Patent Publication Number: US-2017361865-A1

Title: Multiple Piece Pinion Housing For Vehicle Power Steering

Description:
BACKGROUND OF INVENTION 
     This invention relates in general to vehicle power steering assemblies and in particular to a multiple piece pinion housing for use in such a vehicle power steering assembly. 
     Automotive vehicles typically include a power steering assembly to assist in turning steerable wheels of the vehicle. The power steering assembly will typically include a rack and pinion assembly to convert rotational movement of a steering wheel of the vehicle into linear movement to effect turning of the steerable wheels. The rack and pinion assembly includes a pinion that is held within a pinion housing. Typically, the pinion housing comprises a pinion tower, a tube portion housing the rack, and a belt housing, all of which are formed monolithically as a unitary casting for efficiency during fabrication and subsequent assembly. 
     Multiple piece pinion housings for hydraulic power steering systems have been fabricated as a hollow tube connecting a cast pinion tower and a cast belt housing. However, the cast belt housing is heavy and significantly increases vehicle weight. To reduce vehicle weight, the pinion housing may be cast from aluminum. However, casting of the pinion housing requires an extended period of time for the molten aluminum to enter and flow throughout a mold for the large and complex casting. The molten aluminum cools during the extended period of time. As molten aluminum cools, air cavities or voids form. The air cavities increase porosity for the cast pinion housing. Thus it would be desirable to have a lighter weight pinion housing with reduced porosity. 
     SUMMARY OF INVENTION 
     This invention relates to a multiple piece pinion housing for a vehicle power steering assembly. 
     According to one embodiment, a method of fabricating a pinion housing for a vehicle power steering assembly may comprise, individually and/or in combination, one or more of the following features: forming a first housing from a first material, forming a second housing from a second material, and forming a third housing from a third material. The third housing is a stamping. The second material has a lesser unit weight than the first material and the third material has a greater unit weight than the second material. The first, second, and third housings are each formed separately. The formed first, second, and third housings are joined together to form the pinion housing. 
     According to another embodiment, a pinion housing for a vehicle power steering assembly may comprise, individually and/or in combination, one or more of the following features: A first housing formed from a first material, a second housing formed from a second material, and a third housing stamped from a third material. The second material has a lesser unit weight than the first material and the third material has a greater unit weight than the second material. The first, second, and third housings are each formed separately and joined together to form the pinion housing. 
     According to another embodiment, a pinion housing for a vehicle power steering assembly may comprise, individually and/or in combination, one or more of the following features: a plurality of housings formed separately and joined together to form the pinion housing. The plurality of housings includes at least a stamped housing and a cast housing. The cast housing has a lesser material unit weight than the stamped housing. 
     An advantage of an embodiment is a lighter weight pinion housing with reduced porosity. Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view of a vehicle power steering assembly having a first embodiment of a pinion housing in accordance with the present invention. 
         FIG. 2  is an exploded perspective view of the pinion housing of  FIG. 1 . 
         FIG. 3  is a flow chart of a method for fabricating the pinion housing of  FIG. 1 . 
         FIG. 4  is a second embodiment of a pinion housing in accordance with the present invention. 
         FIG. 5  is a flow chart of a method for fabricating the pinion housing of  FIG. 4 . 
         FIG. 6  is a third embodiment of a pinion housing in accordance with the present invention. 
         FIG. 7  is a flow chart of a method for fabricating the pinion housing of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , there is schematically illustrated a portion of a vehicle power steering assembly, indicated generally at  100 . The general structure and operation of the power steering assembly  100  is conventional in the art. For example, the power steering assembly  100  may be as disclosed by U.S. Pat. No. 7,055,646 to Bugosh, the disclosure of which is hereby incorporated by reference in entirety herein. Thus, only those portions of the power steering assembly  100  which are necessary for a full understanding of this invention will be explained and illustrated in detail. Although this invention will be described and illustrated in connection with the particular power steering assembly  100  disclosed herein, it will be appreciated that this invention may be used in connection with other vehicle power steering assemblies, including other electric, hydraulic, or otherwise powered power steering assemblies known to those skilled in the art. 
     The power steering assembly  100  is partially housed in a housing, indicated generally at  102 . The housing  102  includes a portion that is a first embodiment of a pinion housing, indicated generally at  104 , produced in accordance with the present invention. The pinion housing  104  is comprised of a first housing or sub-housing  104 A, a second housing or sub-housing  104 B, and a third housing or sub-housing  104 C, all of which will be discussed further. The housing  102  has further portions that will be discussed. 
     The power steering assembly  100  is associated with first and second front steerable wheels  106 A and  106 B, respectively, of a vehicle and includes a rotatable input shaft  108 . A vehicle steering wheel  110  is operatively coupled to the input shaft  108  for rotation therewith about a steering axis X 1 . A torque sensor  112  encircles the input shaft  108  and is located within a pinion tower cover  114  connected to the second housing  104 B. For example, the pinion tower cover  114  may be bolted to the second housing  104 B. The torque sensor  112  generates signals in response to rotation of the input shaft  108 . The signals are transmitted over a data network  116  to an electronic control unit (ECU)  118 . The signals indicate a direction and magnitude of steering torque applied to the steering wheel  110 . 
     A torsion bar  120  connects the input shaft  108  to a pinion  122  disposed in the second housing  104 B such that the second housing  104 B houses or encloses the pinion  122 . The torsion bar  120  twists in response to the steering torque applied to the steering wheel  110 . When the torsion bar  120  twists, relative rotation occurs between the input shaft  108  and the pinion  122 . 
     The second housing  104 B is attached to the first housing  104 A in a manner which will be discussed. A linearly moveable steering member  124  extends axially through, and is disposed in, the first housing  104 A such that the first housing  104 A houses or encloses the steering member  124 . The steering member  124  is linearly, or axially, moveable along a rack axis X 2 . A rack portion  126  of the steering member  124  is provided with a series of rack teeth which meshingly engage gear teeth provided on the pinion  122 . The steering member  124  further includes a screw portion  128  having an external screw thread convolution. The steering member  124  is connected to the first steerable wheel  106 A by a first tie rod  130 A and the second steerable wheel  106 B by a second tie rod  130 B. The first and second tie rods  130 A and  130 B, respectively, are located at distal ends of the steering member  124 . Linear movement of the steering member  124  along the rack axis X 2  results in steering movement of the first and second steerable wheels  106 A and  106 B, respectively, in a known manner. 
     The power steering assembly  100  further includes a power source  132  drivably connected to a ball nut assembly  134  housed between the third housing  104 C and a ball nut portion  136  of the housing  102 . The power source  132  is illustrated as an electric motor, but may be other than an electric motor. For example, the power source  132  may be a hydraulic system. The ECU  118  controls the power source  132  in accordance with the signals received from the torque sensor  112 . Control signals are transmitted from the ECU  118  to the power source  132  via the data network  116 . 
     The ball nut assembly  134  is operatively connected with the screw portion  128  of the steering member  124 . The power source  132  and ball nut assembly  134  are operatively connected by a pulley assembly  138  that includes a belt between an output of the power source  132  and the ball nut assembly  134 . The pulley assembly  138  is disposed in the third housing  104 C such that the pulley assembly is at least partially enclosed or housed by the third housing  104 C. 
     Rotation of the pulley assembly  138  causes the ball nut assembly  134  to be rotated and thereby produce linear movement of the steering member  124 . The power source  132  rotates the pulley assembly  138  which in turn transmits the drive force of the power source  132  to a ball nut of the ball nut assembly  134 . Because the ball nut is fixed in position on the rack axis X 2 , the steering member  124  is driven to move linearly in response to rotation of the ball nut to, as discussed, effect steering movement of the first and second steerable wheels  106 A and  106 B, respectively, of the vehicle. The power source  132  thus provides steering assist in response to the applied steering torque. 
     In the event of the inability of the power source  132  to effect linear movement of the steering member  124 , the mechanical connection between the gear teeth on the pinion  122  and the rack teeth on the rack portion  126  permits manual steering of the vehicle. 
     Referring now to  FIG. 2 , there is illustrated the first, second, and third housings  104 A,  104 B, and  104 C, respectively, of the pinion housing  104 . Also illustrated are first, second, third, and fourth mounting brackets  140 ,  142 ,  144 , and  146 , respectively, for the pinion housing  104 . 
     The first housing  104 A is formed from a first material, the second housing  104 B is formed from a second material, and the third housing  104 C is formed from a third material. The first and third materials have a greater unit weight than the second material. For example, the first material may be a first grade of steel, the second material may be aluminum, and the third material may be a second grade of steel. Alternatively, the first and third materials may be the same grade of steel. Alternatively, the first material may be aluminum, plastic, or a polymer. Alternatively, the third material may be a high strength plastic 
     As illustrated, the first housing  104 A is a drawn tube, the second housing  104 B is a casting, and the third housing  104 C is a stamping. Alternatively, the first housing  104 A, the second housing  104 B, or the third housing  104 C may be formed using different methods—i.e., different than drawing for the first housing  104 A, casting for the second housing  104 B, or stamping for the third housing  104 C—known to those skilled in the art. Each of the first, second, and third housings  104 A,  104 B, and  104 C, respectively, is formed separately. 
     The pinion housing  104  is formed when the first, second, and third housings  104 A,  104 B, and  104 C, respectively, are joined together. The second housing  104 B is joined to the first housing  104 A. For example, the first housing  104 A may be press fit into the second housing  104 B. The first housing  104 A is also joined to the third housing  104 C. For example, the first housing  104 A may be press fit and welded to the third housing  104 C. 
     Referring now to  FIG. 3 , there is illustrated a method, indicated generally at  148 , of fabricating the pinion housing  104 . The method  148  begins with a step S 1 . In a step S 2 , the first housing  104 A is drawn from the first material. In a step S 3 , the second housing  104 B is cast from the second material. In a step S 4 , the third housing  104 C is stamped from the third material. In a step S 5 , the second housing  104 B is joined to the first housing  104 A and, in a step S 6 , the third housing  104 C is joined to the first housing  104 A. In a step S 7 , the pinion housing  104  is in an assembled state. 
     As illustrated and discussed, the pinion housing  104  is comprised of three pieces: the first, second, and third housings  104 A,  104 B, and  104 C, respectively. Alternatively, the pinion housing  104  may be comprised of more or fewer than three pieces. 
     Referring now to  FIG. 4 , there is illustrated a second embodiment of a pinion housing, indicated generally at  204 , produced in accordance with the present invention. Because the pinion housing  204  is a variation of the pinion housing  104  of  FIGS. 1 and 2 , like reference numerals, increased by 100, designate corresponding parts in the drawings and detailed description thereof will be omitted. 
     The pinion housing  204  has a first housing or sub-housing, indicated generally at  204 A, that is comprised of a first tube  250  and a second tube  252 . The first and second tubes  250  and  252 , respectively, are formed separately and joined together to form the first housing  204 A. For example, the first and second tubes  250  and  252 , respectively, may be welded, bolted, or riveted together to form the first housing  204 A. 
     As illustrated, the first and second tubes  250  and  252 , respectively, are separately drawn tubes. Alternatively, the first and second tubes  250  and  252 , respectively, may be tubes formed other than by drawing. The first tube  250  is formed from a fourth material and the second tube  252  is formed from a fifth material that may be the same as the fourth material. The fourth and fifth materials each have greater unit weights than a second material from which a second housing or sub-housing  204 B is formed. For example, the fourth and fifth materials may be steel of either the same of different grades. Alternatively, the fourth and fifth materials may each be aluminum, plastic, or a polymer. 
     Referring now to  FIG. 5 , there is illustrated a method, indicated generally at  248 , of fabricating the pinion housing  204 . The method  248  begins with a step S 1 . In a step S 2 , the first tube  250  is drawn from the fourth material and, in a step S 3 , the second tube  252  is drawn from the fifth material. In a step S 4 , the first and second tubes  250  and  252 , respectively, are joined to form the first housing  204 A. In a step S 5 , the second housing  204 B is cast from the second material. In a step S 6 , a third housing or sub-housing  204 C is stamped from a third material. In a step S 7 , the second housing  204 B is joined to the first housing  204 A and, in a step S 8 , the third housing  204 C is joined to the first housing  204 A. For example, the first housing  204 A may be press fit to the second housing  204 B and press fit and welded to the third housing  204 C. In a step S 9 , the pinion housing  204  is in an assembled state. 
     Referring now to  FIG. 6 , there is illustrated a third embodiment of a pinion housing, indicated generally at  304 , produced in accordance with the present invention. Because the pinion housing  304  is a variation of the pinion housing  204  of  FIG. 4 , like reference numerals, increased by 100, designate corresponding parts in the drawings and detailed description thereof will be omitted. 
     The pinion housing  304  has a second housing or sub-housing, indicated generally at  304 B, that is comprised of a bottom portion  354  and a top portion  356 . For example, the bottom portion  354  may be a pinion tower bottom and the top portion  356  may be a pinion bowl. The bottom portion  354  is formed separately from the top portion  356 . For example, the bottom portion  354  may be cast separately from casting of the top portion  356 . The bottom portion  354  is formed from a sixth material and the top portion  356  is formed from a seventh material. The sixth and seventh materials may be the same or different. For example, each of the sixth or seventh materials may be steel, aluminum, plastic, or a polymer. The bottom portion  354  and top portion  356  are joined together to form the second housing  304 B. For example, the bottom portion  354  and top portion  356  may be joined by a threaded connection, rivets, bolts, thermal fusion, or chemically. 
     As illustrated, the pinion housing  304  has a first tube  350 , a second tube  352 , the bottom portion  354 , and the top portion  356 , wherein the first and second tubes  350  and  352 , respectively, comprise a first housing or sub-housing  304 A. However, the first housing  304 A may alternatively be formed as a single component—i.e., similar to the first housing  104 A. 
     Referring now to  FIG. 7 , there is illustrated a method, indicated generally at  348 , of fabricating the pinion housing  304 . The method  348  begins with a step S 1 . In a step S 2 , the first tube  350  is drawn from a fourth material and, in a step S 3 , the second tube  352  is drawn from a fifth material. In a step S 4 , the bottom portion  354  is cast from the sixth material and, in a step S 5 , the top portion  356  is cast from the seventh material. In a step S 6 , the first and second tubes  350  and  352 , respectively, are joined to form the first housing  304 A. In a step S 7 , the bottom portion  354  and top portion  356  are joined to form the second housing  304 B. In a step S 8 , a third housing or sub-housing  304 C is stamped from a third material. In a step S 9 , the second housing  304 B is joined to the first housing  304 A and, in a step S 10 , the third housing  304 C is joined to the first housing  304 A. For example, the first housing  304 A may be press fit to the second housing  304 B and press fit and welded to the third housing  304 C. In a step S 11 , the pinion housing  304  is in an assembled state. 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been described and illustrated in its preferred embodiments. 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.