Sensotronic Brake Control System
CHAPTER 1: INTRODUCTION
When drivers hit the brake pedal today, their foot moves a piston rod which is linked to the
brake booster and the master brake cylinder. Depending on the pedal force, the master brake
cylinder builds up the appropriate amount of pressure in the brake lines which - in a tried and
tested interaction of mechanics and hydraulics - then presses the brake pads against the brake
discs via the wheel cylinders. By contrast, in the Mercedes-Benz Sensotronic Brake Control, a
large number of mechanical components are simply replaced by electronics. The brake booster
will not be needed in future either. Instead sensors gauge the pressure inside the master brake
cylinder as well as the speed with which the brake pedal is operated, and pass these data to the
SBC computer in the form of electric impulses. To provide the driver with the familiar brake
feel, engineers have developed a special simulator which is linked to the tandem master
cylinder and which moves the pedal using spring force and hydraulics. In other words: during
braking, the actuation unit is completely disconnected from the rest of the system and serves
the sole purpose of recording any given brake command. Only in the event of a major fault or
power failure does SBC automatically use the services of the tandem master cylinder and
instantly establishes a direct hydraulic link between the brake pedal and the front wheel brakes
in order to decelerate the car safely. The central control unit under the bonnet is the centerpiece
of the electrohydraulic brake. This is where the interdisciplinary interaction of mechanics and
electronics provides its greatest benefits - the microcomputer, software, sensors, valves and
electric pump work together and allowtotally novel, highly dynamic brake management.
In addition to the data relating to the brake pedal actuation, the SBC computer also receives
the sensor signals from the other electronic assistance systems. For example, the anti-lock
braking system (ABS) provides information about wheel speed, while Electronic Stability
Program (ESP®) makes available the data from its steering angle, turning rate and transverse
acceleration sensors. The transmission control unit finally uses the data highway to
communicate the current driving range. The result of these highly complex calculations is rapid
brake commands which ensure optimum deceleration and driving stability as appropriate to
the particular driving scenario. What makes the system even more sophisticated is the fact that
SBC calculates the brake force separately for each wheel [4].
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Sensotronic Brake Control System
1.1. HISTORY OF SBC
In 1999 Mercedes-Benz launched this system under the name Active Body Control (ABC) in
the flagship CL coupé, thereby signaling the advent of a new era of suspension technology.
This electronically controlled suspension system will quickly be followed by the electronic
brake system: Mercedes-Benz and Bosch have teamed up on this benchmark development
project which will shortly enter into series production at the Stuttgart automobile brand under
the name Sensotronic Brake Control or SBC for short. It turns the conventional hydraulic brake
into an even more powerful mechatronic system. Its microcomputer is integrated into the car’s
data network and processes information from various electronic control units. In this way,
electric impulses and sensor signals can be instantly converted into braking commands,
providing a marked safety and comfort gain for drivers [8].
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Sensotronic Brake Control System
CHAPTER 2: LITERATURE REVIEW
Sensotronic Brake Control is an innovative electronically controlled brake system that is faster
and more precise than the conventional braking system. SBC is the name given to an innovative
electronically controlled brake system which will fit to future passenger car models. With
Sensotronic Brake Control electric signals are used to pass the driver’s braking commands onto
a microcomputer which processes various sensor signals simultaneously and, depending on the
particular driving situation, calculates the optimum brake pressure for each wheel [2].
expresses his need of mechatronics in the field of autobile industry. Sensotronic brake control
system helps in efficient braking and it is has dynamic braking management. The features
offered like emergency braking, driving stability, soft stopping, etc. ease the driving efforts
and the braking efficient. The fact cannot be neglected that the additional advantages of
Sensotronic braking system provide high and advanced quality, stability as well as longevity.
Combination of manage ride and handling with driving safety provided by the braking system
in a sustainable and calculable way differentiates it with other braking system in a affirmative
way. This technology by Mercedes and Bosch has taken braking to a new level, which is very
essential [3].
sensotronic brake control (SBC) is the name given to an innovative electronically controlled
brake system which mercedes-benz will fit to future passenger car models. Following on from
the Mercedes innovations abs, ASR, esp. and brake assist, this system is regarded as yet another
important milestone to enhance driving safety. With sensotronic brake control electric
impulses are used to pass the driver’s braking commands onto a microcomputer which
processes various sensor signals simultaneously and, depending on the particular driving
situation, calculates the optimum brake pressure for each wheel [5].
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CHAPTER 3: SBC - THE BRAKES OF THE FUTURE
Sensotronic Brake Control (SBC) is the name given to an innovative electronically controlled
brake system which Mercedes-Benz will fit to future passenger car models. Following on from
the Mercedes innovations ABS, ASR, ESP® and Brake Assist, this system is regarded as yet
another important milestone to enhance driving safety. With Sensotronic Brake Control
electric impulses are used to pass the driver’s braking commands onto a microcomputer which
processes various sensor signals simultaneously and, depending on the particular driving
situation, calculates the optimum brake pressure for each wheel. As a result, SBC offers even
greater active safety than conventional brake systems when braking in a corner or on a slippery
surface. A high-pressure reservoir and electronically controllable valves ensure that maximum
brake pressure is available much sooner. Moreover, the system offers innovative additional
functions to reduce the driver’s workload. These include Traffic Jam Assist, which brakes the
vehicle automatically in stop-and-go traffic once the driver takes his or her foot off the
accelerator. The Soft-Stop function – another first – allows particularly soft and smooth
stopping in town traffic. Mechatronics – a new term is gaining popularity within the automotive
industry and is rapidly developing into the catchword of a quiet technological revolution which
in many fields stands century-old principles on their head. Mechatronics brings together two
disciplines which in many cases were thought to be irreconcilable, namely mechanics and
electronics [1].
Hence automobile functions which hitherto worked purely mechanically and partly with
hydraulic assistance will in future be controlled by high-performance microcomputers and
electronically controllable actuators. These either replace the conventional mechanical
components or else enhance their function. The mechatronic interplay therefore opens up
hitherto inconceivable possibilities to further raise the safety and comfort levels of modern
passenger cars. For example: it was only possible through mechatronics that an electronically
controlled suspension system which instantly adapts to prevailing conditions when driving off,
braking or cornering thus providing a totally new driving experience became a reality. In 1999
Mercedes-Benz launched this system under the name Active Body Control (ABC) in the
flagship CL coupé, thereby signalling the advent of a new era of suspension technology [7].
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Sensotronic Brake Control System
This electronically controlled suspension system will quickly be followed by the electronic
brake system: Mercedes-Benz and Bosch have teamed up on this benchmark development
project which will shortly enter into series production at the Stuttgart automobile brand under
the name Sensotronic Brake Control or SBC for short.It turns the conventional hydraulic brake
into an even more powerful mechatronic system. Its microcomputer is integrated into the car’s
data network and processes information from various electronic control units. In this way,
electric impulses and sensor signals can be instantly converted into braking commands,
providing a marked safety and comfort gain for drivers [1].
3.1. Brake pedal
To turn to the technical side: when drivers hit the brake pedal today, their foot moves a piston
rod which is linked to the brake booster and the master brake cylinder. Depending on the pedal
force, the master brake cylinder builds up the appropriate amount of pressure in the brake lines
which – in a tried and tested interaction of mechanics and hydraulics - then presses the brake
pads against the brake discs via the wheel cylinder. In the Mercedes-Benz Sensotronic Brake
Control, by contrast, a large number of mechanical components are simply replaced by
electronics. The brake booster will not be needed in future either.Instead sensors gauge the
pressure inside the master brake cylinder as well as the speed with which the brake pedal is
operated, and pass these data to the SBC computer in the form of electric impulses. To provide
the driver with the familiar brake feel engineers have developed a special simulator which is
linked to the tandem master cylinder and which moves the pedal using spring force and
hydraulics. In other words: during braking the actuation unit is completely disconnected from
the rest of the system and serves the sole purpose of recording any given brake command. Only
in the event of a major fault or power failure inside the 12V vehicle battery does SBC
automatically use the services of the tandem master cylinder and instantly establishes a direct
hydraulic link between the brake pedal and the front wheel brakes in order to decelerate the
car safely [6].
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Sensotronic Brake Control System
3.2. Control unit
The central control unit under the bonnet is the centerpiece of the electrohydraulic brake. This
is where the interdisciplinary interaction of mechanics and electronics provides its greatest
benefits – the microcomputer, software, sensors, valves and electric pump work together and
allow totally novel, highly dynamic brake management. In addition to the data relating to the
brake pedal actuation, the SBC computer also receives the sensor signals from the other
electronic assistance systems.For example, the anti-lock braking system (ABS) provides
information about wheel speed, while ESP® makes available the data from its steering angle,
turning rate and transverse acceleration sensors. The transmission control unit finally uses the
data highway to communicate the current driving range. The result of these highly complex
calculations is rapid brake commands which ensure optimum deceleration and driving stability
as appropriate to the particular driving scenario. What makes the system even more
sophisticated is the fact that SBC calculates the brake force separately for each wheel [1].
The high-pressure reservoir contains the brake fluid which enters the system at a pressure of
between 140 and 160 bar. The SBC computer regulates this pressure and also controls the
electric pump which is connected to the reservoir. This ensures much shorter response times
than on conventional brake systems. Yet another advantage: full braking power is available
even when the engine is switched off. The hydraulic unit mainly comprises four so-called
wheel pressure modulators. They mete out the brake pressure as required and pass it onto the
brakes. In this way it is possible to meet the microcomputer’s stipulations while each wheel is
slowed down separately in the interests of driving stability and optimum deceleration. These
processes are monitored by pressure sensors inside the wheel pressure modulators.
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Fig 1. Sensotronic Brake Control [8]
3.3. SBC COMPONENTS
3.3.1. Brake Operating Unit
The brake operating unit or BOU is what most would call a “master cylinder”. The BOU
contain a pedal sensor so the control unit is knows how fast and how far the brake pedal is
being depressed. It also has a brake pressure simulator that incorporates a couple of springs
and a floating piston so that the brake pedal feels like a normal master cylinder to the driver.
The simulator is needed since there is no direct hydraulic contact between the brake pedal and
the brake clippers under normal operation.
Fig 2. Brake Operating Unit [1]
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3.3.2. Pedal Valve Sensor
•
Contains two hall effect sensors
•
Converts pedal travel valve to an electrical signals
•
Provide input to SBC control module
Fig 3. Pedal Valve Sensor [8]
3.3.3. Steering-Angle Sensor
The steering-angle sensor is fixed onto the steering shaft, where the hub gear wheel of the
sensor transmits the rotary movement of the shaft to two measuring gear wheels. In each
measuring gear wheel a magnet is mounted, whose field changes its direction in accordance
with the rotational movement. Below each magnet, a GMR sensor element is located to detect
the angle position of the magnet above. The analog values of the GMR elements are converted
into digital information directly on the circuit, which is then sent to the microprocessor via
serial interface. The measuring gears have different numbers of teeth and therefore change
their turning position at different speeds. By means of mathematic functions, it is possible to
determine the absolute steering-wheel angle from the position of the measuring gears. In
addition, this function enables error correction and a plausibility test of individual signals. This
measuring principle enables the measurement of the complete angle range of several steeringwheel turns without the use of a rotation counter [4].
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Sensotronic Brake Control System
Fig 4. Steering-Angle Sensor [8]
3.3.4. Wheel Speed Sensor
In order to improve to a greater extent the electronic assistance systems like antilock braking
system(ABS) provides information about the wheel speed with electronic stability
program(ESP) providing the data from its steering angle, turning rate and transverse
acceleration sensors to SBC computer in the form of sensor signals [8].
Fig 5. Wheel speed sensor [8]
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3.3.5. Traction System Hydraulic Unit
The complex calculations made in order to calculate the current driving range leads to perfect
driving stability and optimum deceleration. Further briefing about the system comes the high
pressure reservoir which contains brake fluid that enters the system at pressure from 140 to
172 bar [8].
Fig 6. Traction system hydraulic unit [8]
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Sensotronic Brake Control System
CHAPTER 4: PRESSURE SENSOR
4.1. THE CONCEPT FOR THE PRESSURE SENSOR
The major requirements of a pressure sensor for X-by-Wire applications, as previously
mentioned, are high precision and reliability as well as multi functionality and flexibility,
features strongly desired in modern sensor design. These requirements have heavily influenced
the design choices. In order to enhance the precision it has been conceived a silicon micro
machined piezo-resistive pressure sensor chip with two different sensitivities: a higher one in
a low-pressure range (0 to 30 bar), where often an elevated resolution is required, and a lower
one at higher pressures (up to 250 bar). Thus, with one single membrane chip, practically two
sensors are obtained. Moreover, as it will be explained further on more in details, the transition
between the two sensitivity levels determines an area with particularly interesting
characteristics that could be used to recalibrate the sensor from offsets without having to
remove it from the system where it normally operates and mount it on a reference bench.
Somehow what could be called a “self-recalibration” ability. Enhancing the reliability and the
therefore the availability of a sensor needs stability in the components and sensor health
monitoring strategies. This latter is possible through an integrated digital electronic that would
hence allow self-test functions. Key point of these procedures is the previously mentioned
recalibration area, which potentially allows monitoring offsets with a precision up to 0.15 %
full scale (FS) without need on integrated actuators and the relative control electronic. A digital
electronic can also be designed, without major difficulties, to integrate a controller for
networking (Controlled Area Network, for example), consequently enhancing the capabilities
and the flexibility of the sensor [1].
4.1.1. Two levels sensitivity and recalibration
The transduction of the physical quantity, pressure in the specific case, into an electrically
measurable figure is performed though piezo-resistive elements implanted on the surface of
the of the silicon chip. This type of transducers is sensitive to the stresses in the two coordinates
defined with respect to the plane where the elements are implanted in the chip. The stresses on
the piezo-resistors induce changes in their resistance that can be detected with rather high
accuracy as unbalance of a Wheaston bridge. The stresses on the chip surface depend on the
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Sensotronic Brake Control System
geometrical characteristics of the latter and on the forces deriving from the applied pressure
[8].
Therefore transducers are usually placed in such a way to have maximum response to the
pressure changes and in order to obtain a constant sensitivity. Normally small variations in the
sensitivity are undesirable as they complicate the calibration process and often reduce the
sensor accuracy. On the contrary, in the presented design, a drastical change in the sensitivity
as been conceived through a major variation of the sensor geometry. This characteristic has
been exploited to realize the two sensitivity ranges.
Fig 7. Sensor chip profile [6]
The sensor consists of a membrane structure at which centre is placed a cylindrical structure
(a centreboss membrane) as shown in fig. 7. As the pressure is applied, from top, the membrane
will move freely downward: this determines a rather sensitive sensor response, which will
continue until 30 bar is reached. At this point the cylinder will enter into contact with the silicon
bulk plate. Consequently the geometrical structure of the sensor will almost instantly change:
the membrane will not be able to move freely any more and will behave more like a ring fixed
at the two sides. The stiffness of the structure will significantly increase, thus the building up
of stresses due to pressure will reduce and thereby the sensitivity will be roughly of a four
factor smaller than the one between 0 and 30 bar. This determines the low sensitivity range
that is specified up to 250bar. Fig. 8 summarises graphically what has been here above
described. Moreover the cylindrical central structure makes the membrane fairly robust and
resistant to overpressures.In silicon the elastic behaviour, opposed to the plastic one, is
dominant. Therefore silicon withstands stresses with almost unchanged characteristics: this is
what makes it a good material for sensors. Thus it can be expected that in the described design
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Sensotronic Brake Control System
the cylindrical central structure and the respective contact area on the silicon bulk will remain
stable. Consequently it can also be expected that the pressure needed to generate the contact
between the two parts will remain constant through the sensor lifetime, thereby thetransition
between the two sensitivity levels will take place always at the same pressure: in fig. 8 this is
defined as Recalibration point.Now, gathering this information together, a contact point is
obtained, which is: mechanically determined, constant and independent from the electrical
characteristics of the transducers. Therefore, if it is possible to evaluate a procedure to
determine this point though the normal sensor operation, than a monitoring and correction of
electrical instabilities such as offset drifts can be achieved without need of a reference sensor
or external action: a simple example of how this could be obtained will be given in the next
paragraph. Moreover, the recalibration principle makes no use of internal actuation system, no
actuator control or extra technology is therefore needed: the sensor integrates what can be
called a passive recalibration and self-test principle. Furthermore such procedure could enable
to avoid long and costly temperature calibrations. Least but not last, the contact or recalibration
point is determined through the sensor technology and can be so defined to be different from
sensor to sensor. In the case the sensor is operating in a network environment where more of
these sensors with different contact pressures are present, it is possible to obtain more
recalibration points, potentially increasing the sensor accuracy [6].
4.1.2. The integrated digital electronic and the self-test
Digital electronic is often thought to be expensive for pressure sensors. This argument usually
does not consider all the potential advantages that it can bring, either because of the difficulty
to have a complete overview on them or as a rather significant research effort is needed to be
able to exploit them completely. Moreover costs of digital electronic are on the long term
continuously decreasingIn the presented design it has been chosen to make use of a digital
electronic in order to implement monitoring and correction strategies in the sensor. Activities
are being carried out to investigate all possible failures of the sensor and evaluate their entity,
this already at design level. Hence eliminate through design as much of them as possible,
particularly those that cannot be automatically detected by the sensor. On the remainder will
be in the first place evaluated methods to individuate the errors (self-test) and, when possible,
correct them without the outside intervention (recalibration). A diagram of this procedure is
described in fig. 8.
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Fig 8. Self-test and recalibration flow diagram [1]
Furthermore network capabilities can be introduced and thereby user tailored functions can be
programmed resulting in an enhanced sensor flexibility.Clearly a complex electronic has not
only advantages consideration has to be taken not to introduce further hardware, but also
software errors. Central point of the self-test strategies is the previously described
“Recalibration point”. The presence of a digital electronic allows performing the drift
monitoring and the recalibration internally. A simple example might help the understanding.
Lets suppose that the sensor is working in a system where the pressure can rise linearly, namely
250 bar in 8 sec., for simplicity lets also suppose that the sensor has an ideal linear behaviour
in the 2 sensitivity ranges (in the real case there will be a linearity error which will ad up to the
calculations, on the other hand though the sensor response could be better described by
polynomialls of higher order, therefore it has been chosen to stay with the simplest case).
During the pressure rise 4 points are sampled through the digital electronic: point one at sensor
output around 0 V and the second around 2 V, in the low pressure range, the third at 2.3 V and
the fourth at 4 V, in the high pressure one as shown in fig. 4 (a wise choice of the points can
influence up to 50% the accuracy with which the recalibration point can be determined). These
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points are used to define the 2 lines, which intersection will determine the contact voltage. This
can be compared with the value stored in the sensor memory at the previous recalibration and,
if the difference exceeds the calculation errors, the new value will substitute the old one: the
sensor response lines will be adjusted and thereby a recalibration will take place. Key point of
this procedure is the dimension of the calculation errors. If the linearity error is not considered,
for the reasons previously given, these depend on the sensor A/D converter resolution and the
sampling frequency. Therefore, with a 10 bit A/D converter and sampling at 1 kHz a
recalibration with approximately a 0.15 % accuracy FS can be obtained. To the reader is left
the little mathematic game that takes to the given value [7].
Fig 9. Example of possible calibration procedure [6]
4.1.3. The sensor design
Defining a concept for a new sensor is no trivial job. Putting this into a realisable design is
even more complex and requires a good deal of experience in sensor manufacturing and
simulation techniques. The transducer chip design has been conceived in collaboration
between EADS (European Aerospace Defence and Space company) Deutschland GmbH and
AKTIV SENSOR GmbH, with the contribution of the Technical University of Berlin. The
electronic design instead was the result of the cooperation of EADS Deutschland GmbH and
ELBAU GmbH [8].
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4.1.4. The chip design
The major difficulty in the design was to realise the change in the mechanical structure in such
a way that the sensor response variation between the two configurations would be possibly
sharp, but most of all that the response with respect to the pressure change would be
monotonous. If this condition is not fulfilled, there is no one to one correspondence between
the transducer response and the applied pressure: there will be different pressures that will
produce the same output signal. Thereby the sensor will be intrinsically unreliable and
therefore unusable. Overcoming this problem means that the piezoresistors (the transducing
elements) have to see always increasing stresses with the rising of the pressure.Therefore the
choice on the pie resistor position on the chip membrane is determinant and with it the results
of the simulation.The choice that has been made in the positioning of the piezo-resistive
elements can be noted that the stress distribution changes significantly before and after the
mechanical contact. Moreover it has been chosen design 90-degree profiles in order to reduce
the previously described risk: this implies using anisotropy etching. etching. The results of the
dry etching process can be seen in fig. 10.
Fig 10. SEM picture of the chip structure and X-ray picture [6]
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4.1.5. The electronic design
The design of the electronic should be maintained to a low level of complexity. Never the less
attention should be given to the design in order to be able to implement all the self-test and
recalibration features allowed by the design, but at the same time avoiding unnecessary over
dimensioning of components that would only reflect itself on an increase of costs. Particular
care should be given in taking advantage of the high resolution in the low-pressure range: for
example, in the case of a linear analogue or Pulse-Width Modulation (PWM) output is desired,
as it normally is in sensor output coding, a high resolution digital to analogue converter is
needed. Moreover, in the design is planned.A volatile memory for storing the calibration
parameters, a non-volatile one for the programming of the self-test and recalibration
algorithms, a PWM module, a CAN module for a bus communication and of course analogue
to digital converter to enable the signal processing. In the first prototype a low level of
integration has been chosen to enable more design flexibility, never the less most of the needed
functions could be performed by a commercially available ASIC which could be integrated in
second stage[8].
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CHAPTER 5: WORKING OF SBC
Mechatronics has played a very crucial role in bringing together two contrasting fields which
in many cases were thought to be irreconcilable, namely mechanics and electronics. Working
through the technical side though the results seem to be easy achieved, actual mechanism is
far more complicated than rest of the braking system with a due consideration as a future
demand and needs. For most the vehicles when driver hit the brake pedal, the movement of
the foot moves a piston rod which is linked to brake booster and master brake cylinder.
Depending on the pedal force, the master brake cylinder builds appropriate amount of brake
pressure in the brake lines which then presses the brake pads against the brake discs via wheel
cylinders. Considering the fact that brake boosters will not be needed in the future, SBC
displaces the uses of brake booster with a sensor that gauges the pressure inside the master
cylinder. Sensors additionally also contribute in measuring the speed with which brake pedal
is operated and pass this data to the SBC computer in the form of electrical pulses. Braking
operation being the most crucial operation in a car, during braking the entire actuation unit is
completely disconnected from the rest of the system and serves the sole purpose of recording
any brake command [4].
The bonnet is the central control unit known as the centerpiece of the electrohydraulic brake
which mainly consists of-microcomputer, software, sensors, valves and electric pumps with
all together lead to a high dynamic brake management. In order to improve this data to a greater
extent the electronic assistance systems like antilock braking system(ABS) provides
information about the wheel speed with electronic stability program(ESP) providing the data
from its steering angle, turning rate and transverse acceleration sensors to SBC computer in
the form of sensor signals. The complex calculations made in order to calculate the current
driving range leads to perfect driving stability and optimum deceleration.Further briefing
about the system comes the high pressure reservoir which contains brake fluid that enters
the system at pressure from 140 to 172 bar. The SBC computer controls the electric pump
which is connected to the reservoir and results in a shorter response time than conventional
breaking system. Another important components of this braking system is the hydraulic unit
which comprises of four pressure modulators which control the brake pressure for each tire
separately as a result slowing them down as monitored by each pressure sensor.
The main performance characteristic of SBC include extremely high dynamics during
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pressure build up and exact monitoring of driver and vehicle behavior using sophisticated
sensors. Brake force control plays a very important role while deciding the braking principle.
Keeping this in mind Mercedes has programmed the system in such a way that when slowing
down from a high speed the larger part of the brake force continues to act in front axle which
prevents hazardous over braking of rear axle. At low speeds or during partial braking the
system automatically increases the brake force share at the rear axle to improve brake system
response [4].
Fig 11. Schematic Diagram for Working of SBC System [8]
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CHAPTER 6: FEATURES OF SBC
6.1. Emergency braking
The main performance characteristics of Sensotronic Brake Control include the extremely high
dynamics during pressure build-up and the exact monitoring of driver and vehicle behaviour
using sophisticated sensors. Mercedes-Benz is thus moving into new dimensions of driving
safety. Take the example of the emergency brake: SBC already recognises the driver’s rapid
movement from the accelerator onto the brake pedal as a clue to an imminent emergency stop
and responds automatically: with the aid of the high-pressure reservoir, the system increases
the pressure inside the brake lines and instantly presses the pads onto the brake discs so that
they can get a tight grip the moment the driver steps onto the brake pedal. As a result of this
so-called prefilling of the brake system, the stopping distance of an SBC-equipped sports car
from a speed of 120 km/h is cut by around three per cent compared to a car featuring
conventional braking technology. Due to electrohydraulic back-up, the performance of Brake
Assist is also improved further. If this system issues the command for an automatic emergency
stop, the quick pressure build-up and the automatic prefilling of the wheel brakes leads to a
shorter braking distance [3].
Fig 12. Comparison between Stopping by SBC and Conventional Braking System [3]
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6.2. Driving stability
It is not just in emergency braking that Sensotronic Brake Control proves its worth, but also in
other critical situations – for example, when there is a risk of swerving. Under such conditions,
the system interacts with the Electronic Stability Program (ESP®) which keeps the vehicle
safely on course through precise braking impulses at all wheels and/or by reducing engine
speed. SBC once again offers the benefits of greater dynamics and precision: thanks to the
even faster and more accurate braking impulses from the SBC high-pressure reservoir, ESP®
is able to stabilise early and comfortably a vehicle which is about to break away. This is
evident, for example, from the results of the VDA lane-change test which suspension engineers
use to simulate a quick obstacle-avoidance manoeuvre and to demonstrate the high capabilities
of the Electronic Stability Program. In conjunction with SBC, ESP® works even more
effectively and significantly reduces vehicle swerving through quick and precise braking
impulses. At the same time the driver’s steering effort is reduced. Due to SBC and ESP® he
or she will have even less difficulty keeping the car on course [5].
Fig 13. Copyright DaimlerChrysler AG [5]
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6.3. Braking in corners
Fig 14. Braking in a curve. Left: conventional. Right: with SBC [5].
Notice the unequal braking force, smaller lateral force, better stability and alignment with
SBC.Even when braking in corners, SBC also offers more safety than a conventional brake
system. This is where the variable and targeted brake force distribution is of particular
advantage to actively influence the car’s compliance steer.While conventional brake systems
always mete out the brake pressure equally to the inner and outer wheels, SBC offers the
possibility of assigning brake forces in a way appropriate to the situation. Hence the system
will automatically increase the brake pressure at the outer wheels because the higher vertical
forces also allow them to transfer greater brake forces. At the same time the brake forces at the
inner wheels are reduced to provide the higher cornering forces needed to stay on course. The
result is a more stable braking behaviour along with optimum deceleration values.
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With the innovative Sensotronic Brake Control Mercedes engineers still stick to the proven
principle of a variable brake force control for the front and rear axles. They program the system
in such a way that, when slowing down from a high speed, the larger part of the brake force
continues to act on the front axle. This prevents a potentially hazardous overbraking of the rear
axle. Again SBC is capable of adapting to the prevailing situation. At low speeds or during
partial braking, the system automatically increases the brake force share at the rear axle to
improve brake system response and achieve even wear and tear of the brake pads [5].
6.4. Comfort
Both the separation of the SBC pedal from the rest of the brake system and the proportional
pressure control using mechatronics serve to increase brake comfort – particularly during sharp
deceleration or when the anti-lock braking system is operational. The usual vibration of the
brake pedal when ABS sets in does not occur, which, Mercedes engineers have found, is not
only a comfort feature of the new system but also offers measurable safety benefits. Their
research in DaimlerChrysler’s Berlin driving simulator has revealed that almost two thirds of
all drivers are startled when ABS pulsation sets in: they do not increase the brake force further
and are even prone to taking their foot off the brake pedal for a short while, thereby lengthening
the stopping distance of their vehicle – in the driving simulator by an average of 2.10 metres 7 feet - during ABS braking from 60 km/h - 37 MPH - on a snow-covered road surface [4].
6.5. SBC add-on functions
Sensotronic Brake Control offers additional advantages in everyday driving situations – when
slowing down ahead of traffic lights, in the wet, in traffic jams or hill starts [8].
6.5.1. SBC Soft-Stop
The so-called Soft-Stop function of the SBC software ensures particularly gentle and smooth
stopping which provides significant comfort benefits particularly around town when you need
to slow down frequently for traffic lights. All this is made possible by the higher-precision
pressure control due to mechatronics. On a wet road surface the system metes out short brake
impulses at regular intervals to ensure that the water film on the brake discs dries off and that
SBC can always operate with optimum effectiveness [3].
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6.5.2. dry-braking
This automatic dry-braking function is activated at regular intervals when the car’s windscreen
wipers are running. The driver does not even notice these ultra-precise brake impulses [2].
6.5.3. Traffic Jam Assist
Traffic Assist: SBC also consists of one of the so-called Traffic Assist function. This
particularly helps while driving in the town. At a traffic signal, the driver needs to constantly
shift between brake and acceleration pedal. Due to Traffic Assist, the driver only needs to
operate the accelerator pedal. As soon as the driver removes his foot from the accelerator pedal,
SBC slows down the vehicle at a steady rate of deceleration until it standstill. This function is
operational up to 60 Km/h or 37 MPH and it is automatically cut-off at higher speeds [7].
6.5.4. Drive-Away Assist
On hills or steep drives the Sensotronic Brake Control Drive-Away Assist prevents the car
from rolling backwards or forwards – stepping onto the brake pedal quickly but sharply is all
it takes to activate the brake. If the driver accelerates, the Drive-Away Assist releases the brake
and allows the car to drive off smoothly [6].
Fig 15. Drive-Away Assist [6]
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6.5.5. The future
The advent of electronics in brake technology opens up new and promising opportunities to
Mercedes engineers - and not only in the disciplines of safety and comfort. By means of SBC
they have also moved a considerable way closer to the realisation of their long-term objective,
namely to be able to automatically guide the cars of the future along the roads with the aid of
video cameras, proximity radar and advanced telematics. For such autonomous vehicle
guidance, the experts need a computer-controlled brake system which automatically acts on
the instructions of an electronic autopilot and stops the car safely [4].
6.6. Sensors and Electronic Unit
Field of mechatronics has created a promising opportunities to the Mercedes engineers not
only in terms of a comfort and safety as well as in a considerable way to the realization of their
long term objectives.
Fig 16. Role of Electronics in Braking [8]
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For such vehicle guidance, the experts need a computer controlled brake system which
automatically acts on the instructions of an electronic autopilot and can stops the car safely. In
order to replace the mechanical components with a view to enhance the functioning of the
braking system, the detailed and precise deigning of high performance microcomputers and
electronically controlled actuators plays an very important role. the Design features of a
modern sensor that include multi functionality, flexibility and reliability for any wire
application. With a view to achieve these factors it is necessary to conceive a silicon micro
machined & piezoresistive pressure sensor chip with higher and lower sensitivities each having
a specified pressure range. Digital electronics is considered out of price for pressure sensors
but still till today they can be used to implement monitoring and correction strategies in the
sensor. The Activities are carried out for the failure analysis at a design level. The most
common evaluation method of these errors is by self- test which correct them without outside
intervention. Sensor design requires a good deal of experience and simulation techniques. The
transducer chip design is mainly carried out by An European Aerospace Defense (EAD) and
the Space Company. For the chip design one of the main difficulties faced were the
correspondence between transducer response and applied pressure. Latest tests have shown the
results that proper positioning of the piezo-resistive elements on the chip membrane with a 90degree profile has been reducing the previously described risk by the significantly showing the
stress distribution changes after the mechanical contact [3]. Thus it will not be wrong to
conclude that the design of electronic should be maintained at a low level of complexity in
order to avoid unnecessary over dimensioning of the components that would further increase
the costs. Instead of a volatile memory for storing the calibration parameters and non-volatile
one for programming of self-tests should be planned while designing [2].
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6.7. Advantages of SBC
Thus, with all the add-ons and features offered by SBC, it becomes easy to enumerate the
advantages that SBC gives over the conventional braking system [6].
1. Improving metering of necessary brake pressure, and each wheel can be precisely
controlled.
2. Reduction in stopping distance in particular during an emergency stop.
3. Increase in active vehicle dynamics safety as the vehicle dynamics control system
ABS and ESP can be used in an optimized manner.
4. Leads to more timely and more comfortable stabilization of the vehicle during ESP
control.
5. Take care of even wear on the brake linings and better response characteristics of the
brake due to optimal brake force distribution between the front and rear axle.
6. Use of the brake force reserve at the rear axle due to growing the brake force share in
the partial braking range and when braking from a low speed.
7. Consequences in more stable braking performance with optimal deceleration values
when cornering as a result of the braking forces being shifted to the outer wheels.
8. No reaction (vibration) on the brake pedal during ABS control intervention functions.
6.8. Limitations
1. The Maintenance is high
2. Electronics parts are costly to replace
3. Some people don’t like the noise of SBC
4. Poor implementation and poor design ultimately leading to its downfall
5. Mercedes decides to stop the technology due to its costly maintenance.
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CHAPTER 7: CONCLUSIONS
•
With reference to the advantages and dis-advantages it is concluded that the SBC system
may take the place of a conventional brake system in the future.
•
Sensotronic Braking Technology is system comprising of mechanics and electronics
which provides its benefits to a greater extent over the conventional braking system.
•
Sensotronic braking system provide uncompromising quality, stability and longevity.
•
One of the most important dis-advantage that is its higher cost due to the electronic
components will get reduced after the adaptation of this system by all automobile
companies. Also the maintenance of the electronic component will be easy when we shall
get familiar with this system.
•
Although if there is a small malfunction in the electronic part of the SBC system, no repair
is available and the part has to be replaced completely. Hence the system maintenance
costs a lot.
•
The sensors, software, electric pumps, SBC microcomputer together allows a highly
dynamic brake system.
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REFERENCES
1. Peter H., “Sensotronic Brake System”, The Mercedes-Benz Page, 16 December (2015).
2. Manas Korde, Himanshu Tayade "Sensotronic Brake Control System", Feb (2022).
3. Mr. Atul B. Takle, Prof. Swapnil R. Umale "Sensotronic Braking System. " (2017).
4. Kant, Bernhard. "Sensotronic brake control (SBC)." Automotive Mechatronics. Springer
Vieweg, Wiesbaden, (2015). 412-415.
5. Mahajan Vrishabh, More Kulbhushan, Kakad Mahesh, ICETEMR-16 March (2016)”.
(424-429).
6. Mohammad Zeeshan, Abhishek B. Lakade " Sensotronic Braking System." IJFEAT
(2016). 132-136.
7. Shah, Hemanshu P. "Sensotronic brake control and brake wear sensor." (2018).
8. www.google.com
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