GB2240518A

GB2240518A - Decoupler for a vehicle steering column

Info

Publication number: GB2240518A
Application number: GB9002603A
Authority: GB
Inventors: Bryan Jones
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1990-02-06
Filing date: 1990-02-06
Publication date: 1991-08-07
Also published as: GB9002603D0

Abstract

A decoupler has one channel-shaped part 34 and one bar part 32 which fits in the channel. The bar and the channel have mating, non-circular cross-sections so that steering torque can be transmitted by the decoupler. The bar part is pulled into the channel part by a clamping device in the form of a screw 52 which pulls the mating surfaces into close contact and establishes a frictional force between them which resists separation. If a force is applied between the two ends of the decoupler which tends to shorten the decoupler, ie a collision force, the force will be resisted by this frictional force; when the collision force reaches a level sufficient to overcome the frictional force axial movement of the bar 32 in the channel occurs and eventually face 58 will contact inclined wall 56 resulting in separation of members 34, 32. The use of the clamping device avoids the need for a shear pin as in previous constructions. <IMAGE>

Description

DECOUPLER FOR A VEHICLE STEERING COLUMN This invention relates to a decoupler for a vehicle steering column. Such decouplers are intended to allow the top end of the steering column to separate from the lower end of the column in the event of a crash, for safety reasons.

One such decoupler is described in GB-A-2 194 922. The assembly described in this specification has two parts, one in the form of a channel and one in the form of a bar which lies in the channel, and a shear pin through the two parts which normally holds them together. The fit between the channel and the bar is such as to transmit steering torque between the two parts, and the shear pin prevents any relative axial movement under normal operating conditions.

According to the present invention, there is provided a decoupler for a motor vehicle steering column, the decoupler comprising a first part in the form of an axially-extending channel, a second part in the form of a bar which fits in the channel and a clamping member which pulls the bar to the bottom of the channel, in a direction generally perpendicular to the longitudinal axis of the bar, to establish a frictional grip between the bar and the walls of the channel.

The use of a frictional grip to hold the two parts together results in a reduction in machining, and with suitable manufacturing techniques the bar and the channel may be connected to one another without any preliminary surface treatment.

The clamping member is preferably adjustable so that the clamping force can be set to a desired Value. Conveniently this can be achieved by making the clamping member as a threaded member so that it can be turned to control the clamping force, and thus the frictional grip which is established between the bar and the walls of the channel.

The channel will have an open side, but the width of the opening may vary along the length of the channel.

Similarly the width of the bar may also vary along the length of the bar. The bar and the channel can be arranged so that the channel has a portion with a narrow opening, the width of the opening being slightly greater than that of a narrow part of the bar but less than that of a wider part of the bar, and a wider part which has a width greater than that of the wider part of the bar. Under normal conditions, the wider part of the bar will be located beneath the narrower part of the opening so that the bar is prevented from escaping from the channel. However when axial, decoupling movement takes place between the bar and the channel, the narrow part of the bar may come to a position beneath the narrow part of the opening, and in this position the bar may become separated in a radial direction from the channel.

The channel may include an inclined end wall and the bar may include a correspondingly inclined end face so that when the bar moves axially along the channel in the direction which shortens the decoupler, then the inclined end face of the bar engages with the end wall of the channel to urge the bar out of the channel.

The threaded clamping member may be a screw or bolt which passes through a slotted aperture in the base of the channel and into a tapped hole in the bar. The slotted aperture in the base of the channel should be of a width slightly greater than the diameter of the shank of the screw, and may lead into an area with a much larger aperture through which the head of the screw can pass in a position where it is intended that the wo parts should be capable of separation.

The channel may be formed by bending a sheet metal strip or plate, with the inclined wall being a separate component welded into place. The bar may be formed by forging.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration showing a motor vehicle steering column; Figure 2 is an exploded view of a decoupler in accordance with the invention; Figure 3 is a plan view of the assembled decoupler; Figure 4 is an elevation, partly in section on the line F-F from Figure 3; and Figures 5 and 6 are respectively radial sections on the lines E-E and C-C.

Figure 1 shows a motor vehicle steering column generally designated 10 and having a steering wheel 12 at one end and a steering rack 14 at the other end connected by means of tie rods 16 to the wheel support knuckles 17 of a pair of front wheels 18. The column has a shaft 20 which can be secured rigidly to the vehicle bodywork by means of mounting plates 22. At the bottom end of the column 20 is a universal joint 24 which connects the bottom of the column to one end of a decoupler 26. The other end of the decoupler is connected by another universal joint 28 to a pinion drive shaft 30.

The decoupler is present in the steering column to ensure that a force which might occur in a front end impact and which would tend to drive the steering gear backwards into the car does not cause a resultant backward movement of the steering column. There will of course be a driver sitting behind the steering wheel 12, and it is important to ensure that the steering column is not forced back into the driver's chest in such an impact.

It will be seen from Figure 1 that the decoupler 26 comprises two parts 32 and 34. The manner in which these two parts are connected to one another and are capable of decoupling from one another will be described with reference to Figures 2 to 6.

Figure 2 shows the two parts of the decoupler, 32 and 34, separated from one another. One part, 32, is in the form of a bar having a wider part 36 and a narrower part 38. At the left hand end of the bar is a yoke 40 for connection to the universal joint 28. The part 32 also has a tapped hole 42.

The part 34 is, over the region 44, in the form of a V - shaped channel as will be more apparent from a consideration of Figures 5 and 6. In the base of the channel there is a slot 46 which leads into an aperture 48.

The right hand end of the part 34 is also in the form of a yoke 50, of a similar nature to the yoke 40, and for connection to the universal joint 24. The relative angular orientations of the yokes 40 and 50 will depend on the construction of the adjacent steering column components to which they are to be connected.

Figures 3 and 4 show the decoupler in its normal assembled condition. The two parts are held in this condition by means of a screw 52 which passes through the slot 46 and into the tapped hole 42 in the bar 32. The shank of the screw 52 is a clearance fit in the slot 46, but the screw has a head 54 which engages on the outer surface of the channel part t34. Tightening of the screw 52 therefore pulls the bar part 32 into the channel. Both the bar part and the channel have a generally V-shaped cross section as is apparent from Figures 5 and 6 and therefore tightening of the screw 52 results in the two parts being pulled together such that friction is created between their mating flanks. The channel part 34 also includes an inclined wall 56, and the bar part 32 has a correspondingly inclined end face 58.

Figure 3 shows how initially the wider part 36 of the bar 32 is held within a part of the channel 34 where the width of the top opening of the channel is restricted by inturned lips 60 (see Figures 5 and 6). Even if the screw 52 was not present, the two parts 32 and 34 would remain connected and capable of transmitting torque from the column 20 to the shaft 30.

However if a force is applied between the two ends of the decoupler in a direction which tends to shorten the decoupler, then this force will first of all be resisted by the friction between the V-shaped parts of the bar 32 and the channel 34. When the load reaches a level sufficient to overcome that friction, axial movement will begin and the bar 32 will move into the channel; the head 54 of the screw will enter the aperture 48 and the narrow part 38 of the bar will lie under the narrow part 44 of the channel.

The inclined end face 58 will also come into contact with the wall 56, and by combination of all these factors the bar 32 will separate, in a radial direction, from the channel part 34.

Because of the clamping action of the screw 52, which determines the friction between the parts 32 and 34, there may be no need for machining or any other surface treatment of the mating flanks. It is helpful if the dimensions of the two parts are such that when the bar is received in the channel, the bar does not make contact with the bottom of the channel. This condition is illustrated in Figures 5 and 6, and it will be seen that this allows for full engagement to be achieved between the mating flanks of the two parts, without this being limited by contact with the bottom of the channel.

No shear pin is required in this construction. The resistance to decoupling is purely a function of the torque load applied to the screw 52.

It is also an advantage of the decoupler described that the swept volume is desirably low. Because the decoupler will rotate in use when the steering wheel is turned, it is desirable that the volume swept during this rotation should be as small as possible and in Figure 6 the boundaries of this swept movement are indicated by a chain-dotted circle 62. The head 54 of the screw lies within this circle.

Claims

1. A decoupler for a motor vehicle steering column, the decoupler comprising a first part in the form of an axially-extending channel, a second part in the form of a bar which fits in the channel and a clamping member which pulls the bar to the bottom of the channel, in a direction generally perpendicular to the longitudinal axis of the bar, to establish a frictional grip between the bar and the walls of the channel.

2. A decoupler as claimed in Claim 1, wherein the clamping member is adjustable so that the clamping force can be set to a desired value.

3. A decoupler as claimed in Claim 2, wherein the clamping member is a threaded member which can be turned to control the clamping force, and thus the frictional grip which is established between the bar and the walls of the channel.

4. A decoupler as claimed in any preceding claim, wherein the channel has an open side with the width of the opening varying along the length of the channel, the width of the bar varies along the length of the bar, and the bar and the channel are arranged so that the channel has a narrow opening region where the width of the opening is slightly greater than that of a narrow part of the bar but less than that of a wider part of the bar, and a wider opening region where the width of the opening is greater than that of the wider part of the bar.

5. A decoupler as claimed in Claim 4, wherein under normal conditions, the wider part of the bar will be located beneath the narrower part of the opening so that the bar is prevented from escaping from the channel.

6. A decoupler as claimed in any preceding claim, wherein the channel includes an inclined end wall and the bar includes a correspondingly inclined end face so that when the bar moves axially along the channel in the direction which shortens the decoupler, then the inclined end face of the bar engages with the end wall of the channel to urge the bar out of the channel.

7. A decoupler as claimed in any preceding claim, wherein the clamping member is a screw or bolt which passes through a slotted aperture in the base of the channel and into a tapped hole in the bar.

8. A decoupler as claimed in Claim 7, wherein the slotted aperture in the base of the channel is of a width slightly greater than the diameter of the shank of the screw, and leads into an area with a larger aperture through which the head of the screw can pass in a position where it is intended that the two parts should be capable of separation.

9. A decoupler as claimed in any preceding claim, wherein the channel is formed by bending a sheet metal strip or plate, with the inclined wall being a separate component welded into place.

10. A decoupler as claimed in any preceding claim, wherein the bar is formed by forging.

11. A decoupler for a motor vehicle steering column, substantially as herein described with reference to the accompanying drawings