This invention relates to improvements in steering column assemblies. It is known to provide a collapsible steering column assembly comprising a steering shaft that is supported within a steering column shroud. To prevent significant injury to the driver in the event of a crash the steering column should be able to collapse as an axial load is applied through the steering wheel, for instance in a front impact where an unrestrained driver is thrown onto the steering wheel.

The steering column shaft may collapse through the use of a weakened section of shaft. However, in a typical modern vehicle the steering shaft is able to collapse telescopically with a first part of the shaft sliding over a second part of the shaft. Advantageously, this same telescopic motion may be used to provide for a range of adjustment of the steering column assembly for reach. In that case, the shaft is typically supported within a shroud that is also telescopic and comprises two portions: an upper shroud portion and a lower shroud portion. A locking mechanism fixes the steering shaft at a desired length, and this is arranged typically so that it is overcome in a crash to permit the desired collapse in length.

To allow a torque to be carried across the two parts of the steering shaft, the end portion of one part of the shaft- typically the upper shaft that is nearest the steering wheel- is hollowed and provided with inwardly extending elongate splines around the circumference of the inner surface. These engage corresponding outwardly facing splines on an end of the other part of the shaft. The splines prevent relative rotation of the two parts of the shaft about their common axis whilst allowing the shafts to slide telescopically. A low friction coating may be provided on the splines in the form of an overmolding, which also has the benefit of allowing the dimensions of the splines to be closely controlled. This is important to prevent the two parts of the shaft tilting relative to one another.

In the event of a crash, the shroud and steering column shaft must be allowed to telescopically collapse, reducing the overall length of the assembly and allowing the steering wheel to move forwards. This is achieved by allowing the upper shaft to move telescopically over- or into- the lower shaft, and similarly for the upper shaft to slide over- or into- the lower shroud. A problem has been observed where the upper part of the shroud reaches a limit of its travel when under a high load, whereby it abruptly impacts the lower part of the shroud. This can cause damage to the shroud and also could introduce a risk to the driver as the force resisting the collapse suddenly increases.

The present invention aims to at least partially ameliorate problems associated with the behaviour of a telescopic steering column assembly at the end of the available collapse travel.

According to a first aspect the invention provides a collapsible steering column assembly comprising a telescopic steering shaft that is supported within a steering column shroud, the telescopic steering shaft comprising:

a first shaft having a hollow end with an inwardly facing wall,

a second shaft that has an end that is located within the hollow end of the first shaft, a damper device located at the end of the second shaft that is located within the hollow end of the first shaft that includes a contact member defining a contact part that contacts the inwardly facing wall, characterized in that a portion of the inwardly facing wall tapers away from the open end of the hollow end, and in which in the event of a collapse of the steering column assembly the damper device is forced to move along the tapered portion whereby it is increasingly deformed radially thereby to provide a resistance to further collapse of the steering column assembly.

The damper device may in normal use of the steering column be located in a region of the hollow end that is not tapered, and may move into the tapered portion during a collapse of the steering column assembly. The non-tapered portion may have an internal diameter that is larger than the tapered portion so that the damper device is deformed by a lesser amount, or is not deformed, by the contact with the inwardly directed wall of the hollow end.

The steering column assembly may include a telescopic column shroud having an upper part and a lower part, the upper and lowe parts being free to move axially relative to one another for all positions of the second shaft relative to the first shaft where the damper part is located outside of the tapered portion, the damper sliding along the inwardly facing wall of the hollow end, so at to permit the reach of the steering column assembly to be adjusted.

The deformation of the damper device on being forced along the tapered portion may comprise bending of a portion of the device, or compression of a portion of the device, or a combination of bending and compression either at the same time or in sequence.

The hollow end may include an inwardly facing wall that is provided with a plurality of inwardly facing elongate splines that each extend axially along the shaft, the tapered portion being located further down the hollow end beyond the splines, the second shaft being provided with a set of outwardly facing elongate splines that each extend axially along the outer surface of the end of the second shaft, the splines of the second shaft inter- engaging the splines of the first shaft to prevent relative rotational movement of the two shafts whilst permitting the two shafts to move axially relative to one another at least in the event of a crash, in which the damper device in a normal use of the steering column assembly contacts the tips of a plurality of the splines of the first portion, thereby to take up any radial free play between the end of the second portion and the first portion at least in the location of the damper device. The tapered region of the bore may be circular in cross section, and may therefore form a part of a cone, but may have other cross sections.

The tapered region of the hollow end may smoothly decrease in diameter at locations further from the open end of the first shaft. By smoothly we mean that there is no sudden step change in the diameter of the bore. The region may taper linearly over a region of at least 1 cm or at least 3cm, or 10cm or more. As the second shaft and first shaft move towards each other the damper device is gradually compressed radially, absorbing energy as it does so. The longer the region of the taper the longer the collapse travel of the steering column assembly over which a gradually increasing resistance force is provided by the compression of the contact device.

The damper device may comprise a radially deformable, for example resilient, contact member that is secured to the second shaft and is placed under a static force, the magnitude of the force setting the outer dimension of the member. Where the outer edge of the member forms part of a circle, the force may set the diameter of that circle.

The static force may compress any combination of compression, tension or bending or twisting force that causes the resilient member to deform into shape that differs from its nature rest shape when no load is applied. Most preferably the force is a compressive force.

The contact member preferably comprises an element that is discrete from the end of the second shaft and is secured to the second shaft by a fastener, the fastener applying a force to the resilient member that controls the outer dimension of the element.

In an alternative, the contact member could be an integral part of the second shaft part.

The contact member may comprise a generally truncated conical shape with an inner diameter and an outer diameter that is secured in a first region towards the inner diameter to the end of the second shaft portion by a fastener, the member being arranged such that the outer edge of the member define the contact portion that engages the tips of a plurality of the splines of the first shaft part. The first region may define a hub of the contact member.

The axis of rotation of the member may be coincident with the axis of rotation of the second shaft part.

The member may be secured to the second shaft part by the fastener such that a second region of the member that is radially offset from the hub of the member engages a profiled surface of the end portion of the second shaft, whilst the hub is axially offset from the end of the second shaft and engages the fastener.

The fastener may be adjustable to vary the force with which the first region of the member is pulled towards the end of the second shaft part, whereby as the hub is pulled closer towards the second shaft part the profiled surface presses on the second region of the member to cause the member to deform, thereby altering the outer radial diameter of the conical member. The fastener may include a biasing means that acts between a fixed part of the fastener and the hub of the contact member. This may comprise a spring, such as a coil spring. The contact member may be secured to the end of the second shaft such that the cone points away from the second shaft, the profiled surface of the end of the second shaft being convex whereby as the fastener draws the conical member onto the terminal end the cone splays and increases in outer diameter. In an alternative, the truncated conical contact member may be secured so that the cone points towards the second shaft, the terminal end portion of the second shaft being convex, whereby the fastener pulls the conical member into the convex terminal end portion causing the outer diameter to be reduced. Where the terminal portion is convex it may be defined by a simple chamfer provided around the end of the second shaft part.

The fastener may comprise a threaded bolt that passes through a hole in the member to engage a threaded hole in the second shaft. The head of the bolt may be provided with a profile suitable for engagement with a suitable tool that allows the bolt to be torqued up. The biasing means, where provided, may comprise a coil spring that is located concentrically around the stem of the bolt.

A single bolt may be provided that engages a threaded hole in the second shaft. The hole may extend axially along the second shaft and may be on the axis of rotation of the second shaft.

As an alternative to a bolt, a threaded stud may be secured to the end of the second shaft part that passes through a hole in the dished member and the dished member secured by a nut.

The thread of the bolt or nut or stud may be provided with a locking compound or adhesive to prevent movement once it has been set , typically during initial assembly. The first shaft part may have a bore that extends along its full length to allow access to the adjustable fastener with the second shaft engaged with the first shaft.

In use, the second shaft part is pushed into the first shaft part and the adjustable fastener adjusted until the member has taken up any unwanted free play. The friction may then be checked to ensure the anti-vibration device is not pressed too firmly onto the inwardly facing splines. This check could alternatively be performed by deliberately vibrating the shaft during adjustment of the fastener and noting from the change in resonant frequency when the member has just come into contact with the splines.

The skilled reader will appreciate that the generally truncated conical member may have many shapes that can all be considered to be generally conical. It may only be conical on one surface- the one that engages the second shaft part. The outer edge need not be continuous, but should extend over at least three regions that are spaced apart by approx. 120 degrees to allow the anti-vibration device to self centre the second shaft part within the hollow end of the first shaft part.

In one preferred arrangement the contact member may comprise a hub portion and a plurality of radially extending fingers or petals that project away from the hub portion and form the generally conical shape, the hub defining the radial inner portion whereby the fastener pulls on the member and the fingers or petals each defining an arcuate outer contact outer portion at the extreme tips of the fingers or petals that engages the splines of the first shaft portion.

It is preferred that the arcuate edges cover as much of a circular path as possible, to contact the maximum number of spline tips.

The terminal portion of the second shaft may press upon each finger or petal in a region approximately midway between the hub and the terminal edge of the petals, each petal acting as an individual leaf spring.

The contact member should be resilient so that as the fastener is loosened the member will move back towards its unstressed shape. It may for instance comprise a metal member such as a spring steel member. But it could be made from a plastically deformable material, accepting that during installation the member can be splayed as more tension is applied but on releasing tension it will not spring back to the original shape. This makes assembly harder but still possible with care. There may be at least 5, or at least 6, petals, each having a radial outer surface defining the contact part that follows an arc that lies on a circle centered on the axis of the member and axis of the telescopic shaft.

Providing petals allows each one to independently adjust as the fastener is adjusted, to give the optimum take up of radial play between the two shaft parts without introducing excess friction.

Each petal may carry an axial protrusion that faces away from second shaft into the hollow end of the first shaft, each protrusion having a radially outermost edge that engages the inner wall of the hollow end portion. Each protrusion, or horn, may be resilient and help to guide each petal along the inner wall.

In use, each protrusion may absorb energy by one or more of bending, shearing or compressing during a collapse.

The member, or at least the portion that engages the splines of the hollow end of the first shaft, may be of a low friction material such as a plastic material. For example, a polietylen material may be used. As well as optimally being a low friction material the material should preferably be hard wearing so that it is not worn away during adjustment of the length of the steering column shaft.

The first shaft portion may comprise an upper portion of the steering column assembly and may be located closer to the steering wheel than the second shaft portion. The end of the first shaft portion may be provided with a plurality of external splines for engaging splines of a steering wheel hub

The lower shroud portion may comprise an input shaft for a torque sensor.

The torque sensor may additionally comprise an output shaft connected to the input shaft by a torsion bar. The output shaft may form an input to a gearbox assembly. The shroud may also be telescopic and may comprise an upper shroud portion and a lower shroud portion, the two being able to move telescopically to vary the length of the shroud.

The upper portion may strike the lower portion when an end of the allowable collapse travel is reached, this strike occurring after the damper device has been forced at least part of the way along the tapered region of the hollow end of the first shaft. Thus, some of the energy of the collapse is absorbed before the two portions of the shroud strike one another, reducing the severity of the impact.

The upper shroud portion may be located towards the end of the steering shaft that is nearest the steering wheel and the lower portion may be located towards the end of the shaft furthest from the steering wheel, the upper portion being at least partially received within the lower portion so that the upper portion can telescopically collapse into the lower portion during a crash.

The first shaft may be located nearest the steering wheel and the second shaft may be located furthest from the steering wheel. The second shaft may be connected to a gearbox assembly and the first shaft to a steering wheel.

The shroud may be secured to the vehicle by a support bracket that includes two support bracket arms that depend from a base portion to embrace the shroud, a clamp rail that is releasably secured to the upper shroud portion, the clamp rail including a slot that extends generally horizontally,

a clamp pin that extends through an opening in each of the arms of the bracket andthe clamp pin carrying a clamp mechanism that is movable between an undamped position in which the rail can move freely relative to the clamp pin and a clamped position in which the rail is fixed relative to the clamp pin.

The steering column assembly may be of fixed length, telescopically collapsing only in the event of a crash, or may be adjustable for reach, or adjustable for rake, or adjustable for both reach and rake. There will now be described, by way of example only, one embodiment of the present invention with reference to and as illustrated in the accompanying drawings of which:

Figure 1 is a cross section of an exemplary steering column assembly according to the present invention in a normal position of use prior to a collapse;

Figure 2 is a view similar to Figure 1 for the steering column assembly during a collapse; Figure 3 is a more detailed view of the portion ; and

Figures 4 and 5 are two embodiments of the damping device of the present invention.

As shown in Figure 1 , a collapsible steering column assembly 100 comprises a two part telescopic steering shaft that is supported within a steering column shroud. The shroud has an upper part 101 , that is located closest to a steering wheel (not shown) and a lower part 102 that is located furthest from the steering wheel and secured to a housing of a gearbox (not shown). The shroud supports the steering shaft which comprises a first (upper) shaft 103 that is closest to the steering wheel and terminates at an upper end with a splined coupling for receiving a hub of the steering wheel. The end of the first shaft 103 that is furthest from the steering wheel is hollowed out, and the inner surface of the hollow end is provided along a portion closest to the open end with a plurality of inwardly facing elongate splines 103a that each extend axially along the inner surface. Each spline has the same height from root to tip, the tips all lying on a circular path that is centered on the axis of the first shaft 103.

Beyond the splines, the inner wall of the bore tapers away from the open end. This extends over a distance of several centimetres. The tapered section has a circular cross section. Also visible is an additional non-tapered region at the bottom of the hollow which, as will be seen, accommodates a non-active part of a damper device towards the end of a collapse of the steering column assembly.

The steering shaft also comprises a second shaft 104 that has an end that is located within the hollow end of the first shaft 103, the end of the second shaft being provided with a set of outwardly facing elongate splines 104a that each extend axially along the outer surface of the end of the second shaft. The splines 104a of the second shaft complement and interengage with the splines 103a of the first shaft to prevent relative rotational movement of the two shaft portions whilst permitting the two shaft portions to move axially relative to one another at least in the event of a crash or during adjustment for reach.

Secured to the end of the second shaft 104, within the hollow end of the first shaft part, is a damper device. The damper device performs two functions. The first is to control energy during a collapse, and the second is to remove radial play between the first shaft and second shaft. The damping device may therefore function as an anti- vibration device to reduce vibration induced rattle of the two parts of the steering shaft.

During normal use of the steering column assembly the damper device occupies a space between the second shaft and the inside of the hollow portion of the first shaft 103, making contact with the tips of the splines 103a of the first shaft part and helping to prevent excess vibration of the steering shaft by modifying the resonant frequency of the two part shaft. To do this, the spacer device must ensure there is no gap between the damper device and the inwardly facing splines, and ideally the contact device applies a very light pressure onto a plurality of the splines around the circumference of the hollow end portion with zero free play so that no radial movement of the second shaft relative to the first shaft is possible in the region where the spacer device is located. The damper device must also remain in contact with the splines over the full normal range of reach adjustment of the column assembly.

Two embodiments of a damper device that can be used within the scope of the present invention are shown in Figures 4 and 5 of the drawings.

Both of the damper devices comprises a resiliently deformable member 108 having a radially outermost edge 1 13 that lies at a constant radius from the axis of the second shaft so that all parts of the outer edge lie on the desired circular path. The contact member 108 is secured to the end of the second shaft by a fastener. The contact device has a generally truncated conical shape with an inner diameter and an outer diameter. More specifically, the member comprises a hub portion 1 12 and a plurality of radially extending fingers or petals 1 14 that project away from the hub portion and form the generally conical shape. Six petals are shown, the outer edge of each petal lying on the circular path and forming a set of six arcs, each spanning about 50 degrees of the circular path. The regions between the petals are cut away right back to the hub of the resilient member. The petals 1 14 define the cone shape.

The resilient contact member 108 is fixed onto the end of the second shaft part by the fastener. This comprises a bolt with a threaded stem 109 and a head 109a. The stem passes through a hole in the hub of the member that is smaller than the head 109a of the bolt (the bolt being on the opposite side of the member to the second shaft) and the stem is engaged into a complimentary thread of a threaded hole in the second shaft. The head 109a of the bolt is provided with a profile suitable for engagement with a suitable tool that allows the bolt to be torqued up.

The bolt holds the contact member such that the hub 1 12 of the member is slightly stood off from the end of the second portion and the head of the fastener pulls the inner portion towards the second shaft 104. The threaded stem of the bolt is therefore placed under tension as the petals of the member 108 are forced into contact with the second shaft part. Each petal 1 14 acts as a leaf spring and is deformed by this contact, causing the outer edge of the petals 1 14 to splay outwards. The amount of tension in the stem 109 of the bolt determines how much the resilient member is splayed and this sets the diameter of the circular path on which the outer edge of the petals lies. The region of the second shaft 104 that contacts the petals 1 14 in this example is chamfered, ensuring the petals 1 14 can slide smoothly over the end of the second shaft as the screw is tightened. The chamfer 1 16 in effect defines a cone shape that complements the cone shape of the contact member, the cone formed by the second shaft being forced into the cone of the contact member by the bolt.

In both of the example, an optional biasing means 120 in the form of a coil spring, is located on the threaded stem 109 of the fastener bolt that acts between the head 109a of the bolt and the hub of the contact member 108. The spring is set so that it is compressed. The spring applies a compressive force onto the contact member, pushing it firmly onto the chamfered end of the shaft part 104, so that the force is dependent on the set position of the bolt and also the amount of compression of the coil spring This alternative arrangement ensures that even if the outer edge of the contact member 108 becomes worn during operation, the spring will compensate this effect by always ensuring the contact member is pressed onto the tips of the teeth in the hollow end of the first shaft. The spring will continue to take up wear until either: (a) the hub of the contact member hits the end of the second shaft, (b) the spring becomes uncompressed or (c) the remaining compressive force in the spring is insufficient to apply the required bending force to the petals of the contact member.

When such a spring 120 is present there is no need to tighten the bolt after column assembly. It can be set on exactly specified distance which ensures correct spring tension before column will be assembled and in the next step on the assembly line column can be assembly. The contact member petals will deform a little bit along with the coil spring to allow the contact member to deform and fit perfectly into the hollow end of the first steering shaft.

Horns 121 are provided on each of the petals 1 14, which further encourage the deformation of the damper device, during impact.

The second embodiment of the damper device differs from the first in the shape of the horns 121 that are provided.

In use the bolt is tightened or loosened to deform the petals 1 14 until a condition is reached in which the diameter of the arcs defined by the outer edge of the contact member is perfectly in contact with no free play with the inner tips of the splines 103a of the first shaft. This helps to lower the resonant frequency of the overall shaft compared with an arrangement without the anti-vibration device, especially where there is only a short overlap of the splines. The screw can be set once during assembly and testing and then left during the life of the steering column assembly. An adhesive applied to the threads of the shaft ensures that the screw cannot work loose over time.

Whilst Figure 1 shows the steering column assembly in a normal position of use, with the contact portion contacting the splines of the upper shaft, Figure 2 shows the steering column assembly during a collapse, just prior to the upper shroud striking the lower shroud. As can be seen, the damper device has been forced into the tapered portion of the hollow end, causing additional radial deformation of the contact member.