De-stroking dual hydrostatic pump

1. An apparatus comprising:

a dual hydrostatic pump to provide hydraulic fluid independently to a pair of motors on drive wheels of a grass mowing machine;

a pump arm on the left and right sides of the dual hydrostatic pump, each pump arm defining a stroke between a neutral position and a full forward position;

an actuator mounting plate having a longitudinal slot and left and right lateral slots;

a left linkage between the left pump arm and a left pivotable control lever, the left linkage sliding in the left lateral slot;

a right linkage between the right pump arm and a right pivotable control lever, the right linkage sliding in the right lateral slot; and

a linear actuator sliding in the longitudinal slot and moving the left and right linkages to vary the ratio of the control lever movement to the stroke imposed on the left and right sides of the dual hydrostatic pump.

2. The apparatus of claim 1 wherein the linkages are slidable in the lateral slots anywhere between a first position wherein both sides of the dual hydrostatic pump are not de-stroked and a second position wherein both sides of the dual hydrostatic pump are de-stroked.

3. The apparatus of claim 1 further comprising an engine speed sensor operatively connected to the linear actuator, the linear actuator moving the linkages based on sensed engine speed.

4. The apparatus of claim 3 wherein the linear actuator can move the linkages to a destroked position if sensed engine speed is lower than a specified value.

5. An apparatus comprising

a dual hydrostatic pump having left and right pump arms, each pump arm moving a separate swashplate;

left and right linkages between the left and right pump arms and left and right control levers; the linkages destroking both sides of the pump simultaneously if engine speed drops below a specified value; the linkages allowing each pump arm to have a first stroke range if the engine powering the pump is above the specified value, and a second smaller stroke range if the engine powering the pump is below the specified value; and

an actuator mounting plate having a plurality of slots in which the linkages slide laterally in response to changes in engine speed.

6. The apparatus of claim 5 wherein the left and right linkages each have legs pivoting further apart if engine speed drops below the specified value.

7. The apparatus of claim 5 further comprising a linear actuator that slides in one of the slots in the actuator mounting plate to change the geometry of the linkages according to sensed engine speed.

8. An apparatus comprising:

a zero turning radius mower having a dual pump hydrostatic transmission and left and right motion control levers; each motion control lever pivotable in a first direction to drive a motor that rotates a drive wheel on the mower in a first direction, and pivotable in a second direction to drive the motor that rotates the drive wheel in a second direction; and

a linkage that destrokes both sides of the dual pump simultaneously in response to decreased engine speed;

the linkage including a slotted actuator mounting plate in which a linear actuator connected to an engine speed sensor moves in a first slot in the plate in response to changes in engine speed, urging a left leg and a right leg of the linkage to move laterally in a second slot and a third slot in the plate.

9. The apparatus of claim 8 wherein the linkage destrokes both sides of the dual pump for forward travel and rearward travel.

10. The apparatus of claim 8 further comprising a damper to urge the motion control levers to neutral positions.

11. The apparatus of claim 8 wherein the linkage is slidable anywhere between a first position wherein both sides of the dual pump are not de-stroked, and a second position wherein both sides of the dual pump are de-stroked.

12. The apparatus of claim 8 wherein the motion control levers have the same range of motion if both sides of the dual pump are not de-stroked or if both sides are de-stroked.