Integrated transfer line for automotive steering system

An apparatus according to this invention for carrying hydraulic fluid in a power assisted automotive steering system, includes a tube having a tube wall formed with a first port that extends though a thickness of the tube wall. A housing includes a wall formed with a second port extending though a thickness of the housing wall. A retainer is secured to the housing. A fluid transfer line includes a first surface that contacts an outer surface of the tube, is formed with a passage communicating with the first port, is sealed against fluid flow past the first surface, and is secured to an outer surface of the tube. A second surface contacting the retainer is formed with a passage communicating with the second port, is sealed against fluid flow past the second surface, and is secured to the housing by the retainer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to automotive steering system. More particularly, it pertains to apparatus for hydraulically sealing and connecting transfer lines to a tube and housing.

2. Description of the Prior Art

A power-assisted, rack and pinion steering system for automotive applications includes a steering shaft controlled manually by the vehicle operator by rotating the vehicle's steering wheel. The steering shaft is connected through a flexible coupling to a pinion gear, which is driveably engaged with a rack located in a relatively thick walled tube. The rack extends laterally from a housing to a mechanism that steers the vehicle's wheels.

The tube also contains a hydraulic double-acting piston, which is secured to the rack. A piston moves in a cylinder located in the tube in response to differential pressure across the piston. A control valve alternately pressurizes and vents the opposite faces of the cylinder in response to rotation of the steering wheel and pinion gear. As the rack moves in opposite linear directions along the tube in response to rotation of the steering wheel, a net hydraulic pressure force produced on the piston assists the vehicle operator to steer the wheels by adding to the force on the rack applied manually by the vehicle operator. In this way, the operator's effort and the degree to which the steering wheel is rotated in order to produce a desired change in direction are reduced.

Transfer lines carry pressurized hydraulic fluid from the housing to the cylinder located in the tube. Generally the housing is formed of cast aluminum, but the tube and transfer lines are of steel. The physical property differences and strength dissimilarities of the metals add to the complicity of the connections at each end of the transfer lines.

There is a long felt need in steering gear design for an efficient, low cost technique to connect the transfer lines to the outer surface of the tube without use of weld stud adapters attached to the rack tube and providing a screw-in attachment to the transfer lines. It is desired that the transfer lines be connected to the aluminum housing using a screw-in attachment, or a metallic bond to a threaded insert, or a slip attachment that is hydraulically sealed.

SUMMARY OF THE INVENTION

The present invention concerns an apparatus for connecting pressure transfer lines to the outer surface of the main rack tube either through a direct connection in which the lines are connected to the tube's outer surface by brazing, soldering or welding, or indirectly using a fitting, which is attached directly to the outer surface of the main rack tube by brazing, soldering or welding and provides a sealed slip attachment with the transfer line.

The opposite end of the transfer lines are connected to the housing either using a threaded insert engaged with screw threads formed in the housing wall, an insert molded in place, or a retainer plate attached to the housing. In either case, the transfer lines are connected to the insert or retaining plate by a brazed, soldered or welded connection, each attachment providing an integral hydraulic seal.

These connections provide simplicity of assembly, allow the transfer lines to be installed during the assembly of the tube to the housing, and easily accommodate diverse applications because of the improved clearance space provided.

An apparatus according to this invention for carrying hydraulic fluid in a power assisted automotive steering system, includes a tube having a tube wall formed with a first port that extends though a thickness of the tube wall. A housing includes a wall formed with a second port extending though a thickness of the housing wall. A retainer is secured to the housing. A fluid transfer line includes a first surface that contacts an outer surface of the tube, is formed with a passage communicating with the first port, is sealed against fluid flow past the first surface, and is secured to an outer surface of the tube. A second surface contacting the retainer is formed with a passage communicating with the second port, is sealed against fluid flow past the second surface, and is secured to the housing by the retainer.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1Ais an external isometric view of a power-assisted rack and pinion steering mechanism for an automotive vehicle. The vehicle operator rotates the steering shaft10about axis12by turning the vehicle's steering wheel. The steering shaft10is driveably connected through a flexible coupling14to a pinion gear, located in a housing18, which also contains a fluid control valve. The pinion gear is driveably engaged with a rack located in a relatively thick walled tube20, which extends transversely from housing18and also contains a hydraulic double acting piston secured to the rack. The rack moves in opposite linear directions along axis16in response to rotation of the steering wheel and pinion gear in opposite angular directions. The tube20and housing18are supported on the frame of the vehicle by mounting brackets22,24.

The piston, located in tube20and secured to the rack, is actuated by pressurized hydraulic fluid supplied to a cylinder located on opposite sides of the piston. A transfer line26carries pressurized fluid to one side of the piston; transfer line28carries pressurized hydraulic fluid to the other side of the piston. As soon inFIG. 1A, transfer line26is directly connected at30to the outer surface of tube20, and transfer line28is directly connected at32to the outer surface of the tube20. The opposite ends of transfer lines26,28are each connected to the wall46of valve-pinion housing18by an insert36, which is threaded or molded in place into the housing wall. The axial outer end of transfer line26is formed with a bend38such that the end of the line is substantially perpendicular to the outer surface of tube20. Similarly, the axial outer end of transfer line28is formed with a bend40so that the transfer line is substantially perpendicular to the outer surface of tube20.

FIG. 1Bshows an end of each transfer line26,28connected to housing18using inserts36′ that are cast integrally with the housing wall46.FIG. 1Cshows an end of each a transfer line26,28fitted in a respective boss on the wall46on the housing18, the bosses being drilled to receive the ends of the transfer lines without inserts.

Turning now toFIG. 2, transfer lines42,44, which extend transversely from the valve-pinion gear housing18, are secured to the outer surface of tube20using weld fittings48,50, respectively. The opposite axial end of transfer lines42,44is secured by a hydraulically sealed connection to the wall46of housing18.

Referring now toFIGS. 3A and 3B, the bend38at the end of transfer line26positions the line substantially perpendicular to the outer surface of tube20such that the transfer line communicates sufficiently with a port61that passes through the wall thickness of the tube to allow fluid flow between the tube and the transfer line. The axial end of the transfer line26is formed with a flared flange60, which is seated on the outer surface of tube20and secured to that surface by soldering, brazing or welding. This connection also seals against the flow of hydraulic fluid between the tube20and line26.

FIG. 3Bshows a transfer line26formed with a flange, preferably formed by axially compressing the tube to produce an overlapping flared flange62, which is seated on the outer surface of tube20and secured to tube20by soldering, brazing or welding. Transfer line26communicates sufficiently with port61to allow fluid flow between the tube20and the transfer line.

FIG. 4Aillustrates a 90-degree weld fitting48secured to the outer surface of tube20by soldering, brazing or welding. Fitting48includes a radial passage66, which communicates with port61and with a lateral passage64. Transfer line42is inserted in the lateral passage64, to which it is secured at68by soldering, brazing or welding. A liquid sealer may be applied around the periphery of the transfer line42where is contacts at68the outer surface70of fitting48to seal against fluid flow and to enhance the seal provided by a connection between transfer line42and fitting48made by soldering, brazing or welding. Transfer line42engages the inner surface of lateral passage64preferably with an interference fit.

FIG. 4Billustrates a weld fitting48′ that is secured to the outer surface of tube20by welding, brazing or soldering. A lateral arm72of fitting48′ is formed during a swedging operation with an angular recess74. Transfer line42is inserted in the lateral passage64and may be sealed and secured to fitting48′ by swedging the fitting in the vicinity of recess74so that it engages the transfer line with an interference fit. The swedged connection is an alternative or a supplement to securing the transfer line42to fitting48′ by soldering, brazing or welding.

The weld fitting48″ shown inFIG. 4Cis secured into the outer surface of tube20by soldering, brazing or welding. Fitting48″ includes a lateral passage68, formed with a recess80containing an O-ring82or a comparable sealing device. Transfer line42is inserted into the lateral passage68and engages the O-ring82and the wall of the lateral passage with an interference fit, thereby sealing the passage against the flow of hydraulic fluid and securing the transfer line to fitting48″.

The weld fitting50shown inFIG. 4Dis secured to the outer surface of tube20by soldering, brazing or welding. The fitting50is formed with an enlarged lateral passage68′, whose diameter is sized to receive transfer line44and the O-ring84, located in the recess86formed on the outer surface of the transfer line44. In this arrangement, an interference fit is produced between the surface of passage68′ and the outer radial surface of O-ring84.

FIG. 4Eshows yet another configuration of a transfer line44and a weld fitting50′, which is secured to the outer surface of tube20by soldering, brazing or welding. A portion of the length of the lateral passage68″ is formed with larger diameter surface90, which is sized to receive a sealing device such as an O-ring92. A portion of the length of transfer line44′ is crimped to form an overlapping flange94that extends radially outward from the surface of transfer line44′ and is spaced axially from the nearest end of the transfer line. A terminal length of the transfer line44′, inserted in passage68″, holds O-ring92in position between flange94and the step between surface90and lateral passage68″. The radial outer surface of flange94frictionally engages surface90with a sufficient interference fit to maintain preloaded compression in the sealing device (92), thereby sealing the connection against the passage of hydraulic fluid and securing the transfer line44′ to the weld fitting50′. The flange also prevents extrusion of the seal84.

Referring now toFIGS. 5A-5C, wall46of housing18is relatively thick in relation to the wall thickness of the transfer lines26,28,42,46and of the tube20, and it is formed preferably of aluminum, other cast metal including, but not limited to zinc, iron, magnesium, whereas the transfer lines and tube are of steel.

AsFIG. 5Ashows, a retainer insert36has external screw threads that engage screw threads tapped into the wall46of housing18, and a central passage102communicating with passage104formed in housing wall46to permit fluid flow between transfer line28and housing18. A length of transfer line28near its end is flared radially outward forming a flange surface that is secured to insert36by welding, soldering or brazing. AsFIG. 1Ashows, the head of inserts36are each formed with a hexagonal surface to facilitate threading them into wall46. The outer surface of the insert can either extend be located outward from the surface of the wall, or flush with the wall surface, or below the wall surface. Alternatively, asFIG. 1Bshows, an insert36′ can be molded in place without having to be machined and screwed into the housing wall46.

FIG. 5Bshows another connection for securing transfer line28′ to housing wall46using a threaded retainer insert36′ formed with external screw threads. The threaded insert36′ is formed with a stepped central passage108, communicating with the passage104in housing wall46, to permit fluid flow between transfer line28and housing18. The outer end of the insert has an enlarged surface110, sized to receive transfer line28′, which is inserted into the insert and is secured to the insert by welding, soldering or brazing at a fillet109. As shown inFIG. 1B, each insert36′ can be molded in place without having to be machined and screwed into the housing wall46. The outer surface of the insert can either extend be located outward from the surface of the wall, or flush with the wall surface, or below the wall surface.

In the transfer line connection ofFIG. 5C, the threaded retainer insert36′ is secured to housing wall46by the engagement of screw threads on its outer surface with the internal screw threads tapped into the wall. The threaded insert36′ is formed with a stepped central passage108, communicating with the passage104in housing wall46, to permit fluid flow between transfer line28″ and housing18. A portion of the length of transfer line28″ is crimped to form an overlapping radial flange112near the axial end of the transfer line, and the length of the tube between the flange and transfer line end is inserted into the enlarge passage110. The transfer line28″ is inserted into the passage110, flange112contacts the adjacent face of the threaded insert36′, and the flange is secured to the adjacent face of insert36′ at113by welding, soldering or brazing. As shown inFIG. 1B, each insert36′ can be molded in place without having to be machined and screwed into the housing wall46. The outer surface of the insert can either extend outward from the surface of the wall, or be located flush with the wall surface, or below the wall surface.

FIGS. 6A-6Cshow alternate connections for securing a transfer line42,44to housing wall46using a retention plate114.

In the connection ofFIG. 6A, the housing wall46is formed with a stepped central opening extending through the thickness of the wall. An intermediate surface116of the opening is located between the hydraulic passage104and the largest diameter portion118formed in the thickness of the wall. A portion of the length of transfer line42is crimped to form an overlapping radial flange122near the axial end of the transfer line, and the length of the tube between the flange and transfer line end is inserted into the opening portions116,118. A sealing device120, such as an O-ring, is fitted among a step in the housing wall46, the flange122, and the length131of the transfer line that extends between the flange and the line end. The retainer plate114is formed with an open central hole through its thickness so that the plate can be moved along the transfer line into engagement with the outer surface of the flange122and into contact with the housing outer surface. A threaded attachment or attachments124secure plate114to the housing wall46. Producing a preloaded fit among O-ring120, wall46, and transfer line42by compressing the O-ring seals the connection. The flare or flange122also prevents extrusion of the seal device120.

When the transfer lines42,44are straight, as shown inFIG. 2, plate114can be deleted, and each the lines is secured to the wall46using the flange122fitted into the opening118.

In the transfer line connection ofFIG. 6B, the wall housing46′ is formed with a single opening126, which extends through the housing wall and is formed with an internal recess128, fitted with a sealing device such as an O-ring130. Retainer plate114is secured to the transfer line42′ by welding, brazing or soldering forming a fillet138at an axial location that is spaced from an end of the tube. Fasteners124secure retainer plate114to the housing wall46. This provides a length of transfer line42′ that is inserted into opening126, overlapping the radial inner surface of the sealing device130and compressing the sealing device to provide a hydraulic seal between opening126and transfer line42′.

Alternatively, as shown inFIG. 6D, a plate114′, secured by attachments124to the wall46, may be joggled over a flange140formed on each transfer line42′″. Recess128contains an O-ring130, or another sealing device.

InFIG. 6Eeach transfer line42,44is formed with a flared flange122, and secured to the wall46by a single retainer plate114″. The wall46is formed with recesses128, each recess containing an O-ring130, or another sealing device. The plate retainers114,114′,114″ allow the transfer lines to rotate, thereby facilitating their installation and assembly.

Referring toFIG. 6C, housing wall46is formed with a single opening129extending entirely through the thickness of the wall. The transfer line42″ is formed with a recess132, which is spaced axially from the end134of the transfer line. The recess132is sized to receive a sealing device136, such as an O-ring. Retainer plate114is secured to the transfer line42″ by welding, brazing or soldering forming a fillet138at an axial location that is spaced from an end of the tube. Retainer plate114is secured by fasteners124to the outer surface of the housing wall46such that the adjacent faces of the retainer plate (114) and housing wall46are in mutual contact. The transfer line42″ is moved into engagement with housing wall46such that the sealing device136engages opening129with an interference fit that compresses the seal136, thereby providing a fluid type connection between the opening129and the transfer line42″.

When the transfer lines42″,44″ are straight, as shown inFIG. 2, plate114can be deleted, and each the lines is then secured to the wall46″ using an interference fit between the outer surface of the line and the opening129.

FIG. 7Ais an external view of a housing10showing transfer lines42,44secured by retainer plates144using a single hex headed attachment integrated into a single retainer plate114′, as shownFIG. 7B.