Valve mechanism for controlling a reciprocating engine power stroke

A valve mechanism, suitable for controlling the flow of a working fluid supplied from a fluid source at a pressure sufficient to operate an engine with a piston reciprocating in a cylinder to generate a rotational output, comprising:

• inlet valve means operable in a first mode for admitting said working fluid into said cylinder at an essentially constant inlet pressure during substantially an entire working stroke of said piston and operable in a second mode for admitting said working fluid at said essentially constant inlet pressure only during a starting portion of a working stroke so that the fluid thus admitted into the cylinder thereafter expands during the balance of the corresponding working stroke;
• and
• mode-changing means responsive to a selected operating parameter of said engine for causing said inlet valve means to change operation of said inlet valve means between said first and second modes of operation thereof.

A method for controlling the flow of a working fluid supplied from a fluid source at a pressure sufficient to operate an engine with a piston reciprocating in a cylinder to generate a rotational output, comprising the steps of:

• providing said working fluid to said cylinder to generate a working stroke in a first mode when an operating parameter of said engine is at less than a predetermined reference value thereof, said first mode being characterized in that the inflow of working fluid takes place at an essentially constant inlet pressure during substantially the entire extent of said working stroke of said piston;
• and
• providing said working fluid to said cylinder to generate a working stroke in a second mode when said operating parameter of said engine exceeds said reference value, said second mode being characterized in that the inflow of working fluid takes places at said essentially constant inlet pressure only during an initial portion of said working stroke, whereafter said inflow is terminated and the quantity of working fluid thus admitted into the cylinder expands during substantially the balance of said working stroke of said piston.