Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
2000-11-27
2002-08-20
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C060S602000, C060S605200, C415S160000
Reexamination Certificate
active
06435167
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
This application claims the priority of 199 56 896.0, filed in Germany, Nov. 26, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an exhaust gas turbocharger and a radial compressor whose vane wheel drives air through guide vanes into a diffuser channel.
Exhaust gas turbochargers are used both on autoignition internal combustion piston engines with quality control as well as on external ignition internal combustion piston engines with quality control in order to increase power or improve exhaust quality by improving cylinder charging with compressed air and increasing the expansion energy of the combustion gases.
Exhaust gas turbochargers are proven auxiliary units of simple construction and long useful life. They include as a rule an exhaust gas turbine with a constant blade geometry driving a rotary compressor with a radial blade geometry. While the exhaust gas turbine cooperates well as a flow machine with the rotary compressor, the two units combined as a turbocharger have different operating characteristics from those of an internal combustion piston engine and can be adapted only with difficulty to the needs of the internal combustion piston engine. If the exhaust gas turbocharger is designed for the nominal point of the internal combustion piston engine, the pumping pressure in the lower rotary speed range is insufficient on account of the relatively large exhaust gas turbine. If, however, the exhaust gas turbocharger is designed for a partial-load point of the internal combustion piston engine, the turbine is too small at the nominal power point. This results in considerable losses of efficiency.
It is known to drive the rotary compressor mechanically in the lower speed range of the internal combustion piston engine, in addition to the exhaust gas turbine, by an electric motor or a gas turbine, or to apply the combustion gases of a combustion chamber additionally to the exhaust gas turbine. These solutions call for a great amount of construction and control.
Exhaust gas turbochargers with a variable blade geometry are also known. European Patent Document EP 0 598 174 A1 describes an exhaust gas turbocharger for an internal combustion engine, whose exhaust gas turbine has a rotor which is surrounded by a guiding means with a volute. The latter has an annular nozzle-like mouth area in which a variable baffle grid with guiding vanes is disposed. With the internal combustion engine running at full load, the passages through the baffle grid are partially opened, while for the engine running at a diminishing partial load the passages through the baffle grid are increasingly opened by rotating a portion of the baffle. If the turbine baffle grid is closed with the engine in the partial load range the speed of the exhaust gas turbine can be maintained at a high level despite the reduced mass flow. The performance graph available on the side of the exhaust gas turbine of the turbocharger is broadened through the variation of the baffle grid. Still, the performance graph of the turbocompressor with constant vane geometry remains basically unchanged.
An exhaust gas turbine for an internal combustion engine is disclosed in German Patent Document DE 196 51 498 C1. The turbine housing is provided with an axial slide which has a baffle grid with guiding vanes and is carried in an annular gap between the turbine casing and an inner guide. A radial annular space is provided to connect the flow between a rotor of the turbine and the turbine casing. In a retracted position, in which the radial annular space is free of the baffle grid, the axial slide frees an outlet opening into an exhaust gas passage. The baffle grid serves to extend the exhaust gas turbine performance graph to lower mass flows.
Exhaust gas turbochargers with a variable blade geometry are also known. European Patent Document EP 0 598 174 describes an exhaust turbocharger for an internal combustion engine, whose exhaust turbine has a runner wheel which is surrounded by a guiding apparatus with a spiral-shaped guiding passage which is swept at least partially diagonally. This passage has an annular-shaped mouth area in which a variable guide grid with guide blades is disposed. When the internal combustion engine is at full load the cross sections of the guide grid are partially opened, while for a diminishing partial-load operation of the internal combustion engine the cross sections of the guide grid are increasingly opened by the rotation of a portion of the guide grid. If the turbine guide grid is closed in the partial-load range of the internal combustion engine the speed of the exhaust turbine can be kept at a high level in spite of the reduced mass flow. The available characteristic chart on the side of the exhaust turbine of the turbocharger is broadened through the guide grid variation. of course, the characteristic chart of the radial compressor of constant blade geometry remains basically unchanged.
An exhaust gas turbine for an internal combustion engine has been disclosed in German Patent Document DE 31 51 414 A1. A radial annular space is provided to connect the flow between a spiral channel in the turbine casing and a runner wheel of the turbine. In the turbine casing a baffle grid with guide vanes is provided, which are axially displaceable by pistons against the force of a return spring and reach into the annular space across the direction of flow of the exhaust gas. The baffle grid is displaceable to two positions, namely to a first position in which it reaches through the annular space such that its inner faces lies against the inside wall of the annular space, and to a second position in which is retracts into an annular chamber adjoining the annular space and its inner lateral faces form flush portions of the inner wall of the annular space. The baffle grid serves to extend the exhaust gas turbine characteristic to lower mass flows.
To be able to make the best use of the advantage on the side of the exhaust gas turbine it is necessary to go all the way to the limits of the performance graph of the rotary compressor, which are determined by the pumping limit and the plugging limit of the compressor. The term, “pumping,” in rotary compressors, is understood to be a back flow of the compressed gaseous medium from a reserve volume on the discharge end of the rotary compressor when the mass flow through the rotary compressor decreases to the extent that the rotary compressor can no longer produce the necessary discharge pressure against the reserve pressure. If the pressure on the discharge end of the rotary compressor has dropped due to the back flow to the extent that the rotary compressor again delivers a corresponding discharge pressure, the pumping in the pumping direction resumes until the reservoir has charged up again and the pumping process is repeated. The “pumping” leads to great mechanical stresses on the exhaust gas turbocharger and entails a noise bothersome to the driver.
What impresses the driver of a vehicle more than the maximum torque and power is the spontaneity of the reaction to gas pedal movement and—especially in the case of supercharged internal combustion engines—the build-up of torque when accelerating from low engine rpm. Since the speed of torque build-up depends on how fast the charging pressure builds up, exhaust gas turbochargers with a variable blade geometry can be used to advantage on the exhaust gas turbine side by largely closing the blades when an acceleration from the partial load range begins so that the exhaust gas turbine accelerates very greatly.
Although a sufficient distance from the pumping limit of the rotary compressor is maintained when idling, pumping can occur briefly when driving. This danger exists especially when the driver of the vehicle, when driving with a high compressor pressure ratio, abruptly backs off the gas pedal and the speed of the internal combustion engine rapidly decreases, e.g., in the case of vehicles with hydrodynamic clutches or torque converte
Finger Helmut
Fledersbacher Peter
Hertweck Gernot
Sumser Siegfried
Wirbeleit Friedrich
Crowell & Moring LLP
Daimler-Chrysler AG
Wolfe Willis R.
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