Abstract:
A wheel assembly for a vehicle includes a rotatable wheel having a selectively adjustable steering angle. A steering actuator is operatively connected to the wheel and is configured to selectively adjust the steering angle of the wheel and not any other wheels. The wheel assembly allows independent control of the steering angle of the wheel. The wheel assembly also facilitates modular construction of vehicles by enabling the packaging of mechanical steering components in a preassembled wheel module with simple electrical connections to a vehicle chassis.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation in part of U.S. patent application Ser. No. 10/309,786, filed Dec. 4, 2002, which claims the benefit of U.S. Provisional Patent Application No. 60/337,994, filed Dec. 7, 2001; this application also claims the benefit of U.S. Provisional Patent Application No. 60/608,585, filed Sep. 10, 2004; each of the aforementioned patent applications is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates to steering actuators for vehicle wheels. 
     BACKGROUND OF THE INVENTION 
     Prior art vehicles typically include a steering system to alter the steering angle of the two front road wheels to alter the direction of vehicle movement. Typical prior art steering systems include an input device such as a steering wheel that is connected by a series of mechanical linkages to the two front wheels. Accordingly, the two front road wheels are mechanically interconnected by the mechanical steering linkages so that the steering angle of one of the front wheels is dependent upon the steering angle of the other front wheel. The mechanical linkages span between the two front wheels, occupying packaging space within the vehicle front compartment with an engine and other vehicle components. 
     SUMMARY OF THE INVENTION 
     A wheel assembly for a vehicle includes a nonrotatable member, such as a chassis frame or a suspension. A wheel is rotatably connected with respect to the nonrotatable member and characterized by a selectively adjustable steering angle with respect to the nonrotatable member. A steering actuator is operatively connected to the wheel and is configured to selectively alter the steering angle of the wheel. The steering actuator is configured to adjust the steering angle of only the one wheel. 
     The wheel assembly allows independent control of the steering angle of the wheel. The wheel assembly also facilitates modular construction of vehicles by enabling the packaging of mechanical steering components in a preassembled module with simple electrical connections to a vehicle chassis. 
     A vehicle is also provided with wheels and two steering actuators. A first steering actuator is operatively connected to a first wheel to selectively alter the steering angle of the first wheel. A second steering actuator is operatively connected to a second wheel to selectively alter the steering angle of the second wheel. Separate and independent steering actuators for each of the two wheels eliminates a steering rack extending between the wheels and thus provides increased packaging space compared to the prior art. Independent control of the steering angles of the rear wheels may provide enhanced vehicle dynamic control. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a vehicle chassis; 
         FIG. 2  is a schematic perspective view of the rear wheels and suspension of the chassis of  FIG. 1 ; 
         FIG. 3  is a schematic perspective view of one of the rear wheels of  FIG. 2 ; 
         FIG. 4  is a schematic rear view of the rear wheel of  FIG. 3 ; and 
         FIG. 5  is a schematic cross sectional view of an alternative wheel arrangement in accordance with the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a portion of a chassis  8  for a vehicle  9  is schematically depicted. The chassis  8  includes a structural frame  10 . The frame includes a first rail  14  and a second rail  18  that are longitudinally oriented and that are spaced a distance apart from one another to form a central cavity  20  therebetween. A third rail  22  is outboard of the first rail  14 . A fourth rail  26  is outboard of the second rail  18 . 
     Cross member  32  rigidly interconnects the first and second rails  14 ,  18 . Cross member  36  rigidly interconnects the first and third rails  14 ,  22 . Cross member  40  rigidly interconnects the second and fourth rails  18 ,  26 . 
     The frame  10  also includes a first node  44 , a second node  48 , a third node  52 , and a fourth node  56 . The nodes, which are preferably cast, substantially rigidly interconnect various members of frame  10 . More specifically, the first node  44  interconnects a first front member  60  with the first rail  14  and the third rail  22 . The second node  48  interconnects a second front member  64  with the second rail  18  and the fourth rail  26 . The third node  52  interconnects a first rear frame member  66  to the first and third rails  14 ,  22 . The fourth node  56  interconnects a second rear frame member  70  to the second and fourth rails  18 ,  26 . Cross member  78  connects the third and fourth nodes  52 ,  56 . Those skilled in the art will recognize other frame configurations that may be employed within the scope of the claimed invention. For example, when body-frame integral construction, also sometimes referred to as “unibody” construction, is employed, the body of the vehicle may be considered a “frame.” 
     The chassis  8  also includes traction motor  84 , which is operatively connected to front wheels  88 ,  92 . In a preferred embodiment, the chassis includes a fuel cell (not shown) to generate electrical energy to power the traction motor  84 , though other sources of electrical energy may be employed within the scope of the claimed invention. Individual rear wheel hub motors  96 ,  100  drive rear wheels  104 ,  108 , respectively. The front wheels  88 ,  92  are rotatably mounted with respect to the frame  10  via a front suspension system. Rear wheels  104 ,  108  are rotatably mounted with respect to the frame  10  via a rear suspension system (shown at  112  in  FIGS. 2-4 ). The wheels each have a tire mounted thereon. An exemplary wheel hub motor, and its relationship with respect to a wheel and suspension system, is shown and described in commonly-assigned, copending U.S. patent application Ser. No. 10/309,786, filed Dec. 4, 2002, and which is hereby incorporated by reference in its entirety. 
     Referring to  FIG. 2 , rear suspension system  112  includes two upper control arms  116 , each being pivotably connected with respect to a respective one of the wheel motor housings  120 . The suspension system  112  includes two lower control arms  124 , each being pivotably connected with respect to a respective one of the wheel motor housings  120 . Shock absorbers  128  are operatively connected with respect to the upper and lower control arms  116 ,  124 . 
     Each motor  96 ,  100  includes a respective rotor (not shown) protruding from the outboard side of its respective housing  120  and rigidly mounted with respect to a respective wheel  104 ,  108  to selectively rotate the wheel. Each rear wheel  104 ,  108  is characterized by by-wire steering. A first rear steering actuator  132 , such as a servomotor or solenoid, is connected to rear wheel  108  via linkage  136  and motor housing  120  to selectively alter the steering angle of rear wheel  108 . A second rear steering actuator  140  is connected to rear wheel  104  via linkage  144  and motor housing  120  to selectively alter the steering angle of rear wheel  104 . Thus, separate steering actuators  132 ,  140  control the respective steering angle of each rear wheel independently, eliminating the need for a steering rod to extend between the two rear wheels and therefore increasing packaging space in the vehicle to accommodate, for example, a hybrid vehicle battery (not shown), which may be at least partially between the rear wheels  104 ,  108 . Separate and independently controllable actuators for the rear wheels may also provide enhanced vehicle dynamic control. Similarly, independent steering actuators may also be employed with the front wheels (shown at  88 ,  92  in  FIG. 1 ). 
     Referring specifically to  FIG. 3 , the vehicle includes a by-wire braking system for all four wheels. A by-wire brake actuator  150  is configured to selectively cause calipers  154  to engage disc  158  to resist or prevent rotation of wheel  108 . More specifically, calipers  154  are a first friction element that is rigidly mounted with respect to the motor housing  120  and chassis  10 , i.e., nonrotating members. The disc  158  is rigidly mounted with respect to the rotor of the motor  100  and the wheel  108  for rotation therewith. The actuator  150  is configured to selectively cause the calipers to contact the disc to create friction and thereby resist the rotation of the wheel  108  with respect to the nonrotating members. 
     The calipers  154 , actuator  150 , and disc  158  are inboard of wheel motor  100  and the corresponding wheel bearing assembly. It should be noted that the use of the wheel motors enables all-wheel drive, in conjunction with the traction motor, with minimal effect on the packaging space between the rear wheels. 
     Referring to  FIG. 5 , an alternative brake design is schematically depicted. Wheel  162  has a wheel motor  166  contained therein. The rotor  170  of the wheel motor  166  is connected to the wheel  162  to selectively cause the rotation thereof. The wheel motor housing  174  is connected to suspension  178 . A drum member  182  is connected to the rotor  170  and the wheel  162  for rotation therewith. The drum member  182  includes a portion  186  that extends radially on the outboard side of the wheel motor  166 , and a portion  190  that extends axially from the outboard side of the motor to the inboard side of the motor. Portion  190  defines inner surface  194 . A brake shoe  198  is mounted with respect to suspension  178  and housing  174 , and is selectively movable into contact with surface  194  to provide friction resistance to the rotation of the drum  182  and, therefore, wheel  162 . Accordingly, drum  182 , and more particularly, surface  194 , is a first friction element positioned inboard of the wheel motor  166 , and shoe  198  is a second friction element positioned inboard of the wheel motor  166 . Locating the brake elements inboard of the wheel motor and bearing assembly facilitates satisfaction of wheel-to-curb design criteria while maintaining satisfactory suspension geometry. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.