pat-head Variable Compression Ratio ( pat-head VCR )
A simple, lightweight and compact, yet robust and fully functional, Variable Compression Ratio mechanism for internal combustion engines.
A continuously-Variable-Compression-Ratio mechanism (pat-head VCR, compression ratio from 7:1 to 20:1) together with a continuously-variable-valve-lift mechanism (VVA-rod-version, valve lift from 0mm to 10+mm) into a "Renault-1.4-Energy" cylinder-head, as exhibited at EngineExpo2009, Stuttgart, Germaqny.
The crankcase has projections comprising pillars and bridges.
The pillars enter, through proper openings, into the cylinder head.
The bridges couple the free ends of the pillars to strengthen the structure and to provide supports to a
control shaft.
The control shaft is pivotally mounted on the cylinder head above the combustion chambers
and, by 'small connecting rods', it is supported on the bridges.
The narrowing between neighboring cylinders, typical in conventional cylinder
blocks, is an available free area for the pillars to pass and an available free surface for sliders.
The pillars connect, as directly as desirable, the tightening screws of the crankshaft bearing caps
to the tightening screws of the bridges.
The gas pressure force on the piston causes a heavy 'column load' on the connecting rod. The equal and opposite gas
pressure force on the cylinder head passes initially to the control shaft, then it is shared between
the two neighboring 'small connecting rods' causing pure 'tension loading', then it is shared among the four neighboring pillars
causing pure 'tension loading' too.
The thrust force from the pistons onto the cylinder wall, several times weaker than the gas pressure force onto the piston,
passes to the crankcase through sliders at the lower, well supported, side of the pillars.
As for the bridges, their bending loads are no heavier than those in the crankshaft bearing caps.
Keeping the rest architecture, scotch-yokes can replace the 'small connecting rods'.
If desirable, needle roller bearings can be used in all joints to bypass lubrication issues, if any.
The crankcase projections neither restrict the size of the intake and exhaust ports, as compared to the conventional
engine, nor restrict the coolant passage areas along the cylinder head.
The spark remains at the center of the combustion chamber.
The synchronization between crankshaft and camshafts is simple and accurate, as explained in the
Key Advantages.
The cylinder block is free from transferring the forces of the cylinder head to the crankcase. This allows a more reliable
sealing of the combustion chamber (cylinder block and cylinder head joined/united in a 'single piece' seems promising).
For the sealing between the crankcase and the cylinder block, an elastic 'O-ring' into a groove of the crankcase,
around the periphery of the cylinder head, is all it takes.
Besides the VCR control shaft, the cylinder head can also host a Desmodromic Variable Valve Actuation (pattakon DVVA) system
to combine both worlds.
The light/partial load operation (down-town traffic, for instance) fits the high compression ratios (VCR) and the short valve
lift / short valve duration / zero valve overlap (DVVA). This combination protects the valves from the piston and allows
well shaped combustion chamber. The high turbulence and swirl (DVVA) cause fast flame propagation that improves the thermal efficiency. The reduced pumping loss (DVVA) and the high compression ratio (VCR) also
improve the thermal efficiency. The thermal efficiency is further improved by the shape of the combustion chamber (smooth/flat piston crowns without valve pockets, as in the animation below, and reduced wall surface).
The heavy load operation, on the other hand, fits the medium-low compression ratios (VCR) and the long valve lift /
extensive overlap (DVVA), allowing high or extreme specific power and downsizing.
