WO2012055540A1

WO2012055540A1 - Steering gear

Info

Publication number: WO2012055540A1
Application number: PCT/EP2011/005380
Authority: WO
Inventors: Olivier Dorison
Original assignee: Trw France Sas
Priority date: 2010-10-25
Filing date: 2011-10-25
Publication date: 2012-05-03
Also published as: FR2966414A1; FR2966414B1

Abstract

A steering gear (10) for a vehicle comprises a housing (12), a rack (16) arranged in the housing so as to be displaceable in a longitudinal direction, a drive (14) for displacing the rack (16) in the longitudinal direction, and a support (24) which supports the rack (16) in a direction transverse to the longitudinal direction, the support (24) being arranged in the housing (12) so as to be displaceable in a longitudinal direction.

Description

Steering Gear

The invention relates to a steering gear for a vehicle, comprising a housing, a rack arranged in the housing so as to be displaceable in a longitudinal direction, a drive for displacing the rack in the longitudinal direction, and a support which supports the rack in a direction transverse to the longitudinal direction.

A steering gear of this type is known from DE 20 2005 007 923. The support is arranged at an outer end of the housing so as to take up bending loads acting on the rack, as close as possible to the outer end of the rack where the bending loads are generated. The problem with this known design however is that the maximum distance between the end of the rack where the bending loads are applied, and the support is at least the length of the travel of the rack between its two end positions.

The object of the invention is to improve the known steering gear such that the rack is subjected to reduced bending moments. To this end, a steering gear of the type mentioned above is provided, which is characterized in that the support is arranged in the housing so as to be displaceable in a longitudinal direction. The invention is based on the idea of reducing the maximum length with which the rack protrudes from the housing and the support. This is achieved by mounting the support displaceably so that it can be retracted into the housing when the respective outer end of the rack is moved towards the housing.

According to a preferred embodiment, the housing is provided with a sliding guide which accommodates the support. This allows to mount the support in a very simple manner, resulting in reduced costs of the steering gear. Preferably, the support is elastically biased against a stop, the stop defining a position of maximum distance of the support from the drive for displacing the rack. This allows to automatically return the support in a defined position in which the overhanging length of the rack is reduced. The elastic biasing force for pressing the support against the stop can be provided by a simple spring, and the stop can be formed from a retaining circlip arranged in a groove in the housing. However, other means can be used as well for providing the biasing action acting on the support and for forming the stop.

According to a preferred embodiment, the rack is provided with a ball joint to which part of a steering linkage can be connected, the support being provided with a contact surface for the ball joint so that the ball joint can displace the support from the position of maximum distance from the rack drive towards the interior of the housing. This allows to automatically withdraw the support from its extended position in which it contacts the stop, towards a position which is more in the interior of the housing, thereby allowing the rack to travel to a position in which the ball joint is arranged in the housing.

According to the preferred embodiment, the support is formed from a sliding element which contacts the housing, and a support element which is accommodated within the sliding element and which supports the rack. This allows using different materials for the sliding element and the support element, each of the materials being adapted to the particular requirements.

According to an alternative embodiment, the support is formed in a unitary piece made from a material which provides both sliding and supporting properties. According to a still further embodiment, the support is formed from a sliding envelope which contacts the housing and the rack, and a metal core which is encapsulated by the envelope and bears bending and compression loads acting on the support. This provides good sliding properties with respect to the housing and the rack while maintaining a high rigidity. The invention will now be described with reference to an embodiment which is shown in the drawings. In the drawings,

- Figure 1 shows a steering gear according to the invention with the rack in a first position,

- Figure 2 shows the steering gear of Figure 1 with the rack in a second position, - Figure 3 shows the steering gear of Figure 1 with the rack in an end position,

- Figure 4 shows a comparison between the bending moment acting on a rack in a prior art steering gear and in a steering gear according to the invention; and

- Figure 5 shows an alternative support which can be used in the steering gear of Figure 1.

In Figure 1 , a steering gear 10 is shown, which features as main components a housing 12, a drive 14 and a rack 16. Rack 16 is arranged within housing 10 so as to be displaceable in a longitudinal direction (please see arrow P in Figure 1) between two end positions, namely a right end position and a left end position. The drive 14 is provided for displacing rack 16 in housing 12, with drive 14 here being formed as a pinion 14 which engages into a toothing 18 formed on rack 16. A yoke 20 is provided which is pressed by biasing means 22 against rack 16 so as to maintain toothing 18 of rack 16 in engagement with pinion 14.

At the outer end of rack 16, a ball joint 17 is provided, to which a steering linkage 19 (shown only in Figure 3) can be connected. The steering linkage 19 transmits the motion of rack 16 to steerable wheels of a vehicle. A second ball joint is typically provided at the other end of rack 16. At an outer end which here is the left hand end of housing 10, a support 24 for rack 16 is provided which is formed from a sliding element 26 and a support element 28. Sliding element 26 can be formed from plastic and has a ring shape. In its interior, sliding element 26 accommodates support element 28 which can be formed from metal and which contacts rack 16 as the bending moment applied to rack 16 is increasing. Support 24 is accommodated slidably in the interior of the housing. To this end, the interior surface of the housing adjacent support 24 forms a sliding guide 30, with sliding guide 30 having a cylindrical surface with a diameter which approximately corresponds to the outer diameter of sliding element 26. At the outer end of the housing, a retaining circlip 32 is provided which forms a stop for support 24, limiting the movement towards the left. On the right side of support 24, a spring 34 is provided which on its left side abuts at sliding element 26 and at its right side is held in a ring-shaped abutment 36. Rack 16 can be displaced by operating pinion 14 in a manner known as such. Support 24 is preferably arranged such that there is not contact between rack 16 and support 24 when no transverse loads act on the rack.

If the rack is displaced towards the left, support 24 remains in the position shown in Figure 1 in which it contacts stop 32. This results in any transverse loads transmitted to rack 16 via ball joint 17 being transmitted into housing 12 by support 24 at a position which is at the outer end of the housing. This results in a reduced bending moment acting on rack 16.

When rack 16 is displaced from the position of Figure 1 , which is a centre position, towards the right, it can assume the position shown in Figure 2, in which ball joint 17 contacts an outer surface 38 of sliding element 26 of support 24. Due to support 24 being arranged displaceably within housing 12, rack 16 can be displaced further towards the right side, resulting in ball joint 17 being "retracted" into housing 12. This results in support 24 being pushed against the action of spring 34 into the housing by ball joint 17 which acts on contact surface 38 of support 24. As can be seen in Figure 3, annular abutment 36 takes up spring 34 until no further movement to the right is possible. The condition shown in Figure 3 represents one of the end positions of rack 16, namely a condition in which it is displaced towards the right as far as possible. Figure 4 shows the maximum lever arm with which transverse forces acting on rack 16 generate a bending moment. In Figure 4a, a steering gear according to the prior art is shown. Rack 16 can be displaced towards the right until ball joint 17 is immediately adjacent a fixed mounting of the yoke 20 in the housing 12 (right end position). The only support for the rack 16 is provided by the yoke 20. The maximum lever arm is present when rack 16 assumes the left end position which is shown here. Any transverse load F acts on rack 16 with a lever arm which is distanced between the center of the ball joint and the position of the yoke 20 in the interior of the housing 12.

Figure 4b shows the geometrical situation with the steering gear according to the invention. In the right end position (not shown), ball joint 17 is arranged in the interior of the housing 12. In the left end position, rack 16 protrudes from the housing 12 unsupported over a distance which is significantly smaller as in the prior art steering gear. Accordingly, the lever arm L₂ with which any transverse load F can apply a bending moment on rack 16 is significantly reduced, even if the vehicle kinematics in view of the extended length of the rack 16 is identical.

Figure 5 shows a support according to an alternative embodiment. Support 24 here consists of a plastic envelope 50 and a metal core 52. Envelope 50 completely surrounds and encapsulates core 52 and is provided for sliding in housing 12 and for contacting rack 16. Core 52 is provided for withstanding the bending moment and compression force, respectively, from rack 16 and for withstanding the compression forced from ball joint 17 at the end of the travel of rack 16. In addition to supporting rack 16, support 24 acts as a rack travel restrictor. By replacing one support 24 against another with a different thickness/width, different rack travels can be permitted. Further, support 24 provides for a soft stop at the end of the travel so as to prevent the generation of noise by support 24 getting in contact with the housing.

Claims

1. A steering gear (10) for a vehicle, comprising a housing (12), a rack (16) arranged in the housing so as to be displaceable in a longitudinal direction, a drive (14) for displacing the rack (16) in the longitudinal direction, and a support (24) which supports the rack (16) in a direction transverse to the longitudinal direction, characterized in that the support (24) is arranged in the housing (12) so as to be displaceable in a longitudinal direction.

2. The steering gear of claim 1 wherein the housing (12) is provided with a sliding guide (30) which accommodates the support.

3. The steering gear of claim 1 or claim 2 wherein the support (24) is elastically biased against a stop (32), the stop (32) defining a position of maximum distance of the support from the drive (14) for the rack (16).

4. The steering gear of claim 3 wherein a spring (34) is provided which biases the support (24) against the stop (32).

5. The steering gear of claim 3 or claim 4 wherein the stop (32) is formed from a retaining circlip (32) arranged in a groove in the housing (12).

6. The steering gear of any of the preceding claims wherein the rack (16) is provided with a ball joint (17) to which part of a steering linkage (19) can be connected, the support (24) being provided with a contact surface (38) for the ball joint (17) so that the ball joint can displace the support (24) from the position of maximum distance from the drive (14) towards the interior of the housing (12).

7. The steering gear of any of the preceding claims wherein the support (24) is formed from a sliding element (26) which contacts the housing (12), and a support element (28) which is accommodated within the sliding element (26) and which supports the rack (16).

8. The steering gear according to any of claims 1 to 6 wherein the support (24) is formed in a unitary piece made from a material which provides both sliding and supporting properties.

9. The steering gear according to any of claims 1 to 6 wherein the support (24) is formed from a sliding envelope (50) which contacts the housing and the rack, and a metal core (52) which is encapsulated in the envelope (50) and bears bending and compression loads acting on the support (24).

10. The steering gear of any of the preceding claims wherein the support (24) is formed as a closed ring.

11. The steering gear of any of the preceding claims wherein the drive comprises a pinion (14) which engages into a toothing (18) provided on the rack (16).