Fluid-working machine with multi-lobe ring cam

A fluid-working machine for a renewable energy generation device, the fluid-working machine comprising:

• a ring cam,
• a plurality of working chambers, and
• a low-pressure manifold,
• the ring cam having an annular working surface extending around an axis of rotation of the ring cam, the annular working surface defining a plurality of waves,
• each working chamber having a piston, each piston in operative engagement with the ring cam working surface,
• the ring cam and working chambers being mounted to rotate relative to each other, cycles of working chamber volume being thereby coupled to rotation of the ring cam relative to the working chambers,
• wherein individual waves of the ring cam working surface have an asymmetric profile,
• wherein the waves have opposite first and second faces, each face extending between a maximum of radius relative to an axis of the rotation and a minimum of radius relative to the axis of the rotation,
• wherein one of the first and second faces is a working face on which cam following elements bear when a pressure in the working chamber is highest compared with a pressure in the low-pressure manifold and the other of the first and second faces is a breathing face, said working faces having convex portions and concave portions, and
• wherein a maximum curvature of the convex portions of the working faces is less than a maximum curvature of the concave portions of the working faces.