Abstract:
A rear wheel steering apparatus comprises an electric motor generating rotational torque, an electric control device controlling the rotation of the electric motor, a motion converting device converting the rotational torque of the electric motor into a propulsion force, an output shaft outputting the propulsion force, a rear wheel steering angle detecting device detecting a steering angle of the rear wheels steered by the output shaft, a regulating member for prohibiting the output shaft from rotating while allowing the output shaft to move axially, a neutral return device manually returning the rear wheels to a neutral position upon failure of the motor or the electric control device, a neutral return detecting device for detecting the return of the output shaft to the neutral position and a neutral return notification device for notifying the return of the output shaft to the neutral position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. §119 with respect to a Japanese Patent Application 2001-137478, filed on May 8, 2001, the entire content of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a rear wheel steering apparatus. More particularly, this invention relates to a rear wheel steering apparatus having a neutral return means for manually returning rear wheels to a neutral position in the case of the failure of an electric motor or an electric control device. 
     BACKGROUND OF THE INVENTION 
     A conventional rear wheel steering apparatus of this kind is disclosed in, for example, U.S. Pat. No. 4,703,945. This apparatus includes an electric motor, a rotational member rotated by the electric motor, a tie rod connecting member for converting a rotational movement of the rotation member into a movement in the direction of a width of the vehicle, a connecting member provided between the rotational member and the tie rod connecting member and able to be driven conversely by an external force from the rear wheels and an engage means provided on the rotational member and being engageable with a manual rotation means for manually giving a rotational movement to the rotational member. 
     In the above mentioned prior apparatus, in case it is possible to rotate a rotational shaft of the electric motor from outside, it is possible to rotate the rotational member by the manual rotation means and thereby the rear wheels can be returned to a neutral position. However, it must depend on intuition of an operator whether the rear wheels were returned to the neutral position or not. Therefore, it is necessary to repeat the running of the vehicle after the rotation of the manual rotation means in order to confirm the going straight ahead of the vehicle and the efficiency of the operation is low. 
     A need exists for a rear wheel steering apparatus which can return the rear wheels to the neutral position efficiently. 
     SUMMARY OF THE INVENTION 
     A rear wheel steering apparatus comprises an electric motor for generating a rotational torque, an electric control device for controlling the rotation of the electric motor, a motion converting means for converting the rotational torque of the electric motor into a propulsion force in the direction of a width of a vehicle and connected to a rotational shaft of the electric motor, an output shaft for outputting the propulsion force in the direction of the width of the vehicle which is converted by the motion converting means, tie rods connecting between the output shaft and rear wheels and having a ball joint, respectively, a housing fixed to the vehicle and accommodating the electric motor, the motion converting means and the output shaft therein, a rear wheel steering angle detecting means for detecting a steering angle of the rear wheels steered by the output shaft, a regulating member connected to the housing and for prohibiting the output shaft from rotating while allowing the output shaft to move in the axial direction, a neutral return means for manually returning the rear wheels to a neutral position in the case of the failure of the electric motor or the electric control device, a neutral return detecting means for detecting the return of the output shaft to the neutral position and a neutral return notification means for notifying the return of the output shaft to the neutral position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     A more complete appreciation of the invention and other advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which: 
     FIG. 1 is a schematic illustration of a steering system of a vehicle applied a first embodiment of a rear wheel steering apparatus in accordance with the present invention; 
     FIG. 2 is a cross sectional view of an essential portion of a first embodiment of the rear wheel steering apparatus in accordance with the present invention; 
     FIG. 3 is a cross sectional view of an essential portion of a first embodiment of the rear wheel steering apparatus in accordance with the present invention; 
     FIG. 4 is a cross sectional view taken along line B—B of FIG. 2; 
     FIG. 5 is a perspective view showing a movable portion of a neutral position return sensor of a first embodiment of the rear wheel steering apparatus in accordance with the present invention; and 
     FIG. 6 is a plan view showing a wiring pattern of the neutral position return sensor of a first embodiment of the rear wheel steering apparatus in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Having generally described the present invention, a further understanding of the invention can be obtained now according to embodiments of the present invention with reference to FIGS. 1 to  6  in the accompanying drawings. 
     FIGS. 1 to  6  show a first embodiment. In FIG. 1, front wheels WFL and WFR are steered by a front wheel steering apparatus  5  in response to a rotational operation of a steering wheel  3 . A steering angle of the front wheels EFL and WFR a re detected by a first front wheel steering angle sensor D 1  detecting a moving amount of a rack of the front wheel steering device  5  and a second front wheel steering angle sensor D 2  provided on a steering shaft. 
     Rear wheels WRL and WRR are steered by a rear wheel steering apparatus  9 . The rear wheel steering apparatus  9  is driven by a brush-less motor  10 . A magnetic pole sensor D 6  which detects a rotational angle of the brush-less motor  10  is provided on an end portion of the brush-less motor  10 . Further, a rear wheel steering angle sensor  71  which detects an actual steering angle of the rear wheels WRL and WRR is connected to a first rear wheel steering shaft  41  for steering the rear wheels WRL and WRR. 
     Further, in a steering system of a vehicle shown in FIG. 1, a first vehicular velocity sensor D 3  and a second vehicular velocity sensor D 4  which detect a velocity of the vehicle and a yaw rate sensor D 5  which detects a yaw rate of the vehicle are provided. 
     Further, in the steering system of the vehicle, a neutral return notification device  7  including a neutral position return sensor  77  provided in a steering angle sensor portion  70  is provided. The neutral return notification device  7  is directly driven by a battery  6  without via an electric control device  8 . Therefore, even if the failure of the electric control device  8  occurs, the operation of the neutral return notification device  7  is not affected. 
     The brush-less motor  10  is controlled by a signal from the electric control device  8 . The electric control device  8  receives each of the sensor outputs from the first front wheel steering angle sensor D 1 , the second front wheel steering angle sensor D 2 , the first vehicular velocity sensor D 3 , the second vehicular velocity sensor D 4 , the yaw rate sensor D 5 , the magnetic pole sensor D 6  and the rear wheel steering angle sensor  71  and calculates a required steering angle of the rear wheels WRL and WRR corresponding to the steering angle of the front wheels WFL and WFR and running conditions of the vehicle. The electric control device  8  drives a brush-less motor  10   50  that the required steering angle is realized. 
     In FIG.  2  and FIG. 3, the rear wheel steering apparatus  9  is mounted via a bracket  17  fixed to a first housing  11  so as to extend in the direction of a width of the vehicle. Namely, the rear wheel steering apparatus  9  extends perpendicular to the advance direction of the vehicle. In FIG.  2  and FIG. 3, the rear wheel steering apparatus  9  which is divided along line A—A is shown. 
     The brush-less motor  10  includes a coil  21  which is fixed to the first housing  11  while being insulated, a hollow shaft  31  which is rotatably supported by bearings  51  and  52  fixed to the first housing  11  and the second housing  12 , a gear  32  formed on a right end portion of the hollow shaft  31  in a body, a magnet  22  fixed to an outer circumference of the hollow shaft  31  and the magnetic pole sensor D 6  which detects the rotational angle of the hollow shaft  31 . 
     The rotational torque of the hollow shaft  31  is transmitted to the planetary gear mechanism  33  via the gear  32 . A carrier  33   a  of the planetary gear mechanism  33  which is located at the last stage is connected to a nut rotatably supported by a bearing  53  fixed to the first housing  11 . The rotational torque of the hollow shaft  31  is amplified by the planetary gear mechanism  33  and is transmitted to the nut  34 . 
     A trapezoid female screw  34   a  is formed on an inner circumference of the nut  34  and is threaded onto a trapezoid male screw  41   a  formed on the first rear wheel steering shaft  41 . A male spline portion  41   b  which is formed on a right end portion of the first rear wheel steering shaft  41  is fitted into a female spline  65   b  formed on an inner circumference of a cylindrical member  65   50  as to be slidable in the axial direction (left and right direction in FIG.  2 ). Further, a worm wheel  65   a  formed on an outer circumference of the cylindrical member  65  is engaged with a worm  62   a . The worm  62   a  is formed on a worm shaft  62  which is supported by bearings  56  and  57  fixed to a third housing  13 . The worm wheel  65   a  and the worm  62   a  constitute a worm &amp; wheel whose rotational efficiency is less than 0 (zero). In the normal condition of this worm &amp; wheel, the first rear wheel steering shaft  41  is not able to relatively rotate with respect to the third housing  13 . 
     Accordingly, when the nut  34  is rotated, the first rear wheel steering shaft  41  is not rotated and is moved in the axial direction. 
     A tie rod  43  having a ball joint  43   a  is fixedly threaded to the right end portion of the first rear wheel steering shaft  41 . A tie rod  43  having a ball joint  43   a  is fixedly threaded to a right end portion of a second rear wheel steering shaft  42  which is fixedly threaded to the right end portion of the first rear wheel steering shaft  41 . Further, the tie rods  43  are connected to knuckle arms (not shown) of the rear wheels WRL and WRR. 
     According to the above structure, the rotational torque of the hollow shaft  31  of the brush-less motor  10  is transmitted to the nut  34  through the planetary gear mechanism  33  and is converted into the axial propulsion force of the first rear wheel steering shaft  41  and the second rear wheel steering shaft  42  by the thread motion or screw motion of the trapezoid female screw  34   a  and the trapezoid male s crew  41   a . Then, the converted axial propulsion force steers the rear wheels WRL and WRR via the tie rods  43 . 
     In FIGS. 3,  5  and  6 , the steering angle sensor portion  70  includes a sensor movable portion  72  comprising an engaging portion  72   d  which engages with a groove  41   c  formed on the outer circumference of the first rear wheel steering shaft  41 , a shaft portion  72   a  rotatably supported on a sensor housing of the rear wheel steering angle sensor  71 , a connecting portion  72 c connecting between the engaging portion  72   d  and the shaft portion  72   a , an arm portion  72   b  fixed to an upper end portion of the shaft portion  72   a  at right angle to the shaft portion  72   a  and brushes  74   a ,  74   b ,  74   c  and  74   d  formed on the arm portion  72   b  in a body. The steering angle sensor portion  70  further includes a wiring pattern portion  73  having wiring patterns  73   a ,  73   b ,  73   c  and  73   d  on which the brushes  74   a ,  74   b ,  74   c  and  74   d  slide and which are formed at the sensor housing in a body so as to be opposite to the arm portion  72   b . The arm portion  72   b  and the brushes  74   a ,  74   b ,  74   c  and  74   d  are insulated each other. The brushes  74   a  and  74   d  are connected electrically with each other via a conductive portion  76  and the brushes  74   b  and  74   c  are connected electrically with each other via a conductive portion  75 . 
     Only the wiring pattern  73   c  of the wiring patterns  73   a ,  73   b ,  73   c  and  73   d  is made as a resistance member. The electric resistance of the resistance member of the wiring pattern  73   c  is thousands to tens of thousands times as many as the electric resistance of the wiring patterns  73   a ,  73   b  and  73   d . Further, the electric resistance of the resistance member of the wiring pattern  73   c  is thousands to tens of thousands times as many as the electric resistance of the wiring pattern which is constituted by the brushes  74   a  and  74   d  and the conductive member  76 . Further, the electric resistance of the resistance member of the wiring pattern  73   c  is thousands to tens of thousands times as many as the electric resistance of the wiring pattern which is constituted by the brushes  74   b  and  74   c  and the conductive member  75 . 
     The brushes  74   a ,  74   b ,  74   c  and  74   d  slide on the wiring patterns  73   a ,  73   b ,  73   c  and  73   d , respectively. The rear wheel steering sensor  71  is constituted by the wiring patterns  73   b ,  73   c  and the brushes  74   b ,  74   c . The neutral position return sensor  77  is constituted by the wiring patterns  73   a ,  73   d  and the brushes  74   a ,  74   d . In this first embodiment, the rear wheel steering angle sensor  71  and the neutral position return sensor  77  are formed in a body in the same senor housing. 
     As shown in FIG. 6, the wiring pattern  73   b ,  73   c  and the brushes  74   b ,  74   c  of the rear wheel steering angle sensor  71  are connected to an electric power source  105  and detecting portion  8   a . The electric power source  105  and the detecting portion  8   a  are provided in the electric control device  8 . Further, the wiring patterns  73   a ,  73   d  and the brushes  74   a ,  74   d  are connected to an electric power source  106 , a resistance  107  and the detecting portion  7   a.    
     The electric power source  106 , the resistance  107  and the detecting portion  7   a  are provided in the neutral return notification device  7 . 
     Accordingly, since the neutral return notification device  7  is directly driven by the battery  6  without via the electric control device  8  and the electric power source  106  of the central position return sensor  77  is different from the electric power source  105  of the rear wheel steering angle sensor  71 , the operation of the neutral return notification device  7  is not affected even if the failure of the electric control device  8  occurs. 
     When the brush-less motor  10  is driven by the electric control device  8 , the first rear wheel steering shaft  41  moves in the axial direction and the rear wheels WRL and WRR are steered. At this time, the engaging portion  72   d  which is engaged with the groove  41  formed on the outer circumference of the first rear wheel steering shaft  41  swings around an axial center of the shaft portion  72   a  and is accompanied by the axial movement of the first rear wheel steering shaft  41  and the arm portion  72   b  swings around the axial center of the shaft portion  72   a  in accompaniment of the swinging of the engaging portion  72   d . Thereby, the brushes  74   a ,  74   b ,  74   c  and  74   d  slide on the wiring patterns  73   a ,  73   b ,  73   c  and  73   d , respectively. 
     In this time, if the brush  74   b  is positioned at a position b 2  on the wiring pattern  73   b  and the brush  74   c  is positioned at a position c 2  on the wiring pattern  73   c , the voltage drop between the positions ci and c 2  on the wiring pattern  73   c  is detected as a voltage signal between the positions bl and c 3 . This voltage signal shows the positions of the first and second rear wheel steering shafts  41  and  42  and shows the steering angle of the rear wheels WRL and WRR. 
     On the other hand, in case the first and second rear wheel steering shafts  41  and  42  stop at a position which is different from the neutral position due to the failure of the electric control device  8 , the failure of the brush-less motor  10 , the lock of the bearings  51 ,  52  and  53  and so on, a jack-handle (not shown) is installed on a two faces width portion  62   b  formed on a top end portion of the worm shaft  62  and the jack handle is rotated in order to return the rear wheels WRL and WRR to the neutral position. 
     When the worm shaft  62  is rotated by the jack-handle, the first rear wheel steering shaft  41  is rotated via the worm  62   a  formed on the worm shaft  62 , the worm wheel  65   a , the cylindrical member  65 , the female spline portion  65   b  and the male spline portion  41   b . Since the first rear wheel steering shaft  41  is rotated with respect to the nut  34  which is not able to rotate, the first rear wheel steering shaft  41  is moved in the axial direction. 
     Simultaneously, the engaging portion  72   d  swings around the axial center of the shaft portion  72   a  in accompaniment with the axial movement of the first rear wheel steering shaft  41  and the arm portion  72   b  swings around the axial center of the shaft portion  72   a  in accompaniment with the swinging of the engaging portion  72   d . Thereby, the brushes  74   a ,  74   b ,  74   c  and  74   d  slide on the wiring patterns  73   a ,  73   b ,  73   c  and  73   d , respectively. 
     At this time, if the brush  74   a  which constitutes the neutral position return sensor  77  is positioned at a position a 2  on the wiring pattern  73   a  and the brush  74   d  is positioned at a position d 2  on the wiring pattern  73   d , the portion al of the wiring pattern  73   a  is grounded. 
     Thereby, in case the first and second rear wheel steering shafts  41  and  42  are positioned at positions different from the neutral position, namely, in case the rear wheels WRL and WRR are positioned at a position which is different from the neutral position, the detecting portion  7   a  detects always a predetermined voltage (High signal). On the other hand, in case rear wheels WRL and WRR are positioned at the neutral position, as mentioned above, the detecting portion  7   a  detects a ground signal, namely 0 volt signal (Low signal) and thereby it is detected that the rear wheels WRL and WRR are positioned at the neutral position. Then, on the basis of the Low signal from the detecting portion  7   a , the neutral return notification device  7  notifies the operator who returns the rear wheels to the neutral position by voice, light and so on that the rear wheels were returned to the neutral position. Thereby, the rear wheels WRL and WRR are returned to the neutral position at the operator&#39;s first try. 
     The sliding distance W of a sliding portion  73   d   1  of the wiring pattern  73   d  on which the brush  74   d  slides is shorter than that of the other wiring patterns on which the other brushes slide. On the other hand, the sliding portion  73   d   1  has a predetermined width. Thereby, the inclination of the rear wheels WRL and WRR with respect to the back and forth direction of the vehicle which the driver does not have a feeling of wrongness is allowed. 
     Next, a second embodiment is described. In the second embodiment, the brushes  74   b ,  74   c , the conductive portion 75 , the wiring patterns  73   a ,  73   d , the electric power source  106 , the resistance  107  and the detecting portion  7   a  shown in FIGS. 5 and 6 are omitted. The neutral position return sensor is constituted by a magnet  82  fixed to the first rear wheel steering shaft  41  and a magnetic change detecting sensor  81  fixed to the third housing  13  and detecting the magnetic change accompanying the movement of the first rear wheel steering shaft  41 . (Therefore, the magnet  82  and the magnetic change detecting sensor  81  are not included in the first embodiment.) 
     The magnetic change detecting sensor  81  is connected to the neutral return notification device  7 . In the same manner as the first embodiment, the electric power source which drives the magnetic change detecting sensor  81  is different from the electric power source of the rear wheel steering angle sensor  71  and is provided in the neutral return notification device  7 . Thereby, even if the failure of the electric control device  8  occurs, the operation of the neutral return notification device  7  is not affected. 
     Further, the signal being fed from the magnetic change detecting sensor  81  to the neutral return notification device  7  is always a predetermined voltage signal (High signal) when the rear wheels WRL and WRR are positioned at a position which is different from the neutral position. When the rear wheels WRL and WRR are positioned at the neutral position, the signal is a 0 volt signal (Low signal). 
     The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiment disclosed. Further, the embodiment described herein is to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.