Variable compression piston arrangement for internal combustion engine

A variable compression piston comprising:

• a first piston reciprocatively disposed in a cylinder, said first piston having an axial blind bore formed therein, said first piston being directly exposed to the pressure prevailing in said cylinder;
• a second piston reciprocatively disposed in said axial blind bore to define a first variable volume chamber therein, said second piston being retained in said blind bore by a retainer, said retainer defining a non-hermetically sealed second variable volume chamber between it and said second piston;
• a piston pin which operatively interconnects a connecting rod with said second piston;
• means defining a passage structure which is fluidly communicable with a source of hydraulic fluid under pressure;
• a stepped bore formed in said piston pin, said stepped bore being arranged to be in constant communication with said passage structure;
• a supply passage formed in said second piston, said supply passage leading from said stepped bore to said first variable volume chamber, said supply passage including a first one-way valve;
• a drain passage formed in said second piston, said drain passage fluidly communicating said first variable volume chamber with said stepped bore;
• a transfer passage which leads from said first variable volume chamber to said stepped bore, said transfer passage including means for restricting the flow of hydraulic fluid therethrough;
• a spool valve reciprocatively disposed in said stepped bore, said spool valve being movable between first and second positions, said spool having first and second lands, said first land having a smaller diameter than said second land, said spool being biased by a spring toward said first position,
• said first and second lands defining an essentially cylindrical chamber within said stepped bore, said cylindrically chamber constantly communicating with said source;
• said first land closing said drain passage and establishing fluid communication between said supply passage and said source when said spool assumes said first position,
• said first land opening said drain passage and one of closing and restricting the fluid communication between said source and said supply passage when it assumes said second position,
• said second land cooperating with said transfer passage, said second land having a reduced diameter portion which defines an annular clearance between it and the wall of said stepped bore, said reduced diameter portion juxtaposing said transfer passage when said spool assumes said first position in a manner that communication between said transfer passage and said cylindrical chamber is established through said annular clearance,
• said second land defining a surface area against which the pressure prevailing in said cylindrical chamber acts to produce a bias which tends to move said spool from said first position to said second position against the bias of said spring.

In an internal combustion engine

• a cylinder;
• a first piston reciprocatively disposed in said cylinder, said first piston having an axial blind bore formed therein, said first piston being directly exposed to the pressure prevailing in said cylinder;
• a second piston reciprocatively disposed in said axial blind bore to define a first variable volume chamber therein, said second piston being retained in said blind bore by a retainer, said retainer defining a second annular variable volume chamber between it and said second piston;
• a piston pin which operatively interconnects a connecting rod with said second piston;
• a valve bore formed in said piston pin, said valve bore being arranged to be in constant communication with a source of hydraulic fluid under pressure;
• a supply passage formed in said second piston, said supply passage leading from said valve bore to said first variable volume chamber;
• a drain passage formed in said second piston, said drain passage fluidly communicating with said first variable volume chamber;
• a valve element disposed in said valve bore, said valve element being responsive to the pressure prevailing in said first variable volume chamber and arranged so that when the pressure in said first variable volume chamber is below a predetermined value, said valve element assumes a first position wherein drain passage is cut-off and communication between said first variable volume chamber and said supply passage is fully established, and when the pressure in said first variable volume chamber is above said predetermined value, said valve element assumes a second position wherein communication between valve bore and said first variable volume chamber by way of said supply passage is one of cut-off and restricted and said drain passage is opened said valve bore comprising a stepped bore formed in said piston pin, and wherein said valve element comprises a spool having first and second lands, said first land being arranged to cooperate with said supply and drain passages.