GB2093561A

GB2093561A - Support element for a motor vehicle steering box rack

Info

Publication number: GB2093561A
Application number: GB8204175A
Authority: GB
Original assignee: RIV SKF Officine di Villar Perosa SpA; RIV Officine di Villar Perosa SpA
Current assignee: SKF Industrie SpA
Priority date: 1981-02-24
Filing date: 1982-02-12
Publication date: 1982-09-02
Also published as: FR2500395B3; GB2093561B; SE449330B; SE8200788L; FR2500395A3; IT8152958V0

Abstract

A motor vehicle steering box comprising a rotatable pinion (2) and a rack (3) mobile axially inside a housing, (1) said box comprises at least one rotatable support element (5) arranged to substantially support the thrust which said pinion (2) applies to said rack (3) during operation, and disposed on the opposite side to said side, said support element (5) being provided with a support surface (6) arranged to roll on a corresponding surface (7) of said rack (3) without sliding, and being carried by a block (8) urged axially towards said rack (3) by elastic means (9). <IMAGE>

Description

SPECIFICATION Support element for a motor vehicle steering box rack This invention relates to a support element for a motor vehicle steering box rack, by means of which said rack is able to move under very reduced friction, so making the motor vehicle steering more smooth and accurate.

The steering box is known to comprise a rotatable pinion, and an axiallyy mobile rack, which engage with each other and are disposed inside a housing, the former being arranged to receive motion from the steering column, and the latter being arranged to control the wheel steering linkage.

Said rack is usually guided by one or more support bushes disposed at its ends. Said bushes can also be of the ball circulation type, described in the preceding utility model application of the present applicant, filed on 3.3.1980 under the title: Steering box fora motor vehicle steering mechanism.

On the opposite side from that where the pinion is located, there is usually disposed a sliding block having a support surface arranged to engage with the corresponding surface of the rack. That component of the force exchanged between the teeth of the pinion and rack which is normal to the rack axis is discharged across said engaged surfaces.

Boxes of the described type have the drawback of requiring a fairly large force on the steering wheel for steering purposes, in particular for moving the vehicle from rest or under certain running conditions. This is due to the large frictional force which arises in the engagement between said support surface and the corresponding engaged surface of the rack, and which opposes the axial movement of said rack.

The object of the present invention is to provide a steering box free from the aforesaid drawbacks.

The invention provides a motor vehicle steering box comprising a rotatable pinion and a rack mobile axially inside a housing, said pinion engaging with said rack and being disposed on one side thereof, characterised by comprising at least one rotatable support element arranged to substantially support thethrustwhich said pinion applies to said rack during operation, and disposed on the opposite side to said side, said support element being provided with a support surface arranged to roll on a corresponding surface of said rack without sliding, and being carried by a block urged axially towards said rack by elastic means.

The present invention will be more apparent from the detailed description given hereinafter by way of example, with reference to the accompanying drawings in which: Figures 1 and 2 are longitudinal sections through parts of a steering box constructed in accordance with the invention; Figures 3, 4 and 5 are sections through various embodiments of the support element of the invention, taken on planes orthogonal to the rack axis.

The steering box according to the invention comprises a housing 1, in which a pinion 2 is rotatably mounted, together with a rack 3 which engages therewith and is mobile axially inside said box. A slide bush or a ball ciculation bush 4, as shown in the detailed view of Figure 2, can be conveniently disposed at one or both ends of said housing for longitudinally guiding the rack.

According to the invention, on the side opposite that on which the pinion 2 is located, there is disposed a rotatable support element indicated by 5, and arranged to substantially support the thrust which the pinion applies to the rack. This support element is provided with a support surface 6 arranged to rotate on a corresponding surface 7 of the rack, but without sliding. The support element 5 is carried by a block 8 which is mobile in a corresponding eeat in the housing 1 having its axis substantially orthogonal to the axis of the rack 3, and is urged towards this latter by a spring 9 disposed between the block and a cover 10 rigid with the housing 1.

The support element 5 can be constituted by a rotatable roller 13, as shown in Figure 3, comprisng a pair of end journals 14, each of which is inserted into a corresponding bush 15 carried by the block 8. In this case, the roller 13 has a substantially cylindrical central surface 16, and a pair of conical surfaces 17 adjacent thereto, these surfaces being disposed in such a manner that all three are in contact with the surface 7 of the rack 3.

According to an alternative embodiment illustrated in Figure 4, the rotatable support 6 can be constituted by an annular element 18 which, by means of a pair of rolling bearings 19, is supported by a spindle 20 carried by the block 8. In this case, the cross-section through the outer surface 6 of the annular element 18 is a circumferential arc, along which the contact between said outer surface and the surface 7 of the rack extends.

Figure 5 shows a further embodiment using a pair of support elements 5, each of which in this case is formed by the outer race of a rolling bearing 21. Each of these latter is mounted on a corresponding pin 22 rigid with the block 8. The axes of said two pins form a contained angle of less than 180", so that the surfaces of the two outer races of said bearings can rest on corresponding V surfaces 23, which form said angle between them.

When the pinion 2 is rotated, it causes the rack 3 to move axially, during which the rack is guided by the ball circulation bearings 4 (or by equivalent sliding bearings). During transmission of motion from the pinion 2 to the rack 3, the teeth of the former apply forces to the teeth of the latter, these forces having a first component in the direction of the axis of the rack 3 (so causing this latter to move with translational motion, thus controlling the steering linkage), and a second component in the direction orthogonal thereto. This latter component is supported by the suppprt element 5, which because of its structure is able to support large forces. During the translatory motion of the rack 3, the support element 5 rotates, so enabling the rack to make movements under very low friction, even when very large forces are transmitted between the pinion and rack.

The presence of the spring 9 improves pressure distribution between the engaged surfaces of the support element 5 and rack 7, indicated by 6 and 7 (or 23 in the case of Figure 6) respectivey, and compensates for any constructionai and assembly irregularities. Said spring is able to compensate for any wear between the engaged elements.

It is apparent that modifications can be made to the various described embodiments of the invention without leaving the scope of the inventive idea.

Claims

1. A motor vehicle steering box comprising a rotatable pinion and a rack mobile axially inside a housing, said pinion engaging with said rack and being disposed on one side thereof, characterised by comprising at least one rotatable support element arranged to substantially support the thrust which said pinion applies to said rack during operation, and disposed on the opposite side to said side, said support element being provided with a support surface arranged to roll on a corresponding surface of said rack without sliding, and being carried bya block urged axially towards said rack by elastic means.

2. A steering box as claimed in claim 1, characterised in that said support surface has a substantially concave profile when viewed in section, so as to be able to rest on said rack surface at several points.

3. A steering box as claimed in claim 2, characterised in that said support element is constituted by a rotatable roller comprising a pair of end journals rotatable in corresponding bearings in said block.

4. A steering box as claimed in claim 1 or 2, characterised in that said support element is constituted by a rotatable annular element supported, by rolling bearings on a spindle carried by said block.

5. A steering box as claimed in claim 4, characterised in that the cross-section through the outer surface of said annular element is a circumferential arc.

6. A steering box as claimed in claim 1, characterised by comprising two rotatable support elements, each of which is constituted by the outer race of a rolling bearing and is arranged to roll on a corresponding flat surface portion provided on said rack, the axes of said two rolling bearings forming a contained angle of less than 1800.

7. A steering box as claimed in claim 6, characterised in that each of said rolling bearings is carried by a pin rigid with said block, said pins forming between them said angle of less than 1800.

8. A steering box as claimed in one of the preceding claims, characterised in that said elastic means are constituted by at least one spring disposed between said block and a cover fixed to said housing.

9. A motor vehicle steering box, substantially as described and illustrated on the accompanying drawings.