Fluid handling – Line condition change responsive valves – Direct response valves
Patent
1993-05-12
1995-03-07
Rivell, John
Fluid handling
Line condition change responsive valves
Direct response valves
137522, 137527, 123323, 188273, F16K 2102, F02D 906
Patent
active
053949013
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an exhaust pressure modulation valve, and in particular to a valve for the exhaust system of a diesel engined vehicle.
Devices known as `exhaust brakes` can be fitted into the vehicle exhaust system and which, by generating a back pressure, can assist the vehicle in braking. Similar devices, termed `warm-up` valves, can also assist in cab heating and in reducing the emission of unburnt hydrocarbons by reducing the time for the engine to reach normal operating temperature.
In general the greater the back pressure generated by an exhaust brake, the more effective the braking effect becomes. But the level of back pressure generated (typically 2-8 bar) must not exceed the maximum design back pressure of the engine, which is limited, for example, by the load of the engine exhaust valve springs.
To limit the back pressure, the exhaust brake, normally a butterfly valve or a sliding gate, must either be locked into a position which is almost but not quite closed, allowing some exhaust gas to escape around the edge, or have one or more bleed passages formed in or around the butterfly or sliding gate. It is usual in practice to drill a hole or holes, and allow the butterfly or gate to sit in a fully closed position. The leakage rate is determined by the size and number of bleed passages and is dictated by the maximum allowable back pressure when the engine is running at the highest speed, and the flow of exhaust gas through the exhaust brake is thus at its maximum. Typically the bleed passages may total 200 mm.sup.2 for a butterfly diameter of 100 mm, about 2.5% of total butterfly area.
It follows that at lower engine speeds, especially in the normal driving range, the bleed holes apertures are larger than is necessary to reach the maximum back pressure at these lower speeds. Accordingly such exhaust brakes are rather ineffective at moderate gas flow rates because the back pressure generated is much less than the maximum permissible.
Warm-up valves are desirable because the time for the engine to reach operating temperature is substantially reduced, typically from 80 to 40 minutes--this leads to a substantial reduction in the emission of unburnt hydrocarbons and a considerable improvement in fuel economy.
The design requirements of a warm-up valve, when used to reduce the time for the engine to reach normal temperature, are not however the same as those applicable to exhaust brakes. In general only a very small bleed passage is required, typically not more than 5 mm in diameter for a butterfly diameter of 100 mm, because the engine is running at tickover speed, and the vehicle is stationary; back pressure generated is about in the range 0.5-2.0 bar, depending on the engine application. In a typical application, the back pressure generated by a warm-up valve will be only about 25% of the maximum back pressure generated during operation of an exhaust brake. A conventional exhaust brake would thus be useless as an aid to reducing engine warm-up time because the bleed apertures are too large to generate significant back pressure at these low engine speeds and gas flow rates.
Warm-up valves may be driver operated, to minimise the time for the cab heater to begin to work, or may be operated automatically in response to emission control apparatus, to reduce the quantity of unburnt hydrocarbons exhausted whilst the engine is warming up.
A particular danger with warm-up valves is that the driver may drive off with the warm-up valve closed; because the bleed passage is very small, the back pressure generated may quickly exceed the design limit of the engine, and engine damage may follow.
The present invention seeks to provide an exhaust pressure modulation valve, which combines the functions of an exhaust brake and warm-up valve and has a single butterfly to close the exhaust tract.
According to the present invention, there is provided an exhaust pressure modulation valve comprising a body having an inlet, an outlet, and a passageway between said inlet and outlet, a butterfly pivotable in the body to
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Baines Robert G.
Thompson Derek
Rivell John
WABCO Automotive (UK) Limited
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