1.16. Brake Testing & Testers
Brake testing is
nothing but the, to calculate the braking efforts and efficiencies of a motor
vehicle. There are two types of testing methods followed for automobile
vehicles such are;
1. Static test or MOT test.
2. Dynamic test or road test
1. Static test or MOT test.
2. Dynamic test or road test
There are at least three different types of brake tester used to calculate the
braking efforts and efficiencies of a motor vehicle. Roller brake testers,
which consist of a chassis with a driven roller system; plate brake testers,
which consist of two parallel measuring plates, and decelerometers which
are usually hand held devices.
1.16.1. Brake testers:
The brake testers are of following two types
1. Static brake tester: parallel plate-type brake testers
2. Dynamic brake tester: Roller brake testers, De-accelerometers
The static brake test is carry under when vehicle is static/stable mode and only wheels are allow to move on tester plates or and rollers. While Dynamic test carried out on road i.e. vehicle brake testing is perform more effectively for actual test.
1.16.1.1. Static brake
tester:
One type of static
brake tester has four tread plates and registering columns. To make the tests,
the car is driven onto the tread plates it specified speed and the brakes are
applied hard.
The stopping force at
each wheel is registered on the four columns. If the readings are too low, or
are unequal brake service is needed.
Fig
1.26: Parallel plate type static brake tester
A plate brake tester as
shown in Fig 1.26, parallel plate testing is a method of measuring
a vehicles braking system in a dynamic test. The unit consists of two moving
parallel plates mounted on force transducers. A measurement of the braking
force is made when a vehicle passes over the plates and then applies its
brakes. The braking action causes the individual plates to ‘slip’ forwards
allowing a calculation of braking force to be made.
Brake imbalance between
the left and right hand side can also be measured by the differences in voltage
measured on each of the force transducers under the chassis. Due to the nature
of it dynamic operation, plate brake testers are far less common than roller
brake testers in UK garages although they are also an extremely accurate method
of measurement.
1.16.1.2. Dynamic
brake tester:
The dynamic brake
tester has rollers in the floor. The two wheels for which brakes are to be
tested are placed on the rollers (as shown in Fig. 1.27). A vehicle
is stable and only wheels are allowed to move on roller. If these wheels are
drive wheels, the wheels are spun at the specified speed by the vehicle engine.
For non-driving wheels, the rollers and wheels are spun by an electric motor.
Then throttle is released or the electric motor is turned off and brakes are applied.
The braking force at wheel registers on meters. This shows if the brake
performs normally or if they need service.
(a). Roller Brake
Testers:
A roller brake tester
is a method of allowing the dynamic assessment of the braking system of a motor
vehicle, whilst the vehicle itself is in a static condition. This type of brake
tester is normally used in UK garages when used as part of an inspection lane
for the MOT test.
Fig
1.27: Dynamic brake tester (roller type)
A roller brake tester
consists of a mechanical floor unit which contains electrical motors, two
independent sets of three measuring rollers, brake force transducers and
additional safety sensors (as shown in fig. 1.27).
The driving rollers
operate at a low (known) speed using a gearbox and motor arrangement and during
a test measurements of the maximum braking force are taken by applying the
vehicle brakes which induces a reaction force on the electric motor itself. An
electric transducer with strain gauges then measures the individual induced
forces which are acting during the deceleration phase in order to calculate the
individual braking forces for each wheel.
In order to minimize
any inaccuracy and variation in the measurement, the roller diameter is
sufficiently large to reduce the effects of the mechanical relaxation, or
flexing, of the tyre itself. A special coating on the rollers is designed to be
very wear resistant and provide good friction values, both in wet and dry
conditions.
A third smaller roller,
on each side between the driving rollers, has two functions: The first is to
detect if a vehicle is present in the roller bed (a built in safety device to
prevent the motor from starting up unless a vehicle is in the brake tester),
the second function is to detect when and if tyre slippage occurs in order to
make the measurement before a maximum, predefined value of time passes.
During the test, the
computer measures the brake force values and the system will calculate the
imbalance between the left and right brake forces of an axle, as well as the
brake efficiency of the service brake and the parking brake provided that a
vehicle weight is either inputted manually or by using an integrated weighing
system.
(b). De-accelerometers:
A de-accelerometer is a
hand held device for measuring dynamic braking forces during a vehicle on road
test. A vehicle de-accelerometer operates as if it were, and it could also be
known as, an accelerometer.
Brake testing is a process of measuring the braking performance of a vehicle. There are various methods of brake testing, and each has its own advantages and disadvantages.
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