EP1737719A1

EP1737719A1 - Improved steering column assembly

Info

Publication number: EP1737719A1
Application number: EP05736021A
Authority: EP
Inventors: Michael Appleyard
Original assignee: TRW Lucas Varity Electric Steering Ltd
Current assignee: TRW Lucas Varity Electric Steering Ltd
Priority date: 2004-04-22
Filing date: 2005-04-21
Publication date: 2007-01-03
Also published as: GB0408907D0; WO2005102818A1

Abstract

A steering column assembly comprises an adjustable portion and a fixed portion, the adjustable portion being secured to the fixed portion by a clamping mechanism that comprises a pin (7) having a head (8) and a shaft which extends from the head through an elongate opening in the adjustable portion and an opening in the fixed portion, a set of teeth (12a, 12b) provided in a locking region of the adjustable portion; a toothed member, such as a toothed block (16), which carries at least one tooth adapted to cooperate with the teeth (12a, 12b) of the adjustable portion; a basing means (14) which biases the head (8) of the pin away from the locking region of the adjustable portion, a resilient connection means (15) which resiliently connects the head (8) to the block, and a clamp assembly which is adapted to draw the head (8) of the pin towards the fixed portion against a resistance force provided by the biasing means (14) so that the adjustable portion is clamped to the fixed portion by the head and further such that teeth of the toothed block (16) are biased into engagement with the teeth (12a, 12b) of the adjustable portion by the resilient connection means (15).

Description

IMPROVED STEERING COLUMN ASSEMBLY

This invention relates to improvements in steering column assemblies, especially but not exclusively to electric power assisted steering assemblies.

It is known to provide a steering column assembly in which a steering wheel is connected to one or more road wheels through a collapsible or telescopic steering column shaft. The shaft is designed to collapse away from a driver of the vehicle if a load is applied to the steering wheel in the event of an accident. The shaft may comprise a single part shaft which has a weakened central section that will concertina under an axial load. Alternatively it may comprise a two part telescopic shaft in which one part slides axially into the other under an axial load.

To locate the steering shaft relative to the vehicle it is typically supported within one or more bearings carried by an adjustable support portion, often referred to as a steering column shroud. The shroud is in turn secured to a fixed portion bolted or otherwise fixed to a part of the vehicle chassis or bulkhead.

In almost all vehicles produced today the column shroud is adjustably clamped to a fixed portion of the vehicle in a way that permits the steering shaft to be adjusted for rake. Optionally the shroud may be adjustably connected to a guide portion which is itself moveable relative to a fixed part of a vehicle to allows it to be adjusted for reach. A lever- which must be located within easy reach of the driver- allows a clamping mechanism to be locked and unlocked for the position of the steering column shroud to be adjusted. This enables the driver of the vehicle to set the steering wheel at the most comfortable position. With the introduction of steering-wheel mounted airbags there has recently been a demand that, once adjusted, the column must be held in place by a positive locking method. By this we mean that, when the clamp is moved into its locked position, there must be greater restraint against subsequent column movement than would be created solely by friction.

It is normal to increase the resistance to movement by providing for a tooth on tooth engagement between a part secured to the fixed portion (the bracket and/or a guide portion) and the adjustable portion. In one known arrangement, the locking clamp pulls a toothed head of a locking pin into engagement with at least one track of teeth on the adjustable portion. However, a basic problem with the use of teeth in this way is that on occasions the tips of the teeth may be exactly in line when the driver attempts to move the clamp to the locked position. This so called tooth-on-tooth problem can either prevent the driver locking the clamp properly or in extreme cases damage the teeth or the locking mechanism.

In accordance with a first aspect the invention provides a steering column assembly comprising an adjustable portion and a fixed portion, the adjustable portion being secured to the fixed portion by a clamping mechanism which is operable between a locked position in which the adjustable portion is clamped against movement relative to the fixed portion and an unlocked position in which it is adjustable for reach relative to the fixed portion, in which the clamping mechanism comprises: a pin having a head and a shaft which extends from the head through an elongate opening in the adjustable portion and an opening in the fixed portion, a set of teeth provided in a locking region of the adjustable portion; a toothed member which carries at least one tooth adapted to cooperate with the teeth of the adjustable portion; a biasing means which biases the head of the pin away from the locking region of the adjustable portion; a resilient connection means which resiliently connects the head to the toothed member; and a clamp assembly which is adapted to draw the head of the pin towards the fixed portion against a resistance force provided by the biasing means so that the adjustable portion is clamped to the fixed portion by the head and further such that teeth of the toothed block are biased into engagement with the teeth of the adjustable portion by the resilient connection means.

The resilient connection between the head and the toothed member, which is preferably a toothed block, allows the teeth of the block to move relative to the head of the pin when placed under a loading. This provides some compliance and helps to prevent damage of the teeth in a tooth-on- tooth situation. The head clamps the adjustable and fixed portions together by friction, either directly between the head and the adjustable member or indirectly through one or more intermediate parts. At the same time the head causes the resilient connection means to urge the toothed block towards the teeth on the adjustable portion. If a tooth-on-tooth situation arises the connection means can deform, by bending or the like, to prevent damage to the teeth. In the event of a crash overcoming the friction caused by the head, the teeth on the block move relative to the teeth on the adjustable portion to bring them together and to prevent further movement.

The biasing means, on the other hand, serves the role of biasing (pushing or pulling) the head and its associated toothed block away from the mating teeth on the adjustable portion when the clamp assembly is released. The biasing means may comprise a first spring member. The resilient connection means may comprise a second spring member. The first and second spring members may comprises separate components which may be separate from the head of the pin. In an alternative one or both of these components may be integral parts of the head of the pin. For example, the second spring means may be formed integral with the toothed block or with the head, perhaps as a resiliently deformable mesh or web connecting the head to the toothed block.

The first spring member may comprise a leaf spring. It may be located at least partially between the head of the pin and the adjustable portion. The spring being flattened when the head is clamped to the shroud. The pin shaft may therefore pass through an opening in the leaf spring. The spring may have a H-shape or X-shape with the arms and legs of the spring being cranked out of the plane of the central portion which is provided with the hole through which the pin shaft passes.

The second spring member may comprise a leaf spring, and in a most convenient arrangement comprises a C-shaped spring having a base which is located at least partially between the head of the pin and adjustable member and arms which curve around the toothed block to pull the block towards the adjustable member.

Preferably the first spring member is located between the adjustable portion and the second spring member so that it biases the second spring member away from the adjustable member as well as biasing the head away.

Of course, the biasing means and the resilient connection means, where separate from the head, may be part of one and the same component, perhaps a single pressed part that functions as both the first and second springs .

The pin shaft may extend through openings in the first and or the second spring members. The head of the pin may be provided within an opening in the toothed block which is larger than the head. The head may be of a size greater than the openings in the first and second springs such that as the pin is locked by the clamp the head cannot pass through the opening.

Where the head of the pin extends through or into an opening in the toothed block, it should be shaped such that when fully clamped the head itself does not force the toothed block into a locked engagement with the teeth of the adjustable portion, this function instead being fulfilled by the resilient connection means. Of course, if the resilient connection means forms part of the head it will be understood that the fixed part of the head should not clamp the toothed block rigidly in place, only the resilient portion.

The fixed part of the head may include a ramped face which co-operates with a corresponding ramped face of the toothed block. The ramped face of the head may face away from the direction of movement of the adjustable portion in the event of a crash. The toothed block may be provided with a corresponding ramped face which cooperates with this.

The teeth of the adjustable portion may have a saw tooth profile in which one side of each tooth has a steeper ramp angle than the other. In this case, the steep sides should have a lower tangent of pressure angle than the value of the friction coefficient between the flanks of the teeth and the corresponding teeth on the toothed block. This ensures that the teeth are not pushed out of disengagement when a load is applied during a crash. The steep sides may face towards the direction in which the adjustable portion moves relative to the fixed portion.

Many different mechanisms can be used within the scope of this invention to pull the head of the pin into the locked position. For example, the pin may be threaded and may carry a nut having a complimentary thread which is rotated by a locking lever to produce an axial movement of the pin. Alternatively or additionally the locking lever may rotate a cam relative to a cam follower or vice versa to clamp the head of the pin when locked.

The fixed portion may comprise a guide portion or guide post and the adjustable portion may comprise an upper shroud. The guide portion may include a channel and the upper shroud may include a rail which is located within the channel. The rail may include the elongate opening through which the pin shaft passes. The rows of teeth may be provided on a separate casting which is riveted or otherwise fixed to the rail.

The guide portion may be rigidly attached to a bracket which is secured to a fixed part of the vehicle body. This provides for a single adjust mechanism which permits reach adjustment to be made. In an alternative, the guide portion may itself be moveable relative to the vehicle body when the clamp is unlocked and fixed only when the clamp is locked.

This may be achieved by passing the shaft of the pin through an opening in a fixed bracket as well as an elongate opening in the guide portion which extends orthogonal to the elongate opening in the adjustable portion.

In an alternative, the opening in the bracket, typically a pressed or cast metal bracket, may comprise an elongate slot which is orthogonal to the axis of the steering shaft and the axis of the pin to permit adjustment of the adjustable portion for rake.

There now follows, by way of example, several embodiments of the invention described with reference to the accompanying drawings, in which:

Figure 1 shows a cross section perpendicular to the steering column, viewed in the direction away from the steering wheel through a steering column according to a first aspect of the invention;

Figure 2 shows an alternative cross section of the steering column assembly; and

Figure 3 is an exploded view of the component parts of the clamping mechanism of the assembly and associated parts.

A steering column assembly for a vehicle, according to a first aspect of the invention is shown in Figure 1 of the accompanying drawings. It comprises a two part steering shaft. The first lower, part (not shown) is optionally connected to an EPAS motor (not shown) at its lower end which outputs a torque through an output shaft to the lower part. The second, upper, part 1 is secured at its upper end to a steering wheel (not shown) . Splines on the two parts prevent them from rotating relative to one another.

The EPAS motor is located within a cast metal housing 2. An elongate guide portion 3 is secured to this housing and defines a lower shroud for the steering shaft 1. As such, the shaft 1 extends through the centre of the guide portion 3 for rotation therewithin. The guide portion 3 extends away along the steering shaft 1 from the motor housing past the point where the two parts inter-engage but stops short of the upper end of the upper part. The remainder of the steering shaft 1 is covered by a hollow tubular upper shroud 4.

A groove 3 a is cast in the inside wall of the guide portion 3. This is sized to accept a locking rail 5 welded to the tubular upper shroud 4. The locking rail 5 may slide within the groove but does not permit rotation of the upper shroud 4.

The guide portion 3 may be fixed rigidly to the vehicle if only reach adjustment is needed. The slidable engagement of the upper shroud 4 and the guide portion 3 allows adjustment of the reach or axial length of the combined shaft 1. However, in this embodiment the rake or angle of the shaft in the vertical plane is also adjustable by means of the guide portion 3 being arranged to pivot relative to the body of the vehicle. A bracket 6 which is fixed to the vehicle provides location for the guide portion 3. Of course, it is necessary to hold the guide portion 3 and the upper shroud 4 in place when the vehicle is driven. This is performed using the following clamping mechanism.

The bracket 6, the guide portion 3, the upper shroud 4 and its locking rail 5 are all provided with openings which are aligned. A shaft 7 of a pin passes through all these holes. The pin shaft 7 is terminated with a fixed head 8 located in the space between locking rail 5 and upper shroud 4. The head 8 is sized such that it cannot be pulled through the opening in the locking rail, or else a suitable spacer or washer is provided to prevent this happening.

The shaft 7 of the pin is threaded and carries a nut 10 on its end opposite the head. The nut, visible in Figure 1 is connected to a lever 11 which can be rotated about the axis of the pin shaft to lock and unlock the clamp. Rotating the handle 11 rotates a cam held captive on the shaft between the nut 10 a cam surface defined by the fixed bracket so as to move the pin axially when locking and unlocking.

The opening in the locking rail 5 is an elongate opening which allows the upper shroud 4 to move along its axis relative to the pin 7. Secured to the rail by rivets is a bar 12 which also has an elongate slot 13 through which the pin shaft passes. The bar 12 defines two rows of teeth 12a, 12b which extend along either side of the slot. The rows of teeth are spaced slightly from the edges of the slot such that a region between the slot edges is provided. When the clamp pin 7 is drawn to the locked position the pin head 8 is drawn towards this region, clamping the rail 5 to the guide portion 3 and the guide portion 3 to the fixed bracket 6 by friction.

The head 8 of the pin is biased away from the rail by a biasing means. This can best be seen in Figure 3 of the accompanying drawings. It comprises a leaf spring 14 having an opening 14a through which the shaft 7 passes. The spring 14 is flattened as the clamp is moved to the locked position. A resilient connection means 15 is also provided which again has an opening through which the pin shaft passes. This comprises a second spring which is located on the pin shaft 7 between the biasing means and the head 8 so that it is also biased away from the locking rail 5.

The second spring is c-shaped and hooks around two opposing edges of a toothed block 16. The toothed block 16 includes a central opening which receives the head 8 of the pin and has two rows of teeth which face the teeth on the rail 5. When the clamp is unlocked the teeth of the toothed block 16 are spaced from the teeth of the rail 5 by the biasing force of the biasing means 14. When clamped they are drawn into engagement with them by the resilient connection means 15. Since this provides some resilience the teeth will not break if a tooth-on-tooth situation occurs. Instead the connection will simply deform.

If the assembly is locked in a tooth-on-tooth situation, only frictional forces will be present to stop the upper shroud collapsing towards the lower guide in a crash. However, as soon as the friction is overcome and the assembly collapses, the teeth will move away from the tooth-on-tooth situation and drop into engagement. This will prevent any further movement.

Saw teeth are used in which the steep sides of the teeth on the rail 5 which have a lower tangent of pressure angle than the value of friction between co-operating tooth flanks. Therefore, the toothed block 16 is not pushed out of engagement when transferring the force of the impact to the teeth on the rail 5. It is notable that the toothed block 16 is a close fit around the head 8 of the pin to transfer forces through the head, the pin shaft 7 and to the guide portion 3.

In a further enhancement, visible in Figure 3 of the accompanying drawings, one side face of the head 8 of the pin has a ramp angle whose tangent is greater than the value of the friction coefficient between corresponding teeth. This ramp faces towards the steering wheel end of the shaft 1. The movement of the toothed block in a crash causes the head to engage the ramp and the ramp forces the toothed block down into the teeth more firmly than the second spring does on its own.

Claims

1. A steering column assembly comprising an adjustable portion and a fixed portion, the adjustable portion being secured to the fixed portion by a clamping mechanism which is operable between a locked position in which the adjustable portion is clamped against movement relative to the fixed portion and an unlocked position in which it is adjustable for reach relative to the fixed portion, in which the clamping mechanism comprises: a pin having a head and a shaft which extends from the head through an elongate opening in the adjustable portion and an opening in the fixed portion, a set of teeth provided in a locking region of the adjustable portion; a toothed member, such as a toothed block, which carries at least one tooth adapted to cooperate with the teeth of the adjustable portion; a biasing means which biases the head of the pin away from the locking region of the adjustable portion; a resilient connection means which resiliently connects the head to the block; and a clamp assembly which is adapted to draw the head of the pin towards the fixed portion against a resistance force provided by the biasing means so that the adjustable portion is clamped to the fixed portion by the head and further such that teeth of the toothed block are biased into engagement with the teeth of the adjustable portion by the resilient connection means.

2. A steering column assembly according to claim 1 in which the biasing means comprises a first spring member.

3. A steering column assembly according to claim 2 in which the first spring member comprises a leaf spring located at least partially between the head of the pin and the adjustable portion and in which the pin shaft passes through an opening in the leaf spring.

4. A steering column assembly according to claim 1 or claim 2 in which the resilient connection means comprises a second spring member.

5. A steering column assembly according to claim^' 4 in which the second spring member comprises a leaf spring having a base which is located at least partially between the head of the pin and adjustable member and arms which curve around the toothed block to pull the block towards the adjustable member.

6. A steering column assembly according to claim 4 or claim 5 in which the first spring member is located between the adjustable portion and the second spring member so that it biases the second spring member away from the adjustable member as well as biasing the head away.

7. A steering column assembly according to any preceding claim in which the head of the pin is provided within an opening in the toothed block which is larger than the head such that as the pin is locked by the clamp the head cannot pass through the opening.

8. A steering column assembly according to claim 7 in which the fixed part of the head includes a ramped face which co-operates with a corresponding ramped face of the toothed block, the ramped face of the head facing away from the direction of movement of the adjustable portion in the event of a crash, and in which the toothed block is provided with a corresponding ramped face which cooperates with the ramped face of the head.

9. A steering column assembly according to any preceding claim in which the teeth of the adjustable portion have a saw tooth profile in which one side of each tooth has a steeper ramp angle than the other, the steeper sides having a lower tangent of pressure angle than the value of the friction coefficient between the flanks of the teeth and the corresponding teeth on the toothed block.

10. A steering column assembly according to any preceding claim in which the fixed portion comprises a guide portion or guide post and the adjustable portion comprises an upper shroud.