Hydrostatic transmission pump

In combination with a well pumping apparatus having, a walking beam pivotally supported for rocking movement and adapted to have a polish rod connected to one end thereof and counterweights to its opposite end, double-acting hydraulic cylinder means operatively connected with said walking beam for imparting rocking movement thereto, and reversing control means operatively associated with said walking beam for sensing the movement of said beam and controlling the action of said double-acting cylinder means in driving said walking beam:

• a substantially closed circuit hydrostatic drive system operatively connected in driving relationsip with said double-acting hydraulic cylinder means and operatively connected with said reversing control means for control thereby, said circuit hydrostatic drive system comprising, a variable displacement reversing swashplate pump, a prime mover operatively connected with said pump for driving the same at predetermined speed, hydraulic circuit means operatively interconnecting each of two discharge/return ports of said pump with one of two inlet/outlet ports of said double-acting hydraulic cylinder means, and means operatively interconnecting said reversing control means with the swashplate of said pump for reversing the same in synchronism with the rocking movement of said walking beam, said reversing control means including a four-way valve and actuating means therefor whereby each time said walking beam rocks up or down said four-way valve is actuated into one of its two operative positions, said four-way valve having a pressure inlet port interconnected with a pressure discharge connection of a make-up pump supplying fluid under pressure to said variable displacement reversing swashplate pump, an outlet port, and a pair of discharge/return ports, and said four-way valve in one of its operative positions having one of said discharge/return ports in communication with said inlet port with the other discharge/return port in communication with said outlet port and in the other of its operative positions having said one of its discharge/return ports in communication with said discharge port and having said other discharge/return port in communication with said inlet port, and wherein said means operatively interconnecting said reversing control means with the swashplate of said pump comprises a second double-acting cylinder means having two inlet/outlet ports each of which is interconnected with one of said discharge/return ports of said four-way valve whereby said second double-acting cylinder means is actuated in one direction when said four-way valve is in one of its operative positions, and linkage means operatively interconnecting said second double-acting cylinder means with said swashplate.