Abstract:
A power steering system includes a first linkage arm pivotally coupled to a cross-link member extending in a transverse direction. Also included is a first shaft generally orthogonal to the first linkage arm and configured to rotate the first linkage arm. Further included is a second linkage arm pivotally coupled to the cross-link member with a pivot location. The power steering system yet further includes an electric actuator. Also included is a linkage member extending from the electric actuator and operatively coupled to an assist portion of the second linkage arm to reduce the steering effort required by a driver of the vehicle.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This patent application claims priority to U.S. Provisional Patent Application Ser. No. 61/761,474, and U.S. Provisional Patent Application Ser. No. 61/761,477, both filed Feb. 6, 2013, and both of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Various linkage arrangements are employed on vehicles to facilitate power assisted steering. One type of linkage is commonly referred to as a “parallelogram” steering linkage with a hydraulic configuration for power assisted steering. Such a linkage arrangement is commonly used on heavy duty trucks, for example. 
     Attempts have been made to effectively integrate electric power steering (EPS) into a “parallelogram” steering linkage architecture. Typically, a manual driver command and an electric power assist reach the linkage structure at the same location in the manner of torque. The torque is added at this location through a rack and pinion interface in an integral gear. However, the tooth pressure at this interface is significant and an adjustment mechanism may be required to periodically remove the lash at that interface. Various other components have been considered to effectively integrate EPS, such as planetary gear sets, worm and worm gears, and harmonic drives. Unfortunately, the efficiency is low for these components and the space available in the vehicle makes it impractical to place reduction mechanisms in the necessary interface location. 
     SUMMARY OF THE INVENTION 
     In accordance with an exemplary embodiment of the invention, a power steering system includes a first linkage arm pivotally coupled to a cross-link member extending in a transverse direction. Also included is a first shaft generally orthogonal to the first linkage arm and configured to rotate the first linkage arm. Further included is a second linkage arm pivotally coupled to the cross-link member with a pivot location. The second linkage arm includes a power portion extending from a first end of the second linkage arm to the pivot location. The second linkage arm also includes an assist portion extending from the pivot location to a second end of the second linkage arm. The power steering system yet further includes an electric actuator. The power steering system also includes a linkage member extending from the electric actuator and operatively coupled to the assist portion of the second linkage arm to reduce the steering effort required by a driver of the vehicle. 
     In accordance with another exemplary embodiment of the invention, a power steering system includes a first linkage arm pivotally coupled to a cross-link member extending in a transverse direction. Also included is a first shaft generally orthogonal to the first linkage arm, the first shaft configured to rotate the first linkage arm upon a command from a driver of the vehicle. Further included is a power portion of the first linkage arm extending from a first end of the first linkage arm to the first shaft. Yet further included is an assist portion of the first linkage arm extending from the first shaft to a second end of the first linkage arm. Also included is an electric actuator. Further included is a linkage member extending from the electric actuator and operatively coupled to the assist portion of the first linkage arm. 
     In accordance with yet another exemplary embodiment of the invention, a power steering system includes a first linkage arm pivotally coupled to a cross-link member extending in a transverse direction of a vehicle. Also included is a second linkage arm pivotally coupled to the cross-link member. Further included is a first shaft generally orthogonal to the first linkage arm and configured to rotate the first linkage arm. Yet further included is an electric actuator. Also included is a linkage member extending from the electric actuator and directly coupled to the cross-link member. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic illustration of a power steering system according to one aspect of the invention; 
         FIG. 2  is a schematic illustration of a power steering system according to another aspect of the invention; 
         FIG. 3  is a perspective view of a linkage arm of the power steering system according to one aspect of the invention; 
         FIG. 4  is a perspective view of the linkage arm of the power steering system according to another aspect of the invention; 
         FIG. 5  is a schematic illustration of a power steering system according to yet another aspect of the invention; 
         FIG. 6  is a schematic illustration of a power steering system according to yet another aspect of the invention; and 
         FIG. 7  is a schematic illustration of a power steering system according to another aspect of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , a portion of a steering system  10  for a vehicle is schematically illustrated. The architecture of the steering system  10  is referred to as a “parallelogram” steering system. It is contemplated that the steering system  10  may be employed in numerous types of vehicles. In one embodiment, the steering system  10  is used in association with heavy duty trucks. 
     The steering system  10  includes numerous components, such as various linkage members, sensors, switches, and accessories. The steering system  10  transfers rotation and torque from an input member, such as a steering wheel assembly (not illustrated) to an output member, such as one or more wheels  12 . The steering wheel assembly is operatively coupled to a linkage arrangement  14  of the steering system  10  with a first shaft  16 , which may be referred to as a pitman shaft. The wheels  12  of the vehicle are turned through movement of the linkage arrangement  14  and, more particularly, though movement of a cross-link member  18 . The cross-link member  18  extends in a substantially transverse or cross-car direction of the vehicle and translates in this direction as well. Translation of the cross-link member  18  imparts movement of numerous other components that link the cross-link member  18  to the wheels  12  of the vehicle. Such intermediary components include a first tie rod  20  rotatably coupled to the cross-link member  18 , as well as one or more additional linkage members  22  that is integrally formed with a first steering knuckle  24  that pivots with respect to a frame of the vehicle. Similarly, a second tie rod  26  is rotatably coupled to the cross-link member  18  and is indirectly coupled to a wheel of the vehicle with a linkage member  28  that is integrally formed with a second steering knuckle  30  that pivots with respect to the frame of the vehicle. 
     In the illustrated embodiment, the linkage arrangement  14  includes a first linkage arm  32  that is pivotally coupled to the cross-link member  18  at a location proximate the first shaft  16 . The first linkage arm  32  is pivotally coupled to the frame of the vehicle via a first pivot joint  34  and is free to rotate in response to an input from the first shaft  16 . A second linkage arm  36  is also pivotally coupled to the cross-link member  18  at a pivot location  38 . The second linkage arm  36  is pivotally coupled to the frame of the vehicle via a second pivot joint  40  proximate a first end  42  of the second linkage arm  36 . The second linkage arm  36  is pivotally coupled to a linkage member  44  proximate a second end  46  of the second linkage arm  36 . The linkage member  44  extends from the second linkage arm  36  to an electric actuator  48  that is operatively coupled to the frame of the vehicle. The operative coupling of the electric actuator  48  to the frame comprises a pivotal connection via a pivot joint  50 . In the illustrated embodiment, the electric actuator  48  comprises a linear actuator that translates the linkage member  44  in a substantially cross-car direction of the vehicle. 
     The second linkage arm  36  comprises two portions. A first portion  52 , which may be referred to herein as a power portion, extends from the first end  42  of the second linkage arm  36  to the pivot location  38  between the second linkage arm  36  and the cross-link member  18 . A second portion  54 , which may be referred to herein as an assist portion, extends from the pivot location  38  to the second end  46  of the second linkage arm  36 . The second portion  54  is directly driven by the linkage member  44  that is translated with the electric actuator  48 . Therefore, the electric actuator  48  provides a power steering assist to the linkage arrangement  14  via the linkage member  44  and the second portion  54  of the second linkage arm  36 . 
     Referring now to  FIG. 2 , the steering system  10  is schematically illustrated to show another exemplary embodiment. The illustrated embodiment is similar in many respects to the embodiment shown in  FIG. 1 , such that similar reference numerals are employed and duplicative description of the previously described components is not necessary. 
     The linkage arrangement  14  of the steering system  10  includes an intermediate linkage member  56  that extends between, and connects, the second linkage arm  36  and the linkage member  44  that is coupled to the electric actuator  48 . The intermediate linkage member  56  is pivotally coupled to the second linkage arm  36  and the linkage member  44 , thereby allowing a direct mounting of the electric actuator  48  to the frame of the vehicle. 
     Referring now to  FIGS. 3 and 4 , with continued reference to  FIGS. 1 and 2 , various embodiments of the second linkage arm  36  are illustrated. The second linkage arm  36  of the exemplary embodiments of  FIGS. 1 and 2  may be configured in numerous manners, with two examples shown in  FIGS. 3 and 4 . In particular, the first portion  52  (i.e., power portion) of the second linkage arm  36  and the second portion  54  (i.e., assist portion) of the second linkage arm  36  may be located in a common plane ( FIG. 3 ) or may be located in distinct planes ( FIG. 4 ). Additionally, regardless of whether the first portion  52  and the second portion  54  are located in a common or a distinct plane, the first portion  52  and the second portion  54  may be angularly displaced from each other along the entire 360 degree spectrum. The embodiment of  FIG. 3  illustrates the first portion  52  and the second portion  54  angularly displaced from each other at about 180 degrees, while  FIG. 4  illustrates the first portion  52  and the second portion  54  angularly displaced from each other at about 90 degrees. As noted above, the angle of displacement may be anywhere along the 360 degree spectrum. 
     Referring now to  FIG. 5 , the steering system  10  is schematically illustrated according to yet another embodiment. The linkage arrangement  14  includes the first linkage arm  32  that is pivotally coupled to the cross-link member  18  at a location proximate the first shaft  16 . The first linkage arm  32  is pivotally coupled to the frame of the vehicle via the first pivot joint  34  and is free to rotate in response to an input from the first shaft  16 . The second linkage arm  36  is also pivotally coupled to the cross-link member  18  at a pivot location  38 . The second linkage arm  36  is pivotally coupled to the frame of the vehicle via the second pivot joint  40 . 
     In the illustrated embodiment, the first linkage arm  32  is elongated to extend away from a first end  60  of the first linkage arm  32  proximate the first pivot joint  34  and past the cross-link member  18  to a second end  62  of the first linkage arm  32 . The first linkage arm  32  is pivotally coupled to the linkage member  44  proximate the second end  62  of the first linkage arm  32 . The linkage member  44  extends from the first linkage arm  32  to the electric actuator  48  that is operatively coupled to the frame of the vehicle. The operative coupling of the electric actuator  48  to the frame comprises a pivotal connection via the pivot joint  50 . In the illustrated embodiment, the electric actuator  48  comprises a linear actuator that translates the linkage member  44  in a substantially cross-car direction of the vehicle. 
     As discussed above in relation to alternative embodiments, the first linkage arm  32  comprises two portions. A first portion  64 , which may be referred to herein as a power portion, extends from the first end  60  of the first linkage arm  32  to the pivotal connection between the first linkage arm  32  and the cross-link member  18  at the location of the first shaft  16 . A second portion  68 , which may be referred to herein as an assist portion, extends from the second end  64  of the first linkage arm  32  and the pivotal connection between the first linkage arm  32  and the cross-link member  18  at the location of the first shaft  16 . The second portion  68  is directly driven by the linkage member  44  that is translated with the electric actuator  48 . Therefore, the electric actuator  48  provides a power steering assist to the linkage arrangement  14  via the linkage member  44  and the second portion  64  of the first linkage arm  32 . 
     Referring now to  FIG. 6 , the steering system  10  is schematically illustrated to show another exemplary embodiment. The illustrated embodiment is similar in many respects to the embodiment shown in  FIG. 5 , such that similar reference numerals are employed and duplicative description of the previously described components is not necessary. 
     The linkage arrangement  14  of the steering system  10  includes an intermediate linkage member  70  that extends between, and connects, the first linkage arm  32  and the linkage member  44  that is coupled to the electric actuator  48 . The intermediate linkage member  70  is pivotally coupled to the first linkage arm  32  and the linkage member  44 , thereby allowing a direct mounting of the electric actuator  48  to the frame of the vehicle. 
     As is the case with the embodiments described above with respect to  FIGS. 3 and 4 , the first portion  60  and the second portion  62  of the first linkage arm  32  of  FIGS. 5 and 6  may be arranged in common or distinct planes and/or may be angularly displaced from each other at any angle in the 360 degree spectrum. 
     Referring now to  FIG. 7 , the steering system  10  is schematically illustrated in accordance with another aspect of the invention. The illustrated embodiment is similar in many respects to the embodiments described above, such that similar reference numerals are employed and duplicative description of the previously described components is not necessary. 
     In the illustrated embodiment, the linkage member  44  extends from the electric actuator  48  and is directly coupled to the cross-link member  18 . It is to be understood that coupling of the linkage member  44  to the cross-link member  18  may be present along any portion of the cross-link member  18 . The illustrated coupling location is merely illustrative and is not intended to be limiting. The first linkage arm  32  and the second linkage arm  36  extend between their respective pivot joints  34 ,  40  and the cross-link member  18 . 
     Advantageously, each above-described embodiment of the steering system  10  allows a currently manufactured parallelogram linkage arrangement to be integrated with the electric actuator  48  and associated linkage member  44  that provides electrical assist to the steering system. Particularly advantageous is the location of the power steering assist that is transferred to the overall linkage arrangement. Specifically, the power assist load is added to the linkage arrangement at a separate location from the command load location, with such a command load being proximate the first linkage arm  32  in one embodiment. Additionally, packaging freedom is achieved by optionally elevating the second portion  54  (i.e., assist portion) relative to the first portion  52  (i.e., power portion), thereby changing the planes that the portions are located in. Such a configuration allows the electric actuator  48  to be mounted at any height in the vehicle simply by customizing the length of the shaft connecting the first portion  52  and the second portion  54 . Modification of the angular orientation of the portions provides yet another degree of packaging freedom. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.