GB2459959A

GB2459959A - Collapsible steering column assembly

Info

Publication number: GB2459959A
Application number: GB0907980A
Authority: GB
Inventors: Michael Appleyard
Original assignee: TRW Ltd
Current assignee: TRW Ltd
Priority date: 2008-05-15
Filing date: 2009-05-11
Publication date: 2009-11-18
Anticipated expiration: 2029-05-11
Also published as: DE102009021499B4; DE102009021499A1; GB0907980D0; GB0808798D0; GB2459959B

Abstract

A collapsible steering column assembly comprising a telescopic housing comprising an inner housing part 20 and a outer housing part 10 which surrounds the inner housing part along part of its length, the inner housing part being arranged so that it can slide into the outer housing part. A steering column shaft 60 passes through the inner housing part and is provided with a first bearing assembly 40 and a second bearing assembly 50. The first bearing assembly is located between the outer tube and the shaft permitting the shaft to rotate within the outer housing. The second bearing assembly is located between the inner tube and the shaft and comprises an inner and outer race whereby one of the inner or outer races is fixed in position relative to the shaft or tube with which it cooperates so as to permit the inner tube to collapse into the outer tube. A plurality of bearing elements is additionally located between the inner and outer races which permit the shaft to rotate within the inner housing. A spacer 70 may be provided spacing the second bearing assembly from the shaft thus providing a sliding engagement.

Description

ADJUSTABLE STEERING COLUMN ASSEMBLY

This invention relates to improvements in telescopic collapsible steering column assemblies. --Many types of collapsible steering column are known. One type is the telescopically collapsible steering column assembly in which an inner housing part slides into an outer housing part to provide the collapse stroke. This collapse allows the housing to move away from the driver as the steering column is struck by the driver's body in an accident. A two part or deformable steering column shaft, that is operatively connected to a steering wheel at one end, is located within the housing assembly. The shaft can also collapse by deforming or telescoping during a crash.

An example of such an assembly is disclosed in the applicant's earlier European patent application published as EP 1 919 755. The inner tube is a sliding fit within the outer tube, and also a sliding fit onto the shaft. A bearing assembly supports the outer tube around the shaft at a point along the shaft beyond the reach of the inner tube. The location of this bearing limits the distance by which the inner tube can slide into the outer tube. The stiffness of the column assembly is determined by the tolerance between the inner and outer tubes and also between the shaft and inner tube. For long column lengths, and in particular with relatively flexible two part steering column shafts, the applicant has appreciated that the assembly may not be sufficiently rigid for some design applications.

According to a first aspect the invention provides a collapsible steering column assembly comprising: a telescopic housing comprising an Inner housing part and a Outer housing part which surrounds the inner housing part along part of its length, the inner housing part being arranged so that it can slide into the outer housing part; a steering column shaft which passes through the inner tube; a first bearing assembly located between the outer tube and the shaft, the assembly comprising an outer race fixed to an inwardly extending wall of the outer tube, an inner race being fixed to the shaft and a plurality of bearing elements located between the races which permit the shaft to rotate within the outer housing; and a second bearing assembly located between the inner tube and the shaft which comprises an outer race which co-operates with an inwardly facing wall of the inner tube and an inner race which co-operates with the shaft, one of the races being fixed in position relative to the shaft or tube with which it co-operates and the other being free to slide over the shaft or tube with which it co-operates so as to permit the inner tube to collapse into the outer tube, and a plurality of bearing elements located between the inner and outer races which permit the shaft to rotate within the inner housing.

It is preferred that the outer race co-operates with the inner tube by being secured in position relative to the inner tube and the inner race co-operates with the shaft, directly or indirectly by a sliding engagement allowing it to move up and down the shaft. This is because preferred to the outer race sliding because it is easier to produce a very smooth finish (for good sliding) on the shaft outer diameter rather than the inner tube inner diameter.

The applicant has appreciated that the provision of two bearing assemblies enables the inherent flexing of the shaft, especially a splined two part shaft, in the tube in tube design to be controlled, especially for long column housing designs as required on some vehicles, and that this is particularly beneficial if the second bearing element is located at an optimum point along the shaft close to the end of the outer housing element into which the inner housing element is inserted.

The outer tube may be provided with an elongate slot along part of its length and a clamp mechanism provided which clamps the outer tube to the inner tube by squeezing the outer tube such that the slot closes up at least partially. This rigidly clamps the outer tube and inner tube together to maximise their radial stiffness.

The second bearing therefore effectively supports the shaft relative to the outer tube albeit via the inner tube.

The inner and outer housing parts may be tubular and arranged concentrically about a common axis shared by the shaft.

The inner race of the second bearing assembly may be spaced from the shaft by a spacer element which is secured to the inner race and which provides a sliding engagement with the shaft.

The spacer may comprise a sleeve which is at least partially of low friction material, or with at least a part coated in low friction material, that is located concentrically around the shaft and which has an inner surface that has the same diameter as the outer diameter of the shaft at the point where the second bearing assembly surrounds the shaft. The sleeve may be resilient such that it accommodates tolerance in the relative sizing of the shaft and bearing race without being either too loose or creating too much friction.

The shaft. may comprise an upper part and a lower part which are connected by a splined connector so that the overall length of the shaft can vary. The splined connection may be located between the first and second bearing assemblies.

The shaft may have a constant outer diameter over a length at least equal to the amount of collapse of the inner housing element into the outer housing element.

It may have an increased diameter beyond that to define an abutment against which the spacer rests to define the limit of collapse movement.

The spacer may include at least two outwardly extending tabs, one of which engages one end of the inner race and the other of which engages the other end of the inner race to prevent relative axial movement between the spacer and the inner race.

Preferably there are four tabs engaging each end of the inner race, spaced equi angularly around the axis of the inner race.

The spacer may comprise an annular split ring meaning that it is a ring which has a section of its circumference missing to permit it to be collapsed to a smaller diameter on assembly for insertion into the inner race. In its relaxed condition the outer circumference of the ring may be equal to the inner circumference of the inner race with the split ends of the ring slightly separated.

The steering column assembly may include an additional tubular spacer sleeve element which is located inside the inner tube and extends between the outer race of the second bearing assembly and part of a component or assembly which is connected to the vehicle structure. This may be a part which is connected to the structure via a pivoting means which allows vertical (rake) adjustment of the steering wheel position. For example, in the case of a steering column which is integrated with an electrical power-assistance system (EPS), the said part or assembly may be the EPS reduction gearbox housing or its cover.

This helps to keep the second bearing assembly axially located in the inner tube in the event that it otherwise is free to move. If the second bearing assembly is a press fit into the inner tube the sleeve may only serve as a back up in the event that it moves accidentally.

The tubular spacer element may be plastic.

The internal wall of the inner tube may be stepped to define an abutment against which the outer race of the second bearing assembly bears.

The first and second bearing assemblies may comprise ball bearing assemblies in which ball bearings are located between the inner and outer races.

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 sectional view of an embodiment of a steering column assembly in accordance with a first aspect of the present invention; Figure 2 is a cross section view of the spacer ring used in the assembly of figure 1; and Figure 3 shows by exaggeration the mode of deformation of the spacer ring when installed by comparing (a) an un-deformed spacer ring against (b) a deformed ring in isometric view.

The steering column assembly shown in Figure 1 of the accompanying drawings comprises a two part telescopic housing 10, 20 which surrounds a telescopic steering shaft 60. The shaft is in two parts, an input shaft and an output shaft, connected by a splined sliding connection which allows one part to telescope into the other. The input shaft would typically be connected to a Cardan-jointed Intermediate Shaft directly, or via an electric power steering EPS gearbox. The Intermediate Shaft connects the steering column to the steering gear which is on the chassis and which is usually of the rack and pinion type. The output shaft may carry a steering wheel.

The housing comprises an outer housing part, outer tube 10, and an inner housing part, inner tube 20. An end section of the inner tube is a sliding fit within the end of the outer tube, and by telescoping the inner tube relative to the outer tube the overall length of the housing can be adjusted.

The outer tube 10 is located concentrically around the shaft 60 by a first bearing assembly 40. This is located around the shaft at a point which is beyond the maximum allowable distance that the inner tube 20 can collapse into the outer tube 10 when measured from the end of the outer tube into which the inner tube is inserted. The first bearing assembly 40 comprises an outer race which is keyed to the inside wall of the outer tube, an inner race which is keyed to the shaft 60 and a plurality of ball bearings retained between the races. The keying prevents relative axial movement between the shaft and the outer tube whilst the ball bearings allow the shaft to rotate within the outer tube.

A second bearing assembly 50 is located between the inside wall of the inner tube and the shaft 60, and is located at a point closer to the end of the outer tube into which the inner tube is inserted than is the first bearing assembly. This bearing assembly 50 comprises an outer race that is press fitted into the inner tube and an inner race that fits around the shaft, the two races retaining ball bearings therebetween. The bearing assembly 50 is prevented from moving axially relative to the inner tube but can slide along the shaft because a spacer ring 70 of low friction material is provided between the inner race and the shaft 60.

A C2 clearance class bearing may be used as the second bearing assembly 50 to minimize internal radial lash. The outer race should be a light press fit into the inner tube, sufficient for retention of the bearing assembly axially but not enough to squeeze out the internal bearing clearance. This is eased by using an inner tube wall that is relatively thin, and therefore quite flexible. A plastic spacer 30 can be provided to limit the axial migration of the bearing to < 1 mm should the press fit to the tube fail to be adequate.

The second bearing assembly 50 helps achieve the target natural frequency for the column when the shaft passing through the inner and outer tubes is relatively long or is in two parts. This is especially the case for those versions with double-adjustment which uses a two part shaft and where a free sliding fit is required between the upper column shaft spline and that of the EPS Input Shaft, the said free sliding fit resulting in reduced bending stiffness across the splined shaft connection. The second bearing assembly is located at an axial position which provides useful benefit for radial stiffness and natural frequency.

Optionally, the outer tube 10 may be split and may clamp onto the inner tube 20 around the second bearing assembly 50 to give lash free contact when in the clamped position and this enhances the potential benefit still further. It is important, though, to minimise radial free play across the second bearing assembly by eliminating clearances between it and the inner housing and the shaft. It is also important that the upper shaft should slide through the inner race of the second bearing assembly with a minimum of friction so that reach adjustment and crash forces are not seriously affected. This is achieved through the use of a special plastic tolerance ring at the inner diameter of the bearing.

The said plastic tolerance ring may be lubricated. The spacer is shown more clearly in the cross section of Figure 2 of the accompanying drawings.

The plastic spacer ring 70 removes radial lash between the second bearing assembly 50 and the shaft 60 while ensuring smooth and relatively low-frictional sliding between the bearing inner race and the shaft. A "Pre-loaded" 3-point contact is guaranteed between the plastic ring and the inner race at points A by means of a "spring" element at S which is manifested in the localised deflection of the ring and which is enabled by a small radial clearance between shaft and ring at C. This ensures that there is zero lash radial lash between bearing and shaft when the small disturbances arise as the steering wheel is subject to sudden shock loads such as those that occur in the frequency test used in industry to determine the resonant vibration frequencies of the assembly. The mode of deformation of the spacer ring is shown in Figure 3 in an exaggerated way to make it more visible (compare with the undeformed spacer ring shown in Figure 2).

The clearance at C is very small, e.g. < 0.100 so that, for the Stiffness Test, when the steering wheel is much more heavily loaded radially (with up to 600N), the compliance of the so-called spring element is quickly bottomed-out and adds little to the deflection measured at the steering wheel.

In assembly of the embodiment of Figure 1 during manufacture, the spacer ring 70 may be fitted to the inner diameter of the bearing inner race, before the second bearing assembly is pressed into the column inner tube, by temporarily distorting it to close the gap G. The tabs T hold the ring in place axially relative to the inner bearing race. Once the shaft is inserted through the ring, the tabs cannot be over-ridden.

Claims

CLAIMS1. A collapsible steering column assembly comprising: a telescopic housing comprising an inner housing part and a outer housing part which surrounds the inner housing part along part of its length, the inner housing part being arranged so that it can slide into the outer housing part; a steering column shaft which passes through the inner tube; a first bearing assembly located between the outer tube and the shaft, the assembly comprising an outer race fixed to an inwardly extending wall of the outer tube, an inner race being fixed to the shaft and a plurality of bearing elements located between the races which permit the shaft to rotate within the outer housing; and a second bearing assembly located between the inner tube and the shaft which comprises an outer race which co-operates with an inwardly facing wall of the inner tube and an inner race which co-operates with the shaft, one of the races being fixed in position relative to the shaft or tube with which it co-operates and the other being free to slide over the shaft or tube with which it co-operates so as to permit the inner tube to collapse into the outer tube, and a plurality of bearing elements located between the inner and outer races which permit the shaft to rotate within the inner housing.
2. A collapsible steering column assembly according to claim 1 in which the outer race co-operates with the inner tube by being secured in position relative to the inner tube and the inner race co-operates with the shaft, directly or indirectly, by a sliding engagement allowing it to move up and down the shaft
3. A collapsible steering column assembly according to claim 2 in which the inner race of the second bearing assembly is spaced from the shaft by a spacer element which is secured to the inner race and which provides a sliding engagement with the shaft.
4. A collapsible steering column assembly according to claim 3 in which the spacer comprises a sleeve which is at least partially of low friction material, or with at least a part coated in low friction material, that is located concentrically around the shaft and which has an inner surface that has the same diameter as the outer diameter of the shaft at the point where the second bearing assembly surrounds the shaft.
5. A collapsible steering column assembly according to claim 3 or claim 4 in which the spacer includes at least two outwardly extending tabs, one of which engages one end of the inner race and the other of which engages the other end of the inner race to prevent relative axial movement between the spacer and the inner race.
6. A collapsible steering column assembly according to any one of claims 3 to 5 in which the spacer comprises an annular ring which has a section of its circumference missing to permit it to be collapsed to a smaller diameter on assembly for insertion into the inner race.
7. A collapsible steering column assembly according to any preceding claim which includes a tubular spacer sleeve element which is located inside the inner tube and extends between the outer race of the second bearing assembly and part of a component or assembly which is connected to the vehicle structure and in which the internal wail of the inner tube is stepped to define an abutment against which the outer race of the second bearing assembly bears.
8. A collapsible steering column assembly according to any preceding claim in which the outer tube is provided with an elongate slot along part of its length and a clamp mechanism is provided which clamps the outer tube to the inner tube by squeezing the outer tube such that the slot closes up at least partially.
9. A collapsible steering column assembly according to any preceding claim in which the inner and outer housing parts are tubular and arranged concentrically about a common axis shared by the shaft.
10. A collapsible steering column assembly substantially as described herein with reference to and as illustrated in the accompanying drawings.