Dynamometers

View A Video on Dynamometers - A Quick Introduction

They come in a variety of shapes and sizes, both of which are determined based on usage and placement of the equipment. The two main types are engine dynamometers and chassis dynamometers. Both are widely used by the automobile industry as well as in industrial and manufacturing plants. Some dynamometers are torque testers; torque testers are usually stationary rollers on which the wheels of a vehicle are placed. The rotation of the vehicle's wheels is then measured by the rollers. The results of such tests vary in accuracy; some can have a margin of error that is less than one percent. Chassis dynamometers are usually 15% to 20% lower in their measurements than other devices because some energy is lost as it travels through the drivetrain. Brake testers are a type of dynamometer used to measure the effectiveness of vehicle brake systems. They should not be confused with brake dynamometers, which are so named because of the process by which they measure performance. Other special dynamometer configurations include PTO dynamometers, hydraulic dynamometers and eddy current dynamometers. Typical applications for dynamometers include measuring torque and RPM on chain or belt drives, gearboxes, fluid power systems, gas or diesel systems, transmissions, turbines and other engines used in automotive, aircraft, aerospace, marine and industrial processes.

Dynamometers take measurements in many different ways. Some varieties can be small instruments composed simply of a transducer, a strain gauge and a display screen. In such devices, the force of the torque is transformed into an electrical signal that is amplified, converted and displayed as a measurement. Other motor testers work by using voltage and current probes attached to input wires of the motor to connect internal voltmeters, ammeters and ohmmeters to the system. Some use a non-contact speed sensor to measure the motor shaft speed and determine the number of rotations per minute. Other options and parameters include a load point test where the motor is tested while under a full load, no load or a locked rotor. Direction, torque, current, voltage, power, efficiency and cut-out speed may be determined by motor tester equipment because of the range of available options that meet the variety of needs. Brake testers are used to check vehicles for brake defects, to verify the effectiveness of repair work, to perform regular safety audits and to test vehicles that have been involved in accidents to determine if their brake systems were functioning at the time of the crash.

Dynos are used in many applications because of the variety of models and variations. Chassis dynamometers measure an engine's torque output at the wheels of an automobile. The vehicle is placed on rollers that turn the wheels at a certain speed. The RPM of the rollers allows a computer to calculate the torque of the engine. Inertia dynos are a kind of chassis dyno that work the same way and are particularly useful for back-to-back runs after changes and improvements have been made to the engine. Hydraulic dynamometers are machines that measure the power of an engine by using a cell filled with liquid to increase its load; they are also a subset of chassis dynos. Engine dynamometers are the other main kind of dynamometer. They require that the engine be removed from a vehicle and are therefore widely used by automobile manufacturers, engine rebuilders, and producers of high-performance vehicles such as race cars. Engine dynamometer tests produce accurate and repeatable results. A brake dynamometer takes measurements by applying variable loads to the engine and observing how the engine maintains the RPM as the braking force attempts to slow it down. Eddy current dynamometers are a type of brake dynos that use a conductor passing through a changing magnetic field to generate a circulating flow of electrons that moves in opposing directions from the movement of the disk, creating a repelling or dragging force between the conductor and the magnet.

One of the earliest dynamometers was the de Prony brake, invented by Gaspard de Prony in 1821. Since then, advancements in technology, materials, machining processes and design have led to much more advanced dynamometer systems. Demand for a machine that could take accurate readings of torque led the way for developments and innovations; today's dynos are complex assemblies that can measure performance very accurately. Depending on context, a dynamometer can be very complex or very simple. Chassis dynamometers, for example, are designed for ease of use. A vehicle drives up onto the frame, is strapped in and is ready to begin testing. A computer is used to start the engine and to bring it through the stages of the test. Depending on the software, the progress and results can be charted on a graph or displayed on a screen. Operators may need to be trained in order to learn the software program and to correctly interpret the results. Engine dynos, on the other hand, take the measurements straight from the engine, which requires a different set of equipment. Again, computers are essential for gathering information and reading it. Though some analog dials and gauges are used, they do not report the final measurement. As dynamometers become more automated, the degree of human error decreases and measurements become faster and more accurate. For this reason, dynamometers are helping to improve the world's understanding and use of engines.

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Dynamometer Types

• Brake dynamometers measure horsepower at the engine's output shaft by applying variable load on the engine and evaluating its ability to maintain its speed as the braking force is applied.
• Brake testers are used to test the effectiveness of a vehicle's braking system. As pressure is applied to the brakes, the force produced is measured, recorded, and displayed by the testing system.
• Chassis dynamometers measure an engine's torque output at the wheels of an automobile. The auto is placed on rollers, on which the tires turn, and the result is then measured. Some chassis dynamometers also work by attaching directly to the wheel hub and measuring its rotation. Chassis dynamometers may be fixed or portable units.
• Dynos are machines that measure the torque of an engine.
• Dynometer is another term for dynamometers.
• Dynomometer is another term for dynamometers.
• Eddy current dynamometers determine the torque of an engine by creating eddy currents by moving a conductor through a changing magnetic field.
• Engine dynamometers are another sub-type of torque testing machines, which are hooked to the engine directly as opposed to the wheel chassis. Research and development departments at workshops and auto manufacturing plants use this style of testing, as the engine can be tested without being inside a vehicle.
• Hydraulic dynamometer are machines that measure the power of an engine by using a cell filled with liquid to increase its load.
• Inertia dynamometers are becoming the most widely used type of dynamometer in the torque-testing sectors of both the commercial and racing automobile industries, because they provide real-world results. The inertia of the roller drums is measured to calculate torque, revealing the rate at which an engine can accelerate a known rotational inertia from one RPM to another.
• Motor tester measure the performance of motors to ensure that they are efficient and safe. The equipment is automatic, performing a sequence of steps to determine whether the demonstrated capabilities of the motor are acceptable.
• PTO dynamometers are measurement and diagnostic equipment used to test the performance of power take off components in engines.
• Repair grade dynamometers are chassis devices used to simulate actual road driving conditions on a motor vehicle. Repair grade dynamometers consist of rollers, power absorbers and inertia simulation, either mechanical or electrical.
  
• Torque testers function basically the same way as dynamometers do, but are designed to test the torque of smaller mechanical devices other than engines. Devices, such as precision screwdrivers and wrenches, need to have their torque tested to ensure quality function.

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Dynamometer Terms Ambient Temperature - Temperature of the surrounding medium. Base Line - A vibration reading of a piece of equipment in good operating condition. The baseline becomes a reference point for testing and monitoring.   Breakdown Torque - Also known as maximum torque or pull-out torque, the highest torque that an AC motor will produce with the application of rated voltage and frequency and no abrupt drop in speed. Chassis - The part of a motor vehicle that includes the engine, the frame, the suspension system, the wheels and the steering mechanism, but not the body. Code Letter - The letter on AC motor nameplates that signifies the locked rotor kilovolt amperes per horsepower at rated frequency and voltage. Dynamometer - A machine that measures the power by absorption derived from an internal combustion engine. Full Load Speed - The RPM for an engine or generator, which is available at torque capacity. Full Load Torque - For an engine or generator, it refers to the torque necessary to produce its rated horsepower at full load speed. Horsepower (hp) - Unit of rate of doing work. One horsepower equals about 550 foot-pounds per second or 746 watts. Inertia - Any motion or movement that is not in a straight line but remains constant in velocity. Locked Rotor Torque - The lowest torque that an engine will produce from a standstill position, as measured from all angular positions of the rotor with rated voltage applied at rated frequency. Output - The product of the torque available to do work times the rated RPM Rotor - The rotating part of a motor or engine. R.P.M. (Revolutions Per Minute) - Unit of measurement to determine power and torque. Throttle - The act of acceleration. Torque - The measure of the force applied to produce rotational motion, usually measured in foot-pounds. Transmission - The gears that transmit power from an automobile engine via the driveshaft to the live axle. Trending - A reading of the variation in the measurement of data over no less than three data measurement intervals. Velocity - The rate of change of position in relation to time. Wide Open Throttle (WOT) - The position of the pedal that allows the maximum amount of air to pass into the intake manifold.

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