| This article is the second in a series of three articles | | | | torque arm that is connected to a load cell. The force |
| highlighting the basics of dynamometer testing. In this | | | | with which the stators are trying to rotate is |
| first article, "What is an Engine Dynamometer," we | | | | measured by the load cell. By measuring the distance |
| reviewed the principle components of the water | | | | from the torque arm to the axis of the absorber, the |
| brake engine dynamometer and how they work. In | | | | amount of torque can be measured. |
| this article we will look at the principle components of | | | | Torque = force x distance |
| the chassis dynamometer (also known as a dyno). | | | | So if we measure the speed, the amount of |
| A chassis dyno is a tool that lets the operator safely | | | | horsepower can be found with this formula: |
| place a controlled load on a vehicle. With the use of a | | | | HP = (torque x rpm)/5252 |
| dyno, a vehicle's primary power train components, | | | | Chassis Dynamometer Operation |
| including the engine, transmission, and differential as | | | | A vehicle or chassis is driven onto a chassis |
| well as vehicle components such as the braking, | | | | dynamometer and the vehicle is secured using straps |
| cooling, and electrical systems, can be properly | | | | or chains typically provided with the dynamometer |
| operated throughout a vehicle's power and speed | | | | system. The vehicle then performs a series of tests |
| range. Deficiencies or errors in the assembly of the | | | | that mimic the operating conditions the vehicle would |
| engine may be discovered before the vehicle is | | | | face during its intended use. These tests can be |
| driven and a thorough assessment of the operating | | | | performed by an operator either inside or outside of |
| condition of the engine can be carried out. Basically | | | | the vehicle, or through an automated test depending |
| the dynamometer is the last test of quality before a | | | | on the control system supplied with the chassis dyno. |
| vehicle is put into service. | | | | What makes up a Chassis Dynamometer System? |
| Chassis Dynamometer Construction | | | | The chassis dynamometer itself is only one element |
| A chassis dynamometer has three major | | | | of the overall chassis dyno system. In general, a |
| components: the roll set, the absorption unit, and the | | | | dyno system consists of a chassis dynamometer plus |
| torque indication system. | | | | a fuel measurement system, a room exhaust |
| Chassis dyno roll sets come in a variety of diameters | | | | system, and a data acquisition and control system. |
| depending on the application. An automotive chassis | | | | Fuel Measurement System |
| dynamometer will typically have smaller roll sets, while | | | | Fuel measurement systems are designed to monitor |
| a large truck dyno will have a larger set. These dyno | | | | engine efficiency during a power run. A typical chassis |
| roll sets are placed in a specially designed frame and | | | | dynamometer fuel measurement system works by |
| are either coupled directly to the dynamometer | | | | initially measuring the total volume of fuel inside the |
| absorption unit or to a belt drive system. Dyno roll | | | | storage tank prior to a test run. As a test run is |
| sets are available in both fixed and adjustable width | | | | performed, the system automatically calculates the |
| versions which can accommodate a variety of | | | | amount of fuel being used and displays the monitored |
| wheelbases for testing multiple vehicles on a single | | | | information on the dynamometer's data acquisition |
| machine. | | | | system. |
| The characteristics of a water brake absorber when | | | | Room Exhaust System |
| used in a chassis dynamometer are very similar to an | | | | The two most common types of room exhaust |
| engine dynamometer. In addition to water brake | | | | systems are hood and pipe systems. Hood systems |
| absorbers, chassis dynos can also be equipped with | | | | are preferred because direct connection to the |
| eddy current and AC regenerative absorption units. | | | | engine or exhaust system is not required. Hood fans |
| An eddy current absorber uses electrical current to | | | | pull make-up air into the room containing the |
| produce a load. Eddy current dynamometers require | | | | dynamometer and removes both engine and room |
| an electrically conductive core, shaft or disc, moving | | | | exhaust. Pipe systems can be powered by a fan to |
| across a magnetic field to produce resistance to | | | | remove engine exhaust. When using a pipe system, a |
| movement. Available in both air cooled and liquid | | | | separate fan-powered room air exhaust system is |
| cooled applications, eddy current chassis | | | | necessary to pull make-up air into the room and to |
| dynamometers provide quick response rates. Most | | | | discharge heat, smoke and fumes. |
| eddy current absorbers use cast iron discs, similar to | | | | Data Acquisition and Control Systems |
| vehicle disc brake rotors, and use variable | | | | Generally a dyno controller contains the |
| electromagnets to change the magnetic field strength | | | | dynamometer system's temperature and pressure |
| to control the amount of braking. | | | | sensors. These sensors are contained within an |
| Much like a water brake absorber, the housing of an | | | | industrial cabinet and are provided with quick |
| eddy current absorber is restrained by a torque arm | | | | disconnects. Data is gathered from the temperature |
| within the chassis dyno assembly that is connected | | | | and pressure sensors, and in many cases an ECM, |
| to a load cell. AC regenerative chassis dynamometers | | | | and are merged with speed, torque and power |
| use an electric motor/generator that is not only | | | | measurements from the dyno and sent to the |
| capable of assisting with bringing the vehicle's drive | | | | dynamometer system's computer. |
| wheels up to speed and act as a motoring chassis | | | | The computer in a data acquisition and dynamometer |
| dyno, but is able to put power absorbed by the | | | | control system interfaces with the controller and the |
| generator function back onto the electrical grid that | | | | dyno and executes all of the embedded control |
| powers the dynamometer. | | | | operations. It's also where new tests are run and |
| In all cases, the absorption unit is restrained using a | | | | reports are created, printed, and stored. |