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Exhaust Brake Systems
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.docx   About Exhaust Brake Systems.docx (Size: 13.77 KB / Downloads: 216)
About Exhaust Brake Systems
Diesel engines, because of the way they operate, do not create vacuum pressure once the throttle is released in order to aid in slowing the vehicle down. For this reason, manufacturers have implemented the use of an exhaust brake, which saves wear and tear on the actual brakes, and makes towing heavy loads a bit safer.
Function
The function of an exhaust brake is to aid in slowing down vehicles with diesel engines without the use of the wheel brakes. Some of these brakes work automatically whenever the driver takes his foot off the accelerator, and some are manually controlled via a switch, or both. Different settings allow the driver to control how the brake is applied.
Features
Exhaust brakes feature a "doorway" which closes when the vehicle is rolling and the accelerator is not being used. When in the closed position, these brakes drastically restrict the flow of exhaust gasses, thus increasing the back pressure inside the engine, which ultimately slows the vehicle down. Most also feature a switch or other control inside the cab, which can be set to either activate the second the driver is off the accelerator pedal, or be activated manually in downhill towing situations only.
Benefits
The biggest benefit of the exhaust brake is that they add slowing power to the regular brakes, preventing them from heating up and glazing, which dramatically decreases their effectiveness. When towing heavy loads, these brakes can save lives. These brakes do not damage the engines, and therefore they can be used over and over safely.
Considerations
If you have a pickup truck that regularly sees heavy payload duty or fifth-wheel trailer action, an exhaust brake can greatly help with stopping power. Tractor-trailer trucks have used similar braking systems for years, and now it is being offered to the general public by companies such as Jacobs and Banks.
Warning
While an exhaust brake can significantly increase slowing and stopping duties, it is by no means a primary braking system. Also, check local ordinances regarding these brakes, because some can create substantial noise and may be illegal. An exhaust brake is not the same as the Jake Brakes used on semi-trucks, but is similar in idea. Some exhaust brakes may lack power at lower RPMs as well, and are mostly used in full-speed applications.
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#2
Presented by:
SHRIGOPAL
DASHARATH SOLANKI
BHANUPRATAP SINGH
HEMRAJ CHOUDHARY
TARESH JATAV
PARIKSHIT SINGH


.docx   ExhaustBraking.docx (Size: 682.68 KB / Downloads: 201)
Diesel Engine Exhaust Braking System
Introduction – An exhaust brake works by restricting the flow of exhaust gases through the engine
Heavy goods vehicles can often require increased braking, in situations where friction brakes could overheat and fail. This is achieved by using an exhaust brake.
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.
Description- This invention relates to an exhaust braking system for an internal combustion engine and in particular, although not exclusively, to such a braking system for a diesel engine.
It is well known that an exhaust braking system for an internal combusiton engine effects secondary braking working in tandem with the normal friction brakes of a large commercial vehicle. A known exhaust brake comprises a housing with a through passage which is arranged to be closed by a blade when braking is required. The exhaust brake generates a back pressure within the exhaust passage which lifts the exhaust valve from its seating and imparts a back pressure within the cylinder on the piston crown to cause retardation or braking of the rotational speed of the engine and subsequently the vehicle. The amount of back pressure is predominantly dependent upon the force exerted by the engine valve spring, since the back pressure must be sufficient to lift the valve from its seat. It will be appreciated that on the engine induction stroke the piston cylinder is vented to the atmophere through the induction manifold by opening the induction valve so that the exhaust gas pressure within the cylinder is released.
Engine manufacturer's have become concerned that when exhaust brakes are used with internal combustion engines the back pressure created by the exhaust brake when lifting the exhaust valves from the valve seats will create a situation in which a piston upon its return to top dead centre will strike the head of the exhaust valve. To avoid this happening, it is common practice for a hole of a predetermined size to be provided through the blade of the exhaust brake so as to limit the back pressure in the exhaust system. It is desireable to increase the efficiency of the exhaust brake so as to produce greater retardational braking of the engine and one way of achieving such an improvement is to increase the back pressure created by the exhaust brake. However, an increase in the back pressure will only serve to hold the exhaust valve open increasing the likelihood of the piston striking the exhaust valve.
Several ways have been tried to overcome this problem, one of which is to increase the strength of the valve springs, but this is often undesirable since the valve operating mechanisms are then subjected to undue wear.
Therefore, there is a need to provide a braking system for an internal combustion engine in which the above disadvantages are overcome.
According to one aspect of the present invention there is provided an exhaust braking system for an internal combustion engine having an inlet valve and an exhaust valve, the system comprising an induction valve arranged to be connected in an induction passage to the inlet valve, an exhaust brake arranged to be connected in an exhaust system connected with an exhaust valve, actuator means connected in a fluid circuit with the induction valve and exhaust brake for operating the induction valve and exhaust brake to close the induction passage and exhaust system when the rotational speed of the engine is to be retarded, timing means connected with the induction valve and exhaust brake for ensuring the exhaust brake is closed no later than the closing of the induction valve, a non-return valve arranged to be connected in the induction passage between the induction valve and the inlet valve for facilitating an increase in pressure within a piston cylinder of the engine to increase the engine retardation, and pressure relief means arranged to be connected in the induction passage or exhaust system for controlling maximum pressure of the braking system.
The timing means preferably comprises a pair of tubes of differing internal diameters, the tube of larger internal diameter having one end thereof connectible to the exhaust brake, and the tube of smaller internal diameter having one end thereof connectible to the induction valve, the opposing ends of the tubes being connected to the actuator means.
The actuator means is preferably a manually operative foot valve which is conveniently connected with the brake pedal of a commercial road vehicle, for example. Alternatively, the valve can be operated independently or may be coupled to the accelerator pedal.
According to another aspect of the present invention there is provided a method of operating an exhaust brake system for an internal combustion engine having a inlet valve and exhaust valve, the method comprising actuating an induction valve arranged to be connected in an induction passage to the inlet valve, actuating an exhaust brake arranged to be connected in an exhaust system connected with the exhaust valve, operating acutator means connected in a fluid circuit with the induction valve and exhaust brake to initiate actuation of the induction valve and exhaust brake through the intermediary of timing means connected with the induction valve and exhaust brake for ensuring the exhaust brake is closed no later than the closing of the induction valve to close the induction passage and exhaust system when the rotational speed of the engine is to be retarded, introducing air into the induction passage through a non-return valve connected in the passage between the induction valve and the inlet valve to facilitate an increase in pressure within the piston cylinder of the engine to increase engine retardation, and controlling the maximum pressure of the braking system by venting the system through pressure relief means arranged to be connected in the induction passage or exhaust system.
In the drawing, there is illustrated a piston cylinder 1 in which a piston 2 is arranged to reciprocate in a known manner. An inlet valve 3 and exhaust valve 4 operable by the usual engine valve operating mechanism (not shown) against valve springs 5 and 6, control the induction of air and expulsion of exhaust gas to and from the piston cylinder respectively. An induction passage 7 is provided with a pneumatically controlled induction valve 8 which is connected in the induction passage and is operable to close the induction passage 7, thereby preventing the flow of air to the engine from air filter 9.
As the piston 2 begins to move upwardly on its next stroke, the exhaust valve 4 is forceably opened by the valve operating mechanism in the usual manner to facilitate expulsion of exhaust gas. During this period pressure increases in the exhaust system 10 and piston cylinder 1 as the the piston 2 compresses the gases within the piston cylinder 1 and exhaust system 10. Therefore, as the piston 2 moves upwardly on the exhaust stroke pressure equalisation occurs between the piston cylinder 1 and exhaust system 10. The force then acting on the inner surface of the head of the exhaust valve 4 is greater than the force acting on the opposite surface of the head of the exhaust valve, so that when the valve operating mechanism releases the exhaust valve, the valve will close under the influence of the valve spring 6 and the force differential between the two sides of the valve head.
One known low compression diesel engine operates with a normal internal compression of approximately 22 psi (151.7 KPa) and in utilising a known exhaust brake system, operates with a back pressure of 22 psi which is built up in the exhaust system and on the induction stroke of the engine, the gases at this pressure are transferred or vented to atmosphere through the air filter 9. Accordingly, the maximum pressure which can be used for retarding that engine is 22 psi which is governed by the strength of the valve springs used on the engine.
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