Embedded Systems In Automobiles

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In today’s world, most electronic devices are based on embedded systems. From home appliances like microwaves and washing machines to entertainment and security systems, embedded systems have found a way into every field.

What an embedded system is

An embedded system is a computer system with a dedicated function within a large mechanical or electrical system, often with real-time computing constraints. Key characteristics of an embedded system are:
1. Sophisticated functionality
2. Real-time operation
3. Low manufacturing cost
4. Low power

Mechanical systems in automobiles have largely been replaced by electronic systems. Today, the automobile industry is making great use of embedded systems. Ranging from wiper controls to complex anti-lock brake controls and air bags, embedded systems have gained overall control of automobiles.

Automobiles that are built around microcontrollers, digital signal processors or both processors are commonly called electronic control units. Many luxury vehicles have come up with a large number of embedded controllers. The first embedded system based automobile, Volkswagen, came in 1968.

Some current trends of embedded systems in automobiles include air bags, event data recorders, anti-lock brake systems, cruise control, rain-sensing wipers, emission control, traction control, automatic parking, in-vehicle entertainment, back-up collision sensors, navigation systems and tire-pressure monitors.

Fig. 1: An automobile with embedded systems

Airbags

Fig. 2: An airbag deployment system

The airbag system is an important safety device that provides extra protection against head-on crash for the passengers, by giving a soft surface to land on. This system works on commands from the airbag control unit, which has a microcontroller. The controller gets power from the battery.

If the collision sensor detects an accident, a signal is sent to the airbag control unit and it is processed by the airbag control unit to determine severity of the impact. If airbag deployment is necessary, the airbag control unit sends a signal to initiate airbag inflators. Inflators are activated through an igniter, causing a chemical reaction that emits nitrogen gas, resulting in the deployment of the airbag cushion.

Fig. 3: An airbag deployment system after crash

An occupant detection system is used to determine if a person is seated in the passenger seat and if he or she is of adequate size to be protected in the event of deployment of the passenger seat airbag. It measures the weight of the passenger to determine if the corresponding airbag should deploy.

In 2012-13, a new type of occupant detection system called electrostatic capacitance sensor was implemented. This system does not use weight to determine whether to turn the occupant detection system on or off.

Electrostatic capacitance represents a material’s capability of storing an electrical charge. When someone is seated or when something is placed on the passenger seat, there is a change to that capacitance value. Change in capacitance value is what electrostatic capacitance sensor occupant detection system uses to determine whether the passenger seat airbag will be on or off.

Event data recorder

An event data recorder is a device installed in automobiles to record information related to vehicle crashes or accidents. It is also known as a black box. The sensing and diagnostics module, which is controlled by a microprocessor, has multiple functions, as given below:
1. Determines if a severe enough impact has occurred to warrant deployment of the airbag
2. Monitors the airbag’s components
3. Permanently records information

Event data recorders record a wide range of data, including whether brakes were applied, speed and time of impact, steering angle and whether seat belt circuits were shown as buckled or unbuckled at the time of the crash.

Fig. 4: Block diagram of an event data recorder

Anti-lock braking system

Up until the 1970s, hitting the brakes too hard could lead to an accident. If the coefficient of slip between tires and the road was too low, hitting the brakes could lead to wheel lock-up. The vehicle would no longer be steerable and would start skidding. The danger is present specially when:
1. Roads are wet and slippery.
2. There are different levels of grip between the tires and the road.

Wheel-speed sensors detect whether a wheel is showing a tendency to lock-up. In case it is, the electronic control unit reduces the braking pressure individually at the wheel concerned. High-speed correction of the braking pressure takes place before the lock-up threshold. The brake-fluid return together with closed-loop brake circuits makes this a safe, reliable and cost-effective system.

An anti-lock brake system is advantageous as:
1. Vehicle remains steerable even during panic braking
2. Shorter stopping distances on all road surfaces

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