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(11) | EP 0 897 767 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Vehicle steering rack and method of manufacturing the rack |
| (57) A steering rack (10) is manufactured in a method including an extruding step, a swaging
step and a broaching step. The extruding step forms a continuous body of extruded
material in the configuration of an elongated cylindrical tube (12) with a first uniform
thickness (T1). The swaging step forms a flattened portion (40) of the tube (12) with
a second uniform thickness (T2) substantially equal to the first uniform thickness
(T1). The flattened portion (40) of the tube (12) has a flattened outer surface (52).
The broaching step forms the rack teeth (60) in a row extending along the flattened
portion (40) of the tube (12) by cutting away material at locations that are spaced
apart along the flattened outer surface (52). |
Field of the Invention
[0001] The present invention relates to a steering rack for use in a rack and pinion steering gear, and also relates to a method of manufacturing the rack.
Background of the Invention
[0002] A rack and pinion steering gear has a housing containing a rack and a pinion. The rack has a longitudinally extending row of rack teeth in meshing engagement with gear teeth on the pinion. The opposite ends of the rack project outward from the housing, and are connected with a steering linkage and a corresponding pair of steerable vehicle wheels. The pinion is connected with the vehicle steering wheel by an input shaft and a torsion bar. When a steering maneuver is being performed, the pinion rotates, and the rack moves longitudinally. The housing also contains a spring-loaded yoke which presses the rack against the pinion to maintain the rack teeth in meshing engagement with the gear teeth on the pinion.
[0003] The rack may be manufactured by the use of extruding and broaching processes. For example, the rack may be formed by extruding metal material in the configuration of an elongated tube. The tube has cylindrical inner and outer surfaces. A broaching process is used to form the row of rack teeth. The broaching process first cuts away some of the metal material along a section of the tube to define a planar outer surface which is recessed from the cylindrical outer surface. This reduces the thickness of the metal material along that section of the tube. The broaching process subsequently forms the spaces between the rack teeth by cutting away additional metal material at locations that are evenly spaced apart along the length of the planar surface. As a result, the crests of the rack teeth are defined by the uncut portions of the planar surface that remain between those locations.
Summary of the Invention
[0004] The present invention comprises a vehicle steering rack and a method of manufacturing the rack. The rack has a flattened portion with a row of rack teeth. The method includes an extruding step and a broaching step, and further includes a swaging step.
[0005] Specifically, the method includes the step of extruding a continuous body of material in the configuration of an elongated cylindrical tube. The tube has a first uniform thickness. The swaging step forms a flattened portion of the tube. The flattened portion has a second uniform thickness substantially equal to the first uniform thickness, and has a flattened outer surface. The broaching step forms the rack teeth in a row extending along the flattened portion of the tube by cutting away material at locations that are spaced apart along the flattened outer surface.
[0006] A steering rack manufactured in accordance with the present invention has increased strength along the row of rack teeth. This is because the swaging step preserves the original extruded thickness of the tube upon forming the flattened portion of the tube. The original extruded thickness, as compared with a reduced thickness, provides the increased strength when the rack teeth have been formed by broaching along the length of the flattened portion of the tube.
[0007] In accordance with a particular feature of the present invention, the swaging step forms a non-cylindrical section of the tube with a triangular cross-sectional configuration. The flattened portion of the tube is one of three flattened portions defining three sides of the non-cylindrical section. The present invention thus provides the rack with additional strength resulting from the triangular configuration.
Brief Description of the Drawings
[0008] The foregoing and other features of the present invention will become apparent to one skilled in the art upon reading the following description with reference to the accompanying drawings, wherein:
Fig. 1 is a sectional view of a steering rack in a partially manufactured configuration;
Fig. 2 is a view taken on line 2-2 of Fig. 1;
Fig. 3 is a sectional view showing the steering rack in a subsequent configuration;
Fig. 4 is a view taken on line 4-4 of Fig. 3;
Figs. 5 and 6 are schematic views showing steps taken in manufacturing the steering rack;
Fig. 7 is a view showing the steering rack in another subsequent configuration;
Fig. 8 is a view taken on line 8-8 of Fig. 7; and
Fig. 9 is a partial view of a vehicle steering gear including the steering rack of Fig. 7.
Description of a Preferred Embodiment
[0009] As shown in Figs. 1 and 2, a steering rack 10 constructed in accordance with the present invention initially comprises a cylindrical metal tube 12. The tube 12 is formed by extruding metal material through a die. This can be performed in any suitable manner known in the art. The tube 12 is thus formed as a single, continuous body of extruded metal material having a uniform cross-sectional configuration fully along its entire length. The cross-sectional configuration of the tube 12 is defined by cylindrical inner and outer surfaces 14 and 16, each of which is centered on a longitudinal central axis 17. The tube 12 has a uniform thickness T1 (Fig. 2) equal to the difference between the inner and outer diameters at the inner and outer surfaces 14 and 16.
[0010] The tube 12 of Fig. 1 is swaged to define an elongated, non-cylindrical section 20 of the tube 12, as shown in Fig. 3. The non-cylindrical section 20 in the preferred embodiment of the present invention is spaced from the opposite ends 22 and 24 of the tube 12. Accordingly, the non-cylindrical section 20 is contiguous with an adjacent pair of cylindrical sections 26 and 28 that extend to the opposite ends 22 and 24 of the tube 12.
[0011] The swaging process is shown schematically in Figs. 5 and 6. Three dies 30 with planar surfaces 32 are used to apply swaging loads to the tube 12 in directions that are offset by 120° about the axis 17, as indicated by the arrows shown in Figs. 5 and 6. The non-cylindrical section 20 of the tube 12 is thus formed with a generally triangular configuration, as shown in Fig. 4, with three flattened side portions 40, 42 and 44 joined by three relatively unflattened corner portions 46.
[0012] The three flattened side portions 40-44 of the non-cylindrical section 20 are alike. Specifically, each has an inner surface 50 and an outer surface 52. The outer surfaces 52 are planar like the planar die surfaces 32. The inner surfaces 50 are substantially planar as a result of the deflection induced by the dies 30.
[0013] The three corner portions 46 of the non-cylindrical section 20 also are alike. Each corner portion 46 has an arcuate outer surface 54 defined by a segment of the cylindrical outer surface 16 of the tube 12. Each corner portion 46 further has a narrow arcuate inner surface 56 defined by a segment of the cylindrical inner surface 14 of the tube 12.
[0014] Next, a broaching process is used to form a longitudinally extending row of rack teeth 60 on the first flattened side portion 40 of the non-cylindrical section 20, as shown in Figs. 7 and 8. The broaching process forms the spaces 62 between the rack teeth 60 by cutting away the metal material at locations that are spaced apart along the outer surface 52 of the first flattened side portion 40. Such a broaching process can be performed in any suitable manner known in the art. The rack teeth 60 in the preferred embodiment of the present invention are thus formed with crests 64 that are defined at least in part by the remaining uncut portions of the outer surface 52.
[0015] In accordance with a principal feature of the present invention, the thickness of the tube 12 is substantially unaffected by the swaging process. Therefore, each flattened side portion 40, 42 and 44 of the non-cylindrical section 20 has a substantially uniform thickness T2 (Figs. 4 and 8) between its inner and outer surfaces 50 and 52, and that thickness T2 is substantially equal to the original extruded thickness T1 (Fig. 2) of the tube 12. This feature of the invention maximizes the thickness of the remaining metal material that defines the rack teeth 60 upon completion of the broaching process. The strength of the rack 10 is increased accordingly. The strength of the rack 10 is further increased by the triangular configuration.
[0016] The rack 10 is installed in a rack and pinion steering gear. Such a steering gear 70 is shown partially in Fig. 9. The steering gear 70 includes a housing 72 containing the rack 10 and a pinion 74. The pinion 74 has an axis of rotation 75, and has helical gear teeth 76 meshing with the rack teeth 60. As known in the art, the opposite ends of the rack 10 are connected with a vehicle steering linkage and a corresponding pair of steerable vehicle wheels. The pinion 74 is connected with the vehicle steering wheel by an input shaft and a torsion bar, also as known in the art. When a steering maneuver is being performed, the pinion 74 rotates about the axis 75, and the rack 10 moves longitudinally along the axis 17.
[0017] The steering gear 70 further includes a yoke 80. The yoke 80, which is sometimes referred to as a rack guide, has a cylindrical peripheral shape centered on an axis 81 which is perpendicular to the axis 17 of the rack 10. The yoke 80 is contained in a cylindrical section 82 of the housing 72 between a closure cap 84 and the rack 10.
[0018] A spring 86 is compressed between the yoke 80 and the closure cap 84. The spring 86 applies an axially directed preloading force which urges the yoke 80 forcefully against the rack 10 in a direction extending from left to right, as viewed in Fig. 9. The yoke 80, in turn, applies the preloading force to the rack 10 so as to hold the rack teeth 60 firmly in meshing engagement with the gear teeth 76 on the pinion 74. Specifically, the yoke 80 has a pair of planar guide surfaces 90 which engage the rack 10 in sliding contact at the planar outer surfaces 52 of the second and third flattened side portions 42 and 44. In this configuration, the two pairs of mating surfaces 90 and 52 establish a rotational interlock that blocks movement of the rack 10 rotationally about the axis 17 relative to the pinion 74.
[0019] According to its broadest aspect the invention relates to a method comprising the steps of: extruding a continuous body of material in the configuration of an elongated cylindrical tube having a first uniform thickness; swaging said tube to form a flattened portion of said tube with a second uniform thickness; broaching said tube to form rack teeth in a row extending along said flattened portion.
[0020] It should be noted that the objects and advantages of the invention may be attained by means of any compatible combination(s) particularly pointed out in the items of the following summary of the invention and the appended claims.
SUMMARY OF THE INVENTION
[0021]
1. A method comprising the steps of:
extruding a continuous body of material in the configuration of an elongated cylindrical tube having a first uniform thickness;
swaging said tube to form a flattened portion of said tube with a second uniform thickness substantially equal to said first uniform thickness, said flattened portion of said tube having a flattened outer surface; and
broaching said tube to form rack teeth in a row extending along said flattened portion of said tube by cutting away said material at locations that are spaced apart along said flattened outer surface.
2. A method wherein said swaging step forms said flattened outer surface as a planar surface.
3. A method wherein said swaging step forms a non-cylindrical section of said tube with a triangular cross-sectional configuration, said flattened portion of said tube being one of three flattened portions defining three sides of said non-cylindrical section.
4. A method wherein said swaging step forms said non-cylindrical section of said tube at a location spaced from the opposite ends of said tube.
5. Apparatus comprising:
a vehicle steering rack having a row of rack teeth which engage a pinion in a steering gear, said steering rack comprising a continuous body of extruded material in the configuration of an elongated tube;
said tube having a cylindrical section with cylindrical inner and outer surfaces;
said tube further having a non-cylindrical section with a flattened portion, said flattened portion having flattened inner and outer surfaces;
said rack teeth being defined between said flattened inner and outer surfaces.
6. Apparatus wherein said cylindrical section of said tube has an extruded thickness between said cylindrical inner and outer surfaces, said non-cylindrical section having a flattened thickness at the crest of each of said rack teeth, said flattened thickness being substantially equal to said extruded thickness.
7. Apparatus wherein said non-cylindrical section of said tube has a triangular cross-sectional configuration, said flattened portion of said non-cylindrical section being one of three flattened portions defining three sides of said non-cylindrical section.
8. Apparatus wherein said non-cylindrical section of said tube is spaced from the opposite ends of said tube.
9. Apparatus wherein said flattened portions of said non-cylindrical section have planar outer surfaces, said apparatus further comprising a vehicle steering gear including a guide structure having a pair of planar guide surfaces engaging a pair of said planar outer surfaces.
10. Apparatus wherein said guide structure comprises a spring-loaded yoke.
extruding a continuous body of material in the configuration of an elongated cylindrical tube having a first uniform thickness;
swaging said tube to form a flattened portion of said tube with a second uniform thickness substantially equal to said first uniform thickness, said flattened portion of said tube having a flattened outer surface; and
broaching said tube to form rack teeth in a row extending along said flattened portion of said tube by cutting away said material at locations that are spaced apart along said flattened outer surface.
a vehicle steering rack having a row of rack teeth which engage a pinion in a steering gear, said steering rack comprising a continuous body of extruded material in the configuration of an elongated tube;
said tube having a cylindrical section with cylindrical inner and outer surfaces;
said tube further having a non-cylindrical section with a flattened portion, said flattened portion having flattened inner and outer surfaces;
said rack teeth being defined between said flattened inner and outer surfaces.
and/or wherein preferably said flattened portions of said non-cylindrical section have planar outer surfaces, said apparatus further comprising a vehicle steering gear including a guide structure having a pair of planar guide surfaces engaging a pair of said planar outer surfaces.
extruding a continuous body of material in the configuration of an elongated cylindrical tube having a first uniform thickness;
swaging said tube to form a flattened portion of said tube with a second uniform thickness;
broaching said tube to form rack teeth in a row extending along said flattened portion.