مصر موتورز مجتمع السيارات - Exhaust brakes!!!!!!!!!!!!!!!

Exhaust brakes

http://moodle.student.cnwl.ac.uk/moo...haustbrake.jpg
Heavy goods vehicles and any car can often require increased braking, in situations where friction brakes could overheat and fail. This is achieved by using an exhaust brake.

An exhaust brake works by restricting the flow of exhaust gases through the engine.

It achieves this by closing a butterfly valve located in the exhaust manifold. This maintains high pressures in the exhaust manifold, and the engine cylinders, which in turn, acts as a brake against the engine rotating. This then slows the road wheels through the transmission, or power train.

Other heavy goods vehicles use an engine brake that operates by altering valve timing, and stopping fuel being injected into the engine.

Since diesel engines lack an intake manifold, there is no intake vacuum when the engine is not fueling. The intake vacuum create the slowing effect felt in gasoline engines when they are going down a hill with the foot off the gas. Many different strategies are used on diesels, the least expensive (and also one of the least powerful) of which is the exhaust brake.

Operation

Exhaust brakes (otherwise known as exhaust retarders) are manufactured by many different companies, including competitors Pacbrake and Jacobs. The brakes vary in design, but essentially operate by closing off the exhaust path from the engine, causing the exhaust gasses to be compressed in the exhaust manifold, and in the cylinder. Since the exhaust is being compressed, and there is no fuel being applied, the engine works backwards, slowing down the vehicle. The amount of negative torque generated is usually directly proportional to the back pressure of the engine.

Performance

Some new innovations increase the exhaust back-pressure by various means, leading to more torque at the flywheel, and therefore more braking power. Braking power is generally measured in horsepower, and hovers around 60%-80% of the engine's maximum power output. More performance is usually easily had by down shifting the vehicle (increasing the leverage , or gear ratio of the engine over the wheels).

Related Items

Exhaust brakes should not be confused with engine brake, which work by holding the exhaust valves closed, although the basic principle of operation is similar.
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Legal implications

Compression braking (also jake brake), a form of engine brake, produces extreme amounts of noise pollution in comparison to exhaust brakes. For this reason, some vehicle original equipment manufacturers prefer to use exhaust brakes, even when the performance is not as good, just because of the noise issues. This is particularly common for delivery vehicles.

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http://www.jakebrake.com/images/g_exhaust_diagram.jpg

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it can save your life after your

brake failure!!!