Abstract:
A self-propelled vehicle capable of making turns with tight turning radii, which comprises a frame with a pair of traction wheels, at least one orientable wheel, and one or more driver&#39;s posts. The vehicle has a single motor that is kinematically connected to a driving shaft and means for functional connection between the driving shaft and each one of the two traction wheels. Each one of the two traction wheels can therefore be actuated independently of the other thanks to the presence of steering means suitable to act on the connection means.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of PCT Application No. PCT/EP01/13947 filed on Nov. 29, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a self-propelled vehicle particularly for making turns with small turning radii.  
         BACKGROUND OF THE INVENTION  
         [0003]    It is known that self-propelled vehicles are already commercially available which allow to make turns with small turning radii.  
           [0004]    Vehicles, such as self-propelled excavators or others, which currently allow to make turns with small turning radii generally use motors that drive one traction wheel each, so as to allow the vehicle to turn about the wheel to which rotation is not transmitted at a given time and which therefore acts as a pivot.  
           [0005]    If achieving turns with even tighter turning radii is sought, the two driving wheels can be made to turn even in opposite directions.  
           [0006]    In a vehicle of the above described type, since the rotation of each driving wheel is controlled by a motor and by a control unit, which is generally hydraulic, high manufacturing and maintenance costs are incurred for such motor.  
         SUMMARY OF THE INVENTION  
         [0007]    The aim of the invention as described hereinafter is to provide a self-propelled vehicle that is capable of making turns with small turning radii without suffering the above mentioned drawbacks.  
           [0008]    An object of the present invention is to provide a self-propelled vehicle having a new transmission and steering system that has immediate response and high reliability.  
           [0009]    Another object of the present invention is to provide a self-propelled vehicle that is constructively very simple, easy to use and low in cost.  
           [0010]    This aim and these and other objects that will become better apparent hereinafter are achieved by a self-propelled vehicle capable of making turns with tight turning radii, having a frame with a pair of traction wheels, at least one orientable wheel, at least one driver&#39;s post, characterized in that it comprises a single motor, a driving shaft kinematically connected to said motor, means for functional connection between said driving shaft and each wheel of said pair of traction wheels, which can thus be actuated independently of the other wheel, and steering means adapted to act on said functional connection means. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    Further characteristics and advantages of the present invention will become better apparent from the following detailed description of a preferred but not exclusive embodiment of a self-propelled vehicle illustrated in the accompanying drawing, wherein the only FIGURE is an exploded perspective view of a self-propelled vehicle provided with a traction and steering apparatus according to the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]    With reference to the drawing, a self-propelled vehicle  1  according to the invention comprises a frame  2  on which there is a driver&#39;s post  3 . The frame  2  of the vehicle supports in any suitable manner a motor  4 , which can be any of an electric or internal-combustion type, and two traction wheels  5 , which are preferably mounted so that they can turn about a same axis.  
         [0013]    The motor  4  is designed to actuate a driving shaft or motion distribution shaft  6 , which is rotatably supported by the frame  2 . This actuation can be achieved advantageously by means of a V-belt  7 , which transmits the motion from a first pulley  8  keyed to the output shaft of the motor  4  to a second pulley  9  keyed to the driving shaft  6 . The kinematic connection between the motor  4  and the shaft  6  can in any case also be achieved in another manner, for example by means of a chain link, a gear transmission and a direct-drive arrangement.  
         [0014]    The motor shaft  6  is designed to provide rotary motion to the two traction wheels  5  independently of each other by way of functional connection means that comprises two intermediate shafts  10 , which are parallel to the driving shaft  6  and can oscillate with respect to the shaft  6 , each supporting a driven pulley  11  and a driving pulley  12  which are connected one another, as explained hereinafter. The driven pulley  11  receives its motion from the driving shaft  6  by means of an elastic belt  13 , while the driving pulley  12  transmits motion to a traction pulley  14  that rotates rigidly with a respective traction wheel  5  by means of a belt  15 , which is also elastic.  
         [0015]    Since the intermediate shaft  10  oscillates with respect to the frame  2 , it can move toward or away from the axis of the respective traction wheel  5 . This entails the possibility to increase or decrease the tension of the belt  15 , with the result that if the tension of the belt  15  is reduced, the belt  15  slips on the traction pulley  14 , consequently making it impossible to transfer the rotary motion to the traction wheel  5 .  
         [0016]    In the exemplary embodiment shown in the drawing, the oscillating movements of the intermediate shaft  10  are actuated by a lever  16 , having one end articulated to a pivot  16   a  that can be fixed to the frame  2  and the other end advantageously shaped as a control handle for the application of force on the part of the operator&#39;s hand. In an intermediate position, and advantageously proximate to its pivot  16   a , the lever  16  further has a hole  17  for accommodating a supporting pivot for an intermediate shaft  10 . A second supporting element  18  for said intermediate shaft  10  is pivoted to the pivot  16   a  of the lever  16  and forms with it a fork-like component. The supporting element  18 , if required, can be anchored to any other suitable point of the lever  16 .  
         [0017]    The lever  16  and the supporting element  18  allow to support each shaft  10  and rigidly couple it to the lever  16 . This implies that through the actuation of the lever  16  the user can control the oscillating motion of the shaft  10  and accordingly can act on the functional connection between the driving shaft  6  and the two traction wheels  5 .  
         [0018]    The angular strokes of the lever  16  are controlled by two opposite springs  19 , which tend to keep the lever  16  in an intermediate (vertical) inactive position, in which both traction wheels  5  are operatively connected to the shaft  10  and therefore to the motor  4 , so that, when the motor is running, the vehicle  1  moves along a straight path.  
         [0019]    The springs  19  are connected to the opposite sides of an element  22  protruding laterally from the frame  2  and defining a slot through which the lever  16  passes and adapted to define the stroke of the lever  16 .  
         [0020]    The connection between the driven pulley  11  and the driving pulley  12  occurs advantageously by interposing a torque-resistant coupling  20  of any suitable kind meant to damp the peaks of quantity of motion during engagement transients.  
         [0021]    Advantageously, the motor shaft  6  is provided, for example at one of its ends, with a respective reverse motion wheel  6   a , while the driving pulleys  12  are kinematically connected to a respective motion inversion wheel that, in FIG. 1, is arranged coaxially with the torque resistant coupling  20  and is supported by the respective intermediate shaft  10 .  
         [0022]    The arrangement of the reverse motion wheel  6   a  and of the respective motion inversion wheel is such that, in case the user, by acting upon the lever  16 , causes the intermediate shaft  10  to oscillate, i.e. to bring it towards the motor shaft  6 , the lateral surfaces of the reverse motion wheel  6   a  and of the motion inversion wheel, respectively, are brought in contact one with the other and thus in a kinematic coupling.  
         [0023]    In this way, it is possible to invert the rotation of one or both the traction wheels  5  (inverting, in practice, the rotation of the driving pulleys  12  that are kinematically connected, or in any case connectable, to the external surface of the torque-resistant coupling  20 ) by acting directly upon one or both levers  16 .  
         [0024]    In case both the motion inversion wheels are kinematically coupled to the respective reverse motion wheels  6   a , a reverse motion of the vehicle will be obtained while, if only one of the motion inversion wheel is kinematically coupled to the respective reverse motion wheel  6   a  (while keeping, at the same time, the other lever  16  in an intermediate position), it is possible to further reduce the steering radius causing the vehicle to steer about its axis.  
         [0025]    The vehicle  1  further has at least one and preferably two self-orientating wheels  21 , which allow easy steering of the vehicle, avoiding slippage on the surface on which the vehicle rests.  
         [0026]    When the operator does not act on the levers  16 , the springs  19  keep such levers in the inactive vertical position. In this condition, the belts  13  and  15  are tensioned and therefore the traction wheels  5  are both operatively connected to the driving shaft  6 ; this position of the two levers  16  accordingly allows the two traction wheels  5  to have the same rotation rate. The rotation rate of the two traction wheels can be optionally controlled by the operator by means of a conventional device for controlling the rotation rate of the motor  4  (a rheostat in the case of an electric motor, an accelerator lever in the case of an internal-combustion engine), but in this configuration the vehicle  1  moves in a straight line.  
         [0027]    If the operator wishes to steer the vehicle  1  for example to the right, he acts by moving back the lever  16  located to his right. The movement of the lever  16  reduces the distance between the intermediate shaft  10  and the axis of the right traction wheel  5 , and this entails loosening the tension of the belt  15 . At this point, the belt  15 , by slipping around the traction pulley  14 , does not transmit motion to the right wheel  5 , which accordingly remains motionless and free. Since the left traction wheel is always engaged in motion with the driving shaft  6 , it still has a given rotation rate, which allows the vehicle to turn right about the right traction wheel, which by having a zero rotation rate acts as a rotation pivot, so that the vehicle steers to the right with the smallest turning radius.  
         [0028]    The same operation, performed with the left lever  16 , allows the vehicle to turn left.  
         [0029]    It is evident that the described self-propelled vehicle  1  allows to achieve the above aim and objects, especially as regards low production costs, constructive simplicity and high reliability.  
         [0030]    All the details may further be replaced with other technically equivalent elements.  
         [0031]    The materials used, as well as the dimensions, may be any according to requirements.  
         [0032]    The disclosures in Italian Patent Application No. VR2000A000119 from which this application claims priority are incorporated herein by reference.