Actuation system for a bent axis motor

Abstract

Methods and systems for a variable displacement bent axis piston motor are described. In one example, a variable displacement bent axis piston motor comprises a bent axis unit (BAU) rotary group including a cylinder block coupled to a drive shaft of the bent axis piston motor, and an electric actuator coupled to a servo piston of the bent axis piston motor, wherein a displacement of the BAU rotary group is controlled by an inclination angle between the drive shaft and a valve plate of the BAU rotary group coupled to the cylinder block, the inclination angle controlled by the servo piston, the servo piston controlled by the electric actuator. The servo piston is controlled by the electric actuator based a feedback control system, which may switch between various control strategies for adjusting the inclination angle based on different driving scenarios.

1 . A variable displacement bent axis piston motor comprising a bent axis unit (BAU) rotary group including a cylinder block coupled to a drive shaft of the bent axis piston motor, and an electric actuator coupled to a servo piston of the bent axis piston motor, wherein a displacement of the BAU rotary group is controlled by an inclination angle between the drive shaft and a valve plate of the BAU rotary group coupled to the cylinder block, the inclination angle controlled by the servo piston, the servo piston controlled by the electric actuator. 
     
     
         2 . The variable displacement bent axis piston motor of  claim 1 , wherein the electric actuator is positioned along a central axis of the servo piston in an inline configuration. 
     
     
         3 . The variable displacement bent axis piston motor of  claim 1 , wherein the electric actuator is positioned to one side of the servo piston, and the servo piston is controlled by the electric actuator via a dedicated transmission gear. 
     
     
         4 . The variable displacement bent axis piston motor of  claim 1 , wherein the servo piston is controlled by the electric actuator based a feedback control system of the variable displacement bent axis piston motor. 
     
     
         5 . The variable displacement bent axis piston motor of  claim 4 , wherein the feedback control system includes:
 one or more pressure sensors that measure an operating pressure of a hydraulic fluid circulating through the BAU rotary group;   one or more speed sensors that measure a rotational speed of the drive shaft;   one or more torque sensors that measure an amount of torque delivered at the drive shaft;   a valve plate angle sensor that measures the inclination angle; and   a piston position sensor that indicates a position of the servo piston within a servo piston chamber of the BAU rotary group.   
     
     
         6 . The variable displacement bent axis piston motor of  claim 5 , wherein controlling the electric actuator based on the feedback control system of the BAU rotary group further comprises actuating the servo piston to a desired position based on a selected control strategy for adjusting the inclination angle of the BAU rotary group, the selected control strategy stored in a memory of a controller of the variable displacement bent axis piston motor, the selected control strategy selected based on one of:
 a speed reference and an output of a speed sensor of the one or more speed sensors;   a torque reference and an output of a torque sensor of the one or more torque sensors; and   a pressure reference and an output of a pressure sensor of the one or more pressure sensors.   
     
     
         7 . The variable displacement bent axis piston motor of  claim 6 , wherein controlling the electric actuator based on the feedback control system further comprises selecting a first control strategy in response to a first driving scenario, and switching to a second control strategy in response to a second driving scenario. 
     
     
         8 . The variable displacement bent axis piston motor of  claim 7 , wherein first control strategy is a speed control strategy, the second control strategy is a pressure control strategy, and the second control strategy is selected in response to the output of the pressure sensor increasing above a threshold pressure. 
     
     
         9 . The variable displacement bent axis piston motor of  claim 8 , wherein the valve plate may be adjusted to a range of inclination angles, each inclination angle of the range of inclination angles corresponding to a location of the servo piston within the servo piston chamber. 
     
     
         10 . The variable displacement bent axis piston motor of  claim 9 , wherein the range of inclination angles extends from an inclination angle of zero, where a plurality of pistons of the cylinder block are aligned with the drive shaft and the displacement of the BAU rotary group is minimized, to a predefined maximum inclination angle where the displacement of the BAU rotary group is maximized. 
     
     
         11 . The variable displacement bent axis piston motor of  claim 10 , further comprising a minimum displacement limiter that stops the valve plate at the inclination angle of zero when the servo piston reaches a first end of the servo piston chamber, and a maximum displacement limiter that stops the valve plate at the predefined maximum inclination angle when the servo piston reaches a second, opposite end of the servo piston chamber. 
     
     
         12 . The variable displacement bent axis piston motor of  claim 1 , wherein a hydraulic or electro-hydraulic actuator is not used to control the servo piston. 
     
     
         13 . A method for controlling an inclination angle of a bent axis unit (BAU) rotary group of a variable displacement bent axis piston motor, the method comprising:
 receiving one a torque request from an operator of the variable displacement bent axis piston motor;   setting the inclination angle of the BAU rotary group based on the torque request;   selecting and applying a torque control strategy for controlling the inclination angle based on the torque request;   in response to a pressure of a hydraulic fluid circulating through the BAU rotary group increasing above a threshold pressure:
 selecting a pressure control strategy for controlling the inclination angle based on a pressure reference; 
 switching from the torque control strategy to the pressure control strategy; and 
 adjusting the inclination angle in accordance with the pressure control strategy; and 
   in response to the pressure being maintained below the threshold pressure, continuing to control the inclination angle using the torque control strategy.   
     
     
         14 . The method of  claim 13 , wherein:
 applying the torque control strategy for controlling the inclination angle further comprises receiving a torque measurement from a torque sensor of the variable displacement bent axis piston motor, and adjusting the inclination angle based on a difference between the torque request and the torque measurement; and   adjusting the inclination angle in accordance with the pressure control strategy further comprises receiving a pressure measurement from a pressure sensor of the variable displacement bent axis piston motor, and adjusting the inclination angle based on a difference between the pressure reference and the pressure measurement.   
     
     
         15 . The method of  claim 13 , further comprising:
 in response to the inclination angle achieving a minimum inclination angle and the pressure being maintained above the threshold pressure, notifying the operator.   
     
     
         16 . The method of  claim 13 , wherein the torque control strategy and the pressure control strategy are selected from a plurality of control strategies stored in a memory of a controller of the variable displacement bent axis piston motor. 
     
     
         17 . A control system for a variable displacement bent axis piston motor, the control system comprising:
 a servo piston coupled to a valve plate of a bent axis unit (BAU) rotary group of the variable displacement bent axis piston motor, the valve plate configured to slide between a first position where a displacement of the BAU rotary group is maximized and a second position where the displacement is minimized, based on a position of the servo piston within a corresponding piston chamber;   a piston position sensor that indicates a position of the servo piston within the corresponding piston chamber;   a pressure sensor that measures an operating pressure of a hydraulic fluid circulating through the BAU rotary group;   a speed sensor that measures a rotational speed of a drive shaft coupled to the BAU rotary group;   a torque sensor that measures an amount of torque delivered at the drive shaft;   an electric actuator configured to adjust the position of the servo piston within the corresponding piston chamber, the electric actuator not including hydraulic components; and   a controller including a processor and instructions stored in a non-transitory memory of the controller that when executed cause the controller to:
 adjust the position of the servo piston based on one of a torque reference, a speed reference, and a pressure reference; and a feedback signal from one of the torque sensor, the speed sensor, and the pressure sensor. 
   
     
     
         18 . The control system of  claim 17 , wherein further instructions are stored in the non-transitory memory that when executed, cause the controller to:
 in a first condition, in response to a first speed reference provided by an operator of the bent axis piston motor, actuate the servo piston based on the first speed reference and a first feedback signal from the speed sensor; and   in a second condition, in response to a second feedback signal from the pressure sensor increasing above a threshold pressure, actuate the servo piston based on the second feedback signal and a desired pressure range.   
     
     
         19 . The control system of  claim 18 , wherein the operator is a driver of a vehicle including the of the bent axis piston motor, the first condition includes the vehicle being operated at a speed on a road with a grade of 0 degrees, and the second condition includes the vehicle being operated at the speed on a road with a grade greater than 0 degrees. 
     
     
         20 . The control system of  claim 18 , wherein further instructions are stored in the non-transitory memory that when executed, cause the controller to:
 in the second condition, in response to the servo piston being actuated to a minimum inclination angle and the feedback signal from the pressure sensor being maintained above the threshold pressure, notify the operator to reduce a speed of the bent axis piston motor.