Ring cam and fluid-working machine including ring cam

Abstract

A fluid-working machine comprising a ring cam, at least one piston defining a working chamber, and at least one valve associated with the or each working chamber for connecting the working chamber alternately to low and high pressure manifolds in phased relationship to cycles of working chamber volume. The ring cam has a wave-like cam working surface for operative engagement with the at least one piston. The waves of the wave-like cam surface each having a leading face and a trailing face and discontinuities, such as apertures to retain bolts, are located in the working surface on whichever of the leading face and the trailing face the at least one piston does least work during normal operation resulting from the flow of fluid into and out of the working chamber in phased relationship to cycles of working chamber volume.

1 . A fluid-working machine comprising a ring cam, a low pressure manifold, a high pressure manifold, at least one piston defining a working chamber, and at least one valve associated with the or each working chamber for connecting the working chamber alternately to the low or the high pressure manifold in phased relationship to cycles of working chamber volume, the ring cam having a wave-like cam working surface for operative engagement with the at least one piston by way of a cam engaging element so as to couple reciprocating motion of the at least one piston to rotation of the ring cam relative to the at least one piston and to thereby define the cycles of working chamber volume; the waves of the wave-like cam surface each having a leading face and a trailing face; characterised by discontinuities in the working surface located on whichever of the leading face and the trailing face the at least one piston does least work during normal operation resulting from the flow of fluid into and out of the working chamber in phased relationship to cycles of working chamber volume. 
     
     
         2 . A fluid-working machine according to  claim 1 , wherein the discontinuities in the working surface located on whichever of the leading face and the trailing face the at least one piston exerts least force during normal operation resulting from the flow of fluid into and out of the working chamber in phased relationship to cycles of working chamber volume. 
     
     
         3 . A fluid-working machine according to  claim 1 , wherein the ring cam comprises at least two segments extending around the circumference of the ring cam; and a support structure to which the said segments are attached; each said segment comprising a piston facing surface, the piston facing surfaces of the segments defining the working surface. 
     
     
         4 . A fluid-working machine according to  claim 3 , wherein the said discontinuities in the working surface are attachment means for securing said segments to the support structure. 
     
     
         5 . A fluid-working machine according to  claim 1 , wherein the said discontinuities are discontinuities between adjacent segments. 
     
     
         6 . A fluid-working machine according to  claim 1 , wherein the said discontinuities are of a first type and that the working surface comprises further discontinuities, of a second type, which are otherwise distributed. 
     
     
         7 . A fluid-working machine according to  claim 1 , wherein each said cam engaging element is biased against the working surface by fluid pressure from within the respective working chamber. 
     
     
         8 . A fluid-working machine according to  claim 1 , wherein the said discontinuities are located in the working surface of only some of whichever of the leading face and the trailing face the pistons do least work during operation resulting from the flow of fluid into and out of the working chamber in phased relationship to cycles of working chamber volume in a first operating mode. 
     
     
         9 . A fluid-working machine according to  claim 1 , wherein the fluid-working machine has a second operating mode in which active cycles of working chamber volume cause the pistons to do a greater amount of work on the said whichever of the leading face and the trailing face the pistons do least work during operation in the first operating mode, and in which said active pumping or active motoring cycles are carried out selectively when the cam engaging element bears on the said whichever of the leading face and the trailing face the pistons do least work during operation in the first operating mode do not have the said discontinuities. 
     
     
         10 . A fluid-working machine according to  claim 1 , wherein each said working chamber comprises one or more electronically controllable valves, and the fluid-working machine comprises a controller, operable to control the or each electronically controllable valve, each said working chamber being selectable by the controller, on a cycle by cycle basis, to conduct an active cycle or an idle cycle, by virtue of control of the or each electronically controllable valve. 
     
     
         11 . A method of operating a fluid-working machine, the fluid-working machine comprising a ring cam, a low pressure manifold, a high pressure manifold, at least one piston defining a working chamber of cyclically varying volume, and at least one electronically controlled valve associated with the or each working chamber for connecting the working chamber alternately to a said low pressure manifold and a said high pressure manifold in phased relationship to cycles of working chamber volume; the ring cam having a working surface for operative engagement with the or each piston by way of a cam engaging element so as to couple reciprocating motion of the or each piston to rotation of the ring cam relative to the or each piston and to thereby define the cycles of working chamber volume; one or more regions of the working surface having a discontinuity;
 the method characterised by limiting the working fluid pressure in a said working chamber when the respective cam engaging element bears on a said discontinuity in the working surface.   
     
     
         12 . A method according to  claim 11 , wherein the net volume of fluid to be displaced by a said working chamber during a cycle of working chamber volume is selected or selectable responsive to the pressure in the high pressure manifold and/or the position of the or each cam engaging element in relation to each said discontinuity, to thereby limit the working fluid pressure in the said working chamber while the respective engaging element bears on a said discontinuity. 
     
     
         13 . A method according to  claim 11 , wherein the method comprises reading discontinuity location data from a computer readable data storage medium which stores data concerning the location of each said discontinuity in relation to the relative orientation of the ring cam. 
     
     
         14 . A kit of parts which, when assembled, forms a fluid-working machine according to  claim 1 . 
     
     
         15 . A computer readable medium storing program code which when executed on a fluid working machine controller, causes the fluid working machine to carry out a method according to  claim 11 .