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A dynamometer or "dyno" for short, is a device for simultaneously measuring the
torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
and
rotational speed Rotational frequency (also known as rotational speed or rate of rotation) of an object Rotation around a fixed axis, rotating around an axis is the frequency of rotation of the object. Its unit is revolution per minute (rpm), cycle per second ...
(
RPM Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...
) of an
engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gen ...
,
motor An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gen ...
or other rotating
prime mover Prime mover may refer to: Philosophy *Unmoved mover, a concept in Aristotle's writings Engineering * Prime mover (engine), motor, a machine that converts various other forms of energy (chemical, electrical, fluid pressure/flow, etc) into energy o ...
so that its instantaneous
power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...
may be calculated, and usually displayed by the dynamometer itself as kW or
bhp BHP Group Limited (formerly known as BHP Billiton) is an Australian multinational mining, metals, natural gas petroleum public company that is headquartered in Melbourne, Victoria, Australia. The Broken Hill Proprietary Company was founded ...
. In addition to being used to determine the torque or power characteristics of a machine under test, dynamometers are employed in a number of other roles. In standard emissions testing cycles such as those defined by the
United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
, dynamometers are used to provide simulated road loading of either the engine (using an engine dynamometer) or full powertrain (using a chassis dynamometer). Beyond simple power and torque measurements, dynamometers can be used as part of a testbed for a variety of engine development activities, such as the calibration of engine management controllers, detailed investigations into combustion behavior, and
tribology Tribology is the science and engineering of interacting surfaces in relative Motion (physics), motion. It includes the study and application of the principles of friction, lubrication and wear. Tribology is highly interdisciplinary, drawing on m ...
. In the medical terminology, hand-held dynamometers are used for routine screening of grip and
hand strength Hand strength measurements are of interest to study pathology of the hand that involves loss of muscle strength. Examples of these pathologies are carpal tunnel syndrome, nerve injury, tendon injuries of the hand, and neuromuscular disorders. Ha ...
, and the initial and ongoing evaluation of patients with hand trauma or dysfunction. They are also used to measure grip strength in patients where compromise of the cervical nerve roots or peripheral nerves is suspected. In the
rehabilitation Rehabilitation or Rehab may refer to: Health * Rehabilitation (neuropsychology), therapy to regain or improve neurocognitive function that has been lost or diminished * Rehabilitation (wildlife), treatment of injured wildlife so they can be retur ...
,
kinesiology Kinesiology () is the scientific study of human body movement. Kinesiology addresses physiological, anatomical, biomechanical, pathological, neuropsychological principles and mechanisms of movement. Applications of kinesiology to human health ...
, and
ergonomics Human factors and ergonomics (commonly referred to as human factors) is the application of psychological and physiological principles to the engineering and design of products, processes, and systems. Four primary goals of human factors learnin ...
realms, force dynamometers are used for measuring the back, grip, arm, and/or leg strength of athletes, patients, and workers to evaluate physical status, performance, and task demands. Typically the force applied to a lever or through a cable is measured and then converted to a moment of force by multiplying by the perpendicular distance from the force to the axis of the level.


Principles of operation of torque power (absorbing) dynamometers

An absorbing dynamometer acts as a load that is driven by the prime mover that is under test (e.g.
Pelton wheel The Pelton wheel or Pelton Turbine is an impulse-type water turbine invented by American inventor Lester Allan Pelton in the 1870s. The Pelton wheel extracts energy from the impulse of moving water, as opposed to water's dead weight like the trad ...
). The dynamometer must be able to operate at any speed and load to any level of torque that the test requires. Absorbing dynamometers are not to be confused with "inertia" dynamometers, which calculate power solely by measuring power required to accelerate a known mass drive roller and provide no variable load to the prime mover. An absorption dynamometer is usually equipped with some means of measuring the operating torque and speed. The power absorption unit (PAU) of a dynamometer absorbs the power developed by the prime mover. This power absorbed by the dynamometer is then converted into heat, which generally dissipates into the ambient air or transfers to cooling water that dissipates into the air. Regenerative dynamometers, in which the prime mover drives a DC motor as a generator to create load, make excess DC power and potentially - using a DC/AC inverter - can feed AC power back into the commercial electrical power grid. Absorption dynamometers can be equipped with two types of control systems to provide different main test types.


Constant force

The dynamometer has a "braking" torque regulator - the power absorption unit is configured to provide a set braking force torque load, while the prime mover is configured to operate at whatever throttle opening, fuel delivery rate, or any other variable it is desired to test. The prime mover is then allowed to accelerate the engine through the desired speed or RPM range. Constant force test routines require the PAU to be set slightly torque deficient as referenced to prime mover output to allow some rate of acceleration. Power is calculated based on rotational speed x torque x constant. The constant varies depending on the units used.


Constant speed

If the dynamometer has a speed regulator (human or computer), the PAU provides a variable amount of braking force (torque) that is necessary to cause the prime mover to operate at the desired single test speed or RPM. The PAU braking load applied to the prime mover can be manually controlled or determined by a computer. Most systems employ eddy current, oil hydraulic, or DC motor produced loads because of their linear and quick load change abilities. The power is calculated as the product of
angular velocity In physics, angular velocity or rotational velocity ( or ), also known as angular frequency vector,(UP1) is a pseudovector representation of how fast the angular position or orientation of an object changes with time (i.e. how quickly an objec ...
and
torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
. A ''motoring dynamometer'' acts as a motor that drives the equipment under test. It must be able to drive the equipment at any speed and develop any level of torque that the test requires. In common usage, AC or DC motors are used to drive the equipment or "load" device. In most dynamometers
power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...
(''P'') is not measured directly, but must be calculated from torque (''τ'') and angular velocity (''ω'') values or force (''F'') and linear velocity (''v''): :P=\tau\cdot\omega :or :P=F \cdot v :where ::''P'' is the power in
watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...
s ::''τ'' is the torque in
newton metre The newton-metre (also newton metre or newton meter; symbol N⋅m or N m) is the unit of torque (also called ) in the International System of Units (SI). One newton-metre is equal to the torque resulting from a force of one newton applie ...
s ::''ω'' is the angular velocity in
radians per second The radian per second (symbol: rad⋅s−1 or rad/s) is the unit of angular velocity in the International System of Units (SI). The radian per second is also the SI unit of angular frequency, commonly denoted by the Greek letter ''ω'' (omega). ...
::''F'' is the force in
newton Newton most commonly refers to: * Isaac Newton (1642–1726/1727), English scientist * Newton (unit), SI unit of force named after Isaac Newton Newton may also refer to: Arts and entertainment * ''Newton'' (film), a 2017 Indian film * Newton ( ...
s ::''v'' is the linear velocity in
metres per second The metre per second is the unit of both speed (a scalar quantity) and velocity (a vector quantity, which has direction and magnitude) in the International System of Units (SI), equal to the speed of a body covering a distance of one metre in ...
Division by a conversion constant may be required, depending on the units of measure used. For imperial or U.S. customary units, :P_\mathrm= :where ::''P''hp is the power in
horsepower Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are the ...
::''τ''lb·ft is the torque in pound-feet ::''ω''RPM is the rotational velocity in
revolutions per minute Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...
For metric units, :P_\mathrm=\tau_\mathrm\cdot\omega :where ::''P''W is the power in
Watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...
s (W) ::''τ''N·m is the torque in
Newton metre The newton-metre (also newton metre or newton meter; symbol N⋅m or N m) is the unit of torque (also called ) in the International System of Units (SI). One newton-metre is equal to the torque resulting from a force of one newton applie ...
s (Nm) ::''ω'' is the rotational velocity in radians/second (rad/s) ::''ω = ωRPM . π / 30  ''


Detailed dynamometer description

A dynamometer consists of an absorption (or absorber/driver) unit, and usually includes a means for measuring torque and rotational speed. An absorption unit consists of some type of rotor in a housing. The rotor is coupled to the engine or other equipment under test and is free to rotate at whatever speed is required for the test. Some means is provided to develop a braking torque between the rotor and housing of the dynamometer. The means for developing torque can be frictional, hydraulic, electromagnetic, or otherwise, according to the type of absorption/driver unit. One means for measuring torque is to mount the dynamometer housing so that it is free to turn except as restrained by a torque arm. The housing can be made free to rotate by using
trunnion A trunnion (from Old French "''trognon''", trunk) is a cylindrical protrusion used as a mounting or pivoting point. First associated with cannons, they are an important military development. Alternatively, a trunnion is a shaft that positions a ...
s connected to each end of the housing to support it in pedestal-mounted trunnion bearings. The torque arm is connected to the dyno housing and a
weighing scale A scale or balance is a device used to measure weight or mass. These are also known as mass scales, weight scales, mass balances, and weight balances. The traditional scale consists of two plates or bowls suspended at equal distances from a ...
is positioned so that it measures the force exerted by the dyno housing in attempting to rotate. The torque is the force indicated by the scales multiplied by the length of the torque arm measured from the center of the dynamometer. A
load cell A load cell converts a force such as tension, compression, pressure, or torque into an electrical signal that can be measured and standardized. It is a force transducer. As the force applied to the load cell increases, the electrical signal change ...
transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and contr ...
can be substituted for the scales in order to provide an
electrical signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...
that is proportional to torque. Another means to measure torque is to connect the engine to the dynamo through a torque sensing coupling or torque transducer. A torque transducer provides an electrical signal that is proportional to the torque. With electrical absorption units, it is possible to determine torque by measuring the current drawn (or generated) by the absorber/driver. This is generally a less accurate method and not much practiced in modern times, but it may be adequate for some purposes. When torque and speed signals are available, test data can be transmitted to a
data acquisition Data acquisition is the process of sampling signals that measure real-world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer. Data acquisition systems, abbreviated by the acro ...
system rather than being recorded manually. Speed and torque signals can also be recorded by a
chart recorder A chart recorder is an electromechanical device that records an electrical or mechanical input trend onto a piece of paper (the chart). Chart recorders may record several inputs using different color pens and may record onto strip charts or circu ...
or
plotter A plotter is a machine that produces vector graphics drawings. Plotters draw lines on paper using a pen, or in some applications, use a knife to cut a material like vinyl or leather. In the latter case, they are sometimes known as a cutting pl ...
.


Types of dynamometers

In addition to classification as absorption, motoring, or universal, as described above, dynamometers can also be classified in other ways. A dyno that is
coupled ''Coupled'' is an American dating game show that aired on Fox from May 17 to August 2, 2016. It was hosted by television personality, Terrence J and created by Mark Burnett, of '' Survivor'', ''The Apprentice'', '' Are You Smarter Than a 5th G ...
directly to an engine is known as an ''engine dyno''. A dyno that can measure torque and power delivered by the power train of a vehicle directly from the drive wheel or wheels without removing the engine from the frame of the vehicle), is known as a ''chassis dyno''. Dynamometers can also be classified by the type of absorption unit or absorber/driver that they use. Some units that are capable of absorption only can be combined with a motor to construct an absorber/driver or "universal" dynamometer.


Types of absorption units

*
Eddy current Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a mag ...
(absorption only) * Magnetic powder brake (absorption only) *
Hysteresis Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of ...
brake (absorption only) *
Electric motor An electric motor is an Electric machine, electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a Electromagneti ...
/
generator Generator may refer to: * Signal generator, electronic devices that generate repeating or non-repeating electronic signals * Electric generator, a device that converts mechanical energy to electrical energy. * Generator (circuit theory), an eleme ...
(absorb or drive) * Fan brake (absorption only) *
Hydraulic Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counter ...
brake (absorption only) * Force lubricated, oil shear friction brake (absorption only) *
Water brake A water brake is a type of fluid coupling used to absorb mechanical energy and usually consists of a turbine or propeller mounted in an enclosure filled with water. As the turbine or propeller turns, mechanical energy is transferred to the wat ...
(absorption only) * Compound dyno (usually an absorption dyno in tandem with an electric/motoring dyno)


Eddy current type absorber

Eddy current (EC) dynamometers are currently the most common absorbers used in modern chassis dynos. The EC absorbers provide a quick load change rate for rapid load settling. Most are air cooled, but some are designed to require external water cooling systems. Eddy current dynamometers require an electrically conductive core, shaft, or disc moving across a magnetic field to produce resistance to movement. Iron is a common material, but copper, aluminum, and other conductive materials are also usable. In current (2009) applications, most EC brakes use cast iron discs similar to vehicle disc brake rotors, and use variable electromagnets to change the magnetic field strength to control the amount of braking. The electromagnet voltage is usually controlled by a computer, using changes in the magnetic field to match the power output being applied. Sophisticated EC systems allow steady state and controlled acceleration rate operation.


Powder dynamometer

A powder dynamometer is similar to an eddy current dynamometer, but a fine magnetic powder is placed in the air gap between the rotor and the coil. The resulting flux lines create "chains" of metal particulate that are constantly built and broken apart during rotation, creating great torque. Powder dynamometers are typically limited to lower RPM due to heat dissipation problems.


Hysteresis dynamometers

Hysteresis dynamometers use a magnetic rotor, sometimes of AlNiCo alloy, that is moved through flux lines generated between magnetic pole pieces. The magnetisation of the rotor is thus cycled around its B-H characteristic, dissipating energy proportional to the area between the lines of that graph as it does so. Unlike eddy current brakes, which develop no torque at standstill, the hysteresis brake develops largely constant torque, proportional to its magnetising current (or magnet strength in the case of permanent magnet units) over its entire speed range. Units often incorporate ventilation slots, though some have provision for forced air cooling from an external supply. Hysteresis and Eddy Current dynamometers are two of the most useful technologies in small ( and less) dynamometers.


Electric motor/generator dynamometer

Electric motor An electric motor is an Electric machine, electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a Electromagneti ...
/
generator Generator may refer to: * Signal generator, electronic devices that generate repeating or non-repeating electronic signals * Electric generator, a device that converts mechanical energy to electrical energy. * Generator (circuit theory), an eleme ...
dynamometers are a specialized type of
adjustable-speed drive Motor drive means a system that includes a motor. An adjustable speed motor drive means a system that includes a motor that has multiple operating speeds. A variable speed motor drive is a system that includes a motor and is continuously variabl ...
. The absorption/driver unit can be either an
alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
(AC) motor or a
direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even ...
(DC) motor. Either an AC motor or a DC motor can operate as a generator that is driven by the unit under test or a motor that drives the unit under test. When equipped with appropriate control units, electric motor/generator dynamometers can be configured as universal dynamometers. The control unit for an AC motor is a
variable-frequency drive A variable-frequency drive (VFD) is a type of motor drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and, depending on topology, to control associated voltage or current variat ...
, while the control unit for a DC motor is a DC drive. In both cases, regenerative control units can transfer power from the unit under test to the electric utility. Where permitted, the operator of the dynamometer can receive payment (or credit) from the utility for the returned power via
net metering Net metering (or net energy metering, NEM) is an electricity billing mechanism that allows consumers who generate some or all of their own electricity to use that electricity anytime, instead of when it is generated. This is particularly importa ...
. In engine testing, universal dynamometers can not only absorb the power of the engine, but can also drive the engine for measuring friction, pumping losses, and other factors. Electric motor/generator dynamometers are generally more costly and complex than other types of dynamometers.


Fan brake

A fan is used to blow air to provide engine load. The torque absorbed by a fan brake may be adjusted by changing the gearing or the fan itself, or by restricting the airflow through the fan. Due to the low
viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...
of air, this variety of dynamometer is inherently limited in the amount of torque that it can absorb.


Force lubricated oil shear brake

An oil shear brake has a series of friction discs and steel plates similar to the clutches in an automobile automatic transmission. The shaft carrying the friction discs is attached to the load through a coupling. A piston pushes the stack of friction discs and steel plates together creating shear in the oil between the discs and plates applying a torque. Torque can be controlled pneumatically or hydraulically. Force lubrication maintains a film of oil between the surfaces to eliminate wear. Reaction is smooth down to zero RPM without stick-slip. Loads up to hundreds of thermal horsepower can be absorbed through the required force lubrication and cooling unit. Most often, the brake is kinetically grounded through a torque arm anchored by a strain gauge which produces a current under load fed to the dynamometer control. Proportional or servo control valves are generally used to allow the dynamometer control to apply pressure to provide the program torque load with feedback from the strain gauge closing the loop. As torque requirements go up there are speed limitations.


Hydraulic brake

The hydraulic brake system consists of a hydraulic pump (usually a gear-type pump), a fluid reservoir, and piping between the two parts. Inserted in the piping is an adjustable valve, and between the pump and the valve is a gauge or other means of measuring hydraulic pressure. In simplest terms, the engine is brought up to the desired RPM and the valve is incrementally closed. As the pumps outlet is restricted, the load increases and the throttle is simply opened until at the desired throttle opening. Unlike most other systems, power is calculated by factoring flow volume (calculated from pump design specifications), hydraulic pressure, and RPM. Brake HP, whether figured with pressure, volume, and RPM, or with a different load cell-type brake dyno, should produce essentially identical power figures. Hydraulic dynos are renowned for having the quickest load change ability, just slightly surpassing eddy current absorbers. The downside is that they require large quantities of hot oil under high pressure and an oil reservoir.


Water brake-type absorber

The
water brake A water brake is a type of fluid coupling used to absorb mechanical energy and usually consists of a turbine or propeller mounted in an enclosure filled with water. As the turbine or propeller turns, mechanical energy is transferred to the wat ...
absorber is sometimes mistakenly called a "hydraulic dynamometer". Invented by British engineer
William Froude William Froude (; 28 November 1810 in Devon – 4 May 1879 in Simonstown, South Africa) was an English engineer, hydrodynamicist and naval architect. He was the first to formulate reliable laws for the resistance that water offers to ships (suc ...
in 1877 in response to a request by the
Admiralty Admiralty most often refers to: *Admiralty, Hong Kong *Admiralty (United Kingdom), military department in command of the Royal Navy from 1707 to 1964 *The rank of admiral *Admiralty law Admiralty can also refer to: Buildings * Admiralty, Traf ...
to produce a machine capable of absorbing and measuring the power of large naval engines, water brake absorbers are relatively common today. They are noted for their high power capability, small size, light weight, and relatively low manufacturing costs as compared to other, quicker reacting, "power absorber" types. Their drawbacks are that they can take a relatively long period of time to "stabilize" their load amount, and that they require a constant supply of water to the "water brake housing" for cooling. Environmental regulations may prohibit "flow through" water, in which case large water tanks are installed to prevent contaminated water from entering the environment. The schematic shows the most common type of water brake, known as the "variable level" type. Water is added until the engine is held at a steady RPM against the load, with the water then kept at that level and replaced by constant draining and refilling (which is needed to carry away the heat created by absorbing the horsepower). The housing attempts to rotate in response to the torque produced, but is restrained by the scale or torque metering cell that measures the torque.


Compound dynamometers

In most cases, motoring dynamometers are symmetrical; a 300 kW AC dynamometer can absorb 300 kW as well as motor at 300 kW. This is an uncommon requirement in engine testing and development. Sometimes, a more cost-effective solution is to attach a larger absorption dynamometer with a smaller motoring dynamometer. Alternatively, a larger absorption dynamometer and a simple AC or DC motor may be used in a similar manner, with the electric motor only providing motoring power when required (and no absorption). The (cheaper) absorption dynamometer is sized for the maximum required absorption, whereas the motoring dynamometer is sized for motoring. A typical size ratio for common emission test cycles and most engine development is approximately 3:1. Torque measurement is somewhat complicated since there are two machines in tandem - an inline torque transducer is the preferred method of torque measurement in this case. An eddy-current or waterbrake dynamometer, with electronic control combined with a variable frequency drive and AC induction motor, is a commonly used configuration of this type. Disadvantages include requiring a second set of test cell services (electrical power and cooling), and a slightly more complicated control system. Attention must be paid to the transition between motoring and braking in terms of control stability.


How dynamometers are used for engine testing

Dynamometers are useful in the development and refinement of modern engine technology. The concept is to use a dyno to measure and compare power transfer at different points on a vehicle, thus allowing the engine or drivetrain to be modified to get more efficient power transfer. For example, if an engine dyno shows that a particular engine achieves of torque, and a chassis dynamo shows only , one would know that the drivetrain losses are nominal. Dynamometers are typically very expensive pieces of equipment, and so are normally used only in certain fields that rely on them for a particular purpose.


Types of dynamometer systems

A 'brake' dynamometer applies variable load on the prime mover (PM) and measures the PM's ability to move or hold the RPM as related to the "braking force" applied. It is usually connected to a
computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...
that records applied braking torque and calculates engine power output based on information from a "load cell" or "strain gauge" and a speed sensor. An 'inertia' dynamometer provides a fixed inertial mass load, calculates the power required to accelerate that fixed and known mass, and uses a computer to record RPM and acceleration rate to calculate torque. The engine is generally tested from somewhat above idle to its maximum RPM and the output is measured and plotted on a
graph Graph may refer to: Mathematics *Graph (discrete mathematics), a structure made of vertices and edges **Graph theory, the study of such graphs and their properties *Graph (topology), a topological space resembling a graph in the sense of discre ...
. A 'motoring' dynamometer provides the features of a brake dyno system, but in addition, can "power" (usually with an AC or DC motor) the PM and allow testing of very small power outputs (for example, duplicating speeds and loads that are experienced when operating a vehicle traveling downhill or during on/off throttle operations).


Types of dynamometer test procedures

There are essentially 3 types of dynamometer test procedures: # Steady state: where the engine is held at a specified RPM (or series of usually sequential RPMs) for a desired amount of time by the variable brake loading as provided by the PAU (power absorber unit). These are performed with brake dynamometers. # Sweep test: the engine is tested under a load (i.e. inertia or brake loading), but allowed to "sweep" up in RPM, in a continuous fashion, from a specified lower "starting" RPM to a specified "end" RPM. These tests can be done with inertia or brake dynamometers. # Transient test: usually done with AC or DC dynamometers, the engine power and speed are varied throughout the test cycle. Different test cycles are used in different jurisdictions. Chassis test cycles include the US light-duty UDDS, HWFET, US06, SC03, ECE, EUDC, and CD34, while engine test cycles include ETC, HDDTC, HDGTC, WHTC, WHSC, and ED12.


Types of sweep tests

#Inertia sweep: an inertia dyno system provides a fixed inertial mass flywheel and computes the power required to accelerate the flywheel (the load) from the starting to the ending RPM. The actual rotational mass of the engine (or engine and vehicle in the case of a chassis dyno) is not known, and the variability of even the mass of the tires will skew the power results. The inertia value of the flywheel is "fixed", so low-power engines are under load for a much longer time and internal engine temperatures are usually too high by the end of the test, skewing optimal "dyno" tuning settings away from the optimal tuning settings of the outside world. Conversely, high powered engines commonly complete a "4th gear sweep" test in less than 10 seconds, which is not a reliable load condition as compared to operation in the real world. By not providing enough time under load, internal combustion chamber temperatures are unrealistically low and power readings - especially past the power peak - are skewed to the low side. #Loaded sweep, of the brake dyno type, includes: ## Simple fixed load sweep: a fixed load - of somewhat less than the output of the engine - is applied during the test. The engine is allowed to accelerate from its starting RPM to its ending RPM, varying at its own acceleration rate, depending on power output at any particular rotational speed. Power is calculated using (rotational speed x torque x constant) + the power required to accelerate the dyno and engine's/vehicle's rotating mass. ## Controlled acceleration sweep: similar in basic usage as the (above) simple fixed load sweep test, but with the addition of active load control that targets a specific rate of acceleration. Commonly, 20fps/ps is used. #Controlled acceleration rate: the acceleration rate used is controlled from low power to high power engines, and overextension and contraction of "test duration" is avoided, providing more repeatable tests and tuning results. In every type of sweep test, there remains the issue of potential power reading error due to the variable engine/dyno/vehicle total rotating mass. Many modern computer-controlled brake dyno systems are capable of deriving that "inertial mass" value, so as to eliminate this error. A "sweep test" will almost always be suspect, as many "sweep" users ignore the rotating mass factor, preferring to use a blanket "factor" on every test on every engine or vehicle. Simple inertia dyno systems aren't capable of deriving "inertial mass", and thus are forced to use the same (assumed) inertial mass on every vehicle tested. Using steady state testing eliminates the rotating inertial mass error of a sweep test, as there is no acceleration during this type of test.


Transient test characteristics

Aggressive throttle movements, engine speed changes, and engine motoring are characteristics of most transient engine tests. The usual purpose of these tests are vehicle emissions development and homologation. In some cases, the lower-cost eddy-current dynamometer is used to test one of the transient test cycles for early development and calibration. An eddy current dyno system offers fast load response, which allows rapid tracking of speed and load, but does not allow motoring. Since most required transient tests contain a significant amount of motoring operation, a transient test cycle with an eddy-current dyno will generate different emissions test results. Final adjustments are required to be done on a motoring-capable dyno.


Engine dynamometer

An engine dynamometer measures power and torque directly from the engine's
crankshaft A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecting ...
(or
flywheel A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, ass ...
), when the engine is removed from the vehicle. These dynos do not account for power losses in the drivetrain, such as the
gearbox Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), differe ...
,
transmission Transmission may refer to: Medicine, science and technology * Power transmission ** Electric power transmission ** Propulsion transmission, technology allowing controlled application of power *** Automatic transmission *** Manual transmission *** ...
, and differential.


Chassis dynamometer (rolling road)

A
chassis A chassis (, ; plural ''chassis'' from French châssis ) is the load-bearing framework of an artificial object, which structurally supports the object in its construction and function. An example of a chassis is a vehicle frame, the underpart ...
dynamometer, sometimes referred to as a rolling road, measures power delivered to the surface of the "drive roller" by the drive
wheel A wheel is a circular component that is intended to rotate on an axle Bearing (mechanical), bearing. The wheel is one of the key components of the wheel and axle which is one of the Simple machine, six simple machines. Wheels, in conjunction wi ...
s. The vehicle is often strapped down on the roller or rollers, which the car then turns, and the output measured thereby. Modern roller-type chassis dyno systems use the "Salvisberg roller", which improves traction and repeatability, as compared to the use of smooth or
knurled Knurling is a manufacturing process, typically conducted on a lathe, whereby a pattern of straight, angled or crossed lines is rolled into the material. Etymology The terms ''knurl'' and ''knurled'' are from an earlier ''knur'' ‘knot in wo ...
drive rollers. Chassis dynamometers can be fixed or portable, and can do much more than display RPM, power, and torque. With modern electronics and quick reacting, low inertia dyno systems, it is now possible to tune to best power and the smoothest runs in real time. Other types of chassis dynamometers are available that eliminate the potential for wheel slippage on old style drive rollers, attaching directly to the vehicle's hubs for direct torque measurement from the axle.
Motor vehicle emissions Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through an ...
development and homologation dynamometer test systems often integrate emissions sampling, measurement, engine speed and load control, data acquisition, and safety monitoring into a complete test cell system. These test systems usually include complex emissions sampling equipment (such as constant volume samplers and raw
exhaust gas Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through an ...
sample preparation systems) and analyzers. These analyzers are much more sensitive and much faster than a typical portable exhaust gas analyzer. Response times of well under one second are common, and are required by many transient test cycles. In retail settings it is also common to tune the air-fuel ratio using a wideband
oxygen sensor An oxygen sensor (or lambda sensor, where lambda refers to air–fuel equivalence ratio, usually denoted by λ) or probe or sond, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analysed. It was ...
that is graphed along with the RPM. Integration of the dynamometer control system with automatic calibration tools for engine system calibration is often found in development test cell systems. In these systems, the dynamometer load and engine speed are varied to many engine operating points, while selected engine management parameters are varied and the results recorded automatically. Later analysis of this data may then be used to generate engine calibration data used by the engine management software. Because of frictional and mechanical losses in the various drivetrain components, the measured wheel brake horsepower is generally 15-20 percent less than the brake horsepower measured at the crankshaft or flywheel on an engine dynamometer.


History

The Graham-Desaguliers Dynamometer was invented by
George Graham George Graham (born 30 November 1944), nicknamed "Stroller", is a Scottish former Association football, football player and manager (association football), manager. In his successful playing career, he made 455 appearances in England's Football ...
and mentioned in the writings of John Desagulier in 1719. Desaguliers modified the first dynamometers, and so the instrument became known as the Graham-Desaguliers dynamometer. The Regnier dynamometer was invented and made public in 1798 by Edmé Régnier, a French rifle maker and engineer. A patent was issued (dated June 1817) to Siebe and Marriot of Fleet Street, London for an improved weighing machine.
Gaspard de Prony Baron Gaspard Clair François Marie Riche de Prony (22 July 1755 – 29 July 1839) was a French mathematician and engineer, who worked on hydraulics. He was born at Chamelet, Beaujolais, France and died in Asnières-sur-Seine, France. Educati ...
invented the de Prony brake in 1821. Macneill's road indicator was invented by John Macneill in the late 1820s, further developing Marriot's patented weighing machine. Froude Ltd, of Worcester, UK, manufactures engine and vehicle dynamometers. They credit
William Froude William Froude (; 28 November 1810 in Devon – 4 May 1879 in Simonstown, South Africa) was an English engineer, hydrodynamicist and naval architect. He was the first to formulate reliable laws for the resistance that water offers to ships (suc ...
with the invention of the hydraulic dynamometer in 1877, and say that the first commercial dynamometers were produced in 1881 by their predecessor company,
Heenan & Froude Heenan & Froude was a United Kingdom-based engineering company, founded in Newton Heath, Manchester, England in 1881 in a partnership formed by engineers Richard Froude and Richard Hammersley Heenan. Expanded on the back of William Froude's pat ...
. In 1928, the German company "''
Carl Schenck Carl Heinrich Johann Schenck was a German technology pioneer and businessman who established ''Carl Schenck Eisengießerei & Waagenfabrik'' in 1881, in Darmstadt, Germany.
Eisengießerei & Waagenfabrik''" built the first vehicle dynamometers for brake tests that have the basic design of modern vehicle test stands. The eddy current dynamometer was invented by Martin and Anthony Winther around 1931, but at that time, DC Motor/generator dynamometers had been in use for many years. A company founded by the Winthers brothers, Dynamatic Corporation, manufactured dynamometers in
Kenosha, Wisconsin Kenosha () is a city in the U.S. state of Wisconsin and the seat of Kenosha County. Per the 2020 census, the population was 99,986 which made it the fourth-largest city in Wisconsin. Situated on the southwestern shore of Lake Michigan, Kenos ...
until 2002. Dynamatic was part of
Eaton Corporation Eaton Corporation plc is an American-Irish multinational power management company with 2021 sales of $19.63 billion, founded in the United States with global headquarters in Dublin, Ireland, and a secondary administrative center in Beachwood, ...
from 1946 to 1995. In 2002, Dyne Systems of Jackson, Wisconsin acquired the Dynamatic dynamometer product line. Starting in 1938, Heenan & Froude manufactured eddy current dynamometers for many years under license from Dynamatic and Eaton.


See also

*
Dynamometer car A dynamometer car is a railroad maintenance of way car used for measuring various aspects of a locomotive's performance. Measurements include tractive effort (pulling force), power, top speed, etc. History The first dynamometer car was probably ...
for railroad usage *
Engine test stand An engine test stand is a facility used to develop, characterize and test engines. The facility, often offered as a product to automotive OEMs, allows engine operation in different operating regimes and offers measurement of several physical variab ...
dynamometer for engines ''e.g.'', combustion engines *
Force gauge A force gauge (also called a force meter) is a measuring instrument used to measure forces. Applications exist in research and development, laboratory, quality, production and field environment. There are two kinds of force gauges today: mechanica ...
*
Fuel economy in automobiles The fuel economy of an automobile relates distance traveled by a vehicle and the amount of fuel consumed. Consumption can be expressed in terms of volume of fuel to travel a distance, or the distance traveled per unit volume of fuel consumed. S ...
*
Hand strength Hand strength measurements are of interest to study pathology of the hand that involves loss of muscle strength. Examples of these pathologies are carpal tunnel syndrome, nerve injury, tendon injuries of the hand, and neuromuscular disorders. Ha ...
dynamometer *
Machine-tool dynamometer A machine-tool dynamometer is a multi-component dynamometer that is used to measure forces during the use of the machine tool. Empirical calculations of these forces can be cross-checked and verified experimentally using these machine tool dynamo ...
*
Universal testing machine A universal testing machine (UTM), also known as a universal tester, materials testing machine or materials test frame, is used to test the tensile strength and compressive strength of materials. An earlier name for a tensile testing machine is ...


Notes


References

* * Dynamometers Automotive technologies Engine tuning instruments Measuring instruments Mechanical engineering Electric power systems components