The present invention relates to a steering arrangement for motor vehicles, comprising a steering shaft, a bearing housing fixed to the vehicle, in which housing the steer¬ ing shaft is rotatably mounted, and a steering wheel joined to the steering shaft, consisting of a steering wheel rim, a steering wheel hub, elements joining the steering wheel rim to the steering wheel hub, and a gas * generator equipped air bag device attached to the steering wheel.

Gas cushion devices or air bags, as they are commonly known, have come into use to a certain extent as a complement to the passive safety system in motor vehicles. Engineering developments in this area were initially directed to entire systems of gas balloons or bags placed in front of the vehicle occupants and mounted in the dashboard or in the steering wheel. Later design develop¬ ment has, however, lately been concentrated to the latter type, i.e. air bag units in the steering wheel.

One such commercially available unit, the so-called "SRS

(Supplementary Restraint System) unit", consists of a sheet metal bowl or box mounted inside the steering wheel rim and containing, in addition to a perforated folded bag, a gas generator. The bowl is open towards the driver and is covered by a padded cover which is opened when the unit is triggered.

In SRS installations known up to now, the unit has been a complement to the rest of the vehicle safety equipment, such as seat belts, padding or upholstery on other com¬ ponents, etc. it has also served as an alternative to previously known passive safety devices in the steering

arrangement in the form of specially designed steering wheel spokes, steering shafts and joints, providing together an intentional controlled collapse of the steer¬ ing system with accompanying controlled energy absorption upon collision.

In a collision, the SRS unit air bag is rapidly inflated, and is thereafter emptied of gas during energy absorption when it is compressed by the occupant's weight and the gas in the bag is pressed out through perforations in the bag. At high collision speeds, the driver may, despite the presence of the air bag, at the end of the course of the collision, strike the steering wheel, and depending on the driver's remaining kinetic energy, the steering wheel rim and the SRS unit can cause injury.

The purpose of the present invention is to achieve a steering arrangement of the type described by way of introduction, which will make it possible to reduce in- juries occurring during a collision, where the energy absorbing bag is not able to absorb sufficient energy to prevent impact against the steering wheel.

This is achieved according to the invention by virtue of the fact that the steering shaft has two mutually non-

-rotatably but axially displaceably connected shaft parts and the bearing means are constructed and fixed so that the length of the steering shaft can be shortened to permit forward displacemenet of the steering wheel at a predetermined loading of the steering wheel and/or the air bag device.

The design according to the invention does not mean that the air bag device is used as an alternative to passive safety arrangements known per se in a steering arrange¬ ment, but it is instead incorporated into a chain of

components in the steering arrangement, the design and calculated dimensions of which provide a controlled course of deformation in several stages.

The invention will be described in more detail with refer¬ ence to examples shown in the accompanying drawings, where Figure 1 shows a perspective X-ray view of a schematically represented vehicle steering wheel.

Figure 2 shows a longitudinal section through a schema- tically represented steering arrangement comprising the steering wheel in Figure 1, and

Figure 3 is a view of the steering arrangement in Figure 2 in a deformed state after driver impact.

The steering wheel 1 shown in the Figures has a steering wheel rim 2, consisting of a steel ring 4 sheathed in a covered foamed plastic jacket 3. The ring 4 is joined via spokes 5 to a steering wheel centre in the form of a hub 6, which is mounted on a steering shaft 7. The spoke-s 5 are dimensioned in a known manner and are designed to be deformed upon a certain loading of the steering wheel rim 2 and comprise for this purpose flat metal bars 8 which are pre-bent at 9 to be able to collapse when loaded. _' " The spokes 5, as is the rim 2, are sheathed in the covered ' foamed plastic jacket 3.

An air bag device, generally designated 10, which can be of a type known per se, known as the SRS unit, is mounted centrally in the steering wheel. The unit 10 is joined to the hub 6 via four essentially Z-shaped flat metal bars

11, which are joined to each other in pairs by means of a pair of metal strips 12 which in turn form the mounting means for the unit 10.

The steering wheel shaft 7 has a tubular upper portion 7a with internal splines and a lower portion 7b with external

splines which are inserted into the upper portion 7a. The portions 7a and 7b are thus axially displaceable but non rotatably joined to each other. The steering shaft 7 is mounted in an upper and a lower bearing 20 and 21, res- pectively, in a tubular bearing housing 22 which has at 23 and 24 schematically indicated mountings in the vehicle. The bearing housing 22 is made of metal and has a corru¬ gated portion 25 intended to provide controlled com¬ pression of the tube when loaded by driver impact during a collision. The upper mounting 23 is designed to withstand less impact than the lower mounting 24. At a certain pre¬ determined loading of the steering wheel, the mounting 23 is broken off and the steering wheel can then be displaced forward as the corrugated portion 25 is compressed and shaft portion 7b is forced into portion 7a.

During a collosion, which triggers the air bag device, the driver is first caught by the air bag. If the collosion is so powerful that the driver, despite the air bag, finally strikes the steering wheel with significant force, energy absorption is provided in a second stage when the flat bars 8 and 11 are deformed as the steering rim 2 and the air bag device 10 are loaded. Energy absorption in a third stage is obtained when the upper tube mounting 23 is broken off and the tube 22 is compressed as shown in Figure 3.