Electronically controlled dampener for hydrostatic transmission

A hydrostatic transmission comprising:

• a fluid motor;
• a variable displacement fluid pump in fluid communication with said fluid motor, said pump having a first fluid displacement rate and a second fluid displacement rate, said second fluid displacement rate being much greater than said first displacement rate;
• a block on which said pump is mounted, said block having a flat surface against which said pump is slidably engaged when said pump is operating at its said first and second fluid displacement rates, said block provided with at least one fluid passage which opens to said flat block surface, fluid which flows from said pump to said motor flowing through said passage;
• a fluid sump external to said block, said block having at least one fluid bleed hole open to said fluid sump;
• and
• means for placing said passage and said sump in fluid communication when said pump is operating at its said first fluid displacement rate and providing a gradual motor response to changes between said pump first and second fluid displacement rates, said means for placing said passage and said sump in fluid communication further including means for maintaining said passage and said sump substantially out of fluid communication when said pump is operating at its said second displacement rate.

A method for dampening the response of a fluid motor to changes in a fluid pump between a neutral position and a drive position in a hydrostatic transmission, and preventing fluid from being pumped by the fluid pump to the motor in the pump neutral position, comprising:

• rotating the pump while maintaining its sliding engagement against a block having at least one passage therethrough;
• operating the rotating pump at a first displacement rate in its neutral position, in which the passage and a sump are in fluid communication, whereby fluid displaced by the pump in its neutral position is directed to the sump;
• progressively decreasing the fluid communication between the passage and the sump while changing from the pump neutral position to the pump drive position by sliding an axially slidable member engaged with the block and having a void provided therein to a position in which the void is substantially out of fluid communication with the passage;
• operating the rotating pump at a second displacement rate greater than the first displacement rate when in its drive position, in which the passage and the sump are substantially out of fluid communication, whereby fluid displaced by the pump in its drive position is directed to the motor through the passage for driving the motor;
• and
• progressively increasing the fluid communication between the passage and the sump while changing the pump from its drive position to its neutral position by sliding the axially slidable member to a position in which the void is in fluid communication with the passage.