 Pressure generates force 1
Naturally, pressure propagates in all directions. If the head gasket is too weak in one spot, then it will whistle out. The cylinder head itself also has to endure a lot. Just look at some of the bolts used to secure
it, which are designed as expansion screws. They are usually tightened in a strict sequence, using the correct torque and angle.
It's easy to underestimate the forces involved here. The image of the two mechanics is still vividly in memory. One happened to be tightening the head bolts of a diesel engine and the other those of a gasoline
engine at the same time. The latter performed the task relatively easily, while the other, lacking the appropriate extension, was clearly visibly strained.
The expansion force of the burning air-fuel mixture is useless unless it is transferred to the respective crank of the crankshaft via the connecting rod and arrives at the clutch as torque. However, there are side
effects. While the gas force acts fairly evenly across the surface of the piston crown, it can practically only transfer the force along the centerline to the crankshaft at TDC or BDC.
But that's exactly when it's pretty pointless: too early at TDC and much too late at BDC. So, if a lot of gas force is generated after TDC, this means a certain tilt of the connecting rod, depending on the number
of degrees after TDC and, fundamentally, on the connecting rod length. As long as l and r are not perpendicular to each other in the image above, the tilt of the connecting rod increases; the shorter l, the
greater the tilt. And tilt automatically means a certain amount of lateral force on the piston.
Once again, a long connecting rod would be ideal here, because with a virtually infinite length l, the lateral force would be zero. However, a lower-tall engine is lighter, and so is the connecting rod with a shorter
length. The force resulting from the combustion pressure is thus divided into a lateral force and a connecting rod force.
If you initiate ignition relatively early, a certain amount of pressure already exists at TDC. And it's precisely at this point that the piston changes sides, when the center of the piston pin and the crankshaft lie on
top exacctly of each other. It would be better if the piston changed sides at even lower pressure.
Here, in a somewhat exaggerated form, you can see how to solve the problem. You move the piston pin slightly toward the first thrust side, i.e., to the left. This causes the piston to change sides before
reaching TDC. The effect of de-axialization is so strong in certain engines that a veritable rattling noise can be heard when the pistons are installed rotated by 180°.
The diagram shows the rapidly changing piston force during a work cycle, with the maximum force at the beginning of the power stroke (360°) being the most important for both the functional sequence and the
dimensioning of the piston. Here, with the same displacement, the diesel engine exhibits higher forces than the gasoline engine, and the turbocharged compared to the freely sucking the higher forces.
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