GB2249288A - Rack-and-pinion power assisted steering system - Google Patents
Rack-and-pinion power assisted steering system Download PDFInfo
- Publication number
- GB2249288A GB2249288A GB8824376A GB8824376A GB2249288A GB 2249288 A GB2249288 A GB 2249288A GB 8824376 A GB8824376 A GB 8824376A GB 8824376 A GB8824376 A GB 8824376A GB 2249288 A GB2249288 A GB 2249288A
- Authority
- GB
- United Kingdom
- Prior art keywords
- pinion
- pinion shaft
- rack
- axis
- bearing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 238000006073 displacement reaction Methods 0.000 claims abstract description 43
- 239000012530 fluid Substances 0.000 claims abstract description 8
- 238000006243 chemical reaction Methods 0.000 claims abstract description 6
- 230000000694 effects Effects 0.000 claims description 9
- 230000008878 coupling Effects 0.000 claims description 7
- 238000010168 coupling process Methods 0.000 claims description 7
- 238000005859 coupling reaction Methods 0.000 claims description 7
- 230000000452 restraining effect Effects 0.000 claims 2
- 230000007935 neutral effect Effects 0.000 description 4
- 239000011435 rock Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D5/00—Power-assisted or power-driven steering
- B62D5/06—Power-assisted or power-driven steering fluid, i.e. using a pressurised fluid for most or all the force required for steering a vehicle
- B62D5/20—Power-assisted or power-driven steering fluid, i.e. using a pressurised fluid for most or all the force required for steering a vehicle specially adapted for particular type of steering gear or particular application
- B62D5/22—Power-assisted or power-driven steering fluid, i.e. using a pressurised fluid for most or all the force required for steering a vehicle specially adapted for particular type of steering gear or particular application for rack-and-pinion type
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Transportation (AREA)
- Mechanical Engineering (AREA)
- Power Steering Mechanism (AREA)
Abstract
A power assisted steering system of the rack and pinion kind has its pinion 6 angularly displaceable about a bearing 8 in response to reaction of the pinion on the rack 5 during the application of a steering input torque. The pinion 6 is displaceable angularly in the plane of the rack 5 to an extent permitted by displacement of a bearing 13 in an elongated seating 15. A pinion shaft extension 11 has extending therefrom a rod 18 which directly connects the pinion shaft to a spool 21 of a valve assembly 7 which controls fluid pressure for a ram that provides power assistance to displacement of the rack bar. The spool 21 has its axis 22 substantially parallel with the plane of the rack 5 and extending radially relative to the pinion axis 16. The rectilinear adjustment provided by displacement of the rod 18 in response to a steering input torque can serve to adjust an electrical switch for control of the power assistance means. <IMAGE>
Description
TITLE "A power assisted steering system"
TECHNICAL FIELD & BACKGROUND ART
The present invention relates to a power assisted steering system and is particularly concerned with such a system having a rack and pinion assembly with power assistance means.
It is known to provide a lateraily displaceable pinion in a power assisted vehicle steering system so that the pinion axis is displaced on the application of a rotatable steering input torque to effect a steering manoevure.
This movement of the pinion actuates the power assistance means to augment steering torque. An example of such a prior proposal is disclosed in our British Patent
Specification No. 2,193,695A where the pinion is borne to be capable of angular displacement along the plane of the rack and in response to its reaction on the rack during the application of a steering input torque to effect a steering manoeuvre. In the preferred arrangements disclosed in
Figures 1 and 6 of G.B. 2,193,695A, the aforementioned angular displacement of the pinion shaft serves to rock a lever which is pivotally mounted on the pinion housing.
An end of the rocking lever is connected to control means (in the form of either an electrical switch or hydraulic valve) so that the control means is actuated by movement of the rocking lever and this controls operation of the power assistance means for the rack and pinion assembly as appropriate to augment the steering input torque during the steering manoevure.
While the power assisted steering system disclosed in
G.B. 2,193,695A has proved to be efficient in operation, it has been found that the preferred arrangements as previously discussed tend to be relatively expensive in so far as the assembly of the rocking lever is concerned and this lever can also have the disadvantage in that it adds considerably to the bulk and weight of the assembly. It is an object of the present invention to provide a power assisted steering system of the kind generally discussed above and by which the disadvantages as previously mentioned may be alleviated.
STATEMENT OF INVENTION & ADVANTAGES
According to the present invention there is provided a power assisted steering system having a rack and pinion assembly with power assistance means and including a pinion shaft rotatable about its axis in response to a steering input torque, a pinion on the shaft engaging a rack extending in a plane on a rack member, said rack member being connected to effect steering in response to longitudinal displacement of the rack in said plane by rotation of the pinion, said pinion shaft being mounted by bearing means for its axis to be angularly displaceable in response to the reaction of the pinion on the rack during the application of said steering input torque; control means having a component which is rectilinearly adjustable to control actuation of the power assistance means, said component being coupled to the pinion shaft to be adjustable rectilinearly in response to angular displacement of the pinion shaft, said rectilinear displacement being in a plane which is substantially parallel to that of the rack.
By the present invention it is envisaged that the pinion shaft is coupled directly, such as through a push/pull rod or similar linkage, to effect rectilinear displacement of the adjustable component that controls actuation of the power assistance means. The rectilinear displacement of the adjustable component is in a plane parallel to that of the plane of the rack so that the relatively direct linkage which is provided between the pinion shaft and the control means alleviates the requirement for the pivotally mounted lever which rocks in response to angular displacement of the pinion to control actuation of the power assistance in accordance with the preferred arrangement disclosed in G.B. 2,193,695.By omitting such a rocking lever as aforementioned the relative weight and bulk of the steering assembly can be reduced with a corresponding reduction in manufacturing and material costs.
Preferably the pinion shaft axis is located in the plane in which the adjustable component of the control means is rectilinearly displaceable so that a simple linkage can be provided between the pinion and the adjustable component. It is also preferred that the rectilinear displacement of the adjustable component is substantially at 900 with respect to the pinion shaft axis.
Bearing in mind that the axis of the pinion shaft is intended to exhibit angular displacement and that this may cause an effective change in the included angle which is formed between the pinion shaft axis and the direction of rectilinear displacement of the adjustable component for the control means, it is preferred that the coupling between the pinion shaft and adjustable component includes one or more universal joints which can accommodate for the aforementioned angular variations. Use of such universal joints, which may be in the form of self aligning bearings, may also be appropriate having in mind that it may not be practical to ensure that the pinion axis is precisely in a plane within which the adjustable component is rectilinearly displaceable and which plane is parallel to the rack plane.
The rectilinearly adjustable component may, for example, control the operation of an electrical switch and/or adjustment of a fluid valve for controlling power assistance in a manner which will be generally known to persons skilled in the art and is broadly discussed in our
Patent Specification G.B. 2,193,695A. Where the adjustable component of the present invention is a spool of a spool valve controlling operation of a power assistance ram then it is preferred that the rectilinear displacement of the spool along its axis in response to angular displacement of the pinion is arranged with the spool axis extending substantially radially from the pinion shaft axis.
DRAWINGS
One embodiment of a power assisted steering system constructed in accordance with the present invention will now be described, by way of example only, with reference to the accompanying illustrative drawings, in which:
Figure 1 shows, in part section, a part of the rack and pinion assembly and the manner in which angular displacement of the pinion controls adjustment of an hydraulic spool valve for a power assistance ram, and
Figure 2 is a scrap section on the line A - A of
Figure 1.
DETAILED DESCRIPTION OF DRAWINGS
The power assisted steering system includes a pinion shaft 1 adapted to receive at one end 2 a steering shaft.
The other end of the pinion shaft 1 is rotatably mounted in a housing 3 which accomodates a rack bar 4 having a rack 5 that engages a pinion 6 on the pinion shaft 1. The teeth of the rack 5 are substantially coplanar and engage with the pinion 6 so that upon rotation of the pinion 6 about the shaft axis 16, the rack bar 4 is displaced longitudinally through the housing 3. The rack bar 4 is connected through a steering linkage (not shown) to steerable road wheels of a vehicle so that longitudinal displacement of the rack bar effects in a steering manoevure.Associated with the rack bar 4 and in conventional manner is a power assistance means in the form of an hydraulic double acting piston and cylinder device or ram (not shown) the flow of hydraulic fluid to and from which is controlled, again in conventional manner, by a spool valve assembly 7 to provide power assistance to the steering manoevure.
Between the end 2 of the pinion shaft 1 and the pinion 6 is a self aligning ball bearing 8 by which the pinion shaft is rotatably mounted in the housing 3. The bearing 8 acts in the manner of an universal joint which permits the pinion shaft 1 to exhibit angular displacement within the housing 3 and for this reason it will be noted from
Figure 1 that ball members in the bearing can roll over a part spherical inner face 8a of an outer race of the bearing. The outer race of the bearing 8 is firmly retained in the housing 3 by an externally threaded plug 9 which screw threadedly engages with the housing 3.
On the side of the pinion 6 remote from the bearing 8, the pinion shaft has an extension 11 on which is firmly mounted the inner race 12 of a rolling bearing 13 having a cylindrical outer race 14. The outer race 14 is accommodated within a seating 15 in the housing 3. The aperture formed by the seating 15 is elongated as shown in
Figure 2 to have a width indicated on the axis X which corresponds to the external diameter of the outer race 14 and a length on the axis Y (which extends perpendicularly to the axis X) which is slightly greater than the external diameter of the outer race 14 so that when the bearing 13 is disposed centrally relative to the seating 15 a clearance C is provided at diametrically opposite sides of the outer race 14 between that outer race and the seating 15 on the axis Y.
In response to a steering input torque, the pinion will rotate about its shaft 16. The axis 16 extends substantially parallel with the plane of the rack 5 and the seating 15 is arranged so that the Y axis is substantially parallel with the plane of the rack 5. As a consequence when the pinion is rotated to effect a steering manoevure, the steering input torque on the pinion 6 will cause a reaction with the rack 5 which results in lateral or angular displacement of the pinion in the housing 3. The pinion consequently pivots about the bearing 8 and is moved in a longitudinal direction opposite to that in which the rack bar 4 is driven. Such angular displacement of the pinion is permissible until the outer race 14 takes up the clearance C and abuts the seating 15 on the axis Y at the appropriate side of the outer race 14.During this angular displacement the pinion is restrained by the seating 15 from displacement in a direction perpendicularly to the plane of the rack 5 (that is in a direction along the axis X in Figure 2). Located on the end of the pinion shaft extension 11 remote from the pinion 6 is a further self aligning bearing 17 through which the shaft extension 11 is coupled in the manner of a universal joint to a push/pull rod 18 which extends substantially radially relative to the pinion axis 16. The rod 18 is coupled through a universal joint 19 to an end 20 of a spool 21 of the spool valve assembly 7. The spool 21 is rectilinearly displaceable along its axis 22 in a spool housing 23 which is bolted to a bracket 24 that extends from the housing 3.
Axial displacement of the spool 21 relative to its housing 23 in one or the opposite sense from a neutral condition controls the flow of high and low pressure hydraulic fluid to the power assistance ram as appropriate to augment the steering input torque during a steering manoevure in known manner. The neutral condition of the valve assembly 7 is intended to correspond with zero input torque and no power assistance being provided and the spool is biased in both senses of its axial direction relative to the housing 23 and to the aforementioned neutral condition by a spring assembly 25.
The valve assembly 7 is mounted so that the spool axis 22 is substantially parallel with the plane of the rack 5, is substantially parallel to the axis Y in Figure 2, and extends substantially radially (at 900) from the pinion axis 16. Furthermore, with zero input torque applied to the pinion shaft 1 the spool 21 will be positioned through the rod 18 for the valve assembly 7 to be in its neutral condition while the bearing 13 will be disposed centrally in the seating 15 for the clearance C to be substantially the same at diametrically opposite sides of the bearing on the axis Y as shown in Figure 2.It is appreciated that in practice it may not always be possible to precisely locate the valve assembly with the spool axis 22 positioned in a plane which includes the pinion axis 16 and parallel to the plane of the rack 5 and the self aligning bearing 17 and joint 19 may accommodate for slight misalignment in this regard. Furthermore, when a steering input torque is applied to effect a steering manoeuvre and during the resultant angular displacement of the pinion 6, there will be an adjustment in the included angle which is formed between the pinion axis 16 and the spool axis 22 - again this adjustment may be accommodated for by the nature of the self aligning bearing 17 and joint 19.
From the aforegoing it will be realised that the direct linkage (albeit through the self aligning bearing 17 and joint 19) by the rod 18 between the angularly displaceable pinion 6 and the spool valve assembly 7 together with the convenient mounting of the spool assembly 7 can provide a relatively compact structure which lends itself to ease of assembly.
Claims (15)
1. A power assisted steering system having a rack and pinion assembly with power assistance means and including a pinion shaft rotatable about its axis in response to a steering input torque, a pinion on the shaft engaging a rack extending in a plane on a rack member, said rack member being connected to effect steering in response to longitudinal displacement of the rack in said plane by rotation of the pinion, said pinion shaft being mounted by bearing means for its axis to be angularly displaceable in response to the reaction of the pinion on the rack during the application of said steering input torque; control means having a component which is rectilinearly adjustable to control actuation of the power assistance means, said component being coupled to the pinion shaft to be adjustable rectilinearly in response to angular displacement of the pinion shaft, said rectilinear displacement being in a plane which is substantially parallel to that of the rack.
2. A system as claimed in claim 1 in which the pinion shaft axis is substantially in the plane in which the adjustable component is rectilinearly displaceable.
3. A system as claimed in either claim 1 or claim 2 in which the rectilinear displacement of the adjustable component is substantially at 900 with respect to the pinion shaft axis.
4. A system as claimed in any one of the preceding claims in which the coupling between the pinion shaft and adjustable component comprises a linkage with universal joint means.
5. A system as claimed in any one of the preceding claims in which the coupling comprises a push/pull rod linkage.
6. A system as claimed in claim 5 when appendant to claim 4 in which the push/pull rod is coupled to the pinion shaft through a self aligning bearing.
7. A system as claimed in any one of the preceding claims in which the rectilinearly adjustable component controls adjustment of a fluid valve for controlling the power assistance means.
8. A system as claimed in claim 7 in which the fluid valve comprises a spool valve assembly a spool of which is coupled to be rectilinearly displaceable along its axis by angular displacement of the pinion shaft.
9. A system as claimed in claim 8 in which the pinion shaft axis and spool axis are substantially co-planar.
10. A system as claimed in either claim 8 or claim 9 in which the spool is displaceable relative to a spool housing and said spool housing is secured relative to a pinion housing in which the pinion is rotatably mounted.
11. A system as claimed in any one of the preceding claims in which the rectilinearly adjustable component controls adjustment of electrical switch means for controlling power assistance.
12. A system as claimed in any one of the preceding claims in which the angular displacement of the pinion shaft is permitted by a first bearing for the pinion shaft in the or a pinion housing and said angular displacement is restricted by a second bearing for the pinion shaft in the pinion housing and which is spaced axially of the pinion shaft from the first bearing.
13. A system as claimed in claim 12 in which the second bearing is accommodated with clearance in a seating in the pinion housing, said seating restraining displacement of the pinion shaft axis in a direction substantially perpendicular to the plane of the rack and permitting displacement of the pinion shaft axis to the extent of said clearance in a direction substantially parallel to the plane of the rack.
14. A system as claimed in either claim 12 or claim 13 in which the pinion is disposed on its shaft axially between the first and second bearings.
15. A power assisted steering system substantially as herein described with reference to the accompanying illustrative drawings.
15. A system as claimed in claim 14 in which the second bearing is located between the pinion and the coupling to the adjustable component.
16. A power assisted steering system substantially as herein described with reference to the accompanying illustrative drawings.
AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS 1. A power assisted steering system having a rack and pinion assembly with power assistance means and including a pinion shaft rotatable about its axis in response to a steering input torque, a pinion on the shaft engaging a rack extending in a plane on a rack member, said rack member being connected to effect steering in response to longitudinal displacement of the rack in said plane by rotation of the pinion, said pinion shaft being mounted by bearing means for its axis to be angularly displaceable in response to the reaction of the pinion on the rack during the application of said steering input torque; control means having a component which is rectilinearly adjustable to control actuation of the power assistance means, said component being coupled to the pinion shaft to be adjustable rectilinearly in response to angular displacement of the pinion shaft, said rectil~inear displacement being in a plane which is substantially parallel to that of the rack and said pinion shaft axis being substantially in the plane in which the adjustable component is rectilinearly displaceable.
2. A system as claimed in claim 1 in which the rectilinear displacement of the adjustable component is substantially at 900 with respect to the pinion shaft axis.
3. A system as claimed in either claim 1 or claim 2 in which the coupling between the pinion shaft and adjustable component comprises a linkage with universal jointlmeans.
4. A system as claimed in any one of the preceding claims in which the coupling comprises a push/pull rod linkage.
5. A system as claimed in claim 4 when appendant to claim 3 in which the push/pull rod is coupled to the pinion shaft through a self aligning bearing.
6. A system as claimed in any one of the preceding claims in which the rectilinearly adjustable component controls adjustment of a fluid valve for controlling the power assistance means.
7. A system as claimed in claim 6 in which the fluid valve comprises a spool valve assembly a spool of which is coupled to be rectilinearly displaceable along its axis by angular displacement of the pinion shaft.
8. A system as claimed in claim 7 in which the pinion shaft axis and spool axis are substantially co-planar.
9. A system as claimed in either claim 7 or claim 8 in which the spool is displaceable relative to a spool housing and said spool housing is secured relative to a pinion housing in which the pinion is rotatably mounted.
10. A system as claimed in any one of the preceding claims in which the rectilinearly adjustable component controls adjustment of electrical switch means for controlling power assistance.
11. A system as claimed in any one of the preceding claims in which the angular displacement of the pinion shaft is permitted by a first bearing for the pinion shaft in the or a pinion housing and said angular displacement is restricted by a second bearing for the pinion shaft in the pinion housing and which is spaced axially of the pinion shaft from the first bearing.
12. A system as claimed in claim 11 in which the second bearing is accommodated with clearance in a seating in the pinion housing, said seating restraining displacement of the pinion shaft axis in a direction substantially perpendicular to the plane of the rack and permitting displacement of the pinion shaft axis to the extent of said clearance in a direction substantially parallel to the plane of the rack.
13. A system as claimed in either claim 11 or claim 12 in which the pinion is disposed on its shaft axially between the first and second bearings.
14. A system as claimed in claim 13 in which the second bearing is located between the pinion and the coupling to the adjustable component.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8824376A GB2249288B (en) | 1988-10-18 | 1988-10-18 | A power assisted steering system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8824376A GB2249288B (en) | 1988-10-18 | 1988-10-18 | A power assisted steering system |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8824376D0 GB8824376D0 (en) | 1988-11-23 |
| GB2249288A true GB2249288A (en) | 1992-05-06 |
| GB2249288B GB2249288B (en) | 1992-09-16 |
Family
ID=10645372
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8824376A Expired - Lifetime GB2249288B (en) | 1988-10-18 | 1988-10-18 | A power assisted steering system |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2249288B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4442546C1 (en) * | 1994-11-30 | 1996-02-15 | Daimler Benz Ag | Servo-assisted rack and pinion steering mechanism for automobile |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2193695B (en) * | 1986-06-09 | 1989-12-20 | Trw Cam Gears Ltd | A power assisted vehicle steering mechanism |
-
1988
- 1988-10-18 GB GB8824376A patent/GB2249288B/en not_active Expired - Lifetime
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4442546C1 (en) * | 1994-11-30 | 1996-02-15 | Daimler Benz Ag | Servo-assisted rack and pinion steering mechanism for automobile |
| US5671637A (en) * | 1994-11-30 | 1997-09-30 | Mercedes-Benz Ag | Servo-assisted rack-and-pinion system |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2249288B (en) | 1992-09-16 |
| GB8824376D0 (en) | 1988-11-23 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20011018 |