Internal Combustion Engine

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The typical car engine shown here is a 4-stroke petrol engine. The chemical energy from burning petrol causes an explosion inside the engine that forces a piston to slide down inside a cylinder. The piston is connected to a crankshaft, and this mechanical energy is transferred through a gearbox to the drive wheels of the car. The four strokes of the engine are:
• Inlet - piston moves down and sucks in air and petrol (from carburettor or fuel injector)
• Compression – piston moves up and compresses the gas mixture
• Power – the spark ignites the mixture and the explosion forces the piston to down
• Exhaust – the piston rises and forces the burnt gases into the exhaust manifold

One piston/cylinder on its own cannot work well. Four cylinders arranged so that one at a time is on a power stroke, provide a smoother and more continuous power output.

A piston engine is incredibly responsive, and more fuel-efficient over a wide power range. This makes piston engines ideal for use in vehicles and explains why, despite poor fuel efficiency and exhaust gases, they are still in use after 125 years.

Substantial improvements in fuel economy have been achieved with sophisticated electronic controls, sensors and direct fuel injection. The toxicity of exhaust gases has been reduced with the introduction of catalytic converters (link).

A diesel-fuelled engine works is a similar way. It is generally more fuel-efficient but has more toxic exhaust gases. Its performance favours specific applications, typically heavy-duty.

Braking System

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A good braking system is essential for stopping your vehicle. Pressing the brake pedal, which is attached, via levers, to the master cylinder, applies pressure to brake fluid, within a network of hydraulic pipes, connected to actuators on the actual brakes at each wheel. The more force a driver applies to the brake pedal, the higher the stopping force that is applied at the wheels. The master cylinder has a reservoir that keeps the system full of brake fluid.

Disk brakes use pads lined with friction material to grab a steel disk that is rotating with one of the road wheels whereas drum brakes have brake ‘shoes’, also lined with friction material, that are pushed against the inside of a rotating drum inside a road wheel.

Front brakes play a greater part in stopping a car than the rear ones because braking throws the car weight forward on to the front wheels. Many vehicles, therefore, have disc brakes, which are generally more efficient, at the front and drum brakes at the rear. The handbrake, which is also considered an emergency brake, is usually connected to the rear brakes by steel cables.

The force applied to the brakes can be boosted by a ‘servo’ that uses either engine vacuum or hydraulic pressure to amplify the force from the master cylinder, so the driver does not have to push the pedal as hard.

In addition to this primary braking system, most modern vehicles are fitted with an electronic Anti-lock Brake System (ABS) to prevent skidding. The ABS can detect any wheel skidding (through electronic sensors) and adjust the braking force on any wheel (using high-pressure pumps). It allows you to brake as hard as possible, and slow down as quickly as possible, during an emergency stop.

Steering System

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A steering system is required to allow the driver to aim the vehicle in the direction of travel by turning the front wheels. The steering wheel in the car is connected to the two front wheels by a combination of gears and levers. To improve the accuracy of the mechanism and to reduce the effort required at the steering wheel, it takes a significant rotation of the steering wheel to make a small change in the angle of direction of the front wheels.

The suspension system is cleverly designed to allow each wheel to move up and down without changing the steering angle. Therefore most of the steering joints have to be ‘knuckle’ or ball-joints.

The system must also ensure that, when cornering, the inner front wheel - which has to travel around a tighter curve than the outer one - becomes more sharply angled. If the steering system gets worn or out of alignment, the tyres will wear out much faster. See suspension system for more details on caster and camber angles.

Most modern cars are fitted with a hydraulic pump to increase the force applied into the steering mechanism and onto the wheels. The hydraulic pumps system reduces the effort that is required to turn the steering wheel.

Car Exhaust System

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The exhaust system is the piping and devices that the burnt gases from the engine travel through before discharging into fresh air. Depending on the system design, the exhaust gas will flow through the following:
• Cylinder head and exhaust manifold on the engine
• A turbocharger (hyperlink) to increase engine power.
• A catalytic converter to reduce air pollution.
• A silencer/muffler (USA) to reduce noise.

An exhaust pipe is designed to carry hot, toxic and noxious gases (including carbon monoxide and oxides of nitrogen) away from the occupants of the car and dilute them into the general atmosphere. The pipe must be heat-resistant, and it must be kept away from anything that can burn or be damaged by heat. For an internal combustion engine the exhaust system has to be "tuned" to prevent the shock waves from colliding. Most countries have regulations setting the limits on gas concentrations in the final exhaust.

Turbocharger: recovers energy from the exhaust gas, to drive a small gas turbine (‘turbo’), coupled to a gas compressor, to boost the pressure of the air going into the engine and improve its power and efficiency.
Catalytic converter: Contains a fine honeycomb mesh, with a large surface area, plated with platinum/palladium/rhodium that converts some of the poisonous exhaust gases into less harmful gases e.g. NO2 into NO,
Silencer/Muffler: a box with sound-absorbing material and baffles to reduce the noise of the final exhaust to atmosphere.
Oxygen (O2) sensors: in modern cars, by monitoring the exhaust gases, the fuel injection system can be finely tuned to optimise combustion in the engine and to minimise harmful gases in the exhaust.

Car Aircon System

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The air conditioning system operates similarly to a refrigerator, using a compressor and a refrigerant gas to remove heat from the air inside the car and release it outside the vehicle. The system has six main components:
· The refrigerant is the gas/liquid that transports the heat and also carries the oil for lubricating the compressor and expansion valve. Common refrigerants used in vehicles are R1234yf, R134a and R12. Some are being phased out for environmental reasons (global warming).
· The compressor draws low-pressure refrigerant gas from the cold evaporator, compresses it and pumps it to the outside condenser radiator. The compressor is driven by a belt off the car’s engine. The compressor starts and stops using an electro-magnetic clutch to engage/disengage the compressor.
· The condenser is the outside radiator where the hot refrigerant gas cools down and condenses back to a liquid.
· The expansion valve (or orifice tube) controls/restricts the flow of the refrigerant liquid from the high-pressure condenser back to the low-pressure evaporator, according to the temperature setting. This is where the refrigerant cools down.

· The evaporator is the cold radiator inside the car that cools the air blown across it by a fan – either fresh air from outside or recirculated air. Here the refrigerant absorbs heat and boils back to a gas. The suction of the compressor creates low pressure.

· The receiver dryer or accumulator is a small storage vessel that contains a desiccant substance to remove any moisture from the refrigerant.

When you start the ‘air-con’ system, the compressor causes low pressure in the evaporator, making it cold. The compressor sends the hot gas to the condenser radiator, which is generally in front of your vehicle’s radiator. The heat is released outside the of the car, and the refrigerant condenses from a gas back to liquid, which then passes through the expansion valve back to the evaporator. This is a continuous cycle.

For heating the air inside the car, there is another radiator that uses hot water from the engine’s cooling system. The control panel in the vehicle allows you to choose the system and set the temperatures for the current conditions. In modern cars, this is highly automated.