Moment of force in physics

Each internal combustion engine is designed for a certain maximum power that it can deliver at a certain number of revolutions of the crankshaft. However, in addition to the maximum power, there is also such a value in the characteristic of the engine as the maximum torque achieved at speeds other than maximum power.

See also - Moment Force Calculator.

Scientifically speaking, the torque is equal to the product of the force on the shoulder of its application and is measured in Newton meters. This means if a force of 1 Newton is applied to a 1 meter long wrench (shoulder) (perpendicular to the end of the wrench), then we get a torque of 1 N*m.

For clarity. If the nut is tightened with a force of 3 kgf, then to unscrew it, you will have to apply a force of 3 kg to the wrench with a shoulder length of 1 meter. However, if you put on an additional 2 meter piece of pipe on a 1 meter long wrench, thereby increasing the lever to 3 meters, then only an effort of 1 kg is required to unscrew this nut. This is what many motorists do when unscrewing the wheel bolts: they either add a piece of pipe, and in the absence of one they simply press on the key with their foot, thereby increasing the force of application to the wheel wrench.

Also, if a weight equal to 10 kg is hung on a meter-long lever, then a torque equal to 10 kgf will appear. In the SI system, this value (multiplied by the acceleration of gravity - 9.81 m / cm^2) will correspond to 98.1 N*m.

The result is always the same - the torque, this is the product of the force by the length of the lever, therefore, either a longer lever is needed, or a greater amount of applied force.

All this is good, but what is the torque in the car for and how does its magnitude affect its behavior on the road?

Engine power only indirectly reflects the traction capabilities of the motor, and its maximum value is manifested, as a rule, at the maximum engine speed. In real life, practically no one drives in such modes, but the engine needs acceleration always and preferably from the moment the gas pedal is pressed. In practice, some cars already from low revs (from the bottom) behave quite briskly, while others, on the contrary, prefer only high revs, and show sluggish dynamics at the bottom.

So many have a lot of questions when they are with a car with a 105-120 hp gasoline engine. change to 70-80 - strong diesel, then the latter easily bypasses a car with a gasoline engine. How can this be?

This is due to the amount of traction on the driving wheels, which is different for these two cars. The amount of thrust directly depends on the product of such indicators as the magnitude of the torque, the gear ratio of the transmission, its efficiency and the rolling radius of the wheel.

How torque is generated in the engine

There are no meter levers and weights in the engine, and they are replaced by a crank mechanism with pistons. The torque in the engine is formed due to the combustion of the fuel - air mixture, which expands in volume and pushes the piston down with effort. The piston, in turn, through the connecting rod transfers pressure to the crankshaft journal. In the engine characteristic, there is no shoulder value, but there is a piston stroke (double the radius of the crankshaft crank).

For any motor, the torque is calculated as follows. When the piston with a force of 200 kg moves the connecting rod to the shoulder of 5 cm, a torque of 10 kgf or 98.1 N*m appears. In this case, to increase the torque, it is necessary either to increase the radius of the crank, or to increase the pressure of the expanding gases on the piston.

The radius of the crank can be increased up to a certain value, but the dimensions of the cylinder block both in width and height will also grow, and it is impossible to increase the radius to infinity. And the design of the engine will have to be significantly strengthened, since inertial forces and other negative factors will increase. Consequently, the developers of the engines were left with a second option - to increase the force with which the piston transmits the force to turn the crankshaft. For these purposes, more combustible mixture must be burned in the combustion chamber and, moreover, with better quality. To do this, change the size and configuration of the combustion chamber, make "placers" on the piston heads and increase the compression ratio.

However, the maximum torque is not available at all engine speeds and for different engines the peak torque is achieved at different modes. Some motors give it out in the range of 1800-3000 rpm, others at 3000-4500 rpm. It depends on the design of the intake manifold and the valve timing, when the effective filling of the cylinders with the working mixture occurs at certain speeds.