19-03-2012, 04:08 PM
BRAKE BY-WIRE CONTOL SYSTEM IN AUTOMOBILES
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. INTRODUCTION
Braking literally means reducing the speed of a vehicle. Brakes squeeze against a drum or disc, and the pressure of the squeezing action is what slows down the motion. In precise terms, brake pads or shoes that press against the brake drum or rotor convert that energy into thermal energy. The cooling of the brakes dissipates the heat and the vehicle slows down.
Types of brakes vary from a simple brake that is used in a bicycle to a complex braking system in a modern vehicle. Main different types depend on how the riders braking intension is carried to the brake actuator and how the friction is applied to the rotating wheel.
Typical type of brake uses hydraulics to connect the user signal to the brake actuator. This is the most popular type used for braking and it is widely used in automobiles. This single circuit hydraulic systems have three basic components – the master cylinder, the slave cylinder and the reservoir. They are joined together with hydraulic hose and filled with a non compressible hydraulic fluid. When the brake pedal is pressed, small piston assembly in the master cylinder is moved. Because the brake fluid does not compress, that pressure is instantaneously transferred through the hydraulic brake line to the slave cylinder where it acts on another piston assembly, pushing it out. That slave assembly is either connected to a lever to activate the brakes, or more commonly, is the brake caliper itself. Because of the arrangement of the slave cylinder, heat from the brakes can be transferred back into the brake fluid. Even though this conventional method has been used for decades, it has some inherent disadvantages.
BRAKE BY-WIRE
A BRAKE-BY-WIRE (BBW) system consisting of electromechanical actuators and communication networks, instead of conventional hydraulic or electro-hydraulic devices, has emerged as a new and promising vehicular braking control scheme. It offers enhanced safety and comfort, cuts off cost associated with manufacturing and maintenance, and eliminates environmental concerns caused by hydraulic systems. The
BBW system has recently invoked a lot of interest for both industry and academia worldwide.
Brake-by-wire system separates the pedal and the brake actuators using an electrical signal. As the name suggests the separation is by a wire. This Technology, transmits drivers braking intension by wire rather than mechanically or hydraulically as in the conventional case.
A still similar system is not commercialized. Reliability of the electronic system may be questionable. However brake by wire systems has the potential of entering to the market due to its technical merits.
The vibrations, which normally occur through the brake pedal when ABS intervenes, can be eliminated as the actuators are matched to the input using a wire. Electronics is much reliable if designed properly than in the conventional case. If one brake horse is broken the total brake system would be lost in the conventional case. But where as in the brake by wire system, each wheel is controlled separately which improves the reliability of the system.
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)
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)