Control device for hydrostatic transmission.

摘要

A hydrostatic transmission such as for a vehicle comprises a variable speed prime mover (10), a variable displacement pump (20) powered by the prime mover (10), a fluid motor (30) powered by the variable displacement pump (20) and, in accordance with the invention a control device (10) which senses the speed of the prime mover (10) and regulates the operation of a control cylinder (60) of the variable displacement pump (20) in accordance therewith so that the speed of the fluid motor (30) is not only respective to speed changes in the operation of the variable displacement pump (20) directly attributable to changes in speed of the prime mover (10) driving the variable displacement pump (20) but also responds to displacement changes in the variable displacement pump (20). A fixed pump (90) powered by the prime mover (10) develops a fluid flow proportional to the speed of the prime mover (10) and this is converted into a corresponding mechanical signal by means of a series orifice (100) which develops a pressure differential proportional to the fluid flow of the fixed displacement pump (90), which sets the operation of a piston and cylinder arrangement (142). The said mechanical signal determines the setting of a compensator valve spool (156) which in dependance upon the position of an associated sleeve (160) determines the supply of high pressure fluid to the spool (176) of a servo arrangement having a control sleeve (182) which is mechanically linked with the displacement control element (40) of the variable displacement pump (20) and furthermore provides a camming surface for a cam follower (198) which in turn acts upon the compensator valve sleeve (160). By this means, a mechanical feedback signal representative of the displacement of the variable displacement pump (20) is transmitted to the control means of the variable displacement pump (20) to maintain the pump displacement proportional to the speed of the prime mover (10).