Machine element or mechanism – Mechanical movements – Rotary to or from reciprocating or oscillating
Patent
1996-07-05
1998-05-12
Herrmann, Allan D.
Machine element or mechanism
Mechanical movements
Rotary to or from reciprocating or oscillating
123 542, 123 546, 1231973, F16H 2134
Patent
active
057492620
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a crank mechanism for an internal combustion engine.
A conventional internal combustion engine employs a crankshaft to convert the reciprocating motion of the piston(s) into output torque to propel a vehicle or to act upon any other load. The crankshaft is inefficient in terms of converting the power available from the fuel combustion into usable output torque. This is because combustion of the fuel/air mixture takes place at approximately the top dead centre (TDC) position of the piston. Not only the crankpin, but also the crankshaft main bearings, are consequently subjected to periodic heavy stresses. What is of greater significance, however, is that, with an internal combustion engine provided with conventional drive gear, the ignited fuel/air pressure forces cannot produce torque when the piston is either at TDC or bottom dead centre (BDC), as the connecting rod and the crankpin are practically in a straight line so that there is no force component tangential to the crank circle. This results in most of the available energy being lost as heat. The torque necessary to carry the crankshaft through these two dead centre positions is supplied by the inertia of the flywheel of the engine. Moreover, by the time the crankshaft has rotated through almost 90.degree. beyond TDC, where the turning moment is a maximum, the piston force is greatly reduced, so that the resulting torque is relatively small.
My International patent application WO91/10848 describes a crank mechanism for an internal combustion engine, the crank mechanism comprising a cylinder, a piston reciprocable within the cylinder, and a rotatable shaft. The piston is in drivable connection with the shaft via a connecting rod, a drive ring and a torque lobe. The connecting rod is pivotally fixed to the piston, and the drive ring is pivotally attached to the free end of the connecting rod. The torque lobe is a circular plate eccentrically mounted on the shaft for rotation therewith about the axis thereof. The drive ring is slidable along, but restrained to, the rim of the torque lobe, and the drive ring is constrained to move around a closed path whereby rectilinear movement of the piston is converted to rotary movement of the torque lobe or vice versa. The drive ring is provided with cam follower means which engage with associated cam track means adjacent to the torque lobe, the cam follower means and the cam track means constituting means for constraining the drive ring to move round the closed path.
A disadvantage of this crank mechanism is the need for the cam track means and the cam follower means, which complicate the design. Moreover, this mechanism requires an anti-reverse device for preventing the torque lobe from rotating in the reverse direction at BDC at the end of the induction stroke.
The present invention provides a crank mechanism for an internal combustion engine, the crank mechanism comprising a cylinder, a piston reciprocable within the cylinder, and a rotatable shaft, the piston being in drivable connection with the shaft via a connecting rod, a drive ring and a torque lobe, the connecting rod being pivotally fixed to the piston, and the drive ring being rigidly attached to the free end of the connecting rod, wherein the torque lobe is a circular plate eccentrically mounted on the shaft for rotation therewith about the axis thereof, wherein the drive ring is an annular sleeve which is a rotatable sliding fit around the rim of the torque lobe, and wherein the axis of the piston is offset with respect to the centre of the output shaft whereby rectilinear movement of the piston is converted to rotary movement of the torque lobe or vice versa.
This mechanism has the advantages of not requiring either cam track/cam follower means or an anti-reverse device, and so is a simpler and more reliable mechanism than my earlier crank mechanism, whilst still having improved torque characteristics.
The invention also provides a crank mechanism for an internal combustion engine, the crank mechanism comprising a plurality
REFERENCES:
patent: 1555598 (1925-09-01), Myers
patent: 1780854 (1930-11-01), Watts et al.
patent: 1995554 (1935-03-01), Ulinski
patent: 2625048 (1953-01-01), Vissat
patent: 3366073 (1968-01-01), Andrews et al.
patent: 3946706 (1976-03-01), Pailler
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