GB2253897A

GB2253897A - A steering wheel assembly for a motor vehicle

Info

Publication number: GB2253897A
Application number: GB9105587A
Authority: GB
Inventors: Roland John Hayward
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1991-03-16
Filing date: 1991-03-16
Publication date: 1992-09-23
Also published as: GB9105587D0

Abstract

The steering wheel (11) has a central hub (12) connected to a steering column shaft (13). An impact absorbing member (22) is retained by the nut (26) which also retains the hub on the shaft. A cover member (21) is arranged in front of the impact absorbing member. In an alternative arrangement, Fig 4, impact absorption is performed by a fluid filled chamber (35) which can expel liquid under pressure created by impact forces through pressure relief valves (39). To shorten the hub, the hub (32) and shaft (33) can have frusto-conical surfaces with interengaging longitudinal serrations, <IMAGE>

Description

A STEERING WHEEL ASSEMBLY FOR A MOTOR VEHICLE The invention relates to steering wheel assemblies for motor vehicles.

According to a first aspect of the invention there is provided a steering wheel assembly for a motor vehicle, the assembly comprising a steering wheel having a central hub for cooperation with a steering column shaft and for rotation therewith, a threaded fastener for retaining the steering wheel on the shaft and an impact absorbing member adapted to be retained by the threaded fastener and to project in a direction away from the shaft.

According to a second aspect of the invention there is provided a steering wheel assembly for a motor vehicle, the assembly comprising a steering wheel having a central hub for cooperation with a steering column shaft and for rotation therewith and impact absorbing means arranged substantially on the opposite side of the hub to the shaft, said means comprising a fluid container and a pressure relief valve to allow fluid to escape from the container when the container is pressurised by impact energy.

According to a third aspect of the invention there is provided an assembly according to Claim 11 wherein a catchment chamber is provided behind the rear wall to contain fluid expelled through the valve.

The invention will now be described by way of example and with reference to the accompanying drawings, of which Fig 1 is a cross-section through a steering wheel assembly according to the first aspect of the invention; Fig 2 is an enlarged view of an impact absorbing member of the assembly shown in Fig 1; Fig 3 is a view on arrow A in Fig 2; Fig 4 is a cross-section through a steering wheel assembly according to the second aspect of the invention; Fig 5 is a scrap-section through a steering wheel assembly showing one known method of fixing a steering wheel hub to a steering column shaft; Fig 6 is a view similar to Fig 5 showing another known method of fixing a steering wheel hub to a steering column shaft; Fig 7 is a scrap-section through a steering wheel assembly according to the third aspect of the invention; and Fig 8 is a section on the line VIII - VIII in Fig 7.

Referring to Figs l to 3, the steering wheel assembly comprises a steering wheel 11 having a central hub 12 of die-cast alloy for cooperation with a steering column shaft 13. The wheel 11 has spokes 14 of round bar section secured to the hub 12 during the casting of the hub. The spokes 14 support a rim core 15 of the same bar section secured to the spokes by welding. A soft plastics covering 16 is moulded onto the metal parts comprising S.e hub 12, spokes 14 and rim core 15, the covering being shaped to define a cavity 17 and a cylindrical recess 19. The cavity 17 is filled with an energy absorbing plastics foam. The cylindrical recess 19 is closed by a substantially flat plastics cover member 21 retained as a snap fit adjacent the open end of the recess.

Thus far described, the steering wheel assembly is conventional. However, in accordance with the first aspect of the invention and with the object of improving the impact absorbing characteristics, the assembly also comprises an impact absorbing member 22 which projects in a direction away from the shaft 13.

The impact absorbing member 22 comprises a tubular portion 23, a radially inwardly directed flange 24 at one end of the tubular portion and an out-turned flange 25 at the other end of the tubular portion. The inwardly directed flange 24 is interposed between the hub 12 and a radial face of a nut 26 which retains the steering wheel 11 on the shaft 13.

The hub 12 has a parallel bore portion having parallel longitudinal serrations which engage similar serrations on the shaft 13 and a frusto-conical or tapered bore portion which engages a similar frusto-conical section or taper on the shaft. Such an arrangement is known and illustrated in Fig 5, whereas Fig 6 shows an alternative threaded fastener in the form of a set bolt which engages a threaded bore of the shaft.

In the event of a vehicle collision in which an object (eg the driver's head) strikes the steering wheel, the cover member 21 receives the impact force and transmits it to the impact absorbing member 22. The out-turned flange 25 helps to prevent the impact absorbing member 22 from cutting into the cover member 21 and is of curved section so that this advantage remains even if the steering wheel is distorted by an impact on the rim.

To adjust the impact absorbing member 22 to given specific energy absorbing characteristics windows 26 are formed in the tubular portion 23 for strength reduction.

Four windows 26 in the form of longitudinal slots are used in this particular embodiment of the invention but other numbers shapes and sizes may be employed to give the required characteristics. The tubular portion 23 may be shaped differently to further give the required characteristics, eg be frusto-conical or trumpet shaped or comprise two cylindrical sections of different outside diameters but substantially the same wall thickness or have circumferential ribs.

As indicated previously, apart from the impact absorbing member 22, all parts of the steering wheel are conventional. Hence the cost of development to provide the required impact absorbing characteristics will be low and, by the use of existing components, tooling costs are minimised.

Referring now to Fig 4, a steering wheel 31 has a central hub 32 secured to a steering column shaft 33. The hub 32 forms part of a relatively rigid rear wall 34 of an annular fluid container 35 comprising a relatively flexible front wall 36, a radially outer cylindrical side wall 37 and a radially inner cylindrical side wall 39.

The container 35 is filled with a liquid, eg silicon fluid, and has pressure relief valves 39 in the hub 32 arranged so that when an impact on the front wall 36 generates sufficient pressure the valves 39 allow fluid to escape to atmosphere in a direction away from the driver. Instead of the pressure relief valve being in the rear wall 34 they may be in the inner side wall 38 as shown at 41 with pipes 42 to provide vent ducts extending through the shaft 33. By suitable siting of the ends of pipes 42 any expelled fluid will be taken outside the passenger compartment.

In a further alternative arrangement (not shown) a catchment chamber is provided behind the rear wall 34 to contain fluid expelled through the valves 39 during an impact.

The second aspect of the invention may be combined with the first. For example, the cavity 17 in face embodiment described with reference to Figs 1 to 3 may be filled with fluid instead of foam and pressure relief valves provided as described above in relation to Fig 4.

Figs 7 and 8 show in greater detail a means of attaching the hub 32 to the shaft 33. At the end of the shaft there is a collar 43 having a frusto-conical surface to match a frusto-conical bore in the hub 32. Both frusto-conical surfaces have longitudinal serrations which interengage to provide a positive drive between the steering wheel and the shaft.

The shaft 33 is threaded for a nut 44 to pull the frusto-conical surfaces together.

The collar is formed by die casting and to facilitate this and provide greater security the shaft has apertures 45 which are aligned with radial passages 46 in a slug 48 inserted in the shaft. One of the radial passages connects with an axial passage 47 which provides a feed passage for molten material during the die casting process.

Typically the collar is formed of zinc alloy and the shaft and slug are of steel. The hub is also typically of die cast zinc alloy so that the serrations, although converging, are formed without complicated machining.

By using interengaging serrations on frusto-conical surfaces according to the third aspect of the invention the axial length of the hub can be reduced. This in turn makes a greater axial length available for energy absorbing devices, either in the steering wheel assembly for example as described above or in the steering column itself.

Claims

1. A steering wheel assembly for a motor vehicle, the assembly comprising a steering wheel having a central hub for cooperation with a steering column shaft and for rotation therewith, a threaded fastener for retaining the steering wheel on the shaft and an impact absorbing member adapted to be retained by the threaded fastener and to project in a direction away from the shaft.

2. An assembly according to Claim 1 wherein the impact absorbing member has a radially inwardly directed flange arranged to be interposed between the hub and a radial face of the fastener.

3. An assembly according to Claim 1 or Claim 2 wherein the impact absorbing member comprises a tubular portion.

4. An assembly according to Claim 3 wherein the tubular portion has one or more windows for strength reduction.

5. An assembly according to any preceding claim wherein the impact absorbing member has an out-turned flange at an end remote from the fastener.

6. An assembly according to Claim 5 when dependent from Claim 3 or Claim 4 wherein the out-turned flange is of curved section.

7. An assembly according to any preceding claim wherein the steering wheel has a substantial.0 flat cover member which is arranged to cover the impact absorbing member.

8. An assembly according to any preceding claim and further comprising impact absorbing means arranged substantially on the opposite side of the hub to the shaft, said means comprising a fluid container and a pressure relief valve to allow fluid to escape from the container when the container is pressurised by impact energy.

9. A steering wheel assembly for a motor vehicle, the assembly comprising a steering wheel having a central hub for cooperation with a steering column shaft and for rotation therewith and impact absorbing means arranged substantially on the opposite side of the hub to the shaft, said means comprising a fluid container and a pressure relief valve to allow fluid to escape from the container when the container is pressurised by impact energy.

10. An assembly according to Claim 8 or Claim 9 wherein the container has a rigid rear wall on the same side as the shaft a relatively flexible front wall on the other side to the shaft and relatively flexible side walls.

11. An assembly according to any of Claims 8 to 10 wherein the valve is connected to a vent duct extending through the shaft.

12. An assembly according to any of Claims 8 to 10 wherein the valve can exhaust to atmosphere through a rear wall of the wheel on the same side as the shaft.

13. An assembly according to Claim 12 wherein a catchment chamber is provided behind the rear wall to contain fluid expelled through the valve.

14. An assembly according to any preceding claim wherein the hub and the shaft have interengaging frusto-conical surfaces with interengaging longitudinal serrations thereon.

15. A steering wheel assembly for a motor vehicle, the assembly comprising a steering wheel having a central hub for cooperation with a steering column shaft, the hub and the shaft having interengaging frusto-conical surfaces with interengaging longitudinal serrations thereon.

16. An assembly according to Claim 14 or Claim 15 wherein the frusto-conical surface on the shaft is provided on a collar formed separately on the shaft.

17. An assembly according to Claim 16 wherein the collar is formed by die casting.

18. An assembly according to Claim 17 wherein the shaft has recesses or apertures filled with material integral with the collar.

19. An assembly according to Claim 18 wherein the apertures connect with passages in a slug inserted in the shaft.

20. A steering wheel assembly substantially as described herein with reference to Figs 1 to 3, Fig 4 or Figs 7 to 8 of the accompanying drawings.