Piston pins and piston pin circlips
The piston pin is the link between the piston and the connecting rod. Owing to the oscillating motion of the piston and the overlay of gas and inertial forces, it is subjected to high loads in alternating directions. Figure 2.1 shows the piston pin load f
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Piston pins and piston pin circlips
2.1
Function of the piston pin
The piston pin is the link between the piston and the connecting rod. Owing to the oscillating motion of the piston and the overlay of gas and inertial forces, it is subjected to high loads in alternating directions. Figure 2.1 shows the piston pin load for a gasoline engine at rated power. The rotational motion of the connecting rod relative to the piston must be compensated for at the bearing locations of the piston pin, in the piston pin boss, and the small end bore. Because of the small relative motions, the lubrication conditions here are poor.
Figure 2.1: Piston pin load
For pistons in gasoline engines of passenger cars with moderate specific power output, the piston pins can be fixed in the small end bore with shrinkage stresses (fixed-pin connecting rod) (Figure 2.2d). This design allows savings due to the elimination of the piston pin circlips and the bushing in the small end bore and makes automatic assembly of the piston, piston pin, and connecting rod easier for large-scale production of engines. In highly stressed gasoline engines and in diesel engines, the piston pin “floats” in the small end bore (Figure 2.2a–c). It needs to be secured with piston pin circlips against sideways motion in the piston (see Section 2.8). In large-bore pistons, the cooling oil is often fed through the connecting rod and the piston pin, which features special oil feeding systems, to the piston pin boss; see Figures 2.12–2.15.
MAHLE GmbH (Ed.), Cylinder components, DOI 10.1007/978-3-658-10034-6_2, © Springer Fachmedien Wiesbaden 2016
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2 Piston pins and piston pin circlips
a)
b)
c)
d)
Figure 2.2: a) floating configuration with parallel support, b) floating configuration with tapered support, c) floating configuration with stepped support, d) fixed-pin connecting rod
2.2 Requirements 2.2.1 General Piston pins must meet the following requirements: ■ Sufficient strength and toughness to withstand the loads without damage ■ High surface hardness, in order to achieve favorable wear behavior ■ High surface quality and shape accuracy for optimal fit with its sliding partners, the piston and connecting rod ■ Low weight, in order to keep inertia forces minimal ■ Stiffness must be matched to the piston design, in order to avoid overloading the piston. Despite these sometimes contradictory requirements, piston pin manufacture must be as simple, and thus economical, as possible.
2.2 Requirements
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2.2.2 Strength Under the effects of the gas and inertia forces, pressure and stress loads act on the piston pin surface, the distribution of which is determined by the deformations of the piston pin bores, piston pins, and small end bore, caused by the forces (see Section 2.4.3). As a result of this pressure distribution, the piston pin is subjected to bending, ovalization, and shearing off. Added to this is a torsional load due to the connecting rod tilting motion. It is neglected because of its limited proportion in the total load. The opposing requirement i
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