Abstract:
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:
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&#39;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&#39;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&#39;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&#39;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 DRAWINGS 
     The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
       FIGS. 1A-1C  are isometric views of a steering gear assembly for an automotive vehicle showing transfer lines secured to a tube and various connections to a housing at the opposite end of the transfer lines; 
       FIG. 2  is an isometric view of a steering gear assembly for an automotive vehicle showing transfer lines secured to a tube in accordance with the present invention; 
       FIGS. 3A and 3B  are cross sections taken at plane  3  of  FIG. 1 ; 
       FIGS. 4A-4E  are cross sections taken at plane  4  of  FIG. 2 ; 
       FIGS. 5A-5C  are cross sections taken at plane  5  of  FIG. 1 ; 
       FIGS. 6A-6E  are cross sections taken at plane  6  of  FIG. 2 ; 
       FIG. 7A  is an external view of a housing showing transfer lines secured by retainer plates; and 
       FIG. 7B  is a view showing the transfer lines of  FIG. 7  secured by a single retainer plate. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1A  is an external isometric view of a power-assisted rack and pinion steering mechanism for an automotive vehicle. The vehicle operator rotates the steering shaft  10  about axis  12  by turning the vehicle&#39;s steering wheel. The steering shaft  10  is driveably connected through a flexible coupling  14  to a pinion gear, located in a housing  18 , which also contains a fluid control valve. The pinion gear is driveably engaged with a rack located in a relatively thick walled tube  20 , which extends transversely from housing  18  and also contains a hydraulic double acting piston secured to the rack. The rack moves in opposite linear directions along axis  16  in response to rotation of the steering wheel and pinion gear in opposite angular directions. The tube  20  and housing  18  are supported on the frame of the vehicle by mounting brackets  22 ,  24 . 
   The piston, located in tube  20  and secured to the rack, is actuated by pressurized hydraulic fluid supplied to a cylinder located on opposite sides of the piston. A transfer line  26  carries pressurized fluid to one side of the piston; transfer line  28  carries pressurized hydraulic fluid to the other side of the piston. As soon in  FIG. 1A , transfer line  26  is directly connected at  30  to the outer surface of tube  20 , and transfer line  28  is directly connected at  32  to the outer surface of the tube  20 . The opposite ends of transfer lines  26 ,  28  are each connected to the wall  46  of valve-pinion housing  18  by an insert  36 , which is threaded or molded in place into the housing wall. The axial outer end of transfer line  26  is formed with a bend  38  such that the end of the line is substantially perpendicular to the outer surface of tube  20 . Similarly, the axial outer end of transfer line  28  is formed with a bend  40  so that the transfer line is substantially perpendicular to the outer surface of tube  20 . 
     FIG. 1B  shows an end of each transfer line  26 ,  28  connected to housing  18  using inserts  36 ′ that are cast integrally with the housing wall  46 .  FIG. 1C  shows an end of each a transfer line  26 ,  28  fitted in a respective boss on the wall  46  on the housing  18 , the bosses being drilled to receive the ends of the transfer lines without inserts. 
   Turning now to  FIG. 2 , transfer lines  42 ,  44 , which extend transversely from the valve-pinion gear housing  18 , are secured to the outer surface of tube  20  using weld fittings  48 ,  50 , respectively. The opposite axial end of transfer lines  42 ,  44  is secured by a hydraulically sealed connection to the wall  46  of housing  18 . 
   Referring now to  FIGS. 3A and 3B , the bend  38  at the end of transfer line  26  positions the line substantially perpendicular to the outer surface of tube  20  such that the transfer line communicates sufficiently with a port  61  that 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 line  26  is formed with a flared flange  60 , which is seated on the outer surface of tube  20  and secured to that surface by soldering, brazing or welding. This connection also seals against the flow of hydraulic fluid between the tube  20  and line  26 . 
     FIG. 3B  shows a transfer line  26  formed with a flange, preferably formed by axially compressing the tube to produce an overlapping flared flange  62 , which is seated on the outer surface of tube  20  and secured to tube  20  by soldering, brazing or welding. Transfer line  26  communicates sufficiently with port  61  to allow fluid flow between the tube  20  and the transfer line. 
     FIG. 4A  illustrates a 90-degree weld fitting  48  secured to the outer surface of tube  20  by soldering, brazing or welding. Fitting  48  includes a radial passage  66 , which communicates with port  61  and with a lateral passage  64 . Transfer line  42  is inserted in the lateral passage  64 , to which it is secured at  68  by soldering, brazing or welding. A liquid sealer may be applied around the periphery of the transfer line  42  where is contacts at  68  the outer surface  70  of fitting  48  to seal against fluid flow and to enhance the seal provided by a connection between transfer line  42  and fitting  48  made by soldering, brazing or welding. Transfer line  42  engages the inner surface of lateral passage  64  preferably with an interference fit. 
     FIG. 4B  illustrates a weld fitting  48 ′ that is secured to the outer surface of tube  20  by welding, brazing or soldering. A lateral arm  72  of fitting  48 ′ is formed during a swedging operation with an angular recess  74 . Transfer line  42  is inserted in the lateral passage  64  and may be sealed and secured to fitting  48 ′ by swedging the fitting in the vicinity of recess  74  so that it engages the transfer line with an interference fit. The swedged connection is an alternative or a supplement to securing the transfer line  42  to fitting  48 ′ by soldering, brazing or welding. 
   The weld fitting  48 ″ shown in  FIG. 4C  is secured into the outer surface of tube  20  by soldering, brazing or welding. Fitting  48 ″ includes a lateral passage  68 , formed with a recess  80  containing an O-ring  82  or a comparable sealing device. Transfer line  42  is inserted into the lateral passage  68  and engages the O-ring  82  and 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 fitting  48 ″. 
   The weld fitting  50  shown in  FIG. 4D  is secured to the outer surface of tube  20  by soldering, brazing or welding. The fitting  50  is formed with an enlarged lateral passage  68 ′, whose diameter is sized to receive transfer line  44  and the O-ring  84 , located in the recess  86  formed on the outer surface of the transfer line  44 . In this arrangement, an interference fit is produced between the surface of passage  68 ′ and the outer radial surface of O-ring  84 . 
     FIG. 4E  shows yet another configuration of a transfer line  44  and a weld fitting  50 ′, which is secured to the outer surface of tube  20  by soldering, brazing or welding. A portion of the length of the lateral passage  68 ″ is formed with larger diameter surface  90 , which is sized to receive a sealing device such as an O-ring  92 . A portion of the length of transfer line  44 ′ is crimped to form an overlapping flange  94  that extends radially outward from the surface of transfer line  44 ′ and is spaced axially from the nearest end of the transfer line. A terminal length of the transfer line  44 ′, inserted in passage  68 ″, holds O-ring  92  in position between flange  94  and the step between surface  90  and lateral passage  68 ″. The radial outer surface of flange  94  frictionally engages surface  90  with 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 line  44 ′ to the weld fitting  50 ′. The flange also prevents extrusion of the seal  84 . 
   Referring now to  FIGS. 5A-5C , wall  46  of housing  18  is relatively thick in relation to the wall thickness of the transfer lines  26 ,  28 ,  42 , 46  and of the tube  20 , 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. 
   As  FIG. 5A  shows, a retainer insert  36  has external screw threads that engage screw threads tapped into the wall  46  of housing  18 , and a central passage  102  communicating with passage  104  formed in housing wall  46  to permit fluid flow between transfer line  28  and housing  18 . A length of transfer line  28  near its end is flared radially outward forming a flange surface that is secured to insert  36  by welding, soldering or brazing. As  FIG. 1A  shows, the head of inserts  36  are each formed with a hexagonal surface to facilitate threading them into wall  46 . 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, as  FIG. 1B  shows, an insert  36 ′ can be molded in place without having to be machined and screwed into the housing wall  46 . 
     FIG. 5B  shows another connection for securing transfer line  28 ′ to housing wall  46  using a threaded retainer insert  36 ′ formed with external screw threads. The threaded insert  36 ′ is formed with a stepped central passage  108 , communicating with the passage  104  in housing wall  46 , to permit fluid flow between transfer line  28  and housing  18 . The outer end of the insert has an enlarged surface  110 , sized to receive transfer line  28 ′, which is inserted into the insert and is secured to the insert by welding, soldering or brazing at a fillet  109 . As shown in  FIG. 1B , each insert  36 ′ can be molded in place without having to be machined and screwed into the housing wall  46 . 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 of  FIG. 5C , the threaded retainer insert  36 ′ is secured to housing wall  46  by the engagement of screw threads on its outer surface with the internal screw threads tapped into the wall. The threaded insert  36 ′ is formed with a stepped central passage  108 , communicating with the passage  104  in housing wall  46 , to permit fluid flow between transfer line  28 ″ and housing  18 . A portion of the length of transfer line  28 ″ is crimped to form an overlapping radial flange  112  near 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 passage  110 . The transfer line  28 ″ is inserted into the passage  110 , flange  112  contacts the adjacent face of the threaded insert  36 ′, and the flange is secured to the adjacent face of insert  36 ′ at  113  by welding, soldering or brazing. As shown in  FIG. 1B , each insert  36 ′ can be molded in place without having to be machined and screwed into the housing wall  46 . 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-6C  show alternate connections for securing a transfer line  42 ,  44  to housing wall  46  using a retention plate  114 . 
   In the connection of  FIG. 6A , the housing wall  46  is formed with a stepped central opening extending through the thickness of the wall. An intermediate surface  116  of the opening is located between the hydraulic passage  104  and the largest diameter portion  118  formed in the thickness of the wall. A portion of the length of transfer line  42  is crimped to form an overlapping radial flange  122  near 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 portions  116 ,  118 . A sealing device  120 , such as an O-ring, is fitted among a step in the housing wall  46 , the flange  122 , and the length  131  of the transfer line that extends between the flange and the line end. The retainer plate  114  is 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 flange  122  and into contact with the housing outer surface. A threaded attachment or attachments  124  secure plate  114  to the housing wall  46 . Producing a preloaded fit among O-ring  120 , wall  46 , and transfer line  42  by compressing the O-ring seals the connection. The flare or flange  122  also prevents extrusion of the seal device  120 . 
   When the transfer lines  42 ,  44  are straight, as shown in  FIG. 2 , plate  114  can be deleted, and each the lines is secured to the wall  46  using the flange  122  fitted into the opening  118 . 
   In the transfer line connection of  FIG. 6B , the wall housing  46 ′ is formed with a single opening  126 , which extends through the housing wall and is formed with an internal recess  128 , fitted with a sealing device such as an O-ring  130 . Retainer plate  114  is secured to the transfer line  42 ′ by welding, brazing or soldering forming a fillet  138  at an axial location that is spaced from an end of the tube. Fasteners  124  secure retainer plate  114  to the housing wall  46 . This provides a length of transfer line  42 ′ that is inserted into opening  126 , overlapping the radial inner surface of the sealing device  130  and compressing the sealing device to provide a hydraulic seal between opening  126  and transfer line  42 ′. 
   Alternatively, as shown in  FIG. 6D , a plate  114 ′, secured by attachments  124  to the wall  46 , may be joggled over a flange  140  formed on each transfer line  42 ′″. Recess  128  contains an O-ring  130 , or another sealing device. 
   In  FIG. 6E  each transfer line  42 ,  44  is formed with a flared flange  122 , and secured to the wall  46  by a single retainer plate  114 ″. The wall  46  is formed with recesses  128 , each recess containing an O-ring  130 , or another sealing device. The plate retainers  114 ,  114 ′,  114 ″ allow the transfer lines to rotate, thereby facilitating their installation and assembly. 
   Referring to  FIG. 6C , housing wall  46  is formed with a single opening  129  extending entirely through the thickness of the wall. The transfer line  42 ″ is formed with a recess  132 , which is spaced axially from the end  134  of the transfer line. The recess  132  is sized to receive a sealing device  136 , such as an O-ring. Retainer plate  114  is secured to the transfer line  42 ″ by welding, brazing or soldering forming a fillet  138  at an axial location that is spaced from an end of the tube. Retainer plate  114  is secured by fasteners  124  to the outer surface of the housing wall  46  such that the adjacent faces of the retainer plate ( 114 ) and housing wall  46  are in mutual contact. The transfer line  42 ″ is moved into engagement with housing wall  46  such that the sealing device  136  engages opening  129  with an interference fit that compresses the seal  136 , thereby providing a fluid type connection between the opening  129  and the transfer line  42 ″. 
   When the transfer lines  42 ″,  44 ″ are straight, as shown in  FIG. 2 , plate  114  can be deleted, and each the lines is then secured to the wall  46 ″ using an interference fit between the outer surface of the line and the opening  129 . 
     FIG. 7A  is an external view of a housing  10  showing transfer lines  42 ,  44  secured by retainer plates  144  using a single hex headed attachment integrated into a single retainer plate  114 ′, as shown  FIG. 7B . 
   In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.