Abstract:
A vehicle has a pair of opposite drive wheels driven by a dual path hydrostatic transmission. Steering and speed/direction controls are effected by changing the displacement and/or direction of fluid flow through the pair of reversible, variable displacement pumps that are respectively coupled to fixed displacement ground wheel drive motors. The control mechanism for accomplishing steering and/or speed/direction control includes a steering rack that is caused to pivot about a fixed post in response to steering wheel movement. A first crank arm is coupled for pivoting in concert with the rack and a second crank arm is coupled for pivoting in concert with a pivot plate about a second axis, the pivot plate having a pair of connection points respectively coupled to control arms of the pair of pumps by a pair of pump control rods. The pivotal motion of the steering rack is transmitted to the pivot plate by a tie-rod coupled between the first and second crank arms. This tie-rod is parallel to a pivot support bar that swings about the fixed post in response to fore-and-aft movement of a speed/direction control lever, the pivot plate being pivotally mounted to the free end of the pivot support bar. Thus, the pivot support bar, first and second crank arms and the tie-rod cooperate to define a four-bar linkage that causes the pivot plate to retain its pivoted position about the second axis during speed/direction control so that such control is made independently of steering, and vice-versa.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a vehicle having ground drive wheels which are hydrostatically driven, and more particularly relates to controls for a dual-path hydrostatic drive system. 
     U.S. Pat. No. 5,649,606 granted to Bebernes et al. on Jul. 22, 1997 discloses a dual-path hydrostatic drive system which is controlled by a steering and ground speed control mechanism including a steering rack in the form of a sector which is pivoted to opposite sides of a neutral position in response to steering wheel operation. This movement of the steering rack is transmitted to a first sprocket of a timing belt drive having a second sprocket joined to an output member that is linked with the hydrostatic transmission pump controllers. 
     This steering control is not entirely satisfactory due to the cost and complexity of the timing belt drive, the latter requiring the center distance between its input and output sprockets to be adjusted to maintain proper belt tension while at the same time maintaining proper alignment between the two sprockets. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a steering and ground speed control mechanism which represents an improvement over the control mechanism disclosed in U.S. Pat. No. 5,649,606. 
     A broad object of the invention is to provide a steering and ground speed control mechanism for a dual-path hydrostatic transmission, the mechanism including a quadrant-shaped steering rack but being more economical and less complex than the control mechanism disclosed in U.S. Pat. No. 5,649,606. 
     A more specific object of the invention is to provide a control mechanism as set forth in the immediately preceding object wherein a four-bar linkage is used for transmitting pivotal motion of the steering rack quadrant to the output plate that is linked to the hydrostatic transmission pump controllers. 
    
    
     These and other objects will become more apparent from a reading of the ensuing description together with the appended drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a left front perspective view of a self-propelled windrower of the type with which the present invention is particularly adapted for use. 
     FIG. 2 is a schematic top plan view showing the placement of the hydrostatic drive system components within the general outline of the windrower shown in FIG.  1 . 
     FIG. 3 is an enlarged top plan view of the control mechanism for the drive system shown in FIG. 2, with the top plate of the mounting frame being shown in phantom outline for revealing components located beneath the plate, these components being shown in a condition corresponding to the steering wheel being in a “centered” position and the speed/direction control lever being in a “neutral” position. 
     FIG. 4 is an enlarged rear elevational view of the structure shown in FIG. 3, but with some parts broken away for clarity. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1 and 2, there is shown a self-propelled vehicle  10  in the form of a self-propelled mower-conditioner having a main frame  12  supported on right- and left-hand front drive wheels  14  and  16 , respectively, and on a pair of rear ground wheels  18  castor-mounted to opposite ends of a cross axle  20  that is mounted to the main frame  12 , in a known manner not shown, for oscillating about a horizontal, fore-and-aft axis located centrally between the wheels  18 . An operator&#39;s cab  22  is supported on the forward end of the main frame  12  and contains a seat  24  mounted to a floor (not shown) of the cab in easy reach of a steering wheel  26  positioned forwardly of the seat. Mounted to a right-hand armrest (not shown) of the seat  24  i a speed/direction control lever  28 . 
     The wheels  14  and  16  are driven by a dual-path hydrostatic transmission system  29  (FIG. 2) including right- and left-hand fixed displacement motors  30  and  32  respectively coupled to the right- and left-hand drive wheels  14  and  16 . Front and rear variable displacement, reversible pumps  34  and  36 , respectively, are conventionally fluid coupled to the motors  30  and  32 , as by respective pairs of supply/return lines (not shown), are mounted centrally on the main frame  12  and are coupled for being driven by an output shaft of the vehicle engine (not shown). The pumps  34  and  36 , respectively have swash plate control arms  38  and  40  that are each mounted for pivotal movement from a centered, zero displacement “neutral” position, as shown, with increasing rearward and forward movement respectively effecting increasing displacement so as to effect increasing forward and reverse driving speeds of the motors  30  and  32 . 
     Referring now also to FIGS. 3 and 4, there is shown a control mechanism  42  for receiving inputs from the steering wheel  26  and the speed control lever  28  and delivering corresponding outputs, in a manner described below, to the swash plate control arms  38  and  40  of the pumps  36  and  34 . Specifically, the control mechanism  42  includes a support structure  44  comprising upper and lower plates  46  and  48 , with the upper plate being adapted for being bolted to the bottom of the operator&#39;s cab  22 . A major portion of each of the plates  46  and  48  is horizontal and these portions are fixed in spaced, parallel relationship by three vertical posts  50 ,  52  and  54 , each having its upper end welded into a respective hole provided in the upper plate  46 , and each having its lower end secured to the lower plate  48  by a respective cap screw  56  threaded axially into the associated post. As considered from front to rear of the support structure  44 , the posts  50 ,  52  and  54  are respectively positioned at a front central, right-hand intermediate and left-hand intermediate locations, with the post  52  being located about midway between the posts  50  and  54  in the fore-and-aft direction. The upper plate  46  includes a u-shaped cylinder and spring mounting bracket  58  formed at the right front thereof. 
     The steering wheel  26  initiates steering input signals which are coupled, by a train of motion transfer elements, for effecting desired movement of the swash plate control arms  38  and  40 , (FIG. 2) respectively, of the pumps  34  and  36 . Upper and lower, self-aligning bearing assemblies  60  and  62  (FIG. 4) are respectively bolted to top and bottom surfaces of, and in alignment with vertically aligned holes provided in, the upper and lower mounting plates  46  and  48  at a location leftwardly and rearwardly of the front post  50 . The steering wheel  26  is coupled in a well known manner, not shown, to a steering shaft  64  mounted for rotation in the bearing assemblies  60  and  62 . A pinion  66  is fixed on the steering shaft  64  at a location spaced a small distance below the upper plate  46 . A quadrant-shaped steering rack  68  has an elongate cylindrical hub  70  mounted for rotation about the rear post  54  and having a lower end spaced above the lower plate  48 . As can best be seen in FIG. 3, the steering rack  70  has an arcuate portion  72  provided with a set of internal gear teeth  74  meshed with the pinion  66 . The arcuate portion  72  has its right- and left-hand ends respectively joined to right- and left-hand arms  76  and  78  which converge rearwardly to a circular portion  80  containing a centrally located hole receiving an upper end section of the cylindrical hub  70 , with the portion  80  being welded to the hub  70 . 
     A return-to-center device is provided for automatically returning the steering rack  70  and, hence, the steering wheel  26  to its centered position upon release of the steering wheel. Specifically, coupled to the quadrant arms  76  and  78 , at respective locations  84  and  86  adjacent right- and left-hand ends of the arcuate portion  72 , are first ends of cables  88  and  90 . Second ends of the cables  88  and  90  are attached to one end of a coil tension spring  92  having its opposite end attached to an eye of an anchor bolt  94  secured to the bottom of the cab  22 . 
     When the control mechanism  42  is in its condition shown in FIG. 3, steering rack  68  will be in a “centered” position, corresponding to the “centered” position of the steering wheel  26 , and the cables  88  and  90  will be equally tensioned by the spring  92 . It will be appreciated then that a rightward steering input from the steering wheel  26  will cause clockwise rotation of the pinion  66 , resulting in the steering rack  68  pivoting clockwise about the post  54 . This movement of the rack  68  will cause the cable  90  to be pulled forwardly, thus further loading the tension spring  92 , while the cable  88  goes slack. Upon release of the steering wheel  26 , the spring  92  will act through the cable  90  to return the steering rack  68  to its “centered” position which results in the pinion  66  being rotated to return the steering wheel  26  to its “centered” position. 
     The vehicle  10  is provided with a brake system, not shown, utilizing pressure-released, spring-applied braking elements so that braking is effected any time fluid pressure for effecting release of the brakes is absent from the system. This fluid pressure is normally supplied by an engine-driven pump and it follows then that braking will automatically be effected any time the engine stops. The source of fluid pressure for effecting release of the brake elements is also used for effecting release of a spring-applied, pressure-released latch embodied in a latch system  96  for releasably retaining the control mechanism  42  in its condition shown in FIG.  3 . 
     Specifically, the latch system  96  includes a one-way, latch-release cylinder  98  and a latch-applying coil tension spring  100 . A head end of the cylinder  98  is connected, as at a pin  102 , to the mounting bracket  58  while a rod end of the cylinder is received between and connected, as at a pin  104 , to upper and lower input arms  106  and  108  (FIG.  4 ), respectively, welded to an elongate latch arm hub  110  pivotally mounted on the post  52 . The spring  100  extends parallel to the cylinder  98  and has hooks at opposite ends respectively attached to a pin  112  extending through a flange forming part of the bracket  58  and to a pin  114  mounted to the input arms  106  and  108  at a location outboard of the cylinder  98 . An extension of the lower arm  108  defines a steering latch arm  116  carrying a vertical latch pin  118 , which, when the rack  72  is in its “centered” position shown in FIG. 3 with no fluid pressure being routed to the cylinder  98 , is biased by the spring  100  to a latch position seated in a semi-cylindrical notch or receptacle  120  provided in the steering rack arcuate portion  72  at a location half-way between the opposite ends thereof on the side opposite from the internal gear teeth  74 . A stop roller  119  is mounted to the upper plate  46  in a location for abutting the arm  116  when the latter is moved to its latch release position by the hydraulic cylinder  98 , as shown in FIG.  3 . 
     Also biased to a latch position by the spring  100  is a speed/direction latch arm  122  welded to a lower portion of the latch arm hub  110  (FIG. 4) and containing an arcuate slot  124  formed at a radius about the post  54  and into which opens a notch or recess  126 . Received in the slot  124  is a speed/direction latch pin  128  carried at the end of a latch pin arm  130  welded to a pivot support bar hub  132  (FIG. 4) at a location diametrically opposite from a pivot support bar  134  having one end joined to the hub  132  and an opposite end joined to a hub  136  pivotally mounted on the pivot post  54  just below the hub  70 . The length of the slot  124  corresponds to the distance traveled by the pin  128  when the speed/direction control lever  28  is moved between extreme “forward” and “reverse” positions, with the notch  126  being at the location in the slot corresponding to the “neutral” position of the control lever  28 . Thus, with the speed/direction control lever  28  in its “neutral” position and the hydraulic cylinder  98  deactivated, the spring  100  will act to move the arm  122  so as to engage the pin  128  in the recess  126 . A “neutral” interlock switch, not shown, is mounted to the arm  122  and has its actuator positioned across the recess  126  for being engaged and moved by the pin  128  for completing a starting circuit (not shown) only when the steering and speed/direction lock pins  118  and  128  respectively, are engaged in the notches or recesses  120  and  126  to thus prevent the vehicle from being started unless the steering wheel  26  is in its “centered” position corresponding to straight ahead travel and unless the speed/direction control lever  28  is in its “neutral” position. 
     It will be appreciated then that control inputs to the control mechanism  42  are effected by the steering wheel  26  and by the speed/direction control lever  28 . Control outputs from the control mechanism  42  occur by way of a horizontal pivot plate  138  fixed, at a location half way between its opposite ends, to an upper portion of a vertical pivot pin  140  (FIG. 4) pivotally mounted in the pivot support bar hub  132 . Coupled to right- and left-hand ends of the plate  138  are front ends of pump control arm rods or links  142  and  144 , respectively, having their rear ends coupled to the pump control arms  40  and  38 . The speed/direction control lever  28  is pivotally mounted to the right-hand arm rest of the seat  24  at a location midway between respective connections to first ends of right- and left-hand push-pull operating cables  146  and  148 , respectively, in a manner not shown but well known in the art. Opposite second ends of the cables  146  and  148  are respectively coupled to right- and left hand ends of a crank arm assembly including right- and left-hand arms  150  and  152 , of equal length, that are joined to the pivot support bar hub  136 . The lengths of the cables  146  and  148  may be adjusted against each other for preventing any erratic movement due to backlash being present in the assemblies containing the cables  146  and  148 . In order to provide a resistance to the movement of the speed/direction control lever  28  so that the operator does not inadvertently make abrupt, large changes in the ground speed of the vehicle  10 , a dashpot  154  is mounted between the crank arm  152  and a pin  156  projecting upwardly from the plate  46 . The dashpot  154  is of a known construction having a piston provided with an orifice through which oil contained in the dashpot cylinder may pass to opposite sides of the piston as the dashpot is extended or retracted. 
     Output signals resulting from steering and/or speed and direction input signals are transferred to the pump swash plate control arms  40  and  38  by the pump control arm rods  142  and  144 , respectively. For the purpose of effecting steering outputs exclusive of speed/direction outputs, and vice-versa, a tie-rod or linkage bar  158  is disposed in parallel relationship to the pivot support bar  134  and has its right- and left-hand ends respectively defined by ball joint couplers  160  and  162 . Associated with each of the ball joint couplers  160  and  162  is a bolt  163 , with the bolt of the coupler  160  being screwed into a threaded hole provided in a pivot plate crank arm  164 , fixed to and projecting rearwardly from the pivot pin  140  at a location spaced below the pivot plate  138 , and with the bolt of the coupler  162  being screwed into a threaded hole provided in a steering rack crank arm  166  fixed to and projecting rearwardly from the steering rack hub  70 . Thus, the support bar  134 , tie-rod  158 , pivot plate crank arm  164  and steering rack crank arm  166  cooperate to form a four-bar linkage. The ball joint couplers  160  and  162  make it unnecessary for the axes of the bolts  163  to be perfectly parallel with each other in order to get the desired parallelogram motion. 
     In operation, steering signals cause rotation of the pinion  66  and, hence, pivotal movement of the rack  68  about the pin  54 , this pivotal movement being transferred to the pivot plate  138  by the crank arm  166 , tie-rod  158  and crank arm  164 . Assuming the vehicle  10  to be stopped with the control mechanism  42  in its condition shown in FIG.  3  and that a right-hand turn is desired, this may be accomplished by rotating the steering wheel  26 , and consequently the pinion  66 , clockwise, as viewed in FIG. 3, resulting in the steering rack  68  being swung clockwise about the post  54  such that the tie-rod  158  effects clockwise rotation of the pivot plate  138 . This causes the right-hand pump control rod  142  to push rearwardly on the control arm  40  of the pump  36  and causes the left-hand pump control rod  144  to pull the control arm  38  of the pump  34  forwardly. The pump  34  then acts to deliver working fluid to drive the right-hand motor  30  in reverse while the pump  36  acts to deliver working fluid to drive the left-hand motor  32  forwardly. A right-hand spin turn is thus effected. It will be appreciated that operation for effecting a right-hand turn while the vehicle  10  is traveling forwardly is accomplished in the same manner except that the right-hand wheel  14  may merely be slowed relative to the speed of the left-hand wheel  16  without being driven in reverse. Further, it will be appreciated that left-hand turns may be similarly effected by turning the steering wheel  26  in the counterclockwise direction. 
     Speed/direction changes are effected exclusive of steering by moving the speed/direction control lever  28  forwardly or rearwardly. Specifically, assuming the vehicle to be traveling forwardly, an increase in forward speed may be effected by pivoting the control lever  28  forwardly. This movement of the lever  28  will result in the cable  148  pushing on the crank arm  152  while the cable  146  pulls on the crank arm  150 . This will cause clockwise rotation of the pivot support bar hub  136  and, hence, rearward swinging of the pivot support bar  134 . The pivot pin  140  and the attached pivot plate  138  are swung rearwardly about the fixed post  54  which results in the pump control arm rods  142  and  144  both being pushed rearwardly which in turn effects rearward pivotal movement of the pump control arms  38  and  40  so as to increase the pump displacements and consequently increase the forward driving speed. Of course a decrease in speed may be similarly effected by pivoting the speed/direction control lever  28  rearwardly towards its centered “neutral” position. Further, it is apparent that direction changes can be effected by moving the control lever across its “neutral” position.