Abstract:
A steering system for motor vehicles including agricultural machines is provided. The system includes a first conventional steering assembly for the front wheels to rotate only each of the front wheels within a respective first predetermined steering angle, each front wheel rotatable to a pre-determined first maximum value within its pre-determined angle. The system also includes a second steering assembly to independently steer a front axle and the front wheels within a second pre-determined steering angle. The second steering assembly is activated only after each of the front wheels have reached its respective first maximum value within its first pre-determined steering angle, during the conventional steering performed by the first conventional steering assembly.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage filing of International Application Serial No. PCT/EP2011/151324 filed on May 31, 2011, which claims priority to Italian Application Serial No. BO2010A000345 filed Jun. 3, 2012, each of which is incorporated herein by reference in its entirety for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention concerns a steering system for motor vehicles, in particular for agricultural machines. 
         [0003]    In particular, the present invention finds an advantageous, but not exclusive, application in the field of agricultural tractors, to which the following description will explicitly refer without losing its general character. 
       BACKGROUND 
       [0004]    As already known, in recent years a new steering system called SuperSteer™ has been introduced by the Applicant. 
         [0005]    In this SuperSteer™ steering system, during the steering step, each hub relating to each front wheel rotates around its own axis, synchronically to the whole front axle, which also rotates around a pin by a determined steering angle. 
         [0006]    This provides the tractor with an optimum manoeuvrability and with a drastically reduced turning radius. 
         [0007]    However, the SuperSteer™ system shows some drawbacks, the main one being that, during the steering of the front wheels, the whole front axle rotates around a vertical axis. This implies a side skid of the whole tractor, which is unwelcome both at low and high speeds. 
         [0008]    In particular, some side skids occurring during the steering at low speeds can be a problem with regard to the control of the implements coupled before or behind the tractor. 
         [0009]    In fact, even at low speeds, said side skids, due to the SuperSteer™ steering, are rather fastidious, in particular when the tractor must operate with a certain accuracy passing among the rows of plants in vineyards and orchards, or with front loaders. In fact, the side skids could lead to unwelcome movements of the implements coupled to the tractor, thus causing the crashing of the same implements against the row posts or against the plants, with resulting relevant damages. 
         [0010]    Therefore, the main aim of the present invention is providing a steering system for motor vehicles, in particular for agricultural machines, which is free from the aforesaid drawbacks and, at the same time, can be provided with a kind of SuperSteer™ steering effect. 
         [0011]    More precisely, in the steering system for motor vehicles object of the present invention, the wheel steering and the front axle steering are separated and mutually independent, at least until they reach some values of the steering angles of the front wheels previously determined by the manufacturer; once these pre-determined values have been surpassed, the front axle and the wheels are synchronically steered, just like a traditional SuperSteer™. 
         [0012]    A further aim of the present invention is providing a steering method for motor vehicles which allows to overcome the aforesaid drawbacks. 
         [0013]    According to the present invention it is therefore realized a steering system for motor vehicles and a corresponding steering method, according to what claimed in the independent claims, or in any one of the claims directly or indirectly dependent from the independent claims. 
       BRIEF DESCRIPTION 
       [0014]    In one aspect of the invention, a steering system for motor vehicles including agricultural machines is provided. The system includes a first conventional steering assembly for the front wheels to rotate only each of the front wheels within a respective first predetermined steering angle, each front wheel rotatable to a pre-determined first maximum value within its pre-determined angle. The system also includes a second steering assembly to independently steer a front axle and the front wheels within a second pre-determined steering angle. The second steering assembly is activated only after each of the front wheels have reached its respective first maximum value within its first pre-determined steering angle, during the conventional steering performed by the first conventional steering assembly. 
         [0015]    The invention may also include a steering system wherein when the front wheels are at a position which is less than their first maximum value of their first pre-determined steering angles the first conventional steering assembly is configured to further rotate each front wheel from a minimum to the first maximum value of its first pre-determined steering angle, and when the front wheels are rotated to a position which is at the first maximum value of their pre-determined steering angles, the second steering assembly activates to simultaneously rotate the front axle between minimum and maximum values within a second pre-determined steering angle, such that the front wheels are further rotatable relative to the rotation of the front axle such that the front wheels are rotatable to a pre-determined second maximum value. 
         [0016]    In another aspect of the invention, a steering method for motor vehicles, including agricultural machines, is provided. The method includes the step of using a first conventional steering assembly for steering front wheels of the vehicle until the front wheels reach pre-determined respective first maximum steering angles. The method also includes the step of activating a second combined steering assembly of both the front wheels and of a front axle on which the front wheels are mounted after the first pre-determined respective steering angles of the front wheels is reached. The method further includes the step of rotating the front axle along a second pre-determined steering angle, causing further rotation of the front wheels, such that the front wheels reach pre-determined second maximum steering angles. 
         [0017]    The method may also include, in the step of activating a second combined steering assembly, activating a signal which produces activation of the second combined steering assembly of both the front wheels and of the front axle on which the front wheels are mounted. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    For a better understanding of the present invention two preferred embodiments are now described, only for exemplificative and not limitative purpose, with a reference to the enclosed drawings, wherein: 
           [0019]      FIG. 1  shows a side view of a first embodiment of an agricultural tractor comprising a first embodiment of a steering system according to the invention; 
           [0020]      FIGS. 2 ,  3 ,  4  show a plan view of the tractor of FIGS.  1 , 9  in different steering arrangements; 
           [0021]      FIG. 5  shows an enlarged plan view of a front portion, in a first arrangement, of the tractor shown in  FIGS. 1 ,  2 ,  3 ,  9 ; 
           [0022]      FIG. 6  shows an enlarged plan view, in a second arrangement, of the front portion shown in  FIG. 4 ; 
           [0023]      FIG. 7  shows a front view of the first embodiment of the steering system according to the invention, wherein the transversal oscillation of the front axle without suspension stands out; 
           [0024]      FIG. 8  shows an enlarged side view of the first embodiment of the steering system according to the invention applied to the agricultural tractor of  FIG. 1 ; 
           [0025]      FIG. 9  shows a side view of a second embodiment of an agricultural tractor comprising a second embodiment (with suspension) of a steering system according to the invention; 
           [0026]      FIG. 10  shows an enlarged side view of the second embodiment of the steering system according to the invention shown in  FIG. 9 ; 
           [0027]      FIG. 11  shows a front view of the second embodiment of the steering system according to the invention, wherein the transversal oscillation of the front axle with suspension stands out; 
           [0028]      FIG. 12  shows an operating position of “maximum elevation” of a suspension comprised in the second embodiment of the steering system according to the invention; 
           [0029]      FIG. 13  shows an operating position of “minimum lowering” of a suspension comprised in the second embodiment of the steering system according to the invention; and 
           [0030]      FIG. 14  shows the maximum stroke of the suspension comprised in the second embodiment of the steering system according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    In  FIGS. 1-8  it is indicated, as a whole, a first embodiment of an agricultural machine, in particular a tractor, on which a first embodiment of a front steering system  100 , which is the specific object of the present invention, is mounted. 
         [0032]    The tractor  10  traditionally comprises a drive  5  to which a back axle  12  with two respective back wheels (W 1 ), (W 2 ), and a front axle  13  having two respective front wheels (W 3 ), (W 4 ) are associated. The drive  5  has a substantially longitudinally symmetrical axis (X). 
         [0033]    The drive  5  is able to support also an engine  7  and a control cab (not shown) and a fixed axle support  11 . 
         [0034]    Moreover, as shown hereinafter, the steering system  100  is controlled by an operator by means of a steering wheel (SW) ( FIG. 1 ). 
         [0035]    The operation of the components of the first embodiment of the system  100  will be explained with explicit reference to  FIGS. 2-8 . 
         [0036]    First of all, the system  100  comprises a pivoting support  101  hinged by means of a rotating pin  102  to the aforesaid fixed axle support  11 . The pivoting support  101  is able to rotate around a vertical axis (Y) which is also the axis of the rotating pin  102 . 
         [0037]    The front axle  13  is associated, in a way which will be better described hereinafter, to the pivoting support  101 . As previously stated, the two front wheels (W 3 ), (W 4 ) are mounted on said front axle  13 . 
         [0038]    As shown in more detail in  FIGS. 5 ,  6 , a hub  103 , associated to the front wheel (W 3 ), is able to rotate around a respective axis (K 1 ). 
         [0039]    Analogously, the hub  104  of the front wheel (W 4 ) is able to rotate around a respective axis (K 2 ). 
         [0040]    The rotation of the wheel (W 3 ) around the axis (K 1 ), controlled by an operator by means of the steering wheel (SW) ( FIG. 1 ), is carried out by means of an arm  105  connected to an oleodynamic actuator  200 . 
         [0041]    As shown in particular in  FIGS. 5 ,  6 , the arm  105  has a first mechanical articulation  106  with the corresponding hub  103 , and a second mechanical articulation  107  with an oleodynamic piston  108  belonging to the oleodynamic actuator  200 . 
         [0042]    Analogously, the rotation of the wheel (W 4 ) around the axis (K 2 ) is carried out by using an arm  109  ( FIGS. 5 ,  6 ), also connected to the oleodynamic actuator  200 . The arm  109  is provided, in turn, with a first articulation  110  with the corresponding hub  104 , and with a second mechanical articulation  111  with the oleodynamic piston  108  belonging to the oleodynamic actuator  200 . 
         [0043]    Therefore, the same oleodynamic piston  108 , suitably controlled by the steering wheel (SW), on the one hand pulls the hub  103 , which rotates by a certain angle (α 1 ) around the axis (K 1 ), while on the other hand pushes the hub  104  so that it rotates around the axis (K 2 ) by an angle (α 2 ) ( FIG. 5 ). 
         [0044]    Incidentally, as known, the two angles (α 1 ), (α 2 ) are different because of the locking geometry of respective hubs  103 ,  104  to the structure of the front axle  13 . 
         [0045]    In the example reported in  FIGS. 3 ,  5  both rotations (α 1 ), (α 2 ) of the front wheels (W 3 ), (W 4 ) are clockwise, so that the whole tractor  10  steers to the right. 
         [0046]    Obviously, if you wished to steer the tractor  10  to the left, the steering of the two front wheels (W 3 ), (W 4 ) should be counter clockwise. 
         [0047]    As shown in more detail in  FIG. 8  (see also  FIGS. 5 ,  6 ), the pivoting support  101 , which is advantageously shaped as a sector of a circle, is able to rotate around the pin  102  (having an axis (Y)) thanks to an actuator  112 , preferably oleodynamic. 
         [0048]    Moreover, the body  112 A ( FIG. 6 ) of said oleodynamic actuator  112  is hinged to the fixed axle support  11  by means of a pin  113  (having a vertical axis (Z)), whereas the free end of its shaft  112 B is hinged to the pivoting support  101  by means of a hinge  114 . 
         [0049]    In other words, the actuator  112  extends between the fixed axle support  11  and the pivoting support  101 , and makes the pivoting support  101  rotate around the axis (Y), thus angularly moving the pivoting support  101  with regard to the fixed axle support  11 . Obviously, during the rotation of the pivoting support  101  around the axis (Y), also the body  112 A of the oleodynamic actuator  112  will rotate around the axis (Z). 
         [0050]    As shown in more detail in  FIG. 8 , the fixed axle support  11  has a groove  11 A, shaped as an arc of a circle (see also  FIGS. 5 ,  6 ), wherein a projection  101 A (also shaped as an arc of a circle) of the pivoting support  101  is inserted. 
         [0051]    In other words, the pivoting support  101  is suspended to the fixed axle support  11  by means of the pin  102  and of the coupling between the projection  101 A and the groove  11 A. 
         [0052]    As always shown in  FIG. 8 , the front axle  13  is, in turn, suspended to the pivoting support  101  by means of two supporting braces  125 ,  126  projecting downward from the pivoting support  101 . The support  126  is shaped so that it lets a motion propeller shaft  127  pass towards the front wheels (W 3 ), (W 4 ). The front axle  13  can transversally oscillate with respect to an axis (H) ( FIGS. 7 ,  8 ) which is also the axis of the two supporting braces  125 ,  126 . 
         [0053]    Therefore, if the oleodynamic actuator  112  is operated, the pivoting support  101  rotates around the pin  102 ; for this reason also the front axle  13 , which is suspended to the pivoting support  101 , will rotate in the same way and by the same angle (β) as previously stated. 
         [0054]    In other words, in a first step, the steering of the front wheels (W 3 ), (W 4 ) will be of the conventional kind until reaching an angle (α 1 *), respectively (α 2 *), pre-determined by the manufacturer. Once overtaken the aforesaid pre-determined values (α 1 *), (α 2 ′) of (α 1 ), respectively (α 2 ), a steering of the Supersteer™ kind, having an angle (β), will add to the first one ( FIGS. 4 ,  6 ). When the vehicle starts to steer according to the Supersteer™ mode, also the front wheels (W 3 ), (W 4 ) keep synchronically rotating, thus moving from (α 1 *), respectively, (α 2 *), to a maximum value (α 1 max), respectively, (α 2 max). Incidentally, also the angle (β) varies from a value 0°, before the operation of the Supersteer™ mode, to a value (βmax). 
         [0055]    Therefore, the “maximum obtainable total steering” will be indicated by a maximum total angle (γmax) given by the sum of the maximum angles (α 1 max) and (βmax), since the angle (α 1 ) relating to the “internal wheel” (W 3 ) with respect to the steering direction is taken as reference angle. 
         [0056]    In this way, above all in case of moderate steering, the aforesaid unwanted side skids of the tractor are avoided because the steering is of the conventional kind. On the contrary, when a very large steering is required, the Supersteer™ steering system steps in. 
         [0057]    In short, the first embodiment of the steering system  100  object of the present invention comprises:
       a first conventional steering assembly  150 , comprising the axle  13 , two hubs  103 ,  104  and the oleodynamic actuator  200  to directly steer the hubs  103 ,  104 ;   and a second Supersteer™ steering assembly  160 , comprising the pivoting support  101 , hinged to the fixed axle support  11 , and an oleodynamic actuator  112  to rotate the pivoting support  101  with regard to the fixed axle support  11  around a pin  102 ; the second steering assembly  160  being able to support also the axle  13  which rotates together with the pivoting support  101 .       
 
         [0060]    As previously stated, the second Supersteer™ steering assembly  160  is operated only after that a conventional steering of the front wheel (W 3 ), (W 4 ) having pre-determined values (α 1 *), respectively, (α 2 ′) has been carried out by means of the first conventional steering assembly  150 . 
         [0061]    In a first possibility, (α 1 *)&lt;(α 1 max), and (α 2 *)&lt;(α 2 max) such that both steering assemblies  150 ,  160  move simultaneously the front wheels (W 3 ), (W 4 ) from (α 1 *), (α 2 ′) to, respectively, (α 1 max*), (α 2 max). 
         [0062]    In a second possibility, (α 1 *)=(α 1 max), and (α 2 *)=(α 2 max) with a subsequent action of the Supersteer™ steering assembly  160  only once achieved angles (α 1 max) and (α 2 max) by using the conventional steering assembly  150  only. 
         [0063]    Therefore, the steering method for motor vehicles, which is the further object of the present invention, comprises:
       a first normal steering step having pre-determined angles (α 1 *), (α 2 *); followed by   a second Supersteer™ steering step having an angle (β), whereas the angles (α 1 ), (α 2 ) vary from initial values (α 1 *), respectively, (α 2 *) to final values (α 1 max), respectively, (α 2 max).       
 
         [0066]    In other words, after having reached the pre-determined conventional steering values (α 1 *), (α 2 *), it is produced a signal which allows a further steering by an angle (β) by means of a Supersteer™ steering, and the completing of (α 1 ), (α 2 ) until reaching the maximum values (α 1 max), (α 2 max). 
         [0067]    The signal which allows a further steering by an angle (β) can be generated by sensors (not shown), e.g. allocated on the hubs  103 ,  104 , and processed by an electronic processor (not shown). In other words, such sensors are able to detect instant by instant the effective values of the angles (α 1 ), (α 2 ) for generating a signal when the values (α 1 *), (α 2 *) have been reached. Moreover, the manufacturer has the possibility to set the values of the angles (α 1 *), (α 2 *) by using a conventional controller (not illustrated) before the sale of the tractor. 
         [0068]    Obviously, the return steering to a rectilinear position is carried out by the Supersteer™ steering system  160  by means of a 0° value return of angle (β), and of a return of the angles (α 1 ), (α 2 ) from the maximum values (α 1 max), respectively, (α 2 max) to values (α 1 *), respectively (α 2 *). Such step is followed by a further step wherein a return of the angles (α 1 ), (α 2 ) to 0° value is achieved by using the conventional steering system  150  of the front wheels (W 3 ), (W 4 ). 
         [0069]    According to a second embodiment of the present invention, the front axle  13  of a tractor  10 * is of the suspended kind ( FIG. 9 ). This second embodiment will be described hereinafter with a reference to  FIGS. 2-6 ,  9 - 14 , wherein the same reference numbers have been used for the components belonging to both embodiments. 
         [0070]    As shown in particular in  FIGS. 10 ,  11  the second embodiment differs from the first one because of the presence of an oscillating intermediate support  130  of the axle  13 ; this intermediate axle  130  belongs to a shock-absorbing apparatus  120 , which will be described hereinafter. 
         [0071]    The oscillating intermediate support  130  is suspended to the pivoting support  101  by means of two pins  131 ,  132  having an axis (H) ( FIGS. 10 ,  11 ). 
         [0072]    The oscillating intermediate support  130  is provided with two ears  133 ,  134  ( FIG. 11 ), each of them being mechanically coupled to the back (or front) part of the front axle  13  by means of a respective pin  135 ,  136  (having an axis (T)). 
         [0073]    As shown in  FIGS. 10 ,  11  two shock-absorbing cylinders  171 ,  172  are arranged between the oscillating intermediate support  130  and the front (or back) part of the front axle  13 ; but also a mono-cylinder system can be used (not shown). 
         [0074]    The shock-absorbing cylinder  171  is hinged to the oscillating intermediate support  130  by means of a pin  173  (having an axis (J 1 )), and to the front axle  13  by means of a pin  174  (having an axis (J 2 )). 
         [0075]    Analogously, the shock-absorbing cylinder  172  is hinged to the oscillating intermediate support  130  by means of a pin  175  (having an axis (J 1 )) and to the front axle  13  by means of a pin  176  (having an axis (J 2 )). 
         [0076]    In use, when the pivoting support  101  rotates around the pin  102  (having an axis (Y)), also the oscillating intermediate support  130  and the front axle  13 , which are both suspended to the pivoting support  101 , will rotate by the same angle. At the same time, the front axle  13  is also cushioned thanks to the presence of the two front (or back) shock-absorbers  171 ,  172  allowing the oscillation of the front axle  13  around the two pins  135 ,  136  ( FIGS. 10-14 ). 
         [0077]    As always shown in  FIG. 11 , a transversal oscillation angle (τ) is formed between the axle  13  and the pivoting support  101 . 
         [0078]    In order to limit the width of the transversal oscillation angle (τ) to a pre-determined maximum value (τmax), between the pivoting support  101  and the oscillating intermediate support  130 , two pairs of end elements  121 A,  121 B are provided, on the one side with respect to the axis (H), and  122 A,  122 B, on the other side (always with respect to the axis (H)). The manufacturer, suitably adjusting the height of the pairs of end elements  121 A,  121 B, respectively,  122 A,  122 B, imposes a certain pre-determined maximum transversal oscillation angle (τmax) of the axle  13 , so that the motor vehicle cannot bend too much laterally, in order to avoid any situation wherein the motor vehicle can be turned over. The advantage of the described situation is that the maximum transversal oscillation angle (τmax) between the pivoting support  101  and the oscillating intermediate support  130  is independent with respect to the vertical position of the suspension and with respect to the steering angles (α 1 ), (α 2 ) of the front wheels (W 3 ), (W 4 ). 
         [0079]    In other words, the maximum value (τmax) of the transversal oscillation (τ) of the front axle  13  is independent from the relative position between the oscillating intermediate support  130  and the front axle  13 . 
         [0080]    Moreover, the maximum value (τmax) of the transversal oscillation (τ) of the front axle  13  is independent from the steering angles (α 1 ), (α 2 ) of the front wheels (W 3 ), (W 4 ). 
         [0081]    In order to better illustrate the operation of the second embodiment of the present invention,  FIG. 12  shows the operating position of “maximum elevation” and  FIG. 13  shows the operating position of “minimum lowering” of the shock-absorbing cylinders  171 ,  172 . 
         [0082]    Furthermore,  FIG. 14  shows the maximum stroke (CS) of the shock-absorbing apparatus  120 , wherein the front wheels (W 3 ), (W 4 ) take the absolute lowest, respectively highest, position. The stroke (CS) of the shock-absorbing apparatus  120  will therefore be given by the distance between the highest and the lowest position between the two wheels (W 3 ), (W 4 ). 
         [0083]    The main advantage of the system, and of the corresponding method according to the present invention, is represented by the fact that with limited steering angles the steering system behaves like a normal system, therefore without implying side skips of the tractor. By increasing the steering angle of the tractor, for instance at the head-land, wherein a possible small side skip of the tractor would have no relevance, a Supersteer™ steering system, which remarkably increases the steering capacity of the tractor, is inserted in series. 
         [0084]    Moreover, when the system according to the present invention is of the suspended kind, it can have the advantages of a dampened axle which avoids, at high speeds, the pitching of the tractor, above all during the road transport.