Method and a device for engine braking a four stroke internal co

Details Method and a device for engine braking a four stroke internal co Method and a device for engine braking a four stroke internal co

1991-09-13

1992-09-15

Argenbright, Tony M.

Internal-combustion engines

Engine speed regulator

Responsive to deceleration mode

123323, F01L 1306, F02D 1304

Patent

active

051468905

DESCRIPTION:

BRIEF SUMMARY
The engine of a vehicle is often used as an auxiliary brake to retard vehicle speed. This particularly applies to heavy vehicles, such as trucks and buses. With regard to heavy vehicles of this category, developments over recent years have resulted in engines of much greater power with unchanged cylinder volume. As a result, the average speed at which such vehicles are driven uphill has increased considerably, meaning that the availability of greater braking power when driving downhill is desirable. Normally, some form of throttle valve is incorporated in the exhaust system with the intention of achieving improved engine braking power. This power, however, is relatively low and often less than half the driving power of the engine.
Furthermore, the resistance of such heavy vehicles to driving has decreased over recent years, meaning that the wheel brakes of the vehicles are subjected to greater loads. When driving in hilly terrain, the wheel brakes should be used as little as possible, primarily for safety reasons. The average speed of the vehicle in hilly terrain is therefore greatly influenced by the available engine braking power, which increases the requirement for a more effective engine brake that will also be capable of reducing wear and tear on the wheel brakes and thereby improve running economy.
A variety of suggestions have, therefore, been made regarding methods and apparatuses for increasing the engine braking power of four stroke internal combustion engines.
In EP-A-193142 there is described a method and an apparatus, where a separate valve is used to establish connection between the combustion chamber and the exhaust system. During engine braking operation this valve is constantly open.
According to GB-A-2162580 engine braking power is increased by a mechanism which prevents the exhaust valve to close completely during engine braking operation. This means that the exhaust valve is constantly open during engine braking operation. A similar apparatus is shown in EP-A-269605.
CH-A-118905 describes an engine with a moveable camshaft. During engine braking operation the inlet valve is constantly closed, while the exhaust valve is opened shortly before the piston reaches its top-dead-centre position, and this cycle is repeated for each revolution of the crank shaft. Thus, during engine braking operation this engine works in a sort of two stroke mode.
The object of the present invention is to provide a method which will further improve engine braking power, and to an arrangement for carrying out the method.
The advantages primarily afforded by the method and the arrangement according to the invention reside in the possibility of increasing compression work during the compression stroke, by placing the cylinder in communication with the exhaust system during the first part of the compression stroke and optionally also during the latter part of the inlet stroke. This will result in a flow of gas into the cylinder from the exhaust system, where overpressure prevails due to the presence of the throttle device in the exhaust system. Consequently, the pressure in the cylinder is increased and internal charging is obtained. Communication between the cylinder and the exhaust system is also reestablished during the latter part of the compression stroke, wherewith gas will flow out of the cylinder and therewith lower the pressure therein, so that the following expansion stroke will produce insignificant or even negative expansion work. The undesirable volume-changing work is decreased during the inlet stroke, by closing communication between the exhaust system and the cylinder as soon as possible after the piston has passed its top-dead-centre position.
The invention will now be described in more detail with reference to the accompanying drawings, in which
FIG. 1 is a schematic, sectional view of a cylinder forming part of an internal combustion engine provided with an inventive arrangement;
FIG. 2 is a diagrammatic illustration of the lifting height of the exhaust valve of an engine according to FIG. 1 in no

REFERENCES:
patent: 4440126 (1984-04-01), Abermeth et al.
patent: 4981119 (1991-01-01), Neitz et al.

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