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Paragraph 8 : Minimum & Maximum compression ratios
According to the invention, the minimum compression ratio selected may be achieved between two end-of-travel limits of the variably timed transmission. The first limit is achieved with a maximum lead angle between the crank of the short-stroke crankshaft [5] and the crank of the long-stroke crankshaft [4], so as to determine at the end of the compression phase ( top dead centre of piston [6] ) the position of piston [8] with respect to the additional volume required for the clearance space [40] to define said minimum compression ratio with an angle of at least 90 between the connecting rod and the crank of the short-stroke crankshaft [5], the second limit is achieved with a smaller lead angle between the crank of the short-stroke crankshaft [5] and the crank of the long-stroke crankshaft [4], proportionally to the reduction of the displacement ratio of the two cylinders [2] and [3], up to the tolerance limit generated by the working area of the two crankshafts [4] and [5], defined by the parallel and close positions of the paired cylinders [2] and [3], according to the following minimum compression ratio formula :

V1 + [ V2 - Vr (α maximum) ] + ve
ve + Va (α maximum)
= P minimum

It is possible to define a higher compression ratio between the displacements of the paired cylinders, so as to reduce the stresses on the variably timed transmission mounted on engines having lower displacements and inversely, it is possible to define a smaller compression ratio between the displacements of the paired cylinders [2] and [3], so as to increase the speed of engines having higher displacements. In practice, Vr (α maximum) should not be deducted from V2, since the mass of air admitted in V1 and V2 depends on the stored calibration between the compression ratio and the supercharging pressure. The maximum compression ratio selected is achieved on the basis of the dimensional values defined for the minimum compression ratio, so that at the start-of-travel of the variably timed transmission, the minimum lead angle between the crank of the short-stroke crankshaft [5] and the crank of the long-stroke crankshaft [4] determines, at the end of the compression phase ( top dead centre of piston [6] ), the position of piston [8] with respect to the additional volume required for the clearance space [10] to define a maximum compression ratio, with the connecting rod [9] of the crank of the short-stroke crankshaft [5] away from its top dead centre, so that said connecting rod [9] forms an angle with the crank of the short-stroke crankshaft [9]. The maximum compression ratio may thus be defined by means of the following formula :

V1 + [ V2 - Vr (α minimum) ] + ve
ve + Va (α minimum)
= P maximum

In practice, Vr (α minimum) should not be deducted from V2, since the mass of air admitted in V1 and V2 depends on the stored calibration between the compression ratio and the atmospheric depression in the intake pipe.

 

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