Abstract:
An electric vehicle which includes in-wheel motor driving devices and an independent-steering apparatus and is capable of making pivot turns within a minimum-required parking space, having a structure without a chassis and a part of the body protruding out of a minimum-required circular space necessary for the wheels to make pivot turning. In a case where the electric vehicle has four wheels including left and right front wheels and left and right rear wheels, an in-wheel motor driving device is incorporated only in the left and right front wheels, only in the left and right rear wheels, or in all of the wheels. An independent-steering apparatus serves for all of the wheels. A kingpin axis in each of the wheels makes an intersection with a road surface on a circle inboard of a vehicle chassis.

Description:
TECHNICAL FIELD 
     The present invention relates to electric vehicles, and particularly to electric vehicles including in-wheel motor driving devices and independent-steering apparatuses for easy pivot turning. 
     BACKGROUND ART 
     Electric vehicles including in-wheel motor driving devices, and electric vehicles including independent steering apparatuses implemented by steering-by-wire system are both already public (Patent Literature 1 and 2). 
     The in-wheel motor driving device includes a motor section which generates a driving force; a speed reducer section which reduces rotating speed of the motor section and outputs the rotating force; and a wheel hub which transmits the output from the speed reducer section to a driving wheel. The speed reducer section is provided by a planetary gear system for example. An onboard motor controller provides electronic control on rotation speed, rotation direction, etc. of the in-wheel motor driving devices (Patent Literature 1 and 2). 
     The independent-steering apparatus implemented by steering-by-wire system uses a steering actuator installed in each vehicle wheels. The apparatus includes a steering angle controller which, in response to the vehicle driver&#39;s operation on the steering wheel, calculates target steering angles and provides electronic control on the steering actuators thereby setting the wheels to appropriate steering angles (Patent Literature 3). 
     An electric vehicle equipped with the independent steering apparatus can make pivot turning, i.e., turning on the spot, by placing the front wheels in a forwardly narrowing pattern, placing the rear wheels in a rearwardly narrowing pattern, and then, if the vehicle is a two-wheel drive type, by rotating the left and the right driving wheels in the front or rear of the vehicle in mutually opposite directions. In a four-wheel drive vehicle, the left and the right wheels are rotated in mutually opposite directions in both of the front and rear pairs, with the front and the rear left wheels rotated in the same direction while the front and the rear right wheels rotated in the same direction. Such a control provides pivot turning. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP-A 2005-7914 
         Patent Literature 2: JP-A 2007-216930 (FIG. 1 and FIG. 4) 
         Patent Literature 3: JP-A 2009-23561 (FIG. 1 and FIG. 3) 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in conventional electric vehicles, the body is made to have a rectangular shape in a plan view following traditional engine-driven automobiles, so the vehicle body is longer in the fore-aft direction. If such a vehicle attempts pivot turning at a place where there is not sufficient space in the vehicle&#39;s widthwise direction, the vehicle will interfere with surrounding objects such as other vehicles and buildings. 
     It is therefore an object of the present invention to provide an electric vehicle which includes in-wheel motor driving devices and an independent-steering apparatus and is capable of making pivot turns within a minimum-required parking space, by providing a structure without a chassis and apart of the body protruding out of a minimum-required circular space necessary for the wheels to make pivot turning. 
     Solution to Problem 
     In order to achieve the above-described object, the present invention provides an electric vehicle which includes: three wheels consisting of a front wheel and a left and a right rear wheels or consisting of a left and a right front wheels and a rear wheel; an in-wheel motor driving device incorporated only in the front wheels, only in the rear wheels, or in all of the wheels. The vehicle further includes an independent-steering apparatus for all of the wheels. With these arrangements, a kingpin axis in each wheel makes an intersection with a road surface on a circle which is defined inboard of a vehicle body. 
     The present invention also provides an electric vehicle which includes: four wheels consisting of a left and a right front wheels and a left and a right rear wheels; an in-wheel motor driving device incorporated only in each of the left and the right front wheels, only in each of the left and the right rear wheels, or in all of the wheels. The vehicle further includes an independent-steering apparatus for all of the wheels. With these arrangement, a kingpin axis in each wheel makes an intersection with a road surface on a circle which is defined inboard of a vehicle body. 
     The vehicle body is generally cylindrical, and preferably a platform is provided in the front of the body. 
     Advantageous Effects of Invention 
     The electric vehicle according to the present invention is capable, with the independent-steering apparatus, of orienting the wheels in directions which enable pivot turning even at a place not spacious enough for a normal turn. Therefore, as far as a space has a width which is wide enough for the vehicle to drive in, the vehicle does not require any more space and can make pivot turning without interfering with the surrounding objects. Thus, even if the vehicle was driven by forward driving into a narrow parking space with a dead end, it is possible to make a pivot turn and get out of the space by forward driving. 
     Also, due to the use of in-wheel driving units, it is possible to provide sufficient space between the left and the right front wheel housings not only in a case where the vehicle is a rear wheel drive type but also in a case where it is a front wheel drive type as well as in a case where it is an all wheel drive type. This allows a platform to be provided in the front portion of the vehicle body, which makes it possible to get out of and get into the vehicle from the entrance side of the parking space even if the parking space is very narrow. 
     Further, since the platform is in the front portion of the vehicle body, there is no need to ensure extra space on the left and/or right side of the vehicle for getting in and out of the vehicle. Combined with the pivot turning advantage at a small space, this helps to promote effective use of parking spaces. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional plan view of an electric vehicle according to Embodiment 1. 
         FIG. 2  is a perspective view of Embodiment 1. 
         FIG. 3  is a cross-sectional plan view of Embodiment 1, showing together with a control block diagram. 
         FIG. 4  is a cross-sectional plan view of Embodiment 1 during a small-radius turn. 
         FIG. 5  is a cross-sectional plan view during a pivot turn. 
         FIG. 6  is a cross-sectional view of an embodiment as an application to a three-wheel vehicle. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described based on the attached drawings. 
     Embodiment 1 
     As shown in  FIG. 1 , an electric vehicle according to Embodiment 1 has a configuration that in its plan view, an outer circumferential edge of a chassis  12  is on a chassis circle C of a radius R 0 . The chassis  12  is composed of a frame  13 , a floor panel  14  on the frame  13 , etc. 
     The frame  13  of the chassis  12  has a shape of a cross in a plan view, having a rectangular center portion  15  including its center O; a front end portion  15   a  and a rear end portion  15   b  in front of and at the rear of the center portion  15 ; and a left side portion  15   c  and a right side portion  15   d  on the left side and on the right side of the center portion  15 . Each of the frame portions  15   a  through  15   d  is surrounded by three sides, i.e., an arc-shaped frame end edge  13   a  of a curvature radius which is identical with the radius R 0  of the chassis circle C, and a left and a right-side frame side edges  13   b ,  13   c.    
     In these frame portions  15   a  through  15   d , each pair of mutually adjacent frame side edges  13   b  and  13   c  provides a squarely recessed space for a wheel housing  16 , and at each of the four housings, a left or a right front wheel  17   a  or  17   b  or a left or a right rear wheel  17   c ,  17   d  is installed. 
     It should be noted here that each of the wheels  17   a  through  17   d  has a suspension, which is not illustrated since it is not directly related to the present invention. 
     The four wheels  17   a  through  17   d  are disposed in such a fashion that their kingpin axes cross the ground at intersections A on a wheel disposition circle D which has a smaller radius R 1  than that of the outer circumferential circle C of the chassis  12 , and that all the four wheels are in a symmetric pattern with each other with respect to two mutually vertical reference lines (X and Y) drawn in the left-right direction and the fore-aft direction to cross each other at the center O of the chassis  12 . 
     The chassis  12  has a cabin  19  which is generally cylindrical as a whole as shown in  FIG. 2 , with a cylinder portion  20  having an outer circumferential surface following an outer circumferential surface of the chassis circle C. The radius R 0  of the chassis circle C is extended to a radius R 2  of a maximum circle E if a wall thickness of the cabin  19  is added. However, the wall thickness of the cabin  19  is negligibly small in comparison to the radius of the chassis circle C, so the maximum circle E is virtually equal to the chassis circle C. 
     Correspondingly to the wheel housings  16 , the cabin  19  has four recesses from the outer circumferential surface of the cylinder portion  20  (see  FIG. 2 ). 
     The cylinder portion  20  has its top opening closed with a circular top panel  21 . Also, there is a platform  22  provided in a front surface of the cylinder portion  20 , i.e., between the left and the right wheel housings  16 . The platform  22  may have a hinged or a sliding door. In addition, the cylinder portion  20  has windows  23 . Also, there is a driver&#39;s seat  25  with a handlebar  25  inside the cylinder portion  20 , i.e., inside the vehicle. The driver&#39;s seat  25  is provided with an accelerator pedal  26  (see  FIG. 1 ) for controlling in-wheel motor driving devices  27  and a brake pedal  30  for braking on the wheels  17   a  through  17   d  which will be described later. 
     It should be noted here that the figures show a rear wheel drive vehicle with the rear wheels  17   c ,  17   d  equipped with in-wheel motor driving devices  27 . However, even if the vehicle is of a front wheel drive type or all wheel drive type, the wheel housing  16  has enough space for the in-wheel motor driving device  27 , and therefore, it is possible to provide sufficient space between the left and the right wheel housings  16 , and thus, there is no problem in disposing the platform  22  at front portion of the cabin  19 . 
     Next, a controller for the wheels  17   a  through  17   d  will be described based on  FIG. 3 . The in-wheel motor driving device  27  includes, as already known, a motor section which generates a driving force; a speed reducer section which reduces rotating speed of the motor section and outputs the rotating force; and a wheel hub which transmits the output from the speed reducer section to a driving wheel. The speed reducer section is provided by a planetary gear system for example. The in-wheel motor driving devices  27  are controlled by a motor control unit  28  which is installed in the chassis  12 , whereby rotation speed, rotation direction, etc. of the rear wheels  17   c ,  17   d  are controlled. 
     Also, an independent-steering apparatus  29  is installed in the chassis  12  for steering control of the wheels  17   a  through  17   d . The independent-steering apparatus  29  is implemented by a steering-by-wire system which will be described next. 
     Specifically, each of the wheels  17   a  through  17   d  is equipped with a steering actuator  31 . As shown in  FIG. 3 , the steering actuator  31  includes a motor  32  and a linear motion mechanism  33  driven thereby. The linear motion mechanism  33  has a nut  34  on a driving shaft of the motor  32 , and a threaded rod  35  threaded through the nut  34 . Typically, the nut  34  and the threaded rod  35  are provided by a ball screw. As the motor  32  is driven, the nut  34  rotates at a fixed position, moving the threaded rod  35  in its axial direction. 
     The threaded rod  35  is connected to an end of an L-shaped knuckle arm  36 . The knuckle arm  36  is swingly connected by a corner pin  37  within a plane, and is connected to an end of a knuckle  38  which has another end connected to the wheel hub. As the motor  32  rotates, the first end of the knuckle arm  36  is moved in a fore-aft direction whereas the knuckle  38  at the second end rotates in a circumferential direction, to set the corresponding one of the wheels  17   a  through  17   d  to a predetermined steering angle θ (see  FIG. 4 ). 
     The steering actuator  31  is controlled by a steering angle control unit  39  installed in the chassis  12 . The chassis  12  is also provided with a handlebar operation-amount sensor  40  which detects an amount by which the handlebar  24  was moved, and a detection signal is inputted to the steering angle control unit  39 . Based on the detection signal which represents the amount of handlebar operation, the steering angle control unit  39  calculates a target steering angle θ and controls the steering actuators  31 . 
     In addition to the above, the driver&#39;s seat  25  has a small-radius turn switch  41  for making a three-point turn when driving into a very narrow road or making a U turn; and a pivot turn switch  42  for making a pivot turn within a very narrow space. When the small-radius turn switch  41  gets turned ON, a small-radius turn signal is inputted to the steering angle control unit  39 . Likewise, when the pivot turn switch  42  gets turned ON, a pivot turn signal is inputted to the motor control unit  28  and the steering angle control unit  39 . The pivot turn switch  42  has a switching position for a left-turn and a switching position for a right-turn. It should be noted here that in place of an ON/OFF switching operation, the small-radius turn may be initiated by automatic recognition method based on the angle of steering made to the steering section and the vehicle driving speed. 
     The automobile according to Embodiment 1 has been described thus far. Next, description will cover functions of the automobile. 
     [Straight Drive] 
       FIG. 3  shows a state when the vehicle is driving straightly. Before the vehicle is moved, a signal from the handlebar operation-amount sensor  40  is picked and based on the signal, the steering angle control unit  39  calculates a steering angle (=0°). Then, the steering actuators  31  are controlled to set the wheels  17   a  through  17   d  to the obtained steering angle. As the accelerator pedal  26  at the driver&#39;s seat  25  is operated, the motor control unit  28  responds to drive the in-wheel motor driving devices  27 , whereby the rear wheels  17   c ,  17   d  are driven to move the vehicle straightly. Forward drive and rearward drive can be switched by using an unillustrated lever for example. 
     [Small-Radius Turning] 
     As shown in  FIG. 4 , when changing the driving directions such as when changing lanes, making a U turn, etc., steering operation is typically performed only to the front wheels  17   a ,  17   b . When it is necessary to make a three-point turn to drive the vehicle into a narrow path or to make a U turn, the small-radius turn switch  41  at the driver&#39;s seat  25  is operated. Then, the small-radius turn signal is inputted to the steering angle control unit  39 , and the unit  39  controls steering actuators  31  of the rear wheels  17   c ,  17   d , thereby setting the rear wheels  17   c ,  17   d  to steering angles −θ′, −δ′ respectively which are given by flipping steering angles θ, δ of the corresponding front wheels  17   a ,  17   b.    
     The above-described control eliminates what is generally known as the difference between a track followed by the front inner wheel and a track followed by the back inner wheel, and therefore enables a change of the driving direction in a small radius. For the sake of maintaining stability of the chassis  12 , however, the steering must be performed at a slower speed than a predetermined limit. Small-radius turning while backing up is achieved by the same control. 
     [Pivot Turning] 
     When pivot turning is necessary at a narrow parking space for example, the pivot turn switch  42  at the driver&#39;s seat  25  is operated. As the pivot turn signal is inputted to the steering angle control unit  39 , the unit  39  controls the steering actuators  31  for setting the wheels  17   a  through  17   d  to such angles that all of the wheels  17   a  through  17   d  have their wheel axes  18  in a radial direction of the wheel disposition circle D as shown in  FIG. 5 . Due to this control, the front wheels  17   a ,  17   b  are set in a forwardly narrowing pattern while the rear wheels  17   c ,  17   d  are set in a rearwardly narrowing pattern. 
     Simultaneously, a pivot turn signal (e.g., for a right turn (see Arrow B in  FIG. 5 )) is inputted to the motor control unit  28 . Then, as shown in  FIG. 5 , the left rear wheel  17   c  rotates in the forward driving direction while the right rear wheel  17   d  rotates in the rearward driving direction. In other words, these wheels are set to rotate in opposite directions. The left and the right front wheels  17   a ,  17   b  follow their respective rear wheels  17   c ,  17   d , i.e., the left front wheel  17   a  is rotated in the forward driving direction while the right front wheel  17   b  is rotated in the rearward driving direction. 
     For a four-wheel drive vehicle, the left wheel and the right wheel are set to rotate in mutually opposite directions in both of the front pair and the rear pair of wheels (namely, the left front wheel  17   a  is set for forward driving; the right front wheel  17   b  is set for rearward driving; the left rear wheel  17   c  is set for forward driving; and the right rear wheel  17   d  is set for rearward driving). At the same time, both of the wheels on the left side are set to rotate in the same direction, with both of the wheels on the right side to rotate in the same direction; namely, the left front wheel  17   a  and the left rear wheel  17   c  are both set for the forward driving whereas the right front wheel  17   b  and the right rear wheel  17   d  are both set for the rearward driving. As a result, the chassis  12  and a body  19  turn on the center O, within the maximum circle E, or virtually within the chassis circle C. 
     In the above-described pivot turning, the minimum space necessary for the turning is practically the space of the chassis circle C. Since the wheel disposition circle D and the body  19  are within the chassis circle C, there is nothing protruding out of the space. Therefore, there is no interference with the surrounding objects. 
     It should be noted here that as shown in  FIG. 5 , part of the wheels  17   a  through  17   d  come out of the chassis circle C during the pivot turning, but such is well absorbed in a normal margin of the parking space and therefore will not pose any substantive problems. 
     Because of these properties, this vehicle provides such an advantage that when driving out of a narrow parking space where the vehicle was driven into by forward driving, the driver can simply make a pivot turn and then get out of the space by forward driving, although drivers in conventional automobiles have to get out of the space by backing up his/her vehicle. 
     Also, since in-wheel motor driving devices  27  are used, it is possible to provide a sufficient space in the front part of the chassis  12  even if the vehicle is of a front wheel drive type. For this reason, it is possible to provide the platform  22  in a front part of the body  19 . This provides a wide view at the time of getting out of the vehicle for increased safety in getting in and out of the vehicle. Also, no extra space is required on the left nor right side of the parking space for getting in and out of the vehicle. Further, even if the vehicle was driven forwardly into a narrow parking space with a dead end, it is possible to get out of the vehicle from the open-end side of the parking space by making a pivot turn. 
     Thus far, description has been made for a four-wheel automobile. However, the present invention is also applicable to three-wheel automobiles as shown in  FIG. 6 .  FIG. 6  shows an embodiment in which the left and the right rear wheels  17   c ,  17   d  are equipped with in-wheel motor driving devices  27 , but the in-wheel motor driving device  27  may be provided only in the front wheel  17   a  or may be provided in each of the three wheels. 
     REFERENCE SIGNS LIST 
     
         
         A Intersection between kingpin axis and ground 
           12  Chassis 
           13  Frame 
           13   a  Frame end edge 
           13   b ,  13   c  Frame side edge 
           14  Floor panel 
           15  Center portion 
           15   a  Front end portion 
           15   b  Rear end portion 
           15   c  Left side portion 
           15   d  Right side portion 
           16  Wheel housing 
           17   a - 17   d  Wheels 
           18  Wheel axis 
           19  Cabin 
           20  Cylinder portion 
           21  Top panel 
           22  Platform 
           23  Window 
           24  Handlebar 
           25  Driver&#39;s seat 
           26  Accelerator pedal 
           27  In-wheel motor driving device 
           28  Motor control unit 
           29  Independent-steering apparatus 
           30  Brake pedal 
           31  Steering actuator 
           32  Motor 
           33  Linear motion mechanism 
           34  Nut 
           35  Screw rod 
           36  Knuckle arm 
           37  Corner pin 
           38  Knuckle 
           39  Steering angle control unit 
           40  Handlebar operation-amount sensor 
           41  Small-radius turn switch 
           42  Pivot turn switch