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    • EMBEDDED SYSTEMS ANTI-LOCK BRAKING SYSTEM ABSTRACT: Embedded system is the recent emerging technology in the field of electronics. An important application of embedded system is Anti-lock brake system (ABS) in automobiles. Anti-lock Braking systems were developed to reduce skidding and maintain steering control when brakes are used in an emergency situation. Anti-lock Brakes are essentially an enhanced or improved version of ordinary brakes. Simply put, the antilock brake system is designed to prevent the brakes from locking up and skidding when braking hard or when braking on wet or slick surfaces. ABS brakes work by automatically actuating the brakes on and off during emergency stops. They are effective in helping drivers avoid accidents. In certain situations, ABS brakes can help to shorten stopping distances. This adds a significant margin of safety for everyday driving by preventing dangerous skids and allowing the driver to maintain steering control while trying to stop. This paper reveals an overview of embedded systems and its application in automobiles. INTRODUCTION An embedded system performs one or a few pre-defined tasks, usually with very specific requirements. Since the system is dedicated to specific tasks, design engineers can optimize it, reducing the size and cost of the product. Embedded systems are often mass- produced, benefiting from economies of scale. In terms of complexity embedded systems can range from very simple with a single microcontroller chip, to very complex with multiple units, peripherals and networks mounted inside a large chassis or enclosure.
    • CHARACTERISTICS OF EMBEDDED SYSTEM  Some have real-time performance constraints that must be met, for reason such as safety and usability.  Some may have low or no performance requirements, allowing the system hardware to be simplified to reduce costs.  An embedded system is not always a separate block - very often it is physically built-in to the device it is controlling.  It often runs with limited computer hardware resources. CPU PLATFORM Embedded processors can be broken into two distinct categories: microprocessors (µP) and microcontrollers (µC). Microcontrollers have built-in peripherals on the chip, reducing size of the system. DEBUGGING Embedded Debugging may be performed at different levels, depending on the facilities available, ranging from assembly- or source-level debugging with an in-circuit emulator or in-circuit debugger. RELIABILITY Embedded systems often reside in machines that are expected to run continuously for years without errors and in some cases recover by themselves if an error occurs. Therefore the software is usually developed and tested more carefully than that for personal computers, and unreliable mechanical moving parts such as disk drives, switches or buttons are avoided. APPLICATIONS  Automatic teller machines (atms).  Avionics, such as inertial guidance systems, flight control hardware/software.
    •  Cellular telephones and telephone switches.  Engine controllers and antilock brake controllers for automobiles.  Handheld calculators, computers, medical equipment.  Household appliances.  Computer peripherals such as routers and printers. ANTI-LOCK BRAKING SYSTEM Antilock braking systems (ABSs) are electronic systems that monitor and control wheel slip during vehicle braking. ABSs can improve vehicle control during braking, and reduce stopping distances on slippery road surfaces by limiting wheel slip and minimizing lockup. Antilock Brakes system is designed to prevent the brakes from locking up and skidding when braking hard or when braking on wet or slick surfaces. Antilock brakes do not necessarily reduce the stopping distance, and in fact may actually increase stopping slightly on dry pavement. But on wet or slick pavement, antilock brakes may reduce the stopping distance up to 25% or more, which could be the difference between a safe stop and an accident. A tire that is just on the verge of slipping (10 to 20% slippage) produces more friction with respect to the road than one, which is locked, and skidding (100% slippage). Once traction is lost, friction is reduced, the tire skids and the vehicle takes longer to stop. COMPONENTS The anti-lock brake controller is also known as the CAB (Controller Anti-lock Brake). A typical ABS is composed of  A central electronic unit.  Four speed sensors (one for each wheel).  Two or more hydraulic valves on the brake circuit.
    •  ABS malfunction indicator lamp. WHEEL SPEED SENSOR The wheel speed sensors (WSS) consist of a magnetic pickup and a toothed sensor ring. As the wheel turns, teeth on the sensor ring move through the pickup magnetic field. This reverses the polarity of the magnetic field and induces an alternating current (AC) voltage in the pickup windings. The number of voltage pulses per second that are induced in the pickup changes in direct proportion to wheel speed. So as speed increases, the frequency and amplitude of the wheel speed sensor goes up. MODULATOR VALVES ABS modulator valves regulate the air pressure to the brakes during ABS action. When not receiving commands from the ECU, the modulator valve allows air to flow freely and has no effect on the brake pressure. The ECU commands the modulator value to either: • Change the air pressure to the brake chamber, or
    • • Hold the existing pressure. The modulator valve usually has three ports: • Supply port: It receives air from a quick release or relay valve. • Delivery port: It sends air to the brake chambers. • Exhaust port: It vents air from the brake chamber(s). Typically, when an ECU detects impending wheel lockup, it activates the solenoids to close the supply port and open the exhaust port. When enough air is vented to prevent wheel lockup, the exhaust valve will close. ELECTRONIC CONTROL UNIT The ABS electronic control module is a microprocessor that functions like the engine control computer. It uses input from its sensors to regulate hydraulic pressure during braking to prevent wheel lockup. The key inputs for the ABS control module come from the wheel speed sensors and a brake pedal switch. The switch signals the control module when the brakes are being applied, which causes it to go from a "standby" mode to an active mode. When ABS braking is needed, the control module kicks into action and orders the hydraulic unit to modulate brake pressure as needed. On systems that have a pump, it also energizes the pump and relay. Like any other electronic control module, the ABS module is vulnerable to damage caused by electrical overloads, impacts and extreme temperatures. MALFUNCTION INDICATOR LAMP (MIL)  Illuminated in key position 2  Goes out with engine running  Illuminated when a fault is present  Will indicate low available voltage (< 10.5 V)
    •  Flickering off and on while engine is running indicates a voltage supply problem WORKING The electronic unit constantly monitors the rotation speed of each wheel. When it senses that any number of wheels are rotating considerably slower than the others it moves the valves to decrease the pressure on the braking circuit, effectively reducing the braking force on that wheel. Wheel(s) then turn faster and when they turn too fast, the force is reapplied. This process is repeated continuously, and this causes the characteristic pulsing feel through the brake pedal. The sensors can become contaminated with metallic dust and fail to detect wheel slip; this is not always picked up by the internal ABS controller diagnostic. ABS CONTROL MODE PRESSURE HOLD Vehicle speed signal indicates wheel is about to lock. Pressure still applied, but can’t increase because ABS control module has activated value y8. PRESSURE RELEASE To reduce pressure at locking wheels (the wheel that has stopped spinning): ABS control module: • Activates return pump • Activates Valve y8 so no more pressure can be applied
    • • Activates valve y9 so pressure at brake can be reduced These valves can be pulsed very rapidly. You can feel this stage of operation through the brake pedal. TRACTION CONTROL The ABS equipment may also be used to implement traction control on acceleration of the vehicle. If, when accelerating, the tire loses traction with the ground, the ABS controller can detect the situation and take suitable action so that traction is regained. Manufacturers often offer this as a separately priced option even though the infrastructure is largely shared with ABS. More sophisticated versions of this can also control throttle levels and brakes simultaneously. DRIVING WITH ABS When vehicle first exceeds 5mph after a start-up, a self-test is performed. With foot on brake pedal, a pulsation will be felt. Driver applies brakes: – If wheels do not approach lock-up, then ABS is not activated and brakes function as in a non-ABS vehicle. – As vehicle is braked, ABS may be able to prevent wheel lock-up by simply holding the brake fluid pressure from going any higher. The driver would not sense this stage of control. – If driver feels brake pedal pulsate, then ABS is reducing brake fluid pressure in order to insure that wheels continue rotate. This action may be accompanied by pump noise.
    • Remember! ABS gives the driver the ability to steer the vehicle in an emergency braking situation. ABS DOs AND DO NOT DOs  DO keep your foot on the brake pedal  DO allow enough distance to stop.  DO practice driving with ABS.  DO consult your vehicle owner’s manual. DO NOTS  DO NOT drive an ABS-equipped vehicle more aggressively.  DO NOT pump the brakes.  DO NOT forget to steer.  DO NOT be alarmed by clicking noises. CONCLUSION Maximum braking effect is achieved with the wheels on the limit of friction, whereas ABS works by releasing the brakes as the wheels break traction, so a skilled driver should be able to exceed the braking performance of an ABS system in a straight line on a consistent surface. When activated, the ABS causes the brake pedal to pulse noticeably. When drivers do encounter an emergency that causes them to brake hard and thus encounter this pulsing for the first time, many are believed to reduce pedal pressure and thus lengthen braking distances, contributing to a higher level of accidents than the superior emergency stopping capabilities of ABS would otherwise promise. Nevertheless, ABS can significantly improve safety and control for drivers in on-road situations if they know
    • not to release the brakes when they feel the pulsing of ABS. PRESENTED BY, M.NAVEEN KUMAR (11ECL197) K.MOHAN PREETH (11ECR083) SECOND YEAR ECE DEPARTMENT, KONGU ENGINEERING COLLEGE, PERUNDURAI, ERODE. MAIL ID:mnaveenkongu@gmail.com CONTACT NO:7200459528
    • not to release the brakes when they feel the pulsing of ABS. PRESENTED BY, M.NAVEEN KUMAR (11ECL197) K.MOHAN PREETH (11ECR083) SECOND YEAR ECE DEPARTMENT, KONGU ENGINEERING COLLEGE, PERUNDURAI, ERODE. MAIL ID:mnaveenkongu@gmail.com CONTACT NO:7200459528