Chassis dynamometers

Theory

HISTORY OF CHASSIS DYNAMOMETERS

THE FIRST (INERTIAL) ROLLER TEST BENCHES

The first generations of chassis dynamometers, based their measurements on the concept of inertia, limiting themselves to developing benches with very heavy rollers, equipped only by an rpm sensor.

Not being equipped with a brake and load cell, these types of test benches provided approximate and not very repeatable performance measurements.

A fixed inertial mass (heavy rollers), such as that of the inertial bench, cannot in any way be adapted to the different powers to be tested.

Not being able to guarantee constant acceleration times during the tests (and adapted to the type of vehicle and power), an inertial bench cannot guarantee repeatable and accurate results, (except in a narrow range of powers, for which the inertial mass of its roller is adequate to reproduce the acceleration times we would have on the road).

A basic concept, to keep in mind when carrying out power tests, is that a load must always be applied to the motor to simulate the same acceleration (or rather the acceleration time) that we would have on a flat road with an even surface and no wind.

Precisely to meet these needs, dynamometric brake benches are born to eddy currents, equipped with load cell.

BRAKED ROLLER BENCHES

Starting in the 1980s, precisely in order to improve the product, the first roller benches equipped with eddy-current brake and load cell appeared on the market, capable of offering excellent repeatability and measurement accuracy (a.k.a. braked test benches).

Such benches, thanks to their greater reliability, versatility and repeatability of results, immediately find their way onto the market; this is also thanks to the possibility of measuring and trace back with greater repeatability and accuracy to the crankshaft power.

Power at the crank shaft: What is meant by power dissipation?

4WD chassis dynamometers

4WD DYNOS WITH LINKED AXLES

Since the 1990s, roller test bench manufacturers have been offering test benches with front and rear axles mechanically connected.

This new type of product is now offered with different technical solutions, including belts, cardan shafts, synchronisation by means of electric motors.

This need arose as a consequence of the increasing number of vehicles on the road, equipped with increasingly complex traction control systems.

Today, working on a free-axis test bench or with simple electronic brake synchronisation (by SW) is often time-consuming, as well as often non-resolving (difficulty or impossibility of carrying out the test).

More and more modern vehicles, to be tested, require benches with a mechanical synchronisation between axes.

Advantages of the mechanically connected axis test bench (linked dynamometers):

They prevent possible damage to the vehicle's transmission systems;
Bench testing is facilitated thanks tothe correct reproduction of driving conditions on the road;
Avoid the typical loss of time to activate functionality such as the DYNO MODE or 'roller bench functionality';

Simple software-based synchronisation is no longer able to guarantee safe working conditions today, especially when testing the latest generation of vehicles, equipped with increasingly sophisticated control and transmission systems.