GB2377471A

GB2377471A - Clamping apparatus with zinc coated clutch plates

Info

Publication number: GB2377471A
Application number: GB0117111A
Authority: GB
Inventors: Colin Andrew Mitchell
Original assignee: NSK Steering Systems Europe Ltd
Current assignee: NSK Steering Systems Europe Ltd
Priority date: 2001-07-13
Filing date: 2001-07-13
Publication date: 2003-01-15
Also published as: GB0117111D0

Abstract

A clamping apparatus 8 suitable for an adjustable steering column 2 comprises clutch plates 14,16 for holding the steering column in it desired position. At least some of the clutch plates are coated with a coating containing zinc. The coating is preferably a resin based metallic zinc primer which may also include organic solvent. The zinc coating increases the coefficient of friction between the clutch plates when clamped together, and when separated the coating provides a good adjustment feel. The apparatus preferably includes a clamp lever 6 for bringing together or separating the clutch plates 14,16.

Description

CLAMPING APPARATUS The present invention relates to a clamping apparatus; in particular for an adjustable steering column for a vehicle.

In known adjustable steering columns, there is an increasing requirement for higher and higher forces to be resisted by clamping apparatus which act to lock the steering column in position. Such clamping apparatus generally uses friction to lock the steering column in position. In an effort to support these higher forces it is now common practice to incorporate a series of plates in the clamping apparatus, which act as clutch places. The friction between the plates is governed by the applied compressive force, plate material and the surface finish. Roughening the surface of the plates increases the friction between them but results in difficulties in smooth but accurate adjustment when the clamping apparatus is unlocked. In particular a poor adjustment feel'arises when che clamping apparatus is unlocked, which is felt by the driver as non-uniform, i. e. fast and loose, low friction resistance to adjustment.

According to the present invention, there is provided clamping apparatus including clutch plates, at least some of the clutch plates being coated with a coating containing zinc.

The present invention preferably also provides an adjustable steering column comprising such clamping apparatus.

In preferred embodiments, such a coating advantageously provides high friction between the plates when the

clamping apparatus is in its locked configuration without producing a poor adjustment feel when the clamping apparatus is in its unlocked configuration.

The coating is preferably zinc rich, such as a coating containing metallic zinc. A preferred coating is an organic solvent based, resin bonded, metallic zinc primer, a preferred example of which is a product known as Xylan ( 5611 available from Whitford Plastics Limited, Christleton Court, Manor Park, Runcorn, Cheshire WAT 1ST, United Kingdom.

A preferred embodiment of the present invention will now be described by way of example and with reference to the drawings, in which: Figure 1 is a perspective illustration of an upper part of rake and reach adjustable steering column, Figure 2 is a graph showing by way of comparison forces required to move a locked adjustable steering column with and without the preferred coating applied to the clutch plates of the clamping apparatus.

As shown in Figure 1, in an adjustable steering column 2 the shaft 4 is held in a predetermined position by clamping apparatus 8 comprising sets 10,12 of interleaved clutch plates 14, 16 which are normally pressed together such that the friction between the plates 14,16 acts to hold the shaft 4 in its predetermined position. The clamping apparatus 8 acts to prevent the shaft 4 from moving when not required to, say during normal driving or more importantly during a crash when the clamping

apparatus 8 has to withstand the force of a driver colliding with the steering wheel (not shown) and also has to support the reaction caused by the firing of an airbag (not shown).

In order to reset the position of the steering column shaft 4, the driver of the vehicle releases a clamp lever 6, which reduces the compressive force pressing the clutch plates 14,16 together. The driver can then adjust the position of the steering shaft by moving the steering wheel (not shown) up or down and in or out. The driver then moves the lever 6 back to its locked position which has the effect of reapplying the compressive force to the clutch plates 14,16 so as to press them together thereby holding the steering column shaft 4 in its new position.

For ease of adjustment by the driver and safety during that operation, the force to lock or release the clamp lever 6 is required to be low, typically less than 4Nm of torque applied to the clamping lever 6. This requires a clamping apparatus 8 which is effective.

The friction and hence the effectiveness of the clamping apparatus 8, has been significantly improved by coating its clutch plates 16,18 with a zinc rich primer.

The coating is an organic solvent based, resin bonded, metallic zinc primer usually used on threaded fasteners for use in building roofing or appliances. The coating is a resin containing metallic zinc in powder form. The coating is typically sprayed on to the degreased clutch

plates 14,16 with a coating thickness of 15-20pm and cured at approximately 220 C for several minutes causing the organic solvent to be evaporated. The coating trade name is Xylan 5611 manufactured by Whitford Plastics.

To illustrate the benefits which the coating provides Figure 2 shows how a clamping apparatus of coated plate compares with a similar apparatus but with plates uncoated. The graph was generated by setting the clamp lever 6 to its locked position with a locking force of 20N applied in a direction parallel to the column centreline (i. e. the typical force applied to the lever by the driver to lock the column) and measuring the force required to nevertheless'forcibly'adjust the locked column. This test was repeated at 30N and in increments up to 60N, the column was fitted with uncoated clutch plates. The full test was then repeated after the clutch plates were replaced with otherwise similar, but coated clutch plates 14,16. As can be seen the force to adjust the locked column was higher when the column was fitted with coated plates given a similar clamp lever locking force.

In addition to resisting a very high force to move the column shaft 4 when the clamp lever 6 is locked, there is a requirement to permit the column shaft 4 to be easily adjusted by the driver of the vehicle when the lever 6 is unlocked. The coating satisfied both of these requirements. In particular it provide a good adjustment feel in that there is a substantially uniform but reduced friction between the coated plates when in their unclamped configuration.

The suitability of the coating is surprising. It is believed that it might be due to metallic zinc in the coating permeating to the surface of the coating away from the metal plate 14,16 substrate such that, for example, opposed contacting coated plates 14,16 surfaces experience a high coefficient of friction therebetween due to high zinc on zinc contact.

Claims

CLAIMS: 1. Clamping apparatus including clutch plates, at least some of the clutch plates being coated with a coating containing zinc.
2. Clamping apparatus according to claim 1, in which the coating is zinc rich.
3. Clamping apparatus according to claim 1 or claim 2, in which the zinc is metallic zinc.
4. Clamping apparatus according to any of claims 1 to 3, in which the coating is a resin based metallic zinc primer.
5. Clamping apparatus according to claim 4, in which the primer includes an organic solvent.
6. Clamping apparatus according to any preceding claim in which the coating is Xylan 5611.
7. Clamping apparatus according to any preceding claim for an adjustable steering column.
8. Clamping apparatus substantially as hereinbefore described with reference to the accompanying Figures.
9. An adjustable steering column for a vehicle comprising clamping apparatus according to any preceding claim.