Machine element or mechanism – Mechanical movements – Rotary to or from reciprocating or oscillating
Patent
1991-07-03
1994-05-10
Herrmann, Allan D.
Machine element or mechanism
Mechanical movements
Rotary to or from reciprocating or oscillating
74 51, 74 45, F16H 2118
Patent
active
053097793
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a new type of crank mechanism and a variant thereof, in order to improve thermodynamic efficiency and to reduce the quantity of polluting masses for every cycle and to attenuate the closing forces between the piston and the cylinder wall.
These aims will be pursued operating by means of the particular kinematism on the law that regulates the motion of the piston in function of crank angle.
BRIEF DESCRIPTION OF THE DRAWINGS
Two embodiments of the invention will be shown in the following drawings:
FIG. 1 shows a schematic representation of a crank mechanism according to the present invention;
FIG. 2 shows the positions and the characteristic angles coinciding with the four dead centers of the crank mechanism;
FIGS. 3, 4, 5, 6, respectively, schematically represent the rods positioned at the four dead centers;
FIG. 7 is a sectional view taken along line 7--7 of FIG. 8;
FIG. 8 is a top view of a single crank mechanism according to the present invention;
FIG. 9 is a sectional view taken alone line 9--9 of FIG. 10; and
FIG. 10 is a top view of a twin crank mechanism according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The crank mechanism of the present invention is formed, in its schematic description (FIG. 1) and in its real one (FIGS. 7 and 8) by a traditional crank mechanism (rods A-B and B-C) in which the connecting rod small end (point C) is pivotally or hingedly connected to two rods (rods C-D and E-C) rod C-D has an extremity pivotally or hingedly connected to the crankcase (point D) while the other rod E-C is pivotally or hingedly connected by means of the extremity E to two other rods (rods G-E and E-F). These last rods have in this way, each have an extremity coinciding with the point E and the other two extremities are respectively pivotally or hingedly connected to the crankcase (point G) and to the piston pin (point F).
KINEMATIC ANALYSIS
The crank mechanism of the present invention has the characteristic of having four dead centres, if as dead centres we intend the positions of the rods (namely when there are particular alignments of the rods) in which the piston has null velocity.
In this way, the mechanism will be at a dead centre position when there is the alignment of the rods of the traditional crank mechanism (rods A-B and B-C) or when the rods C-D and E-C are aligned. These situations are represented in FIGS. 3, 4, 5 and 6, which show respectively the external dead centre and the three internal dead centres. Two of these last internal dead centres correspond to an end stroke position (FIGS. 5 and 6) while other internal dead centre corresponds to a position of the piston too much near the end stroke position (FIG. 5). In other words, from the external dead centre the piston begins its upward run which has a catch when there is an alignment of the rods C.sub.1 -D and E.sub.1 -C.sub.1 (FIG. 4). Then, the piston reverses its run moving away only a little from the position occupied previously and that corresponds with the dead centre which is one of the component crank mechanism (FIG. 5), and then the piston goes up again and reaches the third dead centre which corresponds to the alignment of the rods C.sub.3 -D and E.sub.3 -C.sub.3 FIG. 6. The crank completes itself with the outside ram travel, carrying back the piston to the external dead centre.
Summing up, the outside stroke (induction and expansion stroke) is subtended by the angle .theta..sub.u, (FIG. 2) the inside stroke (compression and exhaust stroke) is subtended by the angle .theta..sub.i, and the angle .theta..sub.M subtends the catch of the piston in the neighbourhood of internal dead centre (FIG. 2); namely between the first and the third internal dead centre, the piston moves itself with such small velocities and shiftings (a few hundredth of millimeter for an angle .theta..sub.M of 60 degrees and a run of 70 millimeters) that we can consider it as in a stopped position.
In more detail, from the external dead center in which the extremit
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Herrmann Allan D.
Laub David W.
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