BMW ABS and Automatic Stability Control
Integral ABS and ASC (Automatic Stability
Control): New Riding Dynamic Control Systems for BMW
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provides tons of technical detail on their motorcycles
and accessories, and the following information is a
lightly edited translation of a large document provided
by the BMW press office. Since webBikeWorld
visitors can't seem to get enough when it comes to
detailed information, read on!
BMW Integral ABS and Pressure Modulator and Brake Line
Photos and text courtesy
of BMW AG
Entering its next generation, BMW Motorrad Integral ABS
is taking a quantum leap in the process of evolution,
advancing from a stand-alone solution acting only on the
brakes into a fully networked all-round system.
new generation of Integral ABS, BMW Motorrad provides
for additional dynamic riding control systems with a
reduction in technical
requirements and features. And following the
customer’s wishes, this new generation also opens up the
option in future for further-reaching rider assistance
The first step in this direction is BMW Motorrad ASC
Control available as of 2007. This system serving
to control drive spin on a production motorcycles is
being introduced as an optional extra on the touring
models in the BMW K and Boxer Series.
Once again, therefore, BMW is acting as the pioneer in
the introduction of
advanced safety technologies on the motorcycle. This
the leadership which BMW Motorrad has shown in the area
of active safety
for more than 15 years.
Choosing the right development partner for both systems,
obviously had to focus on that partner’s specific
competence in control
technology and the networking of functions within the
vehicle. In recent years, major car suppliers have
become aware of the technical challenges presented by
the motorcycle with its specific riding dynamics and the
growing potential for motorcycle control systems in the
decisive point in pre-selection
of the development partner was the willingness and
ability to develop
specialized solutions suitable for use on BMW
motorcycles. So taking this
into account, joint development of the new generation of
ABS brake technology
started together with Continental-Teves in early 2003.
BMW Integral ABS Components
BMW's Integral ABS (Anti-Lock Braking System)
BMW Motorrad’s new Integral ABS technology has been
developed separately from the previous system and the
entire layout of the system has been newly conceived
from the ground up.
progress in technology
in both hydraulics and electronics, the development
succeeded in simplifying the architecture of the system
while at the same time
enhancing its functions to an even higher standard.
The result is supreme stopping power and very short
stopping distances even without electrical power
assistance on the brakes.
BMW Motorrad’s new Integral ABS is no longer based on
principle or, respectively, the ram pressure process
used on previous generations,
but instead is conceived as a valve system.
Carried over from automotive applications, this control
concept is now able to ensure a very high standard of
all-round comfort and convenience in every respect.
In particular, feedback of brake pressure modulation
on the brake lever has been reduced by recent
development of the control valves and management to such
an extent that it no longer has any kind of adverse
effect, thus paving the way for introduction of the new
system also in the topmost segment of BMW motorcycles.
The new Integral ABS system applies brake pressure on
the front wheel brake
solely by means of a hydraulic circuit, thus acting
entirely in response to the
operating forces applied on the hand lever. This, in
turn, ensures a more direct
feeling of the brakes particularly important to the
sports-minded rider. And now the rider no longer
has to get used to any change in control or operation of
the brakes when switching over from a motorcycle without
The new system naturally maintains the proven
that is automatic activation of the rear-wheel brake
when operating the front wheel
brake. Pressing the foot brake alone, however, the rider,
as in the
case of a conventional system, activates only the wheel
brake at the rear.
As with the previous system, the advantages of this
integral brake are ideal brake force distribution on
both wheels under all conditions, naturally taking load
conditions into account, as well as enhanced control
enabling the rider to detect at an early point the risk
of the rear wheel lifting off when applying the brakes
all-out, and to take appropriate counter-action.
To provide the desired integral function, brake pressure
for the rear-wheel
circuit is generated and built up by an electronically
controlled hydraulic pump. This offers the
advantage of pressure management and control completely
independent of the front wheel circuit – which is the
prerequisite for dynamic, adaptive and, ultimately,
consistently ideal brake force distribution to the rear
wheel as well as fully independent brake management and
In the event of any deficiencies in the hydraulic pump
or electrical components,
the rear-wheel brake acts hydraulically as with a
overriding the integral function. This has no
effect on the proper operation of the front-wheel brake,
the only difference being that the ABS function is no
longer operative in the event of such a deficiency.
BMW Motorcycle Automatic Stability Control (ASC)
Automatic Stability Control is a meaningful, additional
particularly on a high-torque motorcycle and when riding
conditions with slippery surfaces. Indeed, ASC is
the logical counterpart to ABS.
Automatic Stability Control prevents the rear wheel from
when accelerating all-out and thus avoids any loss of
side forces and stability
which otherwise would make the rear wheel swerve out of
control. Lift-off detection and intervention
serves furthermore to prevent the front wheel from
moving up when accelerating under full power.
together, these two
functions enhance riding stability and thus help to
ensure a higher standard of
safety on the road. And last but not least, the rider is
able to deactivate ASC
at any time, also while riding.
Like ABS, ASC is naturally also subject to certain
restrictions in bends due to
the riding physics of a motorcycle. And it is essential
to note that ASC is not able to push forward, let alone
override, the physical limits to the stability of a
motorcycle when leaning over in a bend.
In its basic principles, the system and its various
functions are quite
straightforward: The ABS wheel sensors determine the
speed at which the
wheels are turning. Registering any sudden change
in the difference in speed front-to-rear, the electronic
control unit is able to detect any risk of the rear
wheel spinning, engine management responding immediately
by intervening in the ignition angle to take back engine
Should this not be
sufficient, that is should a greater reduction of engine
power be required,
fuel injection will be cancelled out for a certain time.
This kind of control and management is fast and
sensitive, with any effects on riding comfort and
dynamics being virtually negligible.
The History of BMW Motorcycle ABS
Looking back at a
Pioneering Achievement. Motorcycle experts
certainly waxed lyrical back then in spring 1988,
expressing their admiration for a “revolution in
technology” and “the most significant progress ever made
in the area of active safety”.
This was when BMW became the first motorcycle
manufacturer in the world
to introduce an electronic/hydraulic anti-lock brake
system (ABS) in the
BMW K100 motorcycle. Originally weighing in at
24.5 lbs. (11.1 kg), BMW Motorrad’s revolutionary ABS
was a great success from the start, with some 70 per
cent of all purchasers ordering their K100 with ABS as
early as in 1989.
by the end of 1995,
approximately 60,000 BMW motorcycles had been delivered
with the first generation of ABS technology. In
its configuration and system structure, this motorcycle
ABS was quite different from the systems used in the
automobile: Anti-lock brakes in the automobile
incorporated hydraulic valves with cycle management
serving to modulate brake pressure – a principle
inevitably subject to a certain degree of unwanted
At the time, therefore,
using the valve systems
available back then, the pressure pulses generated
of the brakes with ABS were clearly noticeable on the
brake lever. This kind of feedback – or backlash,
as one might also say – was regarded as unacceptable on
the motorcycle, especially considering the wish to
introduce the new technology on a broad scale.
of the brake
pedal and unusual noises during application of the
brakes with ABS had
initially irritated customers right from the start when
was introduced for the first time in the passenger car.
Precisely this is why BMW Motorrad, cooperating at the
time with FAG Kugelfischer,
developed a plunger system operating without the
or backlash. In this case a plunger masterminds
the volume of brake fluid and, accordingly, the pressure
acting on the brake whenever ABS is active.
The brake lever (that is the hand brake or foot brake
lever) is hydraulically
separated in the ABS mode by a mechanical ball valve
thus avoiding any kind
of pressure pulse the rider might feel on the lever.
Positive response from customers confirmed from the
start that this was the appropriate technical solution.
The next generation of ABS brake technology, BMW
Motorrad ABS II,
entered the market relatively soon in 1993. This was at
the same time as the
first model in BMW Motorrad’s brand-new generation of
This new generation of ABS was hardly more than half
the weight at
13.14 lbs. (5.96 kg) of the first generation, and was far more
compact in its dimensions. Reliability was
enhanced to an even higher level through the use of
electronic systems in modern digital technology.
The most significant improvement, however, involved
the control system, integrated travel measurement
determining the appropriate travel of the plunger in the
system during the first control cycles and thus
providing optimum brake pressure after just a few
cycles, with only minimum adjustment being required
thereafter (unless the rider encountered a sudden change
in frictional coefficient).
this meant soft and smooth brake control up to the
tires’ maximum level of
friction, capitalizing on the motorcycle’s brake power.
As a result of this superior technology, the number of
BMW motorcycles equipped with ABS quickly rose to almost
90 per cent in Germany and an impressive 78 per cent on
average for all markets.
by the year 2000,
some 200,000 BMW customers the world over had opted for
with ABS. The third generation of ABS brake technology, BMW
Motorrad Integral ABS,
was presented at the INTERMOT 2000 Motorcycle Show and
entered the market in spring 2001.
Once again, this was a
revolutionary step into the
future, with electrical brake power assistance being
realized for the first time
on a motorcycle. With operating forces reduced to
a minimum, this new technology ensured maximum brake
power and performance enabling even the inexperienced
rider to shorten stopping distances to a minimum
whenever required in an emergency.
Further special features were the integral brake
function connecting the front
and rear wheel brake circuits. The overall configuration
of the system with
internal pressure sensors being used for the first time
adaptive distribution of brake forces on the two wheels
of the motorcycle. Despite this enhanced range of
functions, the system was once again lighter than
before, weighing just 9.59 lbs. (4.35 kg), approximately
20 per cent less than ABS II.
The third generation of ABS brake technology with
integral control continued its outstanding story of
success in BMW motorcycles: By the year 2005, more than
80 per cent of all BMW motorcycles were fitted with this
revolutionary system, some models even exceeding the 90
per cent mark.
In all, more than 280,000 BMW motorcycles featuring
Integral ABS were delivered to customers by the end of
2005, the total number of all BMW motorcycles with ABS
delivered to customers even exceeding the figure of
500,000 units by September 2003.
ABS was also introduced as a standard feature on BMW
Motorrad’s entry level
F650GS in the year 2000. This is a BOSCH valve
system without an integral function, since compact
dimensions, very low weight, and an attractive price are
the essential criteria for the lighter motorcycles in
An enhanced system based on this technology was
introduced in 2006 in the new F800 S/ST midrange models
as well as the new R1200S Sports Boxer and weighs just
3.3 lbs. (1.5 kg).
BMW Integral ABS System
Function and Technology of the
New Generation of BMW Integral ABS
Introducing the new generation of ABS brake
technology, BMW Motorrad is changing over to a new, even
more advanced system featuring valve-based pressure
control also on Integral ABS.
hydraulics, in the area of
control valve technology, and in electronics now allows
the same comfortable
operation of the system with minimum feedback as in the
case of plunger
systems or ram pressure concepts. In its
fundamental configuration of brake hydraulics and valve
management, BMW Motorrad’s new Integral ABS is
comparable with other valve-controlled ABS systems.
The special features of BMW’s system lie in
of pressure management, the use of intelligent control
strategies, and in the
integral function. The latter is a semi-integral
system, meaning that whenever the rider applies the
front-wheel brake by means of the hand brake lever, the
brake circuit for the rear wheel is automatically also
activated in the same process.
The foot brake lever, on the other hand, acts
solely on the rear
wheel brake. BMW Motorrad’s new Integral ABS is being introduced
on all models in the new K and Boxer generation (with
the exception of the
BMW R 1200 S), replacing the previous system.
Hydraulic and pressure control functions.
The overall principle followed by BMW Motorrad’s new
Integral ABS is relatively simple: Brake pressure
generated manually by the rider via the brake lever and
the main brake piston is transferred via an open valve
(the intake valve) directly to the appropriate wheel
as the wheel sensors
and electronic management determine that a wheel is
about to lock,
the intake valve is closed and an outlet valve arranged
in parallel in the wheel
brake circuit is briefly opened. This allows brake
fluid to flow through the outlet valve into a reservoir
(low-pressure storage), very quickly reducing brake
pressure on the appropriate wheel brake (if necessary
down to zero).
This operation of the valves is accompanied by
activation of an electrically driven hydraulic pump
delivering the brake fluid flowing out of the wheel
brake circuit back into the control circuit and thus
setting off the volume in the respective brake circuit.
Then, once the wheel is able
to turn again freely, the
outlet valve is closed and the intake valve is opened,
the hydraulic connection between the brake lever and the
main brake piston. Now brake pressure built up by the rider via the brake
lever once again
increases hydraulic pressure in the brake calipers.
Appropriate control and
operation of the valves, finally, serves to modulate
brake pressure, adjusting
the stopping forces acting on the wheel to the current
frictional coefficient and
road conditions. Analogue pressure management for fine-tuning system
pressure. Modern hydraulic valves with an
adjustable cross-section are featured on the intake
Appropriately controlled and operated,
they allow continuous,
ongoing management of volume flow in building up
pressure on the wheel,
thus providing analogue-based pressure control of the
a significantly higher standard of control quality and
precision over previous
valve systems with a fixed, pre-set opening
cross-section limiting their
operation to simple “black-or-white” control when
opening and closing.
In conjunction with appropriate control strategies,
BMW Motorrad’s new Integral ABS is able to build up
pressure quickly during the control cycles and adjust
system pressure with a high level of precision.
This, in turn, reduces
pressure pulses and, accordingly, any “kick-back” effect
on the hand lever,
making the entire control process smoother and more
comfortable. Three additional pressure sensors in the system
With system pressure being masterminded and
determined in this way, and with previous cycles being
evaluated, the system is able to specifically control
brake pressure as needed, setting pressure to the
respective level required and thus reducing the number
and intensity of control functions during operation of
the brakes in the ABS mode.
there is no sudden change in frictional coefficient,
only fine-tuning of brake
pressure is then required after the first control
cycles. This ensures smooth
and comfortable application of the brakes with optimum
stopping power close
to the respective friction limit.
And with modulation of brake pressure being
relatively small, variations in wheel load and,
accordingly, movements of the vehicle are kept to a
minimum, enhancing riding stability and giving the rider
an even better feeling of all-round safety.
BMW Motorrad’s new Integral ABS no longer requires an
servo. Rather, recent developments in brake hydraulics
ensure very rapid buildup
of pressure and – just as important – virtually
spontaneous reduction of
pressure in the control phase. This ensures
immediate reaction of the system under all conditions to
the rider’s specific need for brake power as well as
smooth and precise control by means of hydraulic
Wheel brake circuits separated completely from one
another. The brake circuits for the front and rear wheel on BMW
Motorrad Integral ABS
are separated completely from one another, and are not
linked by any kind of
This ensures a clear and
straightforward brake feeling at
all times with a clearly defined pressure point
particularly on the front-wheel
brake under all conditions. Brake pressure on the front wheel is generated in the
by the rider via the main brake piston in the control
lever and acts directly on
the front brake caliper.
Wherever the ABS control
function is required,
the electronic control unit modulates brake pressure via
the valves in the brake
circuit, as described in the foregoing. The rear-wheel brake is also operated in the usual way
by the rider pressing
down the foot brake lever.
As long as the rider presses down the foot brake
lever only, the foot brake will generate the brake
pressure desired in an all-mechanical/ hydraulic
process, pressure acting on the rear-wheel brake only.
necessary (that is with the wheel threatening to lock),
brake pressure is
controlled appropriately via the ABS valve system. Integral brake with electro-hydraulic pressure
To activate the integral function, brake pressure for
the rear-brake is generated
actively via an electro-hydraulic high-pressure pump as
soon as the rider pulls the hand brake lever. The pump is switched on
automatically every time
the rider uses the front-wheel brake and is masterminded
by the pressure
sensors in the front-wheel brake circuit.
Geared to brake pressure on the front wheel,
appropriate pressure is built up automatically on the
rear-brake in accordance with the brake force
distribution predetermined by the control unit, the rear
wheel thus being decelerated ideally with every
application of the front-wheel brake (semi-integral
Even when using the integral function, the rider has the
option to brake the
rear wheel harder via the foot brake lever than the
integral system as such
would allow. This he can do up to the rear wheel
locking point where ABS cuts in.
Should the brake pressure applied by the rider be
weaker than the pressure
generated via the integral function, the rider’s
operation of the foot brake is
not taken into account and the rear-wheel brake is
applied in accordance with
the integral function. Ideal brake force
distribution between the front and rear wheel changes as
a function of the load the motorcycle is carrying.
integral brake is also able
to take load conditions into account by adjusting
accordingly. Comparing wheel locking pressure in
the wheel circuits, pressure measurement within the
system provides an indication of the load the motorcycle
is currently carrying and adjusts brake force
distribution accordingly whenever the brakes are applied
in the ABS mode.
In all, electro-hydraulic generation of brake pressure
for the integral function
ensures perfect adjustment of rear-wheel brake pressure
under all conditions
as a function of front-wheel deceleration (ideal
distribution), load conditions,
and the frictional coefficient. Only this method
of generating pressure is really able to give priority
to the rider’s specific wishes and operation of the
brakes, whenever appropriate.
And should the hydraulic pump ever fail to operate, the
parallel hydraulic circuit
on the foot brake lever will act by itself, the
rear-wheel brake operating in the
same way as a conventional hydraulic brake.
Semi-integral function for extra safety and stability.
A point to be emphasized once again here, since it is
is the advantage of the semi-integral brake concept with
optimum distribution of brake power on both wheels.
When applying the brakes under “normal” conditions
below the maximum limit of deceleration, that is in the
most common situation in everyday traffic, the rear
wheel is able to convey significant stopping power to
Since lateral guidance
forces on the tire decrease as a function of increasing
brake power, better
distribution of brake power between the two wheels
enhances both safety
reserves and lateral stability. This advantage is
particularly significant in braking maneuvers often
forced upon the rider in a bend, where the degree of
stopping power and deceleration required depends on the
specific situation encountered by the rider.
Should the rider apply the brakes in such a situation
only on one wheel, the wheel involved (generally the
front wheel) has to convey the full power of the brake
and is therefore only able to build up a low level of
lateral support and guidance.
The integral system, by contrast, distributes brake
power ideally to both
wheels, providing a higher level of lateral and side
support on each wheel
(naturally as long as the brakes do not enter the ABS
mode). This ensures maximum brake stability within
the physical limits applicable in each case.
Apart from increasing side forces, the semi-integral
function also ensures
better detection of a rear wheel lifting off when
applying the brakes all out.
While conventional two-channel ABS brake systems are
only able to evaluate wheel speed signals, BMW
Motorrad’s integral system provides more information,
monitoring both pressure signals in the two brake
circuits and the speed of both wheels and thus
determining the degree of stopping power and,
accordingly, any tendency of the rear wheel to lift off.
The system is therefore able to effectively counteract
such behavior in good
time by specifically reducing brake pressure on the
front wheel in the interest
of enhanced riding stability and maximum stopping power.
And a further
advantage is that the system actively detects current
riding conditions, thus
also taking the load the motorcycle is currently
carrying into account. Compact and light pressure
modulator serving as the heart of the system.
All function units of BMW Motorrad Integral ABS are
housed within the
pressure modulator. This compact control system
accommodates the control valves, pressure sensors and
hydraulic pumps including their electric motor, as well
as the electronic management system.
The pressure modulator is therefore quite literally the
“heart” of BMW Motorrad’s
Integral Brake System. Nevertheless, the entire
unit weighs just 5.1 lbs. (2.3 kg) and is therefore
approximately 50 per cent lighter than the former
Diagnostic Functions and Fail Safe Operation
BMW Motorrad’s new Integral ABS also benefits from full
control: all functions and sensors are permanently
monitored by the system’s
electronic “brain”. Compared to the former system, the duration of the
initialization phase after switching on the ignition is
now far shorter.
Malfunctions, should they occur at
all, are saved in a non-volatile memory and may be
out in the workshop. Should the electrical or electronic
components suffer a
deficiency, in turn, the control valves are moved
mechanically (by springs)
to their basic setting, thus always maintaining a direct
between the brake controls and the brake calipers, as in
the case of a conventional brake system without ABS.
brakes will operate as usual in terms of brake power and
application, only ABS
control and, where applicable, the integral function no
longer being available. Deactivation of ABS for
On the R1200GS and R1200GS Adventure, the rider once again has
the option to
deactivate BMW Motorrad’s new Integral ABS for off-road
use. Even when
ABS is deactivated, however, the system maintains its
which may often prove very helpful when riding off-road.
To hold the motorcycle
in position on a slope with loose ground beneath, for
all the rider has to do with Integral ABS is pull the
hand brake lever. This will apply the brake on the
rear wheel with a good and strong effect, keeping the
motorcycle safely in position and preventing it from
Setting off in such a situation is also facilitated
by the system, since the rider no longer needs his foot
to apply the brakes and is therefore able, whenever
necessary, to use both feet for extra support on the
Function and Technology
of BMW’s New ASC
ASC (Automatic Stability Control) limits and controls
spin on the rear drive
wheel. It therefore prevents the rear wheel from
spinning out of control under acceleration on slippery
surfaces and helps to avoid a possible loss of lateral
Acting as the logical counterpart to ABS, ASC is the
first step towards
enhanced rider assistance systems controlling riding
dynamics on the motorcycle.
Currently BMW is the only motorcycle manufacturer in the
offer traction support as an option on series production
motorcycles: Upon the
introduction of ASC in 2007, customers will be able to
order this revolutionary new system for all Boxer models
with the exception of the R1200S Sports Boxer and the
ASC is available only in combination with Integral ABS
(while ABS without
ASC is naturally still available as before). ASC
assists the rider when accelerating on difficult and
slippery surfaces, and offers extra safety particularly
on rapidly changing road surfaces difficult to assess in
terms of surface grip and friction.
It is not
for maximum acceleration or for accelerating all-out
while leaning over sharply,
for example in a bend. Within the usual limits of
physics, however, Automatic Stability Control is able to
reduce any side swerve effect of the rear wheel also in
a bend, thus helping to enhance the motorcycle’s riding
But it is
important to note that ASC cannot enhance the natural,
physical limits to the stability of a single-track
vehicle, and that it does not relieve the rider from the
need to use engine power appropriately when leaning over
to a low angle.
An additional function of ASC is that it prevents the
front wheel from lifting
off when accelerating under full power – again an
important contribution in the
interest of extra safety. Function and control. ASC
uses the ABS wheel sensors to monitor the speed at which
the wheels are turning and also applies the diagnostic
functions offered by these sensors.
Wheel spin, in turn, is determined by the engine’s
electronic “brain” comparing
the speed of the front and rear wheels. Should the
system detect any tendency of the rear wheel to spin, electronic engine
intervene accordingly, setting drive forces to the limit
the tire is still able to
convey. The first step in this process is to
reduce torque by adjusting the ignition angle (or, to be
more specific, by retarding the ignition timing point).
Should a greater reduction of engine power be
appropriate, fuel injection will
be stopped for a certain period. An advantage of this control function is that it is
quick and sensitive, with
hardly any impairment of riding comfort and dynamic
performance. The rider is informed of the function
when active by a telltale flashing on and off quickly in
the control panel.
And if the rider does not wish to
use ASC, he is able to
deactivate the system at any time, also while riding,
simply by pressing a
control button. Additional off-road set-up for the GS models. An additional
off-road set-up has been developed and
memorized within the
control system for off-road use of the R1200GS and
This special off-road mode takes wheel slip and spin
conditions on loose
surfaces into account, allowing a higher level of spin
under such circumstances. Pressing the ASC button, the rider is able to switch
over from the road
to the off-road mode and vice versa. It is important to
note that the off-road setup is not suitable for road
Supreme functional safety and reliability through
control systems. ASC Automatic Stability Control has been developed
BMW Motorrad’s new Integral ABS and the ASC software
part of the overall engine control electronics.
saves the need for
a separate ASC control unit, reducing weight and space
accordingly. Full integration of the system also
saves the need for additional connections in the
interest of enhanced safety and minimum risk of
Like all electronic control functions, ASC also features
a defect memory for reading out information when the
motorcycle is serviced. And should, finally, ASC not be available, the rider is
informed accordingly by
the telltale on the control panel.
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