Abstract:
In a vehicle steering transmission device, a first gear is rotatable on a rotational axis to rotate in accordance with a vehicle steering operation, a second gear is rotatable on the rotational axis and connectable to a vehicle wheel so that an orientation of the vehicle wheel is changed, an intermediate gear engages with the first and second gears, a support member is rotatable on the rotational axis while supporting the intermediate gear in such a manner that the intermediate gear is rotatable on another rotational axis which another rotational axis intersects the rotational axis and extends perpendicularly to the rotational axis, and a driving device drives the support member to rotate on the rotational axis so that a differential rotational motion is generated between the first and second gears.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a vehicle steering transmission device for transmitting a vehicle steering operation by a vehicle driver to a vehicle wheel, and a vehicle steering apparatus for steering the vehicle in accordance with the vehicle steering operation. 
   In a prior art vehicle steering transmission device as disclosed by JP-A-2000-302050, a vehicle steering operation by a vehicle driver is transmitted to a vehicle wheel through an planetary gear train. 
   BRIEF SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a vehicle steering transmission device and a vehicle steering apparatus including the vehicle steering transmission device, in which a radial size of the vehicle steering transmission device can be decreased in comparison with the prior art vehicle steering transmission devices. 
   According to the invention, a vehicle steering transmission device for transmitting a vehicle steering operation by a vehicle driver through for example, a steering wheel or a joy stick to a vehicle wheel rotatable on a vehicle wheel axis so that an orientation of the vehicle wheel axis or the vehicle wheel is changed in accordance with the vehicle steering operation, includes, a first gear being rotatable on a rotational axis to rotate in accordance with the vehicle steering operation, and a second gear being rotatable on the rotational axis and connectable to the vehicle wheel so that an orientation of the vehicle wheel is changed. An intermediate gear engages with the first and second gears to transmit a rotation between the first gear and the second gear (that is, from the first gear to the second gear, or from the second gear to the first gear) through the intermediate gear. A support member is rotatable about a first rotational axis while supporting the intermediate gear in such a manner that the intermediate gear is rotatable on another rotational axis that intersects the first rotational axis and extends perpendicularly to the first rotational axis to generate a differential rotational motion between the first and second gears. A driving device drives the support member to rotate on the rotational axis so that the differential rotational motion is generated between the first and second gears in accordance with an orbital motion of the intermediate gear around the first rotational axis as well as a rotation of the intermediate gear on the other rotational axis. 
   Since support member supports the intermediate gear in such a manner that the intermediate gear is rotatable on the other rotational axis which another rotational axis intersects the first rotational axis and extends perpendicularly to the first rotational axis, the intermediate gear can face each of the first and second gears in a direction parallel to the rotational axis. Thus, the intermediate gear does not need to extend to an radially outside position with respect to the first and second gears. Therefore, a radial size of the vehicle steering transmission device can be decreased in comparison with prior art vehicle steering transmission device including respective planetary gear trains. 
   If the support member includes at least a worm wheel segment (at least a circumferential part or segment of a worm wheel or the worm wheel), and the driving device includes a worm engaging with the worm wheel segment so that the support member is rotationally driven on the rotational axis by the driving device through the engagement between the worm wheel segment and the worm, a rotational position of the support member can be kept stationary without a braking mechanism added to the vehicle steering transmission device. The driving device may include a motor to generate a torque for rotating the support member on the rotational axis. 
   If a radius of a pitch circle on which the first gear and the intermediate gear engage with each other is equal to a radius of a pitch circle on which the second gear and the intermediate gear engage with each other, a transmission gear ratio through the vehicle steering transmission device is kept at 1:1 when the support member is rotationally stationary, so that conventional steering mechanism other than the planetary gear trains are usable with the vehicle steering transmission device of the invention. 
   It is preferable that the first gear, second gear and intermediate gear are bevel gears. 
   It is also preferable for decreasing the radial size of the vehicle steering transmission device that gear teeth of the first gear are opposite or face gear teeth of the second gear through the intermediate gear in a direction parallel to the rotational axis. 
   In a vehicle steering apparatus for steering a vehicle in accordance with a vehicle steering operation by a vehicle driver, in which a vehicle wheel is rotatable on a wheel axis, the steering transmission device and a connecting member are arranged between the steering transmission device and the vehicle wheel so that the vehicle steering operation is transmitted through the steering transmission device and the connecting member to the vehicle wheel to change an orientation of the vehicle wheel. 
   Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross sectional view showing an embodiment of a transmission device of the invention. 
       FIG. 2  is a cross sectional view taken along a line II—II in  FIG. 1 . 
       FIG. 3  is a perspective view of the transmission device of  FIG. 1 . 
       FIG. 4  is a view showing an embodiment of a vehicle steering apparatus of the invention. 
       FIG. 5  is a diagram showing a proportional control characteristic of steering gear in accordance with vehicle speed. 
       FIG. 6  is a cross sectional view showing another embodiment of the transmission device of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An embodiment of a driving force transmission device of the invention is described with reference to  FIGS. 1–3 . 
   A driving force transmission device  10  includes a frame  11  mounted fixedly. The frame  11  supports an input rotary shaft  12  in a rotatable manner at an end portion  11 A, and an output rotary shaft  13  in a rotatable manner at another end portion  11 B. The input rotary shaft  12  and output rotary shaft  13  are arranged on a common axis. 
   In a gear box  11 C defined by the frame  11 , an input gear  14  fixedly mounted on an end of the input rotary shaft  12  and an output gear  15  fixedly mounted on the output rotary shaft  13  are arranged on the common axis and opposite to each other. The input gear  14  and output gear  15  are bevel gears having the same diameter and shape. 
   A rotary support member (carrier)  16  is arranged between the input rotary shaft  12  and output rotary shaft  13 . The rotary support member  16  is arranged on the common axis of the input rotary shaft  12  and output rotary shaft  13 , and supported at both ends thereof by respective ball-bearings  17  and  18  on the input rotary shaft  12  and output rotary shaft  13  in a rotatable manner on the common axis of the input gear  14  and output gear  15 . 
   The rotary support member  16  includes monolithically four support shafts  19  extending at an intermediate area between the input rotary shaft  12  and output rotary shaft  13  in an axial direction radially from and perpendicularly to the rotary axis of the input rotary shaft  12  and output rotary shaft  13 . 
   The four support shafts  19  have respective lengths equal to each other, cross each other as seen on an imaginary plane perpendicular to the axial direction of the input rotary shaft  12  and output rotary shaft  13  and are connected fixedly at outer ends thereof to a ring member  20  coaxial with the rotary support member  16 , in other words, coaxial with the input rotary shaft  12  and output rotary shaft  13 . That is, the ring member  20  is supported through the four support shafts  19  on the rotary support member  16  coaxially. 
   Intermediate gears  21  of bevel gears are supported by the four support shafts  19  respectively to rotate on the four support shafts  19  and engage with both the input gear  14  and output gear  15 . In this case, a radius of a pitch circle on which the input gear  14  and each of the intermediate gear  21  engage with each other is equal to a radius of a pitch circle on which the output gear  15  and each of the intermediate gears  21  engage with each other. 
   That is, the intermediate gears  21  form respective bevel gear engagements with each of the input gear  14  and output gear  15 , and the ring member  20  has its rotational axis coaxial with the common axis of the input rotary shaft  12  and output rotary shaft  13  and the rotary support member  16  to be rotatable with respect to each of the input rotary shaft  12  and output rotary shaft  13 . The intermediate gears  21  rotate (orbit) along a circumference of the input gear  14  and output gear  15  according to a rotation of the ring member  20  while engaging with the input gear  14  and output gear  15 . 
   In this structure, when the ring member  20  is fixed to be prevented from rotating, a rotation of the input rotary shaft  12  is transmitted to the input gear  14  and intermediate gears  21  so that the intermediate gears  21  rotate without orbital motion, because the ring member  20  is fixed. 
   Therefore, since the radius of the pitch circle on which the input gear  14  and each of the intermediate gears  21  engage with each other is equal to the radius of the pitch circle on which the output gear  15  and each of the intermediate gears  21  engage with each other, the input gear  14  and output gear  15  have a common rotational degree, that is a rotational amount of the input shaft  12  and a rotational amount of the output shaft  13  are equal to each other, that is, a gear ratio (transmission ratio) is substantially 1:1. 
   On the other hand, if the ring member  20  is not fixed to be freely rotatable, the rotation of the input shaft  12  transmitted to the intermediate gears  21  generates the rotation of the ring member  20  as well as the intermediate gears  21  to prevent a rotational force from being transmitted to the output shaft  13 , because the ring member  20  is not fixed. 
   Therefore, by adjusting a rotating amount and rotating direction of the ring member  20 , a rotation transmitting amount from the input rotary shaft  12  to the output rotary shaft  13  is freely adjustable, that is, a relationship between an operating amount at an input side and an operated amount at an output side is freely adjustable. In other words, the transmission ratio can be continuously increased and decreased. 
   An outer peripheral portion of the ring member  20  includes a worm wheel (spur gear) (including at least a worm wheel segment as a circumferential part of the worm wheel)  22  engaging with a worm gear  25  fixed to an output rotary shaft  24  of an electric motor  23  mounted on the frame  11 . 
   Therefore, in accordance with control of a rotating direction and rotating amount of the electric motor  23 , the rotating direction and rotating amount (rotating angle) of the ring member  20  is adjusted to increase and decrease continuously the transmission ratio, so that in accordance with the control on the rotating direction and rotating amount of the electric motor  23 , the relationship between the operating amount at the input side and the operated amount at the output side is freely adjustable to enable an input and output gear ratio (transmission ratio) to be freely and continuously adjustable. 
   Further, by preventing the electric motor from rotating, the ring member  20  is prevented from rotating by an braking effect on an engagement between the worm gear  24  and worm wheel  22 , so that the input and output gear ratio becomes necessarily about 1:1. 
   In the driving force transmission device as described above, since the input gear  14  and output gear  15  are opposed to each other on the common axis, and the shafts  19  for the intermediate gears  21  extend perpendicularly to the rotary shafts  12  and  13  for input gear  14  and output gear  15 , the device can be made compact in the radial direction of the input rotary shaft  12  and output rotary shaft  13 . 
   An embodiment in which the driving force transmission device  10  of the invention is applied to a steering apparatus of an automobile is explained with reference to  FIG. 4 . 
   The input rotary shaft  12  of the driving force transmission device  10  is connected to a steering wheel  50 . The output rotary shaft  13  of the driving force transmission device  10  is connected to a tie rod  52  through a gear box  51  such as a rack-and-pinion mechanism or a ball screw mechanism. Opposite ends of the tie rod  52  are connected to knuckle arms  54  of left and right vehicle wheels  53  respectively. 
   Incidentally, the gear box  51  can include power-steering performance. 
   The rotation of the output rotary shaft  13  is converted by the gear box  51  to an axial displacement (movement) of the tie rod  52  so that the vehicle wheels  53  are operated through the knuckle arms  54 . 
   In this structure, the rotation of the steering wheel  50  is transmitted to the vehicle wheels  53  through a steering angle transmission mechanism including the input rotary shaft  12 , driving force transmission device  10 , output rotary shaft  13 , gear box  51 , tie rod  52  and knuckle arms  54 . 
   As described above, a force transmitting amount, that is, the transmission ratio of the driving force transmission device  10  is continuously adjustable in accordance with the control of the rotating direction and rotating amount of the electric motor  23 , and the input-output transmission ratio becomes about 1:1 when the motor  23  is stopped (in not-driven condition). 
   The control of the rotating direction and rotating amount of the electric motor  23  as well as the stop thereof is performed in accordance with an instruction from a controller  60 . 
   The controller  60  is of microcomputer type, and receives data regarding an rotating angle of the steering wheel  50  measured by a steering wheel angle sensor  61 , a steered angle (an actual orientation angle) of the vehicle wheels  53  by a steering angle sensor  62  and a vehicle speed measured by vehicle wheel speed sensors  63 . The controller  60  calculates a target steered angle of the vehicle wheels  53  preferable at each timing from a vehicle moving condition and an estimated vehicle driver&#39;s intention on the basis of such data, compares it with an output of the steering angle sensor  62  (the actual orientation angle), and controls the electric motor  23  so that the actual orientation angle of the vehicle wheels  53  is made equal to the target steered angle when they are different from each other. 
   Further, the controller  60  adjusts the transmission ratio of the driving force transmission device  10  in accordance with the vehicle speed measured by the vehicle wheel speed sensors  63 . A variable gear ratios steering control (VGRS control) in accordance with the vehicle speed is brought about basically in such a manner that the steering gear ratio (input/output) increases in accordance with an increase of the vehicle speed as shown in  FIG. 5 . 
   Therefore, during a low vehicle speed such as when putting the vehicle into a garage, an increased steering gear ratio is obtained so that a great amount of the actual orientation angle is obtained by a small operating amount of the steering wheel to increase steering responsiveness. On the other hand, during a high vehicle speed such as driving on a highway, a decreased steering gear ratio is obtained so that a small amount of the actual orientation angle is obtained by a great operating amount of the steering wheel to improve a stability for straight driving. 
   Further, the controller receives data regarding a yaw rate of the vehicle measured by a yaw rate sensor  64  and a transverse acceleration measured by a transverse acceleration sensor (transverse G sensor)  65 . By controlling the rotating direction and rotating amount of the electric motor  23  of the driving force transmission device  10  on the basis of such data, a steering operation for obtaining a stabilizer effect to prevent the vehicle from moving transversely when receiving a transverse wind during proceeding in high speed, an automatic counter steering operation for restraining a spin or skid-out during proceeding long a curved coarse, and a control for increasing an reactive force applied to the steering wheel are obtainable. 
   A steered angle control system including the controller  60  includes a fault diagnosis performance so that when a fault is detected by the controller  60 , the controller prevents the electric motor from being driven, makes the transmission ratio of the driving force transmission device  10  to be 1:1, and reports the fault to the vehicle driver with an alarm light or sound (not shown). 
   For preventing the electric motor from being driven, an electric source (electric current) is instantaneously interrupted when the fault occurs in the electric motor  23 , and the electric current is decreased gradually during a predetermined time period (short time) when the fault does not occur in the electric motor  23 . In the latter case, it is prevented that the vehicle driver feels uncomfortable or a stability of the vehicle is deteriorated momentarily, on switching between driving condition and not-driving condition in response to the instantaneous interruption of the electric current. 
   As described above, the steering apparatus using the driving force transmission device  10  of the invention has unique effects of that the adjusting control of the steering gear ratio is obtainable as a main goal, and the transmission ratio (input output gear ratio) of the driving force transmission device  10  is made to be about 1:1 as a fail-safe function by preventing the electric motor  23  from rotating. Therefore, the operated rotational amount of the steering wheel  50  is made equal to the rotating amount of the output rotary shaft  13  to enable the automobile to be driven similarly to the conventional automobile even when the fault occurs in the steered angle control system. 
   Further, since the input output gear ratio of the driving force transmission device  10  is made to be about 1:1 when the electric motor  23  is prevented from rotating, the steering gear mechanism such as the rack and pinion mechanism or the ball-screw mechanism used in the conventional vehicle does not need to be changed for being mounted on the steering apparatus. 
   Further, when the fault or abnormality does not occurs, the gear ratio of the driving force transmission device  10  may be about 1:1 to satisfy the moving condition of the vehicle, so that the electric power is not needed to obtain the input-output gear ratio of 1:1 and to enable an electric power saving. 
   Incidentally, the driving force transmission device  10  is not limited to the above described embodiments, and may have a worm wheel  26  engaging with the worm gear  24  at an annular axial end portion of the ring member  20  other than the outer periphery of the ring member  20  so that a radial size of the driving force transmission device  10 ′ is further decreased. 
   Further, the device may be modified within the scope of the invention by, for example, making a number of the intermediate gears  21  more than four. 
   Further, the radius of the pitch circle on which the input gear  14  and each of the intermediate gears  21  engage with each other may be different from the radius of the pitch circle on which the output gear  15  and each of the intermediate gears  21  engage with each other, so that the transmission ratio is made to be other than 1:1 when the ring member is fixed. 
   Further, the input gear  14  and output gear  15  may be face gears, while the intermediate gears  21  may be a spur gear. 
   Further, the ring member  20  may be fixed by an additional braking means or brake motor other than the braking function by the engagement between the worm gear  25  and the worm wheel  22 . 
   It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.