Abstract:
A steering cable arrangement wherein front wheel steering drums turn at different rates to keep the axes of the front wheels intersecting with the axis of the rear wheels at a single point. The cable path between the two drums is altered by the steering cables being threaded around sheaves on an arm whose position is controlled by a cam follower following a cam slot in at least one of the drums.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to co-owned U.S. application Ser. No. 13/675,043, filed on Nov. 13, 2012, the contents of which are incorporated herein by reference in their entirety. 
     FIELD OF INVENTION 
     This invention relates to a cable steering linkage for vehicles. 
     BACKGROUND OF INVENTION 
     Many schemes have been devised for a linkage between two front wheels of a vehicle so that the axes of each of the front wheels intersect on a single point on the common axis of the rear wheels. This geometry is sometimes referred to as Ackerman geometry of the steering, referring to the fist inventor of a linkage that approximated this geometry. Many of these linkages are complex and expensive to manufacture, others only approximate the Ackerman geometry, and most don&#39;t accommodate a zero turning radius of a vehicle. 
    
    
     
       DRAWINGS 
         FIG. 1  shows the Ackerman geometry 
         FIG. 2  shows a vehicle turning in zero radius circle. 
         FIG. 3  is a perspective of a construction vehicle with the steering system of embodiments of the invention 
         FIG. 4  shows detail perspective of the steering mechanism  120   
         FIGS. 5   a  and  5   b  schematically show the steering mechanism  120   
         FIG. 6  shows a schematic of an arrangement with a sliding member 
         FIG. 7  shows a schematic of an arrangement similar to  FIG. 6  with pivoting member 
         FIG. 8  shows dual mechanisms of  FIG. 5   a    
         FIG. 9  shows an arrangement with a steering wheel 
     
    
    
     DETAILED DESCRIPTION 
     This application discloses a steering mechanism to be used with the log handling apparatus disclosed in co-owned U.S. application Ser. No. 13/675,043, or with other suitable vehicles.  FIG. 1  illustrates the Ackerman geometry of steering. In order for all of the wheels to roll, without any tendency to be forced to slide sideways they must have the orientation as illustrated. The left front wheel axis  10 , the right front wheel axis  20  and the rear wheel axis  30  intersect a common point  40 . In other words, they roll in circles with a common center. At high speeds it is not necessarily desirable for all wheels to turn in circles with a common center, however slow moving vehicles carrying heavy loads perform best when the axes of all wheels intersect at a single point. It is also desirable for some slow moving construction vehicle to be able to turn in a circle of minimum radius.  FIG. 2  illustrates the wheels of a vehicle turning with one rear wheel at the center of the common circles. It is this geometry that heretofore has been difficult to achieve. 
       FIG. 3  gives an overall view of a vehicle with the cable steering system. The vehicle may be a log handling apparatus as disclosed in co-owned U.S. application Ser. No. 13/675,043, or any other suitable vehicle. The right steering drum  90  is coupled to the right front wheel  60  by means of a steering column such that rotation of the right steering drum  90  controls the direction of the right front wheel. Likewise the left steering drum  130  is coupled to the left front wheel  70  and controls the direction of the left front wheel  70 . The steering tiller  80  turns the right steering drum  90  and as a result controls the direction of the right front wheel  60 . Rear wheels  50  typically do not change direction. The steering mechanism  120  is shown in detail in  FIG. 4 . 
       FIG. 4  shows detail perspective of the steering mechanism  120 . Right steering drum  90  is shown without a top disk so that the cam slot  180  and cam follower  170  are visible. Cam follower  170  is part of arm  100 . Arm  100  rotates on pivot  160 . Cam follower  170  in cam slot  180  controls rotation of the arm  100  about pivot  160 . A first cable  140  affixed to the right steering drum  90  and left steering drum  130 . The first steering cable  140  leaves the left steering drum  130  from a counterclockwise direction. The cable then passes around a first turning pulley  190   a . This pulley is not essential to the operation of the turning mechanism however it reduces error in the path length of the steering cables. First steering cable  140  then passes clockwise around a first sheave  110   a  at one end of the arm  100  and then counterclockwise around a second sheave  110   b  at the other end of arm  100  and then onto the right steering drum in a counterclockwise direction. A second steering cable  150  affixed to the right steering drum  90  and left steering drum  130 . The second steering cable  150  leaves the right steering drum  90  from a counterclockwise direction. The cable then passes counterclockwise around first sheave  110   a  at one end of the arm  100  and then clockwise around second sheave  110   b  at the other end of arm  100 . Second steering cable  150  then passes around a second turning pulley  190   b  (which again is not essential) and then onto the left steering drum in a counterclockwise direction. 
     Note that the path length from where the first steering cable  140  leaves the left steering drum  130  to where it goes onto the right steering drum  90  may be changed by the angle of the arm. Similarly, the path length from where the second steering cable  150  leaves the right steering drum  90  to where it goes onto the left steering drum  130  may be changed by the angle of the arm. If the arm  100  turns clockwise on pivot  160  the path of first steering cable  140  becomes longer and thus has taken up slack in the first steering cable making it effectively shorter. At the same time, the path of second steering cable  150  becomes shorter by the same amount as first steering cable lengthens. Thus, the sum of the path lengths of the two steering cables remains essentially constant (differing only by any unintentional slack in the system). As a result the two steering drums would turn so the angle of the axis of the left front wheel to the axis of the rear axle and the angle of the axis of the right front wheel to the axis of the rear axle has changed. 
     In  FIGS. 5   a  and  5   b , which show the mechanism schematically, the actual steering drum surface is not shown so that the reader can more easily trace the paths of the steering cables. Also the two steering cables are shown as different line types to facilitate tracing their paths.  FIG. 5   a  shows the steering mechanism schematically with the wheels in their straight-ahead position.  FIG. 5   b  shows the result of turning the right front wheel  60  to the left. The cam follower  170  in the cam slot  180  caused the arm  100  to rotate clockwise about Pivot  160 . This action caused the path of first steering cable  140  to be longer (and the path of second steering cable  150  to be shorter by the same amount) resulting in the left steering drum  130  turning more to the left than the right steering drum  90 . 
     The shape of the cam slot can be determined two ways. First by empirical means, a marker may be substituted for the cam follower and a surface for the marker to mark on substituted for the surface in which the cam slot would be cut. The two front wheels are then steered according to the geometry of  FIG. 1 . The marker would then trace the path to be followed by the cam follower. A second way is to solve geometrically the path the cam follower should follow and plot it on the drum. 
     The turning pulleys  190   a ,  190   b  reduce an error that would introduced in the lengths of the paths of the steering cables were they not used. Also in practice, turnbuckles (not shown) are used to make fine adjustments to the length of the steering cables. 
     The essence of this invention is:
         the wheels are steered by cables on drums that in turn control the direction of the wheels,   the path lengths of the cables are controlled in such a manner that when one path length gets longer the other path length gets shorter by substantially the same amount, that is the sum of the path lengths is substantially constant,   and the ratio of the path lengths is controlled by a cam on at least one of the steering drums.       

     ADDITIONAL EMBODIMENTS 
     The above discussion described an embodiment of the present invention, however there are many other arrangements of cables, drums, cams, sheaves, and pulleys that fall within the spirit of the invention. 
       FIG. 6  shows another such arrangement. In this arrangement left or right movement of sliding member  6200  changes the path length of first steering cable  6140  and second steering cable  6150  such that as one path becomes longer the other path becomes shorter by the same amount and consequently the cables never become slack. Cam follower  6170  (in cam slot  6180 ) on one end of sliding member  6200  controls the position of the sheaves  6110  so as to rotate the left steering drum  6130  and left front wheel  670  and the right front steering drum  690  and right front wheel  660  according to the Ackerman geometry. Turning pulleys  6190  are fixed. Additional arrangements might have a sliding member move top to bottom in the figure as opposed to left and right. 
       FIG. 7  illustrates an arrangement where a pivoting arm  7200  moves a single pair of sheaves  7110  top to bottom in the figure to lengthen and shorten first steering cable  7140  and second steering cable  7150 , such that as one path becomes longer the other path becomes shorter by the same amount and consequently the cables never become slack. Cam follower  7170  (in cam slot  7180 ) on one end of pivoting arm  7200  (which pivots on pivot  7160 ) controls the position of the sheaves  7110  so as to rotate the left steering drum  7130  and left front wheel  770  and the right front steering drum  790  and right front wheel  760  according to the Ackerman geometry. Turning pulleys  7190  are fixed. 
     Still more arrangements can be made by using cam controlled sliding members to the turn arms with sheaves. Additional configurations may be made by using cam controlled pivoting members to actuate sliding members. Once the concept of changing cable path length is understood, the possible arrangements of parts is nearly endless, but they all fall within the spirit of this invention. 
       FIG. 8  illustrates an arrangement similar to  FIG. 5   a  except two arms (each having sheaves  8110 ) are used instead of one. Note that the cam slots are reshaped so that each moves the arm  8100  by half the amount they did in  FIGS. 5   a  and  5   b . Like  FIG. 5   a , the cam follower  8170  in the cam slot  8180  causes the arm  8100  to rotate clockwise about pivot  8160 . This action caused the path of first steering cable  8140  to be longer (and the path of second steering cable  8150  to be shorter by the same amount) resulting in the left steering drum  8130  (and left front wheel  870 ) turning more to the left than the right steering drum  890  (and right front wheel  860 ). 
       FIG. 9  is similar to  FIG. 8  except that a steering wheel  9210  has been introduced. Like  FIG. 8 , two arms  9100  (each having sheaves  9110 ) are used instead of one. Each of the cam slots  9180  are shaped so that each moves the arm  9100  by half the amount they did in  FIGS. 5   a  and  5   b . Like  FIG. 8 , the cam follower  9170  in the cam slot  9180  causes the arm  9100  to rotate clockwise about pivot  9160 . This action caused the path of first steering cable  9140  to be longer (and the path of second steering cable  9150  to be shorter by the same amount) resulting in the left steering drum  9130  (and left front wheel  970 ) turning more to the left than the right steering drum  990  (and right front wheel  960 ). With this arrangement there is symmetry turning the right or left. This concept of symmetrical arrangements could be applied to any of the schemes presented here. 
     CONCLUSIONS, RAMIFICATIONS AND SCOPE 
     As the reader can see this mechanism provides a precise and economical linkage between wheels to achieve Ackerman geometry. While there are many specifics shown in the embodiments presented here, the scope of the claims and their equivalents determine the scope of this invention. The term cable, as used in the claims, includes all flexible low-stretch linear material such as rope, line, chain and the like. In the claims, where the sum of path lengths is said to be constant, it is meant that the sum is substantially constant so that any error is not material to the operation of the mechanism. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.