arms' rotating movement is replaced by a rotation-like straightening of the spring rods from a bent position in which the brackets 30, 3 1 in the loosened position are located apart from each other (fig. 4a), to a straightened position in which the brackets in the tightened position are located close to each other (fig. 4b). Moreover, figs. 4a and b illustrate a further variant of the centrally located threaded portions, the threaded portion 32 in this case being composed of a screw which is rotatable in relation to the inner bracket 30,

but axially immovable, while the threaded portion 33 is composed of a threaded hole in the outer bracket 3 1.

Figs. 5a and b illustrate cross sections through a fourth embodiment of the tightening device according to the invention. Here, link arms 34 are linked at a first end nearest the centre axis 61 to their claw arm 5 in a rotating joint 36, and at a second end furthest from the centre axis 61 linked to the inner bracket 30 in a rotating joint 37. The rotating joints 36, 37 may be in the form of fork joints, in order to give the claw arm stability. In this embodiment the outer bracket 3 1 consists of a rotatable disk, and is provided with a crank handle 53. The centrally located threaded portion 32 in the inner bracket 30 is composed of a securely fixed screw, while the threaded portion 33 is composed of a rotatable nut which is securely fixed to the outer bracket 31, thereby fulfilling the same function as a threaded hole.

The rotational movement is generated by turning the crank handle 53, thus causing the outer bracket 3 1 with the nut 33 to rotate in relation to the screw 32. As explained earlier, an axial movement of the two brackets towards each other is thereby generated, and the outer bracket 3 1 comes into abutment against the claw arm 5 and the first end of the link arm at the rotating joint 36 at a contact point 52 (fig. 5a). The link arm 34 is thereby pressed against the inner bracket 30 and forced to rotate about the rotating joint 37, with the result that the claw arm 5 with the grip-hook is pulled towards the centre axis 61 as explained with reference to figs. 2a and b.

In the above, the invention has been explained with reference to individual embodiments. It is clear, however, that a number of variants are possible within the scope of the invention, associated, for example, with the shape of the brackets, this naturally being adapted to suit the production method, which may be stamping or casting. Furthermore, the centrally located threaded portions and devices for executing the rotational movement thereon may be varied in a number of ways, this process being capable of being adapted to enable the execution of the rotational movement to be performed with the same tool which is used on the vehicle's wheel nuts. These and similar changes can be performed by a person skilled in the art without deviating from the invention as it is defined in the claims.