Most of them spend lot of time with their Automobiles. Every ones expectations is for better performance, safe to drive, user friendly and security in the ongoing development of Automobiles. Modern mechatronics can be applied to make their expectations come true with smarter mechanisms, via improved efficiencies, speed controls and system interaction.
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Before the evolution of Information technology and microprocessor embedded mechanical systems, Mechatronics was simple and mainly focused on servo-technology, such as automotive door openers, servo valves and AC/DC servo motors etc. Nowadays the mechanical systems are reliable, accurate and have a very high efficiency especially in automobiles with electronic engine controls technology that enabled the on-impact triggering of airbags, evolution of sophisticated sensors, active and passive safety devices has predicted a record in car navigation system.
4.1 Car engine management
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Fig: 1 Car engine management
Car engine management system consists of many electronic control systems involving microcontrollers, the engine control system being one, its aim is to control the amount of fuel to be injected into each cylinder, ignition, Engine revolution limit, turbochargers wastage control, variable cam timing and gear controls. The system consists of sensors supplying, after suitable signal conditioning, the input signals to the microcontroller and its providing output signals via drivers to actuate actuators. Figure: 1 shows some of these elements in relation to an engine.
The engine speed sensor is an inductive sensor, basically a toothed metal disk mounted on the crank shaft and stationary detector that functions to cover a magnetic coil through which the current passes through, as these metal teeth begins moving past the coil, the magnetic field is distracted and thus a wave of pulses in the current is created. The temperature sensor is usually a thermistor whose resistance varies according to the temperature. The mass air flow sensor may be a hot wire sensor, as air passes over a heated wire it will be cooled, the amount of cooling depending on the mass rate of flow. When temperature reaches more than 300 centigrade the sensor becomes permeable to oxygen ions and a voltage is induced between the electrodes. [Ref 5]
4.2 Electronic stability control
These control system uses sophisticated sensors, the cars central computer and mechanical actions for a safe drive. The electronic stability control system doesn't work by itself, it also uses the cars other safety and regulatory devices, to correct problems before they get into accidents.
4.2.1 Yaw control sensor
This sensor is located as close as possible to the centre of the car. If the experiences a movement in vertical or side by side axis the Electronic stability system detects that car is swinging, as soon as it detects it activates the brake system and reduce the throttle to lower the speed. The sensor differentiate between the direction of the steering wheel and the direction the car is headed, the cars computer then makes necessary corrections to bring the vehicles direction of travel in line. [Ref 1]
Fig: 2 Sensor fusion of a car
ESC (Electronic stability control) information fed into the cars central computer through 3 types of sensor
4.2.2 Wheel speed sensors
Wheel speed sensor is used to measure the speed of the wheel with which the computer can then compare to the speed of the engine. This sensor is located at each wheel. [Ref 1]
4.2.3 Steering angle sensors
It measures the direction the driver aims to drive the car, if it is deviated from the cars actual direction, the ESC system will come in line. This sensor is located at the steering column of a car. [Ref 1]
4.2.4 Rotational speed sensors
The sensor consists of a magnetoresistive sensor element. The frequency of the digital current output signal is proportional to the rotational speed of the gear wheel.
4. Cruise control acceleration and deceleration
The cruise control system controls the speed of a car by adjusting the throttle position. Instead of pressing a pedal, cruise control actuates the throttle valve by a cable connected to an actuator. The throttle valve controls the power and speed of the engine by limiting how much air the engine takes in. In Figure 3, you can see two cables connected to a pivot that moves the throttle valve. One cable comes from the accelerator panel, and another from the actuator. When the actuator is engaged, it adjusts the throttle by moving the cable connected to the pivot, when the cruise control system is engaged the pedal moves up and down since the actuator also pulls on the cable that is connected to the gas pedal. [Ref 2]
Fig: 3 One cable is connected to the gas pedal, the other to the vacuum actuator.
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In most of the cars the throttle unit is controlled by the actuators powered by engine vacuum. These systems use a small, electronically-controlled valve to regulate the vacuum in a diaphragm. This works in a similar way to the brake booster, which provides power to the brake system. [Ref 2]
Fig: 4 The electronically-controlled vacuum actuator
that controls the throttle
4.4 Airbag Inflation
The goal of an airbag is to inflate rapidly during automobile collision and prevent the passenger's from striking interior objects. Majority cases of death are due to air bags and seat belt is not worn. There are three parts to an airbag that help to achieve its function
Fig: 6 the airbag and inflation system stored in the steering wheel
Fig: 7 the airbag and inflation system stored in the steering wheel
The bag itself is made up of a thin nylon fabric, which is folded into the steering wheel or dashboard or, more recently, the seat or door.
Advance systems have solid state crash sensors that contain a piezoelectric crystal or a micro machined accelerometer, a device used to measure acceleration or vibration shock built into a microchip that produces an electrical signal when jolted.
The airbag's inflation system is by the reaction of sodium azide with potassium nitrate to produce nitrogen. Hot blasts of the nitrogen inflate the airbag. [Ref 3]
4.5 Power door locks
In this system the door lock/unlock switch actually sends power to the actuators that unlock the door. In more complicated systems, the body controller decides when to do the unlocking. The body controller is similar to a computer which monitors all of the possible sources of locking and unlocking signal in a car. The system monitors the radio frequency and unlocks the doors when the correct digital code is received from the radio transmitter. When the actuator moves the latch up, it connects the outside door handle to the opening mechanism. When the latch is down, the outside door handle is disconnected from the mechanism so that it cannot be opened.
Fig: 8 Inside a car door
In a specific interval of time, the body controller supply power to the door lock actuator to unlock the door. The construction of actuator system is very simple. A small electric motor turns a series of spur gears that serve as a gear reduction. The last gear drives a rack-and-pinion gear set that is connected to the actuator rod. The rotational motion of the motor is converted to linear motion by the rack in order to move the lock. [Ref 5]
Mechatronics can be defined as the intersection of mechanics, electronics, computers and controls. The synergistic use of aspects of each of these fields in designing products and processes is driving advances in automobiles - the actual cars and components, as well as the equipment needed to build, diagnose and service them.