Importance

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Abstract

A rotary fluid pressure device (11) comprising a gerotor motor of the type including a spool valve member (51) cooperating with a housing (13) to define a nominal valve overlap (X). The motor has a drive shaft (53) for transmitting the rotational movement of a gerotor star (27) to the spool valve member (51) and output shaft (49), such that, under high torque loads, the drive shaft (53) is subjected to drive twist, which would normally effect valve timing. In accordance with the invention, the spool valve member (51) and the housing are provided with a valve overlap (Y) which is substantially greater than the nominal overlap (X). The star (27) defines, on its profile (85), first (87) and second (89) recesses which permit communication between the minimum (30) and maximum (32) volume transition chambers and the respective expanding (29) and contracting (31) volume chambers (FIG. 8). The result is an improvement in both mechanical and volumetric efficiency, as well as smoother operation at low speed and high pressure.

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First Claim