Abstract:
A rack drive assembly adapted for use in the vehicle electric power steering assembly includes a steering member operatively connected to a vehicle steering wheel; an electric motor for effecting axial movement of the steering member upon rotation of the vehicle steering wheel; a planetary gear assembly operatively coupled to the electric motor; and a pinion assembly operatively disposed between the planetary gear assembly and the steering member whereby operation of the electric motor is operative to effect axial movement of the steering member, wherein the electric motor includes an output shaft which defines a motor axis and the pinion assembly includes an output shaft which defines a pinion axis, wherein the pinion axis is coaxial with the motor axis and perpendicular with respect to an axis of the steering member.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates in general to vehicle electric power steering assemblies and in particular to an improved rack drive assembly adapted for use in such a vehicle electric power steering assembly. 
     One known electric power steering assembly for turning steerable wheels of a vehicle includes a ball nut for transmitting force between an axially movable rack member and an electric motor. Upon actuation of the electric motor of the power steering assembly, the ball nut is driven to rotate relative to the rack member. The rotational force of the ball nut is transmitted to the rack member by balls to drive the rack member axially. The axial movement of the rack member by the balls effects turning movement of the steerable wheels. 
     The electric motor in the above-described electric power steering assembly can be coupled to drive the ball nut in various known methods. One such method includes a belt drive assembly wherein an output shaft of the electric motor is connected via a belt to a pulley assembly. The pulley assembly typically includes a pulley which is operatively fixed to the ball nut so that the ball nut rotates with the pulley when the electric motor is actuated. This type of electric power steering assembly has advantages over other known electric power steering assemblies. However, in this type of electric power steering assembly, one or more disadvantages may be in the overall size, cost, packaging and/or operating characteristics of one or more of the components of the rack drive assembly, in particular of the pulley assembly and/or the ball nut assembly, may not be desirable or optimal. 
     Thus, it would be desirable to provide an improved structure for a rack drive assembly of an electric power steering assembly which reduces and/or improves upon one or more of the above disadvantages and is relatively simple and inexpensive. 
     SUMMARY OF THE INVENTION 
     This invention relates to an improved structure for a rack drive assembly adapted for use in a vehicle electric power steering assembly. 
     According to an embodiment, the rack drive assembly adapted for use in the vehicle electric power steering assembly may comprise, individually and/or in combination, one or more of the following features: a steering member configured to be disposed in a rack housing and including a first rack portion and a second rack portion, the first rack portion operatively connected to a vehicle steering wheel; an electric motor operatively connected to the second rack portion for effecting axial movement of the steering member upon rotation of the vehicle steering wheel; a planetary gear assembly operatively coupled to the electric motor; and a pinion assembly operatively disposed between the planetary gear assembly and the second rack portion whereby operation of the electric motor is operative to effect axial movement of the steering member by the electric motor actuating the planetary gear assembly, which in turn actuates the pinion assembly, which in turn actuates the steering member via the second rack portion; wherein the electric motor includes an output shaft which defines a motor axis and the pinion assembly includes an output shaft which defines a pinion axis, wherein the pinion axis is coaxial with the motor axis and perpendicular with respect to an axis of the steering member. 
     According to this embodiment, an isolator is provided in a connection which couples together the planetary gear assembly and the pinion assembly. 
     According to this embodiment, the isolator includes rubber elements provided on at least one of the planetary gear assembly and the pinion assembly. 
     According to this embodiment, a mounting member is provided between the electric motor and the rack housing, the mounting member configured to contain at least a portion of the planetary gear assembly and at least a portion of the pinion assembly. 
     According to this embodiment, the mounting member includes internal teeth which are operative to engage with teeth provided on planet gears of the planetary gear assembly. 
     According to this embodiment, the planetary gear assembly includes a sun gear operatively connected to an output shaft of the electric motor and a plurality of planet gears configured to be actuated by the sun gear and in turn configured to actuate the pinion assembly. 
     According to this embodiment, the planet gears are configured to be coupled to a carrier of the planetary gear assembly, and the carrier is configured to be operatively coupled to the pinion assembly. 
     According to this embodiment, an isolator is provided in a connection which couples together the carrier of the planetary gear assembly and the pinion assembly. 
     According to another embodiment, the rack drive assembly adapted for use in the vehicle electric power steering assembly may comprise, individually and/or in combination, one or more of the following features: a steering member configured to be disposed in a rack housing and including a first rack portion having first rack teeth and a second rack portion having second rack teeth, the first rack portion operatively connected to a vehicle steering wheel; an electric motor operatively connected to the second rack portion for effecting axial movement of the steering member upon rotation of the vehicle steering wheel; a planetary gear assembly operatively coupled to the electric motor; and a pinion assembly operatively disposed between the planetary gear assembly and the second rack portion, the pinion assembly having teeth which engage the teeth of the second rack portion whereby operation of the electric motor is operative to effect axial movement of the steering member by the electric motor actuating the planetary gear assembly, which in turn actuates the pinion assembly, which in turn actuates the steering member via the second rack portion; wherein the electric motor includes an output shaft which defines a motor axis and the pinion assembly includes an output shaft which defines a pinion axis, wherein the pinion axis is coaxial with the motor axis and perpendicular with respect to an axis of the steering member. 
     According to this embodiment, an isolator is provided in a connection which couples together the planetary gear assembly and the pinion assembly. 
     According to this embodiment, the isolator includes rubber elements provided on at least one of the planetary gear assembly and the pinion assembly. 
     According to this embodiment, a mounting member is provided between the electric motor and the rack housing, the mounting member configured to contain at least a portion of the planetary gear assembly and at least a portion of the pinion assembly. 
     According to this embodiment, the mounting member includes internal teeth which are operative to engage with teeth provided on planet gears of the planetary gear assembly. 
     According to this embodiment, the planetary gear assembly includes a sun gear operatively connected to an output shaft of the electric motor and a plurality of planet gears configured to be actuated by the sun gear and in turn configured to actuate the pinion assembly. 
     According to this embodiment, the planet gears are configured to be coupled to a carrier of the planetary gear assembly, and the carrier is configured to be operatively coupled to the pinion assembly. 
     According to this embodiment, an isolator is provided in a connection which couples together the carrier of the planetary gear assembly and the pinion assembly. 
     According to yet another embodiment, the rack drive assembly adapted for use in the vehicle electric power steering assembly may comprise, individually and/or in combination, one or more of the following features: a steering member configured to be disposed in a rack housing and including a first rack portion and a second rack portion, the first rack portion operatively connected to a vehicle steering wheel; an electric motor operatively connected to the second rack portion for effecting axial movement of the steering member upon rotation of the vehicle steering wheel; a planetary gear assembly operatively coupled to the electric motor; and a pinion assembly operatively disposed between the planetary gear assembly and the second rack portion whereby operation of the electric motor is operative to effect axial movement of the steering member by the electric motor actuating the planetary gear assembly, which in turn actuates the pinion assembly, which in turn actuates the steering member via the second rack portion; wherein the electric motor includes an output shaft which defines a motor axis and is operatively coupled to the planetary gear assembly, the pinion assembly includes an output shaft which defines a pinion axis and which is operatively coupled to the second rack portion, wherein the pinion axis is coaxial with the motor axis and perpendicular with respect to an axis of the steering member. 
     According to this embodiment, an isolator is provided in a connection which couples together the planetary gear assembly and the pinion assembly. 
     According to this embodiment, the isolator includes rubber elements provided on at least one of the planetary gear assembly and the pinion assembly. 
     According to this embodiment, a mounting member is provided between the electric motor and the rack housing, the mounting member configured to contain at least a portion of the planetary gear assembly and at least a portion of the pinion assembly, wherein the mounting member includes internal teeth which are operative to engage with teeth provided on planet gears of the planetary gear assembly. 
     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 THE DRAWINGS 
         FIG. 1  is a partially exploded view of a portion of an embodiment of a vehicle electric power steering assembly. 
         FIG. 2  is an enlarged view of a selected component of the vehicle electric power steering assembly illustrated in  FIG. 1 . 
         FIG. 3  is an enlarged view of another selected component of the vehicle electric power steering assembly illustrated in  FIG. 1 . 
         FIG. 4  is an enlarged view of another selected component of the vehicle electric power steering assembly illustrated in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , there is illustrated an embodiment of a vehicle electric power steering assembly, indicated generally at  10 , constructed in accordance with the present invention. The illustrated vehicle electric power steering assembly  10  is an electric “direct motor drive” rack and pinion steering assembly and is associated with the front driven wheels (not shown) of the vehicle. The general structure and operation of the electric power steering assembly  10  is conventional in the art. Thus, only those portions of the electric power steering assembly  10  which are necessary for a full understanding of this invention will be explained and illustrated in detail. Also, although this invention will be described and illustrated in connection with the particular electric power steering assembly  10  disclosed herein, it will be appreciated that this invention may be used in connection with other electric power steering assemblies. 
     The illustrated electric power steering assembly  10  includes a “one-piece” rack housing, indicated generally at  12 , and a steering or rack member, indicated generally at  14 , configured to be disposed therein. The steering member  14  is linearly (or axially) movable along a rack axis X. The steering member  14  is connected with steerable wheels (not shown) of the vehicle through tie rods (not shown) located at the distal ends of the steering member  14 . Linear movement of the steering member  14  along the rack axis X results in steering movement of the steerable wheels in a known manner. 
     In the illustrated embodiment, the steering member  14  includes a first rack portion  14 A which is provided with a series of first rack teeth (shown in phantom in  FIG. 1  at T 1 ) along a portion thereof, which meshingly engage gear teeth (not shown) provided on a pinion (not shown) which is operatively connected to a steering wheel (not shown) of the vehicle via an input shaft  16 . In the illustrated embodiment, the steering member  14  further includes a second rack portion  14 B which is provided with a series of second rack teeth T 2  along a portion thereof which, as will be discussed below, meshingly engage gear teeth T 3  provided on a pinion assembly, indicated generally at  18 . 
     The illustrated electric power steering assembly  10  further includes an electric motor, indicated generally at  20 , which as will be discussed below, is operatively or “drivably” configured to be connected to the pinion assembly  18  via a planetary gear assembly, indicated generally at  22 , for effecting axial movement of the steering member  14  upon rotation of the vehicle steering wheel. In the event of the inability of the electric motor  20  to effect axial movement of the steering member  14 , the mechanical connection between the gear teeth on the pinion and the first rack teeth T 1  on the first rack portion  14 A of the steering member  14  permits manual steering of the vehicle. 
     As shown in  FIG. 1 , in the illustrated embodiment, the pinion assembly  18  includes a main pinion body or output shaft  24 , a pinion bearing  26 , a pinion nut  28 , and a pinion plug  30 . The pinion assembly  18  is rotatably supported in a stepped opening  12 A provided in the housing  12  by the bearing  26 , the nut  28 , and the plug  30  and its teeth T 3  held in meshing engagement with the teeth T 2  of the steering member  14  by a yoke member  32 . 
     As best shown in  FIG. 2 , in the illustrated embodiment, the pinion main body  24  includes an annular-like plate  34  having a first plurality of “upstanding” projections or legs  34 A, and a second plurality of projections or legs  34 B, for a purpose to be discussed below. In the illustrated embodiment, the first plurality of legs  34 A are preferably formed from the same material as the main body, for example preferably from “high strength” steel or other “high strength” metals. The second plurality of legs  34 B are formed from preferably a rubber material, such as for example Hydrogenated Nitrile Butadiene Rubber (HNBR), Neoprene Rubber or other similar polymers, and are preferably bonded to the plate  34 . As can be seen, the second plurality of legs  34 B are arranged in a manner such that a respective one of such legs  34 B is disposed on each side of the legs  34 A and so that there is a gap, indicated generally at G, defined between each pair of legs  34 B. Also, in the illustrated embodiment, each gap G is aligned with another gap G on an opposite side of the plate  34 . 
     In the illustrated embodiment, the pinion body  24  defines a pinion axis Y and is provided with the external teeth T 3  at least along a portion thereof. In the illustrated embodiment, the pinion axis Y is oriented coaxial with an axis Y 1  of the output shaft  20 A of the motor  20  and perpendicular with the rack axis X. Alternatively, the particular construction, configuration and/or design of the pinion assembly  18  and its associated components, may be other than illustrated and described, if so desired. 
     As shown in  FIG. 1 , in the illustrated embodiment, the planetary gear assembly  22  includes a carrier  40 , a sun gear  42  and a plurality of planet gears  44 . The sun gear  42  is configured to be “rotatably” attached to an output shaft  20 A of the electric motor  20  and is provided with external gear teeth T 4 . In the illustrated embodiment, each of the planet gears  44  is disposed or carried on the carrier  40  by a dowel or pin member  46  which is disposed in an opening  40 A provided in the carrier  40 . Each of the planet gears  44  includes external gear teeth T 5  which meshingly engage with the gear teeth T 4  of the sun gear  42 , for a purpose to be discussed below. 
     As best shown in  FIG. 3 , in the illustrated embodiment the carrier  40  is generally cup or dome like shaped and includes a plurality of ribs or spoke-like members  48  arranged in wagon-wheel like pattern as shown therein on an lower or underside portion thereof. A respective one of the ribs  48  is configured to be received or captured in a respective one of the gaps G provided between each pair of the legs  34 B of the pinion assembly  18  so as to rotatably connect together the carrier  40  and the pinion assembly  18  as will be discussed below. Alternatively, the particular construction, configuration and/or design the planetary gear assembly  22  and its associated components, and/or the connection between the planetary gear assembly  22  and the pinion assembly  18 , may be other than illustrated and described, if so desired. 
     In the illustrated embodiment, the electric power steering assembly  10  further includes a mounting plate or member  50 . The mounting plate  50  is configured to be disposed between and secured to both the housing  12  and the motor  20 . To accomplish this, preferably a first set of threaded fasteners  52  are provided to secure the mounting plate  50  to the motor  20 , and a second set of threaded fasteners  54  are provided to secure the mounting plate  20  to the housing  12 . As shown in  FIG. 2 , in the illustrated embodiment, the mounting plate  50  is provided with internal gear teeth T 6  which meshingly engage with the external gear teeth T 5  of the planet gears  44 . Alternatively, the particular construction, configuration and/or design the mounting plate  50  may be other than illustrated and described, if so desired. 
     In operation in the illustrated embodiment, when the electric motor  20  is actuated the output shaft  20  will drive or rotate the sun gear  42  in a first direction, for example clockwise. In turn, the sun gear  42  will drive the planet gears  44  in a second opposite direction, for example counterclockwise, with the planet gears  44 , along with the carrier  40  via the pins  46 , tracking or running around the internal teeth T 6  of the mounting plate  50 . In turn the carrier  40  via the connection of the ribs  48  thereof in the gaps G of the pinion assembly  18 , will cause the pinion assembly  18  to rotate in the same direction as that of the carrier  40 . Such rotation of the pinion assembly  18  will result in linear movement of the rack member  14 . 
     A potential advantage of the electric power steering assembly  10  is that the “direct drive” provided by the electric motor  20  to the rack member  14 , via the planetary gear assembly  22  and the pinion assembly  18 , allows the electric motor  20  (i.e., the axis Y 1  and/or the output shaft  20 A of the electric motor  20  and the axis Y and/or the output shaft  24  of the pinion assembly  18 ), to be located perpendicular to the rack axis X to thereby provide for smaller packaging requirements compared to known belt drive gears. 
     Also, with the electric motor  20  oriented perpendicular to the rack axis X, the electric motor  20  (along with the planetary gear assembly  22  and the pinion assembly  18 ), can be rotated about the rack axis X to any desired position to accommodate any package requirement. Also, the rubber legs  34 B on the pinion assembly  18  may act as an isolator or damper to minimize or reduce any potential noise, vibration and harshness from electric motor  20  and through the planetary gear assembly  22  and the pinion assembly  18  from being transmitted to the rack member  14 . In addition, the planetary gear assembly  22  will not experience the wear or stretch that occurs to the belt in a belt drive gear. 
     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.