It is very important that the braketest gives a realistic picture of
the dynamic behaviour of the car as when braking on the road. This can
only be accomplished when testing with the car in movement
|
Brakedynamics are displayed for each wheel and the maximum brakeforce
is shown in figures, including the handbrake. Retardation is calculated.
Difference in brakeforce L/R and F/R is stated. With sideslip plate
the side-slip is measured for front and rear wheels. Pedal force
and brake force amplification is measured with an optional pedal
force gauge. |
The brakes are the most important safety equipment on a car. Therefore
it is very important that the braketest gives a realistic picture of the
dynamic behaviour of the car while braking on the road.
It should be remembered that the braking result is dependent not only
on the brakes but also on the equipment “above” the wheels and the brakes,
namely the suspension system, shock absorbers and the chassis, the weight
of which parts are transferred to the road by means of the wheel struts,
wheels and tires. Further-more modern cars are increasingly equipped with
technical support systems designed to help the driver in critical and
unforseen situations by damping or cor-recting any wrong decisions.
Most cars are fitted with limiter valves or proportional valves which
control the distribution of the brakeforce between the front and rear
wheels in order to avoid blocking of the rearwheels which may result in
skidding. Nowadays an increasing number of cars are also fitted with ABS-systems
and a number of vehicles are constructed with 4-wheel drive.
The mechanical construction of the wheel struts, suspension and steering
gear in modern cars is complicated and designed to optimize the dynamic
behaviour of the car under all driving conditions including braking. All
these relations have to be taken into consideration when evaluating the
safety of a car.
When the brake is activated in a moving car, the weight of the vehicle
is propelled dynamically against the front axle causing the front brakes
to be dominating. It is very important to register this dy-namic course
of the brake force in order to conclude how the car brakes under realis-tic
conditions.
The use of a modern plate-braketester which incorporates measuring of
the dy-namic brake force and weight of each wheel is a natural consequence
of this development. On a plate-braketester the braking ability of a car
can be tested under completely realistic conditions as the test is made
when the car is moving at a speed of 10-15 km/h. Through modern com-puter
technology all forces are measured several thousand times pr. second thereby
ensuring that all details in the dynamic flow are measured.
The measured results are displayed in colours on a big colour screen making
it easy to observe the dynamic flow of brakeforce and suspension. On the
OPTO-PLUS plate-braketester model 510 the dynamic brakeforces and the
dynamic weight are shown for each wheel sepa-rately. Limiter- and proportional
valves , ABS-systems and permanent 4-wheel drive systems are functioning
realistically as on the road and can therefore be analysed for correct
function.
Time used for such an analyzis is minimal and corresponds roughly to the
time it takes to drive over the plates and brake the car. Therefore the
plates can be installed in a driving lane in the work-shop, either flush-floor
or simply mounted on top of an even floor.
Also in relation to the client who wants his car tested this form of test
is excellent. Car owners today are increas-ingly aware of the safety aspects
of their cars and want to know how they stand in respect to the condition
of their vehicles. The plate-braketester is an instrument offering a quick
analysis of a realistic test where the results are displayed in an easy
comprehensible form in coloured graph-ics. Terms like steering gear, brakeforces,
suspension etc. are easily understood as is the result of the test without
it beeing necessary to use many explanations. For the workshop this is
an excellent oppor-tunity to offer their customers a service product which
increases their satisfac-tion and at the same time augments the image
of the workshop.
Traditionally a roller-braketester is the most used type of brake tester
whereas a plate-braketester like the OPTO-PLUS 510 is relatively new,
its development having been made possible through ap-plication of modern
PC-based systems with big computing power enabling the test results to
be shown in graphic form and in colours.
A test on a roller-braketester can be understood as “the road turning
“ under the wheels, while the car itself stands still. According to its
nature this kind of test is static and in reality only the effect of the
braking function is tested whereas the dynamic influence from weightdistribution,
limiter-and pro-portional valves, suspension, wheels and tires are not
taken into consideration.
Whether one or the other system is the better is dependent on the individual
needs of the workshop and the required range of tests. Both systems have
their advantages and deficiencies. Modern Plate Tester design has considerable
advantages, making it very useful as a test instrument.
In the table below a comparison has been made between the 2 systems and
their main characteristics. This picture shows the suspension dynamics
for each wheel. At the same time a dampingfactor is calculated for each
wheel as well as the L/R symmetry. Total weight and testspeed are indicated.
| Rollertester | Platetester | |
| Measuring Method | Static: The weight distribution is static. Cars normally has 60% of the total weigh on the front axle and 40% on the rear axle. Measuring results in analog or digital form. |
Dynamic: The weight distribution is dynamic. At a normal braking action 80-90% of the total weight is on the front axle. The dynamic brakeforces is shown in graphic form for each wheel. Keyvalues are displayed with figures with diagnostic comments. The weight of each wheel are measured dynamicly and the suspension action are displayed in graphic form. The damping for each wheel are calculated with the symmetry Left /right. The deceleration is calculated. |
| Brake control valves |
Proportional valves and limiter valves out of action on rear wheels | Proportional- and limiter valves functions as on the road. The function is tested and can be observed on the test results |
| 4-Wheel drive | Vehicles with 4-wheel drive can only
be tested on special testers with double roller sets. On a roller tester the pedal force is higher on the rear wheels than on the front wheels to block thewheels. The measured brakeforces on the front and rear axle are not related to the result on the road. |
Braking with 4-wheel drive function as on the road. The pedal force is the same for the service brake. The measured brake forces for front and rear wheels are related to the results on the road. |
| Spoilers | Vehicles with spoilers or low suspension tend to have problems with a proper contact on a rollertester. | Functions as on the road. |
| Ovality | Measured over several revolutions with constant pedal force. | Is measured over a fraction of a revolution. |
| Testtime | Test of servicebrake and handbrake takes 3-5 minutes. | A complete test can be performed on 30 sec. |
| Testspeed | Normally 5 km./h. At this speed the ABS system is inactive and in most cases it requires that all 4-wheels turns. | Normal test at 8-15 km./h. Higher speed possible for test of ABS systems. |
| Installation | Requires installation in floor with 3
phase power. Can be installed in the driveway |
Installed on top of floor with 220V power. |
| User friendly | Many vehicles are difficult to test as they tend to jump off the rollers. | Everybody can use a plate tester. Drive on and brake! On the monitor all results are displayed in color with graphics with text and numbers. |