This invention relates to a steering column locking assembly.

Vehicle steering columns incorporate devices to inhibit vehicle theft. Two known types incorporate a fixed lock bolt and a tolerance ring to hold a lock collar in position. One type has the lock collar on the steering column tube and the other type has the lock collar on a steering wheel hub. Both of these types require tight tolerances on the components in order to achieve the torque profiles required. In addition, in practice, one of the materials required needs to be extremely hard, requiring non-standard material.

EP-A-0 129 522 and US-A-4 854 141 (equivalent to EP-A-2 046 621) both disclose steering column locking devices which have not used a swaging process to be formed, and this means that the material cannot be worked as much as required to produce the effect desired in the present invention, with corresponding difficulty in ascertaining the accuracy of the level or torque needed to allow for relative rotation.

According to a first aspect of the present invention, there is provided a steering column lock assembly comprising a first part and a second part, one of said parts being a steering column tube with an outer portion of circular section and the other of said parts being a steering column lock collar having a cylindrical inner portion fitting on said outer portion of the steering column tube, characterised in that said first part is plastically

deformed on said second part, such that relative movement between the two parts is resisted below a predetermined level of torque whilst relative rotation occurs at values of torque above said predetermined value.

According to a second aspect of the present invention, there is provided a steering column lock assembly comprising a cylindrical steering column tube having at least three axially spaced portions, the second axially spaced portion being between the first axially spaced portion and the second axially spaced portion, the diameter of the first axially spaced portion being greater than the diameter of the second axially spaced portion; and a hollow cylindrical lock collar having at least two axially spaced portions, the first axially spaced portion having a diameter smaller than the diameter of the second axially spaced portion, one of the axially spaced portions having a plurality of circumferentially spaced axially extending slots, the lock collar being positioned about the steering column tube with the lock collar first axially spaced portion being positioned about the steering column tube second axially spaced portion, the steering column tube first axially spaced portion diameter being greater than the lock collar first axially spaced portion diameter.

According to a third aspect of the present invention, there is provided a method of making a steering column lock assembly comprising a first part and a second part, one of said parts being a steering column tube having an outer portion of circular section and the other of said parts being a steering column lock collar having a cylindrical inner portion fitting on said outer portion of said steering column, characterised by plastic deformation said

first part onto said second part in such a manner that the two parts resist relative movement below a predetermined torque value and allow relative rotation at torque above said predetermined value.

The swaging may be such as to cause deformation of one or both of said parts.

A layer of plastics material may be provided between the two parts. The plastics material layer may be a separate layer and/or may be provided on the inside of the lock collar and/or on the outer portion of the steering column tube.

The invention also extends to a vehicle steering column incorporating such a locking assembly and to a vehicle incorporating same.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing, in which: -

Figure 1 is a diagrammatic side view, partly in cross-section, of a steering column locking assembly, and

Figure 2 is a perspective view of a lock collar shown in Figure 1 but prior to forming.

The drawing shows a cylindrical upper steering column tube

1 about which is fitted a cylindrical lock collar 2. Prior to fitting, the lock collar 2 is basically unformed and, once in place, is swaged into position onto a cylindrical outer portion of the steering column tube 1.

The lock collar 2 can be mechanically reduced to attach the lock collar to the steering column tube 1 by a Vailling process or with the use of a hydraulic press. A Vailling process is where the tube or shaft is formed by pushing it into a die, over a mandrel, or a combination of both. Swaging uses hammers to beat the metal into a different shape. The material changes that occur during these processes are different and sometimes the processes cannot be interchanged due to finished component material requirements. In general, Vailling hardens a material, and therefore, without annealing, cannot work the material as much. Preferably, the lock collar 1 is swaged on the steering column tube 2. Also, preferably, the lock collar 1 is swaged on the steering column tube 2 as the tube 2 is being formed.

The swaging process is arranged such that a certain predetermined amount of torque resistance is provided between the tube 1 and lock collar 2, the intention being that only a finite amount of torque is accepted and then rotation between the two parts occurs at any value above that. Once the torque load drops below a critical predetermined level, the lock collar 2 must once again transmit torque from the tube 1. It is the intention that this relative movement can occur several times without significantly changing the critical torque value.

The swaging also has the effect of maintaining the relative axial position of the lock collar 2 at all times, even during a crash. The zone A-A indicates the swaging zone. The steering column tube 1 is divided into three axially extending portions 10, 11, 12 and the locking collar 2 is divided into two axially extending portions 13, 14.

Preferably, the diameter of the steering column tube first and third axially spaced portions 10, 12 is greater than the diameter of the steering column tube second axially spaced portion 11. The lock collar first axially spaced portion 13 is positioned about the steering column tube second axially spaced portion 11 and the diameter of the steering column tube first axially spaced portion is greater than the diameter of the lock collar first axially spaced portion 13. The inner diameter of the lock collar second axially spaced portion 14 can be greater than the outer diameter of the steering column first axially spaced portion 10 creating a clearance 20 between the lock collar second axially spaced portion 14 and the steering column first axially spaced portion 10.

If desired, an anti-friction material 3 can be included and could, for example, be a plastics coating on the collar 2 or on the tube 1. Alternatively, or in addition, the material 3 could be in the form of a plastics tube which is also swaged between the tube 1 and collar 2.

The amount of torque required to make the lock collar 2 slip can be adjusted by varying the length of the swaged zone, the amount of force used in the swaging process or the amount and type of anti-friction material, or any combination thereof.

The lock collar 2 has a number of slots 2A in any one of which a lock pawl 4 can be engaged to lock the steering column and wheel.