An overview ofEMBEDDED SYSTEMS

IN AUTOMOBILES

By Amber Deep SinghEN. No-22/10

Dept. of Electronics and CommunicationNIT Srinagar

What is ABS?“An anti-lock brake system is a feedback control system that modulates brake pressure in response to measured wheel deceleration, preventing the controlled wheels from becoming fully locked.”

It’s main functions are that it• Reduces stopping distance.• Maintains steerability.• Maintains lateral stability.

The Operation of ABS

Typical ABS Components

Wheel Speed Sensors (up to 4) Electronic Control Unit (ECU)

Brake Master Cylinder, Hydraulic Modulator Unit with Pump and Valves

Vehicle’s Physical Brakes

Wheel Speed Sensor (WSS)

Magnetic field changes as toothed gear wheelrotates, resulting in a signal with frequency related to the angular velocity of the axle.

Electronic Control Unit

• The signal from the WSS is proportional to angular velocity. By differentiating this signal, acceleration of each wheel is known. If a wheel is decelerating too quickly the brake pressure is modulated.

• A fifth input to the ECU is from a brake pedal switch. This signal can shift program execution from a standby to an active state

Hydraulic Modulator Unit

The hydraulic modulator unit contains the ABS pump as well as solenoid valves for each brake line.The fifth line - far right - is from the brake master cylinder, which is connected to the brake pedal.

Valves and Brakes

The Solenoidal valves modulate the brake pressure up to 20 times per second, effectively realizing the ideal tire slip percentage.ABS ‘pumps’ the brakes much faster than any driver could.

Adaptive Cruise Control(ACC)with Collision Avoidance

What is ACC?

• Adaptive Cruise Control (ACC) is an automotive feature that allows a vehicle's cruise control system to adapt the speed to the traffic environment.

• ACC allows cars to keep safe distances from other vehicles on busy highways. The driver can set the speed of his car and the distance between his car and others. When traffic slows down, ACC alters vehicle speed using moderate braking.

PRINCIPLE OF ACC

ACC works by detecting the distance and speed of the vehicles ahead by using either a Lidar system or a Radar system .The time taken by the transmission and reception is the key of the distance measurement while the shift in frequency of the reflected beam by Doppler Effect is measured to know the speed. The brake and throttle controls are done to keep the vehicle in a safe position with respect to the other.

CONSTITUENTS OF AN ACC SYSTEM

• A sensor (LIDAR or RADAR) usually kept behind the grill of the vehicle to obtain the information regarding the vehicle ahead. The relevant target data may be velocity or distance.

• A controller which receives the sensor data and process it to generate the commands to the actuators of brakes, throttle or gear box.

Working of ACC