Patent Publication Number: US-2019185049-A1

Title: Steering Rack

Description:
BACKGROUND 
     The present invention relates to vehicle steering systems, and more particularly to a steering rack construction. 
     SUMMARY 
     In some aspects a steering rack is provided having a toothed member and a base body each extending along longitudinal axis comprising: a toothed region disposed on the toothed member extending along the longitudinal axis; a first contact area disposed on the tooth member extending along the longitudinal axis; a first toothed member end area disposed at a first longitudinal end of the toothed member and a second toothed member end area disposed at a second longitudinal end of the toothed member; a receptacle disposed on the base body, the receptacle configured to accept the toothed member; a second contact area disposed on the base body extending along the longitudinal axis, the first and second contact areas being attached to each other; and a first receptacle end area disposed on the base member at a first longitudinal end of the receptacle and a second receptacle end area at a second longitudinal end of the receptacle, wherein the first receptacle end area and the first toothed member end area are attached to each other, and wherein the second receptacle end area and the second toothed member end area are attached to each other. The first receptacle end area and the first toothed member end area define a first end seam on an outer surface of the steering rack and the second receptacle end area and the second toothed member end area define a second end seam on the outer surface of the steering rack. The first and second contact areas define two contact surfaces seams extending along the longitudinal axis between the first and second end seams on the outer surface of the steering rack. The seams define a closed loop. The base body has a first base body region adjacent the receptacle defining a first outer circular sector having a first radius from the longitudinal axis, extending along the longitudinal axis and away from the first receptacle end area and a second base body region adjacent the second receptacle end area defining a second outer circular sector having a second radius from the longitudinal axis, extending along the longitudinal axis and away from the receptacle, wherein the toothed member has a first outer member region between the first toothed member end area and the toothed region and a second outer member region between the second toothed member end area and the toothed region, and wherein the first outer member region has the same first radius as the first outer circular sector and the second outer member region has the same second radius as the second outer circular sector. The first and the second radius are identical. Two contact surfaces seams are arranged in a plane which is parallel to the longitudinal axis. The base body is a tube with a tube wall and the two contact surfaces seams are arranged in a plane with a radial distance to the longitudinal axis. The base body is a tube with a tube wall and the two contact surfaces seams are arranged in a plane in which the longitudinal axis is arranged. The toothed member has angled areas between the outside teeth and the first and second member regions defining partial elliptical surfaces. The first receptacle end area and the first toothed member end area and the second receptacle end surface and the second toothed member end area are radially extending and parallel to each other. The toothed member has wall segments extending along the longitudinal axis arranged on either side of the teeth of the toothed section and ending in the toothed member end areas. The first end seam and the second end seam define circular sectors on the outer surface of the steering rack. The toothed member and the base body are welded together. Advantages of the proposed steering rick may be a reduction in weight with an optimized material utilization. It is also suitable for high volume applications. Simple tube concepts and existing production equipment may be used. This design may allow the use of high strength, high cost, or thicker materials only in the areas needed. Further advantages may be cost savings by reducing expensive materials. A performance improvement may also be obtained with less mass to accelerate or decelerate during steering. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal section of a steering rack assembly according to one embodiment of the invention. 
         FIG. 2  shows a steering rack of the steering rack assembly of  FIG. 1 , wherein 
         FIG. 2A  is a perspective view of the steering rack, 
         FIG. 2B  shows an exploded view of the steering rack of  FIG. 2A , 
         FIG. 2C  shows a top view of the steering rack of  FIG. 2A , 
         FIG. 2D  shows a first cross section along the lines IId-IId in  FIG. 2A  and 
         FIG. 2E  shows a second cross section along the lines IIe-IIe in  FIG. 2A . 
         FIG. 3  shows perspective view of a steering rack according to a second embodiment of the invention, wherein 
         FIG. 3A  shows a perspective view of the steering rack, 
         FIG. 3B  shows a first cross section along the lines IIIb-IIIb in  FIG. 3A  and 
         FIG. 3C  shows a second cross section along the lines IIIc-IIIc in  FIG. 3A . 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
     A longitudinal section of a steering rack assembly  10  is shown in  FIG. 1 . The steering rack assembly  10  includes a pinion  12  and a steering rack  14 . The pinion  14  is in engagement with teeth  15  of a toothed member  16  of the steering rack  14 . The steering rack  14  has the shape of a tube. But other cross sections are also possible. 
     As can be better seen in  FIG. 2 , the toothed member  16  is attached to a base body  18  of the steering rack  14 . The toothed member  16  and the base body  18  are welded together. The toothed member  16  and the base body  18  may be laser welded but other methods may also be applied. The steering rack  14  has a longitudinal axis  20 . The base body  18  is made from a circular tube with an outer radius  21  and a tube wall  22  but other cross sections may also be used. The wall thickness may be between 3-4 mm. In areas such as the ends of the steering rack  14  it can be thicker such as for example around 24 mm so inner tie rods can be inserted. 
     The toothed member  16  has a toothed region  24  extending along the longitudinal axis  20 . The base body  18  has a recess extending along the longitudinal axis  20  and defining a receptacle  26  in which the toothed member  16  is arranged. 
     The toothed member  16  has a first contact area  28  extending along the longitudinal axis  20  and the receptacle  24  has a second contact area  30  extending along the longitudinal axis  20 . The first and second contact areas  28 ,  30  are attached to each other. The receptacle  24  has a first receptacle end area  24 . 1  at a first longitudinal end of the receptacle  24  and a second receptacle end area  24 . 2  at its second longitudinal end. The toothed member  16  has a first toothed member end area  16 . 1  at a first longitudinal end of the first member  16  and a second toothed member end area  16 . 2  at its second longitudinal end. The first receptacle end area  24 . 1  and the first toothed member end area  16 . 1  are attached to each other. The second receptacle end area  24 . 2  and the second toothed member end area  16 . 2  are also attached to each other. The first receptacle end area  24 . 1  and the first toothed member end area  16 . 1  as well as the second receptacle end area  24 . 2  and the second toothed member end area  16 . 2  are radially extending and parallel to each other. As shown in  FIG. 2 , the end areas  24 . 1 ,  16 . 1  and  24 . 2 ,  16 . 2  are flat surfaces. But they could also be rounded, angled or shaped differently depending on the need. 
     The first receptacle end area  24 . 1  and the first toothed member end area  16 . 1  define a first end seam  32 . 1  on an outer surface of the steering rack  14 . The second receptacle end area  24 . 2  and the second toothed member end area  16 . 2  define a second end seam  32 . 2  on the outer surface of the steering rack  14 . The first end seam  32 . 1  and the second end seam  32 . 2  define circular seam sectors extending over an angle  33  of the outer surface of the steering rack  14 . The angle  33  is about 170° around the longitudinal axis  20  but could range from 120° to 180°. The first and second axial contact areas  28 ,  30  define two contact surfaces seams  34 ,  36  extending along the longitudinal axis  20  between the first and second end seams  32 . 1 ,  32 . 2  on the outer surface of the steering rack  14 . The seams  32 . 1 ,  32 . 2 ,  34 ,  36  define a closed loop ( FIG. 2C ). This results in a smooth surface of the steering rack  14 . The two contact surfaces seams  34 ,  36  are arranged in a plane  38  which is parallel to the longitudinal axis  20 . Furthermore, the two contact surfaces seams  34 ,  36  are arranged in the plane  38  with a radial distance  40  to the longitudinal axis  20 . The seams  32 . 1 ,  32 . 2 ,  34 ,  36  are obtained through a welding operation. Therefore, the first receptacle end area  24 . 1  and the first toothed member end area  16 . 1 , the second receptacle end area  24 . 2  and the second toothed member end area  16 . 2  as well as the first and second axial contact areas  28 ,  30  are attached to each other along their respective seams  32 . 1 ,  32 . 2 ,  34 ,  36  but contact each other on the remaining parts of the surfaces. 
     The base body  18  has a first base body region  42 . 1  adjacent the receptacle  24  defining a first outer circular sector extending along the longitudinal axis  20  and away from the receptacle  24 . The first outer circular sector has the radius  22  from the longitudinal axis  20  but could also have a different first radius. The base body  18  has a second base body region  42 . 2  adjacent the receptacle  24  defining a second outer circular sector extending along the longitudinal axis  20  and away from the receptacle  24 , hence in an opposite direction of the first base body region  42 . 1 . The first outer circular sector has the radius  22  from the longitudinal axis  20  but could also have a different second radius. The toothed member  16  has a first member region  44 . 1  between the first toothed member end area  16 . 1  and the toothed region  24  and a second member region  44 . 2  between the second toothed member end area  16 . 2  and the toothed region  24 . The first member region  44 . 1  has the same first radius as the first outer circular sector of the first base body region  42 . 1 . The second member region  44 . 2  has the same second radius as the second outer circular sector of the second base body region  42 . 2 . The first and second radius are identical but could be different from each other. This results in contiguous neighboring surfaces after a welding operation which reduces mechanical stress. In the embodiment shown the first and second outer circular sectors have the same radius since the base body  18  of the steering rack  14  is made from a tube. But they could be of different dimensions or shapes. The outer circular sectors of the first and second base body region  42 . 1 ,  42 . 2  as well as the outer radius of the first and second member regions  44 . 1 ,  44 . 2  extend over the angle  33  around the longitudinal axis  20 . Axially extending side areas  46  of the teeth  15  extending along the longitudinal axis  20  are also on radius  21 . The toothed member  16  has angled areas  48  between the outside teeth and the first and second member regions  44 . 1  and  44 . 2 . In the embodiment shown these angled areas  48  define partial elliptical surfaces. 
     The receptacle  24  can be laser cut or manufactured by another suitable cutting operation such as milling or stamping. The toothed member  16  can be cut from a round material with a saw which makes two D-shaped parts. These can then be inserted into receptacles  24  and finally attached with a weld operation. Then the teeth  15  can be cut prior to the toothed member  16  being inserted in and attached to the receptacle  24  or afterwards. This can also be used for the second embodiment described below. Other processes for manufacturing the toothed member may be a wobbling process, cold or warm forging, stamping from flat sheet, broaching from solid material, grinding from solid material or powdered metal. Further manufacturing steps for the steering rack  14  may be grinding, end finishing (threading), heat treatment and straightening. 
       FIG. 3  shows a second embodiment of a steering rack  140 . The steering rack  140  is tubular with a tube wall  220 . The steering rack  140  also has a toothed member  160  and a base body  180 . The steering rack  140  extends along a longitudinal axis  200  and has an outer radius  210 . The toothed member  160  is arranged in a receptacle  260  of the base body and has a toothed region  240 . The toothed member  160  has a first contact surface  280  extending along the longitudinal axis with which it is attached to a second contact area  300  of the receptacle  240  also extending along the longitudinal axis. The receptacle  240  has a first receptacle end area  24 . 1  and a second receptacle end area  24 . 2 . The toothed member  160  has a first toothed member end area  160 . 1  and a second toothed member end area  160 . 2 . The first receptacle end area  240 . 1  is attached to the first toothed member area  160 . 1  and define a first end seam  320 . 1 . The second receptacle end area  240 . 2  is attached to the second toothed member end area  160 . 2  to define a second end seam  320 . 2 . The first and second end seams  320 . 1  and  320 . 2  extend over an angle  330  of 180° around the longitudinal axis  200 . The first and second contact surfaces  280 ,  300  define contact surfaces seams  340 ,  360 . The contact surfaces seams  340 ,  360  are arranged in a plane  380 . The axis  200  lies in the plane  380 . 
     The base body  180  has a first base body region  420 . 1  adjacent the receptacle  240  defining a first outer circular sector  420 . 1  extending along the longitudinal axis and away from the receptacle  240 . The base body  180  has a second base body region  420 . 2  adjacent the receptacle  240  defining a second outer circular sector extending along the longitudinal axis  200  and away from the receptacle  240  opposite the direction of the first base body region  420 . 1 . The toothed member  160  has a first member region  440 . 1  between the first toothed member end area  160 . 1  and the toothed region  240  and a second member region  440 . 2  between the second toothed member end area  160 . 2  and the toothed region  240 . The first member region  440 . 1  has the same first outer circular sector as the first base body region  420 . 1 . The second member region  440 . 2  has the same second outer circular sector as the second base body region  420 . 2 . 
     The toothed member  160  has wall segments  500 ,  520  extending along the longitudinal axis and being arranged on either side of teeth  150  of the toothed section  160  and that end in the first contact area  280 . Axially extending side areas  460  of the teeth  150  extending along the longitudinal axis  200  which are also the side areas of the wall segments  500 ,  520  also are on radius  210 . The toothed member  160  has angled areas  480  between the outside teeth  150  and the first and second member regions  440 . 1  and  440 . 2 . In the embodiment shown these angled areas  480  define partial elliptical surfaces.