Engine

Details Engine Engine

1999-03-26

2001-05-01

McMahon, Marguerite (Department: 3747)

Internal-combustion engines

Adjustable combustion chamber

Piston in head adjusted

C123S197400

Reexamination Certificate

active

06223703

ABSTRACT:

This invention relates to an engine, and in particular to 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. The crankpin and the crankshaft main bearings are consequently subjected to periodic heavy stresses. What is of greater significance, however, is that, with an inner 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° beyond TDC, where the turning moment is a maximum, the piston force is greatly reduced, so that the resulting torque is relatively small.
Thus, in the four-stroke version of a conventional internal combustion engine, the crankshaft has to revolve twice to complete all the strokes necessary for full operation. The strokes are:
1. The induction stroke during which the inlet valve is open, the exhaust valve is closed, and a fuel and air mixture is drawn into the cylinder as the piston descends.
2. The compression stroke, during which the inlet and exhaust valves are closed, the fuel/air mixture is compressed as the piston rises, and is ignited by a timed spark a number of degrees before TDC.
3. The power stroke, during which the inlet and exhaust valves are closed, and the burning, hence rapidly expanding mixture, forces the piston down at an initially high pressure and temperature. The pressure and temperature, however, fall rapidly as the piston reaches BDC.
4. The exhaust stroke, during which the inlet valve is closed, the exhaust valve having been opened about 60° before BDC on the power stroke (to assist removal of exhaust gases, i.e. scavenging). The ascending piston displaces most of the used gases out of the exhaust valve until the piston is again at TDC for the induction stroke.
It should be noted that, at TDC at the end of the compression stroke, although the pressure in the cylinder is at almost a maximum, the ability of the crank to turn, i.e. the turning moment, is zero. Furthermore, owing to the fuel having been ignited before TDC, the time that this takes before the piston reaches TDC, is time when a reverse turning moment is being applied to the piston. Because the engine is unable to reverse during this period due to a flywheel giving inertia, the work generated by the expanding gases can only be converted into heat which eventually heats the cooling water or air, as the case may be, which surrounds the cylinder and so is not available for doing work on the piston.
During the early part of the power stroke, the turning moment increases approximately with the sine of the angle of rotation from TDC, so does not reach a maximum value until around 90° of rotation, when the pressure in the cylinder has fallen to almost half of its initial value. Much more heat is lost during this time and is, therefore, not available for work on the piston. By the time the piston has reached BDC on the power stroke, the exhaust valve has opened at about 60° before BDC, preventing any pressure remaining in the cylinder from acting on the piston and the correcting rod to produce crankshaft rotation. The exhaust gases are, therefore, released at a higher temperature and pressure than they would be if released at BDC. The early opening of the exhaust valve is necessary in the conventional engine to utilise this higher pressure to increase the velocity of the exhaust gases to ensure their adequate removal from the cylinder before the induction stroke commences. This exhaust pressure is lost to atmosphere and is not available for work on the piston.
Thus, the pressure is at maximum around TDC, whilst the turning arm reaches a maximum at about 80° to 90° after TDC, as is shown in
FIG. 1
which is a graph showing both the pressure p in the cylinder and the turning arm m over the power stroke. As it is the product of the pressure and the turning arm length normal to the pressure direction which produces the output torque of the engine, then clearly the engine would be greatly improved if these parameters could be matched (i.e. rise and fall together). The output torque t of a conventional engine over the power stroke is shown in FIG.
2
.
According to a first aspect, the present invention provides an engine comprising a cylinder, a combustion chamber, a piston reciprocable within the cylinder, a connecting rod and a rotatable output shaft, the piston being in drivable connection with the output shaft via the connecting rod, a drive ring and a torque lobe, wherein the torque lobe is a circular plate eccentrically mounted on the output 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 connecting rod is slidably mounted with respect to a carrier fixed to the drive ring for axial movement relative thereto, one end of the connecting rod being pivotally fixed to the piston, the other end of the connecting rod being engageable with a cam fixed to the torque lobe whereby rectilinear movement of the piston is converted to rotary movement of the torque lobe or vice versa, the cam and the mounting of the connecting rod with respect to its carrier being such that the turning moment of the output shaft is maximised substantially at the same tine as the pressure of expanding gases resulting from ignition within the combustion chamber is maximised.
Advantageously, means are provided for biassing the connecting rod towards the output shaft relative to the carrier, and preferably a spring acting between the connecting rod and the carrier constitutes the biassing means.
The arrangement may be such that said other end of the connecting rod engages the cam only over the power and exhaust strokes of a four-stroke cycle. In this case, the cam may have first and second cam faces, said other connecting rod end engaging the first cam face on the power stroke, and engaging the second cam face on the exhaust stroke.
Conveniently, the engine further comprises detachable locking means for locking the connecting rod to the carrier prior to the commencement of the induction stroke. Preferably, the locking means is such that the connecting rod is locked to the carrier only over the compression and induction strokes, thereby preventing the spring biassing the connecting rod towards the output shaft and into engagement with the cam. The locking means may be constituted by a pair of alignable holes within the connecting rod and the carrier and by a locking member movable between a first, unlocked position in which it lies wholly within one of said holes, and a second, locked position in which it lies partially within both holes. Preferably, said one hole is within the carrier.
In a preferred embodiment the engine further comprises means for biassing the locking member towards its second position. A leaf spring may constitute said biassing means, one end of the leaf spring being fixed to the carrier, the other end being engageable with the locking member.
Advantageously, the engine further comprises actuating means for releasing the locking means prior to the commencement of the power stroke. The actuating means may be constituted by an actuating rod engageable with an unlocking member housed at least partially within the hole in t

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