Dyna / Dyno Vehicle diagnostics
With the massive arrival of embedded electronics, the functions offered by automobile manufacturers have become ever more complex. Automobile mechanics are faced wtih new problems with these functions, which depend on numerous calculators and actuators spread through internal information networks in the vehicle (multiplexing).
Out of warranty service providers must equip themselves with new methods and tools in order to understand the precise workings of the automobile and produce the diagnostic data associated with the various functions.
This is how a Dyno works where we do vehicle diagnostics on
A chassis dyno is equiped with large rollers, usually sunk into a pit. The car is driven onto the dyno, so that the drive wheels rest on the rollers. Dyna tuners all differ with their output figures but how how it works is the same. The car is strapped down so it cannot move laterally or longitudinally, with non-driving wheels choked on 2 wheel drive dynamometers.
On a 4 wheel drive chassis dyno, the distance between the front and the rear sets of rollers can be changed to cater for dynotuning different wheel-based cars. Front-wheel-drive cars tend to be more unstable on dynas than RWD cars, so when dynotuning FWD cars, small “trainer wheels” are locked into place either side of the front wheels. A large fan is placed at the front of the car to cool the radiator and any other heat exchangers located there. The dyna tuner sits in the driver’s seat and operates the accelerator, clutch and brake. The steering wheel does not need to be touched.
The dyno tuner controls speed and other factors via a hand-held pendant that contains controls for load. The simplest test is a power pull.
The ‘ramp speed’ (rate at which the dynamometer lets the engine speed increase) is set and the car is run at very low rpm in the selected gear.
Any gear can be used, but second, third or fourth gears are usually selected.
The higher the gear the lower the tractive effort trying to pull the car of the dyno.
Very powerful cars therefore sometimes tested in the higher gears, although second gear is most commonly used.
The tuner instructs the dyno as to the type of test being undertaken holds the low rpm in the selected gear and then gives the engine maximum throttle.
Flicking a switch allows the dyno to ramp up in speed.
As the engine rpm increases, the dynas software draws a trace on a PC screen, showing the power being developed.
When the engine redline is reached, the test may be completed, or a switch on the controller may be flicked, causing the dyno to then ramp the engine back down.
Averaging ramp-up and ramp-down power pulls removes from the reading the inertia of the dynamometers rollers.
The comparison of Dynas and a bathroom scale is the best to illustrate this philosophy.
If you follow a strict diet and you want to know if it is working or not, simply stand on a scale. By using your clothes to gauge the result you can easily be mislead.
Similarly, by trying to feel if the vehicle’s performance is better or worse by driving it on the road could also be misleading. Choose the correct Dyna Tuners to tune your Vehicle! Better than only being able to test the output of your car make sure the Dyna being used has a brake facility. This way you will know if the tuner has the ability to simulate road conditions and enable him to monitor engine-tuning specifications under load.
Many years of experience are definitely the best reference any Dyna Tuner or Dyna Teacher could have. Contact your local SAC Branch.