Variable compression ratio mechanism for reciprocating internal combustion engine

A variable compression ratio mechanism for a reciprocating internal combustion engine including a piston moveable through a stroke in the engine and having a piston pin and a crankshaft changing reciprocating motion of the piston into rotating motion and having a crankpin, the variable compression ratio mechanism comprising:

• a plurality of links mechanically linking the piston pin to the crankpin;
• a control shaft to which an eccentric cam is attached so that a center of the eccentric cam is eccentric to a center of the control shaft;
• a control link connected at one end to one of the plurality of links and connected at the other end to the eccentric cam;
• and
• a control-shaft actuating means for driving the control shaft within a predetermined controlled angular range and holds the control shaft at a desired angular position so that a compression ratio of the engine continuously reduces by driving the control shaft in a first rotational direction and so that the compression ratio continuously increases by driving the control shaft in a second rotational direction opposite to the first rotational direction;
• the actuating means comprising:
• (i) a reciprocating block slider linked at a first end portion to the control shaft;
• (ii) a rotary member being in meshed-engagement with a second end portion of the slider by a meshing pair of screw-threaded portions, so that rotary motion of the rotary member is converted into axial sliding motion of the slider to drive the control shaft in one of the first and second rotational directions;
• and
• (iii) a substantially cylindrical casing cooperating with the slider and the rotary member to define a hydraulic pressure chamber facing an axial end face of the second end portion of the slider so that working-fluid pressure in the hydraulic pressure chamber forces the slider in the same axial direction as a direction of action of a reciprocating load acting on the slider during down stroke of the piston, the reciprocating load acting on the slider in axial directions of the slider during up and down strokes of the piston.