PSI - Issue 5

Lucjan Witek et al. / Procedia Structural Integrity 5 (2017) 369–376 Lucjan Witek et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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The definition of the crankshaft boundary condition is very complex task. The crankshaft is supported on five bearings. Moreover, four crank pins are connected with the connecting rods (which transfers the loads from the pistons). The left surface of the collar is connected with the clutch (Fig. 5a). In the numerical analysis all mentioned boundary conditions are defined. The lateral circular surface of collar was fully constrained (T R = 0, T  = 0, T Z = 0, Fig. 5a). On the cylindrical surfaces of bearing journals I-V the displacements on R (radial) direction are equal to 0 (Fig. 5b). Between the crank pins (1-4) and the connecting rods (Fig. 5b) the master-slave contact with the friction coefficient of 0.05 was defined.

Table 2. Loads acting on crankshaft defined in numerical analysis.

Load number

Type of load

Maximum load acting on the piston no 1 (after ignition of fuel mixture in cylinder 1 , for α = 7 O after TDC) Maximum load acting on the piston no 2 (after ignition of fuel mixture in cylinder 2 , α = 7 O after TDC) Maximum load acting on the piston no 3 (after ignition of fuel mixture in cylinder 3 , α = 7 O after TDC) Maximum load acting on the piston no 4 (after ignition of fuel mixture in cylinder 4 , α = 7 O after TDC)

1 2 3 4 5 6 7

Centrifugal force of crankshaft subjected to rotation (n = 2000 RPM)

Inertial load of piston and fragment of connecting rod (in result of reciprocating motion)

Inertial load of fragment of connecting rod (in result of rotary motion)

In presented study the complex load cases were defined for the crankshaft model. In preliminary step the separated loads were defined as is seen in Tab. 2. The loads 1-4 are related with the maximum forces acting on each piston during work of the engine. These forces are resulting from a high pressure of exhaust gases after ignition of fuel mixture. The maximum pressure acting on the piston surface (6.5 MPa) was taken from indicator plot of the engine (Fig. 6a). The maximum force occurs when the crankshaft has a position α = 7 O after top death centre (TDC) (Fig 6). The value of piston force (calculated by multiplication of maximum pressure (6.5 MPa) and the diameter of the piston (95mm) equals 46.07 kN. The load no. 5 (Tab. 2, centrifugal force) is related to the rotation of the crankshaft with the speed at which the maximum power is obtained. In order to calculate the centrifugal forces the shaft rotational speed (n = 2000 RPM), the axis of rotation (Z, Fig. 5) and material density (7800 kg/m 3 ) was defined. The mass of the piston of considered engine is 0.95 kg whereas the mas of connecting rod 0.48 kg. The load no. 6 (Tab. 2) is related to inertial load of the piston and segment of connecting rod (in result of reciprocating motion of both mentioned elements). Load no. 7 is an inertial force of connecting rod in result of rotary motion. Loads 5-7 are computed through finite element calculations. a) b)

Fig. 6. (a) Indicator plot of naturally aspirated diesel engine S-4003. (b) Position of the crankshaft and connecting rod during the work of the engine