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The traditional exhaust brake device is a butterfly valve switch method to close the exhaust pipe, so that the piston in the exhaust stroke by the gas back pressure to prevent the engine running and produce a braking effect, to achieve the purpose of controlling the speed of the exhaust Valve braking is based on a conventional butterfly valve brake.
When the butterfly throttle valve is closed, the diesel engine works like a compressor under the gravity drag of the car. The exhaust pressure in the exhaust pipe may be increased enough that after the intake stroke, the exhaust valve of the cylinder near the bottom dead center of the piston is opened by the pressure wave generated by the exhaust gas pushed out by the piston of the adjacent cylinder. It has been experimentally verified that this phenomenon will occur in all current brake mechanisms of the butterfly valve. The exhaust valve braking device (EVB) is the phenomenon that the exhaust valve is automatically opened by the pressure wave during the braking process, and the evacuation valve The valve remains open during engine braking to increase engine braking efficiency.
When the exhaust valve is opened by pressure waves, the exhaust valve brake mechanism prevents the opened exhaust valve from closing (holding about 1-2 mm of travel). In this way, part of the compressed air leaks out of the cylinder during the compression stroke. Even after the piston has reached top dead center, the exhaust valve is still open. In this way, the compressed air expands into the exhaust pipe through the gap of the exhaust valve, so that the speed of the piston that moves downward during the expansion stroke is greatly reduced, so that the compression work is prevented from driving the engine again. At the beginning of the exhaust stroke, the exhaust valve is fully opened by the movement of the rocker arm, the oil discharge hole on the rocker arm of the exhaust valve is opened, the lubricant oil is ejected, and the slider assembly returns to the position under the action of the return spring. The above process is repeated in cycles, thereby increasing the braking power of the diesel engine. In principle, the engine exhaust brake power is generally less than the engine can send power. Taking a 200kw (about 270 horsepower) engine as an example, the maximum power is 200kw; the exhaust braking power is only 20kw at an engine speed of 1000rpm, only 60kw at 2000rpm, and 2800rpm It reaches 120kw.
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