WO2010050856A1

WO2010050856A1 - A device and method for automatically adjusting torque transmitting ability of a turbocompound transmission

Info

Publication number: WO2010050856A1
Application number: PCT/SE2008/000621
Authority: WO
Inventors: Jan Arnell
Original assignee: Volvo Lastvagnar Ab
Priority date: 2008-10-30
Filing date: 2008-10-30
Publication date: 2010-05-06
Also published as: BRPI0823134A2; EP2340366B1; RU2478802C2; CN102187071A; EP2340366A1; US20110196587A1; CN102187071B; EP2340366A4; RU2011121517A; US9932890B2

Abstract

Device and method for automatically adjusting torque transmitting ability of a hydrodynamic coupling (6) in a transmission (5, 6, 7, 8) arranged between a power turbine (4) and a crank shaft (3) in a turbocompound combustion engine (1). Said method comprising the steps of: -continuously registering a value for one or several of; a. engine load parameter for said combustion engine and/or, b. temperature in said combustion engine and/or, c. parameters for indicating NVH in said transmission; -if parameters a to c has passed a predetermined value for each of said parameters, then braking a power turbine side of said hydrodynamic coupling and continuously adjusting said torque transmitting ability of said hydrodynamic coupling in dependence of the development of said parameters a to c. Advantage is increased control of said transmission and engine performance, especially lower noise and exhaust emissions, and accelerated heating of the engine during cold starts, but also better auxiliary braking.

Description

A device and method for automatically adjusting torque transmitting ability of a turbocompound transmission

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device and method for controlling the torque transmitting ability of a transmission arranged between a crankshaft of an turbocompound combustion engine and a power turbine of said turbocompound combustion engine.

In particular, the invention will find its application in connection with automotive vehicles, and relates to a device (see claim 1) and method (see claims 6 and 10) for improved control of said transmission. The invention also relates to a computer program, when run on a computer, computer program product and a storage medium, such as a computer memory.

BACKGROUND OF THE INVENTION

A turbocompound combustion engine, such as disclosed in for example US5884482, is equipped with a turbocharger turbine arranged for receiving exhaust gas from said combustion engine. Such a turbocompound combustion engine is further equipped with a power turbine arranged for receiving said exhaust gas from said turbocharger turbine. Pressure force from the exhaust gases is transmitted to a crank shaft of the engine via a transmission to be used for vehicle propulsion. Said transmission driven by the power turbine and connected to the crankshaft comprises a hydrodynamic coupling. The hydrodynamic coupling is used in order to avoid transmission of damaging irregular rotation to the power turbine and gearing on the power turbine side of the hydrodynamic coupling. The irregular rotation is the result of the combustions occurring in the different cylinders of the engine during a relatively very short period of time of a turn of the crank shaft. A combustion creates a sudden temporary rotational acceleration of the crank shaft, which has negative exhaustive effect on mechanical parts of the engine. Said hydrodynamic coupling reduces the transmission of said negative effect.

When the combustion engine is turned off and said hydrodynamic coupling is in its off-state and not rotating, part of the coupling can never be fully drained from fluid (oil) . This means that when the combustion engine is started and the exhaust pressure in the exhaust pipe has not yet been built up in order to be able to drive the power turbine, the combustion engine will experience an extra resistance in rotation due to the partly filled hydrodynamic coupling transmitting moment of inertia from the inertia of the non-rotating power turbine and the belonging gearing on the power turbine side of the hydrodynamic coupling. Said extra resistance is hard to control and the performance of the combustion engine just after start can be uncertain.

A technical problem addressed by the present invention is how to provide a more advanced transmission between the power turbine and the crank shaft, which will be able to offer an increased overall combustion engine control.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved transmission between the power turbine and the crank shaft that will increase the controllability of the hydrodynamic coupling and the power turbine.

Moreover, the present invention seeks to provide increased control of the transmission between the power turbine and the crank shaft in order to increase the overall performance of the engine, especially for lowering noise and exhaust emissions from the engine, and accelerated heating of the combustion engine during cold starts but also for a better auxiliary braking performance .

Thus, the primary object of the present invention is to solve the above problems and to provide an improved method for controlling said transmission. This is achieved by a device as discussed in the introduction, the characteristics of which are defined by claim 1. The object is also achieved by a method as discussed in the introduction, the characteristics of which are defined by claims 6 and 10 respectively.

The device according to the invention is a combustion engine of the turbocompound type, which comprises

(includes, but is not necessarily limited to) : a turbocharger turbine arranged for receiving exhaust gas from a combustion in said combustion engine; a power turbine arranged for receiving said exhaust gas from said turbocharger turbine; a transmission driven by the power turbine and connected to a crankshaft of the combustion engine; said transmission comprising a hydrodynamic coupling.

This embodiment is characterized in that a braking device is arranged for braking a power turbine side of the hydrodynamic coupling. In one embodiment of the invention said torque transmitting ability of said hydrodynamic coupling is continuously adjustable.

In another embodiment of the invention said braking device is arranged to brake said power turbine side of the hydrodynamic coupling to at least a rotational speed below a rotational speed of a combustion engine side of the hydrodynamic coupling.

In a further embodiment of the invention said braking device is arranged to brake said power turbine side of the hydrodynamic coupling to zero rotational speed.

In a further embodiment of the invention said torque transmitting ability of said hydrodynamic coupling is arranged to be adjustable when said braking device is braking said power turbine side of the hydrodynamic coupling to a rotational speed at least below a rotational speed of said combustion engine side of the hydrodynamic coupling in order to continuously adjust retarding torque.

In one embodiment of the invention said combustion engine further comprises a first cooling device of said hydrodynamic coupling that is integrated with a second cooling device of said combustion engine, and where the embodiment according to the invention is characterized in that said first and second cooling devices are arranged to transport heat to said combustion engine during a cold start of said combustion engine and where said heat is produced when said braking device is braking said power turbine side. The method according to the invention is a method for automatically adjusting torque transmitting ability of a transmission arranged between a power turbine and a crank shaft in a turbocompound combustion engine, said transmission comprising a hydrodynamic coupling, and said method comprising the steps of:

-continuously registering a value for one or several of; a. engine load parameter for said combustion engine and/or, b. temperature in said combustion engine and/or, c. parameters for indicating NVH (noise vibration harshness) in said transmission;

-if one or several of parameters a ^'to c has passed a predetermined value for each of said parameters in one first direction, then braking a power turbine side of said hydrodynamic coupling and continuously adjusting said torque transmitting ability of said hydrodynamic coupling in dependence of the development of one or several of said parameters a to c.

In one embodiment according to the invention said method is characterized in braking said power turbine side of the hydrodynamic coupling to at least a rotational speed below a rotational speed of a turbocompound combustion engine side of the hydrodynamic coupling. In one further embodiment said power turbine side is braked to zero rotational speed.

In a further embodiment according to the invention said method is characterized in that continuously adjusting — £ — said torque transmitting ability in such a way and until a registered value for each of said one or several parameters a to c has returned back and passed said predetermined value in an opposite direction compared to said first direction.

In another embodiment according to the invention said method is characterized in that releasing said braking device when a registered value for each of said one or several parameters a to c has returned back and passed said predetermined value in an opposite direction compared to said first direction.

The method according to the invention is also a method for automatically adjusting torque transmitting ability of a transmission arranged between a power turbine and a crank shaft in a turbocompound combustion engine, said transmission comprising a hydrodynamic coupling, and said method comprising at least the steps of: - registering that auxiliary braking power is demanded;

- if auxiliary braking power is demanded, then braking a power turbine side of said hydrodynamic coupling to a rotational speed at least below a rotational speed of said turbocompound combustion engine side of the hydrodynamic coupling and adjusting said torque transmitting ability of said hydrodynamic coupling in dependence of demanded braking power.

In a further embodiment of the previous described method said braking of the power turbine side is performed only during a decrease of output torque of said turbocompound combustion engine in order to substantially decrease exhaust gas pressure produced by said turbocompound combustion engine.

In an alternative auxiliary braking embodiment of the invention said braking of the power turbine side is performed only when exhaust gas flow is bypassed said power turbine in order to substantially decrease exhaust gas pressure driving said power turbine.

In one further auxiliary braking embodiment said power turbine side is braked to zero rotational speed.

The invention also relates to a computer program comprising program code means for performing all the steps of any one of the method claims when said program is run on a computer.

The invention also relates to a computer program product comprising program code means stored on a computer readable medium for performing all steps of anyone of the method claims when said program product is run on a computer.

The invention also relates to a storage medium, such as a computer memory or a nonvolatile data storage medium, for use in a computing environment, the memory comprising a computer readable program code to perform the method of method claim.

Further advantageous embodiments of the invention emerge from the dependent patent claims following patent claim 1. BRIEF DESCRIPTION OF THE DRAWING

The present invention will be described in greater detail below with reference to the accompanying drawings which, for the purpose of exemplification, shows further preferred embodiments of the invention and also the technical background, and in which: Figure 1 diagrammatically shows a view of a turbocompound combustion engine according to one embodiment of the invention. Figure 2 diagrammatically shows a more detailed view of the transmission arranged between a crankshaft and a power turbine of said turbocompound combustion engine. Figure 3 discloses a computer arrangement for controlling said transmission according to the invention.

DESCRIPTION OF THE INVENTION

Figure one discloses one example embodiment of the invention, where a turbocompound combustion engine 1 comprises at least one cylinder-piston arrangement 2 connected to a crankshaft 3 in a known manner. The crankshaft can be connected to driven wheels (not shown) of a vehicle (not shown) . In the exemplified embodiment of the invention said crankshaft 3 is connected to a power turbine 4, via a transmission comprising a first set of gear wheels 5, a hydrodynamic coupling β, a braking device 7 and a second set of gear wheels 8. The power turbine 4 can be driven by exhaust gases from the combustion in said cylinder. The exhaust gases are provided to said power turbine 4 via a first exhaust pipe 9, a turbocharger turbine 10 according to known art arranged for receiving exhaust gas from a combustion in said cylinder and for supercharging inlet air to the combustion in said cylinder, and a second exhaust pipe 11. Down stream of said power turbine 4 said exhaust gases can be further processed in an exhaust after treatment system 12 according to known art. The torque transmitting ability of the hydrodynamic coupling and the braking arrangement can be controlled by a control unit 13. Said control unit can be arranged to control said hydrodynamic coupling and the braking arrangement in dependence of different parameters, which can be measured by different sensors 14.

Figure.2 discloses a more detailed exemplified embodiment of said transmission 21 according to the invention. As can be seen two of the three gear wheels in the first gear wheel set 5 are not disclosed in figure 2. Only one gear wheel 25 is disclosed. In corresponding way only one gear wheel 28 is disclosed of said second gear wheel set 8. Gear wheel 25 is non- rotatably attached to a shaft 22, which is non- rotatably attached to an engine^' side of said hydrodynamic coupling 23. A power turbine side of the hydrodynamic coupling 24 is via another shaft 25 non- rotatably connected to said gear wheel 28 and also an outer wall 34 of the hydrodynamic coupling. The gear wheel 28 meshes with a gear wheel connected to said power turbine 4. A space 29 between the two sides of the hydrodynamic coupling can be filled with different volumes of a working fluid (for example oil) . The amount of working fluid in said space decides the torque transmitting ability of the hydrodynamic coupling according to known art. The working fluid flows into the hydrodynamic coupling via a channel 30 in said shaft (see arrow 31) . The emptying of working fluid is in the exemplified embodiment regulated by a tube 32, which can be positioned in different levels in an axial direction of the tube (indicated by arrows 33) is performed according to known art (see for example GB2182121) . Thus, the level of the tube decides the amount of working fluid in said space and, thus, the torque transmitting ability of the hydrodynamic coupling. The braking device 7 disclosed in figure 1 (not disclosed in figure 2) can be arranged to lock or brake one of^' the parts fixedly or rotatably connected to the power turbine side of the hydrodynamic coupling. Said brake or lock as such is known art, and can be realized for example via one or several wet couplings or other known braking arrangement. Said parts can be one of or several of the parts between said power turbine side of the hydrodynamic coupling 24 and said power turbine 4. Thus, the braking device, when braking, slows down or hinders the power turbine side of the hydrodynamic coupling from rotating faster that the engine side of the hydrodynamic coupling 6.

The tube 33 can be positioned with a swivel arm (not shown) connected to a lower end (when looking at figure 2) of the tube 33. The arm can be driven by, for example, an electric servo motor and controlled by said control unit 13. In this way the torque transmitting ability of said hydrodynamic coupling can be continuously adjustable both when the braking device 7 is active, that is, braking and when said braking device is released.

The working fluid flowing through said hydrodynamic coupling can be part of a closed loop fluid system 15 with connecting pipes and a fluid pump. Said fluid system 15 can also be a part of or integrated with an lubricating system of said turbocompound combustion engine 1. When said fluid is performing work in said hydrodynamic coupling by transmitting torque, friction will give rise to production of heat. This heat can be cooled by a cooling system integrated in said fluid system 15, which cooling system can be a cooling system of the turbocompound combustion engine or a separate hydrodynamic coupling cooling system.

According to one embodiment of the invention said control unit 13 is programmed to automatically adjust the torque transmitting ability of said transmission . The control unit is programmed to continuously register a value for one or several of; a. engine load parameter for said combustion engine and/or, b. temperature in said combustion engine and/or, c. parameters for indicating NVH in said transmission;

If one or several of parameters a to c has passed a predetermined value for each of said parameters in one first direction, then said control unit 13 is programmed to brake a power turbine side of said hydrodynamic coupling and to continuously adjust said torque transmitting ability of said hydrodynamic coupling in dependence of the development of one or several of said parameters a to c.

The engine load parameter can be measured by said sensor 14 in a known way, for example via torque sensor or measuring injected fuel amount in the engine and calculating torque to be produced from the injected fuel amount. According to one embodiment of the invention the control unit can be programmed to brake the power turbine side of said hydrodynamic coupling and to continuously adjust said torque transmitting ability of said hydrodynamic coupling, when registering an engine load value below a predetermined first engine load value, for example corresponding to when the engine is idling. According to the invention said control can be programmed to adjust the torque transmitting performance (retarding performance when braking device is active) of said hydrodynamic coupling in such a way that the engine will be exposed to an engine load that is at least said predetermined first engine load value. In such engine condition said control unit can be programmed to expose the engine to a load that lies within an interval of which range lies just above said predetermined first engine load value. Noxious emissions produced in a combustion engine during low engine load will be decreased. Thus, when there is enough load from a vehicle travel resistance that will cause an engine load which exceeds said predetermined first engine load value, then said control unit can be programmed to release said braking device, thus the retarding effect from the hydrodynamic coupling will end, and the control unit will regulate the torque transmitting ability of the hydrodynamic coupling to a level which results in a rotational speed of the power turbine that will be optimized for best power turbine efficiency.

In corresponding way and according to another embodiment of the invention said control unit can be programmed to register the temperature of the combustion engine, for example in the cooling system of the combustion engine via a temperature sensor 14, which can also be used in said cooling system of the combustion engine to regulate the cooling performance of said cooling system. According to one embodiment of the invention the control unit can be programmed to brake the power turbine side of said hydrodynamic coupling and to continuously adjust said torque transmitting ability of said hydrodynamic coupling, when registering a temperature value below a predetermined first engine temperature value, for example a value that indicates the limit for a combustion engine cold start. According to the invention said control unit can be programmed to adjust the torque transmitting performance (retarding performance when the braking device is active) of said hydrodynamic coupling in such a way that the engine will be exposed to an increased engine load that will accelerate engine temperature increase so that engine working time during cold start temperatures will decrease. According to one embodiment of the invention the amount of working fluid in said hydrodynamic coupling can be controlled in such a way so that a certain amount of heat will be produced, which for a specific engine and environmental configuration gives a certain temperature rise in said engine. This is beneficial with regard to decreasing noxious emissions produced in a combustion engine. When an engine working temperature above said predetermined first engine temperature value is registered then said control unit is programmed to release said braking device and said hydrodynamic coupling will be controlled as to maximize efficiency of said power turbine.

In corresponding way and according to a further embodiment of the invention said control unit can be programmed to register said parameters for indicating NVH in said transmission (especially NVH in gear wheels 5) . Said parameters for indicating NVH can for example be a combination of amount of injected fuel in the combustion engine and combustion engine rotational speed (a combustion engine rotational speed map) . NVH is most likely to occur during idle rotational speed of said combustion engine in combination with low load on the combustion engine. According to the invention said control can be programmed to adjust the torque transmitting performance (retarding performance when the braking device is active) of said hydrodynamic coupling in such a way that the engine will be exposed to an slightly increased engine load that will tighten the transmission between the crank shaft and the braking device and, thus, no NVH will occur between the gear wheels 5. The benefit of this is that noise emissions from said transmission will decrease. When the control unit is registering that engine load and rotational speed is above predetermined values, said control unit is programmed to release said braking device and said hydrodynamic coupling will be controlled as to maximize efficiency of said power turbine.

Methods for cylinder balancing or correction of amount of injected fuel in each cylinder in relation to injected fuel amount in the other cylinders is something that is well known in the art. The registration of NVH. as described above can be a measure of how well the balancing of fuel amount between the cylinders has been performed. Irregularities between the cylinders can create noise from rattling gear wheels such as gear wheels 5.

As mentioned above said control unit can be arranged to control said hydrodynamic coupling and the braking arrangement in dependence of each of said mentioned parameters, which can be measured by different sensors 14. According to one embodiment of the invention said control unit 13 can be programmed to register a value for two or several of said three parameters and control said hydrodynamic coupling and said braking arrangement in dependence of the development of those parameters.

Now an embodiment of the invention will be described where said hydrodynamic coupling is used as an auxiliary vehicle brake, which completes the braking power of an, for example, engine compression brake (not showed) arranged in said turbocompound combustion engine 1. When, for example, engine compression braking or other auxiliary braking is demanded or will be demanded, then according to one embodiment of the invention said control unit 13 can be programmed to activate said braking device 7 and fill said hydrodynamic coupling so that an additional braking power will be transmitted to driven wheels of the vehicle. The braking power of an engine compression brake according to known art is dependent of rotational speed of the combustion engine 1. Said compression brake produces more braking power at high rotational speeds compared to low rotational speeds. Thus, the use of said hydrodynamic coupling as an auxiliary brake is especially beneficial at low engine rotational speeds. The braking power produced by said hydrodynamic coupling auxiliary brake can be controlled by varying the filling level of said hydrodynamic coupling and/or by varying braking power from the braking device 7. This can be done in dependence of, for example, at least demanded vehicle speed.

According to one embodiment of the invention when said hydrodynamic coupling is used as an auxiliary brake said control unit can be programmed to only activate said hydrodynamic coupling auxiliary brake during a gearshift of a gearbox arranged between said combustion engine 1 and said driven wheels. During a gearshift output torque from the engine is decreased to around zero. This means also that exhaust gas pressure is decreased substantially and said turbine 4 will be substantially relieved from driving force from the exhaust gases. When there is none or almost no driving force on the power turbine 4 it is easier to decrease the turbine side (4 and 8) to zero rotational speed with said braking device 7 and stress on the power turbine 4 and said second gear wheel set 8 will be minimized during the retardation of said turbine side.

In another embodiment according to the invention said hydrodynamic coupling auxiliary brake can be activated during a decrease of combustion engine output torque without a gearshift. This will also decrease driving force on the power turbine from said exhaust gas pressure. Said decrease of engine output torque can be an output torque decrease due to ordinary engine control or engine control due to demanded auxiliary braking power.

In an further alternative embodiment of the invention said hydrodynamic coupling auxiliary brake can be activated only during when the exhaust gas flow bypasses said power turbine. This can be done by a bypassing conduit (not shown) connecting the second exhaust pipe 11 with the aftertreatment system 12. The exhaust flow through said bypass conduit can be controlled by said control unit 13 through a valve arranged in said bypass conduit according to known art. This will also substantially decrease exhaust gas pressure driving said power turbine and stress on the power turbine 4 and said second gear wheel set 8 will be minimized during the retardation of said turbine side .

When the hydrodynamic coupling auxiliary brake is to be deactivated, that is the braking device 7 is released, and said power turbine is accelerated by the exhaust gas pressure said control unit can be programmed to control the filling level of said hydrodynamic coupling (that is torque transmitting ability of said hydrodynamic coupling) so that overspeed of said power turbine 4 is avoided.

In a further embodiment said hydrodynamic coupling can be used alone as an auxiliary brake, that is without additional braking power from other auxiliary brakes such as an engine compression brake.

When the braking device 7 in all the above mentioned embodiments of the invention is said to brake the turbine side of the hydrodynamic coupling, the amount of braking power must be so that rotational speed of the turbine side of the hydrodynamic coupling drops below the rotational speed of the engine side of the hydrodynamic coupling in order to gain the mentioned beneficial effects of the different embodiments of the invention. The most powerful beneficial effect of the different embodiments of the invention will usually occur when the power turbine side of the hydrodynamic coupling is braked to zero rotational speed. Thus, if possible said control unit 13 can be programmed to brake said power turbine side to zero rotational speed in all above mentioned embodiments of the invention. Thus, in such an embodiment the only regulation of the retarding performance of the hydrodynamic coupling will be performed by regulating the torque transmitting ability of the hydrodynamic coupling 6.

Figure 3 shows an apparatus 500 according to one embodiment of the invention, comprising a nonvolatile memory 520, a processor 510 and a read and write memory

560. The memory 520 has a first memory part 530, in which a computer program for controlling the apparatus

500 is stored. The computer program in the memory part 530 for controlling the apparatus 500 can be an operating system.

The apparatus 500 can be enclosed in, for example, a control unit, such as the control unit 13. The data- processing unit 510 can comprise, for example, a microcomputer.

The memory 520 also has a second memory part 540, in which a program for controlling the transmission according to the invention is stored. In an alternative embodiment, the program for controlling the transmission is stored in a separate nonvolatile data storage medium 550, such as, for example, a CD or an exchangeable semiconductor memory. The program can be stored in an executable form or in a compressed state.

When it is stated below that the data-processing unit 510 runs a specific function, it should be clear that the data-processing unit 510 is running a specific part of the program stored in the memory 540 or a specific part of the program stored in the nonvolatile recording medium 550.

The data-processing unit 510 is tailored for communication with the memory 550 through a data bus 514. The data-processing unit 510 is also tailored for communication with the memory 520 through a data bus 512. In addition, the data-processing unit 510 is tailored for communication with the memory 560 through a data bus 511. The data-processing unit 510 is also tailored for communication with a data port 590 by the use of a data bus 515.

The method according to the present invention can be executed by the data-processing unit 510, by the data- processing unit 510 running the program stored in the memory 540 or the program stored in the nonvolatile recording medium 550.

The invention should not be deemed to be limited to the embodiments described above, but rather a number of further variants and modifications are conceivable within the scope of the following patent claims.

Claims

PATENT CLAIMS

1. A combustion engine (1) of the turbocompound type, which comprises: a turbocharger turbine (10) arranged for receiving exhaust gas from a combustion in said combustion engine; a power turbine (4) arranged for receiving said exhaust gas from said turbocharger turbine; a transmission (5, 6, 7, 8) driven by the power turbine and connected to a crankshaft (3) of the combustion engine; said transmission comprising a hydrodynamic coupling (6), characterized in that a braking device (7) is arranged for braking a power turbine side (24) of the hydrodynamic coupling.

2. A combustion engine as in claim 1, characterized in that torque transmitting ability of said hydrodynamic coupling is continuously adjustable.

3. A combustion engine as in one of the preceding claims, characterized in that said braking device is arranged to brake said power turbine side of the hydrodynamic coupling to at least a rotational speed below a rotational speed of a combustion engine side (23) of the hydrodynamic coupling.

4. A combustion engine as in one of the preceding claims, characterized in that said braking device is arranged to brake said power turbine side of the hydrodynamic coupling to zero rotational speed.

5. A combustion engine as in one of claims 2 to 4, characterized in that said torque transmitting ability of said hydrodynamic coupling is arranged to be adjustable when said braking device is braking said power turbine side of the hydrodynamic coupling to a rotational speed at least below a rotational speed of said combustion engine side of the hydrodynamic coupling in order to continuously adjust retarding torque.

6. A combustion engine as in the preceding claim, where a first cooling device of said hydrodynamic coupling is integrated with a second cooling device of said combustion engine, characterized in that said first and second cooling devices are arranged to transport heat to said combustion engine during a cold start of said combustion engine and where said heat is produced when said braking device is braking said power turbine side.

7. Method for automatically adjusting torque transmitting ability of a transmission (5, 6, 7, 8) arranged between a power turbine (4) and a crank shaft (3) in a turbocompound combustion engine (1) , said transmission comprising a hydrodynamic coupling (6), and said method comprising the steps of:

-continuously registering a value for one or several of; a. engine load parameter for said combustion engine and/or, b. temperature in said combustion engine and/or, c. parameters for indicating NVH in said transmission;

-if one or several of parameters a to c has passed a predetermined value for each of said parameters in one first direction, then braking a power turbine side (24) of said hydrodynamic coupling and continuously adjusting said torque transmitting ability of said hydrodynamic coupling in dependence of the development of one or several of said parameters a to c.

8. The method as claimed in the preceding claim, characterized in braking said power turbine side of the hydrodynamic coupling to at least a rotational speed below a rotational speed of a turbocompound combustion engine side (23) of the hydrodynamic coupling.

9. The method as claimed in the preceding claim, characterized in braking said power turbine side to zero rotational speed.

10. The method as claimed in one of claims 8 or 9, characterized in that, continuously adjusting said torque transmitting ability in such a way and until a registered value for each of said one or several parameters a to c has returned back and passed said predetermined value in an opposite direction compared to said first direction.

11. The method as claimed in the preceding claim, characterized in that, releasing said braking device when a registered value for each of said one or several parameters a to c has returned back and passed said predetermined value in an opposite direction compared to said first direction.

12. Method for automatically adjusting torque transmitting ability of a transmission (5, 6, 7, 8) arranged between a power turbine (4) and a crank shaft (3) in a turbocompound combustion engine (1) , said transmission comprising a hydrodynamic coupling, and said method comprising at least the steps of:

- registering that auxiliary braking power is demanded/

-if auxiliary braking power is demanded, then braking a power turbine side (24) of said hydrodynamic coupling to a rotational speed at least below a rotational speed of said turbocompound combustion engine side (23) of the hydrodynamic coupling and adjusting said torque transmitting ability of said hydrodynamic coupling in dependence of demanded braking power.

13. The method as claimed in the preceding claim, characterized in that said braking of the power turbine side is performed only during a decrease of output torque of said turbocompound combustion engine in order to substantially decrease exhaust gas pressure produced by said turbocompound combustion engine.

14. The method as claimed in claim 10, characterized in that said braking of the power turbine side is performed only when exhaust gas flow is bypassed said power turbine in order to substantially decrease exhaust gas pressure driving said power turbine.

15. The method as claimed in one of claims 12 to 14, characterized in braking said power turbine side to zero rotational speed.

16. A computer program comprising program code means for performing all the steps of any one of the claims 6 to 12 when said program is run on a computer.

17. A computer program product comprising program code means stored on a computer readable medium for performing all steps of anyone of the claims 6 to 12 when said program product is run on a computer.

18. A storage medium, such as a computer memory (520) or a nonvolatile data storage medium (550), for use in a computing environment, the memory comprising a computer readable program code to perform the method of claim 6 to 12.