Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Reexamination Certificate
2002-12-31
2004-05-11
Nguyen, Hoang (Department: 3748)
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
C060S611000
Reexamination Certificate
active
06732523
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for controlling a charge pressure in an internal combustion engine with an exhaust gas turbocharger.
An exhaust gas turbocharger (ATL) is composed of two turbo machines: a turbine and a compressor which are mounted on a common shaft. The turbine uses the energy contained in the exhaust gas to drive the compressor which sucks in fresh air and forces precompressed air into the cylinders of an internal combustion engine. The exhaust gas turbocharger is connected in terms of fluid flow to the internal combustion engine by means of the stream of air and exhaust gas. Exhaust gas turbochargers are used in internal combustion engines in passenger cars and lorries and in large-scale internal combustion engines. In particular in the case of passenger car exhaust gas turbochargers, owing to the large rotational speed range it is necessary to control the exhaust gas turbocharger in order to obtain a virtually constant and precise charge pressure in a relatively wide rotational speed range.
Control devices are known for making available a specific setpoint charge pressure. It is necessary to take into account the fact that the charge pressure which is generated at the exhaust gas turbocharger generally depends on the operating point of the internal combustion engine. One possible way of influencing the charge pressure of an exhaust gas turbocharger is provided by exhaust gas turbochargers with variable turbine geometry (VTG). The process of controlling the charge pressure using the variable turbine geometry is carried out by means of a VTG actuator whose actuation is accompanied by the definition of a manipulated variable. In order to control the charge pressure it is also possible to use a charge pressure control valve (WASTEGATE) which is arranged at the exhaust gas end. During this exhaust gas-end control, a portion of the exhaust gases is conducted around the turbine so that a smaller stream of exhaust gas flows through the turbine, depending on the stream of exhaust gas conducted around.
DE 197 09 955 A1 discloses a method for controlling an internal combustion engine which is provided with a control device which has physical models of a supercharger device and of an intake tract. These models are used to determine estimated values for the charge pressure and for the air mass flow rate into the cylinders which are used to control the internal combustion engine.
DE 42 14 648 A1 discloses a method for controlling an internal combustion engine having a turbocharger and an exhaust gas feedback, in which method the rotational speed of the supercharger shaft is determined by integrating the difference between the power levels of the compressor and of the turbine of the turbocharger. A charge pressure signal is then calculated on the basis of the rotational speed of the supercharger shaft. The charge pressure signal is then used, together with further signals, to control the internal combustion engine.
SUMMARY OF THE INVENTION
The invention is based on the object of making available a method for controlling the charge pressure, which uses simple means to permit the charge pressure to be set precisely and reliably.
The object can be achieved by a method for controlling a charge pressure in an internal combustion engine with an exhaust gas turbocharger consisting of a turbine and a charge air compressor in which a manipulated variable is determined for setting the charge pressure which is emitted by the charge air compressor and has the following method steps:
determining the power or the torque of the compressor,
determining the power or torque loss which occurs during the transmission from the turbine to the compressor, and
determining the power or the torque of the turbine from the power or the torque of the compressor and the power or torque loss, and determining a predefined setpoint value for the manipulated variable as a function of the power or the torque of the turbine.
An embodiment according to the present invention can be an apparatus for controlling a charge pressure in an internal combustion engine with an exhaust gas turbocharger consisting of a turbine and a charge air compressor in which a manipulated variable is determined for setting the charge pressure which is emitted by the charge air compressor comprising:
means for determining the power or the torque of the compressor,
means for determining the power or torque loss which occurs during the transmission from the turbine to the compressor, and
means for determining the power or the torque of the turbine from the power or the torque of the compressor and the power or torque loss, and means for determining a predefined setpoint value for the manipulated variable as a function of the power or the torque of the turbine.
The power or the torque of the compressor can be determined using an isentropic compressor efficiency level, the isentropic compressor efficiency level being determined by means of a first characteristic diagram as a function of the following variables:
pressure downstream of the compressor,
fresh air mass flow rate fed to the internal combustion engine,
ambient pressure and
ambient temperature.
The rotational speed of the turbine can be calculated by means of a second characteristic diagram as a function of the following variables:
mass flow rate across the compressor,
exhaust gas pressure downstream of the compressor, ambient pressure, and
ambient temperature.
The second characteristic diagram may additionally depend on the value of the manipulated variable for the charge pressure. The rotational speed of the turbine can be measured. The power or torque loss can be determined as a function of the rotational speed of the turbine by means of a predetermined characteristic curve. The manipulated variable for the charge pressure may be determined as a function of the isentropic efficiency level of the turbine, and the isentropic efficiency level of the turbine is determined using a third characteristic diagram as a function of the following variables:
mass flow rate across the turbine,
exhaust gas temperature and
exhaust gas pressure upstream of the turbine,
the third characteristic diagram depending additionally on the value of the manipulated variable for the charge pressure.
The manipulated variable for the charge pressure can be calculated by a fourth characteristic diagram as a function of the following variables:
exhaust gas mass flow rate,
exhaust gas pressure upstream of the turbine and
exhaust gas temperature,
and a turbine pressure ratio which depends on the isentropic efficiency level of the turbine which is determined. The manipulated variable for the charge pressure can be determined by means of a characteristic diagram as a function of the temperature ratio at the turbine and the following variables:
exhaust gas mass flow,
exhaust gas pressure upstream of the turbine and
exhaust gas temperature.
The manipulated variable for the charge pressure can act on a variable turbine geometry. The manipulated variable for the charge pressure can further act on a charge pressure valve which is arranged at the exhaust gas end. The mass flow rate across the charge pressure valve can be obtained as the difference between the exhaust gas mass flow rate and a maximum turbine mass flow rate.
As mentioned above, according to one embodiment of the invention, in a first step in the method the power or the torque of the compressor is determined. The power and torque of the compressor are linked to one another by means of the rotational speed of the turbocharger, the torque being inversely proportional to the rotational speed of the turbocharger, and proportional to the power of the compressor. According to the invention, in a second step the power or torque losses which occur during the transmission from the turbine to the compressor are determined. In particular gap losses, frictional losses of the shaft etc. are taken into account here. In order to determine the power loss or the torque loss, it is assumed that the losses are dependent on the power or the t
Birkner Christian
Nienhoff Michael
Oestreicher Wolfgang
Stadler Wolfgang
Baker & Botts L.L.P.
Nguyen Hoang
Siemens Aktiengesellschaft
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