Abstract:
A compensating means ( 28 ) for compensating for different wheel turn angles in a vehicle, the vehicle having a plurality of wheels ( 12, 14, 16, 18 ) at least two of which ( 12, 14 ) are operatively connected by a drive system ( 22, 30 ) so as to turn simultaneously, the compensating means being adapted to be used with the drive system; the compensating means ( 28 ) including a first rotatable means ( 46 ) for rotation about a central shaft ( 44 ), a second rotatable means ( 48 ) for rotation about the central shaft ( 44 ), the first means ( 46 ) and the second rotatable means ( 48 ) being concentric, and a connecting means ( 52, 54 ) operatively connecting the first rotatable means ( 46 ) and the second rotatable means ( 48 ) for limited relative angular movement therebetween.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to an improved steering system for a hand-propelled vehicle and refers particularly, though not exclusively, to an improved all-wheel steering system for such vehicles.  
         REFERENCE TO RELATED APPLICATION  
         [0002]    The invention of this application is particularly useful with the invention disclosed in our earlier Australian patent application PP1990 filed Feb. 26 1998 (our“earlier Application”), the contents of which are hereby incorporated by reference. However, the present invention is not to be limited to use only with vehicles of the category described in our earlier application.  
         DEFINITIONS  
         [0003]    Throughout this specification reference to a vehicle is to be taken as including all hand-propelled or hand-drawn vehicles of the general category described in our earlier Application.  
           [0004]    Furthermore, reference throughout the specification to a drive system is to be taken as including all forms of drive system in the general category as described in our earlier Application.  
         BACKGROUND TO THE INVENTION  
         [0005]    In our earlier Application there is described a system for providing multi-wheel steering, normally four-wheel steering, for smaller hand-propelled vehicles such as supermarket trolleys, work trolleys, and the like. In certain instances, there needs to be incorporated a form of compensation so that, for example, the angle of turn of the radially outer wheels will be different to that of the radially inner wheels. This is particularly important in a device such as a supermarket trolley which can turn corners very tightly to negotiate the aisles of a supermarket. Therefore, there needs to be a differentiating mechanism to allow this to happen without scrubbing the tyres of the wheels.  
           [0006]    Furthermore, although the invention of our earlier Application will tend to stabilise wheel movement, over uneven terrain there could be shock transmitted from one wheel through the drive system. Therefore, by having a compensating mechanism, there will also be included the ability to compensate for limited, unwanted adverse movement of a particular wheel or wheels.  
           [0007]    It is therefore the principal object of the prevent invention to provide a compensating means for a vehicle (as hereinbefore defined) so that the drive system (as hereinbefore defined) will allow for different radii of different wheels.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0008]    With the above and other objects in mind, the present invention provides a compensating means for compensating for different wheel turn angles in a vehicle (as hereinbefore defined), the vehicle having a plurality of wheels at least two of which are operatively connected by a drive system (as hereinbefore defined) so as to turn simultaneously, the compensating means being adapted to be used with the drive system; the compensating means including a first rotatable means for rotation about a central shaft; a second rotatable means for rotation about the central shaft, the first rotatable means and the second rotatable means being concentric, and a connecting means operatively connecting the first rotatable means and the second rotatable means for limited relative angular movement therebetween.  
           [0009]    Preferably, the vehicle is a supermarket trolley. More preferably, it has four wheels, all of which are linked by the drive system. Advantageously, the drive system is in the form of a cable, belt, v-belt, chain, or the like.  
           [0010]    The first rotatable means may be a cylindrical drum, as may be the second rotatable means. Preferably, the central shaft extends upwardly beyond the second rotatable means.  
           [0011]    The connecting means may include a pin attached to the first rotatable means and extending upwardly through an elongate, arcuate slot in the second rotatable means. More preferably, the pin extends upwardly beyond the second rotatable means.  
           [0012]    There may be provided a biasing system including two generally parallel and spaced apart arms pivotally attached to the second rotatable means at one side thereof and extending beyond the opposite side, there being provided a spring operatively connecting the two arms, the central shaft and the pin being located between and acting upon and being acted upon by the two arms.  
           [0013]    It is preferred that the compensating means be mounted to the vehicle by means of an arm pivotally attached to the vehicle and to the compensating means, the arm having a spring between it and the vehicle. 
       
    
    
     DESCRIPTION OF DRAWINGS  
       [0014]    In order that the invention may be fully understood there shall be described a number of embodiments incorporating the principal features of the present invention, the description being with reference to the accompanying illustrative drawings in which:  
         [0015]    [0015]FIG. 1 is a schematic top-plan view of the compensating means of the present invention;  
         [0016]    [0016]FIG. 2 is a side view of the compensating means of FIG. 1;  
         [0017]    [0017]FIG. 3 is a front view of the compensating means of FIGS. 1 and 2;  
         [0018]    [0018]FIG. 4 is an enlarged top-plan view of the compensating means of FIGS.  1  to  3 ;  
         [0019]    [0019]FIG. 5 is a front view corresponding to FIG. 4;  
         [0020]    [0020]FIG. 6 is a view corresponding to FIG. 1 showing the respective angles when a left turn is being undertaken;  
         [0021]    [0021]FIG. 7 is a view corresponding to FIG. 6 but without the angles indicated, and showing a sharp left turn;  
         [0022]    [0022]FIG. 8 is a view corresponding to FIG. 7 but showing independent wheel movement;  
         [0023]    [0023]FIG. 9 is, a top-plan view of a second embodiment of the present invention;  
         [0024]    [0024]FIG. 10 is an end view of the embodiment of FIG. 9;  
         [0025]    [0025]FIG. 11 shows the embodiment of FIGS. 9 and 10 in a left turn position; and  
         [0026]    [0026]FIG. 12 is a view corresponding to FIG. 11 but in a right turn position. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0027]    To refer firstly to FIGS. 1, 2 and  3  there is shown a vehicle generally designated as  10  and which in this instance is to represent a common device such as a supermarket trolley.  
         [0028]    The vehicle  10  has four wheels  12 ,  14 ,  16  and  18  each mounted on a vertical swivel or castor axle  20  and which is concentric with and attached to a gear or drum  22 . Two further idler gears  24 ,  26  are provided. A compensating means generally designated as  28  is also included. A continuous belt  30  passes around the gears  22 ,  24 ,  26  as well as the compensating means  28  (as will be described below) such that a four-wheel steering is created in accordance with our earlier Application.  
         [0029]    The belt  30  is preferably a form of belt having a number of evenly-spaced openings  32  along its length, with the gears  22 ,  24 ,  26  having projections  34  to engage in openings  32  so that the belt  30  can drive gears  22 ,  24 ,  26 , and via versa. In this way, rotation of any one wheel  12 ,  14 ,  16 ,  18  about its castor axle  20  will cause movement of the belt  30  by means of the gear  22  for that particular wheel, and this will cause the other gears  22 ,  24 ,  26  to also rotate to effect steering.  
         [0030]    To now refer to FIGS. 4 and 5, there is shown in some detail the compensating means  28 . Here, there is an arm  36  which at one end  38  is pivotally attached to the vehicle  10  by means of a pivot pin  40 . At its other end  42  mounted on the arm  36  in a secure manner is a central shaft  44 . Mounted on central shaft  44  for rotation relative thereto is a first rotating means  46  which, as shown, is a cylindrical drum of greater diameter than height. In this instance, the height of the first rotating means  46  is slightly greater than the height of the belt  30 . The first rotating means  46  has a number of projections  34  which are adapted to engage at openings  32  on belt  30 . Therefore, movement of belt  30  will cause a rotation of first rotating means  46 , and vice versa.  
         [0031]    Also mounted on central shaft  44  is a second rotating means  48  which is generally the same as first rotating means  46 , although this need not always be the case. The shaft  44  extends upwardly above the upper surface  50  of second rotating means  48 .  
         [0032]    The second rotating means  48  also has a number of projections  34  which engage in openings  32  of belt  30 . Therefore, similarly, movement of belt  30  will cause movement of second rotating means  48 , and vice versa. It is to be noted from FIGS.  1  to  5  that the belt  30  passes around first rotating means  46  In the opposite way to that of second rotating means  48 .  
         [0033]    Securely attached to first rotating means  46  and extending upwardly therefrom is a pin  52 . Pin  52  passes through an elongate, arcuate slot  54  in second rotating means  48 . The slot  54  has a first end  56  and second end  58 . The pin  52  projects upwardly beyond the upper surface  50  of second rotating means  48 .  
         [0034]    Mounted on upper surface  50  are two generally parallel arms  60 ,  62  pivotally attached thereto by pivot pins  64 . The arm  60 ,  62  extend across the substantial portion of the upper surface  50  and beyond the circumference of second rotating means  48 . At the outer ends  66  the two arms  60 ,  62  have an upwardly extending lug  68  to which is connected one end of a spring  70 . Located between the arms  60 ,  62  is the upper end of central shaft  44  and pin  52 .  
         [0035]    It is preferred that the arm  36  is biased relative to the vehicle by means of a second spring  72 .  
         [0036]    As can be seen from FIG. 6, if the vehicle  10  is moving along a curve, the radius of curvature for the wheels  12 ,  18  will be quite different to that of the wheels  14 ,  16 . In this instance it is assumed that the radius of curvature for the wheel  12  is 1.53 metres—a fairly common radius in a supermarket situation. As can be seen, that radius of curvature would also pass through the castor axle  20  of wheel  18 . However, the radius of curvature for wheel  14  is 2.12 metres, for a standard supermarket trolley. That means that the angle of turn required for wheel  14  will be different to the angle of turn required for wheel  12 . Given the radii concerned, the angle required for wheel  12 , compared to the longitudinal axis, is 16 degrees. For wheel  14 , it is 11 degrees. A similar angle of 11 degrees is required for wheel  16 , and again an angle of 16 degrees is required for wheel  18 .  
         [0037]    Therefore, when the vehicle  10  is turned to the position shown in FIG. 6, wheel  12  will turn to the left, as will wheel  14 . Wheel  16 ,  18  turn to the right. Therefore, the belt moves as shown in the direction of the arrows.  
         [0038]    To refer now to FIG. 4, where the arrows have been supplanted, as the belt  30  move to the leg as indicated, the first rotating means  46  will be moved by the belt  30  in a generally clockwise direction. Therefore, pin  52  will act upon arm  60  so that pin  52  will slide in slot  54  towards end  56 . Arm  60  will pivot about the pin  64  and adopt the position as shown in FIG. 6. There will be resistance to arm  62  moving in a similar manner by virtue of arm  62  being pivoted around its pin  64  and acting on the upper end of central shaft  44 . Therefore, the arm  62  will not tend to follow arm  60 . However, by virtue of arm  60  being attached to second rotating means  48  it will cause some rotation of that second rotating means  48 . Therefore, the belt  30  on the right side of the compensating means  28  will move, but by a lesser amount. This is because that part of the belt passes around the second compensating means  48 . As such, the angle of the wheels  14 ,  16 , will be less than for the wheels  12 ,  18  and thus the necessary compensation is created.  
         [0039]    The degree of difference in the relative movement will vary according to the lengths of arm  60 ,  62  and in particular to the respective distances between pin  64  to central shaft  44 , and central shaft  44  to the upper end  66  of the arm  60 ,  62 . Also of significance is the tensile strength of spring  70 .  
         [0040]    As is shown in FIG. 7 for a sharp left turn, the extent of movement means that the resistance of the spring  70  is substantially overcome, and thus the second rotating means  48  will rotate about central shaft  44  by almost as much as first rotating means  46 . In this way the difference in angle between wheels  14 ,  16  as against wheels  12 ,  18  will be less as a percentage of the total angular movement. A difference of 5 degrees in  16  is a far greater percentage than a difference of 6 degrees in 45 degrees.  
         [0041]    In FIG. 8 there is shown the difficulty than can occur when one wheel (in this instance wheel  12 ) is subjected to sudden, sharp movement such as by a pot hole, crack or the like. In this instance the resistance in spring  70  is substantially overcome such that the wheels  14 ,  16  remains substantially straight-ahead, yet wheels  12 ,  18  can move to the relevant position. Clearly, upon the pot hole, crack or the like being overcome, wheels  12 ,  18  will return to the straight-ahead position.  
         [0042]    The effect of the spring  70  will also tends to bring both rotating means  46 ,  48  to the position as shown in FIGS.  1  to  3 —the straight-ahead position. Therefore, upon a turn or curve being completed, a user does not have to return the vehicle  10  to the straight-ahead position, it will automatically assume that position.  
         [0043]    Spring  72  assists in maintaining tension on the belt  30  at all times, and can also act as a shock-absorber in the event of sudden impact upon one or more of the wheels.  
         [0044]    To now refer to FIGS.  9  through to  12 , there is shown a second embodiment. In this second embodiment, like components have like reference numerals but with the addition of a prefix number  2 .  
         [0045]    Here, there is a vehicle  210  having four wheels  212 ,  214 ,  216  and  218 . Each of the wheels is mounted to the vehicle  210  by a cast or axle  220 . The wheels  212 ,  218  are arranged as a front and rear pair and the wheels  214 ,  216  are arranged as a front and rear pair. A compensating means  228  is placed between wheels  212 ,  214 .  
         [0046]    Each of the wheels  212 ,  214 ,  216 ,  218  has a larger diameter disc  274  and a smaller diameter disc  276 . As can be seen, With the left pair of wheels  212 ,  218 , the larger diameter discs  274  are above the smaller diameter discs  276 , and contact each other. In this way, if wheel  212  moves to the right, wheel  218  turns to the left. A similar situation applies with the wheels  214 ,  216 , except that their smaller diameter disc  276  is above the larger diameter disc  274 , but the larger diameter discs  274  still contact each other such that the same reverse angle movement occurs.  
         [0047]    With this arrangement, instead of belt  30  contacting the first and second rotating means,  46 ,  48  the larger diameter discs  274  contact the rotating means  246  and  248 . In all other respects, the compensating means  228  operates the same as the compensating means  28 .  
         [0048]    If one refers to FIGS. 11 and 12, it can be seen that for left turn and right turn, the wheels  212 ,  218  move at the same angle, and the wheels  214 ,  216  move at their angle (which may be an angle different to the wheels  212 ,  218 ) but the compensating means  228  will provide for the necessary change in angle.  
         [0049]    Naturally, the invention is not limited to the drive arrangements as shown in the two embodiments, and any form of drive arrangement may be used, including a chain, or other suitable device. Furthermore, there may be less than the four wheels illustrated, with the invention also being suitable for three wheeled, or more than four wheel steering systems.  
         [0050]    Whilst there has been described in the foregoing description preferred embodiments of an improved steering system for a hand-propelled vehicle it will be understood by those skilled in the technology concerned that many variations or modifications in details of design or construction may be made without departing from the scope of the present invention.  
         [0051]    It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.  
         [0052]    It will also be understood that the term“comprises” (or its grammatical variants) as used in this specification is equivalent to the term “includes” and should not be taken as excluding the presence of other elements or features.