Abstract:
The object of the present invention is to provide a driving apparatus for a vehicle, which is capable of improving the operability and safety of a vehicle driving by enabling a fine correction to the steering amount with a simple apparatus. The apparatus employs the first and second operation devices, for which the steering gains are differentiated for the improvement.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a driving apparatus which steers the steered wheels of a vehicle.  
         BACKGROUND OF THE INVENTION  
         [0002]    A steering system employing a steering wheel as a driving apparatus, which steers the steered wheels of a vehicle, has been known. The steering system converts the rotational motion of a steering wheel into the linear motion of a rack axis in a steering gearbox, thus driving a link mechanism connected to the rack axis to steer the steered wheels.  
           [0003]    In recent years another driving apparatus with joysticks instead of a steering wheel to steer the steered wheels of a vehicle has been proposed. This type of driving apparatus is disclosed in the patent gazette Japanese Laid-Open Patent 9-301193 as a prior example. This driving apparatus has at least two joysticks (control knobs) and performs the acceleration/deceleration or the turning of a vehicle with the operation of the joysticks in the direction of forward, backward, rightward or leftward. For example, a vehicle is accelerated when a forward operational force is added to the respective joysticks or it is decelerated when a backward operational force is added to them. And, the steered wheels are turned to the right when a rightward force is added to the respective joysticks or they are turned to the left when a leftward force is added to the respective joysticks. The respective joysticks are functionally equivalent and a driver can select and operate only one joystick or operate a plurality of joysticks simultaneously. When a plurality of joysticks are simultaneously operated, provision for the operational contradiction among joysticks is made by prioritizing each joystick and accepting the operation with a joystick in the order of priority. This type of driving apparatus is more advantageous than the prior driving apparatus with a steering wheel because the layout flexibility and reliability are improved and the access from the right or left seat is selectable with a plurality of joysticks.  
           [0004]    However, this type of driving apparatus has had difficulty in giving a small correction to the steering amount, which is one of basic performances required for steering. The steering wheel is able to rotate (operate) more than two revolutions; on the other hand the joystick is only able to operate within the tilt amount (tilt displacement) in the direction of forward/backward or right/left. So it is necessary to make the steering amount per unit operational amount (angle) of joystick bigger than the steering amount per unit operational angle of a steering wheel, however in doing so a fine correction of steering amount was difficult since the steered wheels made a large steering with a small operational amount. All the joysticks disclosed in the patent gazette Japanese Laid-Open Patent 9-301193 are of the same function, namely of the same characteristics. Therefore, it was difficult to give a fine correction to the steering amount, which had been realized by the steering wheel, since the operation was actually equivalent with one joystick operation even if selection or prioritization was made.  
           [0005]    Further, the driving apparatus had problems that it required a complex control device for switching the respective joysticks or prioritizing them when a plurality of joysticks was in operation simultaneously, and confirmation by a driver of the switching operation or the operable joystick.  
         SUMMARY OF THE INVENTION  
         [0006]    Therefore, the object of the present invention is to provide a driving apparatus, which enables the improvement of operational performance of a vehicle in driving, by allowing a fine correction of steering amount with a simple structure when a steering of steered wheels is performed with an operation device composed of joysticks etc.  
           [0007]    The present invention to address the above issues according to the appended claim  1  provides a driving apparatus for a vehicle, which has an operation device operated by a driver, and in which an operation amount monitoring unit equipped in the operation device detects the operation amount of the operation device and a control device controls the steered wheels of a vehicle with the detected value, wherein the operation device comprises a first and a second operation devices, the control device comprises a steering amount setting unit which determines the steering amount for the steered wheels based on the resultant of the first detected operation amount resulting from the operation of the first operation device and the second detected operation amount resulting from the operation of the second operation device, and a first steering gain which is a ratio of the steering amount of steered wheels to the operation amount of the first operation device and a second steering gain which is a ratio of the steering amount of the steered wheels to the operation amount of the second operation device are differentiated The driving apparatus thus structured is capable of differentiating the steering amount per unit operation amount of the first and the second operation devices by setting the first and the second steering wheel gains different, as well as making the respective first and second operation devices contribute to the setting of the steering wheel amount. For example, in the case the gain of the second operation device is lower than that of the first operation device, it will be possible to utilize the second operation device as a fine adjustment means for the first operation device, since it can be set so that the steering amount per unit operation amount of the second operation device is less than that of the first operation device. Therefore, it will promote the operational performance of a vehicle as well as the improvement of the accuracy of steering wheel angle. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is an overall view illustrating the structure of a driving apparatus according to the preferable embodiment of the present invention.  
         [0009]    [0009]FIG. 2( a ) is a perspective view showing the configuration of a first operation device. FIG. 2( b ) is a perspective view showing the configuration of a second operation device. FIG. 2( c ) is a perspective view showing another configuration of a second operation device.  
         [0010]    [0010]FIG. 3 is a graph showing the output characteristics of a steering torque sensor.  
         [0011]    [0011]FIG. 4 is a graph showing the output characteristics of a steering amount sensor of the first and second operation devices.  
         [0012]    [0012]FIG. 5 is a block diagram showing the data processing performed in a driving apparatus for a vehicle. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    The preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.  
         [0014]    [0014]FIG. 1 is a structural view of the driving apparatus according to the embodiment of the present invention.  
         [0015]    As shown in FIG. 1, a driving apparatus  1  enables CWB (Control By Wire) without a steering wheel, including a first operation device  2  and a second operation device  3 . The operation amount of the first operation device  2  and the operation amount of the second operation device  3  are processed with the different gains in a control device  4 , with the results of which a steering motor  5  is driven to steer wheels W, W.  
         [0016]    The steering of the steered wheels W, W is performed by converting the linear motion of a rack axis  7  of a steering gear  6  to the steering motion of the steered wheels W, W through tie rods  8 ,  8 . The linear motion of the rack axis  7  is performed by the steering motor  5  and a ball screw mechanism  9  instead of a rack and pinion mechanism of the prior art. The position of the rack axis  7  during the linear motion is detected with a rack position sensor  10  and fed back to the control device  4 . Such a publicly known sensor as a linear encoder or a potentiometer etc. is employed for the rack position sensor  10  and a combination of plural sensors is possible. Numeral  12  referring to a first operation amount detection unit, numeral  19  a steering reaction force motor and numeral  22  a second operation amount detection unit in FIG. 1 will be described in detail later.  
         [0017]    The first operation device  2  will be described in detail.  
         [0018]    As shown in FIG. 2( a ), the first operation device  2  includes a first lever  11  operated by a driver, the first operation amount detection unit  12  for detecting the operation amount of the first lever  11  and a frame portion  13  for supporting the first operation amount detection unit  12 .  
         [0019]    A driver will operate the first lever  11  by gripping its top with his right or left hand. The end  14   a  of a rod  14  is fixed to the lower part of the first lever  11 . The rod  14  is fixed perpendicular to the first lever  11  and supported with bearings etc. at wall portions  13   a ,  13   b ,  13   c  and  13   d  of the frame portion  13 . It will allow such an operation that the first lever  11  can be tilted in a rotation-like motion in the right or left direction with the rod  14  as an axis. Hereinafter, the explanation will be made by referring to steering the steered wheels in the right direction by tilting the first lever  11  to the right with the rod  14  as an axis, as the right steering, on the other hand steering the steered wheels in the left direction by tilting the first lever  11  to the left with the rod  14  as an axis, as the left steering.  
         [0020]    A steering torque sensor  15  and a steering amount sensor  16 , which are included in the first operation amount detection unit  12 , are disposed in the longitudinal direction of the rod  14 .  
         [0021]    The steering torque sensor  15 , which is composed of a publicly known sensor using strain gauge etc., will improve the response by detecting the torque added to the first lever  11  when the operation is started or the direction of the steered wheels W, W is changed. The characteristics of the output of the steering torque sensor  15  are shown in FIG. 3. When the first lever  11  is in the neutral position, the steering torque sensor  15  will give no output, but when the first lever is tilted for the right steering, the steering torque sensor  15  will give a positive detected value TS and the detected value TS will increase with the increase of the torque added to the first lever  11 . On the other hand, when the first lever is tilted for the left steering from the neutral position, the detected value TS will be negative, and it will decrease with the increase of the torque added to the first lever  11 . The detected value TS of the steering torque sensor  15  is sent to the control device  4  through a harness (signal transmission cable), and used for FF (Feed-Forward) control to be described later.  
         [0022]    The steering amount sensor  16  includes a potentiometer for detecting the rotation angle of the rod  14  resulting from the operation of the first lever  11 . The steering amount sensor  16  gives the operation amount of the first lever  11  as an output of voltage (detected value RS 1 ). As shown in FIG. 4, a reference voltage is given when the first lever  11  is in the neutral position, and when the right steering is performed, the detected value RS 1  will increase according as the rotation amount of the first lever  11 , on the other hand when the left steering is performed, the detected value RS 1  will decrease according as the rotation amount of the first lever  11 . The detected value RS 1  of the steering amount sensor  16  is sent to the control device  4  through the harness, with which the control device  4  determines the steering amount of the steered wheels W, W as a principle value.  
         [0023]    Another end of the rod  14  has a pulley, which is connected to the rotation axis of a steering reaction force motor  19  with a belt  18 .  
         [0024]    The steering reaction force motor  19  generates a reaction force (steering reaction force) of the reverse direction and amount, according as the position and the direction of the first lever  11  with the reception of the signal from the control device  4 , thus improving the operational performance and the steering accuracy. For example, in the case the first lever  11  is further tilted to the right while the right steering is being carried out, the steering reaction force motor  19  will generate the steering reaction force in the reverse direction of the right steering. The bigger the operation amount of the first lever  11  is, the bigger steering reaction force the steering reaction force motor  19  will generate, enabling a driver to feel the current steering angle and his operation amount with the magnitude of the reaction force. On the other hand, when the first lever  11  is operated to tilt back to the neutral position from the right steering, a driver can smoothly tilt back the first lever  11  to the neutral position, since the steering reaction force motor  19  does not generate the steering reaction force. Therefore, a driver can perform an optimum steering, since he can easily recognize the current steering status. When the first lever  11  is operated to tilt back to the neutral position, the steering reaction force motor  19  may be instead adjusted so that it assists the return of the first lever  11 .  
         [0025]    There is provided with a centering mechanism  20 , which assists the first lever  11  to go back to the neutral position, between the first lever  11  and the steering amount sensor  16 . The centering mechanism  20  includes a plate  20   a  fixed to the rod  14  and centering springs  20   b ,  20   b , the hooks of which are fixed on both edges of the plate  20   a , and the lower hooks of the centering springs  20   b ,  20   b  are fixed to a bottom  13   e  of the frame portion  13 . Therefore, when a left steering is, for example, performed, the centering spring  20   b  expands, which is located in the front in FIG. 2( a ), assisting the first lever  11  to return to the neutral position with the reaction force created by contracting back to its original length. When the first lever  11  is tilted back to the neutral position, the reaction force of the centering spring  20   b  will assist the first lever  11  to return.  
         [0026]    The second operation device  3  will be described in detail with reference to FIG. 2( b ).  
         [0027]    The second operation device  3  is provided for giving a fine adjustment to the steering by the first operation device  2 , including a second lever  21  operated by a driver, a second steering amount sensor  22  for detecting the operation amount of the second lever  21  and a frame portion  23  for supporting the second steering amount sensor  22 .  
         [0028]    The second lever  21  is gripped by the right or left hand, which is another hand different from the hand for the first level  11 . Under the second lever  21  is fixed an end portion  24   a  of a rod  24 . The rod  24  is fixed perpendicular to the second lever  21  and supported with bearings etc. at wall portions  23   a  and  23   b  of a frame portion  23 . It will allow such an operation that the second lever  21  can be tilted in a rotation-like motion in the right or left direction with the rod  24  as an axis. Hereinafter, the explanation will be made by referring to steering the steered wheels in the right direction by tilting the second lever  21  to the right with the rod  24  as an axis, as the right steering, on the other hand steering the steered wheels in the left direction by tilting the second lever  21  to the left with the rod  24  as an axis, as the left steering.  
         [0029]    The second steering amount sensor  22  is composed the same as the first steering amount sensor  16 . It gives a reference voltage when the second lever  21  is in the neutral position as shown in FIG. 4, and a detected value RS 2  will increase when the second lever  21  is tilted further for the right steering, on the other hand the detected value RS 2  will decrease when the left steering is made. The detected value RS 2  is sent to the control device  4  through the harness and used for the fine adjustment of steering amount.  
         [0030]    As shown in FIG. 2( c ), it is possible to select an operation device  3   a , in which a second lever  21   a  is aligned with the rod  24  so that the steering amount may be controlled with the rotation of the second lever  21   a . In this case, the right steering is made by rotating the second lever  21   a  to the right and the left steering by rotating the second lever  21   a  to the left.  
         [0031]    A motor similar to the steering reaction force motor  19  may be prepared for the second operation device  3  to give an approximately same operation feeling to the right and left levers  11  and  21 , however it would be preferable to dispense with this type of motor for the second operation device  3  in order to give a clear recognition to a driver about the roles of the first and second devices  2  and  3 .  
         [0032]    In this connection, the first and second operation devices  2  and  3  may be respectively placed at the right and left of a driver&#39;s seat or two of them may be placed in front of a driver&#39;s seat.  
         [0033]    The control device  4  will be described in detail.  
         [0034]    As shown in FIG. 5, the control device  4  includes, CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory) and ECU (Electronic Control Unit  4 ), electrically connected to the first operation device  2 , the second operation device  3  and the gear box  6  through the harness of signal transmission cable.  
         [0035]    The control device  4  includes, the second steering amount sensor  22  of the second operation device  3 , the first steering amount sensor  16  of the first operation device  2 , a steering control unit  31  which drives the steering motor  5  of the gearbox  6  receiving the detected values of the first steering amount sensor  16  of the first operation device  2  and the steering torque sensor  15 , and a steering reaction force control unit  32  which controls the steering reaction force motor  19  of the first operation device  2 .  
         [0036]    A steering control unit  31  includes, a gain adjusting unit  33 , a target rack position setting unit  34 , a deviation calculation unit  35 , a steering motor control signal output unit  36  and a steering motor drive circuit  37 . The gain adjusting unit  33  sends an output signal MS 2 , which is a gain reduced signal of the detected value RS 2  received from the second steering amount sensor  22  of the second operation device  3 . The target rack position setting unit  34  determines the target value for the position of the rack axis  7  according to the driver&#39;s operation amount, taking into account the output signal MS 2  and the detected value RS 1  of the first steering amount sensor  16  of the first operation device  2 . The deviation calculation unit  35  calculates the deviation based on the target of rack position and the current rack position. The steering motor control signal output unit  36  generates an output signal DS (direction signal+PMW signal) which drives the steering motor  5  according to the deviation. The steering motor drive circuit  37  drives the steering motor  5  based on the output signal DS. The target rack position setting unit  34  and the deviation calculation unit  35  refer to a steering amount setting unit according to the appended claim.  
         [0037]    The gain adjusting unit  33  sets the steering amount per the unit operation angle of the second operation device  3  less than that of the first operation device  2 . It does so by reducing the gain of the detected value RS 2  (the second steering gain), which is the operation amount of the second operation device  3 , compared with the gain of the detected value RS 1  (the first steering gain) of the first operation device  2 . Therefore, the control device  4  sets the operation amount of the first operation device  2  as a principle value and performs an addition or subtraction of the small output signal MS 2  resulting from the operation amount of the second operation device  3  as a compensational value, thus determining a target rack position TRS, namely a steering amount. Therefore, a driver can perform a relatively large steering with the first operation device  2  and a fine adjustment with the second operation device  3 , resulting in an accurate and stable steering.  
         [0038]    The gain set for the gain adjusting unit  33  will be determined for each type of vehicle. It is possible to prepare a map, which defines the variation of the gain with the speed and steering amount of a vehicle, and make the gain vary in accordance with the map.  
         [0039]    The target rack position setting unit  34  composes the detected value RS 1  and the output signal MS 2  after their level adjustment, and determines the target rack position by carrying out a map retrieval with the resultant value as an address. The level adjustment is a process that the respective voltages of the detected value RS 1  and the output signal MS 2  are converted so that they have a positive voltage in the case of the right steering and a negative voltage in the case of the left steering, having them biased to define the respective neutral positions of the first operation device  2  and the second operation device  3  as zero point. With this type of process, for example, when the first operation device  2  is in the right steering condition and the second operation device  3  is in the right steering condition, the resultant value will increase. Subsequently, if the first operation device  2  holds the right steering condition and the second operation device  3  is changed to the left steering condition, the resultant value will decrease to reliably track the variation of the steering amount, thus enabling a constant setting of correct target rack position.  
         [0040]    The deviation calculation unit  35  calculates the deviation between the target rack position signal TRS and the current rack position signal PS measured by the rack position sensor  10 . It determines the steering direction is rightward if the deviation is positive, or leftward if it is negative, thereby giving a deviation signal DRS with an appropriate polarity and magnitude for each case.  
         [0041]    The steering motor control signal output unit  36  performs P (Proportional), I (Integral) and D (Differential) processing for the deviation signal DRS to generate a control signal CS and compose it with a control signal FCS to be described later. Further, it sends the output signal DS (direction signal+PWM signal) which is representative of the polarity and magnitude of the resultant value, to a steering motor drive circuit  37 . The steering motor control signal output unit  36  improves the tracking performance for the movement of the rack axis  7  relative to the target rack position with the PID function mentioned before.  
         [0042]    The steering control unit  31  has an FF control unit  38 , which gives the control signal FCS to the steering motor control signal output unit  36  based on the detected value TS of the steering torque sensor  15  of the first operation device  2  to perform an FF control, thus improving the initial steering response. So, in such a case as an initial operation that the operation amount of the first lever  11  is not large but the torque added to it is large, it is possible to improve the steering response, since the rack axis  7  can be moved in advance of the subsequent increase in the operation amount of first lever  11 . The control signal FCS is determined with the map of the detected torque value TS and the drive amount of the steering motor  5  in the FF control unit  38 .  
         [0043]    The steering reaction force control unit  32  includes a target steering reaction force setting unit  39 , a steering reaction force motor control signal output unit  40  and a steering reaction force motor drive circuit  41 . The target steering reaction force setting unit  39  determines the target reaction force to be added to the first lever  11  based on the detected value RS 1  of the first steering amount sensor  16  of the first operation device  2  and the deviation signal DRS of the deviation calculation unit  35 . The steering reaction force motor control signal output unit  40  collects the target reaction force signal TMS sent from the target steering reaction force setting unit  39  and gives a control signal MCS to drive the steering reaction force motor  19 . The steering reaction force motor drive circuit  41  is composed of an electrical circuit for driving the steering reaction force motor  19  based on the control signal MCS.  
         [0044]    The target steering reaction force setting unit  39  decides in which direction of the right or left the first lever  11  is currently positioned relative to the neutral position based on the detected value RS 1  of the first steering amount sensor  16 , and also makes a decision on the direction and amount of steering based on the deviation signal DRS, thereby determining the direction and amount of the steering reaction force to be generated by the steering reaction force motor  19 .  
         [0045]    Steering of the vehicle, on which the drive control device  4  is mounted, will be described in detail.  
         [0046]    When a driver operates the first lever  11  rightward from the neutral position for steering, the torque added to the first lever  11  will be large at the initial stage of operation, though the operation amount of the first lever  11  is small. The FF control unit  38  of the steering control unit  31  determines the control signal FCS for the steering motor control signal output unit  36  retrieving the torque map with the detected torque value TS as an address, for the steering torque sensor  15  gives a detected torque value TS (positive output). The rack axis  7  starts the linear motion and moving leftward according to the control signal FCS in advance of the subsequent main operation of the first lever  11 .  
         [0047]    The control device  4  sets the target rack position based on the operation amount of the first lever  11  and calculates the deviation between the target rack position and the current rack position. The steering motor  5  drives the rack axis leftward according to the deviation. On the other hand, the steering reaction force control unit  32  determines the steering reaction force to be added to the first lever  11  and drives the steering reaction force motor  19 , giving the leftward steering reaction force to the first lever  11 .  
         [0048]    If the first lever  11  is operated rightward further, the steering amount will increase rightward, as well as the increase of the leftward steering reaction force. On the other hand, if the first lever  11  is operated leftward, the steering reaction force will disappear as well as the decrease of the steering amount.  
         [0049]    When the second lever  21  is operated rightward, in the same direction of the first lever  11 , while the first lever  11  is being operated rightward, the steering amount will increase rightward, since the target rack position increases by the output signal MS 2 , which is created by reducing the gain of the detected value RS 2  of the operation amount of the second lever  21 . On the other hand, when the second lever  21  is operated leftward, the steered wheels W, W will accordingly return toward the neutral position, since the target rack position will decrease by the output signal MS 2 , which is created by reducing the gain of the detected value RS 2 .  
         [0050]    Next explanation is about the case that a driver operates the first lever  11  leftward starting from the neutral position.  
         [0051]    The FF control unit  38  of the steering control unit  31  determines the control signal FCS for the steering motor control signal output unit  36  by retrieving the torque map with the torque output TS as an address, for the steering torque sensor  15  of the first operation device  2  gives the output TS (negative value in this case) at the initial stage of operation like the rightward operation. The rack axis  7  starts the linear motion and moving rightward based on the control signal FCS in advance of the subsequent main operation of the first lever  11 .  
         [0052]    The control device  4  sets the target rack position based on the operation amount of the first lever  11  and calculates the deviation of the current rack position PS relative to the target rack position. The steering motor  5  operates according to the deviation and moves the rack axis  7  rightward. On the other hand, the steering reaction force control unit  32  of the control device  4  determines the steering reaction force to be added to the first lever  11  and drives the steering reaction force motor  19 , giving the rightward steering reaction force to the first lever  11 .  
         [0053]    If the first lever  11  is operated leftward further, the steering amount will increase leftward, as well as the increase of the rightward steering reaction force. On the other hand, if the first lever  11  is operated rightward, the steering reaction force will disappear as well as the decrease of the steering amount.  
         [0054]    When the second lever  21  is operated leftward, in the same direction of the first lever  11 , while the first lever  11  is being operated leftward, the steering amount will increase leftward, since the target rack position decreases by the output signal MS 2 , which is created by reducing the gain of the detected value RS 2  of the operation amount of the second lever  21 . On the other hand, when the second lever  21  is operated rightward, the steered wheels W, W will accordingly return toward the neutral position, since the target rack position will increase by the output signal MS 2 , which is created by reducing the gain of the detected value RS 2 .  
         [0055]    Steering as described before, in which the combination of the first and second levers  11  and  21  is utilized and the second lever  21  is used as a fine adjustment means for the first lever  11  by setting the gain of the second lever  21  less than that of the first lever  11 , will improve the operability and steering accuracy.  
         [0056]    It will now be appreciated from the foregoing description that the present invention is not limited to the particular illustrated embodiment discussed above and may be carried out in various modified forms. For example, as the method of differentiating the first and second steering gains, the different gains may be defined for the detected value RS 1  of the first steering amount sensor  16  resulting from the operation amount of the first lever  11  and the detected value RS 2  of the second steering amount sensor  22  resulting from the operation amount of the first lever  21 . And the FF control with the steering torque is not necessarily required.