Patent Application
20110294621
The present invention relates to a method for controlling the power transmission in a drive train, especially of a motor vehicle, in detail with the features according to the preamble of claim 1 and a drive train especially of a motor vehicle according to the preamble of claim 6.
Vehicle drive trains with a turbo-charged and mechanically charged (supercharged) internal combustion engine are well-known to the person skilled in the art and are also known as turbocharger-turbocompound systems. During turbocharging, a compressor which compresses the fresh air supplied, to the internal combustion engine is driven by means of an exhaust gas turbine which is arranged in the exhaust gas stream of the internal combustion engine. The drive connection between the exhaust gas turbine and the compressor is usually a purely mechanical one, as also advantageously according to the present invention.
In the case of a turbocompound, the drive power of the mentioned or an additional exhaust gas turbine in the exhaust gas stream of the internal combustion engine is added to the mechanical drive power of the internal combustion engine in that the exhaust gas turbine drives the crankshaft of the internal combustion engine at least indirectly. A hydrodynamic coupling is usually arranged for reducing the torsional oscillations in the drive connection between the exhaust gas turbine and the crankshaft.
Although the mentioned turbocharger-turbocompound systems can improve the efficiency of the drive train in many load ranges, the known systems come with the disadvantage that load ranges can also occur in which the overall system has a worse efficiency and/or more unfavorable emissions than comparable systems without turbocharger and without turbocompound.
The present invention is based on the object of providing a drive train and a method for controlling the power transmission in a drive train, especially a motor vehicle drive train, in which the mentioned disadvantages are avoided. In particular, a strategic control shall be created which optimizes the utilization of existing powers for improving the efficiency in the overall load profile.
The object in accordance with the invention is achieved by a method with the features of claim 1 and a drive train with the features of claim 6. Advantageous and especially appropriate embodiments of the invention are provided in the dependent claims.
The method in accordance with the invention can be applied to a drive train, especially a motor vehicle drive train, which comprises both turbocharging and also mechanical charging by means of a turbocompound. The drive train therefore comprises an internal combustion engine which drives an output shaft at an engine speed nmotor, and produces an exhaust gas stream. Furthermore, an exhaust gas turbine, which is also known as an exhaust gas power turbine, is arranged in the exhaust gas stream, which exhaust gas turbine is in a drive connection with the output shaft or can at least optionally be switched into such a connection in order to transmit drive power of the exhaust gas turbine onto the output shaft of the internal combustion engine. En accordance with the invention this shall be understood as being not only the direct transmission of the drive power of the exhaust gas turbine onto the output shaft of the internal combustion engine, but also any load state in which the drive power of the exhaust gas turbine is added up to the drive power of the internal combustion engine in order to drive the drive train, especially the drive wheels of a motor vehicle.
A compressor, which is usually a turbocompressor, is arranged in a fresh air stream supplied to the internal combustion engine, which compressor is in a drive connection with the exhaust gas turbine and is driven by the same in order to charge the internal combustion engine with a predetermined charging pressure pBp. This type of turbocharging is known to the person skilled in the art and therefore need not be explained in further detail. It is understood that the compressor according to a first embodiment is in continual and especially purely mechanical drive connection with the exhaust gas turbine or is switchable into such a drive connection according to an alternative embodiment, in that a respective coupling is provided between the exhaust gas turbine and the compressor. It is also possible to provide a further drive unit such as an electric motor for driving the compressor in addition to the “exhaust gas turbine” drive unit.
A power-controlled hydrodynamic coupling is provided in the drive connection between the exhaust gas turbine and the output shaft The description of the power-controlled hydrodynamic coupling shall he understood within the Lewis of the present invention in such a way that a control of the torque transmitted by means of the hydrodynamic coupling is also included, with a respective power transmission being obtained by a respectively obtained speed.
As a result, drive power of the exhaust gas turbine is transmitted hydrodynamically onto the output shaft by means of the hydrodynamic coupling, which occurs depending on the current power control in order to thereby transmit drive power of the exhaust gas turbine onto the primary wheel of the hydrodynamic coupling, from there hydrodynamically to the secondary wheel of hydrodynamic coupling and from there output shaft. It is understood that such operating states can also occur in which the secondary wheel of the hydrodynamic coupling, is driven by the output shaft of the internal combustion engine at a higher speed than the primary wheel of the hydrodynamic coupling revolves. In such an operating state there is a hydrodynamic power transmission from the secondary wheel of the hydrodynamic coupling to the primary wheel of the hydrodynamic coupling depending on the currently provided power control. Since the primary wheel of the hydrodynamic coupling which is connected to the exhaust gas turbine at least indirectly, especially purely mechanically, is also in a drive connection, especially also a purely mechanical drive connection, with the compressor arranged in the fresh air stream, it is possible in the latter mentioned operating state to transmit drive power hydrodynamically from the output shall of the internal combustion engine, which is also known as a crankshaft, to the compressor in order to drive the same and charge the internal combustion engine.
A bypass is advantageously provided in the exhaust gas stream parallel to the exhaust gas turbine which optionally can be opened and closed in order to guide exhaust gas optionally passed the exhaust gas turbine. The term of bypass shall be understood in accordance with the invention in such a way that both an emission of the exhaust gas stream guided past the exhaust gas turbine to the ambient environment and a renewed feeding into an exhaust gas line behind the exhaust gas turbine shall be included. It is possible to control the drive power which the exhaust gas turbine generates from the exhaust gas energy by opening and closing the bypass. It is also possible to provide another possibility according to one embodiment of the invention instead of or in addition to the provision and opening or closing of the bypass in order to adjust or control the power input of the exhaust gas turbine. For example, the exhaust gas turbine can he provided with a variable turbine geometry in order to control the power input of the exhaust gas turbine by adjusting the rotor blades and/or guide blades.
The following steps and are provided according to the method in accordance with the invention.
The speed nmotor of the internal combustion engine is detected or calculated from at least one other detected variable. Furthermore, the speed ncc of the compressor is detected or calculated from at least one other detected variable. Moreover, the charging pressure pap is detected or calculated from at least one other detected. variable.
A reference charging pressure pBP
it is principally also possible to describe the charging of the internal combustion engine by a value other than the charging pressure. For example, another reference variable describing the charging state of the internal combustion engine can be predetermined alternatively or in addition, and accordingly a variable other than the charging pressure which describes the charging of the internal combustion engine can he detected or calculated. The compressor speed (corresponding to the reference speed) or the pressure ratio via the compressor (in the case of a respective predetermination of a reference pressure ratio) shall be mentioned as examples for such other variables describing the charging of the internal combustion engine.
The power transmission in the drive train is optimized in accordance with the invention by controlling the hydrodynamic power transmission of the hydrodynamic coupling, which occurs in such a way that at least the four following conditions are always fulfilled:
1. If the speed of the secondary wheel of the hydrodynamic coupling is higher than the speed of the primary wheel, the charging pressure pBP is lower than the reference charging pressure pBP
2. If the speed of the secondary wheel of the hydrodynamic coupling is higher than the speed of the primary wheel and either the charging pressure pBP is larger than the reference charging pressure pBP
3. If the speed of the secondary wheel of the hydrodynamic coupling is lower than the speed of the primary wheel, the charging pressure pBP is lower than the reference charging pressure pBP
4. Tithe speed of the secondary wheel of the hydrodynamic coupling is lower than the speed of the primary wheel and either the charging pressure PDp is larger than the reference charging pressure pBP
The method in accordance with the invention can also be provided without the optional opening and closing of a bypass, e.g. by another open-loop or close-loop control of the power input of the exhaust gas turbine. It is also possible however to omit such an open-loop or closed-loop control of the power input entirely. As has already been explained above, it is finally also possible to choose another variable instead of the charging pressure or the reference charging pressure which describes the charging or the charge state of the internal combustion engine.
In the case of the first two conditions, the bypass to the exhaust gas turbine is advantageously completely closed or the exhaust gas turbine is adjusted or controlled in such a way that it takes up the maximum possible power from the exhaust gas and converts the same into drive power. Under the second and the fourth condition, the charging pressure pBP can be larger than the reference charging pressure pBP
The power control (torque control) of the hydrodynamic coupling can occur in different ways which arc known to the person skilled in the art. It occurs especially advantageously in accordance with the invention by changing the degree of filling of a working chamber formed by the primary wheel and the secondary wheel. As is known, the power transmission occurs in hydrodynamic couplings by way of a cycle flow of a working medium in the working chamber between the bladed wheels, usually from the primary wheel to the secondary wheel, and according to the present invention in specific operating states also from the secondary wheel to the primary wheel. if the working chamber can be discharged completely or in. a substantially complete manner, the power transmission can also be interrupted completely.
In accordance with an advantageous embodiment, a temperature-dependent control (power control or torque control) of the hydrodynamic coupling is provided. The temperature of the working medium, especially an oil, of the hydrodynamic coupling is detected for this purpose at a suitable location or is calculated from another detected variable, If an external working medium cycle is provided for the hydrodynamic coupling, it is possible for example to detect the working medium temperature behind the working chamber in the direction of flow of the working medium, i.e. the working medium which has left the working chamber and especially the hydrodynamic coupling. If the temperature exceeds a predetermined temperature limit value, it can be determined that the hydrodynamic coupling is being operated at the point of the highest power loss. By partly tilling or discharging the coupling or the working chamber of the hydrodynamic. coupling it is then possible to reduce the power loss of the hydrodynamic coupling and thus also he temperature of the working medium in the hydrodynamic coupling or behind the hydrodynamic coupling. The decision whether the working chamber is to be filled or discharged can he made depending on the measure by means of which a comparatively better overall efficiency of the internal combustion engine or the drive train is achieved.
In accordance with an alternative embodiment, the power control or torque control of the hydrodynamic coupling occurs in such a way that an flow restrictor, especially an annular slide valve, is introduce more less into the cycle flow of the working medium in the working chamber. The stronger the cycle flow is disturbed thereby, the stronger the reduction in the power transmission or the transmitted moment. If a respective flow restrictor is provided for disturbing the cycle flow, the hydrodynamic coupling can be arranged to he filled at all times in one embodiment, especially arranged in a fully filled manner, i.e. there is always a predetermined maximum quantity of working medium in the working chamber at all times. Alternatively, the coupling can also be dischargeable in order to interrupt the power transmission completely. In this ease too, the degree of filling of the working chamber with working medium is not adjustable in a purposeful manner, which means that no control of the tilling is provided. It is understood that it is possible according to a further embodiment to combine a filling control with an flow restrictor for optional disturbance of the cycle flow in the working chamber.
A drive train in accordance with the invention is characterized in that a control apparatus is provided which controls the power transmission or the torque transmission in the hydrodynamic coupling. The control apparatus is provided with one or several data inputs which receive the speed of the internal combustion engine, the speed of the compressor, the charging pressure and a predetermined reference charging pressure as input variables and provide them to the control apparatus fur further processing. The presently described method in accordance with the invention is performed by the control apparatus depending on these input variables, in that it accesses the hydrodynamic coupling in a controlling manner, e.g, via a filling control or the drive of an flow restrictor, and opens or closes the bypass around the exhaust gas turbine. Instead of the charging pressure or the reference charging pressure, or in addition to the same, another variable can be used which describes the charging state of the internal combustion engine.
It is alternatively or additionally possible to detect the mentioned variables during the operation of the drive train in a non-continuous manner, but to store characteristics and/or at least one characteristic diagram in the control apparatus, from which the necessary variables for control in accordance with the invention can be derived. Such characteristics or such a characteristic diagram can be produced from tests on test stands for example, or the respective characteristic diagram or characteristics can he produced when starting up a learning system. For example, the characteristic diagram can provide the mentioned input variables depending on the current engine output, especially depending on the current engine torque and the current engine speed as input variables for setting the power transmission in accordance with the invention. Accordingly, the term of input variable of the control apparatus shall be understood in a respectively wide way.
It is understood that input variables can also be provided electronically by a control device, especially a vehicle control device.
The invention will be described below by reference to an exemplary embodiment. Individual details shown in the drawing and described below can be implemented not only in combination but also individually or in individual groups, wherein:
The internal combustion engine 1 produces an exhaust gas stream 2, in which presently two exhaust gas turbines, namely the first exhaust gas turbine 3 and the second exhaust gas turbine 9, are arranged in series with respect to each other and are supplied with exhaust gas in such a way that they convert exhaust gas energy into drive power. In this case, the second exhaust gas turbine 9 is arranged before the first exhaust gas turbine 3 in the direction of flow of the exhaust gas and drives a compressor, which in this ease is designated as second compressor 8, which compresses fresh air of a fresh air stream 4 and supplies the same to the internal combustion engine 14 charging the same. in this case, the second compressor 8 is connected via a common shaft 10 with the second exhaust gas turbine 9, or the respective blade wheels of the compressor 8 and the exhaust gas turbine 9 which are each arranged as turbomachines are carried by the common shaft 10. The compressor 8 further represents a high-pressure stage, whereas the exhaust gas turbine 9 represents a low-pressure stage.
A first compressor 5 is provided in the direction of flow of the fresh air in the fresh air stream 4 before the second compressor 8, which first compressor represents a low-pressure stage and is driven by means of the first exhaust gas turbine 3. The illustrated drive connection is a purely mechanical drive connection, in the present case by a shaft 3.1 of the exhaust gas turbine 3 via a gearwheel, especially a spur-gear stage, onto the primary wheel 6.1 of the hydrodynamic coupling 6, via a second gearwheel stage, which is again arranged as a spur-gear stage, and fluffier onto the shaft 5.1 of the compressor 5 which then rotatably carries the respective blade wheel of the compressor 5.
The exhaust gas turbine 3 is simultaneously connected via the hydrodynamic coupling 6 in a drive connection with the output shaft 1.1 of the internal combustion engine 1, which occurs in such a way that the drive connection is guided via the working chamber 6.3 or the flow circuit of working medium in the working chamber 6.3, and thereby the hydrodynamic power transmission is provided which dampens the torsional. oscillations.
The power transmission with the hydrodynamic coupling 6 can be controlled for example by purposeful changing of the degree of filling of the working chamber 6.3 of the hydrodynamic coupling 6, both the power transmitted in a first operating state by the output shaft 1.1 via the hydrodynamic coupling 6 onto the compressor 5 and also the power in a second operating state which is transmitted by the exhaust gas turbine 3 via the hydrodynamic coupling 6 onto the output shaft 1.1. A control apparatus 11 is provided for the purposeful setting of the degree of tilling in the working chamber 6.3, which control apparatus accordingly accesses the hydrodynamic coupling 6 in a controlling manner, such that it opens and/or closes a valve in the inlet into the working chamber 6.3 and/or a valve in the outlet of the working medium out of the working chamber 6.3, and especially moves the same in a controlling manner to a predetermined intermediate position (closed-loop control position).
The control apparatus 11 receives specific input variables, e.g. via a CAN bus 13, which are at least the speed nmotor of the internal combustion engine 1, the speed ncc of the compressor 5, the charging pressure pp with which the internal combustion engine once charged, which means the one that is set at the end of the fresh air stream 4, in this case behind the second compressor 8, and is introduced into the engine housing for combustion with a respective fuel, and further a predetermined reference charge compressor pBP
The control apparatus 11 determines further whether a bypass 7 to the exhaust gas turbine 3 for the exhaust gas of the exhaust gas stream 2 is opened or closed, e.g. in that it actuates a valve 7.1 or throttle or flap or the like in the bypass 7 or at a branch-off point or also at the point of the renewed unification with the exhaust gas line.
An especially rapid filling can be achieved when, as is shown in
Δt1=f(Δn, Δs, Qmax
Short-term overdriving is therefore provided which accelerates the change in This overdriving is especially advantageous in the case of a so-called feed-controlled hydrodynamic coupling that is flowed through with constant discharge cross-section of the working medium.
Although
The illustrated overdriving can also be provided in an increase in the output of the hydrodynamic coupling by introducing an flow restrictor into the working medium circuit in that the throttling is set at first it a comparatively stronger or weaker way and then to a predetermined reference value.
Δt2 designates the time of the change in filling in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 061 711.3 | Dec 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/008892 | 12/11/2009 | WO | 00 | 8/3/2011 |
