The invention relates to an internal combustion engine including an exhaust gas turbine connected, via a power transmission, to the crankshaft of the internal combustion engine, and to a method of operating such an engine.
DE 103 55 563 A1 discloses an internal combustion engine with an exhaust gas turbine which is integrated into the exhaust duct of the engine and in which the exhaust gas flow of the internal combustion engine is expanded. The exhaust gas turbine is coupled to the crankshaft of the engine via a power transmission which may comprise a shift transmission or an infinitely variable transmission. The internal combustion engine know from DE 103 55 563 already has a high efficiency, however, the exhaust turbine integrated into the exhaust duct and coupled to the crankshaft via a power transmission is not operable at optimal efficiency under all operating conditions so that there is a need for optimizing the efficiency of the arrangement.
It is therefore the object of the present invention to provide a further optimized internal combustion engine of this type and a method of operating such an engine.
In an internal combustion engine with a crankshaft and an exhaust gas duct including an exhaust gas turbine which is coupled to the crankshaft via a variable transmission, a control unit is provided for controlling the transmission ratio of the variable transmission such that the speed of the turbine is adapted to the flow speed of the exhaust gas through the turbine in such a way that the turbine is operated at optimal efficiency.
In this way, the turbine can operate at optimized efficiency at practically all operating points of the internal combustion engine so that the overall efficiency of the internal combustion engine can be improved over the state of the art. The control unit automatically adjusts the transmission ratio of the transmission to an optimal setting such that an efficiency-optimized ratio of the speed of the turbine coupled to the crankshaft via the transmission and the flow speed of the exhaust gas through the turbine is obtained.
The invention also resides in a method of operating an internal combustion engine with an exhaust gas turbine coupled to the crankshaft of the engine with such an adjustable transmission ratio transmission for optimized efficiency.
Preferred embodiments of the invention will become more readily apparent from the following description thereof on the basis of the accompanying drawings.
The efficiency of the power turbine 14 which is coupled to the crankshaft 16 by way of the transmission 15 depends, on one hand, on the flow speed of the exhaust gas through the turbine 14 and, on the other hand, on the speed of the turbine 14. Examinations have shown that such a turbine 14 is operated at optimal efficiency when a certain relationship is maintained between the flow speed of the exhaust gas through the turbine 14 and the rotational speed of the turbine.
In accordance with the present invention, a control unit 17 is provided which automatically adjusts the transmission ratio of the power transmission 15 such that the turbine 14 is operated in the optimal range. The transmission 15 may be an automatically shifted shift transmission or an infinitely variable transmission.
For the automatic adaptation of the transmission ratio of the transmission 15 the control unit 17 preferably calculates the flow speed of the exhaust gas through the turbine 18 from the combustion air flow supplied to the internal combustion engine 10 and the fuel amount supplied to the internal combustion engine. If the internal combustion engine includes exhaust gas recirculation, the recirculation exhaust gas flow is taken into consideration for the calculation of the exhaust gas flow speed in addition to the combustion air flow and the fuel flow.
On the basis of the flow speed of the exhaust gas through the turbine 14 calculated in this way and the known speed of the crankshaft 16, the control unit 17 determines the transmission ratio of the respective transmission 15 in such a way that the turbine 14 has a speed which is optimized for the particular flow speed of the exhaust gas. In this way, it is ensured that the turbine 14 is always operated at an optimal speed with respect to the flow speed of the exhaust gases and consequently, is always operated at an optimal efficiency. An efficiency-optimized ratio of the speed (rpm) of the turbine 14 coupled to the crankshaft 16 by way of the transmission 15 and the flow speed of the exhaust gas through the turbine 14 is maintained in this way.
In the preferred embodiment of
The invention is of course not limited to the arrangement as shown in
Also in the arrangements of FIGS. 3 to 5, the transmission ratio of the transmission 15 can be automatically controlled by the control unit 17 in accordance with the invention in such a way that the power turbine 14 is always operated with optimized efficiency by maintaining a predetermined ratio between the speed of the power turbine 14 and the flow speed of the exhaust gas through the power turbine 14.
Also in the embodiments of FIGS. 6 to 8, the transmission ratio of the transmission 15 can be automatically so controlled by the control unit 17 that a desired ratio between the speed of the turbine 14 and the flow speed of the exhaust gas through the turbine 14 is maintained so as to operate the turbine 14 with optimized efficiency.
In each of the embodiments of
The power turbine 14 which is coupled to the crankshaft 16 via the transmission 15 may have a variable turbine geometry that is it may have an adjustable inlet vane structure. The variable turbine geometry may include a radial guide vane structure with pivotable vanes or an axially movable guide vane structure. The use of a turbine with a variable turbine geometry has the advantage that the pressure difference in the turbine 14 can be adjusted while the optimum ratio between the flow speed of the exhaust gas through the turbine 14 and the speed of the turbine can be maintained. A turbine with a variable turbine geometry can be used in connection with a step-shift transmission or an infinitely variable automatic transmission 15.
If several power turbines 14 are each coupled to the crankshaft 16 by a transmission 15, the control unit 17 adjusts the transmission ratio of each transmission 15 in such a way that the efficiency-optimized ratio between the speed of the respective turbine 14 and the exhaust gas flow speed through the respective turbine 14 is maintained.
The invention is preferably used in connection with Diesel engines in commercial vehicles. However, the invention is not limited to this particular application; rather, the invention may just as well be used in connection with Diesel internal combustion engines for passenger cars and also in connection with gasoline internal combustion engines.