Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Reexamination Certificate
1999-11-02
2001-07-24
Denion, Thomas (Department: 3748)
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
C060S602000, C123S562000
Reexamination Certificate
active
06263673
ABSTRACT:
The invention relates to a method for operating a supercharged internal combustion engine and to a device for this purpose.
DE 43 10 148 A1 discloses a supercharged internal combustion engine with two exhaust-gas turbochargers arranged in parallel. Arranged in the charge-air line of a supercharger is a regulatable stop valve which is changed into the opening or the closing position depending on the operating state of the internal combustion engine. When the stop valve is in the closing position, the respective supercharger is cut off from the charge-air supply, whereas, in the opening position, both superchargers participate in the supply of charge air. Depending on the setting of the stop valve, an adjustable overall output of the two superchargers, with correspondingly different boost pressures, is generated.
The position of the stop valve is regulated as a function of the engine speed. In the lower speed range, the stop valve is in the closing position, and the only exhaust-gas turbocharger which operates is the one which is not cut off from the charge-air supply and which is designed as a small supercharger of low inertia. On account of the low inertia, the compressor of the smaller supercharger builds up a higher boost pressure in the lower speed range than would be possible in this speed range with of a larger compressor.
Beyond a medium speed, the stop valve is opened, and the second supercharger is cut in and takes over an increasing proportion of the supply of charge air.
The advantage of this arrangement is that the small exhaust-gas turbocharger can be designed optimally for low speeds. The situation where the larger supercharger enters the compressor pumping range at low speeds is avoided. By contrast, at higher speeds, the higher output of the larger supercharger can be utilized. Altogether, high overall efficiency is achieved thereby.
The problem on which the invention is based is to increase the operating reliability of supercharged internal combustion engines by means of simple measures.
SUMMARY OF THE INVENTION
Turbochargers are increasingly used not only in the fired operating mode, but also in the engine-braking mode, in which very high power values may be generated. In order, if a turbocharger fails, to avoid a sudden power drop, particularly in the engine-braking mode, and to prevent a dangerous situation, according to the innovation the exhaust-gas turbochargers are not operated simultaneously, but only individually, thereby considerably increasing the degree of safety against a supercharging failure. The two exhaust-gas turbochargers connected in parallel give the supercharged internal combustion engine a redundant design.
One exhaust-gas turbocharger advantageously performs the function of a main supercharger and the second exhaust-gas turbocharger the function of a reserve supercharger which is used only in emergencies or at regular intervals for a safety check or according to another predeterminable mode.
As the criterion for changing over between the turbochargers, a characteristic quantity characterizing the operation of the internal combustion engine is measured and is compared with a desired value. In the event of an inadmissible deviation, a control signal is generated in a regulating and control unit in order to actuate a change-over device, via which one of the superchargers can be cut off and the other supercharger cut in. A state variable of the internal combustion engine may be adopted as the characteristic quantity, for example the boost pressure, the charging speed of the currently activated supercharger, the mass air flow conveyed into the intake tract or the turbine inlet pressure; these state variables can be determined at low outlay by means of sensors and signal generators and can be compared with a predetermined or calculated desired value in the regulating and control unit.
The time may also be taken into account as a characteristic quantity, in that switching back and forth between the superchargers takes place after a predetermined timespan has elapsed. This may either be carried out for the purpose of cutting in the reserve supercharger for a short timespan, even during regular operation, without an emergency, in order to test its functioning capacity; it may also be expedient, however, to operate the two superchargers alternately, in order to achieve a uniform load on both superchargers and increase the overall lifetime of the apparatus; in this design, both superchargers are treated as being of equal rank and both superchargers preferably have an identical design.
Mixed operation is also possible, in which, basically, there is a change-over to the second supercharger in emergencies only, when a state-variable limit value is exceeded, but, to check functioning capacity, there is also normally a change-over to the reserve supercharger for a usually short time span during regular operation.
The method and the apparatus can be used both in the engine-braking mode and in the fired drive mode. In order to achieve high braking powers, preferably at least one turbine, in particular the turbine of the main supercharger, is equipped with variable turbine geometry for the variable setting of the effective turbine cross section; both turbines expediently have a variable turbine geometry.
In the engine-braking mode, the variable turbine geometry is changed into a build-up position with reduced turbine cross section in order to increase the exhaust-gas back pressure. The built-up exhaust gas flows with high momentum between the remaining flow ducts of the turbine geometry and impinges onto the turbine wheel which is driven and which transmits power to the compressor, with the result that the combustion air sucked in is raised to an increased boost pressure, so that an increased pressure prevails both on the inlet side and on the outlet side of the cylinders of the internal combustion engine. In the engine-braking mode, the piston has to perform compression work against the high excess pressure in the exhaust-gas tract during the compression and push-out stroke, thereby achieving a high braking action.
Malfunctions of the turbocharger currently used can be detected, for example, via a desired-value/actual-value comparison of the state variable considered or of a quantity derived from the state variable considered. If the change in time of the state variable, in particular the boost pressure, exceeds a limit value and/or the level of the state variable falls short of a lower limit, there is, with high probability, damage to the turbocharger. The actuation of the change-over device and the rapid change to the second turbocharger make it possible to avoid a power breakdown both in the fired mode and in the engine-braking mode. The second turbocharger remains in operation until repair measures are carried out on the first turbocharger and the regulating and control unit is reset to the initial state.
A malfunction detected in the regulating and control unit is expediently documented and indicated.
In an advantageous development, the maximum permissible boost pressure is limited to a maximum value in order to prevent component overload, which may occur, for example, due to a jammed turbine geometry in the engine-braking mode and the resulting sharply rising turbine power at an increasing engine speed. In order to limit the boost pressure, a safety valve is provided downstream of the compressors in the intake tract and is expediently arranged in addition to the redundant design with two parallel exhaust-gas turbochargers to be operated alternately. If appropriate, however, boost-pressure limitation by means of the safety valve is also employed in internal combustion engines with only one turbocharger or in internal combustion engines with two turbochargers which may also be operated simultaneously as a function of the operating state.
REFERENCES:
patent: 4422296 (1983-12-01), Dinger et al.
patent: 4982567 (1991-01-01), Hashimoto et al.
patent: 5005359 (1991-04-01), Tashima et al.
patent: 5035114 (1991-07-01), Shibata et al.
patent: 5036663 (1991
Schmidt Erwin
Sumser Siegfried
Calcaterra Mark P.
Daimler-Chrysler AG
Denion Thomas
Trieu Thai-Ba
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