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Brake by Wire

Last Update:

09/06/2016

Introduction

Brakes have progressed from the primitive wooden block against wheel system to today’s highly sophisticated technologies like mechanical, hydraulic to even brake-by-wire. Instead of mechanical force applied through the brake pedal, today’s advanced brake by wire technology uses electrical and electronic controls to actuate brakes and apply just the right pressure to bring the vehicle to a safe halt. Although the technology has changed over time dramatically, the basic principle of brake application remains the same.

History

The genesis of brake by wire lies in the aerospace industry. Brake by wire renders superfluous a number of mechanical components like pumps, hoses, fluid, belts and vacuum servos, thus making the aircraft lighter. Besides, the electronic braking system is far more reliable and has a number of safety and redundancy features. The same principles were transplanted to the automotive field resulting in development of electronic based hydraulic and pneumatic braking systems with mechanical systems included as backup.

  • GM had a brake by wire system installed in its EV1 electric car as far back as 1996 whereas the current BMW 7 series have highly advanced brake by wire.
  • Toyota, an innovative car maker, installed brake by wire in 2001 in its Estima hybrid vehicle. Lexus RX 400H got it in 2005.
  • Mercedes came up with its own version named Sensotronic Brake Control and fitted the SL class with this system in 2001.

However, the first electronic based four wheel braking system could probably have been developed by Bosch and Mercedes Benz. Their joint cooperation resulted in a brake system fitted to the Mercedes S class in 1978 leading to further developments in 2006 in the Brake Distronic Plus system that used radar to sense distance between vehicles and bring the vehicle to a stop even if driver does not actuate the brakes.

Evolution and adoption

  • Rake by wire eliminates cumbersome, leak-prone hydraulic and air lines. As a result the system is simpler and automatic with fewer components.
  • We can find brake by wire technology applied to hydraulic braking systems and to pneumatic systems in a hybrid model.
  • Additionally, a purely electric brake by wire system was developed, using an electric motor to apply braking force.
  • In a true electronic brake by wire system there is no use made of hydraulics.  
  • DC motor powered actuators move calipers instead of hydraulic cylinder and piston arrangements. 

Components

The main components of a BBW are:

  • Processor in the ECU of the car integrated with
  • Sensors that are linked to
  • Actuators through
  • Communication network connected with calipers and linked to

Memory that is integrated with the ECU.

How It Works

  • The driver pushes the brake pedal that transmits a signal to the ECU that, in turn, generates commands to be sent to the four independent braking systems at each wheel.
  • The ECU also calculates amount of ABS and the vehicle stability while computing the force required to be applied to the calipers through the actuators worked through the communication network or data bus.
  • A controller at each caliper deciphers signals from the ECU and generates commands fro the power unit that actuates a DC motor to apply braking force.
  • Two sensors measure parameters such as the actuator’s speed and position at each caliper.
  • Carefully calculated braking force is then applied to bring the vehicle to a safe halt.

Advanced systems may employ clamp force sensors as well as other sensors to sense distance of vehicles in front or rear and automatically apply brakes.

Effectiveness and challenges

  • Brake by Wire is responds very fast and applies carefully calculated braking force with precision that would bring a vehicle to stop without skidding.
  • The system is free of noise and vibration.
  • The unit occupies much less space than conventional hydraulic and pneumatic systems since it does away with master cylinders and associated hoses.
  • Brake by Wire systems are environment friendly since they are free of toxic hydraulic brake fluids.

Disadvantages

  • It is expensive. Few companies even discontinued use of the Bosch developed sensotronic brake by wire in the premium cars reverting to traditional hydraulics for cost effectivity and affordability to masses.
  • The system is prone to software glitches, ECU failure, failure of sensors, electronic component failure and high replacement costs for spares. Further, it’s servicing required to go to only authorized service centers.
  • Even F1 drivers, whose cars were equipped with Break by Wire for the rear brakes, took some time to familiarize themselves with the control, responsiveness and other factors, so different from mechanical systems where there was feedback aiding judgement. Regular drivers also find it difficult to adapt to computer interface and systems.

Maintenance Tips

  • Sensors provide information that helps the ECU send and receive signals. Sensors need to be kept clean and free of interference.
  • Mechanical jams need to be checked. If a sensor is not included to check this, then the ECU will send activating signals but signal will not translate to force. Hence better maintenance is more critical in Brake by Wire systems.

Brake by wire is touted as the braking system of the future. However, implementation is still slow while costs have yet to come down to affordable levels, especially in sophisticated systems such as the Sensotronic by Bosch.

 

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