Exhaust brake

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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.

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

What is an Exhaust Brake? And its Performance[edit]

With the development of highways, logistics and the pace of life, weight and velocity of vehicles has become more and larger, which has reduced the safety of driving an auto-mobile. The braking load of vehicles increases quickly so that the primary brake system is easily overloaded and can be damaged by overheating, possibly resulting in brake failure. In addition, for vehicles in the mountains, hills and city, the driver will need to use the main braking system frequently for security reasons, which leads to a reduction of average speed, which affects the operating cost. The road hazards related to heavy goods vehicles are partly due to inefficient brake systems, or the failure of brakes. The commonly used braking system in these heavy duty trucks is the "Jake" brake used on diesel big rigs and dump trucks. A Jake brake works by using hydraulic pressure to momentarily open the exhaust valve at the end of the compression stroke, venting off the compressed air into the exhaust system. That’s where all the noise comes from. The braking of a Jake brake occurs because of the pumping loss compressing the air, and then eliminating the compressed air “rebound” on the power stroke. Additionally, there’s a pumping loss as the piston descends on the power stroke with both valves closed and no combustion [1].

An exhaust brake is a valve which essentially creates a back-pressure in the exhaust system, which applies enough force onto the engine's pistons to slow the engine. 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. Under these conditions, the exhaust flow from the cylinders is bottlenecked and rapidly builds pressure in the exhaust system upstream from the exhaust brake. Depending on engine speed, this pressure can easily reach up to 60 PSI maximum working pressure. Maximum working pressure is limited as part of the design of an exhaust brake. In this example, that same 60 PSI also remains in the cylinder for the entire exhaust stroke (exhaust valve open) and exerts 60 PSI on the piston top to resist its upward movement. We can think of this as negative torque, slowing the engine for a braking effect. This might be even thought as just the opposite of the power stroke, and in effect, it is. Thus, simply restricting the exhaust flow can generate substantial braking. That’s what makes an exhaust brake so effective.

The report will first give an overview on the background of working of IC engines and define the reason of employing the Exhaust Brakes on the Diesel Engines. Next section of the report discuses about the material, components and measurement systems used in the fabrication of project model. Subsequent sections of the report will give detailed information regarding to the selection procedure and fabrication procedure of the model. The remainder of the report will focus on the performance testing and pressure measurements. Finally, the advantages, limitations and suggested modifications will be discussed with conclusion of the whole project study. [1][2]

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. also these concept of exhaust braking deals with optimization of engine exhaust gases to apply the brakes with the help of butterfly valve in the diesel and petrol engines

PEDAL-OPERATED BUTTERFLY VALVE: The butterfly valve made up of acrylic material made in the circular shape, having three peripheral circular cut on it. These circular cuts are given because it is not expected to block whole cross section of the exhaust pipe. If there were no holes, the engine would stop instead of slowing down. In the project, actual engine is not used but a blower; still this type of the valve is used to correlate it with actual arrangement.

The butterfly valve is actuated through hydraulic linkages in actual working model. This consists of a hydraulic pressure pump which is connected to the butterfly valve. This pump controls the operation of butterfly valve in following manner: When brakes are applied by the driver, the cylinder reduces its pressure so that valve gets closed and restricts the path of exhaust gases. In this position butterfly valve remains perpendicular to the flow of exhaust gases and thus creates back pressure on the engine. This butterfly valve has some holes (may be one to three) into it so that there would not be complete blockage in the exhaust pipe. This assures the avoidance of abnormal damage due to high pressure.

Now when brakes are removed by the driver, cylinder generates pressure into it so that butterfly valve gets opened and allows the exhaust gases to flow into exhaust pipe. In this position butterfly valve remains parallel to the path of exhaust gases and thus releases the pressure on the engine and again speed increases.

In the project, there is not such cylinder pressure mechanism but a simple linkage. To create a tension to apply brakes, a pedal brake is connected to the elastic rubber so that there will be pressure force to apply and release butterfly valve like in actual arrangement.

Legal implications[edit]

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.

  • future modification

1) Turbocharged Exhaust Brakes Turbocharger is commonly used to improve power and reduce fuel consumption ratio. Study on effect of turbocharger on exhaust brake for diesel engines had practical significance. When butterfly valve is closed, in the exhaust manifold there is no exhaust emissions so the turbine blades of the turbocharger cannot work, but because turbine blades has the blocking effect, and this effect can make lower inlet pressure of the diesel engine than it with no turbocharger, so air intake into the engine reduces which not only reduces the fuel consumption but also speed of the engine.

2) Two stage pressure control Increase in the back pressure with the help butterfly valve can also be achieved by operating in two stages i.e. two valves can be used. This also ensures the efficient working of valve and long its long life by avoiding valve failure. Such type of arrangement is found to be very useful in case of heavy duty trucks. Because to create sufficient back pressure to slow down the engine speed, it requires large force from the valve which is possible by two valves arrangement.

3) ARIS Actuator Valve Usually pneumatic or hydraulic actuators are used to operate the butterfly valve. But with the large force of exhaust such type of actuators turns to be inefficient. Hence ARIS type of valve actuator which is widely used in the industries provides effective valve operating force.

Images[edit]

References[edit]

  • Ma, J., Chen, Y., Yu, Q., Guo, R.: Distance control for automotive’s stopping with retarder.
*China Journal of Highway and Transport 16(1), 108–112 (2003) (in Chinese)
*Chengye Liu1 and Jianming Shen: Effect of Turbocharging on Exhaust Brake

Performance in an Automobile (2003)

*C.J. Baker: www.bankspower.com/techarticles/show/17-how-an-exhaust-brake-works