Internal-combustion engines – Adjustable combustion chamber – Piston in head adjusted
Reexamination Certificate
2000-11-16
2002-09-03
McMahon, Marguerite (Department: 3747)
Internal-combustion engines
Adjustable combustion chamber
Piston in head adjusted
C123S0780AA
Reexamination Certificate
active
06443107
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for adjusting the compression ratio of internal combustion engines, and more specifically to a method and apparatus for adjusting the position of the crankshaft with eccentric crankshaft main bearing supports.
Designs for engines having eccentric crankshaft main bearing supports have been known for sometime. In these engines the eccentric main bearings are rotated to adjust the position of the crankshaft's axis of rotation. Poor rotational alignment of the eccentric main bearing supports is a problem for these engines because even small amounts of main bearing misalignment can cause rapid main bearing failure.
Significant forces bear down on the eccentric main bearing supports during operation of the engine. In modern passenger car engines main bearing loads can exceed 50 MPa. The forces exerted on the eccentric main bearing supports are at times significantly different from one eccentric main bearing support to the next. For example, in multi-cylinder engines a clockwise torque may be applied on a first eccentric main bearing support from the combustion pressure bearing down on the first piston, connecting rod and crank throw, and a counterclockwise torque may be applied on a second or third eccentric main bearing support from the inertial forces of the second piston and connecting rod pulling up on the second crank throw. As a second example, in a single cylinder engine having two eccentric main bearing supports the torque applied to the crank throw and the resistive torque at the power take off end of the crankshaft cause uneven loading on the eccentric main bearing supports. These large unequal forces are a problem because they cause the eccentric sections to rotate out of alignment with one another causing rapid failure of the crankshaft main bearings.
In U.S. Pat. No. 887,633, and in German patent DE 3644721 A1 a pinned linkage is show for adjusting the rotational alignment of the eccentric main bearing sections. U.S. Pat. No. 4,738,230 shows dowels extending from each eccentric main bearing support that are fitted into slots located in a slidable bar for adjusting the rotational alignment of the eccentric main bearing supports. U.S. Pat. Nos. 5,572,959 and 5,605,120 show gear teeth extending from eccentric main bearing supports that engage a layshaft with mating gears for adjusting the rotational alignment of the eccentric main bearing supports. U.S. Pat. No. 1,160,940 shows a bail shaped frame that connects adjacent eccentric sections for adjusting the rotational alignment of the eccentric sections. Poor alignment of the main bearings is a significant problem for each of these systems. In addition to poor main bearing alignment a number of these systems are not mechanically functional for other reasons, are impractical for mass production manufacture and assembly, and/or are not functional for engines having more than two main bearings. For example, U.S. Pat. No. 1,160,940 shows a bail shaped frame that is weakly connected to the eccentrics and that does not have a rigid construction. In addition to not rigidly hold the bearings in alignment. the system is not mechanically functional because the connecting rod does not clear the bail shaped frame. The system is also not functional for engines having more than two main bearings because it is not possible to slide the eccentric main bearing support onto the center crankshaft journal or journals.
A further problem with engines having rotatable eccentric main bearing supports in a fixed engine housing is that the location of the crankshaft rotational axis changes with change of compression ratio, making use of a conventional in-line clutch impossible. Geared power take-off couplings for engines having an adjustable crankshaft rotational axis are shown in the prior art, however a problem with these systems is that heavy structural reinforcing is required to rigidly hold the gear set in alignment. In addition to the problem of added weight, engine housing length is also increased.
German patent DE 3644721 A1 shows a gear set mounted to the free end of one of the eccentric crankshaft main bearing supports. The gear set has an intermediary shaft and an output shaft. The output shaft points generally away from the crankshaft, and has a fixed axis of rotation for all compression ration settings. A problem with the system shown in German patent DE 3644721 A1 is that during periods of high engine torque the end eccentric main bearing support may bend out of alignment, resulting in damage to the crankshaft main bearing. The gear set is also bulky and increases cranktrain friction losses due to the increased number of bearings and gear friction. U.S. Pat. No. 4,738.230 shows a first spur gear mounted on the crankshaft and a second spur gear having an axis of rotation that is concentric with the axis of rotation of the main bearing supports. These gears are too small to carry the torsional loads of the engine. U.S. Pat. No. 4,738,230 also shows a power take-off system having an internal or annular gear set. Heavy and lengthy structural reinforcing is required for holding the ring gear shaft in rigid alignment with the gear mounted on the end of the crankshaft. U.S. Pat. Nos. 5,443,043, 5,572,959 and 5,605,120 show a crankshaft having a fixed axis of rotation and an upper engine that changes position relative to its supporting frame when the compression ratio is changed. While a conventional in-line clutch can be employed with this arrangement, the position of the upper engine is changed when the compression ratio is changed, and the inertial mass of the upper engine prevents rapid adjustment of compression ratio.
SUMMARY OF THE INVENTION
In the present invention, a rotatable rigid crankshaft cradle is employed for holding the crankshaft main bearings in alignment. The crankshaft cradle is rotatably mounted in the engine on a pivot axis, and the crankshaft is mounted in the crankshaft cradle on a second axis off-set from the pivot axis. An actuator rotates the crankshaft cradle and adjusts the position of the crankshaft axis of rotation and the compression ratio of the engine. The crankshaft cradle rigidly holds the main bearings in precise alignment at all times and provides long bearing life. The crankshaft cradle provides rigid support of crankshafts for single and multi-cylinder engines, ranging from crankshafts having two main bearings for single and two cylinder engines, to crankshafts having five or more main bearings for in-line-four cylinder engines, V
8
engines, as well as other engines. In addition to providing a long main bearing life, the variable compression ratio mechanism of the present invention is reliable and has a low cost.
Referring now to
FIGS. 3
,
4
and
5
, in the preferred embodiment of the present invention a crankshaft cradle
60
is rotatably mounted in the engine housing on a pivot axis E, and a crankshaft
61
is mounted in the crankshaft cradle on a second axis A off-set from the pivot axis. The cradle includes two or more main bearing supports or eccentric members
62
and structural webbing
64
for rigidly holding the eccentric members and main bearings in alignment. One or more bearing caps
68
are fastened to the cradle with bolts or another type of fastener for securing the crankshaft in the cradle. The bearing caps are removable from the cradle permitting assembly of the crankshaft in the cradle. Operation of the main bearings without failure requires precise alignment of the main bearing supports at all times. According to the present invention, adjacent main bearing supports are held in rigid alignment at all times by structural webbing
64
. More specifically. the structural webbing holds the main bearing supports in rigid alignment at all times providing a long service life for the main bearings.
FIG. 9
shows a second embodiment of the present invention. As shown in
FIG. 9
, crankshaft cradle
146
includes a first eccentric member, or main bearing support
160
and a second eccentric member, or ma
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