SuperFlow AutoDyn, Operator'S Manual

Page: 69 / 208

AutoDyn
Operators Manual
Section 6 - Page 16
CH6 AutoDyn Operation.fm
6.8 All Wheel Drive Considerations
Running a vehicle on an All Wheel Drive chassis dynamometer presents some very particular
circumstances. The standard situation is a Four or All Wheel drive vehicle is tested on the dyno in
all wheel drive mode. In this case, the rear wheel power is measured by the rear roll and the front
wheel power is measured by the front roll. Then the two are added together to provide total power.
However, when a two wheel drive vehicle is tested, the non-driven axle and dyno roll is presented
as inertia (drag) to the torque load cell on the driven roll. This drag, along with the inertia of the
eddy current absorbers, is measured by the load cell on the driven roll and calculated as part of
the absorber power of that roll. The load cell on the non-driven roll continues to measure torque
but it is a negative value since it is drag. Ideally this negative value is cancelled out by the positive
inertia and dyno loss power calculations on the roll. But this rarely happens.
What results is a negative power calculation from the non-driven roll added to the positive power
calculation from the driven roll and a lower total power readout than what is really there.
This problem is averted by the use of software switches to “turn off” the non-driven power
calculation. These switches are Specification channels that can be set from the WinDyn
Specifications editor or from the Specs menu on the handheld. The following are excerpts from the
channel descriptions in chapter 9 of this manual.
Channel 88 - FWD Default Value 1
Used only on AWD systems
Channel 88 is used to select whether the front rollset power calculations
are to be used on the AWD system. A zero in this channel disables the
front rollset power calculations in the final wheel power calculation. This
channel is not used on the 2WD or
AD-11
systems.
Channel 89 - RWD Default Value 1
Used only on AWD systems
Channel 89 is used to select whether the rear rollset power calculations
are to be used on the AWD system. A zero in this channel disables the
rear rollset power calculations in the final wheel power calculation. This
channel is not used on the 2WD or
AD-11
systems.
Table 6-1 describes the various modes available on the AWD system. It is recommended that this
page be copied and placed near the dyno for reference.