Concepts and Development Trends for Efficiency Improvement of Hydrostatics in Mobile Applications 2002-01-1422
In mobile vehicles such as earth moving machines, agriculture machines, forest machines, industrial and mining lifters there is a demand for sophisticated performance. Since the requirements on productivity are very high for mobile machinery, high output capacity combined with high overall efficiency over a wide velocity range is therefore of great importance.
A traditional solution for drive train in mobile machinery is to use a hydrodynamic transmission (torque converter) in series with a multi-speed shiftable gearbox. For heavy machines, engine power above 150 kW, torque converters have been used exclusively until a few years ago. However, the development of hydrostatic drive concepts and microprocessor control have made it possible to be competitive with converter drives. Joining pumps, motors and mechanical gears in smart concepts, so called power split transmissions, has make it possible to keep prescribed output power and velocity range without the need of sophisticated power shift gearboxes.
In constant pressure hydraulic systems gas loaded accumulators can be used for energy storage. During braking and lowering of loads, the kinetic energy of the load can be stored in the accumulator and then the energy will be reused for acceleration and lifting of the load. Secondary controlled motors and hydrostatic transformers are components that can be used in conjunction with accumulators to improve the overall efficiency of hydrostatic systems.
The need is also growing for technology that is capable of not only efficiently producing high-quality works, but also being environmentally friendly. In that sense, high efficient hydrostatic systems with good controllability would be extremely useful in a large quantity of outdoors industrial applications.
The aim of this paper is to show how the advantage of hydrostatics can be exploited to reach high capacity, high overall efficiency and controllability required for high productivity.