WO2007024884A2

WO2007024884A2 - Staked retention of bearing in a power assisted steering system

Info

Publication number: WO2007024884A2
Application number: PCT/US2006/032818
Authority: WO
Inventors: Thomas C. Lauver; Ken Eaton
Original assignee: Trw Automotive U.S. Llc
Priority date: 2005-08-24
Filing date: 2006-08-22
Publication date: 2007-03-01
Also published as: WO2007024884A3

Abstract

A steering assembly includes a housing having a bore formed therein such as for receiving a rack slidably disposed in the bore. A bearing is disposed in the bore. A portion of the housing is deformed forming a flange. The flange retains the bearing in the housing.

Description

TITLE

STAKED RETENTION OF BEARING IN A POWER ASSISTED STEERING SYSTEM

BACKGROUND OF THE INVENTION

This invention relates in general to power assisted steering systems, such as are commonly used in vehicles. In particular, this invention relates to an improved method of retaining a bearing for rotatably supporting a portion of a power assist assembly within a housing for such a power assisted steering system.

Many vehicles in common use, such as automobiles, vans, and trucks, include a power assisted steering system for allowing a driver to pivot a pair of ground-engaging vehicle xvheels about respective turning axes and, thus, control the direction of movement of the vehicle. A typical power assisted steering system includes a steering assembly and a power assist assembly. The steering assembly includes a steering wheel that is manually rotated by the driver to pivot the vehicle wheels about their respective turning axes. The power assist assembly is responsive to the amount of torque that is exerted by the driver to rotate the steering wheel for generating a force that assists in pivoting the vehicle wheels, thereby reducing the amount of torque that the driver would otherwise have to manually apply to the steering wheel.

The steering assembly typically includes a rack and pinion mechanism that includes a steering shaft connected to the steering wheel for rotation therewith. The steering shaft has a helical pinion gear provided thereon that cooperates with a corresponding plurality of gear teeth provided on a transversely extending rack. The opposed ends of the rack are connected to the vehicle wheels such that linear movement of the rack causes pivoting movement of the vehicle wheels. When the steering wheel is rotated by the driver, the helical pinion gear provided on the i steering shaft rotates relative to the rack. The cooperation of the helical pinion gear with the plurality of gear teeth provided on the rack causes the rack to move linearly relative to the steering shaft, resulting in pivoting movement of the vehicle wheels. The power assist assembly typically includes a sensor that generates a signal that is representative of the amount of torque that is exerted by the driver to rotate the steering wheel and a hydraulic or electric actuator that is responsive to the sensor signal for selectively rotating an output shaft. The output shaft is connected through a ball nut and screw mechanism to the rack. The ball nut and screw mechanism includes a ball nut portion that is connected to the output shaft of the actuator for rotation therewith and a screw portion that is provided on the rack.

When the output shaft is rotated in response to the sensor signal, the ball nut portion of the ball nut and screw mechanism is rotated relative to the screw portion thereof. As a result, the screw portion exerts a force on the rack that assists in pivoting the vehicle wheels. In the past, the ball nut portion of the ball nut and screw mechanism has been supported for rotation by a bearing that was supported on a housing of the power assisted steering system. The bearing was press fit into a recess provided in the housing of the power assisted steering system and retained therein by a retaining structure, such as by a lock nut, adhesive, or a retaining ring or circlip. Although effective, it has been found that the use of such known retaining structures has been relative difficult and expensive to install. Thus, it would be desirable to provide an improved method of retaining a bearing for rotatably supporting a portion of a power assist assembly within a housing for such a power assisted steering system that is relatively simple and inexpensive.

BRIEF SUMMARY OF THE INVENTION

This invention relates to an improved method of retaining a bearing for rotatably supporting a portion of a power assist assembly within a housing for a power assisted steering system The steering assembly includes a housing having a bore formed therein for receiving a rack slidably disposed in the bore. The housing preferably includes a radially inwardly projecting stop within the bore. A bearing is disposed in the bore of the housing. A portion of the housing is deformed radially inwardly forming a flange, thereby retaining the bearing in the housing. In one embodiment of the invention, the bearing has opposed first and second surfaces. The first surface abuts against the stop. The second surface abuts the flange.

The invention also relates to a method of retaining the bearing in the housing. Firstly, there is provided a steering assembly housing having a bore formed therein. The housing includes a radially inwardly projecting stop, such as for example, in the form of a shoulder formed in the bore. The bearing includes first and second opposed surfaces. The bearing is inserted into the bore such that the first surface of the bearing abuts the stop. A portion of the housing is deformed to form a radially extending flange abutting the second surface of the bearing, thereby retaining the bearing in the housing. The flange can be formed with the assistance of a tool assembly.

Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWTNGS

Fig. 1 is a schematic elevational view of a rack and pinion steering system having a bearing mounted therein in accordance with this invention.

Fig. 2 is an enlarged cross-sectional view of a portion of the steering system of Fig. 1.

Fig. 3 is a further enlarged cross-sectional view of a portion of the steering system shown in Fig. 2 illustrating in greater detail the mounting of the bearing. Fig. 4 is an exploded perspective view of a portion of the steering system illustrated in Figs. 1-3 and a staking tool assembly used to mount the bearing on the housing.

Fig. 5 is a cross-sectional view of the assembled tool assembly and steering housing of Fig. 4.

Fig. 6 is an enlarged view of a portion of the tool assembly of Fig. 5 illustrating the method of mounting the bearing prior to deformation of the housing.

Fig. 7 is an enlarged view of a portion of the tool assembly of Fig. 5 illustrating the method of mounting the bearing after deformation of the housing. Fig. 8 is a perspective cross-sectional view of a portion of the housing illustrating the shoulder prior to deformation.

Fig. 9 is a perspective cross-sectional view of the portion of the housing shown in Fig. 8 illustrating one of the deformed flanges formed in the housing for retaining the bearing.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, there is illustrated in Fig. 1 a power assisted steering assembly, indicated generally at 10. As will be explained in detail below, the steering assembly 10 includes a bearing 110 which is retained in a housing 30 of the steering assembly 10 by deformation of a portion of the housing 30 in accordance with the present invention.

As schematically shown in Fig. 1, the steering assembly 10 includes a steering wheel 12. The steering wheel 12 is manually rotated by the driver of the vehicle in which the steering assembly 10 is installed when the driver wishes to turn the vehicle. The steering wheel 10 is rotatably connected to an input shaft, schematically illustrated at 14. The input shaft 14 is rotatably connected to a steering shaft or torsion bar, schematically illustrated at 16. The input shaft 14 may be rotatably connected to the torsion bar 16 by a universal joint 18. The universal joint 18 permits a rotational connection between the input shaft 14 and the torsion bar 16 while accommodating an angular misalignment between the rotational axes of the input shaft 14 and the torsion bar 16. The torsion bar 16 is connected to a steering shaft 20. If needed, the connection between the torsion bar 16 and the steering shaft 20 may be connected with a universal joint (not shown). The torsion bar 16 includes a worm gear or pinion 22 having helical teeth 24 formed therein, the reason for which will be explained below. The pinion 22 may be a separate component connected to the steering shaft 20 or integrally formed on an end of the steering shaft 20. The input shaft 14, the torsion bar 16, the steering shaft 20, and the pinion 22 may be formed from a single component or any multiple number of components.

The steering assembly 10 includes a housing, indicated generally at 30. The housing 30 can be formed of a single piece or from multiple components. For example, as shown in Figs. 1 and 2, the embodiment of the steering assembly 10 shown in the drawings is a two piece housing including an inboard housing 32 and an outboard housing 34. As shown in the partial schematical cross-section of Fig. I₅ the steering shaft 20 is rotatably mounted in an angled extension portion 36 of the housing 30. The extension portion 36 can be integral with the inboard housing 32 or may be a separate component attached to the housing 30. The housing 30 may be made of any suitable material, such as metal, and more preferably, die cast aluminum.

As best shown in Fig. 2, the housing 30 includes a bore 31 generally defined by a bore 40 formed in the inboard housing 32 and a bore 42 formed in the outboard housing 34. A rack 44 is slidably disposed in the bores 40 and 42 along a longitudinal axis A. The rack 44 is generally an elongated bar having a longitudinally extending row of rack teeth 46. The teeth 46 of the rack 44 are in meshing engagement with the teeth 24 of the pinion 22. Preferably, only a portion of the rack 44 is formed with the longitudinally extending row of rack teeth 46. This portion of the rack 44 with the teeth 46 is generally in the vicinity of the meshing engagement with the pinion 22. The steering assembly 10 may also include a spring loaded yoke (not shown) movably mounted in the housing which presses the rack 44 against the pinion 22 to maintain the rack teeth 46 in meshing engagement with the teeth 24 on the pinion 22.

As shown in Fig. 2, the rack 44 further includes a threaded portion 50 defining helical teeth 52. As will be explained in detail below, the teeth 52 of the threaded portion 50 engage with a ball nut assembly, indicated generally at 54 in Fig. 2. As shown in Fig. 2, the rack 44 includes ends 56 which extend outward from the housing 30. The ends 56 can be integral with the rack 44 or can be separate components connected to the rack 44. For example, the ends 56 can be elongated members coupled to the rack 44 via a ball socket connection (not shown). The steering assembly 10 may also include boot seals 57 for protecting and sealing the rack 44 and the components in communication with the bores 40 and 42 of the housing. The ends 56 are connected to respective tie rods, indicated schematically at 58, which are connected to steering knuckle arms 60. The steering knuckle arms 60 are connected to steered wheels 62 in a conventional manner. The ends 56 of the rack 44 may also be operatively connected with other suspension members, such as wheel axles, shock absorbers, upper and lower suspension arms, as is conventionally known in the art.

The steering assembly 10 further includes a power assist assembly, indicated generally at 70, as best shown in Fig. 2. The power assist assembly 70 includes a sensor, such as a torque sensor 71 for detecting the force or torque imparted by the driver. The sensor 71 can be mounted on the steering wheel 12, the input shaft 14, the torsion bar 16, or the steering shaft 20. The power assist assembly 70 preferably includes an electric motor 72 having a rotational output shaft 74. The power assist assembly 70 can be any suitable apparatus which converts the rotational output motion of the motor 72 to an assisting force on the rack 44 for longitudinal movement of the rack 44 within the bore 31 of the housing 30.

The output shaft 74 of the motor 72 is connected to a pulley 76. The pulley 76 includes a central bore 77 which receives the output shaft 74. The pulley 72 is connected to the output shaft 74 such that they are rotationally coupled, wherein rotation of the output shaft 74 causes rotation of the pulley 76. The pulley 76 can be rotationally connected to the pulley 76 by any suitable manner, such as by a key 78 extending outwardly from the output shaft 74 disposed in a groove or keyway 80 formed in the bore 77 of the pulley 76. Of course, it should be understood that any suitable rotational connection can be used to connect the output shaft 74 to the pulley 76, such as with a spline connection. Preferably, the pulley 76 is a toothed pulley, such that the pulley 76 includes a plurality of teeth 82 formed circumferentially about an outer cylindrical surface of the pulley 76. The teeth 82 engage with a flexible toothed belt 84. In the embodiment shown in the figures, the power assist assembly 70 includes a ball nut assembly, indicated generally at 90. The ball nut assembly 90 includes a ball nut 92. The ball nut 92 is generally in the shape of a sleeve which is disposed over the threaded portion 50 of the rack 44. The ball nut 92 includes an internal helical thread 94 formed therein. A plurality of balls 96 are disposed in one or more helical grooves 98 defined by the region between the internal helical threads 94 of the ball nut 92 and the teeth 52 of the threaded portion 50 of the rack 44. As will be explained below, rotation of the ball nut 92 creates an assisting force for longitudinal movement of the rack 44 within the bore 31 of the housing 30.

The ball nut assembly 90 preferably is a recirculating ball and nut assembly which includes a ball return mechanism (not shown). The ball return mechanism can be a conduit which deflects the balls 96 from one end of the ball nut 92 to the other end in a recirculating continuous path in the groove 98. Alternatively, the ball nut 92 may include internal deflectors or internal conduits (not shown) such that the balls 96 generally make one revolution of the threaded portion 50 of the rack 44 and are guided back through the internal deflector. In this configuration, the ball nut assembly 90 may include multiple deflectors for multiple single revolution paths for the balls 96. The ball nut assembly 90 further includes a pulley 100 disposed about the ball nut 92. Preferably, the pulley 100 is a toothed pulley having a plurality of teeth 102 formed circumferentially about an outer cylindrical surface of the pulley 100. The teeth 102 engage the toothed belt 84. The pulley 100 is rotationally connected to the ball nut 92. For example, the pulley 100 can include internal splines 104 which engage external splines 106 foπned on the outer cylindrical surface of the ball nut 92.

The steering assembly 10 further includes a bearing 110. The bearing 110 supports the ball nut assembly 90 within the bore 31 of the housing 30 and permits low frictional rotation of the ball nut 92 relative to the housing 30. As best shown in Fig. 3, the bearing 110 includes an inner race 112 and an outer race 114. The inner race 112 includes an outer circumferential groove 116 formed therein. The outer race 114 includes an inner circumferential groove 118 formed therein. A plurality of balls 119 are disposed between the inner and outer races 112 and 114 and are rollingly engaged with the grooves 116 and 118. The inner race 112 is mounted on the ball nut 92, such as by a press fit. Additionally, a circlip 120 may be used to retain the bearing 110 on the ball nut 92. The circlip 120 is inserted into a circumferential groove 122 formed on the ball nut 92.

It should be understood that the bearing 110 can be any suitable bearing mechanism which permits low frictional rotation of the ball nut 92 relative to the housing 30. Preferably, the bearing 110 is a four point ball bearing. In a four point ball bearing, the grooves 116 and 118 are preferably arc shaped raceways whose centers of curvature are offset with respect to one another so that during radial loading, the balls 119 contact the grooves 116 and 118 at four points. This four point structure helps to provide these bearings with the capability of transmitting high axial loads in both directions.

The bearing 110 is disposed in a multi-stepped recess 130 formed in the outboard housing 34 of the housing 30. The recess 130 defines a shoulder 132 formed between a first diameter portion 134 and a second diameter portion 136 of the bore 31 of the housing 30. The second diameter portion 136 has a greater diameter than the first diameter portion 134. The shoulder 132 defines a stop for the bearing 110 when inserted during installation. The inner race 112 of the bearing 110 is retained from axial movement on the ball nut 92 by a radially outwardly extending flange 133 of the ball nut 92 and the circlip 120. The recess 130 further includes a third diameter portion 138 defining a generally cylindrical wall 140. Note that the cylindrical wall 140 may or may not be completeby cylindrical about 360 degrees for permitting clearance for the belt 84.

The outer race 114 of the bearing 110 is retained in the recess 130 by one or more flanges 150. The outer race 114 of the bearing 110 is retained from axial movement within the recess 130 by being disposed between the shoulder 132 and the flanges 150. The shoulder 132 abuts a first surface 152 of the outer race 114, and the flanges 150 abut an opposed second surface 154 of the outer race 114. As will be discussed in more detail below, the flanges 150 are formed by deforming a portion of the outboard housing 34 of the housing 30.

The operation of the steering assembly 10 will now be described. When a steering maneuver is desired, the driver rotates the steering wheel 12 in the desired rotational direction. Rotation of the steering wheel 12 causes rotation of the input shaft 14, torsion bar 16, steering shaft 20, and the pinion 22. The meshing engagement between the teeth 24 of the pinion 22 and the teeth 46 of the rack 44 causes the rack 44 to move longitudinally within the bore 31 of the housing 30 along the axis A. Longitudinal movement of the rack 44 causes movement of the tie rods 58 and the steering knuckle arms 60 which pivot the vehicle wheels 62 relative to the vehicle based on the direction of the longitudinal movement of the rack 44. To provide an assisting force on the rack 44, the power assist assembly 70 is actuated. The torque sensor 71 detects the driver's input and a controller (not shown) regulates the speed of the electric motor 72 accordingly. The controller may be connected to other sensors, such as vehicle speed sensors for determining the appropriate speed of the motor 72. Actuation of the motor 72 rotates the output shaft 74 causing rotation of the pulley 76 and the belt 84. Rotation of the belt 84 causes rotation of the pulley 100 and the ball nut 92. Rotation of the ball nut 92 imparts a force on the rack 44 in the longitudinal direction along axis A, thereby assisting in causing movement of the rack 44 within the bore 31 of the housing 30. As state above, the flanges 150 which retain the bearing 110 in the housing 30 are formed by deforming a portion of the outboard housing 34 of the housing 30. There is illustrated in Fig. 8, a cross-sectional portion of the outboard portion 34 of the housing 30 illustrated prior to deformation to form the flanges 150, shown in Fig. 9. The outboard portion 34 of the housing 30 includes a shoulder 160. A portion of the shoulder 160 is deformed radially inwardly from the second diameter portion 136 of the bore 31. The flange 150 can be formed into any suitable shape which retains the bearing 110 within the recess 130. As shown in Fig. 9, only a portion of the shoulder 160 and not its entirety need be deformed to form the flange 150. Preferably, a plurality of circumferentially spaced apart flanges 150 are formed to retain the bearing 110. The flanges 150 can be equally spaced apart from each other. For example, six flanges 150 may be formed from the shoulder 160 spaced sixty degrees from one another. The formation of the flanges 150 of the present invention preferably are able to handle the relatively high impact loads, e.g., twenty kN to forty-four kN, imparted on the ball nut assembly 90 by the power assist assembly 70.

There is illustrated in Figs. 4 and 5 a tool assembly 170 for use in forming the flanges 150. The tool assembly generally includes a base 172, a staking tool 174, and a press tool 176. The base 172 includes a tubular body 180 having an open end 182 and a cavity 184 for receiving the rack 44. Note that the rack 44, the ball nut 92, and the bearing 110 are preferably provided as an assembly. The base 172 further includes a flange 186 at the open end 182. The flange 186 receives the press tool 176. The staking tool 174 includes a through bore 190 formed therein for receiving the rack 44. The staking tool 174 preferably includes a plurality of wedge shaped bosses 192 formed circumferentially about an upper cylindrical circumferential edge 194 of the staking tool 174. The shape and number of bosses 192 correspond to the desired shape and number of flanges 150 formed on the outboard housing 34.

To form the flanges 150 with the assistance of the tool assembly 170, the staking tool 174 is positioned on the flange 186 of the base 172. The assembly of the rack 44. the ball nut 92 and the bearing 110 are inserted into the outboard housing 34 such that the bearing 110 is disposed in the recess 130 and the surface 152 of the outer race 114 rests against the shoulder 132 of the outboard housing 134, as best shown in Fig. 6. The rack 44 is then inserted into the cavity 184 of the base 172. The press tool 176 is then positioned at the end of the outboard housing 34 opposite from the staking tool 174, as shown in Fig. 5.

Prior to forming the flanges 150, the tool assembly 170 and the assembly of the rack 44, the ball nut 92, and the bearing 110 are positioned as shown in Figs. 5 and 6. To form the flanges 150, a compressive force is applied on the staking tool 174 and the press tool 176. The compressive force causes the bosses 192 to deform a portion of the shoulder 160 during which the material is pushed radially inwardly until the desired flange 150 is formed, as shown in Fig. 7. As best shown in Figs. 6 and 7, the bosses are preferably wedge shaped. The wedge shape of the bosses 160 function as a cutting and forming die to push the deformed portion of the shoulder 160 radially inwardly. Although the present invention was shown and described with respect to a belt driven electrically powered steering assist system, it should be understood that the invention could be practiced with other steering systems. For example, the system could be configured as a column drive steering wherein the steering assist assembly is connected to the input shaft 14 or torsion bar 16. Alternatively, the present invention may be practiced with steering systems incorporating direct drives in which the output of the motor 72 is connected to the ball nut assembly 54 via gears.

In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.

Claims

CLAIMS What is claimed is:

1. A vehicular steering system comprising: a power assist assembly including a rotatable component; a housing having a bore formed therein; and a bearing disposed in said bore of said housing and supporting said rotatable component for rotation, wherein a portion of said housing is deformed forming a flange, thereby retaining said bearing in said housing.

2. The vehicular steering system of claim 1, wherein a plurality of circumferentially spaced apart deformed flanges are formed in said housing for retaining said bearing in said housing.

3. The vehicular steering system of claim 2, wherein at least six circumferentially spaced apart deformations are formed in said housing.

4. The vehicular steering system of claim 1, wherein said portion of said housing is deformed radially inwardly from a generally cylindrical wall of said bore.

5. The vehicular steering system of claim 1, wherein said housing defines an axis and includes a radially inwardly projecting stop formed in a wall of said bore, and wherein said bearing has opposed first and second surfaces, said first surface abutting against said stop and said second surface abutting said flange.

6. The λ'ehicular steering system of claim 5, wherein said bearing includes an inner race and an outer race, said outer race having said first and second surfaces, and wherein said steering system further includes: a ball nut mounted on said inner race of said bearing; a rack slidably disposed in said housing for connecting with steered wheels of a vehicle, said rack having helical teeth formed thereon for engagement with said ball nut; and a motor having an output shaft operatively connected with said ball nut.

7. The vehicular steering system of claim 5, wherein said first and second surfaces of said bearing extend radially relative to said axis.

8. The vehicular steering system of claim 5, wherein said bore is a stepped bore including first and second diameter portions defining a circumferential shoulder therebetween, and wherein said stop is defined by said shoulder.

9. The vehicular steering system of claim 8, wherein said bore includes a third diameter portion defining a second shoulder between said second diameter portion and said third diameter portion, and wherein said flange is formed by deforming a portion of said second shoulder.

10. The vehicular steering system of claim 9, wherein a plurality of circumferentially spaced apart deformed flanges are formed in said second shoulder of said housing for retaining said bearing in said housing.

11. The vehicular steering system of claim 10, wherein at least six circumferentially spaced apart deformations are formed in said housing.

12. The vehicular steering system of claim 9, wherein said second shoulder, prior to deformation, defines a plane which is perpendicular to said axis.

13. The vehicular steering system of claim 5, wherein said bearing is a ball bearing including an inner race and an outer race, and wherein said outer race has said first and second surfaces.

14. A vehicular steering system comprising: a housing having a stepped bore formed therein and including first and second diameter portions defining a first shoulder therebetween, said stepped bore of said housing further including a third diameter portion defining a second shoulder between said second diameter portion and said third diameter portion; a bearing disposed in said bore of said housing, said bearing having an inner race and an outer race including a first radially extending surface and an opposed second radially extending surface, said first radially extending surface abutting against said first shoulder of said housing, wherein a portion of said housing at said second shoulder is deformed radially inwardly forming a flange abutting said second radially extending surface, thereby retaining said bearing in said housing; a ball nut mounted on said inner race of said bearing; a rack slidably disposed in said housing for connecting with steered wheels of a vehicle, said rack having helical teeth formed thereon for engagement with said ball nut; and a motor having an output shaft operatively connected with said ball nut.

15. The vehicular steering system of claim 14, wherein a plurality of circumferentially spaced apart deformed flanges are formed in said second shoulder of said housing for retaining said bearing in said housing.

16. A method of retaining a bearing in a housing of a vehicular steering system comprising the step of: a. providing a housing having a bore formed therein and including a radially inwardly projecting stop; b. providing a bearing having opposed first and second surfaces; c. inserting the bearing into the bore such that the first surface abuts the stop; d. deforming a portion of the housing to form a radially extending flange abutting the second surface, thereby retaining the bearing in the housing.

17. The method of claim 16, wherein the housing is provided with a stepped bore including first and second diameter portions defining a shoulder therebetween, and wherein the stop is defined by the shoulder.

18. The method of claim 17, wherein the bore of the housing is provided with a third diameter portion defining a second shoulder between the second diameter portion and the third diameter portion, and wherein the flange is formed by deforming a portion of the shoulder.

19. The method of claim 17, wherein the flange is formed with the assistance of a tool assembly including a staking tool and a press tool having a boss formed thereon, wherein step (d) is performed by positioning the housing on the staking tool such that the boss is positioned adjacent the shoulder, the press tool is then positioned such that the housing is between the press tool and the staking tool, and a compressive force is applied on the staking tool and the press tool such that the boss deforms the portion of the shoulder adjacent the boss, thereby forming the flange.