Patent Application
20080277178
The present invention relates to a steering wheel assembly having a centrally located stationary support member for receiving a driver's side airbag module that does not rotate with the steering wheel.
A conventional airbag module is mounted on the hub of a vehicle steering wheel, and the hub is coupled to a steering shaft. The airbag module rotates in unison with the steering wheel. Since the deployment of the airbag may occur at different rotational orientations of the steering wheel with respect to the vehicle driver, the airbag has to be circular or symmetrical to always provide a protection surface of the same shape to the driver.
Recently steering wheel assemblies have been provided that allow an airbag module to remain stationary with respect to the vehicle during rotation of the steering wheel. This type of airbag module is known as a stationary driver's side airbag module. Stationary driver's side airbag modules may provide airbags having shapes other than circular, since there is no rotation of the airbag module the same with respect to the driver. Stationary driver's side airbag modules allow localized increases of the airbag volume, so airbags may be designed to fit the internal volume of a particular vehicle when deployed to better protect the driver regardless of the rotational orientation of the steering wheel.
US 2003/0067147 A1 discloses a stationary driver's side airbag that comprises a rotatable steering wheel encompassing an accessible space and coupled to the respective shaft by a planetary gear system. The planetary gear system transfers torque applied to the steering wheel ring portion directly to the steering shaft. An airbag module is positioned within the accessible space encompassed by the steering wheel and remains stationary during rotation of the steering wheel.
DE 2 131 902 discloses a steering wheel provided with a non-rotating driver's side airbag module. Rotation of the steering wheel is transmitted to the steering shaft either directly, by matching the internal teeth of the steering hub with the external teeth of the shaft, or indirectly by way of planetary gears interposed between the hub teeth and the shaft teeth. In both cases a space is left between the shaft and the steering hub for housing of both the electric wires and the stationary support members to which the driver's side airbag module is fixed. This is achieved for the steering hub and the respective shaft a gear ratio different than 1:1, i.e. by providing the hub with a greater diameter than the shaft and using the gap between them for the passage of the wires and the stationary support members.
Solutions employing planetary gears, such as shown in FIG. 2 of DE 2 131 902, have several drawbacks. First, the steering wheel is not directly mounted on the steering shaft leaving a discontinuity in the structure. Because of the increasing of the mechanical clearance that occurs as the gears wear with usage, rotation of the steering wheel does not match with the rotation of the steering shaft. When planetary gears are provided for connecting the steering hub to the steering shaft, it is necessary that the gears have exact dimensions to avoid damping of the force transmitted by the driver to the steering shaft or the occurring of an offset between the rotation angle of the steering wheel ring portion and the rotation of the steering shaft. If one of the stationary driver's side airbag module components has dimensions different from what is specified, a non-uniform rotation of the steering wheel ring portion may occur, for example due to the imperfect matching between the gears. Another drawback is that rotation of the steering shaft is in the opposite direction with respect to the rotation imparted by the driver to the steering wheel ring portion. The steering box of the vehicle has to be designed to overcome such a drawback to reverse the direction of rotation imparted by the steering shaft to the vehicle wheels. This leads to an increase in the vehicle production costs.
Prior art assemblies provided with gears for coupling the steering hub to the steering shaft are complicated and require high accuracy in the manufacture of the gears, increasing production time and costs.
DE 3 413 009 A1 discloses a steering wheel provided with a stationary driver's side airbag module wherein the steering wheel hub is directly coupled to a steering shaft in a conventional way. Two gears are provided for maintaining the driver's side airbag module stationary: a first gear matching the driver's side airbag module and a second gear matching the steering shaft. The first and the second gear are coupled to the same driving shaft that is rotatably lodged within a seat of the steering hub. When the driver rotates the steering wheel ring portion, the second gear is rotated about its own axis by the steering shaft and is also rotated about the steering wheel's axis of rotation by the steering wheel hub pushing the driving shaft. The same movement is transmitted by the driving shaft to the first gear. The gear ratio between the first gear and the driver's side airbag module and between the second gear and the steering shaft is chosen such that the driver's side airbag module rotates in the opposite direction with respect to the steering wheel ring portion, thereby remaining stationary. Such a solution requires two expensive “clock spring” connectors to be used for cabling the driver's side airbag module. A first connector is arranged on the steering shaft side of the hub and a second connector is arranged on the driver side of the hub, wired to the first one through the same hub. Another drawback of the solution according to DE 3 413 009 A1 is that the coupling of the driving shaft with the respective seat provided in the steering hub is critical. Inaccuracy in the machining of the seat may easily lead to misalignment of the first and second gears, thereby inducing small movements of the driver's side airbag module when the steering wheel ring portion is rotated.
U.S. Pat. No. 4,541,301 discloses a steering wheel assembly wherein the driver's side airbag module is kept stationary by a coiled element that screws or unscrews itself through a hub opening when the steering wheel is rotated clockwise or counter clockwise. The coiled element has a first end coupled to a stationary support member of the vehicle, a second end fixed to the module and wound around the steering shaft. The main drawback of such solution is that the coiled element does not sufficiently resist torsion to avoid the driver's side airbag module from incurring in small movements. In other words, due to its shape, the coiled element does not provide the necessary mechanical strength to maintain stationary the driver's side airbag module in all the operating conditions.
US 2003/0164060 A1 discloses a steering wheel for a vehicle provided with a second shaft other than the steering shaft. The second shaft is supported via bearings by a stationary hub, which includes a driver's side airbag module housing, such that it is rotatable about its own axis and is coupled to the steering shaft by an arm or an electronic actuator. The actuator includes a position sensor for detecting an angular displacement of the second shaft from a selected origin and producing a signal indicative of the angular displacement. Such a signal is transmitted to a road wheel actuator so that the position of the road wheels properly corresponds with the position of the steering wheel.
Generally, solutions based on a plurality of shafts are complicated and expensive. Duplication of the steering shaft facilitates passing the airbag module wiring harness easily inside the steering wheel column, but requires accurate design and assembly, expensive mechanical components and eventually electronic devices. Conventional assemblies provided with a plurality of gears or shafts are cumbersome. Vehicle steering columns, i.e. the various components of the vehicle around and comprising the steering shaft, have to be redesigned to accommodate such assemblies.
FR 2 833 916 discloses a steering wheel wherein the driver's side airbag module is kept quasi-stationary by an electric motor that rotates the driver's side airbag module in the opposite direction with respect to the steering wheel ring portion but for an initial angle. Such a solution is cumbersome, complicated, expensive and difficult to assemble and to set. Moreover an electronic control unit is needed to sense the rotation of the ring portion of the steering wheel and operate the motor consequently.
There is a need for a reliable and compact driver's side airbag module that does not rotate with the steering wheel and that can be fitted on existing steering columns without having to redesign the same.
The present invention provides a steering wheel having a centrally located stationary support member that overcomes the drawbacks of known solutions, being at the same time economical, reliable and simple to manufacture and assemble. The disclosed steering wheel has a centrally located stationary support member that overcomes the drawbacks of prior art solutions related to the mechanical coupling between the steering wheel and the steering shaft and at the same time overcomes the drawbacks of prior art solutions related to the electrical connections of the driver's side airbag module. The disclosed steering wheel has a centrally located stationary support member that can be directly mounted on common steering columns in a conventional way with no need for redesigning of the said steering columns.
There is provided in accordance with the present invention a steering wheel assembly comprising a steering wheel armature, including a central hub portion fixable to a vehicle column shaft and a spoke and further comprising: a first drum that is freely rotatable only about the steering shaft's axis of rotation and has a sidewall, a second drum that has a sidewall and is freely rotatable about a second axis only, the second axis being either parallel to and spaced apart from the steering shaft's axis of rotation or intersects the steering shaft's axis of rotation, a stationary means for providing a stationary support member for attachment to a driver's side airbag module, and wherein both the first drum and the second drum are rotated around their respective axes by the spoke engaging their sidewalls.
A steering wheel assembly according to the present invention overcomes drawbacks of the prior art. The new steering wheel assembly does not require modification of the steering shaft, i.e. the steering wheel assembly is ready to be fitted on common steering shafts of conventional vehicles in a known way.
The new steering wheel assembly has no toothed gears, which are expensive and require strict tolerances.
The overall dimensions of the new steering wheel assembly are comparable to, or smaller than, those of a conventional steering wheel assembly provided with an airbag module.
With particular reference to
The steering wheel assembly 1 shown in
The steering wheel assembly 1 shown in
With reference to
In both the first and second embodiments, the first drum 9 is arranged to freely rotate about the steering shaft's axis of rotation X.
In the first embodiment the second drum 10 is arranged to freely rotate about a second axis Y, which is inclined with respect to and intersects the steering shaft's axis of rotation X, as shown best in
The first bearing race member 12 and the second bearing race member 13 are positioned along the steering shaft 6, separated by the central hub portion 18 of the armature lying in between. The first bearing race member 12 is located nearer the front of the vehicle, while the second bearing race member 13 is located nearer the driver's seat. The central hub portion 18 does not rotate about the two bearing race members 12, 13, but remains separated from the same, to avoid any friction during operation of the steering wheel assembly. The distance between the first and the second bearing race members 12, 13 depends on the lengths of the two drums 9, 10. The first bearing race member 12 is fixed to a stationary part of the vehicle, such as the steering column shaft cover or “jacket”, for instance by clamps and screws.
The steering wheel assembly 1 is provided with a stationary support 11 having the function of providing a stationary support member 8 for the driver's side airbag DAB and/or other devices, and of supporting both drums 9, 10 on the respective axes X, Y. The support comprises a first bearing race member 12 and a second bearing race member 13, both positioned, at least in part, inside the first drum 9. The first bearing race member 12 is positioned on the side of the steering wheel assembly 1 facing the vehicle steering column, while the second bearing race member 13 is positioned on the side facing the driver's seat and the driver. The first and second bearing race members 12, 13 are preferably machined metal parts provided with seats, such as grooves, for lodging the bearings assisting rotation of the drums 9, 10. The steering shaft 6 rotates inside the bearing race members 12, 13 when the driver rotates the rim 3 but the bearing race members 12, 13 remain stationary. The bearing race members 12, 13 generally have an annular shape and the steering shaft 6 is inserted in their central hole. Preferably the shaft 6 rotates within the bearing race members 12, 13 without touching the internal surfaces thereof. In other words, the diameter of the central hole of the bearing race members 12, 13 is larger than diameter of the steering shaft 6, to avoid any friction during rotation of the steering shaft 6.
In both the first and the second embodiments, bearings are provided for supporting the first and the second drums so that they can be free to rotate. Preferably at least two bearings are provided for supporting each drum. The bearings may be ball bearings, roller bearings, self-oiling bearings, bearing linings, etc., which resist axial and radial loads and have axis of rotation strictly coaxial with the respective geometrical axis. The ball bearings may be of different types, for example radial ball bearings, i.e. bearings capable of resisting radial loads or radial-oblique ball bearings, i.e. bearings capable of resisting main radial loads and minor axial loads, axial-oblique ball bearings, i.e. bearings capable of resisting main axial loads and minor radial loads. Alternatively, the steering wheel assembly may be provided with both axial and radial ball bearings.
The bearings 14, 15, 16, 17 are seated on suitable bearing seats provided by the first and second bearing race members 11, 12. The skilled person will understand that if the drums 9, 10 are positioned on parallel spaced apart axes, the bearing seats are also parallel, while if the second drum 10 is inclined with respect to the first drum 9, the bearing seats of the bearings of the second drum 10 are inclined with respect to the bearing seats of the bearings of the first drum 9.
As shown best in
In general the bearings 14-17 may be ball bearings, roller bearings, self-oiling bearings, bearing linings, etc., which resist axial and radial loads and have axis of rotation strictly coaxial with the respective geometrical axis.
Preferably the ball bearings are “oblique” ball bearings that withstand loads applied not only in the radial direction but also minor axial loads. As it can be seen in
The first and second bearing race members 12, 13 are separated and spaced along the steering shaft's axis of rotation X, i.e. along the shaft 6 when the steering wheel assembly is fitted on it, by interposition of the steering wheel hub portion 18 (
The armature 5 may be manufactured as a single part, in that the rim 3, spokes 2 and hub portion 18 may be a single element. Preferably, as shown in
As the second or internal drum 10 is allowed to rotate about its axis Y only, and the first or external drum 9 is allowed to rotate about the steering shaft's axis of rotation X only, the support 11 has no degree of freedom, thereby remaining stationary. In other words the first and second bearing race members 12, 13 are not affected by rotation of the rim 3 by the driver and provide for a centrally located stationary support member 8 onto which a stationary device, e.g. including a driver side airbag module (DAB), can be mounted. In particular, the first bearing race member 12 is fixed to a coupling element 20 provided with means to be clamped on the shaft covering or jacket 7. As shown best in
The weight of the stationary support 11, i.e. the weight of the first and second bearing race members 12, 13, is held by the steering column covering. Therefore possible oscillations of the hub portion 18, for example caused by geometrical defects of the machined portion 6 of the shaft 6, do not affect the driver's side airbag module, i.e. do not impart oscillations to the stationary support member 8.
Even if the first and the second bearing race members 12, 13 are not directly coupled, the link between them comprising the rotatable inclined drums 9, acts such that the bearing race members 12, 13 cannot rotate.
The second embodiment of the steering wheel assembly according to the present invention is shown in
Functioning of the second embodiment is equivalent to operation of the first embodiment. The drums 9, 10 are rotated by the force imparted by spokes 2 on their slots 19, 19. As the first drum 9 can rotate about the axis X only and the second drum 10 can rotate about the axis Y only, no motion is transmitted to the support 11, i.e. the first and second bearing race members 12, 13 remain stationary. A driver's side airbag module, as the one shown in
The first bearing race member 12 and the second bearing race member 13 are both provided with axial through-holes 23 wherein the electric conductors, such as wires, directed to the airbag module may pass.
Electric conductors, usually needed for activation of the airbag module, can be lodged in a flexible coil, for instance made of a plastic material, of the type disclosed in EP-A-1707469. The coil 24 is shown in
Alternatively the steering wheel assembly 1 is provided with two clock-spring connectors (not shown) coupled one to the other. A first connector can be arranged next to the first bearing race member 12 and the second connector can be arranged next to the second bearing race member 13. A hole is provided through the central hub portion 18 through which connectors are electrically coupled.
The steering wheel assembly of either the first or the second embodiment can be realized by inserting in the first drum 9, in sequence, the first bearing race member 12, with its ball bearings 14, 16 mounted on, the second drum 10, the central hub portion 18 of the armature, the second bearing race member 13, with its ball bearings 15, 17 mounted thereon, and by closing the first drum 9 with the cap 21, thereby pressing all the aforementioned components within the first drum 9 with minimum or null clearance. In the assembled configuration, shown in
Installation of the new steering wheel assembly on a vehicle can be accomplished in an extremely short time by simply sliding the hub portion onto the steering shaft 6, matching the machined teeth of both components. Then the coupling portion 20 is clamped onto the column shaft covering 7, thereby locking the support 11 against any rotation.
Advantageously, the steering wheel assembly 1 does not require toothed gears, such as planetary gears, which are expensive and require strict tolerances to avoid failures, and can be fitted on existing steering columns in a short time, with no need for redesigning the vehicle structures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07009274.7 | May 2007 | EP | regional |
