EP1395480A2

EP1395480A2 - Rack bushing with two-part seal

Info

Publication number: EP1395480A2
Application number: EP02744284A
Authority: EP
Inventors: John Saarinen
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 2001-05-18
Filing date: 2002-05-16
Publication date: 2004-03-10
Also published as: WO2002095269A2; WO2002095269A3; EP1395480A4; AU2002339882A1

Abstract

A hydraulic steering gear (10) comprises a tubular housing (16) partially defining a chamber (24) for receiving fluid under pressure. An annular bushing (30) supports a rack (20) for axial movement in the chamber (24) .The bushing has a cylindrical inner surface (32) with a groove (50) defined by a bottom surface (52) and two end surfaces (54, 56) .A seal assembly (60) is received in the groove (50) for sealing between the rack (20) and the bushing (30) .The seal assembly (60) includes a first seal member (62) located in the groove (50) in sealing engagement with the bottom surface (52) of the bushing (30), and a second seal member (64) located in the groove (50) in sealing engagement with the first sealing member (62) and with the rack (20) .The second seal member (64) is disposed radially between the first seal member (62) and the rack (20) .

Description

RACK BUSHING WITH TWO-PART SEAL

Background of the Invention Technical Field

The present invention relates to an apparatus for sealing a fluid chamber, and particularly to apparatus for sealing a fluid chamber of a fluid power assisted rack and pinion steering gear.

Description of the Prior Art

U.S. Patent No. 5, 181,581 describes a rack bushing made from a hard plastic material. A resilient lip seal is connected with the bushing for sealing between the bushing and the rack.

Summary of the Invention

The present invention is a hydraulic power assist rack and pinion steering gear comprising a tubular housing partially defining a chamber for receiving fluid under pressure. A rack extends axially through the chamber in the housing. An annular bushing supports the rack for axial movement in the chamber. The bushing has a cylindrical inner surface defining a passage extending longitudinally through the bushing for receiving the rack therethrough. The bushing has a groove in the inner surface defined by a bottom surface and two end surfaces. A seal assembly is received in the groove for sealing between the rack and the bushing. The seal assembly includes a first seal member located in the groove in sealing engagement with the bottom surface of the bushing. The seal assembly includes a second seal member located in the groove in sealing engagement with the first sealing member and with the rack. The second seal member is disposed radially between the first seal member and the rack.

Brief Description of the Drawings

The foregoing and other features of the present invention will become apparent to one skilled in the art to which the present invention relates upon consideration of the following description of the invention with reference to the accompanying drawings, in which:

Fig. 1 is a schematic illustration of a fluid power assisted rack and pinion steering gear with parts cut away and constructed in accordance with the present invention;

Fig. 2 is an enlarged view of a portion of Fig. 1 showing a rack bushing and seal assembly in accordance with the present invention; and

Fig. 3 is a further enlarged view of a portion of the assembly of Fig. 2.

Detailed Description of the Invention

The present invention relates to an apparatus for sealing a fluid chamber, and particularly to apparatus for sealing a fluid chamber of a fluid power assisted rack and pinion steering gear. The present invention is applicable to various steering gear constructions. As representative of the present invention, Fig. 1 illustrates a fluid power assisted rack and pinion steering gear 10.

The steering gear 10 is connected with a pair of steerable vehicle wheels (not shown) in a known manner by steering linkage 12 at one end of the steering gear and by steering linkage (not shown) at the opposite end 14 of the steering gear. The steering gear 10 includes a housing 16, a pinion 18, and a rack 20. The rack 20 has an outer surface 28 and extends longitudinally through a tubular portion 22 of the housing 16. The tubular housing portion 22 partially defines a fluid chamber 24. A piston (not shown) is fixed to the rack 20 at a location within the chamber 24.

Upon rotation of the vehicle steering wheel (not shown) , fluid under pressure is directed against the piston, causing the rack 20 to move within the housing 16 in a direction parallel to an axis 26. Axial movement of the rack 20 moves the steering linkage connected to the ends of the rack thus turning the steerable wheels of the vehicle.

An annular bushing 30 supports the rack 20 for axial movement relative to the housing 16. The bushing 30 is preferably injection molded of a plastic material suitable for use in the environment of a hydraulic fluid power assisted rack and pinion steering gear. The bushing 30 could, alternatively, be made from another material, such as aluminum. The bushing 30 has parallel, cylindrical inner and outer side surfaces 32 and 34, which extend parallel to the axis 26. The inner side surface 32 defines a passage 36 through which the rack 20 extends .

A snap ring groove 38 is formed in the outer surface 34 of the bushing 30. A snap ring 40 is received in the groove 38. The snap ring 40 engages in a corresponding groove 42 in an inner surface of the housing 16 to lock the bushing 30 in position axially in the housing. Any other known bushing retention method could be used in place of the snap ring 40. An annular seal groove 50 (Fig. 3) is formed in the inner surface 32 of the bushing 30. The seal groove 50 has a generally rectangular cross sectional configuration defined by a bottom surface 52 and spaced end surfaces 54 and 56. The bottom surface 52 has a cylindrical configuration centered on the axis 26 at a location spaced radially outward from the rack 20. Each one of the end surfaces 54 and 56 has an annular configuration centered on the axis 26.

A seal assembly 60 is received in the seal groove 50, in the bushing 30, for sealing between the bushing and the rack 20. The seal assembly 60 includes a first seal member 62 and a second seal member 64.

The first seal member 62 is located in the groove 50, in sealing engagement with the bottom surface 52 of the groove. The second seal member 64 is located in the groove 50, in sealing engagement with the outer surface 28 of the rack 20.

The first seal member 62 is disposed between the second seal member 64 and the bottom surface 52 of the groove 50. The second seal member 64 is disposed between the first seal member 62 and the outer surface 28 of the rack 20.

In the illustrated embodiment, the first seal member 62 is an annular O-ring and the second seal member 64 is an engineered plastic sealing ring. The O-ring 62 is made from a resilient material such as neoprene and when in its free state has a round cross-sectional configuration. The O-ring 62 has an outer surface 63.

The second seal member 64, the engineered plastic sealing ring, is an annular member made from a material such as Vespel® brand plastic, or glass reinforced PTFE, or graphite reinforced PTFE. The second seal member 64 has a generally rectangular cross-sectional configuration including parallel inner and outer surfaces 66 and 68 and parallel end surfaces 70 and 72.

Both the seal ring 64 and the O-ring 62 are narrower (axially) than the groove 50. At all times, the inner surface 66 of the seal ring 64 seals against the outer surface 28 of the rack 20. The outer surface 68 of the seal ring 64 seals against the outer surface 63 of the 0- ring 62. The outer surface 63 of the O-ring 62 seals against the bottom surface 52 of the groove 50. When the seal assembly 60 is loaded by oil under pressure from one side of the chamber 24 in the housing 16, as indicated by the arrows in Fig. 3, the seal assembly moves to the opposite side of the groove 50. The one end surface 72 of the seal ring 64 seals against the one end surface 56 of the groove 50.

The O-ring 62 deforms under this fluid pressure, and the outer surface 63 of the O-ring is pushed firmly against the bottom surface 52, the end surface 56 of the bushing 30 and surface 68 of seal ring 64. The deformation of the O-ring 62 also helps to push the seal ring 64 radially inward against the outer surface 28 of the rack 20. Therefore, the seal ring 64, as backed up by the O-ring 62, seals even better against the outer surface 28 of the rack 20. As a result, an improved seal is effected between the rack 20 and the bushing 30 by the seal assembly 60.

In the illustrated embodiment, a second (optional) seal assembly 60a, identical to the seal assembly 60, is provided. The second seal assembly 60a is located in a second seal groove 50a. The second seal groove 50a is spaced axially from the seal groove 50. The seal grooves 50 and 50a are preferably located as close as feasible to the axial center of the bushing 30. Providing two seal assemblies 60 and 60a can help to improve the sealing function of the rack bushing 30. The invention can be used with one, two or more seal assemblies, depending on the application. From the foregoing description of the invention, those skilled in the art will perceive improvements, changes and modifications in the invention. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.

Claims

Having described the invention, I claim:

1. A hydraulic power assist rack and pinion steering gear comprising: a tubular housing partially defining a chamber for receiving fluid under pressure; a rack extending axially through said chamber in said housing; an annular bushing supporting said rack for axial movement in said chamber, said bushing having a cylindrical inner surface defining a passage extending longitudinally through said bushing for receiving said rack therethrough; said bushing having a groove in said inner surface defined at least partially by a bottom surface; and a seal assembly received in said groove for sealing between said rack and said bushing, said seal assembly including a first seal member located in said groove in sealing engagement with said bottom surface of said bushing, said seal assembly including a second seal member located in said groove in sealing engagement with said first sealing member and with said rack, said second seal member being disposed radially between said first seal member and said rack.

2. A steering gear as set forth in claim 1 wherein said first seal member is an O-ring and said second seal member is an engineered plastic sealing ring.

3. A steering gear as set forth in claim 2 wherein said groove is defined at least partially by a bottom surface and two end surfaces, said O-ring seals against said bottom surface and against a first one of said end surfaces and against said seal ring, and said seal ring seals against said outer surface of said rack and against said first one of said end surfaces.

4. A steering gear as set forth in claim 3 wherein said groove is wider than said seal assembly, said seal assembly being movable axially in said groove to effect a seal against one of said end surfaces of said groove.

5. A steering gear as set forth in claim 1 further including a second groove in said inner surface of said bushing spaced axially from said first groove, said second groove being defined by a second bottom surface and two second end surfaces; and a second seal assembly received in said groove for sealing between said rack and said bushing, said second seal assembly including a first seal member located in said second groove in sealing engagement with said second bottom surface of said bushing, said second seal assembly including a second seal member located in said second groove in sealing engagement with said first sealing member and with said rack, said second seal member of said second seal assembly being disposed radially between said first seal member and said rack.