[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
V8 Differential Story (long)
From the 91 V8 Quattro Engineering Factbook
Automatic Trans "Intelligent" Electronic Locking Center Differential:
A computer controlled electronic multi-disc clutch couples and
uncouples during driving to provide smooth modulation of torque
between front and rear axles. This center differential locking clutch
is activated when a given difference in wheel rotational speed occurs.
Whenever excess wheel slip at one or more wheels is detected, the
center differential locks up. Torque is divided 50/50 when lockup
condition does not exist. With lockup power (torque) can be divided
0/100 to 100/0
Input information for calculating the degree of slip is transmitted
to the control system by the four wheel-speed sensors that also serve
the ABS. The control unit works so quickly that impending wheel spin
is recognized in less than twenty thousandths of a second. The
automatic locking provides maximum traction at all times - and
consequently maximum acceleration on all road surfaces.
This applies particularly in cornering: the car's tendency to
moderately understeer due to its chassis tuning remains unaffected.
This is a major advantage of Quattro over the other systems: it is
more predictable regardless of circumstances, because the basic
driveline reaction characteristics remain the same.
In the extreme, the drive torque can be completely redistributed by
the locking function to the front or rear axle. When decelerating or
braking, the center differential lock is immediately disengaged, so
that ABS control is not adversely affected in any way. The locking
system is also deactivated when the transmission control unit
recognizes that the vehicle is coasting or when a constant cruising
speed of 62mph is attained.
Five-Speed Manual Transmission with Torsen Center Differential:
For those who prefer the sportiness of a manual transmission, the
V8 Quattro is also available with a five-speed providing quicker
acceleration (0-60 7.1 sec vs. 8.7sec) and a slightly higher top
speed, (152mph vs. 146mph) the five-speed also differs in the method
of power transfer within the Quattro system: a Torsen differential is
used in place of the electronic center differential found in the
Torsen Rear Differential
For good traction on roads that have less grip on one side - for
example a snow covered road that has been cleared on only one side - a
second differential lock is desirable.
This is achieved in the V8 Quattro with a Torsen self-locking
differential (conventional 80,90,100, and 200 Quattros, use a Torsen
center differential) that divides torque at the rear axle. The locking
effect of the gear system integrated into the Torsen differential can
instantaneously distribute between 20 and 80 percent of the available
torque as needed between the two rear wheels. Torque transfer occurs
automatically, according to wheel grip; it is not activated by the
driver and is effective up to maximum speed. Since the locking action
of the Torsen differential only occurs when the engine is under load,
the ABS function remains in effect over the entire speed range. The
advantages of optimum power distribution can be utilized even when
cornering at high speeds.
Raytheon Optical Systems