Variable displacement hydraulic servomotor system

Hydraulic servo system comprising:

• a bidirectional variable-displacement hydraulic motor having a displacement control member movable between a first lower-displacement position and a second higher-displacement position, said motor also having a pair of fluid flow ports either of which may receive hydraulic pressure fluid while the other of said pair of ports discharges returned hydraulic fluid dependent upon the direction of rotation of said bidirectional motor;
• resilient means yieldably biasing said displacement control member to said first position;
• a source of pressurized hydraulic fluid, said source also including a reservoir for receiving returned hydraulic fluid at a comparatively lower pressure;
• directional control valve means communicating said source with said hydraulic motor to supply said pressurized hydraulic fluid selectively to either one of said pair of ports while receiving returned fluid from the other of said pair of ports for flow to said reservoir;
• flow control means interposing between said other port of said motor and said reservoir for throttling said returned fluid flow dependent upon the flow rate thereof, said flow control means substantially not throttling said returned fluid flow below a selected flow rate thereof, and providing an increasing flow-dependent throttling of said returned fluid flow at and above said selected fluid flow rate;
• double-acting hydraulic actuator means having a pair of oppositely directed pressure fluid responsive faces, said hydraulic actuator means operatively connecting with said displacement control member to move the latter between said first and said second positions thereof;
• pressure responsive bistable valve means communicating with said pair of fluid flow ports of said motor and moving between a first position and a second position dependent upon the sense of fluid pressure differential between said pair of motor ports, said bistable valve means communicating the one of said pair of motor ports having the lower fluid pressure with the one of said pair of oppositely directed pressure fluid responsive faces of said actuator means which is disposed to assist said resilient means in urging said displacement control member to the first position thereof, said bistable valve means further communicating the other of said pair of motor ports having the higher fluid pressure with the other of said pair of oppositely directed pressure fluid responsive faces of said actuator means;
• pressure differential responsive metering valve means interposing between said bistable valve means and said other oppositely directed pressure fluid responsive face of said actuator means to respond to said higher fluid pressure, and said metering valve means also communicating with said lower fluid pressure communicating between said bistable valve means and said one pressure fluid responsive face of said actuator means, said metering valve means closing communication of said higher fluid pressure to said other face of said actuator means so long as the pressure differential between said higher pressure and said lower pressure is less than a determined value, and metering flow of said higher fluid pressure to said other pressure responsive face of said actuator proportionately to said pressure differential at and above said determined value;
• said actuator means moving said displacement control member between said first position and said second position in response to flow of said higher pressure fluid to said other pressure fluid responsive face thereof in accord with the pressure balance between said pair of oppositely directed faces thereof;
• whereby said servomotor may drive or brake movement of a resisting or assisting load, respectively, in either of two opposite directions under control of said directional control valve, said servomotor operating at said lower displacement so long as the fluid pressure differential thereacross is less than said determined value of said metering valve means and proportionately increasing in displacement with fluid pressure differentials above said determined value until said higher displacement is achieved, an assisting load condition operating said motor as a pump to pressurize said returned fluid above said source while said flow control means throttles said returned fluid to provide load braking at and above said selected flow rate, and said bistable valve means shifting between said first and second positions thereof to communicate said pair of motor ports with said metering valve means and said actuator means for displacement control of said motor in both directions of operation and with resisting and assisting load conditions.

In a hydraulic servomotor system having a bidirectional rotary output drivingly connecting with a variable load which is movable in either of two opposite directions in accord with rotational direction of said rotary output, and which load may either resist or assist movement thereof by said servomotor, the method of controllably effecting movement of said load by impelling or braking movement thereof with said servomotor including the steps of:

• utilizing a variable-displacement hydraulic motor having a rotary output shaft and a pair of fluid inlet/return ports as said servomotor, the inlet or return function of each one of said pair of ports being dependent upon direction of rotation of said output shaft:
• drivingly coupling said output shaft with said load;
• yieldably biasing said servomotor to a low-displacement condition;
• providing pressure fluid flow from a source thereof to a selected one of said pair of ports and receiving returned fluid flow from the other of said pair of ports to result in rotation of said output shaft and load movement;
• sensing the fluid pressure differential between said pair of ports;
• upon said fluid pressure differential reaching a determined level, progressively increasing the displacement of said servomotor to a high-displacement condition as a function of said pressure differential above said determined level to provide increased impelling or braking torque to said load;
• sensing the flow rate of said returned fluid flow from said servomotor;
• and
• upon said returned fluid flow rate reaching a selected level indicative upon assisting load condition, progressively throttling said returned fluid flow as a function of said returned fluid flow rate to provide increasing braking torque to said load.

Variable displacement hydraulic servomotor apparatus comprising:

• a housing defining a cavity therein and journaling a rotatable shaft in said cavity;
• a cylinder member drivingly carried upon said shaft for rotation therewith within said cavity and defining a plurality of circumferentially arrayed axially extending bores therein;
• a plurality of plunger members respectively received reciprocally in said plurality of bores to cooperatively define a plurality of variable-volume chambers expanding and contracting in response to reciprocation of said plunger members;
• a swash plate member pivotally carried by said housing within said cavity and variably angularly disposed relative to a transverse radial plane, each one of said plurality of plunger members engaging with said swash plate member for reciprocation in the respective one of said plurality of bores in response to rotation of said shaft;
• said housing defining a pair of fluid inlet/return ports each for respectively receiving or discharging hydraulic fluid dependent upon direction of rotation of said shaft;
• fluid flow communicating means communicating said plurality of variable-volume chambers with one of said pair of inlet/return ports during contraction of said chambers and with the other of said pair of inlet/return ports during expansion of said chambers with shaft rotation in one direction, shaft rotation in the opposite direction reversing the sense of said expansion or contraction of said plurality of chambers relative to said pair of ports;
• resilient means yieldably urging said swash plate member to a first low displacement position whereat volume change of said plurality of variable-volume chambers is of lesser value,
• a pair of bores opening to said cavity;
• a pair of pressure responsive piston members respectively received in said pair of bores and cooperatively associating with said swash plate member to urge the latter individually in opposite pivotal directions respectively in response to fluid pressure applied thereto;
• flow path means communicating each of said pair of inlet/return ports with each of said pair of pressure responsive piston members;
• bistable valve means interposing in said flow path means in a first position communicating one of said pair of ports with one of said pressure responsive piston members and communicating the other of said pair of pressure responsive piston members, and in a second position communicating said one port with the other piston member and said other port with said one piston member, said valve means shifting between said first and said second positions in response to fluid pressure differential between said pair of ports to communicate the lower fluid pressure to the first of said pair of pressure responsive piston members assisting said resilient means and the higher fluid pressure to the second of said pair of pressure responsive piston members,
• pressure differential responsive metering valve means for interposing in said flow path means between said bistable valve means and said second pressure responsive piston member, and said metering valve means communicating with said pair of ports and closing said communication so long as said pressure differential is below a certain value, at and above said certain value said metering valve means progressively metering fluid flow to said second pressure responsive piston member as a function of said pressure differential.