Internal-combustion engines – Four-cycle – Variable clearance
Reexamination Certificate
2002-10-02
2004-09-14
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Four-cycle
Variable clearance
C123S0480AA
Reexamination Certificate
active
06789515
ABSTRACT:
TECHNICAL AREA
The present invention relates to a method and a device that is reactive and consumes very little energy, for continuous optimization of the compression ratio, particularly of alternating-piston engines. This invention is particularly relevant to increasing the energy efficiency of engines that are not used continuously at full load or that use multiple fuels with different octane ratings. This invention is compatible with a very low pollution level and adapts in particular to alternating-piston engines whose cylinders are disposed flat, either in a “V” configuration or in-line. In the present document, the term “compression ratio” designs the geometric compression ratio of an alternating-piston internal combustion engine.
PRIOR ART
Continuous optimization of the compression ratio is relevant in reducing fuel consumption and the contribution to the greenhouse effect for applications where the engines are not at full load and for engines that use multiple fuels with different octane ratings.
Combustion in spark ignition engines operated at very low loads is more complete when the compression ratio is optimized during operation. Carbon monoxide, hydrocarbon, and particle emissions are hence lower.
Continuous optimization of the compression ratio is relevant in keeping an engine in the spark ignition operating mode by compressing a premixture of fuel and oxidant. Such a method of operation, described in particular in patent WO 99 42718 A, enables a very low nitrogen oxides emission level to be reached.
Moreover, optimization of the compression ratio is compatible with the usual systems for reducing nitrogen oxide emissions such as exhaust gas recycling (EGR) systems or nitrogen oxide catalysts.
The prior art already contains a number of solutions for modifying the compression ratios of alternating-piston engines. A summary is provided below.
One known solution for changing the compression ratio consists of placing a moving part in the cylinder head. Patent WO 99 13206 A describes one example. This part must slide in the presence of gases undergoing combustion. The interstices must be minimized to limit unburned particles. The moving part is placed in the cylinder head with the valves and participates in the shape of the combustion chamber.
U.S. Pat. No. 2,770,224 refers to an engine whose block, divided into two articulated parts, enables the distance between each piston and the corresponding cylinder head to be varied. Patent WO 93 23664 A discloses a solution for controlling this type of device. The separation force of the two parts of the engine block is used to reduce the compression ratio and store energy. The stored energy is then used to increase the compression ratio when the engine load decreases. The operating hysteresis is limited by the energy supplied by an activator. The engine block is designed and dimensioned to provide sufficient mechanical strength for the link between the two articulated parts of the engine block, and to minimize vibrations.
Patent WO 95 29329 A describes a device having two cams at the head of each connecting rod. The angular setting of these two cams is a function of the engine load and enables the distance between each piston and the corresponding cylinder head to be modified.
One category of solutions is to modify the length of the connecting rod, for example by adding an articulation modifying the straightness of the connecting rod. Patents EP 0 520 637 A and DE 195 02 820 A belong to this category of solutions. The additional parts that transmit forces between the pistons and the crank pins must be designed and dimensioned as a consequence to ensure the required reliability.
Another category of solutions adapted more particularly for in-line engines includes cams mounted on the crankshaft bearings to modify the distance between the crankshaft axis and the cylinder head. Patents FR 2,669,676 A, U.S. Pat. No. 1,872,856, U.S. Pat. No. 4,738,230, and DE-A-3,601,528 describe devices that may be classified in this category. The rigidity of the crankshaft bearings must be compatible with the required service life. Patent DE 297 19 343 U discloses a device for ensuring the alignment between the crankshaft and the transmission.
A crank pinion mounted at the end of the crankshaft meshes with an internally toothed wheel mounted on the flywheel. The teeth of these gears must withstand the rotary vibrations of the crankshaft and meet service life and noise requirements.
Patent WO 91 10051 A refers to a cam placed between the foot of each connecting rod and the corresponding crankshaft crank pin, whose angular setting is achieved by means of gears. The gears must be designed and built to and meet service life and noise requirements.
Patents JP 7527/90, JP 7528/90, JP 125166/90, and EP 0 438 121 A1 relate to a cam mounted either at the head or at the foot of each connecting rod, whose angular position is hydraulically actuated and stabilized by a removable finger. This finger must be designed and dimensioned to ensure the required reliability and service life. This device enables the compression ratio to be adjusted discontinuously.
DESCRIPTION OF INVENTION
The invention relates to a method and device for continuous optimization of the compression ratio within ranges determined by design, particularly for in-line, V, or opposed engines. The invention has the advantage, as far as the necessary technologies are concerned, of being compatible with the technologies currently used for cylinder heads, cylinder blocks, crankshafts, and their connections with the transmissions. It also has the advantage, as far as its implementation is concerned, of allowing the use of technologies similar to technologies used in alternating-piston engines that are well understood and are of proven reliability. The particular embodiments according to the invention have other advantages listed in this description.
The present invention applies to internal combustion engines with alternating pistons driven by a crankshaft. Each of these engines has one or more combustion chambers and a crankcase. The crankcase is defined in the present description and claims as the part (or rigid assembly of parts) that provides the link between the combustion chamber or chambers and the fixed parts of the crankshaft bearings. The axis of rotation of the crankshaft journals is called the crankshaft axis. These engines also have one or more cylinder heads that is/arc distinct from or integral with the crankcase. Each piston is connected to a crankshaft crank pin, particularly by a piston axis, a connecting rod, and a cam. This cam is located between the foot of the connecting rod and the crankshaft crank pin that corresponds to a given combustion chamber. The change in angular setting of one of the cams relative to the crankcase brings about a change in the compression ratio of the corresponding combustion chamber. In the description and claims of the present invention, a piston is at the top dead center for each complete revolution of the crankshaft when the distance between this piston and the corresponding cylinder head is at a minimum.
The method according to the invention consists of modifying the compression ratio of each combustion chamber by carrying out the functions described below, with possible differences included within tolerances compatible with correct operation and implementation options:
moving a point in a plane orthogonal to the crankshaft axis;
maintaining a geometric axis in a plane orthogonal to the crankshaft axis and articulating this geometric axis around the point where the projection of the point referred to in the previous subparagraph intersects the plane of rotation of this geometric axis;
choosing another geometric axis contained in a plane also orthogonal to the crankshaft axis and maintaining parallelism and a fixed distance between the two aforesaid geometric axes so that their direction when the piston is at the top dead center and the direction of movement of the point referred to in the first subparagraph above are different;
maintaining a fixed
Benton Jason
Institut Francais du Pe'trole
Yuen Henry C.
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