Table 1 Configuration of the engine to which the connecting rod belongs

Crankshaft  radius (mm) 48。5

Connecting rod length (mm) 141

Piston diameter (mm) 86

Mass of the piston assembly  (kg) 0。434

Mass of the connecting rod (kg) 0。439

Izz about the center of gravity (kg m2) 0。00144

Distance of CG from crank-end centre (mm) 36。4

Maximum gas pressure (bar) 37。3

loading conditions was performed for a typical forged

Dynamic analysis of loads and stresses in connecting  rods 617

Fig。 1 Piston pressure versus crank angle  diagram used to calculate forces at the connecting rod ends

obtained as a function of any of the engine para- meters listed in Table 1, as well as any engine speed。 Figure 2 shows variation of angular velocity and angular acceleration over one  complete engine cycle at the maximum engine speed of 5700 r/min, using the data listed in Table 1 and piston pressure plot of Fig。 1。 Variations of angular velocity and angular acceleration from 08 to 3608 are identical to their variations from 3608 to 7208。

On the basis of the velocities and accelerations obtained, inertia load and reaction forces at the connecting rod ends can then be generated for differ- ent engine speeds。 At any point of time during the engine cycle, forces calculated at  the  ends form the external loads, whereas inertia load forms the internal load acting on the connecting rod。 These result in a set of completely equilibrated external and internal loads。

Stress at a point on the connecting rod as it under- goes a cycle consists of two components, a bending stress component and an axial stress component。 The bending stress depends on the bending moment, which is a function of load at the CG normal to the connecting rod longitudinal axis,    as

Fig。 2 Variations of angular velocity and angular acceleration of the connecting rod over one complete engine cycle at a crankshaft speed of 5700 r/min

well as angular and linear acceleration components normal to this axis。 Variation of each of these three quantities over 08 – 3608 is identical to the variation over 3608 – 7208 (see Fig。 2 for variations of angular velocity and acceleration)。 Therefore, for any given point on the connecting rod, the bending moment varies in an identical fashion between 08 and 3608 crank angle as it varies between 3608 and 7208 crank angle。 The axial load variation, however, does not follow the same cycle of repetitive pattern, as one cycle of axial load variation consists of the entire 7208 crank angle。 This is because of the vari- ation in gas load, one cycle of which consists of 7208 crank angle。

Figure 3 shows variations  of  forces  acting  at the crank end (Fig。 3(a)), as well as the piston pin end (Fig。 3(b))。 The positive axial load at the crank end is the compressive load in the figure due to the co-ordinate system used (as shown on the con- necting rod in Fig。 3)。 A similar analysis was per- formed at other engine speeds (i。e。 4000 r/min and 2000 r/min)。 The results indicated that as the speed increases, the tensile load increases, whereas the maximum compressive load at the crank end decreases。 However, although this results in a reduc- tion of the compressive mean load, load range or amplitude increases only slightly with the increasing engine speed。 Effect of engine speed on produced stresses is further discussed in section 4。