Roller dynamometer

Mobile test bench for cars

A roller dynamometer is a functional test bench for vehicles in which the performance measurement is carried out by transferring the wheels to a roller. The drive or braking power is usually measured on the wheel. The vehicle is brought to the test stand on its own axle.

Measurement of drive power

The vehicle is fixed on the test stand and accelerated in high gear. The engine speed is picked up by a speed sensor. If the tests take longer, the vehicle radiator is blown by a blower. The wheel performance can be determined in two ways. Either by measuring the acceleration of the test stand rollers or by directly measuring the torque acting on the rollers . In the first case, the moment of inertia of the rollers must be known. The drive torque can be determined from the moment of inertia and the run-up time, and from this the power can be determined via the angular speed. In the second case, the rollers are braked by a coupled brake and the braking torque is measured. In both cases, the power must first be calculated using the measured values.
${\displaystyle M_{\text{Rad}}=J\cdot {\cfrac {\mathrm {d} \omega }{\mathrm {d} t}}}$

With the help of the roller dynamometer, the engine power can be determined indirectly via the wheel power. If you want to know the absolute engine power that the vehicle engine can deliver to its flywheel, you must u. a. The power loss in the drive train of the vehicle (transmission, axle drive, etc.) and the rolling resistance of the tires can also be recorded and added to the wheel power.

The measurement results are usually sufficiently accurate; for more precise results, the engine would have to be removed and taken to a special engine test bench.

Measurement of braking power

The roller / plate brake test bench for testing vehicle brakes on cars, trucks or trailers is more well- known and often used in the main inspection . The test stand rollers are driven and the required drive torque is measured or calculated from the speed and power consumption of the test stand motor.

See also

• Roller dynamometer Munich-Freimann , a railway test facility built from the mid-1970s, especially for testing high speeds

literature

• Max Bohner, Richard Fischer, Rolf Gscheidle: Expertise in automotive technology. 27th edition, Verlag Europa-Lehrmittel, Haan-Gruiten, 2001, ISBN 3-8085-2067-1
• Peter Gerigk, Detlev Bruhn, Dietmar Danner: Automotive engineering. 3rd edition, Westermann Schulbuchverlag GmbH, Braunschweig, 2000, ISBN 3-14-221500-X