Internal-combustion engines – Adjustable combustion chamber – Piston in head adjusted
Patent
1996-10-23
1998-08-11
McMahon, Marguerite
Internal-combustion engines
Adjustable combustion chamber
Piston in head adjusted
F16C 904
Patent
active
057913021
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an engine with a variable compression ratio.
BACKGROUND OF THE INVENTION
It is known to vary the compression ratio of an engine by varying the effective length of the rod connecting each piston to a crank pin on the crank shaft or by varying the height of the piston crown. One earlier proposal has been to use an eccentric sleeve interposed at the so-called small end between the gudgeon pin of the piston and the connecting rod. With the eccentric aligned at right angles to the connecting rod, the length of the rod is at its mean value and could be increased or decreased by rotating the eccentric in the appropriate direction towards the top or bottom dead centre positions, respectively.
Though the forces acting on the eccentric as a result of piston inertia and the pressures in the combustion chamber tend to move the eccentric automatically in the desired directions during each operating cycle, there is a risk that if the eccentric reaches a top or bottom dead centre position then no torque is ever developed to dislodge it from this position and the system locks up in a maximum or minimum compression ratio position. Even near these end positions, the torque may not be able to overcome the frictional forces on the eccentric.
To mitigate these problems, it was proposed in WO92/12337 to use a spring biassing the small end of the connecting rod at right angles to its length to centre the eccentric in its mean position but a very strong spring is required to be able to resist the full pressure and inertial loads on the connecting rod and for this reason the proposal did not prove practicable. Natural oscillation of the spring also risked interfering with the movements of the eccentric.
OBJECT OF THE INVENTION
The present invention therefore seeks to provide an engine that uses an eccentric to vary the effective length of the connecting rod that does not rely on springs to avoid locking up of the eccentric in dead centre positions.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a variable compression ratio internal combustion engine wherein each piston is connected to a crank pin on the crankshaft by means of a connecting rod that is formed in two parts, the first part being rotatably secured to the crank and the second part being rotatably secured to a gudgeon pin of the piston, wherein the two parts are connected to one another by coupling means including two eccentrics having axes of eccentricity that are inclined to one another so that the eccentrics cannot both lie in a dead centre position at the same time.
The term "axis of eccentricity" is used to describe the line that passes through the two centres of rotation of an eccentric which may also be considered as the crank throw or the line of maximum offset.
Because the two eccentrics can never both lie in a dead centre position, one can now allow one of the eccentrics to reach the dead centre position thereby enabling direct transmission of the load while relying on the other eccentric to move the coupling out of that position and prevent locking up of the coupling when the load is reversed.
Preferably, the axes of eccentricity of the two eccentrics lie at right angles to one another, one being moved into its dead centre position by compression in the connecting rod and the other being moved into its dead centre position by tension in the connecting rod.
Advantageously, the part of the connecting rod rotatable about the gudgeon pin is formed of two pairs of links, each pair lying on a respective side of the connecting rod, the links in each pair each being pivoted about the gudgeon pin at one end and about a respective one of the two eccentrics at the other end, and the links in each pair being resiliently coupled to one another to permit a limited degree of movement of the eccentric towards and away from one another.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described further, by way of example, with reference to the accompanying drawings,
REFERENCES:
patent: 3861239 (1975-01-01), McWhorter
patent: 4215660 (1980-08-01), Finley
patent: 4517931 (1985-05-01), Nelson
patent: 4957069 (1990-09-01), Mederer
patent: 5595146 (1997-01-01), Bollig et al.
Drouillard Jerome R.
Ford Global Technologies Inc.
McMahon Marguerite
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