Robert D. Mitchell

Product Information Manager


Woodcliff Lake, New Jersey...Effective with September 1993
production, the 5-speed automatic transmission of the BMW 530i
Sedan and Touring and 540i Sedan incorporates a new refinement that
could be said to revolutionize the way an automatic transmission
responds to its driver, to environmental conditions and to the
driving situation at hand. It's called Adaptive Transmission
Control, or ATC. 

For some years now, BMW's electronically controlled automatic
transmissions have offered the driver several choices of "shift
modes," or programs. Typically, an Economy mode, aimed at everyday
driving and always engaged when the driver put the selector lever
in "D," provides upshifts at relatively low vehicle speeds with an
eye to best fuel economy, quietness and smoothness. A Sport mode
causes upshifts and downshifts to occur at higher engine speeds,
enhancing response. Depending on the BMW model, there has also been
either a Manual mode to give the driver full control over shifts,
or a Winter mode to help reduce wheelspin when starting up on snow
or ice. ATC goes two fascinating steps further by: 

	Increasing the number of modes from three to nine. 
	Making the mode selections automatically. 

And in case this raises a question of whether driver choice is
thereby reduced, let us state going in that it most definitely does
not; instead, ATC employs highly sophisticated electronic logic to
recognize what is going on with the driver, the environment and
traffic, and does a remarkable job of making the transmission
respond ideally in view of all that. You could even say that it
improves driver choice, in that it relieves the driver of having to
think about selecting a mode and frees him or her to concentrate on
traffic and the road. 

At the same time, ATC eliminates some minor operational drawbacks
that have been present in automatic transmissions since they first
came into use back in the Thirties -- mainly to the irritation of
particularly skilled or sensitive drivers. 

To accomplish these remarkable results, ATC employs the following
"recognition" elements, and controls the transmission accordingly: 

	Driver-Type Recognition 
	Environmental Recognition 
	Driving-Situation Recognition. 

Driver Type Recognition. Utilizing the remarkable capabilities of
microprocessors, this logic is able to track how the driver has
been "behaving" over the past few seconds. If, for example, the
driver has been stepping hard on the accelerator, the logic
concludes that he or she is in a sporty mood, and selects and holds
either of the two available Sport modes. As with the manually
selected Sport mode in other BMW models, this causes upshifts and
downshifts to take place at higher engine speeds, and one of these
modes will be held for a period of time (generally 5-10 seconds)
after the system has made its decision. 

Likewise, quick accelerator-pedal movements cause selection of one
of the Sport modes. If there are no abrupt accelerator movements
for a certain length of time, one of two economy-oriented shift
modes (similar to the manually selected Economy mode of other BMW
models) is selected; upshifts and downshifts take place at lower
engine speeds and fuel economy is optimized. 

In another recognition of accelerator-pedal movements, whenever the
driver releases the accelerator quickly and the transmission is in
a lower gear (say 1st through 4th), ATC will not allow an upshift.
Thus the engine braking of the lower gear remains in effect --
surely a bonus in this situation, when the driver wants to slow
down anyway -- and (as smoothly as this transmission shifts) the
lack of an unwanted shift is bound to be a subtle plus as well.
Environmental Recognition. The logic detects any increase in
driving resistance, such as when the car is carrying an
above-average load or is climbing or descending a grade; or a
decrease in traction, such as on ice or snow. In the former case,
it selects one of two available Mountain modes and prevents
unwanted upshifts, or even causes a downshift if the driver applies
the brakes on a downhill run. In the latter, it selects a Winter
mode; moving off from rest, for example, the transmission will
select a higher gear rather than 1st. Driving-Situation
Recognition. In stop-and-go traffic, the logic detects that
throttle openings and road speeds have remained below certain
limits for a period of time. The transmission then rules out 1st
gear, reducing unwanted "shift activity" that can make this
bothersome kind of driving even more so. This is referred to as a
Stop-and-Go mode. For driving on a winding road, the logic detects
when the car is cornering above a certain "g" level; if the driver
releases the accelerator and the transmission is in a lower gear,
that gear will be held, eliminating unwanted or awkward downshifts
under this circumstance. 

In addition to ATC, the 5-Series 5-speed automatic does retain a
2-position console mode switch marked "A" and "M." The "A" position
denotes Adaptive, with operation as described. In the "M" mode, the
driver can select any gear from 1st through 4th manually via the
shift lever. So this particular driver choice, which seems the only
one ATC might not be able to make effectively, remains to give the
BMW driver pure manual operation when desired. 

Adaptive Transmission Control is a remarkable step forward. In a
sense, it makes an automatic transmission as responsive to the
driver's wishes as a good manual transmission, yet without
requiring any additional manual control. You can't ask for much
more than that. BMW believes that it is yet another contribution to
making the BMW driver a Better Driver.