DYNAMOMETER AND POWER MEASUREMENT Flashcards
a device for simultaneously measuring the torque and rotational speed (RPM) of an engine, motor or other rotating prime mover so that its instantaneous power may be calculated
dynamometer
used to provide simulated road
loading of either the engine or full powertrain
dynamometer
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.
dynamometer
are used for routine
screening of grip and hand strength, 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.
dynamometer
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.
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 that records applied braking torque and calculates
engine power output based on information from a “load cell” or “strain gauge” and a speed sensor.
brake 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.
inertia dynamometer`
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).
motoring dynamometer
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.
Steady state
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.
Sweep 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.
Transient test:
Types of sweep tests
Inertia sweep, Loaded sweep
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.
Inertia sweep:
Loaded sweep, of the brake dyno type, includes
Simple fixed load sweep:, Controlled acceleration sweep:,Controlled acceleration rate: sweep test, steady state testing
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.
Simple fixed load 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 sweep:
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.
Controlled acceleration rate:
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.
sweep test
Transient test characteristics
Aggressive throttle movements, engine speed changes, and engine motoring
A dyno that is coupled directly to an engine is known as
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
chassis dyno.
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 type absorber
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.
Eddy current dynamometers
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 dynamometer
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.
Hysteresis dynamometers
are a specialized type of adjustable-speed
drive. The absorption/driver unit can be either an alternating current (AC) motor or a
direct current (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.
Electric motor/generator dynamometers
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 of air, this variety of dynamometer is inherently
limited in the amount of torque that it can absorb.
Fan 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.
Force lubricated oil shear brake
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.
Hydraulic brake
Invented by British engineer William Froude in 1877 in response to a request by the
Admiralty to produce a machine capable of absorbing and measuring the power of large
naval engines,[4] water brake absorbers are relatively common today.
Water brake-type absorber
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.
Compound dynamometers
