Issue 30

G. Belingardi et alii, Frattura ed Integrità Strutturale, 30 (2014) 469-477; DOI: 10.3221/IGF-ESIS.30.57 471 The main design data of the four helical gears are reported in Tab. 1 (engagement 1, Gears 1 and 2; engagement 2, Gears 3 and 4). All gears have been calculated according to ISO 6336 Standard [7-10]. In this work the engagement 2 has been considered (gears 3 and 4). Gear 1 Gear 2 Gear 3 Gear 4 Pressure angle α 20 20 20° 20° Helix angle β 30 (L.H.) 30 (R.H.) 30° (R.H.) 30° (L.H.) Normal module m n 1.5 1.5 2 mm 2 mm Number of teeth Z 22 68 34 75 Face width b 42 42 30 mm 30 mm Table 1 : Main design dimensions of gear’s engagement 1 (input drive) and engagement 2 (final drive) M ULTIBODY M ODEL he simulation of meshing gears has been analysed (see Fig. 2). To obtain a correct simulation of this complex system, a lot of preliminary tests has been done in order to tune both kinematic and dynamic parameters. The final goal is to achieve a good matching between the multibody response and the corresponding theoretical one. In this paper two different type of contact have been realized; the first (Fig. 2 on the left) consists of two rigid bodies in contact, the second (Fig. 2 on the right) consists of two rigid-flexible bodies, simulating the gears web as a rigid body and the rim as flexible. Since the system is very complex, the computational time is very high. So, it was necessary to properly calibrate the simulation before its starting. The best compromise between parameter’s calibration and the computational time has been searched. Contact parameters have been changed from the default ones because the consequent increase in computation time is widely justified by the obtained improvement in the quality of the results. Figure 2 : Multibody automotive transmission system, full-rigid on the left and rigid-flexible on the right. G EARS INTERNAL DYNAMIC FACTOR tandard design procedures compare the gears strength with a calculated stress value, in both bending and pitting cases. The most common approach used in calculation of these stress values, as widely described in ISO Standard 6336 part 1 [7], involves the use of influence factors, derived from results of research and field service. The influence factors may be distinguished between two categories, factors which are determined by gear geometry or which have been established by convention and factors which account for several influences and which are dealt with as independent of each other; in this last group is included the Internal Dynamic Factor K v . As a matter of fact, even when the input torque and speed are constant, significant vibration of the gear masses and resultant dynamic tooth loads can exist. These loads result from the relative displacements between the mating gears as they vibrate in response to an excitation known as transmission error. T S