<P> Some expensive, high performance crankshafts also use heavy - metal counterweights to make the crankshaft more compact . The heavy - metal used is most often a tungsten alloy but depleted uranium has also been used . A cheaper option is to use lead, but compared with tungsten its density is much lower . </P> <P> The shaft is subjected to various forces but generally needs to be analysed in two positions . Firstly, failure may occur at the position of maximum bending; this may be at the centre of the crank or at either end . In such a condition the failure is due to bending and the pressure in the cylinder is maximal . Second, the crank may fail due to twisting, so the conrod needs to be checked for shear at the position of maximal twisting . The pressure at this position is the maximal pressure, but only a fraction of maximal pressure . </P> <P> In a conventional piston - crank arrangement in an engine or compressor, a piston is connected to a crankshaft by a connecting rod . As the piston moves through its stroke, the connecting rod varies its angle to the direction of motion of the piston and as the connecting rod is free to rotate at its connection to both the piston and crankshaft, no torque is transmitted by the connecting rod and forces transmitted by the connecting rod are transmitted along the longitudinal axis of the connecting rod . The force exerted by the piston on the connecting rod results in a reaction force exerted by the connecting rod back on the piston . When the connecting rod makes an angle to the direction of motion of the piston, the reaction force exerted by the connecting rod on the piston has a lateral component . This lateral force pushes the piston sideways against the cylinder wall . As the piston moves within the cylinder, this lateral force causes additional friction between the piston and cylinder wall . Friction accounts for approximately 20% of all losses in an internal combustion engine, of which approximately 50% is due to piston cylinder friction </P> <P> In a paired counter-rotating crankshaft arrangement, each piston is connected to two crankshafts so lateral forces due to the angle of the connecting rods cancel each other out . This reduces piston - cylinder friction and therefore fuel consumption . The symmetrical arrangement reduces the requirement for counterweights, reducing overall mass and making it easier for the engine to accelerate and decelerate . It also eliminates engine rocking and torque effects . Several counter-rotating crankshaft arrangements have been patented, for example US2010 / 0263621 . </P>

What is the function of crankshaft in a car