Technology – Combustion engines                         04/19/2020                     Flywheel – Cornelis sketches                     In order to crush the unevenness of the gearbox from the combustion engine, …

A large cast iron disc, the flywheel, is mounted on the end of the crankshaft to compress the combustion engine’s unevenness. Thanks to its inertia, this wheel ensures, among other things, that the engine does not stop immediately when we start from a standstill. On the other hand, this inertia hampers the ability to climb the engine quickly. That sounds complicated, but is it?

When we look at a 1-cylinder four-stroke engine, only half a revolution is applied. After that, one and a half revolutions of negative work take place, this as a result of the pressing of the exhaust gas, the suction of fresh mixture and the compression of that mixture. The rotating mass of the flywheel – actually a large cast iron disc at the end of the crankshaft, on the outside of the engine block – ensures that the engine continues to run after the working stroke until the next working stroke. With multi-cylinder engines, the working strokes follow each other increasingly closely, but this is not entirely contiguous. Without a flywheel, those drive peaks would lead to jerky behavior. The flywheel largely filters out this irregularity.

When accelerating from a standstill, the speed of the engine (idle) and that of the wheels (stationary) must be brought to the same level when the clutch is released. In order to prevent the engine speed from equalizing that of the wheels (standstill) with less skilled drivers, the flywheel with its mass will try to prevent the engine from stalling as much as possible. The ultimate goal is for the input side of the transmission to have the same speed as that of the crankshaft.

The disadvantage of such a heavy iron wheel is that it is an inhibiting factor when climbing in rpm. That is why motorsport often uses lighter (or even without) flywheels than for street use.

In addition to its mass inertia, the flywheel can also be used for the connection between the engine and the transmission. This connection can be made by pressing the clutch plate against the flywheel. Furthermore, the flywheel is perfect for screwing on the clutch pressure group or the pump of the fluid coupling. A little further out, on the outer edge of the flywheel we usually see the teeth in which the starter motor gear can engage to start the engine. In addition, some flywheels have an additional sprocket that serves as a signal generator for the sensor on which the engine management bases the crankshaft position and the speed. Are we there yet? No, in the center of the flywheel we often see a bearing on which the input shaft of the gearbox can rest. This prevents the coupling from swinging in the round. The flywheel itself must also be perfectly balanced to eliminate unwanted vibrations and vibrations, as with the wheels, pieces of lead are not stuck on the flywheel, but the opposite happens: the imbalance is removed by grinding off pieces of the flywheel or drill small holes in it.

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