Dynomometers test the performance of an engine by letting it run for long intervals at high speeds; however, the vehicle does not move and can be operated by a computer system.
Some dynomometers are constructed of a frame that holds the vehicle above engine mounts, an absorption unit like a rolling cylinder, a heat exchanger and a torque measuring device.
Some models require hydraulic fluid, water or oil to operate. Modern dynomometers are computer controlled and are able to graph the capabilities and horsepower output of the engine in terms of the torque capacity, the maximum power absorption and the maximum rotary speed.
There are also additional features that are able to provide an analysis of emissions and reaction time. Interface options include a control console, a computer or a remote control. Dynomometers are used to measure the torque and RPMs for chain or belt drives, gearboxes, fluid power systems, gas or diesel systems, transmissions, turbines and other applications.
They are predominantly found in the automotive industry but are used for aircraft, aerospace, marine and industrial processes where engines and motors are critical.
Chassis and engine dynomometers are the two main kinds of this machine. The difference is that chassis dynos measure an engine’s output through the wheels of the vehicle, whereas engine dynos take readings directly from the engine itself. For chassis dynomometers, the vehicle is placed on the frame and lowered onto the rollers.
It is strapped into place and a computer starts the ignition through a spark plug. The wheels turn the absorption unit, which absorbs the energy; they are usually large metal cylinders. The computer measures how quickly the cylinders rotate and, along with factoring in the weight of the cylinders, determines the torque.
The reading is often 15% to 20% lower than a reading taken by an engine dynomometer because the energy experiences losses due to friction throughout the drivetrain. Engine dynos take measurements straight from an engine, which makes them more accurate. The torque measuring device is connected to the crankshaft or flywheel; a liquid may be used to provide resistance and cooling for the engine.
These machines are used frequently to test new engines that have not yet been installed in a vehicle or to examine an engine that is being rebuilt. Since the reading is taken directly from the engine and does not include any power loss from the drivetrain, the measurement may be referred to as engine horsepower.