brake by wire system full report
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15-02-2010, 07:18 PM



.doc   BRAKE BY WIRE SYSTEM.doc (Size: 448.5 KB / Downloads: 280)
ABSTRACT
Recent advances in dependable embedded system technology as well as continuing for improved handling and passive and active safety improvement, have led vehicle manufactures and suppliers to actively pursue development programme in computer controlled by wire system. These subsystems include steer and brake by wire and are composed of mechanically developed sets of actuators and controllers connected through multiplexed, in making computer network.
Electromechanical brake by wire systems realize on electronic control of an electric motor to provide braking without hydraulic back up. This allows flexibility in the packaging and the modularity of the design
INTRODUCTION
BRAKE BY WIRE SYSTEM is an application of mechatronics, which is the integration of electronic devices and mechanical systems in order to improve the performance of the system.
Recent advances in dependable embedded system technology as well as continuing for improved handling and passive and active safety improvement, have led vehicle manufactures and suppliers to actively pursue development programme in computer controlled by wire system. These subsystems include steer and brake by wire and are composed of mechanically developed sets of actuators and controllers connected through multiplexed, in making computer network. There is no mechanical link to the driver. Steer and brake by wire provide a number of packaging and assembling advantages over conventional subsystems. For instance electromechanical brake by wire subsystems requires no hydraulic fluid to store or load at the assembly plant and permit more modular assembly; thus reducing the number of parts to be handled during production. Steer by wire systems have no steering column and may also eliminate cross production cost packaging and traffic safety.
The by wire technology as in drive, brake and steer is gaining ground and is undoubtedly an automation solution of the future. The argument to the support such by wire systems include reduced production cost and improved traffic safety. Emerging drive by wire technologies offer new possibilities for designing the braking characteristics of road vehicle. When sensors, controllers, and actuators enormous flexibility is achieved in terms of control devices applied and in terms of transfer functions of the braking systems replace the mechanical link between the brake pedal and disc brake. This offers new possibilities for optimizing the braking systems for mass produced vehicle. However the flexibility is of even greater advantage in the area of car adjustment for drivers with the physical disabilities
Electromechanical brake by wire systems realize on electronic control of an electric motor to provide braking without hydraulic back up. This allows flexibility in the packaging and the modularity of the design.
The transition to purely electrical braking system will take place step by step via systems with mechanical or hydraulic back up. Development and production of next generation of electrical braking systems upto purely electric braking systems.
Luxury carmakers like BMW, MERCEDES and AUDI are targeting the 2004 model year for the introduction of brake by wire systems. There are lots of forms explained by Delphi motors and chassiss systems operation manager without Motorola inc.,Austin texas. Electromechanically brake (EMB) and electrohydraulically brake are the two important brake by wire systems. But in this EMB is the most developed and most advanced. EMB realizes on electronic control of electric motor to provide braking without hydraulic back up. Itâ„¢s likely to enter vehicles within 2005-10 model years and it will need 42V technology according to the trend. He expects to see EMB employed in some compact cars by 2004 to 2005 so that reliability data can be collected and analyzed.
CONVENTIONAL BRAKING SYSTEM
Primary function of the braking is to the bring the vehicle to rest in the shortest possible distance and secondly, they must be enable to control the vehicle to be retained when the descending long hills. The first demand calls for brake which can apply large braking torques to the brake drums while the second calls for brake that can be dissipate large quantities of heat without large temperature rise.
Conventional braking system is shown below
Conventional braking systems have many components like pedal,booster,master cylinder, drum brake and disc brake etc.. The front wheel has disc brake than drum brake. The disc brake is more efficient than drum brake during the emergency stopping. The master cylinder is the major component in the conventional braking system.
THE MASTER CYLINDER
Here is where you'll find the master cylinder:
Master cylinder location
Diagram of master cylinder
Inside the master cylinder will be seen here, there are two pistons and two springs .
THE MASTER CYLINDER IN ACTION
When you press the brake pedal, it pushes on the primary piston through a linkage. Pressure builds in the cylinder and lines as the brake pedal is depressed further. The pressure between the primary and secondary piston forces the secondary piston to compress the fluid in its circuit. If the brakes are operating properly, the pressure will be the same in both circuits.
If there is a leak in one of the circuits, that circuit will not be able to maintain pressure. Here you can see what happens when one of the circuits develops a leak. When the first circuit leaks, the pressure between the primary and secondary cylinders is lost. This causes the primary cylinder to contact the secondary cylinder. Now the master cylinder behaves as if it has only one piston. The second circuit will function normally, but you can see from the animation that the driver will have to press the pedal further to activate it. Since only two wheels have pressure, the braking power will be severely reduced.
TYPES OF BRAKE BY WIRE
Conventional braking system is changed to advanced brake by wire system. Brake by wire systems can be classified into two.
1. ELECTRO MECHANICAL BRAKE BY WIRE (EMB)
2. ELECTRO HYDRAULIC BRAKE BY WIRE (EHB)
EHB is the brake by wire system with hydraulic back up. EHB falls somewhere between conventional hydraulic systems and EMB systems. It will show up on some luxury cars in the 2000 model year and could also be considered brake by wire according to the trend. Though each wheel is assigned a conventional hydraulic caliper (caliper is basically a mechanism that squeezes the brake pad against the brake disc to produce the friction that slows the cars) an electronically controlled valves controls the actual braking force (the pressure of the fluid it releases)
Instead of pedal directly pushing the hydraulic servo, brake fluid pressure is governed by electric pump connected to the brake pedal by wire, press the pedal, activate the pump, and brake the car.
NEW BRAKING SYSTEM BY WIRE
New braking system use more and more electrical components. This is mainly because of two reasons, energy saving and installation simplification by modular design.
ELECTRO MECHANICAL BRAKE BY WIRE (EMB)
EMB is the fully brake by wire systems without hydraulic back up is still being debated. EMB realizes on electronic control of an electric motor to provide braking safely and stably are at the heart of the push the automotive brake by wire technology especially for a braking and steering combination. The goal is to make the average driver as skilled as a professional test course driver in bringing the vehicle back to a safe and stable condition from an unsafe one. Controlling the brake at each wheel individually as is done in brake by wire and helping the driver steer through a skid may prevent the accident.
By wire system also have a manufacturing and design advantages. Brake by wire modules would plug into the corners of a car, near each wheel, connected by a wire to a micro controller connected by wires to the brake pedal making the car assembly easier and faster than putting a plumbing systems in the car. Also no hydraulic lines or fluid means that there is no fluid to renew or spills that can ruin paint.
An EMB by wire system looks deceptively simple. Wires convey the driverâ„¢s pressure from a sensor on the brake pedal to micro controller that relays the signal to electromechanical brake actuators at each wheel. In turn the modular actuators squeezes the brake pads against the brake disc to slow and stop the car
In a brake by wire system, braking action desired by the driver is transmitted by an electrical signal to each brake, rather than by hydraulics or, in the case of heavy trucks, by air pressure. Brake by wire minimizes brake wear by evenly spreading the load across all wheel brakes. This increases the life of brake linings by 20 percent. All brake linings wear at the same rate and can be replaced at the same interval, saving on down time for maintenance. Also, brake response time is much quicker with electronic braking, shortening the stopping distance of the vehicle. If a tractor is towing a trailer equipped with an electronic braking system, the brakes will respond immediately and simultaneously on both the tractor and trailer.
COMPONENTS
¢ Four wheel brake modules
¢ Electronic controller
¢ Electronic pedal module with pedal feel simulator and sensors for monitoring driver settings
SPECIAL REQUREMENTS FOR BRAKE BY WIRE SYSTEMS
¢ Actuators; the brake actuator has to be free of braking torque in case of power loss.
¢ Sensors; triple redundancy is needed for the pedal sensors to get one valid pedal measurement by the loss of one sensor.
¢ Power supply; two independent power supplies are needed.
¢ Communication; the communication system between the components has to be fail-operational after one fault.
¢ Software; the software has to be certified.
To reach these requirements new technologies have to be developed for actuators, communication and electronic components. Redundancy is needed in sensors, electric components, communication and power supply.
WORKING OF EMB
EMB is considered to brake by wire because it does away with hydraulic link between the brake pedal and brake pad. EMB put a motor driven caliper separated by 42V power at each wheel (42V technology refers to the system voltage being embraced by car makers and suppliers who see the standard 12V battery as insufficient to supply the power. Whether the 42V system voltage will be supplied by second lead acid battery and existing 12V battery remains uncertain). Electronic control and caliper operate through a multiplex signal send by a sensor in the brake pedal. Micro controllers on each wheel are connected to the master controller with the ability to interrupt the signal between the pedal and caliper that seeks the brake pad against the brake disc to produce the friction that slows the car.
COMPARISON WITH EMB AND CONVENTIONAL BRAKE
Working of EMB explained earlier, compare that to the conventional brake on a car today. Pressing the brake pedal applies the hydraulic pressure (via hydraulic fluid) to force the pad in the caliper assembly against the spinning the brake disc on each wheel the friction produced between the disc and pad slows the car.
ADVANTAGES
¢ Assistance functions (ABS, BA, ESP,...) could be realized only by software and sensors without additional mechanical or hydraulic components.
¢ Electrical interfaces instead of hydraulic interfaces, allow easier adapting of assistance systems.
¢ Reduction of packaging problems.
¢ No brake fluid, no bleeding, and simple maintenance, ecological.
¢ Nearly rest torque free.
¢ No mechanical links between the brake components and the engine compartment, improving passive safety.
¢ No perceptible noise emission when braking.
¢ Reduced costs for assembly during line production.
FILO CONCEPT OF CAR
Bertone, a leading automotive design house, and SKF designed the Filo concept car, the automotive industries leading supplier of bearing and sealing solutions. FILO is a drive by wire concept car. It is steered, braked and accelerated utilizing by wire technology.
With the FILO, driver input (steering, accelaration, braking and gear shifting) is translated into electric signals that go by wire to electromechanical control unit. Electric motors take over the conventional mechanical or hydraulic functions with integrated sensors and measurement systems determining the position, force and displacement. The electronic logic between the actuators and driver controls offers vehicle designers an easier way of making the vehicle feel the programmable to suit the different drivers.
The FILO concept uses the drive by wire technology engineered by SKF, enabling a radical re-evaluation of the man-machine interface and the architectural of a carâ„¢s interior. STILE BERTONE has created a living space inside a car devoid of the traditional constraints imposed on position and freedom of movement.
Mechatronics, combination of the mechanical devices under intelligent, electrical control is at the heart of the FILO. It is these technique that allows much of the interior redefinition allowing for a reassessment of a driver interacts with the vehicle and environment in which it is being driven
Stile Bertone utilizes drive by wire technology to redesign the interior architecture of the automobile and create living space devoid of traditional constraints imposed on positions and freedom of movement.
Finally freed of the bulky and potentially dangerous steering column, the designers have been able to consider a dash board free of obstructions and constraints, a large free surface simple, clean relaxing. A central binnacle houses the information and driving equipment while the air outlet disappears and the air-conditioning is diffused evenly. The waved floor offers various possibilities for the driver to rest his feet, no longer restricted the presence of pedals. Both front and rear seas have the appearance of lounge sofas with the rear positioned higher than that of front to give greater visibility for the passengers. Entrance to the car is made easier due to the absence of the central pillar. A much closer link between the environment of the home and the car is inevitable.
Bertone strongly believe that by utilizing fly-by-wire technology, the overall safety and level of function will be improved. It will be increasingly possible to integrate the comfort and luxuries of the home with the automobile. Safety is improved in collision and there is a reduction of industrial investment to change from right to left hand drive. By-wire is also an environmentally friendly technology dispensing with hydraulic oil for the braking and power steering systems. The feel for the driverâ„¢s controls from the Mechatronics actuation systems is provided by a close looped sensor and feed back system. The car is a true concept in not only a appearance but, perhaps more importantly in function. Bertone have shown with the Filo that use of technology have already proven in other industries-such as aerospace- can not only functionally improve the vehicle but also increase the safety. FILO drive by wire technology, Bertone developed jointly with the SKF has made it possible to radically rethink the man-car interface and car interior architecture. No more pedals, therefore: wires control steering, accelarator, gearbox, and clutch. And inside STILE BERTONE has created living space unhampered but the usual restrictions to the freedom of position and movement
CONCLUSION
This paper presents various types of electrical braking systems and their system structure starting from the conventional to new brake by wire systems (EMB). EMB is the fully brake by wire systems without hydraulic back up. The goal of brake by wire is to make the average driver as skilled as professional driving in stabilizing the car. The electric controllers instead of hydraulic linkages is used, yielding energy saving and flexibility of installation. Electric braking system by wire pursues this trend and offers additional advantages since no hydraulic system is required. EMB by wire systems without hydraulic back up is purely brake by wire were discussed. It has been stated that redundant fail safe structure for electrical and electronic components to be established due to the fact that no mechanical or hydraulic linkages between he braking system are available.
Future innovative braking function such as vehicle dynamic intervention, collision avoidance, tracking assistance, automatic lateral guidance and finally autonomous driving functions will be implemented in a systems compound of various vehicles. Future braking systems thus have to be integrated into a system compound of in terms of interfaces and functions. The brake by wire principle becomes absolutely necessary when this innovative function is to be achieved. The customer will produce transition to the purely electric braking system step by step, both for safety reasons and acceptance. The path will be lead from electrical braking via brake by wire system with hydraulic or mechanical back up system towards purely electromechanical brake by wire systems.
REFERENCES
¢ IEEE SPECTRUM (April 2001)
¢ howstuffworks.com
¢ delphi.com
¢ bmw.com
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