FRICTION TESTING SYSTEM, COMPUTER-IMPLEMENTED FRICTION-TESTING METHOD FOR A RAIL VEHICLE, COMPUTER PROGRAM AND NON-VOLATILE DATA CARRIER

In a rail vehicle () a control unit () controls a set of brake/traction units () by control signals (B A B A B A B A) to apply a respective brake/traction force to a respective wheel axle ( to cause retardation/acceleration of the rail vehicle (). The control unit () obtains a first wheel speed signal (ω) indicating a rotational speed of at least one first wheel (), and obtains a second wheel speed signal (ω) indicating an average rotational speed of at least one second wheel (). The control unit () produces a first control signal (BF; A) to the first brake/traction unit () such that this unit applies a gradually increasing brake/traction force to the first wheel axle () until an absolute difference (|ω−ω|) between the first and second wheel speed signals (ω; ω) exceeds a threshold value. The control signals are produced such that an average brake/traction force applied to the at least one second wheel axle () is gradually decreased when the brake/traction force applied to the first wheel axle () is gradually increased. In response to the absolute difference (|ω−ω|) exceeding the threshold value, the control unit () determines a parameter (μ) reflecting a friction coefficient (μ) between the wheels () and a set of rails () upon which the rail vehicle () travels.