Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Reexamination Certificate
2000-06-14
2001-06-26
Nguyen, Hoang (Department: 3748)
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
Reexamination Certificate
active
06250079
ABSTRACT:
The present invention relates to turbo-charged internal combustion engine with at least four cylinders and an exhaust manifold having an exhaust conduit from each cylinder, the exhaust conduits being combined into two groups, each of said groups opening into an individual inlet to one of two separate channels, each of said channels opening into a turbine housing.
The technology of collecting the exhaust conduits in a multi-cylinder turbo engine into two groups and maintaining the exhaust flow separation between the two groups up to the turbine rotor has been utilized in turbo-charged diesel engines for quite some time and, lately, has also been applied in four-cylinder tubo-charged gasoline engines, using twin-entry type exhaust turbines having a turbine housing with a separate inlet for each of two separate channels into the turbine housing chamber in which the turbine rotor rotates.
By combining the exhaust conduits from the first and fourth cylinders and from the second and third cylinders, respectively, the exhaust side of the engine is divided into two cylinder groups, which provides optimum gas exchange. This separation has the result that shortcircuiting compression waves on the exhaust side cannot disturb the gas exchange, since cylinders connected to the same turbine inlet lie 360 crankshaft degrees from each other. A normal exhaust cam in a number of four-cylinder gasoline engines available on the market has a cam profile which keeps the exhaust valve open for 240 crankshaft degrees and therefore the pressure wave from one cylinder cannot reach the adjacent cylinder. Another advantage and a result thereof is that the pressure wave can only go through the turbine. This results in higher available turbine power at lower r.p.m and thus also to higher charge pressure and higher engine torque at low r.p.m. than when using a common single-entry turbine.
This separation has, however, proved to result in decreased performance at high r.p.m. The pressure ratio over a twin-entry turbine varies more than over a single-entry turbine during one engine work cycle. The pressure ratio and the velocity at which the exhaust jet strikes the turbine rotor are mathematically related and if one increases, then the other increases as well. The ratio between the peripheral velocity of the turbine rotor and the velocity of the exhaust jet determines the turbine efficiency, and if the pressure ratio varies too much, then the efficiency curve will also vary greatly, thus reducing the mean efficiency. The exhaust counter-pressure will when increase for a given charge pressure and the extractable power will decrease, since the pump work increases. The higher pressures which the separation provides during the exhaust phase also contribute to increasing the pump work.
The purpose of the present invention is to achieve a turbo-charged internal combustion engine of the type described by way of introduction which has the good low r.p.m. properties of the twin-entry turbine engine but lacks its disadvantageous high r.p.m. properties.
This is achieved according to the invention by virtue of the fact that the channels are provided with a valve arrangement, comprising a valve element, which can be set in a first position, in which the exhaust flows from the two conduit groups are each led separately into the interior of its turbine housing, and a second position, in which the exhaust flows from the two conduit groups are permitted to mix with each other prior to entry into the interior of the turbine housing.
In the second position, the separation of the exhaust flow into two separate flows is broken by a shortcircuit between the channels in the interior of the turbine housing, so that a single mixed exhaust jet from the two manifold groups strikes the turbine rotor. By shortcircuiting at high r.p.m., the poor high r.p.m. properties of the twin-entry turbine are eliminated and the engine will then work at high r.p.m. as a single-entry turbine engine.
In a further development of the engine according to the invention, the valve arrangement has an outlet to a shunt opening into an exhaust conduit on the downstream side of the turbine housing, and the valve element can be set to a third position, in which the exhausts from the two exhaust conduits can flow through the shunt to the exhaust conduit on the downstream side of the turbine housing by-passing the turbine housing. This provides a valve arrangement which is both a shortcircuit valve and a waste-gate valve.
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Giselmo Kent
Martinsson Ingemar
Zander Lennarth
AB Volvo
Nguyen Hoang
Young & Thompson
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