Comparative Analysis of the Hydrostatic Drive System for a Midi Wheel Loader

The article presents a qualitative and quantitative comparative analysis of the currently used hydrostatic-mechanical wheel drive systems on the example of a wheel loader. In addition to the conventional systems in common use, the analysis also takes into account the future system of direct, individual wheel drive by means of a variable displacement hydrostatic pump-motor. The object generating the boundary conditions for comparison is a typical midi class wheel loader weighing 8 tonnes. Current hydrostatic drive systems for wheeled chassis have a number of limitations due to the configuration of the entire drive system as well as the design of the hydrostatic pumps and motors themselves. Beginning with the typical drive made up of axle and an intermediate gearbox driven by a bent axis variable displacement motor and ending with the aforementioned pump-motor solution, there are significant differences in the actual useful functionality of all drive systems. This functionality translates into the static and dynamic characteristics of the individual drive systems, significantly influencing wheel loader performance, operating economy, reliability and operator comfort. At present, individual direct wheel drive systems are built using slow-speed motors with stepwise or infinitely variable displacement, but within a given range, which imposes limitations on the system’s use. One of the fundamental parameters is the maximum speed of the wheeled chassis equipped with such a system, limited to several km/h, while an innovative system based on a hydrostatic pump-motor with variable displacement does not have this limitation.