Types of Dynamometer
Name: M. Hassan Bhatti Lab. Attendant: Sir Wasif
Roll #: 2016-ME-24 Subject: IC Engine
What is Dynamometer:
Dynamometer, or "dyno" for short, is a device for measuring force, moment of force
(torque), or power. For example, the power produced by an engine, motor or other rotating
prime mover can be calculated by simultaneously measuring torque and rotational speed
(rpm).
A dynamometer can also be used to determine the torque and power required to operate a
driven machine such as a pump. In that case, a motoring or driving dynamometer is used.
A dynamometer that is designed to be driven is called an absorption or passive
dynamometer. A dynamometer that can either drive or absorb is called a universal or active
dynamometer.
In addition to being used to determine the torque or power characteristics of a machine
under test (MUT), dynamometers are employed in a number of other roles. In standard
emissions testing cycles such as those defined by the US Environmental Protection Agency
(US EPA), dynamometers are used to provide simulated road loading of either the engine
(using an engine dynamometer) or full powertrain (using a chassis dynamometer).
Types:
Prony Brake Dynamometer:
A simple type, known as the Prony brake. It consists of two blocks of wood, each of which
embraces rather less than one half of the pulley rim. The two blocks can be drawn together
by means of bolts, cushioned by springs, so as to increase the pressure on the pulley. One
block carries an arm to the end of which pull can be applied by means of a dead weight or
spring balance. The friction torque on the pulley may be increased until it balances the
torque due to the available power.
Rope-Brake Dynamometer:
In this brake two or more ropes rest on the rim of a pulley. They are spaced evenly across
the width of the rim by means of wooden blocks positioned at different points round the
rim. The total pull on the slack ends of the ropes is registered on a spring balance, while
the pull on the tight end is provided by dead weights. Friction torque on the pulley may be
increased by increasing the dead load by addition of weights.
Eddy Current Dynamometer:
One of the oldest forms of dynamometers is the eddy-current dynamometer. The simplest
form consists of a disc which, driven by the engine under test, turns in magnetic field. The
strength of the field is controlled by varying the current through a series of coils located on
both sides of the disc. The revolving disc acts as a conductor cutting the magnetic field.
Currents are induced in the disc and, since no external circuit exists, the induced currents
heat the disc. For larger power absorptions, the heating of the disc becomes excessive and
difficult to control.
Swinging Field D.C. Dynamometer:
DC shunt motors are used as swinging field dynamometer. DC motor is supported in
trunnion bearing to measure the reacting torque that the outer stator and field coil tend to
rotate due to magnetic drag. The torque is measured with an arm and swinging equipment
and spring scale in the usual manner.
This shunt motor dynamometer can run as a generator and motor also. That is it is reversible
and it works as a motoring and power generating unit. When it is used as a generator, the
electrical energy produced is dissipated in resistor. When used as motoring device dc
energy is supplied from outside and used as starting device for an engine. The load and
operation is controlled by varying field current.
Electric Dynamometer:
The electric generator can be used for loading the engine, but the output of the generator
must be measured by electrical instruments and corrected in magnitude for generator
efficiency. The electric load connected to the generated may be Lamp-bank used in
laboratory work.
Hydraulic Dynamometer:
The hydraulic dynamometer works on the principle of dissipating the power in the fluid
friction rather than in dry friction. In principle its construction is similar to that of a fluid
flywheel. It consists of an inner rotating member or impeller coupled to the output shaft of
the engine. This impeller rotates in a casing filled with some hydraulic fluid. The outer
casing, due to the centrifugal force developed, tends to revolve with the impeller, but is
resisted by a torque arm supporting the balance weight.
