Abstract:
Disclosed is a self propelled walk behind mower comprised of a tractor unit and a mowing deck. The tractor unit is hydrostatically driven with a unique control system whereby the forward speed of the tractor is set by operating an electric rocker switch with an operator&#39;s thumb. Hand levers are used to turn the tractor to the left and the right. The tractor unit comprises two drive wheels and a third wheel that is pivotally attached, letting the tractor unit stand upright when no implements are attached. Implements attach to the front of the tractor through a movable attachment so that the tractor and implement can closely follow the contour of the ground while keeping the operator controls in a convenient position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims benefit of and priority to U.S. Provisional Patent Application Ser. No. 60/391,057 entitled “Walk Behind Mower” by Dean M. Walker, filed Jun. 21, 2002, the entire contents of which are specifically incorporated herein by reference for all it discloses and teaches. 

   BACKGROUND OF THE INVENTION 
   a. Field of the Invention 
   The present invention pertains generally to walk-behind mowers and specifically to walk-behind mowers that have electric speed control. 
   b. Description of the Background 
   Walk-behind mowers including a tractor unit and a mowing deck attached to the front of the tractor have been commercially available for a long time. Typically, the tractor has only two wheels and the mowing deck is rigidly connected to the forward end of the tractor. A serious disadvantage with such types of mowers is that the quality of cutting is not as good as desired, since the mower can ‘scalp’ the grass in some areas and leave the grass too long in other areas because the mowing deck is not able to closely follow the contour of the ground. 
   The operator controls for self-propelled walk behind mowers tend to be difficult to use while meeting the requirements of safety and operability. In some cases, the operator must continually grip two hand levers in order for the mower to move forward at a constant speed. Such a system is prone to operator fatigue. 
   It would therefore be advantageous to provide a mower that more accurately follows the contour of a lawn during mowing and further provides a set of operator controls that are not prone to operator fatigue. 
   SUMMARY OF THE INVENTION 
   The present invention overcomes the disadvantages and limitations of the prior art by providing a mower that has a deck removably attached to a walk behind, self-propelled tractor. The tractor has a set of operator controls that includes a rocker switch that is used to set the forward speed of the tractor and two hand levers that are used to brake each wheel individually for steering. The tractor is propelled using individual hydrostatic drives on each of two main drive wheels and has a third wheel pivotally mounted rearwardly that provides stability to the tractor when no implements are attached. The tractor has an articulated mower deck mounted to the front. The arrangement is better able to closely follow the contour of the ground during mowing of uneven surfaces and places the operator controls in a more comfortable and controllable position. 
   The present invention may therefore comprise a self propelled walk behind mower comprising: a tractor unit having left and right drive wheels and a tail wheel pivotably mounted rearwardly of the drive wheels for stability, the tractor having an internal combustion engine mounted between the drive wheels and the tail wheel, the drive wheels being independently powered by left and right hand hydrostatic drive units, the tractor unit further having a forward end; and a mower deck having two wheels pivotally mounted to the front of the mower deck, the mower deck mounted to the forward end of the tractor unit wherein the mower deck is able to pivot up and down and tilt side to side relative to the tractor unit such that the mower deck may follow the contour of the ground. 
   The present invention may further comprise a control system for a self propelled walk behind mower comprising: a speed lever disposed to be operated by the operator, the speed lever being connected to an actuator, a pair of adjustable stops moved in parallel by the actuator; a left lever being operably connected to a left stop and further connected to a left hydrostatic drive unit, the left lever being disposed to be operated by an operator&#39;s left hand, the left hydrostatic drive having a forward speed being limited by the obstruction of the left stop against the adjustable stop, the left lever adapted to bias the left stop against the adjustable stop and further being adapted to slow the left hydrostatic drive by the actuation of the left lever by the operator; and a right lever being operably connected to a right stop and further connected to a right hydrostatic drive unit, the right lever being disposed to be operated by an operator&#39;s right hand, the right hydrostatic drive having a forward speed being limited by the obstruction of the right stop against the adjustable stop, the right lever adapted to bias the right stop against the adjustable stop and further being adapted to slow the left hydrostatic drive by the actuation of the left lever by the operator. 
   The present invention may further comprise a method of controlling a self propelled walk behind mower comprising: activating a speed lever to move an actuator, the actuator being connected to adjustable stops, the adjustable stops disposed to simultaneously move a left stop and a right stop such that a left hydrostatic drive and a right hydrostatic drive connected to a left drive wheel and a right drive wheel are simultaneously activated to move the mower in a forward direction; activating a left lever that is operably connected to the left hydrostatic drive and further limited in travel by the adjustable stops, the activating of the left lever causing the left hydrostatic drive to slow down, causing the mower to turn to the left; and activating a right lever that is operably connected to the right hydrostatic drive and further limited in travel by the adjustable stops, the activating of the right lever causing the right hydrostatic drive to slow down, causing the mower to turn to the right. 
   The advantages of the present invention are that the mower is better able to follow the contour of the ground due to the articulated connection of the mower deck to the three wheeled tractor. Further, the positioning of the operator controls while following various ground contours is more comfortable and thus safer and less fatiguing. The control system for the mower allows for infinitely adjustable forward speed without requiring the operator to continually hold any handles other than an operator presence switch, further decreasing the fatigue of the operator. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, 
       FIG. 1  is an illustration of an embodiment of the present invention showing a tractor and an operator. 
       FIG. 2  is an illustration of a second view of an embodiment of the present invention showing a tractor and an operator. 
       FIG. 3  is an illustration of an embodiment of the present invention comprising a tractor and a mowing deck. 
       FIG. 4  is an illustration of the effect of the articulated arrangement of a tractor and a mowing deck. 
       FIG. 5  is an illustration of a rear view of an embodiment of the present invention. 
       FIG. 6  is an illustration of the underside of an embodiment of a tractor showing the control linkages. 
       FIG. 7  is an illustration of an embodiment of the linkages used to control the tractor. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates an embodiment of the present invention showing a tractor  100  and an operator  102 . The tractor  100  has a drive wheel  104  and a third wheel  106  that pivots but is not driven or steered. The engine  108  powers the tractor. The operator controls  110  are also shown in the present figure. 
     FIG. 2  illustrates a second view of an embodiment of the present invention showing a tractor  200 , a first drive wheel  202 , and a second drive wheel  204 . The drive wheel  202  is powered by a hydro-axle  206  and drive wheel  204  is powered by hydro-axle  208 . 
   The hydro-axles  206  and  208  are powered by an engine and are controlled by an operator to direct the movement of the tractor  200 . The hydro-axles  206  and  208  may be capable of infinitely adjustable speed control based on the input from the operator. Steering is achieved through differential speeds applied to the drive wheels  202  and  204 . The hydro-axles  206  and  208  may further be capable of reversing direction. In the case where one hydro-axle is moving in reverse and the other hydro-axle is moving forward at the same speed, the tractor  200  may turn about an axis defined at the midpoint of the axis of the two wheels  202  and  204 . 
   The deck attachment arms  210  and  212  along with the deck attachment receiver  214  may be used to attach a mowing deck or other implement on the front of the tractor  200 . The deck attachment arms  210  and  212  are pivotally attached to the tractor  200 . The deck attachment receiver  214  may receive a (i.e. compliant connector) whereby a mowing deck may flexibly move with respect to the tractor  200 . The compliant mechanism allows the deck to tip up and down and further tilt side to side to follow the contour of the ground. 
     FIG. 3  illustrates an embodiment of the present invention comprising a tractor  300  and a mowing deck  302 . The mowing deck  302  is attached to the tractor  300  by sliding the deck attachment arms shown in  FIG. 2  into receivers such as receiver  304 . The deck  302  is supported at the tractor end by the deck attachment arms and at the opposite end by wheels  306  and  308 . The suspension  310  couples the mower deck  302  to the tractor  300 . 
   The deck  302  is able to move up and down with respect to the tractor  300  as well as rotate side to side to some extent. In the present embodiment, the mower deck may articulate plus or minus about 5 degrees with respect to the longitudinal vertical plane. The ability of the deck to follow the contour of the ground greatly enhances the mower&#39;s ability to leave a consistent and aesthetically pleasing lawn over rough contours. 
   The three wheeled design of the tractor  300  is such that the tractor is stable when no implements are attached. With the prior art two wheeled tractors, the tractor would tip over when not balanced by a mowing deck or other implement on the front. By having a third wheel, the drive wheels may be positioned as far forward as possible to give the implement, such as a mower deck, increased ability to follow the contours of the ground. 
   The third wheel further allows various implements of different weights and balances to be attached to the tractor and still operate smoothly. If the third wheel were not present and a heavy implement were attached to the front, the balance and feel of the machine would be drastically different than if the machine had a light weight implement, or none at all. Further, since the prior art machines are balanced differently for different weight implements, there would be increased operator fatigue with the prior art machines. 
   The deck  302  is able to articulate with respect to the tractor  300  along the horizontal plane. Since the tractor  300  is fully supported by two drive wheels  312  and the third wheel  314 , the operator controls  316  will stay in a more comfortable position when mowing over a crest of a hill or when traversing a low spot. 
     FIG. 4  illustrates the effect of the articulated arrangement of a tractor  400  and a mowing deck  402 . The operator  404  is in a comfortable position with respect to the operator controls  406  as the tractor  400  crests the hill  408 . If the articulated arrangement were not present, the position of the tractor  400  may be illustrated by the phantom position  410 . In the phantom position  410 , the operator controls  412  would be significantly higher and more difficult to reach for the operator  404  than in the present embodiment  400 . When the mower traverses a valley, the articulated arrangement of the tractor  400  and the mowing deck  402  keeps the operator controls  406  in a much more convenient position for the operator  404 . 
     FIG. 5  illustrates a rear view of an embodiment of the present invention. The tractor  500  is shown from the rear with a mower deck  502 , a left drive wheel  504 , a right drive wheel  506 , and a third wheel  508 . The operator controls  510  comprise left and right hand grips  512  and  514 , respectively, left and right hand controls  516  and  518 , left and right operator presence levers  520  and  522 , and a thumb switch  524 . 
   The thumb switch  524  sets the forward speed control of the tractor  500 . The thumb switch  524  is a three-position rocker switch movable by the operator&#39;s right thumb. As the operator presses the switch  524  in the forward position, the tractor  500  moves forward faster. As the operator releases the switch  524  to the center position, the forward speed is maintained. When the operator wishes to slow down, the rear position of the switch  524  may be pressed to slow down the tractor  500 . 
   The hand controls  516  and  518  allow the operator to steer the tractor  500  by slowing or reversing the wheel associated with the respective hand control. For example, during forward motion, the operator may squeeze the left hand control  516  to slow the left hand drive wheel  504  and cause the tractor  500  to turn to the left. The sharpness of the turn is dictated by the amount that the operator grips the respective hand control. The hydro-axle system may have the capability of reversing the drive wheels. In such a case, squeezing the hand control completely will cause the drive wheel to reverse direction, allowing the tractor  500  to execute a zero radius turn. Likewise, simultaneously squeezing both hand controls completely will cause the tractor  506  to move in reverse. 
   The PTO engagement lever  526  may be used to engage the power take off for an implement such as the mower deck  502 . The lever  526  may engage a mechanical clutch mechanism that transmits power to the deck  502 . 
   Left and right operator presence levers  520  and  522  may be connected in parallel such that only one switch is necessary for the tractor to sense the operator presence. One or both of the levers  520  and  522  may be necessary for the tractor  500  to operate. For example, if the tractor were moving forward and the operator removed both hands from the controls  510 , the levers  520  and  522  would disengage and the tractor would shut down or otherwise halt motion. When the PTO lever  526  is engaged, releasing both of the operator presence levers  520  and  522  will kill the engine and halt operation. 
   The left and right hand controls  516  and  518  are connected to left and right hand control linkages  528  and  530 , respectively. The linkages  528  and  530  are connected to the hydro-axles though a mechanism that sets the forward speed of the hydro-axles simultaneously. 
     FIG. 6  illustrates the underside of an embodiment of a tractor  600 . The left and right drive wheels  602  and  604  and the third wheel  606  are shown. Left and right hydro-axles  608  and  610  are connected to the wheels  602  and  604 , respectively. The control linkages  612  and  614  are the control linkages  528  and  530  shown in  FIG. 5 . The control linkages  612  and  614  are connected to rotary links  616  and  618 , which connect to connecting links  620  and  622 , which connect to the hydro-axle input controls  624  and  626 . This mechanism is the connection between the handle grips operated by the operator and the hydro-axles that control the forward and reverse speeds of the tractor. 
   The rotary links  616  and  618  are mounted on a limiting shaft  628 . The limiting shaft  628  has stops, not shown in the present figure, that simultaneously limit the amount of travel the rotary links  616  and  618  can rotate. As the electric actuator  630  rotates the limiting shaft  628  through the lever  632 , the rotary links  616  and  618  move to a position whereby the connecting links  620  and  622 , the input controls  624  and  626 , and thus the hydro-axles  608  and  610  are simultaneously engaged to move forward. The electric thumb switch  524  of  FIG. 5  may be connected to the actuator  630  to change the forward speed of the tractor. At any time that the tractor is in a forward motion, the hand levers may be actuated to slow the speed of the tractor, bring the tractor to a halt, or reverse the motion of the tractor. 
   The term hydro-axle refers to a hydrostatic drive with an integrated, load carrying axle. For the present embodiment, the hydro-axle offers a compact and cost efficient design. Those skilled in the arts would appreciate that alternative designs comprising a hydrostatic drive with a separate axle system would be possible while maintaining within the scope and intent of the present invention. 
     FIG. 7  illustrates an embodiment of the linkages used to control the tractor. The operator controls  702  comprise the left and right hand grips  704  and  706 , operator presence levers  708  and  710 , and control levers  712  and  714 . Control levers  712  and  714  are connected to control linkages  716  and  718 , respectively, that are connected to left and right rotary linkages  720  and  722 . Each rotary link  720  and  722  are connected to connecting links  724  and  726  that connect to the independent hydro-axles not shown. 
   A limiting shaft  728  is shown in an exploded state in three pieces for clarity, but is rigidly connected in operation. The limiting shaft  728  has left and right stop plates  730  and  732  as well as a link  734  connected to an electric actuator  736 . 
   The rotary link  720  is mounted on the limiting shaft  728  and comprises an input arm  738 , and output arm  740 , and a stop plate  742 . The stop plate  742  has an adjustment screw  744 . When assembled, the stop plate  742  and adjustment screw  744  is positioned to press against the limiting shaft stop plate  730 . 
   When the electric actuator  736  moves, the stop plates  730  and  732  move simultaneously against the stop plates  742  and  746  to limit the amount of travel of the stop plates  742  and  746 . As the travel of the respective stop plates are changed, the position of the rotary links  720  and  722  are changed, thusly changing the inputs to the independent hydro-axles and causing the tractor to change speed. Since the left and right hydro-axles are changed equally and simultaneously, the tractor will move in a straight line. At any time the tractor is moving in a straight line, an operator may change the speed of one or both wheels by actuating the levers  712  or  714 . 
   The stop plates  730  and  732  change the limit on the maximum forward speed of the respective wheel, thus the actuation of levers  712  or  714  serve to slow the respective hydro-axle and thus the drive wheel. The benefit of the present embodiment is that the electric actuator  736  can be used to set the forward speed of the tractor and the operator does not need to grip the control levers  712  and  714  during normal forward speed. Since the operator is not required to continually grip the levers  712  and  714  during normal forward motion, the fatigue and discomfort of other walk behind mowers is alleviated. Another benefit of the electric actuator  736  is that the forward speed can be adjusted to the operator&#39;s preference. In some situations where tight turning may be critical, the speed may be adjusted to be somewhat slow. In situations where long stretches of straight motion are required, the operator may adjust the speed to be higher. As the operator approaches a turn, the speed can be simply lessened with a thumb switch such that the turn can be executed without difficulty. 
   Alternative arrangements for the forward speed control are possible. In the present embodiment, the operator uses an electric switch to actuate an electric actuator that moves two stops simultaneously. In other embodiments, the operator may move a mechanical lever to directly actuate the stops. Alternatively, hydraulic or other methods of actuation are possible by those skilled in the arts while maintaining within the scope of the present invention. 
   The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.