Robert D. Mitchell

Product Information Manager

Woodcliff  Lake, New Jersey...Much of BMW's engineering effort is
devoted to enhancing the driver's ability to control his or her vehicle,
especially under challenging driving conditions. For 1994, the Bavarian
automaker has taken another decisive step in this direction by making
its All Season Traction system available in all 6-, 8- and 12-cylinder
models as either optional or standard equipment. 

Many types of traction control systems are available on the market
today. At the bottom end of the technological spectrum, some respond to
incipient wheelspin by applying the brakes to the driving wheels only;
others merely reduce engine power. 

BMW has taken the "high road" by engineering a system that not only does
both -- and does so by relatively sophisticated means -- but adds a
further mode of operation to help improve driver control under
conditions of reduced traction.  Appropriately, we call our system All
Season Traction. 

FOR 1994 
In 1993, the All Season Traction system was available only on our V-8
5-Series models and the 7- and 8-Series. For 1994, availability has been
extended to all four BMW Series as follows: 

         3-Series - optional on all 6-cylinder models (325i Sedan, 325is
         Coupe, 325i Convertible) 5-Series - standard on 530i Touring,
         optional on all other models 
         7-Series - standard on 750iL, optional on 740i and 740iL 
         8-Series - standard on all models. 

According to the technology employed in the various models, the All
Season Traction is either fully integrated with the anti-lock braking
system (ABS) or configured as a separate control unit that utilizes the
ABS wheel-speed sensors. In either case, the operation is the same and
the basic system components are as follows: 

	Electronic control system, with inputs from wheel-speed sensors
        and outputs to engine controls and brake system 
	Engine controls (electronic throttle, Digital Motor Electronics
        engine-management system) 
        Brake hydraulic control unit (shared with ABS). 
All Season Traction influences both engine  power and the rear brakes
(all BMW models sold in the U.S. have rear-wheel drive) to limit
wheelspin.  The system continually processes data from the ABS
wheel-speed sensors.  Anytime a drive wheel begins to lose traction --
this is indicated by one or  both drive wheels significantly  exceeding
the rotational  speed of the  other wheels -- the All Season Traction
system goes into action.  It does so in the following steps: Reduction
of engine torque.  BMW has engineered this function  to achieve  not
only smooth, driver- friendly action  but also minimum  effect on
exhaust emissions.  Four types  of action  take place to reduce  engine
torque  once  the system  has sensed  incipient  wheelspin: 

        Progressive closing of the electronic throttle.  This
        servo-controlled throttle, which has no mechanical connection to
        the  accelerator  pedal, functions by electric/electronic  means
        either in tandem with the normal mechanical throttle (6- and
        8-cylinder engines) or as the normal throttle (V-12 engines, in
        which there  are two electronic  throttles). 
        Retarding of ignition timing. Via the DME system. 

        Smooth  phase-out of ignition  and fuel injection.  Also via the
        DME system. Prevention of any shifting by automatic transmission
        (not applicable with manual transmission)  so as not to add a
        possibly disturbing influence. 

           Selective application of rear brakes. If the reduction of
           engine torque is not sufficient to bring wheelspin under
           control, All Season Traction then  begins to apply the rear
           brakes -- individually as one or the other wheel tends to
           spin  until the spin is brought under control. 

Extensive tests have shown that  there is no perceptible increase  in
brake  wear even if All Season Traction  is used often. 

An  additional  refinement of  All Season Traction, not found  in many
competing  systems, is the  so-called  Motor Speed  Regulation  (MSR)
under  deceleration.  On very slippery surfaces, merely letting  off the
accelerator  pedal could  cause enough  engine-braking  effect  (i.e.,
the engine slowing down the car) to  induce  wheel slip.  If wheel  slip
begins to occur  under deceleration  in this manner, MSR utilizes the
system's sensing and control capabilities to increase engine speed
slightly, achieving a further  improvement  in  driving  stability
under  these  difficult conditions. 

Many equally  sophisticated  safeguards have been  built into the All
Season Traction system. If, for example, the driver applies the brakes
while the system is acting on the brakes to control wheelspin, the
system's control function is immediately canceled.  And because it is
inherently smoother to control engine  torque than the brakes, the
system releases rear-wheel brake action as soon  as engine torque has
been reduced to a level that will control wheelspin. 

The  system is also  self-diagnosing.  It includes two  redundant  main
microprocessors, which continuously compare data; if they aren't
identical, the system switches off automatically. Anytime  a  system
fault  is recognized by the diagnosis circuitry, an  instrument-panel
warning light comes on; every relevant function  (individual wheel-speed
sensors, hydraulic valves, low brake fluid, idle speed, etc.)  is

Under certain  rare conditions, such as starting off in deep snow,
traction may be better served by switching off the system.  This is done
with  a console switch;  however, so that the system is always ready to
perform, each  time  the ignition is switched on, All Season Traction is
automatically  switched on  too. 

In the  BMW models available with  manual transmission  (325 models,
525i and 530i Sedan, 850CSi, All Season Traction  offers a rare
combination  of capabilities:  Few competitive models  are available
with traction  control and  a  manual transmission. BMW  believes that
All Season Traction  makes a significant  contribution to  Better
Driving by helping  the driver  cope with difficult road conditions, and
is  pricing the system so that it is highly  competitive with other
makes' traction  control  systems.