Abstract: In a pressure motor for electro-rheological fluids comprising a housing (1) surrounding two operating chambers (A, B), a piston (3) moveable in the housing (1), an inlet channel (22) for supplying, and an outlet channel (23) for discharging an electro-rheological fluid, and electro-rheological valves (1a, 1b, 2a, 2b) comprising an annular gap (8) which in each case connects an operating chamber (A and B) to the inlet channel (22) or the outlet channel (23) and whose boundary surfaces form electrodes for the generation of an electric field, the electro-rheological valves (1a, 1b, 2a, 2b) are formed by bores (6) which penetrate through the housing wall in the longitudinal direction and by mandrels (7) which are arranged in the bores (6) and are insulated from the housing (1), where the bores (6) and the mandrels (7) co-define annular gaps (8) of a constant gap width and the mandrels (7) can be connected to a high voltage and the housing (1) can be connected to earth potential.

Abstract: The performance of an eddy current brake is controlled by controlling the magnetic flux in its housing by changing the energizing voltage of the energizing coil of the brake in accordance with a signal obtained by comparing a signal representative of the desired brake performance with a signal representative of the actual magnetic flux measured in the housing at a location of substantially homogeneous flux distribution. The desired performance signal may be a signal representative of the difference between a desired rotational speed signal and the actual rotational speed signal, or it may be a signal representative of the difference between a desired torque signal and an actual torque signal. The desired performance signal may also be a signal representative of the difference between a signal obtained by comparing desired and actual rotational speed signals with a signal representative of actual torque. A Hall generator is used to measure actual flux.