chapter  8
62 Pages

Testing of Driveline Systems and Multiwheel Drive Vehicles

The analysis of problems arising during the course of design and manufacture of differentials makes it possible to validate the need to test the mechanisms from among the number of batch-produced units directly at the plant, and the need for experimental testing of newly designed and upgraded mechanisms. The testing of differentials batch produced at the plant includes monitoring the stability

of the manufacturing technology, which consists in checking the serviceability of the fully assembled mechanisms, plotting their performance curves, and partial running-in to provide for preliminary breaking-in of the rubbing surfaces. This is done by means of test rigs, frequently located directly in the manufacturing area. In addition, batch-produced differentials are checked out in the course of delivery and periodical field-tests of the vehicles on which they are installed. Experimental investigations of new and upgraded differentials are performed on special

test stands and on vehicles directly under open-road conditions. Depending on the aspects of interest and on the test stands that are used, stand testing of newly designed differentials can be subdivided into certain methods. In the first place, these are investigations for determining the internal forces of the differentials that work on determining their performance and checking for conformance of their actual locking properties to those underlying the design. The main purpose of these tests consists in verifying analytic studies and calculations of the differentials. Experimental checking is carried out, in the first place, of the predicted performance of the lockers, for example, the locking coefficient (torque bias) in limited slip differentials. For this reason, after a newly designed differential is constructed, it is necessary to check the similitude of the actual locking coefficient to that assumed in the design. This is done on a special stand or directly on the vehicle where the differential will be used. It must be remembered here that a more precise performance curve of a differential can be obtained only after preliminary running-in of the mechanism. The relative motion of the three principal elements (the case and the two output shafts) of

a differential under load and experimental determination of its locking coefficient are usually implemented on an open-type multipurpose stand. Figure 8.1 provides a general view of such a stand while Figure 8.2 illustrates the design of its balancing-braking device. The rotation is transmitted from an electric motor through a gearbox, a Cardan shaft, and

a worm-gear speed reducer to the differential being tested, installed in the housing of the central reduction gear. The rotation from the output shafts of the differential is then

transmitted by means of Cardan shafts to two balancing-braking devices. Each of the Cardan shafts is pinned to braking drum 2, the shaft of which is held in tapered bearings of the moving hub of balancing lever 5. The support 6 of the braking mechanism is rigidly connected to the hub. For this reason, the friction torque that appears between the brake drum and the brake shoes is transmitted to the hub of the lever only after the brake is actuated by means of a loading device located on the support of the braking device (not shown in Figure 8.2). To reduce losses in rolling of the balancing lever, its shaft 3 rests on the tapered roller bearing installed in stationary frame 4 of the balancing-braking device. The balancing levers are connected to strain-gage dynamometers that provide a readout of the magnitude of torques at the output shafts of the differential being tested. The gearbox of the stand allows operating the stand at a variety of speed modes, including relative rotational velocities of the principal elements of the differential within the range of 0.65-2.24 rad=s. The use of adapters allows placing and testing differentials of different sizes.