Internal-combustion engines – Transmission mechanism from piston – Crankshaft and connecting rod
Reexamination Certificate
2001-06-08
2003-03-04
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Transmission mechanism from piston
Crankshaft and connecting rod
Reexamination Certificate
active
06526935
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
REFERENCE TO SEQUENCE LISTING OR APPENDIX
Not Applicable
FIELD OF THE INVENTION
This invention relates to variations in the rotating assemblies which alter the motion of the piston in internal combustion engines and similar machines.
BACKGROUND OF THE INVENTION
Since internal combustion engines were called “explosion engines” in the late 19th century there has been a continual quest to improve upon the purely sinusoidal curve generated by the crankpin, and therefore the piston in the theoretical case of an infinite rod length, of the simple, reliable and relatively inexpensive configuration used almost exclusively from that period through the entire 20th century.
Some of the earliest inventions sought to provide complete scavenging of the cylinder on the exhaust stroke. Otto cycle engines were limited to compression ratios as low as 3:1 by the quality of the gasolines available, and some even burned the gaseous products of incomplete combustion of coal or wood. These dimensions would result in the dilution of the already poor quality of the incoming charge by 33% unthrottled. The proposed solutions frequently involved an eccentric around the crankpin rotated by gearing so as to add to the upstroke every other revolution on the exhaust stroke. The higher compression ratios, higher flow velocities and valve overlap of modem engines have solved this problem to the extent that exhaust gases are now being reintroduced into the cylinder to control emissions.
A problem that was also frequently addressed is that of piston/cylinder wear. The most commonly placed blame was on the side thrust caused by the connecting rod angle relative to the cylinder centerline. To reduce this angle and therefore the side thrust the accepted norm for rod length to stroke ratio was 5:1. The approach to this problem by those not offering unusual alignment of cylinders or multiple pistons and cranks per cylinder often was a hypocycloidal planetary gear drive. This drive can eliminate rod angularity, but when configured to do so restricts the gear ratio and the ratio of crank to eccentric offset to a single value each. Compared to the conventional engine with an equal total stroke, it reduces the moment arm and therefore the directly applied torque. Rotating the angular alignment can vary the point at which the reduced moment arm is at its maximum, but this also reduces the stroke length. Individual event (intake, compression, expansion and exhaust) strokes remain equal. Also, this problem has been overcome by materials and lubrication so that now very successful engines operate with rod length to stroke ratios of less than 1.5:1.
Another limitation that has received copious attention but limited solution is the lack of tangential force on the crank when the cylinder pressure is highest. In the conventional engine cylinder volume is at its minimum and therefore pressure near its highest, depending on ignition and burning characteristics, when the piston, crankpin and axis of crankshaft revolution are in a straight line at top dead center (TDC). Maximum pressure multiplied by zero moment arm still equals zero torque. Many inventions have in their objects addressed the dilemma of highest cylinder pressure at lowest crank moment and vice versa. P-V diagrams and isentropic events involving perfect gases reveal no loss of efficiency from this condition. Correspondingly, from a practical observation of the process at TDC when the piston is trying only to push the crankshaft out of the block rather than rotate it due to zero moment arm, there is, also due to lack of moment arm no increase in volume within the cylinder. Since there is no increase in volume there is no decrease in pressure in this theoretical ideal situation. The same evaluation is extended as the inertia of the rotating mass continues to rotate the crankshaft. The first few degrees of the sinusoidal path increase the moment arm and therefore the volume very little, but this also decreases the pressure very little. Under these ideal conditions, which do not exist in reality, there is no loss of energy or efficiency. Under real world conditions there is pressure transmitted to the contacting surfaces resulting in friction losses. There are heat losses at the elevated temperatures of combustion and since time is directly proportional to angular velocity rather than the variable piston speed, more heat is lost when the piston moves slowly away from TDC.
In an attempt to provide more torque during the beginning of the power stroke some early designs have proposed additional links between piston and crankshaft, often including a pivoting shaft anchored on the housing to keep all the rods in place. This added size, as well as increased the mass which had to reverse direction several times per cycle, making an assembly incapable of operating at speeds greater than the steam engines of their day.
Cardioid cycle embodiments provide positive moment arm at TDC and more rapid drop of the piston not only because of the advanced angle of the mainshaft along the sinusoidal curve at TDC, but because the total offset of the rod journal from the mainshaft axis of rotation is also increasing rapidly.
Another attempt at reducing this limitation has been to offset the crankshaft from the cylinder centerline. One reason that this has not been accepted as standard practice is that it exacerbates the side force on the piston on one stroke at least, and was first proposed during a time when this problem was of more concern. More importantly, TDC still occurs when the piston, crankpin and crank axis are aligned so that there is no moment arm. This alignment does increase the length of the moment arm between the dead center points and the 90 degree location, and also creates unequal upstroke and downstroke lengths and durations.
The more numerous designs, especially in later disclosures, have concentrated on the eccentrics placed around the crankpin inside the rod or sometimes in the piston around the pin. The amount of offset available in this space usually restricts the effective change in piston path to a small percentage of the total stroke and a means must be provided to rotate the eccentric. Larger offsets are possible, but probably would require counterweights and other expensive modifications.
Fuel efficiency has become a primary object of many inventions. From a theoretical approach there are two areas which are known to produce results and which have not been fully developed. These are the full expansion to ambient pressure and temperature the products of combustion and compression to optimum pressure the pre-combustion mixture. In a conventional Otto cycle engine after 160 degrees of expansion the piston has completed over 97% of its stroke and the exhaust valve is opening. At this point there can be 10% to 15% of the maximum pressure remaining and unrecoverable. There have been numerous attempts to extract this energy by more complete expansion methods using auxiliary cylinders and chambers such as compressing the charge in a small cylinder and transferring it into a larger cylinder for expansion. These methods add complexity, lose heat by conduction and sometimes involve more than four strokes for each cycle. Eccentrics and offset crankshafts have been proposed to extend the expansion stroke but the small increases in stroke available with these methods yield little in efficiency. They also usually affect the length of one or all of the other strokes.
Modifications, innovations and new designs affecting compression ratios are certainly some of the most numerous proposed advances in internal combustion engine technology. Conventional engines have a fixed compression ratio which, for performance and efficiency, in the case of spark ignition engines must be as high as practicable for the octane rating of the fuel used, yet low enough to prevent detonation under worst case conditions. There is wide variation between the optimum compre
Benton Jason
Kamen Noah P.
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