Hydraulically controlled hydrostatic transmission

Abstract

A hydrostatic transmission system includes a pump including a rotatable swash plate, wherein rotation of the swashplate effects a change in volumetric displacement of the pump. An actuator is coupled to the swashplate, the actuator operative to effect rotation of the swashplate to change the volumetric displacement of the pump. An electronic controller is operatively coupled to the actuator, the electronic controller configured to command the actuator to effect rotation of the swashplate.

What is claimed is: 
     
         1 . A pump control system, comprising:
 a pump including a swash plate tiltable about a swashplate tilt axis, wherein rotation of the swashplate changes the title angle and effects a change in volumetric displacement of the pump;   an actuator drivingly coupled to the swashplate, the actuator operative to displace the swashplate about the tilt axis to change the volumetric displacement of the pump; and   a fluid power control device operative to vary fluid power provided to the actuator in response to a control signal; and   a controller operatively coupled to the fluid power control device, the controller configured to generate the control signal to modulate the fluid power provided by the fluid power control device to the actuator to effect rotation of the swashplate.   
     
     
         2 . The pump control system according to  claim 1 , further comprising an input device operatively coupled to the controller, the input device operative to provide an input command corresponding to an output characteristic of a hydrostatic transmission, wherein the controller is configured to control an angular orientation of the swashplate based on the input command. 
     
     
         3 . The pump control system according to  claim 1 , further comprising a sensor communicatively coupled to the controller, the sensor operative to detect an angular position of the swashplate and to provide the detected angular position to the controller. 
     
     
         4 . The pump control system according to  claim 1 , wherein the controller is configured to effect rotation of the swashplate independent of a user supplied command. 
     
     
         5 . The pump control system according to  claim 1 , wherein the fluid power control device comprises an electronically-operated valve. 
     
     
         6 . The pump control system according to  claim 5 , wherein the electronically-operated valve comprises a pressure control valve. 
     
     
         7 . The pump control system according to  claim 1 , wherein the actuator comprises a hydraulic actuator. 
     
     
         8 . The pump control system according to  claim 7 , wherein the hydraulic actuator comprises a linear actuator or a rotary actuator. 
     
     
         9 . The pump control system according to  claim 1 , wherein the actuator is directly coupled to the swashplate. 
     
     
         10 . The pump control system according to  claim 1 , wherein the actuator is indirectly coupled to the swashplate. 
     
     
         11 . The pump control system according to  claim 1 , wherein the actuator comprises a ball-screw actuator. 
     
     
         12 . The pump control system according to  claim 1 , further comprising a prime-mover coupled to the pump and operative to provide mechanical power to the pump module. 
     
     
         13 . The pump control system according to  claim 1 , further comprising a hydrostatic transmission. 
     
     
         14 . A zero-turn lawn mower, comprising:
 a prime mover; and   a hydrostatic transmission, the hydrostatic transmission including the swashplate control system according to  claim 1 .   
     
     
         15 . A method for controlling volumetric displacement of a hydraulic pump having a swashplate tiltable about a swashplate tilt axis, wherein rotation of the swashplate changes the title angle and effects a change in volumetric displacement of the pump, and an actuator drivingly coupled to the swashplate, the actuator operative to displace the swashplate about the tilt axis to change the volumetric displacement of the pump, the method comprising using an electronic controller to modulating hydraulic power provided to the actuator to effect rotation of the swashplate. 
     
     
         16 . The method according to  claim 15 , wherein modulating hydraulic power includes using a fluid power control device to modulate fluid power to the actuator. 
     
     
         17 . The method according to  claim 15 , further comprising:
 receiving at the controller a user-initiated command corresponding to an output characteristic of the hydrostatic transmission; and   controlling an angular orientation of the swashplate based on the user-initiated command.   
     
     
         18 . The method according to  claim 15 , further comprising:
 receiving at the controller position data corresponding to an angular orientation of the swashplate; and   controlling an angular orientation of the swashplate based on the position data.   
     
     
         19 . The method according to  claim 15 , wherein using the electronic controller to modulate hydraulic power provided to the actuator includes modulating pressure independent of a user supplied command.