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An exhaust brake is a means of slowing a diesel engine by closing off the exhaust path from the engine, causing the exhaust gases 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.
Exhaust brakes are manufactured by many companies, including competitors Pacbrake and Jacobs. The brakes vary in design, but essentially operate as described above. More advanced exhaust brakes have exhaust pressure modulation (EPM) that controls the back pressure which in turn improves the braking performance across a range of engine speeds.
[1] An exhaust brake is a device that essentially creates a major restriction in the exhaust system, and creates substantial exhaust back pressure to retard engine speed and offer some supplemental braking. In most cases, an exhaust brake is so effective that it can slow a heavily-loaded vehicle on a downgrade without ever applying the vehicle’s service brakes
Performance
Some innovations increase the exhaust back-pressure by various means, leading to more torque at the flywheel, and therefore more braking power. Braking effectiveness is measured in units of power and is about 60 to 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). See also Jake brake.
Legal implications
Compression brakes, a form of engine brakes, produce excess 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. However, combining exhaust brakes and compression braking increases their effectiveness while significantly cutting back on noise pollution.
Numerous cities, municipalities, states, and provinces ban the use of unmuffled compression brakes.
Images
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Variable exhaust brake -
Exhaust brake & turbo assembly -
Exhaust brake shutter assembly
References
- ^ An exhaust brake is a device that essentially creates a major restriction in the exhaust system, and creates substantial exhaust back pressure to retard engine speed and offer some supplemental braking. In most cases, an exhaust brake is so effective that it can slow a heavily-loaded vehicle on a downgrade without ever applying the vehicle’s service brakes