Patent Publication Number: US-7909132-B2

Title: Apparatus for use in turning steerable vehicle wheels

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus for use in turning steerable vehicle wheels in response to rotation of a steering wheel. 
     BACKGROUND OF THE INVENTION 
     A known vehicle steering apparatus includes a steering member which is axially movable to effect turning movement of steerable vehicle wheels. A pinion is disposed in meshing engagement with a rack portion of the steering member. A steering column interconnects the pinion and a vehicle steering wheel. 
     In addition, this known steering apparatus includes a ball nut assembly which is connected with an externally threaded portion of the steering member. A motor is connected with the ball nut assembly. The motor is operable to effect rotation of the ball nut assembly relative to the steering member. A steering apparatus having this general construction is disclosed in U.S. Pat. No. 4,735,271 and U.S. Pat. No. 7,055,646. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an apparatus which includes a pinion which is disposed in meshing engagement with a rack portion of a steering member. The steering member is movable relative to a vehicle to effect turning movement of steerable vehicle wheels. A steering column interconnects the pinion and a vehicle steering wheel. A ball nut assembly is connected with an externally threaded portion of the steering member. 
     In accordance with one of the features of the present invention, a first motor is connected with a steering column at a location between the pinion and the steering wheel. A second motor is connected with the ball nut assembly. The second motor is operable to effect rotation of the ball nut assembly relative to the steering member. 
     In accordance with another feature of the present invention, a closed loop assembly is connected with the steering column. The closed loop assembly includes a first control unit which is connected with a first sensor and the first motor. The first sensor provides an output to the first control unit as a function of torque applied to and rotation of the steering wheel. A feedback sensor is connected with the first control unit. The first control unit is operable to effect operation of the first motor as a function of the outputs from the first sensor and the feedback sensor. 
     In accordance with another feature of the present invention, an open loop assembly includes the second motor and a second control unit. The second control unit is connected with at least one of the first sensor and the feedback sensor. The second control unit is operable to control operation of the second motor as a function of the output from at least one of the first sensor and the feedback sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features of the present invention will become more apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which: 
         FIG. 1  is schematic illustration depicting a construction of an apparatus constructed in accordance with the present invention to turn steerable vehicle wheels. 
     
    
    
     DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION 
     An apparatus  10  ( FIG. 1 ) is constructed in accordance with the present invention and is used to turn steerable vehicle wheels. The apparatus  10  includes a steering member  12  which is connected to steerable vehicle wheels  14  and  16 . Upon rotation of a steering wheel  20 , force is transmitted through a steering column  22  to a steering gear  24 . 
     The steering gear  24  includes a pinion  28  which is rotatable under the influence of force transmitted through the steering linkage  22 . The steering member  12  includes a rack portion  32  having rack gear teeth disposed in meshing engagement with the pinion  28 . In addition, the steering member  12  has an externally threaded portion  36  which is disposed in a coaxial relationship with the rack portion  32 . 
     A ball nut assembly  38  extends around the externally threaded portion  36  and has a plurality of balls (not shown) which are disposed in engagement with the externally threaded portion. The ball nut assembly  38  is rotatable about a longitudinally extending central axis  40  of the steering member  12 . Rotation of a ball nut assembly  38  relative to the steering member  12  is effective to move the steering member axially relative to a housing  44 . The housing  44  encloses the pinion  28  and ball nut assembly  38  along with at least a portion of the steering member  12 . 
     A reversible electric motor  48  is operable to rotate the ball nut assembly  38  relative to the steering member  12 . The electric motor  48  has an output shaft  50  which is connected to a drive pulley  52 . The drive pulley  52  is connected with the ball nut assembly  38  by a drive belt  54 . The drive belt  54  transmits force to the ball nut assembly  38  to rotate the ball nut assembly about the central axis  40  of the steering member  12  during operation of the motor  48  and rotation of the drive pulley  52 . The ball nut assembly  38  and drive pulley  52  may have the same construction as is disclosed in U.S. Pat. No. 7,055,646. Of course, they may have a different construction if desired. 
     A closed loop assembly  60  is connected with the steering column  22 . The closed loop assembly  60  is a control system which automatically acts to maintain a desired output through the steering column  22  to the pinion  28  in response to rotation of the steering wheel  20 . The closed loop assembly  60  includes a gear unit  64  which is connected with the steering column  22  at a location between the steering wheel  20  and pinion  28 . 
     A first or upper sensor  66  is connected with the steering column  22  at a location between the gear unit  64  and the steering wheel  20 . A first control unit  68  is connected with the sensor  66 . The sensor  66  provides an output to the control unit  68  as a function of the torque applied to and an angular rotation of the steering wheel  20 . 
     A first reversible electric motor  72  is connected with the control unit  68  and the gear unit  64 . The gear unit  64  is a differential gear assembly having a known construction. However, it is contemplated that the gear unit  64  may include a single spur gear which is connected with the steering linkage  22  and driven by a spur gear connected with the electric motor  72 . 
     The first motor  72  may be operated to cause the gear unit  64  to assist the operator in rotating the steering wheel  20 . The first motor  72  may also be operated to resist rotation of the steering wheel  20  to provide “feel” to the operator rotating the steering wheel. The control unit  68  effects operation of the motor  72  to either assist or resist steering wheel rotation as a function of vehicle operating conditions. 
     A feedback sensor  76  is connected with the control unit  68 . The feedback sensor  76  provides an output to the control unit  68  as a function of rotation of and torque applied to a portion of the steering linkage  22  connected to the output of the gear unit  64 . The feedback sensor  76  is connected to a portion of the steering column  22  disposed between the gear unit  64  and pinion  28 . 
     The control unit  68  compares the output from the feedback sensor  76  with the output from the first sensor  66 . The control unit effects operation of the reversible electric motor  72  as a function of the outputs from the first sensor  66  and the feedback sensor  76 . 
     An open loop assembly  82  includes an electronic control unit  84  which is connected with the reversible electric motor  48 . The electronic control unit  84  is connected with the first sensor  66  by a conductor  86 . The electronic control unit  84  connected with the feedback sensor  76  by a conductor  88 . 
     The electronic control unit  84  compares the output of the two sensors  66  and  76  and effects operation of the motor  48  as a function of the output of these two sensors. However, it is contemplated that the electronic control unit  84  may be connected with only one of the sensors, for example the first sensor  66 . Alternatively, the electronic control unit  84  may be connected with only the feedback sensor  76 . Regardless of which sensor or sensors the electronic control unit  84  is connected, the electronic control unit effects operation of the motor  48  to drive the belt  54  and rotate the ball nut assembly  38  to obtain movement of the steerable vehicle wheels  14  and  16  corresponding to rotation of the steering wheel  20 . 
     In addition to being responsive to the torque applied to and the angular rotation of the steering wheel  20 , the electronic control units  68  and  84  may have inputs which vary as a function of vehicle speed and sensed lateral acceleration of a vehicle. Thus, the electronic control unit  68  has an input, over a conductor  94 , which is a function of vehicle speed. Similarly, the electronic control unit  68  has an input, over a conductor  96 , which is a function of lateral acceleration of the vehicle. Similarly, the control unit  84  has an input over a conductor  98 , which is a function of vehicle speed and an input, over a conductor  100 , which is a function of lateral acceleration of a vehicle.