GB2580189A - A steering column assembly - Google Patents

Abstract

A steering column assembly for a vehicle has a shroud 102, a gearbox 106 with a gearbox housing, a steering shaft 104 supported by shroud 102 and engaging a gear assembly, a bracket assembly 110 with a mounting part securable to a fixed part of the vehicle, and a clamp mechanism 122 movable between an unclamped position allowing shroud 102 to be adjusted for rake and a clamped position in which shroud 102 is fixed relative to bracket assembly 110. The assembly also has a resilient counter balance member spanning a gap between bracket assembly 110 and the gearbox housing, and fixed at a first location to bracket assembly 110 and at a second location to the gearbox housing or to a part of the steering column assembly fixed relative to the gearbox housing, so as to control the relative positions of bracket 110 and the gearbox housing.

Description

A STEERING COLUMN ASSEMBLY

The present invention relates to improvements in steering column assemblies. More particularly, the invention relates to electric power steering column assemblies that are adjustable for rake.

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.

A typical collapsible steering column assembly comprises a telescopic shroud, having an outer shroud portion and an inner shroud portion, an end of the inner shroud portion extending into the outer shroud portion. The outer shroud portion may be located closer to the steering wheel, or further from the steering wheel than the inner shroud portion. A telescopic steering shaft, also having an upper and lower shaft part, is supported inside the shroud through one or more bearing assemblies. The steering wheel is fixed to the upper shaft portion. In some cases, the shroud will not include two portions and instead the shroud will simply move relative to the bracket.

The part of the shroud closest to the wheel must be able to move, or collapse, during a crash so as to allow the steering wheel to move forwards relative to the vehicle body but be prevented from moving during normal use. There is also a need to fix the shroud relative to the vehicle body to define the rake position of the steering wheel.

This is typically achieved by a clamp mechanism that secures the shroud to a support bracket that is in turn fixed to the vehicle body, perhaps to a cross beam provided behind the dashboard of the vehicle. The clamp mechanism may be adjustable to permit reach adjustment, or rake adjustment, or both, of the steering wheel. In the event of a crash the shroud must be able to move, and this is achieved if it is able to break free of the clamp mechanism, or for the support bracket to be able to break free of the vehicle body, to allow the steering column assembly to collapse telescopically.

A lever may be provided on an end of the a clamp bolt that forms a part of the clamp mechanism that the driver can push or pull to rotate the clamp bolt and thereby operate the clamp mechanism.

Steering column assemblies are known which comprises a bracket assembly configured to be secured to a fixed part of the vehicle and including two arms that depend from a base portion to embrace the shroud, the shroud being located in the void defined between the two arms. The clamp mechanism includes a clamp pin that extends through an opening in each of the arms of the bracket asssembly and a slot in the shroud, typically in a rail that is fixed to a top surface of the shroud. In use, the clamp mechanism may be moved between an unclamped position in which the shroud can be adjusted for rake relative to the bracket assembly and a clamped position in which the shroud is fixed relative to the bracket assembly. This can be effectively achieved if the clamp mechanism applies a pressure to the outside of each arm, pushing the arms onto the shroud to grip the shroud in position.

An object of the present invention is to improve on the aforementioned steering column assemblies.

According to a first aspect, there is provided a steering column assembly for a vehicle, the steering column assembly comprising: a shroud; a gearbox comprising a gearbox housing; a steering shaft, which is supported by the shroud and which engages the gear assembly; a bracket assembly having a mounting part configured to be secured to a fixed part of the vehicle; and a clamp mechanism that is movable between an unclamped position in which the shroud can be adjusted for rake relative to the bracket assembly and a clamped position in which the shroud is fixed relative to the bracket assembly; characterised by further comprising a resilient counter balance member that spans a gap between the bracket assembly and the gearbox housing, the counter balance member being fixed at a first location to the bracket assembly and at a second location to the gearbox housing or a part of the steering column assembly that is fixed relative to the gearbox housing, the counter balance member in use controlling the relative position of the bracket assembly and the gearbox housing.

The steering assembly may in use be secured to the vehicle such that it is able to pivot around an axis that passes through an opening in the gearbox housing and the counter balance member may be sufficiently resilient to function as a spring to control the movement of the shroud relative to a part of the bracket assembly during rake adjustment of the steering column assembly. It may be configured to at least partially support or to fully support the shroud when the steering column assembly is in a position of use fitted to a vehicle and carrying a steering wheel such that with the clamp mechanism in the undamped condition the rake does not self-adjust or that the shroud moves automatically to a rake position that is substantially midway between the highest and lowest positions of the steering wheel. Of course, other default rests positions could be chosen depending on the pre-load applied to the counter balance member during manufacture or installation of the steering column assembly.

The counter balance member may be relatively inextensible to prevent any relative movement of the gearbox housing and bracket assembly in a direction parallel to the axis of the steering shaft, and may be relatively inextensible to prevent any relative movement of the gearbox housing and part of the bracket assembly in a generally horizontal direction, i.e orthogonal to the axis of the steering shaft. This helps assure that any fixings on the mounting bracket and gearbox housing, or holes for fixings, line up with corresponding features of the vehicle body to which the assembly is to be fixed.

The bracket assembly may comprise a support bracket that in use is fixed to a mounting bracket that is in turn secured to the vehicle body so it does not move, the shroud being releasibly fixed to the support bracket by the clamp mechanism whereby the shroud is indirectly fixed to the mounting bracket. The mounting bracket would typically be secured to a fixed part of the vehicle body such as a cross beam located behind the dashboard of the vehicle that runs from one side of the vehicle to the other.

The counter balance member may be fixed to the bracket assembly at the first location and may define a leaf spring connecting the first and second locations. The leaf spring may be bent when placed under a load to permit rake adjustment of the steering column assembly during use.

The second location may be located adjacent a pivot axis around which the gearbox rotates when the steering is adjusted for rake. in one arrangement, the counterbalance member may be secured to a pivot bolt that secures the gearbox housing to a fixed point on the vehicle, for instance by passing the pivot bolt through one or more holes in the counterbalance member.

The counter balance member may comprise a plate having a thickness in a direction parallel to the pivot axis that is considerably smaller than the width of the counter balance member in a plane parallel to the axis of rotation.

The plate may function as a leaf spring by resiliently deforming along a section that extends between the first and second locations. The plate may be the sole functional spring element of the counter balance member.

The counterbalance member may be the primary functional spring element of the steering column assembly that supports the free weight of the shroud and steering shaft and other movable parts when the clamp mechanism is unclamped. This ensures that it does not drop down surprisingly into the lap of the driver when the clamp mechanism is undamped.

The plate may be formed from a sheet of material that has a uniform thickness, being relatively wide compared with its depth and span a gap, along the axis of the steering shaft, between the bracket assembly and the gearbox housing. The length of plate spanning the gap may be substantially equal to the width of the plate where it spans the gap. The plate may therefore be relatively wide which helps stop the mounting bracket twisting relative to the gearbox housing.

To help reduce twisting, the counter balance member may be secured to the bracket assembly using at least two fixings spaced apart along a line that is orthogonal to the long axis of the steering shaft and offset from a vertical plane that contains the axis of the steering shaft.

The fixings may comprise bolts, each bolt passing through an opening in the counter balance member and an opening in the bracket assembly.

The counter balance member may include a secondary leaf spring that is connected at one end to the plate of the counter balance member and at the other to the gearbox housing or a part of the steering column assembly fixed relative to the gearbox housing at a third location offset from the second location, such as a pivot bolt that supports the gearbox.

In this arrangement there are two separate leaf springs defined, each helping to counterbalance the shroud and the bracket assembly. The plate is resilient and defines one leaf spring and the secondary leaf spring defines the other.

The secondary leaf spring may comprise an elongate metal strip. This may project substantially orthogonally from the plate towards the shroud. It may be secured by a fixing, such as a bolt, to an end face of the gearbox housing that faces the bracket assembly. The strip may include at least one bend or kink along its length.

In a rest position, prior to assembly of the steering column assembly, the counter balance member may support the weight of the shroud when the assembly is held by the bracket assembly so that the steering column assembly is substantially at the mid position for rake. By this we mean it is midway between the highest rake position (steering wheel fully raised) and the lowest rake position (steering wheel fully lowered).

The bracket assembly may include a base that is connected to the vehicle body when in use and two arms that depend from a base portion to embrace the shroud The damp mechanism may comprise a clamp pin that extends through an opening in each of the arms of the bracket assembly and a slot in the shroud; and whereby the clamp mechanism in use secures the shroud to the two arms of the bracket by squeezing the two arms onto the shroud when in the clamped position The clamp mechanism may include a cam mechanism located at one end of the clamp pin on the opposite side of an arm to the shroud. This may vary in length between the clamped and unclamped position to squeeze the bracket arms onto the shroud. An end stop my be provided at each end of the clamp pin, such as a head or nut.

The cam mechanism may include a fixed cam part and a moving cam part. Movement of the lever may act to rotate the moving cam part relative to the fixed cam part. Cam surfaces of the moving cam part and fixed cam part may result in a length of the cam mechanism changing due to this rotation.

The cam mechanism may include a part that fits within the opening in the leaf in one of the arms of the support bracket. This part may prevent the rotation of a fixed cam part of the cam mechanism and may take the form of a block or a pair of locating pins.

In the clamped position, the two bracket arms may be compressed between the cam mechanism and opposing sides of the shroud An embodiment of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a side view of a first embodiment of a steering column assembly in accordance with the first aspect; Figure 2 is a perspective view of the embodiment of Figure 1; Figure 3 is an alternative side view of the embodiment of Figure I in the clamped position showing the application of forces during a crash where a dummy strikes the steering wheel; Figure 4 is a side view of a second embodiment of a steering column assembly in accordance with the first aspect; Figure 5 is a top view of the second embodiment; and Figure 6 is a perspective view of the second embodiment from the opposite side to the one shown in Figure 5.

Referring firstly to Figure 1, there is shown a steering column assembly 100 comprising a shroud 102 that houses a shaft 104. The shaft 104 is configured to be attached to a steering wheel (not shown). The shaft 104 is supported by a bearing assembly (not shown) in a conventional manner that allows rotation of the shaft 104 relative to the shroud 102.

At one end of the shroud is a gearbox comprising a gearbox 106 housing that contains a gearset (not shown). The gearset includes an output shaft that is mechanically connected to a steering rack which is connected to the road wheels of the vehicle, and an input shaft that connects to the steering shaft. It also includes a connection to an electric motor which enables an assistance torque to be applied to the steering shaft. This may comprise a worm gear attached to the motor and a worm wheel that is attached to the output shaft, although many other arrangements are possible.

The shroud 104 is telescoping with an inner part secured to the gearbox housing 106 and an outer part sliding telescopically over the inner part and being spaced apart from the gearbox housing 106 so it is nearer to the steering wheel. This sliding movement permits the distance between the steering wheel and the gearbox housing 106 to be adjusted so that the driver can set the reach of the steering wheel to a preferred position. In simpler designs, this telescopic movement simply permits the steering shroud to collapse in the event of a crash but does not normally permit reach adj ustment A pivot pin 108 passes through a bore in an upper region of the gearbox housing 106.

The pivot pin 108 has an axis that is orthogonal to the axis of the steering shaft and substantially horizontal, and during adjustment for rake the whole steering column assembly may pivot around this pivot pin. Looking at Figure 1, the axis of rotation extends out of the sheet, and three solid lines marked A,B and C indicate the location of the free end of the steering shaft for the uppermost rake, mid-rake and lowermost rake positions of the steering column assembly. Figure I therefore shows the assembly at the mid-rake position. Note also that the force Fg shown in the drawing corresponds to the effect of gravity which absent any resistance from the steering column assembly would pull it down to the lowermost rake position.

A bracket assembly 110 secures the shroud to the vehicle body at a distance from the gearbox, typically a cross beam located behind a dashboard of the vehicle. This bracket assembly comprises a base plate 112 that is secured to the cross beam and a depending support bracket part 114 secured to the mounting bracket. Holes 116 are provided for receiving mounting bolts that secure the base plate 112 to the cross beam.

The base plate 112 is secured to the vehicle by frangible connectors (not shown) at locations 118, and the support bracket part 114 includes two arms 120 that depend in a substantially vertical direction and provide support and stability to the shroud 102.

The shroud 102 is releasibly secured to the arms 120 of the support bracket part 114 by a clamp mechanism 122 in any one of a range of rake positions, and typically in any one of a range of reach positions. When the clamp mechanism 122 is clamped the shroud cannot move and is fixed to the vehicle body through the bracket assembly.

The clamp mechanism 122 may take a variety of forms within the scope of the invention. in one example it may comprises a clamp pin 122 that passes through generally vertical slots in the arms of the support bracket part 114 and a horizontal slot in a clamp rail 124 of the shroud 102. The clamp pin 122 has a stop at one end that prevents the clamp pin 122 being drawn through the support bracket. At the other end, a cam mechanism that is rotated by use of a lever 126, which can be seen in Figure 3 but is obscured in Figure 1 and Figure 2 enables an effective length of the clamp pin 122, i.e. the length of the clamp pin 122 between the cam mechanism and a stop at the other end of the clamp pin, to be varied. These cam mechanisms are well known and may typically comprises a fixed cam part and a moving cam part, the moving cam part being rotated by the rotation of the lever pushing against the fixed cam part and extending the length of the cam mechanism.

In the unclamped position of the clamp mechanism 122, there is sufficient freedom of movement of the arms 120 of the support bracket 114 to allow adjustment of the reach and rake position of the steering column assembly 100 without undue exertion from a user.

The clamping mechanism 122 is shown in the undamped position in Figure I. Of course, other clamp mechanism and arrangements of support bracket may be provided within the scope of the present invention.

Prior to fitting the steering column assembly 100 to the vehicle it is desirable to provide a retaining mechanism that prevents excessive relative movement between the bracket assembly 110 and the gearbox housing. The reason for this is that otherwise the axial movement of the telescopic shroud could cause the shroud and bracket assembly to be pulled free from the gearbox if it is handled carelessly. Another reason is that providing a fixed relative location makes it easier to align the bolts for the base plate with holes in the vehicle body as the gearbox pivot is put into place. Various methods have been used in the past, such as the use of temporary cable ties to secure the mounting bracket to the gearbox assembly during installation which must then be cut free prior to completion of the installation.

In the steering column assembly 100 of Figure I. a resilient counter balance member 130 is provided that spans a gap between the base plate of the bracket 110 and the gearbox housing 106. The counter balance member 130 is fixed using two bolts 131, 132 at a first location to the bracket assembly and is fixed using a further two bolts 133,134 at a second location to a top face of the gearbox housing 106 dose to the pivot axis of the pivot pin 108.

The counter balance member in use control the relative position of the bracket assembly 110 and the gearbox 106 housing during installation, and also controls the resting rake position of the steering column assembly after installation at times when the clamp mechanism is unclamped. To achieve this the counter balance member 300 is sufficiently resilient to function as a leaf spring to control the movement of the shroud relative to the base plate 112 of the bracket assembly 110 during rake adjustment of the steering column assembly. As can be seen from Figure 1, the distance Li from the pivot to the free end of the steering shaft 104 that carries the steering wheel is slightly greater than the distance from the point where the counter balance member is secured to the gearbox housing to the free end. Therefore, as the shroud moves up or down for rake, the counter balance member will deform resiliently as the mounting bracket does not move.

In this example, the counter balance member is a metal plate formed from sheet material of uniform thickness, generally lying in a single plane apart from three stiffening ribs 135 and a gentle curve along its length. The plate has a width that is similar to the spacing between the gearbox housing 106 and the base plate 112. This means the plate is highly resistant to twisting which may occur if the two parts of the shroud move out of axial alignment, but can readily bend because the plate is relatively thin and hence not stiff in that direction. A steel material may be used for this plate.

An alternative steering column assembly 200 is shown in Figures 4 to 6 of the drawings. This is the same as the first embodiment and so like components have been indicated by the same reference numerals for clarity and brevity of explanation. There is a counter balance member 400 as with the first embodiment but it differs in its shape and the location points for fixing the counter balance member in place.

As can be seen, the counter balance member 400 comprises a metal plate 402, or other material, and an additional leaf spring member 404 in the form of an elongate strip of metal that is connected at a first end to the resilient plate. In fact as shown this is integral to the plate and is formed by cutting out a u-shaped channel into the body of the plate and bending out the material surrounded by the channel to form the strip. A second end of the elongate strip is connected to the end face of the gearbox housing 106 by a bolt 406. This additional leaf spring 404 may be tuned to work with the resilience of the plate 402 to give the counterbalance spring force that supports the weight of the shroud and other parts that move with the shroud. The plate 402 may therefore be stiffer against bending and twisting than the plate of the first embodiment giving greater control of movement of the shroud in the event of a crash which may apply a torsional force to the plate.

Note also that the plate 402 is fixed using bolts 408 at the mounting bracket end and is fixed at the opposite end by providing holes in the plate through which a pivot bolt for the gearbox is passed. Because the pivot bolt is in effect fixed to the gearbox housing, attaching the plate 402 to pivot bolt effectively fixes it to the gearbox housing. The use of the pivot bolt as a fixing in this way eliminates the need for a separate fixing to secure the plate 402 to the gearbox housing reducing complexity and in turn cost.

Claims (11)

1. CLAIMS1. A steering column assembly for a vehicle, the steering column assembly cornprising: a shroud; a gearbox comprising a gearbox housing; a steering shaft, which is supported by the shroud and which engages the gear assembly; a bracket assembly having a mounting part configured to be secured to a fixed part of the vehicle; and a clamp mechanism that is movable between an unclamped position in which the shroud can be adjusted for rake relative to the bracket and a clamped position in which the shroud is fixed relative to the bracket assembly; characterised by further comprising a resilient counter balance member that spans a gap between the bracket assembly and the gearbox housing, the counter balance member being fixed at a first location to the bracket assembly and at a second location to the gearbox housing or a part of the steering column assembly that is fixed relative to the gearbox housing, the counter balance member in use controlling the relative position of the bracket assembly and the gearbox housing.
2. 2. A steering column assembly according to claim I which is configured such that in use it is secured to the vehicle such that it is able to pivot around an axis that passes through an opening in the gearbox housing and the counter balance member is sufficiently resilient to function as a spring to control the movement of the shroud relative to part of the bracket assembly during rake adjustment of the steering column assembly'.
3. 3. A steering column assembly according to claim 1 or claim 2 in which the counter balance member is configured to at least partially support or to fully support the shroud when the steering column assembly is in a position of use fitted to a vehicle and carrying a steering wheel such that with the clamp mechanism in the undamped condition the rake does not self-adjust or that the shroud moves automatically to a rake position that is substantially midway between the highest and lowest positions of the steering wheel.
4. 4. A steering column is relatively inextensible to prevent any relative movement of the gearbox housing and bracket assembly in a direction parallel to the axis of the steering shaft and relatively inextensible to prevent any relative movement of the gearbox housing and bracket assembly in a generally horizontal direction, i.e. orthogonal to the axis of the steering shaft
5. 5. A steering column assembly according to any preceding claim in which the bracket assembly comprises a mounting bracket that defines the mounting part and a support bracket, the support bracket being fixed to the mounting bracket and the shroud being releasibly fixed to the support bracket by the clamp mechanism whereby the shroud is indirectly fixed to the mounting bracket, the counter balance member being fixed to the mounting bracket at the first location and defining a leaf spring connecting the first and second locations
6. 6. A steering column assembly according to any preceding claim in which the second location is located adjacent a pivot axis around which the gearbox rotates when the steering is adjusted for rake.
7. 7. A steering column assembly according to any preceding claim in which the counter balance member comprises a plate having a thickness in a direction parallel to the pivot axis that is considerably smaller than the width of the counter balance member in a plane parallel to the axis of rotation.
8. 8. A steering column assembly according to claim 7 in which the plate functions as a leaf spring by resiliently deforming along a section that extends between the first and second locations.
9. 9. A steering column assembly according to claim 8 or claim 9 in which the plate is substantially flat and spans a gap, along the axis of the steering shaft, between the mounting bracket and the gearbox housing.
10. 10. A steering column assembly according to any one of claim 7 to 9 in which the plate includes a secondary spring element that is connected at one end to the plate and at the other to the gearbox housing or any other convenient part of the steering column assembly that is fixed relative to the gearbox housing.
11. 11. A steering column assembly according to any preceding claim in which the counter balance member is the primary functional spring element of the steering column assembly that supports the shroud when the clamp mechanism is unclamped.