This article is the second in a three-part series highlighting the basics of dynamometer testing. In this first article, “What is an Engine Dynamometer?”, we review the main components of a water braked engine dynamometer and how they work. In this article, we will look at the main components of the chassis dynamometer (also known as a dynamometer).

A chassis dynamometer is a tool that allows the operator to safely place a controlled load on a vehicle. With the use of a dyno, the major components of a vehicle’s powertrain, including the engine, transmission, and differential, as well as vehicle components, such as the braking, cooling, and electrical systems, can be operated correctly. across the entire power and speed range of a vehicle. Deficiencies or errors in the engine mounting can be discovered before the vehicle is driven and a thorough assessment of the engine’s operating condition can be carried out. Basically, the dyno is the last quality test before putting a vehicle into service.

Chassis Dynamometer Construction

A chassis dynamometer has three main components: the roller set, the absorption unit, and the torque indicating system.

Chassis dynamometer roller sets come in a variety of diameters depending on the application. An automobile chassis dyno will typically have smaller roller sets, while a large truck dyno will have a larger set. These dynamometer roller sets are placed in a specially designed frame and are directly coupled to the dynamometer absorption unit or to a belt drive system. Dyno roller sets are available in fixed and adjustable width versions that can accommodate a variety of wheelbases to test multiple vehicles on a single machine.

The characteristics of a water brake damper when used on a chassis dyno are very similar to those of an engine dyno. In addition to water brake dampers, chassis dynamometers can also be equipped with AC and eddy current regenerative absorption units. An eddy current absorber uses electrical current to produce a charge. Eddy current dynamometers require an electrically conductive core, shaft, or disc, which is moved through a magnetic field to produce resistance to motion. Available in air-cooled and liquid-cooled applications, Eddy Current Chassis Dynamometers provide fast response rates. Most eddy current absorbers use cast iron discs, similar to vehicle disc brake rotors, and use variable electromagnets to change the strength of the magnetic field to control the amount of braking.

Like a water brake damper, the housing of an eddy current damper is restrained by a torque arm within the chassis dynamometer assembly that is connected to a load cell. AC Regenerative Chassis Dynamometers use an electric motor/generator that is not only capable of assisting in accelerating the vehicle’s drive wheels and acts as a motorized chassis dynamometer, but can also return the energy absorbed by the generator function to the electrical grid. which feeds the dynamometer.

In all cases, the absorption unit is restrained by a torque arm that is connected to a load cell. The load cell measures the force with which the stators try to rotate. By measuring the distance from the torque arm to the shock shaft, the amount of torque can be measured.

Torque = force x distance

So if we measure speed, the amount of horsepower can be found with this formula:

CV = (torque x rpm)/5252

Chassis Dynamometer Operation

A vehicle or chassis is driven on a chassis dynamometer and the vehicle is secured by straps or chains that are typically provided with the dynamometer system. The vehicle then goes through a series of tests that mimic the operating conditions the vehicle would face during its intended use. These tests can be performed by an operator either inside or outside the vehicle, or through an automated test based on the control system supplied with the chassis test stand.

What Constitutes a Chassis Dynamometer System?

The chassis dynamometer itself is just one element of the overall chassis dynamometer system. In general, a dyno system consists of a chassis dynamometer plus a fuel metering system, a room exhaust system, and a data acquisition and control system.

fuel metering system

Fuel metering systems are designed to monitor engine efficiency during power operation. A typical chassis dyno fuel metering system works by initially measuring the total volume of fuel within the storage tank prior to a test. As a test is performed, the system automatically calculates the amount of fuel being used and displays the information monitored on the dynamometer’s data acquisition system.

room exhaust system

The two most common types of room exhaust systems are the hood and pipe systems. Hood systems are preferred because a direct connection to the engine or exhaust system is not required. Hood fans introduce make-up air into the room containing the dyno and remove exhaust from the engine and room. Piping systems can be powered by a fan to remove exhaust from the engine. When a ducted system is used, a separate fan driven room exhaust system is required to pull make-up air into the room and discharge heat, smoke and vapors.

Control Systems and Data Acquisition

Typically, a dyno controller contains the temperature and pressure sensors of the dyno system. These sensors are contained within an industrial cabinet and feature quick disconnects. Data is collected from temperature and pressure sensors and, in many cases, an ECM, and is merged with the dyno speed, torque and power measurements and sent to the dyno system computer.

The computer in a dynamometer control and data acquisition system interfaces with the controller and dynamometer and performs all integrated control operations. It is also where new tests are run and reports are created, printed, and stored.