Patent Publication Number: US-2022220886-A1

Title: Casella hydraulic variable compression ratio piston

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a variable compression ratio piston which changes height relative to a common connecting rod to modify the compression ratio in a typical internal combustion engine. 
     (2) Description of the Related Art 
     In modern internal combustion engines, a higher compression ratio yields more power and greater fuel efficiency. Compression ratio is thus defined as the largest cylindrical volume atop the piston, at bottom dead enter, divided by the smallest cylindrical volume atop the same piston at top dead center. By definition, a fixed compression ratio only allows combustion efficiency to occur at maximum engine torque and load with only partial combustion at lesser loads due to the partial filling of the cylinder. Partial filling occurs when only small injection of fuel and air are required for smaller engine loads or when the total mix of fuel and air does not completely fill the cylinder due to air friction and greater piston speeds. 
     A variable compression engine, however, constantly changes the compression ratio to match the combination of air/fuel mix and engine load, thereby achieving full and efficient combustion at every engine speed. Variable compression does make for an overly complex and expensive engine design. 
     The hydraulic variable compression ratio piston, however, is a more reliable, simpler, and cheaper build, and still allows the flexibility of a variable compression engine. 
    
    
     BRIEF SUMMARY OF THE INVENTION 
     This invention changes compression by doing a partial movement of the piston relative to the connecting rod. As the combustion wave front pushes against the piston, the piston shrinks down relative to the connecting rod, much like a shock absorber, to avoid harmful pre-detonation in the case of excessive combustion pressure at the current compression ratio, for example, 12 to 1. This partial movement is achieved by the rotation of the eccentric piston pin. 
     The relative position of the piston stays fixed at its current compression ratio. The compression ratio only changes when power levels and inertia of the piston and connecting rod at bottom dead center increases or decreases. 
     This control of the compression ratio is achieved with a combination of return springs to the eccentric and an opposing contra-acting lifter to the eccentric. The function of the return springs, to return the eccentric to its original position, is opposed and controlled by the opposing lifter, installed within the piston. 
     The lifter eventually loses oil and contracts, but very slowly at lower combustion and engine loads. At higher combustion and greater engine loads, the lifter expands as the return springs contract. The eccentric therefore only turns when there are changes in the combustion pressure. If power levels remain the same, the opposing lifter holds its position against the eccentric return springs, and the compression ratio stays the same. 
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  depicts the variable compression piston at its highest, at top dead center, with the eccentric piston pin at its lowest position in the eccentric. In this depiction the compression ratio is at its highest, for example 12 to 1. 
       FIG. 2  depicts the variable compression piston at its lowest, at bottom dead center, with the eccentric piston pin at its highest position in the eccentric. In this depiction the compression ratio is at its lowest, for example 8 to 1.