Abstract:
A vehicle such as a lawn and garden tractor is adapted to utilize conventional steering and propel controls with a drive and steer type transmission. The transmission permits the vehicle to be driven and steered through its rear drive wheels, thereby permitting it to turn about one wheel and/or about an axis between its wheels. Front castered wheels enable the vehicle to easily steered by the drive wheels. A conventional type steering wheel is provided with a mechanical linkage extending between it and the transmission. Conventional type controls are also provided to propel or power the vehicle in a forward or rearward direction and within a range of speeds. With conventional type steering and propel controls adapted to be utilized with the drive and steer type transmission, operation of spin-turn vehicles is made simple and more efficient as well as reducing the time required to learn to operate and maneuver the vehicle.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     Four commonly owned and related patent applications have been filed concurrently with this patent application on Mar. 26, 1999, and their disclosures are intended to be fully incorporated by reference herein. They include “Lawn Tractor Vehicle”, Ser. No. 09/277,351, “Steering Device for Drive and Steer Transmission”, Ser. No. 09/277,418, “Effective Gear Reduction in Lawn Tractor Transmission”, Ser. No. 09/277,344, and “Mechanism for Correct Steering in Reverse”, Ser. No. 09/277,346, issued Oct. 10, 2000 as U.S. Pat. No. 6,129,164. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to vehicles equipped with transmissions that enable their drive wheels to be separately powered to steer the vehicle and more particularly to small vehicles such as lawn and garden tractors equipped with such transmissions. 
     2. Description of the Related Art 
     It is known to provide small vehicles such as lawn mowing vehicles with hydrostatic motors for each drive wheel so that they can be powered individually. This permits the drive wheels to be powered forwardly and rearwardly in unison as well as at different speeds. Accordingly, the vehicle can be driven forwardly, rearwardly, steered by the drive wheels and turned about a vertical axis between the wheels. Vehicles equipped with such drive arrangements are sometimes referred to as having zero-turn or spin-turn capability. 
     Conventionally, the drive wheels have been controlled through separate hand levers. The hand levers serve to control both forward and reverse movement of each wheel as well as its speed. As the control lever is moved further forwardly or rearwardly of a neutral position, the speed increases. When one control lever is moved further from the neutral position than is the other lever, the vehicle turns since the speed of that wheel is increased relative to the other wheel. These types of hand controls require lengthy experience for an operator to become proficient in coordinating the forward speed and turning of the vehicle. 
     It is also known to provide large vehicles with transmissions that propel two drive wheels and individually steer each of them. These drive and steer type transmissions have taken the form of dual differential gear sets as well as planetary gear sets. They have been utilized primarily on tracked vehicles such as rice combines, tanks and skid-steer loaders. Recently, similar transmissions have become available in smaller configurations that provide for the wheel driving and steering functions to be controlled through separate input control devices. These devices permit forward, neutral and reverse propelling control for the two wheels with overriding control of each propelled wheel through a steering portion. With the advent of these transmissions, it would be desirable to adapt smaller vehicles such as lawn and garden tractors to utilize them. Further, it would be desirable to utilize forward, reverse and turn controls with which most individuals expected to use such vehicles would be familiar. Towards these ends, it would be desirable to utilize a conventional steering wheel with such transmissions as well as foot controls typically used with these vehicles. This would be particularly desirable since vehicles such as lawn and garden tractors are typically used infrequently, so that the operators would not be expected to develop the skills necessary for operating twin hand control levers. Therefore, it would be desirable to outfit a lawn and garden tractor with a steering wheel and foot controls for use with drive and steer type transmissions. 
     Such applications would provide a lawn and garden tractor with zero or drive and steer capability that would be more maneuverable around obstacles and in tight spaces since it could turn about an axis through its mowing unit or through itself. Further, productivity could be improved since the deck could be maneuvered to cut exactly where desired, thereby minimizing the movement of the deck over areas already cut. Additionally, it would be more comfortable and efficient for a new user to operate since they would most likely be familiar with the conventional steering wheels and foot controls used in lawn and garden tractors as well as automobiles. 
     SUMMARY OF THE INVENTION 
     Towards these ends, there is provided a vehicle such as a lawn and garden tractor which is adapted to utilize conventional steering and propel controls with a drive and steer type transmission. The transmission permits the vehicle to be driven and steered through its rear drive wheels, thereby permitting it to turn about one wheel and/or about an axis between its wheels. Front castered wheels enable the vehicle to be easily steered by the drive wheels. 
     A conventional type steering wheel is provided with a mechanical linkage extending between it and the transmission. Conventional type foot control pedals are also provided to propel or power the vehicle in a forward or rearward direction and within a range of speeds. 
     With conventional type steering and propel controls adapted to be utilized with the drive and steer type transmission, operation of spin-turn vehicles is made simple and more efficient as well as reducing the time required to learn to operate and maneuver the vehicle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a schematic side view of a lawn and garden type vehicle equipped with a dual differential type drive and steer transmission, a steering wheel and foot controls. 
     FIG. 2 illustrates a front elevated schematic perspective of the drive and steer type transmission and the steering and foot control assemblies. 
     FIG. 3 illustrates a schematic view similar to FIG. 2, but taken from beneath the vehicle. 
     FIG. 4 illustrates an enlarged perspective view of the foot pedal arrangement shown in FIG.  3 . 
     FIG. 5 illustrates a further enlarged view of the foot control lever arm and linkage shown in FIG.  4 . 
     FIG. 6 illustrates a schematic view of the dual differential power train components. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Looking first to FIG. 1, there is illustrated a schematic side view of a lawn and garden type vehicle  10  wherein the present invention is utilized. The vehicle  10  includes a frame  12  upon which front castered wheels  14  and rear drive wheels  16  are mounted, with a drive and steer type transmission  18  provided at the rear thereof. In the particular embodiment illustrated in FIG. 1, the transmission is a dual differential drive and steer type transmission. Further carried on the forward end of the frame  12  is an engine  20  as well as a downwardly and forwardly sloping hood structure  22  that encloses the engine  20 . At the rear portion of the frame  12  is an operator station  24  with a seat  26  supported on a rear fender deck  28 , a steering wheel  30 , foot controls  32  and a parking brake  34 . A mower deck  36  is supported beneath the frame  12  and between the front and rear wheels  14  and  16 . Looking now to FIGS. 2 and 3, there is illustrated in schematic and perspective views the transmission  18 , and steering and foot controls  38  and  40  for the vehicle of FIG.  1 . The transmission  18  is a dual differential drive and steer type transmission having a forward drive portion  42  for propelling the wheels, as well as a rear steering portion  44  coupled with the forward drive portion  42 . As is also schematically illustrated in FIGS. 2,  3  and  6 , the drive and steering portions  42  and  44  each have a pair of laterally extending left and right axles  46  and  48  with the drive wheels  16  being supported on the axles  46  and  48 . The left and right axles  50  and  52  of the rear steering portion  44  (See FIG. 6) are coupled with the respective left and right axles  46  and  48  of the driving portion  42  through gear arrangements that extend between each pair of left and right axles  46 - 50  and  48 - 52 . A reversing gear  54  is provided between the right steering and drive axles  52  and  48  so that the left and right drive axles  46  and  48  are powered in opposite directions by the inputs from their respective steering axles  50  and  52 . 
     Each of the drive and steering transmission portions  42  and  44  have separate hydraulic pump motor combinations for powering their differentials  56  and  58  and their respective axles  46 - 48  and  50 - 52 . As shown in FIG. 6, the two hydrostatic pumps  60  and  62  are each powered through a respective input shaft  64  and  66 . The shafts  64  and  66  are each powered by sheaves  68  and  70  which are rotatably driven by a V-belt  72 . A second V-belt  74  driven by the drive shaft of the engine  20  is used to power the first pulley sheave  68 . As best illustrated in FIGS. 2 and 3, each hydraulic pump  60  and  62  has its own swash plate control shaft  76  and  78 . As shown in FIG. 6, the swash plate for the drive portion pump  60  is designated  80  while the swash plate for the steering portion pump is designated  82 . 
     Looking as well to FIGS. 4 and 5, there is illustrated the foot pedal arrangement  40  for controlling the forward and reverse speed of the drive portion  42  of the transmission unit  18 . This arrangement includes a forward pedal  84 , as well as a reverse pedal  86 . The pedals  84  and  86  are supported on respective first and second pivot shafts  88  and  90 , which are carried on a set of brackets  92  supported by the frame  12  (see particularly FIG.  4 ). A single pedal, such as a treadle pedal arrangement mounted on a single shaft with a single push-pull linkage rod connected to the transmission unit  18  could also be utilized, if desired. The forward pedal  84  is mounted to a forward pedal arm  92  which is rigidly connected with the first or primary pivot shaft  88  for swinging movement. Additionally connected to the first shaft  88  is a control arm  96  (See FIG. 5) that swingably moves about the axis of the first pivot shaft  88  as the forward pedal  84  is depressed. The control arm  96  is in turn coupled with a linkage or propel rod  98  which extends between the control arm  96  and the swash plate lever  100  of the drive portion  42  of the transmission  18 . The rod  98  is coupled with the swash plate control lever  100  through a universal or ball joint coupling  102  to accommodate the linear movement of the rod  98  and the swinging movement of the swash plate lever arm  100 . 
     The foot pedal arrangement  40  further includes the reverse pedal  86  which is swingably supported on the secondary or second pivot shaft  90 . The reverse pedal  86  is supported by an arm  104  which includes an extension  106  rearwardly of the secondary shaft  90 . To the extension  106  is swingably coupled a reversing linkage consisting of a first link  108  and second link  110 . The first link  108  is swingably coupled with the extension  106  while the second link  110  is rigidly coupled to the first pivot shaft  88 . As the reverse pedal  86  is depressed, it swings about the secondary shaft  90  with its rear portion or extension  106  swinging in an upwardly arc. Accordingly, the reversing linkages  108  and  110  serve to rotate the primary shaft  88  in a counterclockwise direction as viewed in FIG. 4 as the reverse pedal  86  is depressed. As the primary shaft  88  is rotated in a counterclockwise direction, the control arm  96  rigidly mounted to it rotates rearwardly to shift the rod  98  rearwardly and swing the swash plate lever arm  100  in a rearwardly direction, thereby powering the pump  112  in a reverse mode. 
     Returning to FIGS. 2 and 3, there is illustrated the steering assembly  38  for controlling the steering unit  44  of the dual differential transmission  18 . The steering assembly  38  includes the steering wheel  30  coupled for rotation with a steering shaft  114 . While a conventional steering wheel is preferred, an elongated bar, tiller or similar structure adapted to rotate or be turned about an axis could be utilized. The steering shaft  114  is supported in upper and lower bushings  116  which are in turn carried by the frame  12 . At the lower end of the steering shaft  114  is rigidly mounted a pinion  118  which has teeth  120  around its periphery. The teeth  120  are adapted to mesh with teeth  122  carried on a sector gear  124 . The sector gear  124  is in turn rigidly mounted to a sector shaft  126  supported on a bracket  128  carried by the frame  12 . The sector shaft  126  is adapted for swinging movement about a generally vertical axis to accommodate the rotational movement of the sector gear  124 . Looking to FIG. 3, it can be seen that the lower end of the sector shaft  126  is rigidly mounted with a steering arm  130 . The arm  130  swings in an arc as the sector shaft  126  is rotated by the sector gear  124 . The steering arm  130  is secured to a universal type ball joint coupling  132  which receives a steering link or rod  134  that extends rearwardly and is received in a similar type of universal or ball joint coupling  136  at the top end of the steering pump swash plate control lever  138 . The steering swash plate control lever  138  in turn is rigidly coupled with the steering pump swash plate control shaft  78  so that fore and aft movement of the steering rod  134  will swing the swash plate control lever  138  and adjust the swash plate  82  of the steering pump  62 . Accordingly, as the steering wheel  30  is turned, the sector gear  124  is rotated and the steering arm  130  is swung in either a forward or rearward direction to pull or push the steering linkage  134  and adjust the swash plate  82  of the steering pump  62 . 
     Looking now to FIGS. 2 and 6, the general operation of the dual differential drive and steer type transmission  18  will be reviewed. The dual differential transmission  18  includes the two separate hydrostatic differential transmissions, one  42  for propelling the driving wheels  16  and one  44  for steering those wheels  16 . The separate cases for the two transmissions are depicted by the dotted lines enclosing each of them. The hydrostatic pumps  80  and  82  of both transmissions  42 - 44  are powered by the V-belt  72  which in turn is powered by the V-belt  74  coupled with the engine  20 . As illustrated in FIG. 6, each pump  80 - 82  is driven by a respective input shaft  64 - 66  that is coupled with a respective V-belt pulley  68 - 70  driven by the engine V-belt  74 . The hydraulic pump  80  of the propel unit  42  drives an hydraulic motor  112  which rotates an output shaft  140  and the associated gear  142 . The gear  142  in turn transmits rotational power through shaft  144  and gear  146  to a ring gear  148  of the propel differential  56  to power the left and right axles  46  and  48  in the same direction. The left and right drive axles  46 - 48  are provided with gears  150 - 152  between the differential  56  and the wheels  16  mounted at the outer end portions of the axles  46 - 48 . The adjustable swash plate  80  in the variably reversible pump  60  permits the direction of the axles  46 - 48  and their respective wheels  16  as well as their speeds to be adjusted. 
     The input shaft  66  of the steering unit  44  is coupled to a hydrostatic pump  62  which drives a steering motor  154 . The output shaft  156  of the motor is coupled with the steering differential  58  to power the left and right steering axles  50 - 52  in the same direction. The left axle  50  of the steering unit  58  is provided with a large gear  158 , while the right axle  52  is provided with a smaller gear  160  in the preferred embodiment. This smaller gear  160  is mounted to mesh with the reversing gear  54  provided on a separate shaft carried by the frame  12 . The gears  158 - 150  on the left axles  50 - 46  of the steering and propel units  58 - 56  mesh to provide a direct drive between the two axles  50 - 46 . The reversing gear  54  on the right side of the vehicle and the gear  152  on the right axle  48  of the propelling unit  56  also mesh to interconnect the two axles  48 - 52 . In this manner, power to the steering differential  58  will rotate the axles of the left and right axles  50 - 52  of the steering unit  58  in the same direction. Rotational motion transmitted from the left axle  50  of the steering unit  58 , through the gear  158 , and to the gear  150  coupled with the left axle  46  of the drive unit  56  serves to drive the left axle  46  of the drive unit  56  in the opposite direction as the left axle  50  of the steering unit  58 . The right axle  52  of the steering unit  58 , which is coupled with the reversing gear  54 , serves to drive the right axle  48  of the propel unit  56  in the same direction. Thus, the rotational motion imparted by the steering unit  58  to the left propel axle  46  as well as the right propel axle  48  is the same although in opposite directions. Accordingly, the left axle  46  is accelerated in one direction while the right axle  48  is accelerated in the reverse direction when the steering differential  58  is powered by the pump  154 . 
     In operation, the vehicle  10  will operate as follows. The operator would utilize the steering wheel  30  and foot controls  40  in their conventional manner. The engine output shaft powers the drive belt  74  to rotate the pulleys  68  and  70  and input shafts  64 - 66  on the propel and steer transmissions  42 - 44 , See FIG.  6 . To move forward, the operator depresses the forward pedal  84 , which rotates the forward pedal arm  98  and its linkage control arm  96 . As the linkage control arm is moved forwardly, it pulls the propel linkage rod  98  forwardly and swings the swash plate control lever  100  forwardly. Accordingly, the hydrostatic pump  60  powers the propel motor  112  to power the differential  56 , the left and right axles  46 - 48  and their attached wheels  16  in a substantially identical forward speed. Should the operator desire to propel the vehicle  10  in a rearwardly direction, he would depress the reverse pedal  86 , and through the linkage best illustrated in FIG. 4, move the propel linkage control rod  98  in a reverse direction to swing the swash plate control lever  100  and the swash plate control shaft  76  in a reverse direction, thereby powering the hydrostatic pump  112  in a reverse manner to drive the propel differential  56  and their associated axles  46 - 48  and wheels  16  in a reverse and generally equal speed. 
     To steer the vehicle  10 , the operator turns the steering wheel  30  which rotates the steering shaft  114 . The teeth  120  on the pinion gear  120  engage the sector gear  124  to rotate the shaft  126 . The steering arm  130  coupled to the sector shaft  126  is swung to either pull or push the steering linkage rod  134  and move the steering swash plate  82  forwardly or in reverse. As the swash plate  82  is moved, hydrostatic fluid is diverted to the steering motor  154  to drive the steering differential  58  and power the left and right axles  50  and  52 . The gear  158  on the left side of the steering axle  50  drives the gear  150  of the left propel axle  46  to power it in one direction while the reversing gear  54  between the right axle  52  of the steering unit  44  and the right axle  48  of the propel unit  42  powers the right axle  48  of the propel unit  42  in a reverse and equal direction. With the present arrangement, there is provided familiar steering and foot control assemblies for actuating the dual differential drive and steer type transmission. The caster wheels  14  provided at the forward end of the vehicle  10  permit it to swing easily in one direction or the other as the drive wheels  16  are propelled at incrementally different speeds to execute turns of the vehicle. 
     Alternately, a planetary gear type transmission could be utilized in place of the dual differential type transmission. With such a transmission, separate electric, hydraulic or other power inputs could be provided to propel the wheel axles and provide steering inputs to one of the planetary gear sets, as for example, the ring gear sets. Accordingly, the steering wheel and its related linkage would be coupled with the steering input while the foot controls and their related linkage would be coupled with the propel input.