Different types of dynamometers can be used in a test bench depending on the application. Sometimes users have different alternatives regarding the technology they can employ. In this article, we compare these alternatives to help you decide which type of dynamometer best suits your application.
By Technology
Hydraulic Dynamometers
| Advantages | Disadvantages |
|---|---|
| - Lower Cost | - Low braking torque at low RPM |
| - Compact size even for high power | - Expensive infrastructure (pumps, water tanks, cooling tower) |
| - Low Inertia | - The cooling element (water) is also involved in braking, creating a compromise between braking torque and dissipated power |
| - Allows testing at stabilized load for an indefinite time (limited only by the heat dissipation capacity of the cooling tower) | - Reduced working range (related to the previous point). The same dynamometer can be adjusted to work at low RPM with high torque or at high RPM with low torque, but not both |
| - Like all engine dynamometers, it is necessary to remove the engine from the vehicle for testing | |
| - High wear due to cavitation and turbulence. More frequent maintenance |
Eddy Current Electric Dynamometers
| Advantages | Disadvantages |
|---|---|
| - High braking torque even at very low RPM | - Higher Cost |
| - High precision control even in very different torque and RPM ranges | - Higher inertia |
| - Braking control is independent of cooling (except in air-cooled dynamometers) | - In water-cooled dynamometers, a cooling installation is necessary (pumps, tanks, cooling tower) although slightly simpler than for a hydraulic dynamometer |
| - Allows precise automatic control | - In air-cooled dynamometers, full power braking can only be done for a short time, then switching to a 1/3 lower power regime depending on the dissipation capacity of the dynamometer |
| - High durability, simple and less frequent maintenance | |
| - In the case of air-cooled dynamometers, no additional infrastructure is required |
AC or DC Electric Dynamometers
| Advantages | Disadvantages |
|---|---|
| - The same advantages as eddy current dynamometers | - High Cost |
| - Lower inertia than Eddy dynamometers | - Higher inertia than a hydraulic |
| - Possibility to also use them as a motor for testing transmissions and other passive elements | - The controller is very expensive |
| - Only available for low and moderate power |
Inertial Dynamometers
| Advantages | Disadvantages |
|---|---|
| - Low cost | - Cannot be tested at stabilized load |
| - Simplicity and speed of testing | - The load is always the same and depends on acceleration |
| - Very repeatable | - Requires a good acquisition and processing system to obtain good results |
| - Low maintenance | - Low accuracy as there is influence from external factors such as unmeasured friction (bearings, wheel rolling, chains or transmission belts) and inertia of other rotating elements (engine flywheel, gearbox, wheels) |
| - Does not require additional infrastructure | - Heavy weight |
| - Not homologable unless coupled with a dynamometer |
By Application
Engine Dynamometers
| Advantages | Disadvantages |
|---|---|
| - Only the engine is measured, without influence from other transmission elements (unless some type of transmission is incorporated) | - It is necessary to disassemble the engine for testing, which requires infrastructure external to the vehicle (fuel supply, starter, ignition, wiring and ECU in the case of electronic injection, throttle cable, engine cooling system) |
| - Homologable under standards | - Only provides information about the engine, which can be a disadvantage for some applications |
| - The engine can be tested under highly controlled conditions (controlled coolant temperature, alternator, starter and other subsystems dismounted) |
Chassis Dynamometers
| Advantages | Disadvantages |
|---|---|
| - Quick for mounting and dismounting the vehicle. Allows testing many vehicles in a short time or many changes in a short time (rollers) | - Very imprecise if you want to measure engine power, as it is impossible to determine the actual losses between engine and wheels |
| - Measures the effective power that reaches the ground | - Without a coupled dynamometer it is difficult to calibrate |
| - Measures both engine and transmission at the same time | - Influence of vehicle components on the measurement result (in rollers without dynamometer) |
| - It is possible to estimate, although with low accuracy, the performance of the transmission separately (deceleration test) | - High cost compared to an engine dynamometer |
| - Requires more workshop surface for installation | |
| - Greater difficulty to soundproof |