Exhaust brake
Encyclopedia
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.
Since diesel engines lack a throttle valve on the intake manifold, there is no intake vacuum when the engine is not using fuel. The intake vacuum creates the drag effect felt in gasoline engines when going down a hill with the throttle closed.
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.
age, or gear ratio
of the engine over the wheels).
See also Jake brake
.
, a form of engine brakes, produce excess amounts of noise pollution
in comparison to exhaust brakes. For this reason, some vehicle original equipment manufacturer
s prefer to use exhaust brakes, even when the performance is not as good, due to the noise issues. 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.
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
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.
Since diesel engines lack a throttle valve on the intake manifold, there is no intake vacuum when the engine is not using fuel. The intake vacuum creates the drag effect felt in gasoline engines when going down a hill with the throttle closed.
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.
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 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 leverLever
In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...
age, or gear ratio
Gear ratio
The gear ratio of a gear train is the ratio of the angular velocity of the input gear to the angular velocity of the output gear, also known as the speed ratio of the gear train. The gear ratio can be computed directly from the numbers of teeth of the various gears that engage to form the gear...
of the engine over the wheels).
See also Jake brake
Jake brake
A compression release engine brake, frequently called a Jake brake or Jacobs brake, is an engine braking mechanism installed on some diesel engines...
.
Legal implications
Compression brakesJake brake
A compression release engine brake, frequently called a Jake brake or Jacobs brake, is an engine braking mechanism installed on some diesel engines...
, a form of engine brakes, produce excess amounts of noise pollution
Noise pollution
Noise pollution is excessive, displeasing human, animal or machine-created environmental noise that disrupts the activity or balance of human or animal life...
in comparison to exhaust brakes. For this reason, some vehicle original equipment manufacturer
Original Equipment Manufacturer
An original equipment manufacturer, or OEM, manufactures products or components that are purchased by a company and retailed under that purchasing company's brand name. OEM refers to the company that originally manufactured the product. When referring to automotive parts, OEM designates a...
s prefer to use exhaust brakes, even when the performance is not as good, due to the noise issues. 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.