Hydrostatic drive systems

In a hydrostatic drive system having an adjustable pump, an adjusting element on said pump, a pump servo piston connected to and capable of moving said adjusting element, said servo piston being movable in a cylinder, a main feed line from said pump, a plurality of consumers of pressure fluid, a branch feed line connecting each said consumer to said main feed line, a return line from each consumer to a reservoir, a switching means in each branch line, a pair of adjustable parallel connected restrictors in each branch line, an adjusting element in each of said parallel connected restrictors loaded on one side with the pressure in said branch feed line and on the other with a control pressure and a spring, the control pressure being identical on all parallel connected restrictors, a separate branch control line delivering said control pressure to each parallel connected restrictor from a common control pressure line, check valve means opening toward the common control line in each branch control pressure line, an adjustable measuring restrictor in each branch line leading to a consumer and a control pressure line connected to said branch line between said adjustable measuring restrictor and the consumer, the improvement comprising said switching means including a valve housing having a plurality of longitudinal bores corresponding to the number of consumers, a main spool movable in each said bore, said main spool being hollow at each end, an inlet port in said housing connected to the main feed line and to each bore, an outlet connected to said control pressure means and each bore adjacent the inlet connection with the bore, secondary valve spools in each of the hollow ends of said main spool, spring means acting on each spool to urge the spools towards the ends of said main spool, and a plurality of radial passages spaced lengthwise on the main spool communicating with said hollow ends and forming with the secondary spools said parallel connected restrictors, an inlet chamber in the housing communicating with said bore intermediate its ends and communicating between said bore and the feed line, an exhaust chamber at each end of the housing communicating with the bore and said reservoir, a work chamber at each end of the housing intermediate the inlet and exhaust chambers and connected to the consumers of pressure fluid, a spring means in each of said hollow ends acting on said secondary spools to urge them towards the two ends of said spool, the plurality of spaced radial passages in said main spool communicating with said hollow ends, said radial passages being spaced so that in a working postion they communicate between and variably restrict flow between the work chambers and one of the inlet chambers in one position and the exhaust chambers in a second position, and wherein in each work position the radial passages in the main spool and the sensing grooves and passages in the secondary spools are arranged so that when the main spool is moved to connect the inlet chamber with a work chamber the end of the secondary piston on the end through which such connection is made opposite the spring is connected with a radial passage acting as a measuring restrictor and the end of the secondary spool loaded by the spring is connected through a radial passage in the main spool through a sensing passage in the secondary spool and the other secondary spool on the end of the main spool connecting the opposite work chamber and the exhaust chamber, the spring end of the secondary spool connects the opposite work chamber through the sensing groove at that end and a sensing passage with the end of the secondary spool opposite the spring to move the secondary spool against the spring to connect the work chamber and exhaust chamber, and wherein the side of the secondary spool loaded with the pressure spring can also be connected through a check valve with the work chamber connected with the consumer.