RACK AND PINION GEAR

Rack and pinion gears are used to convert rotation into linear motion.The circular pinion engages teeth on a flat bar - the rack. Rotational motion applied to the pinion will cause the rack to move to the side, up to the limit of its travel.The rack and pinion arrangement is commonly found in the steering mechanism of cars or other wheeled, steered vehicles.A good example of a ‘rack and pinion’ gear system can be seen on trains that are designed to travel up steep inclines. The wheels on a train are steel and they have no way of griping the steel track. Usually the weight of the train is enough to allow the train to travel safely and at speed along the track. However, if a train has to go up a steep bank or hill it is likely to slip backwards. A ‘rack and pinion’ system is added to some trains to overcome this problem. A large gear wheel is added to the centre of the train and an extra track is, with teeth, called a ‘rack’ is added to the track. As the train approaches a steep hill or slope the gear is lowered to the track and it meshes with the ‘rack’. The train does not slip backwards but it is pulled up the steep slope.

Application:-

Rack and pinion gears provide a less mechanical advantage than other mechanisms, but greater feedback and steering sensation. A rack and pinion gear gives a positive motion especially compared to the friction drive of a wheel in tarmac. In a rack and pinion railway, a central rack between the two rails engages with a pinion on the engine allowing a train to be pulled up very steep slopes.

Rack and pinions gears are commonly used in the steering system of cars to convert the rotary motion of the steering wheel to the side to side motion in the wheels. The steering wheel rotates a gear which engages the rack. As the gear turns, it slides the rack either to the right or left, depending on which way the wheel is turned. Rack and pinion gears are also used in some scales to turn the dial that displays a weight.

MULTIPOINT FUEL INJECTION

Fuel injection is a method or system for admitting fuel into the internal combustion engine.There are basically two ways of admitting fuel one is through carburetor and other is fuel injection system.But presently the most used injection system are MPFI in petrol engine and CRDI in diesel engine.

Multi point fuel injection is a system wherein fuel is injected into individual cylinders based on commands from "on board engine management system computer"-popularly known as Engine control unit.ECU receives feed back from several sensors like engine speed sensor, fly wheel position sensor, vehicle speed sensor, atmospheric temp. sensor, accelerator pedal position sensor intake airflow sensor. Then ECU control the correct amount of fuel to be injected and the proper time at which the fuel will be injected at any speed and load condition. This ensure maximum power output at minimum fuel.

MPFI systems are of three types, first is BATCHED in which fuel is injected to the cylinders in groups, without precisely bringing together to any particular cylinder’s intake stroke, the second one is simultaneous in which fuel is injected at the same time to all the cylinders and the third one is sequential in which injection is timed to coincide with each cylinder’s intake stroke.

ADVANTAGES OF MPFI

• More uniform air-fuel mixture will be supplied to each cylinder, hence the difference in power developed in each cylinder is minimum.
• The vibrations produced in MPFI engines is very less, due to this life of the engine component is increased.
• No need to crank the engine twice or thrice in case of cold starting as happen in the carburetor system.
• Immediate response, in case of sudden acceleration and deceleration.
• The mileage of the vehicle is improved.
• More accurate amount of air-fuel mixture will be supplied in these injection system. As a result complete combustion will take place. This leads to effective utilization of fuel supplied and hence low emission level.