SuperFlow AutoDyn, Руководство оператора

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Theory Of Testing
Volume 2, 9/10/04
Section 8 - Page 7
the gearbox, some in the clutch, some in the chain, belt, or drive shaft, some in the bearings, and
some will be lost in the tire. Most of these mechanical losses are fairly predictable. The tire losses
are the biggest variable.
When a tire rolls on a surface, the deformation of the carcass and rubber in and around the contact
patch requires some energy which is converted into heat. The source of this energy is the engine
power, so some of this power will be lost as heat. It is unfortunately not possible to easily measure
this power loss.
Following variables have an impact on the magnitude of this loss:
• Relative radius of the contact surface to the tire radius. On a flat road, the radius of
curvature of the road is infinite and the tire deformation is determined by load, tire
structure and tire pressure. On a chassis dyno, the smaller the diameter of the
dynamometer roll, the greater the deformation and thus losses in the tire. This
explains why a large roll is better than a small one and a single roll is better than a
cradle roll system (which results in two successive deformations per revolution).
SuperFlow’s uses a large diameter single roll possible resulting in the lowest tire
losses.
• Downforce on the tire. The greater the weight on the tire, the greater the tire
deformation and thus the power losses. There is a common misconception that the
vehicle should be weighted or pulled down to avoid tire slip on the roll. While it is true
that there is a traction limit, beyond which loss of traction may result, our testing
shows that this is not a problem on any motorcycle under 200hp wheel horsepower or
any automobile under 500hp wheel horsepower. The knurl of the SuperFlow roll has
been selected to provide greatest traction with negligible tire wear. Pulling the vehicle
down
excessively with rear tie-down straps will greatly increase the tire losses,
increase the risk of tire damage (due to the build-up of heat in the carcass), and
reduce the accuracy of the power measurement.
• Tire pressure and temperature. The tire pressure will have an effect on the
deformation, and the tire temperature will have an effect on the rate of increase of the
heat build-up. For best results, the tire should be inflated to its highest nominal
pressure (as for high speed road use) and the tire temperature should be kept
constant. The tire pressure will have a more significant effect on the accuracy and
repeatability of the power measurement than the tire temperature.
8.3 Accuracy Of The Chassis Dynamometer
The power measurement of the inertia dynamometer is based on the inertia of the roll and the
measured acceleration rate. A highly accurate result can only be obtained if the inertia value and
the acceleration are measured with high precision. The eddy current dynamometer uses both the
inertia power calculation and the eddy current power calculated by roll torque calibration, added
together for the total power measurement. Power consumed by the dynamometer itself is also
factored in on both types as parasitic losses.
SuperFlow has developed highly accurate electrical measuring technology for its EIS emissions
dynamometers used in government-mandated programs. This sophisticated technology allows us
to determine the equivalent vehicle inertia values to the nearest pound.