Karl-Erik Rydberg

Hydrostatic Drives in Heavy Mobile Machinery–New Concepts and Development Trends

The use of hydrostatic transmission as vehicle drives is primarily motivated by its large range of continuously variable speed, high maneuverability and a possibility to increase the overall efficiency. Consequently an optimally designed system can provide low fuel consumption and thereby low exhaust gas emission. Modern technology involving electro-hydraulic systems, microprocessor control and control theory makes it easier to utilize the advantage of these properties than using traditional hydro-mechanical control. The requirements on productivity are very high for mobile machinery. High output capacity and a wide velocity range are therefore of great importance. To meet these requirements an ordinary hydrostatic transmission is generally used with a mechanical gearbox connected in series. The main drawback in this concept is the high cost in using a gearbox, which can switch gear ratios without jerks and other disturbances in speed and torque transmission. By joining pumps, motors and fixed gears in smart concepts, it is possible to keep prescribed output and velocity range without the need of a multi-speed mechanical gearbox. Two-motor concept and hydro-mechanical split power transmissions are representing interesting solutions. The natural control quantities of the transmission are the output shaft speed or torque. By using microprocessor control the flexibility of the control system increases which makes it possible to adapt different control loops for different states of driving, also taking into account simultaneous use of other hydraulic equipment on the vehicle. INTRODUCTION In mobile vehicles such as earth moving machines, agriculture machines, forest machines, industrial and mining lifters there is a demand for sophisticated performance. A wheel loader is a good example of a vehicle where maneuverability and torque/speed conversion range are of great importance. In order to reach a satisfying productivity a very large torque/speed conversion range is required. This demand is quantified by the Theoretical Range (TR), which is defined as highest vehicle speed over lowest speed where maximum engine power can be transferred by the drive train to the traction wheel, see Figure 1. A TR-value of 10 to 15 is often required in this application. In other words, the requirements on the drive transmission in a wheel loader or another construction machine are very high.

An improved pi control for active damping of a hydraulic crane boom system

To reduce the low-frequency hydraulic-mechanical oscillations when a hydraulic crane boom system (HCBS) works, an improved PI control strategy based on fuzzy scheduling set-point weighting was proposed for the active damping control of a HCBS. By using a range camera and an electronic feedback control, the damping on the crane tip can be adjusted artificially. A co-simulation technique of HOPSAN and MATLAB is used in the controller design. Simulation results show that the proposed PI control system is with less overshoot and fast response. And the tip damping during HCBS working is improved.