Mechanical performance of v-ribbed belt drives

The design and shape of a v-ribbed belt affects its radial movement in the pulley grooves. When rib bottom/ groove tip contact occurs the wedge action decreases. The beginning of the contact depends on belt tension, fit between rib and groove, wear and material properties. For the first time a non-contact laser displacement meter has been used for dynamic measurements of the radial movement of a v-ribbed belt (type 3PK) around the arc of wrap running on a belt testing rig. Accurate and repeatable results are possible. By the help of this device, the radial movement and the beginning of the rib bottom/groove tip contact around the arc of wrap have been determined experimentally for tested v-ribbed belts. This point plays an important role in the mechanical performance of v-ribbed belt drives. Two sizes of standard pulleys were used for mechanical testing. These were paired with nominal effective diameters, de =45 mm and de =80 mm. Tests were carried out at the speed of c.o =2000 RPM and two different values of total belt tensions (F, + F,) for three different types of rib bottom/groove tip contact. (i) Without contact (ii) With contact (iii) Mixed contact. Slip, torque loss and maximum torque capacity have been measured experimentally during the tests. A v-ribbed belt is assumed to be a combination of a flat belt and a v-belt with the same radial movement of the two parts. Based on these assumptions a new theory is developed for the mechanical performance of v-ribbed belt drives, which gives a new modification to Euler's equation (capstan formula). By the help of Maple V (mathematical standard library software) numerical solutions for theoretical modelling give the variation of non-dimensional values of v-ribbed belt tension, flat belt part of v-ribbed belt tension, v-belt part of v-ribbed belt tension, radial movement and sliding angle with the length of active arc. This theory has been developed to obtain expressions for speed loss (slip) in linear and non-linear zones. The experimental and theoretical results show that the radial movement and slip of the v-ribbed belt with rib bottom I groove tip contact is slightly less than the values without contact. However, in spite of more or less apparent similar performance of v-ribbed belt with and without rib bottom contact, it is found experimentally and theoretically that the compressed rubber of the belt (between cord and pulley) is subjected to a variable internal shear force around the pulley after contac