|Fill, compress, generate torque, expel|
The piston-stroke engine compresses air or an air-fuel mixture by means of a piston operating inside the cylinder and transmits the
pressure developing from the combustion as torque to the drive.
|Crank mechanism generates strokes and converts force into torque|
The piston is connected through the connecting
rod with the crankshaft. In combination with the piston pin they form the crank mechanism. The piston moves during one rotation of the crankshaft from the bottom-dead-centre (BDC) to the top-dead centre (TDC) and back. In BDC the distance
between piston and crankshaft is shortest, in TDC they are the furthest apart. This definition is also clear in case of a horizontal engine (e.g., opposed cylinder engines). A stroke evolves with half a rotation of the
crankshaft. Half a stroke corresponds to the centre distance between main bearing and big-end bearing. The pressure on the piston is transmitted as a force to the connecting rod and as torque to the crankshaft.
|Load due to high revs/large stroke - piston velocity|
The piston velocity is very different during the engine run. It begins at zero and increases to more than 22 m/s (=80 km/h), featuring an extra large stroke and/orvery high revs, then falls back to zero, however, again.
This happens during every stroke and with every piston. Two-stroke engines and racing engines may reach even clearly higher piston velocities. In the vehicle technology the medium piston velocity is usually calculated as a characteristic for the load of the piston at maximum speed.
|Operational smoothness: more cylinders, better balanced masses|
How is it possible to overcome empty strokes for engines with less than 4 cylinders? How to overcome the dead centres? No piston-stroke engine (except maybe the radial engine) can start from a standing position.
The engine always needs an idling speed. As is the rule, the idling speed is the higher, leaving out other factors, the fewer cylinders the engine has. Some older engines with few cylinders clearly exhibit their untrue
idle running. The larger piston weight and perhaps the larger weight of the connecting rod at that time contribute negatively, too. In this case the two-stroke engine should be clearly
favoured over the four-stroke engine. Two-stroke engine engineers claim that their three-cylinders are comparable in terms of operational
smoothness to four stroke-six-cylinder engines. All connected flywheel masses, like the crank mechanism
(today more rotary than up and down moving masses),
balance shafts, the flywheel, parts of the motor control unit, auxiliary aggregates and - the secondary flywheel masses in the gearbox if the clutch is non operational - help to reduce this central problem of the piston-
|Rotary engine generally less susceptible to vibration than piston engine|
|Cylinders help each other to get over the respective dead centers|
Until today the prestige of a car grows with the number of cylinders under its hood, in spite that the cubic capacity remains the same. Although it is not at all easy to distinguish the noise of a four cylinder engine with
offset shafts from that of a six-cylinder car. Let alone to tell apart the eight from the twelve cylinder engine purely by listening. There is no multi-cylinder engine in which there is exactly the same stroke for two cylinders
during a whole stroke. By suitable kinks in the crankshaft they help each other in turns over the respective dead centres. This
means, e.g., for the eight-cylinder engine that four cylinders
are at dead centres and the other four right in the middle of the stroke.
|Cylinder block and crank case: one or two parts|
The cylinders or the cylinder block in which the single cylinders are poured with one another, form the basis of the piston-stroke engine. In addition, some engines feature a crankcase which is screwed together with
the cylinder block. The crankcase is absolutely necessary in case of individually arranged cylinders. The crankshaft rotates in the crankcase which is connected via the connecting rod and piston pin to the piston as a
|Cylinder head to oil pan, standing, or (semi-) lying|
While the bottom is mostly formed by the oil pan, the cylinder head with gasket and cylinder head cover is arranged upwards. We should in fact not use the concepts "top" and "bottom", because there are also engines
featuring horizontal cylinders, in line as well as opposed cylinder engines and V engines. The cylinder head
accommodates (at least with the passenger car) also quite a few of the
motor control unit parts amongst whom are the camshafts and their drives, and the transmission elements with the valves and their springs.
|Auxiliary systems complement the construction|
This covers the piston-stroke engine. We did not mention the engine control units, and the cooling and lubrication system. And where do you assign the parts of the exhaust system, which have to do anything with
engine management? The starter and the generator should be mentioned, too. 01/08