SE540867C2

SE540867C2 - A method and arrangement for controlling a hybrid powertrain

Info

Publication number: SE540867C2
Application number: SE1750471A
Authority: SE
Inventors: Fredrik Sunden; Linus Eriksson; Patrik Molin
Original assignee: Scania Cv Ab
Priority date: 2017-04-21
Filing date: 2017-04-21
Publication date: 2018-12-11
Also published as: DE102018002893A1; SE1750471A1

Abstract

The invention relates to a method for controlling a powertrain (3) of a hybrid vehicle (1), the powertrain (3) comprising: a combustion engine (2); an electric machine (4); a gearbox (6) comprising an input shaft (10) coupled to the electric machine (4); and a clutch (12) arranged to selectively transfer torque between the combustion engine (2) and the input shaft (10), the method comprising, when the vehicle (1) is at standstill and no gear is engaged in the gearbox (6): controlling (s101) the clutch (12) to a position enabling a predetermined torque to be transmitted from the combustion engine (2) to the input shaft (10); and controlling (s102) the rotational speed of the electric machine (4), such that the clutch (12) is slipping.

Description

A method and arrangement for controlling a hybrid powertrain.

TECHNICAL FIELD The present invention relates to a method for controlling a powertrain, a control arrangement, a powertrain comprising such a control arrangement, a vehicle, a computer program and a computer-readable medium. The present invention more specifically relates to a method for controlling a powertrain of a hybrid vehicle.

BACKGROUND Hybrid vehicles may comprise a combustion engine and an electric machine for propulsion of the vehicle. A clutch is typically arranged between the combustion engine and the gearbox. The clutch may comprise a flywheel connected to the crankshaft of the combustion engine and a clutch disc connected to the input shaft of the gearbox. The clutch may also comprise an integrated clutch damper adapted to, for example, dampen vibrations caused by ignition pulses in the combustion engine and thereby avoid induction of vibrations in the gearbox. In parallel hybrid vehicles the electric machine is coupled to the input shaft of the gearbox. The electric machine arranged on the input shaft will cause great inertia downstream of the clutch disc, which may affect the damping ability of the clutch damper. The risk for vibrations induced in the driveline is thereby increased. Such vibrations may cause gear rattle in the gearbox which often results in an occurrence of noise, which may be unpleasant for the operator of the vehicle.

Vibrations in the driveline and occurrence of noise are commonly known problems and different solutions exist for reducing such vibrations/noise. Document US2016/0082824 A1 discloses a method for damping vibrations occurring when the intake/exhaust valve of the engine of a hybrid vehicle is frozen. The method comprises to determine if the engine water temperature is lower than a threshold value, detect engine vibrations and control the clutch to slip based on a request drive force of the vehicle. The slip amount of the clutch is made smaller when the request drive force is relatively larger as compared to when the request drive force is relatively smaller. For example, if the request drive force is relatively small and can be delivered by the electric machine alone, the clutch is opened and the vibrations are not transmitted to the drive wheels.

SUMMARY OF THE INVENTION Despite known solutions in the field, it would be desirable to develop a method for controlling a powertrain of a hybrid vehicle, which reduces the occurrence of vibrations and noise in the powertrain.

An object of the present invention is therefore to achieve a new and advantageous method for controlling a powertrain of a hybrid vehicle, which reduces the occurrence of vibrations and noise when the vehicle is at standstill.

Another object of the invention is to achieve a new and advantageous control arrangement, a powertrain, a vehicle, a computer program and a computerreadable medium which reduces the occurrence of vibrations and noise when a hybrid vehicle is at standstill.

The herein mentioned objects are achieved by a method for controlling a powertrain of a hybrid vehicle, a control arrangement, a powertrain, a vehicle, a computer program and a computer-readable medium according to the independent claims.

Hence, according to an aspect of the present invention a method is provided for controlling a powertrain of a hybrid vehicle, the powertrain comprising: a combustion engine; an electric machine; a gearbox comprising an input shaft coupled to the electric machine; and a clutch arranged to selectively transfer torque between the combustion engine and the input shaft. The method comprises, when the vehicle is at standstill and no gear is engaged in the gearbox: - controlling the clutch to a position enabling a predetermined torque to be transmitted from the combustion engine to the input shaft; and - controlling the rotational speed of the electric machine, such that the clutch is slipping.

The method according to the invention is performed when the combustion engine is active. Since the vehicle is standing still with the gearbox in neutral it is assumed that the rotational speed of the combustion engine is the idling speed.

The powertrain suitably comprises an energy storage device connected to the electric machine. The energy storage device may be a battery arranged to drive the electric machine. The energy storage device may be connected to the electric machine via a converter/inverter.

As described in the background parallel hybrid vehicles having the electric machine arranged on the input shaft of the gearbox will cause great inertia downstream of the clutch disc. Thus, in situations where the clutch normally would dampen ignition pulses (combustion vibrations) from the combustion engine the damping effect would be deteriorated and the ignition pulses would excite vibrations in the powertrain downstream of the clutch. It has been identified that situations of standing still with the combustion engine active may be suitable for charging an energy storage device of the vehicle. To charge the energy storage device the clutch must be engaged, such that torque can be transmitted from the combustion engine to the electric machine. The electric machine will in this case act as a generator and charge the energy storage device. When a vehicle is at standstill with the combustion engine active the operator of the vehicle may have engaged a gear in the gearbox to be prepared to drive off. In order to be able to charge the energy storage device while standing still the gearbox must be in neutral to avoid that torque is transmitted via the gearbox to the drive wheels of the vehicle. The method may thus comprise the step of ensuring that no gear is engaged in the gearbox. Thus, in the cases where the vehicle is at standstill with the combustion engine active and a gear engaged, the method may comprise to first control the gearbox to neutral before performing the other method steps. In a situation where a parallel hybrid vehicle is standing still with the combustion engine active, the clutch engaged and the gearbox in neutral, the clutch might not be able to damp vibrations from the combustion engine due to the inertia caused by the electric machine. Vibrations and noise from the combustion engine may thereby be induced into the gearbox. Vibrations in the gearbox may cause gear rattle since no gear is engaged and the gear rattle would cause noise. Thus, charging the energy storage device in a parallel hybrid vehicle by means of the combustion engine while standing still will increase the risk of vibrations in the powertrain and the occurrence of noise. By controlling the clutch to a position enabling a predetermined torque to be transmitted from the combustion engine to the input shaft it is ensured that the energy storage device can be charged by means of the combustion engine. By also controlling the rotational speed of the electric machine, such that the clutch is slipping, the combustion vibrations will result in variating speed in the clutch slip instead of being transmitted into the gearbox. An efficient way of charging the energy storage device and at the same time reducing the noise and vibrations from the gearbox is thereby achieved.

Controlling the clutch to a position enabling a predetermined torque to be transmitted from the combustion engine to the input shaft of the gearbox may comprise controlling the clutch to an at least partially engaged state. The torque transmitted from the combustion engine to the input shaft through the clutch, depends on the position of the clutch. The clutch position is herein defined as the position of a clutch actuator of the clutch. The position of the clutch actuator affects the applied clutch force, which in turn affects the torque transmitted through the clutch. A certain position of the clutch (clutch actuator) thus corresponds to a certain amount of torque being transmitted through the clutch.

According to an embodiment of the invention the predetermined torque corresponds to a power required to charge the energy storage device. The clutch may thus be controlled to a position corresponding to a power required to charge the energy storage device. The method may comprise the step of determining the state of charge of the energy storage device and determining how much it should be charged. The predetermined torque may thereby be a torque required to be able to charge the energy storage device as desired.

When the clutch is slipping, the flywheel and the clutch disc are slipping against each other. Controlling the rotational speed of the electric machine, such that the clutch is slipping suitably means controlling the rotational speed of the electric machine, such that there is a difference in rotational speed over the clutch. That is, the rotational speed of the electric machine is controlled, such that a difference in rotational speed is obtained between the flywheel and the clutch disc. This difference is suitably obtained by braking the electric machine and thus applying a negative torque on the electric machine. Thus, the rotational speed of the electric machine is suitably controlled by applying a torque on the electric machine, such that a difference in rotational speed is obtained between the flywheel and the clutch disc. The method according to the invention thus comprises to control the torque applied on the electric machine to achieve a rotational speed of the electric machine which makes the clutch start slipping. According to an embodiment of the invention the rotational speed of the electric machine is controlled to be lower than the rotational speed of the combustion engine. The combustion engine is assumed to be operated in the idling speed. The rotational speed of the electric machine may thus be controlled to be lower than the idling speed of the combustion engine. The rotational speed of the electric machine may be controlled to be close to the rotational speed of the combustion engine. If the slip amount (the difference in rotational speed) is too high the energy losses and the wear on the clutch disc will be high. The rotational speed of the electric machine may therefore be controlled, such that the difference in rotational speed between the flywheel and the clutch disc is low enough to limit the wear of the clutch disc and to keep the energy losses relatively low. The rotational speed of the electric machine may thus be controlled to achieve a slip amount that limits the wear of the clutch disc. However, if the slip amount is too small there is a risk for stick-slip phenomenon to occur, which is not desired. The rotational speed of the electric machine may therefore be controlled, such that the slip amount is large enough to avoid stickslip phenomenon in the clutch. The rotational speed of the electric machine may be controlled to be within a range of 10-50 rpm lower than the idle speed of the combustion engine. The lower value of the range may be defined as the point below which stick-slip phenomenon may occur. However, the point where stickslip phenomenon occurs in a clutch varies depending on the configuration of the clutch and the lower value of the range may thereby vary depending on the clutch. The higher value of the range may be defined as the limit above which the wear of the clutch disc and the energy losses is too high. The rotational speed of the electric machine may also be determined as a function of the predetermined torque to be transmitted through the clutch. The rotational speed of the electric machine may thus be controlled depending on the configuration of the clutch and/or the predetermined torque to be transmitted through the clutch.

The rotational speed of the electric machine may be controlled to achieve so called micro slipping of the clutch.

According to an aspect of the invention a control arrangement for controlling a powertrain of a hybrid vehicle is provided. The powertrain comprises: a combustion engine; an electric machine; a gearbox comprising an input shaft coupled to the electric machine; and a clutch arranged to selectively transfer torque between the combustion engine and the input shaft. The control arrangement comprising: - means for, when the vehicle is at standstill and no gear is engaged in the gearbox, controlling the clutch to a position enabling a predetermined torque to be transmitted from the combustion engine to the input shaft; and - means for, when the vehicle is at standstill and no gear is engaged in the gearbox, controlling the rotational speed of the electric machine, such that the clutch is in a slipping state.

It will be appreciated that all the embodiments described for the method aspect of the invention are also applicable to the control arrangement aspect of the invention. That is, the control arrangement may be configured to perform any one of the steps of the method according to various embodiments described herein. The control arrangement may thus comprise means for ensuring that no gear is engaged in the gearbox.

The means for ensuring that no gear is engaged in the gearbox; the means for controlling the clutch to a position enabling a predetermined torque to be transmitted from the combustion engine to the input shaft; and the means for controlling the rotational speed of the electric machine, such that the clutch is in a slipping state, may e.g. be different software modules/portions in a control unit, program code or similar.

According to an aspect of the invention a powertrain of a hybrid vehicle is provided, the powertrain comprising: a combustion engine; an electric machine; a gearbox comprising an input shaft coupled to the electric machine; and a clutch arranged to selectively transfer torque between the combustion engine and the input shaft. The powertrain further comprises a control arrangement as described above. The powertrain thus further comprises a control arrangement comprising means for, when the vehicle is at standstill and no gear is engaged in the gearbox: controlling the clutch to a position enabling a predetermined torque to be transmitted from the combustion engine to the input shaft; and controlling the rotational speed of the electric machine, such that the clutch is in a slipping state.

Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following details, and also by putting the invention into practice. Whereas embodiments of the invention are described below, it should be noted that it is not restricted to the specific details described. Specialists having access to the teachings herein will recognise further applications, modifications and incorporations within other fields, which are within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS For fuller understanding of the present invention and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which: Figure 1 schematically illustrates a vehicle according to an embodiment of the invention; Figure 2 schematically illustrates a powertrain of a hybrid vehicle according to an embodiment of the invention; Figure 3 illustrates a flow chart for a method for controlling a powertrain according to an embodiment of the invention; and Figure 4 schematically illustrates a control unit or computer according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS Fig. 1 schematically illustrates a hybrid vehiclel according to an embodiment of the invention. The vehicle 1 includes a powertrain 3 comprising a combustion engine 2, an electric machine 4, a gearbox 6 and clutch (not shown) arranged between the combustion engine 2 and the gearbox 6. The gearbox 6 is connected to the drive wheels 8 of the vehicle 1 via an output shaft of the gearbox 6. The vehicle 1 may be a so called parallel hybrid vehicle 1 where the electric machine 4 is coupled to an input shaft of the gearbox 6. The vehicle 1 may be a heavy vehicle, e.g. a truck or a bus. The vehicle 1 may alternatively be a passenger car.

Fig. 2 schematically illustrates a powertrain of a hybrid vehicle according to an embodiment of the invention. The powertrain may be a powertrain 3 of a hybrid vehicle 1 as disclosed in Figure 1. The powertrain 3 comprises a combustion engine 2; an electric machine 4; a gearbox 6 comprising an input shaft 10 coupled to the electric machine 4; and a clutch 12 arranged to selectively transfer torque between the combustion engine 2 and the input shaft 10. The powertrain 3 is thus a so called parallel hybrid powertrain where both the combustion engine 2 and the electric machine 4 are connected to the input shaft 10 of the gearbox 6. The torque acting on the input shaft 10 will thereby be the sum of the torque from the combustion engine 2 transferred through the clutch 12 and the torque provided by the electric machine 4. The gearbox 6 also comprises an output shaft 20 connected to the drive wheels 8. The clutch 12 comprises a flywheel 12’ connected to the combustion engine 2 and a clutch disc 12” connected to the input shaft 10 of the gearbox 6. When the clutch 12 is in an engaged state torque can be transmitted from the combustion engine 2 to the gearbox 6 through the clutch 12 and when the clutch 12 is in a disengaged (open) state no torque can be transmitted from the combustion engine 2 to the gearbox 6 via the clutch 12.

The powertrain 3 further comprises an energy storage device 30 connected to the electric machine 4. The energy storage device 30 may be a battery arranged to drive the electric machine 4. The electric machine 4 may also be adapted to act as a generator wherein the electric machine 4 can be used to charge the energy storage device 30.

The powertrain 3 also comprises a control arrangement 40, which may comprise at least one control unit 42 and a computer 44 connected to the control unit 42. The combustion engine 2, the clutch 12, the electric machine 4 and the gearbox 6 are suitably arranged in communication with the control arrangement 40. The control arrangement 40 may thus be configured to control the combustion engine 2, the clutch 12, the electric machine 4 and the gearbox 6. The control arrangement 40 may specifically be configured to, when the vehicle 1 is at standstill and the gearbox 6 is in neutral, control the clutch 12 to a position enabling a predetermined torque to be transmitted from the combustion engine 2 to the input shaft 10, and to control the rotational speed of the electric machine 4, such that the clutch 12 is slipping. This way, the energy storage device 30 may be charged by means of the electric machine 4 and the slipping clutch 12 will prevent combustion vibrations from propagating into the gearbox 6.

Figure 3 illustrates a flow chart for a method for controlling a powertrain of hybrid vehicle according to an embodiment of the invention. The powertrain may be the powertrain 3 as disclosed in Figure 2 and the hybrid vehicle may be the vehicle 1 as disclosed in Figure 1. The method comprises, when the vehicle 1 is at standstill and no gear is engaged in the gearbox 6: controlling s101 the clutch 12 to a position enabling a predetermined torque to be transmitted from the combustion engine 2 to the input shaft 10; and controlling s102 the rotational speed of the electric machine 4, such that the clutch 12 is slipping.

The method may comprise to determine that the vehicle 1 is standing still with the combustion engine 2 active and no gear engaged in the gearbox 6. The method may alternatively comprise to determine that the vehicle 1 is standing still with the combustion engine 2 active. The method may also comprise to ensure that no gear is engaged in the gearbox 6. That is, if a gear is engaged in the gearbox 6, the method may comprise to control the gearbox 6, such that no gear is engaged. Thus, the method is performed when the vehicle 1 is at standstill with the combustion engine 2 active. Since the vehicle 1 is standing still with the gearbox 6 in neutral it is assumed that the rotational speed of the combustion engine 2 is the idling speed. By performing the method according to the invention, these situations can be used to charge the energy storage device 30 and at the same time ensure that the noise from the gearbox 6 is reduced.

The step of controlling s101 the clutch 12 to a position enabling a predetermined torque to be transmitted from the combustion engine 2 to the input shaft 10 of the gearbox 6 may comprise controlling the clutch 12 to an at least partially engaged state. When the clutch 12 is engaged torque can be transmitted from the combustion engine 2 to the input shaft 10. The input shaft 10 will thereby rotate and the electric machine 4 connected to the input shaft 10 will act as a generator and charge the energy storage device 30. The torque transmitted from the combustion engine 2 to the input shaft 10 through the clutch 12, depends on the position of the clutch 12. The clutch position is herein defined as the position of a clutch actuator of the clutch 12. The position of the clutch actuator affects the applied clutch force, which in turn affects the torque transmitted through the clutch 12. The method may thus comprise to control the clutch 12 to a position, in which the applied clutch force is such that a predetermined torque is transmitted via the clutch 12. The predetermined torque may correspond to a power required to charge the energy storage device 30. The predetermined torque may correspond to a desired power to charge the energy storage device 30. The clutch 12 may thus be controlled to a position corresponding to a power required/desired to charge the energy storage device 30. The predetermined torque may thereby be determined based on the state of charge of the energy storage device 30 and based on how much the energy storage device 30 should be charged. The method may thus comprise the step of determining the state of charge of the energy storage device 30 and determining how much it should be charged.

The step of controlling s102 the rotational speed of the electric machine 4, such that the clutch 12 is slipping may comprise controlling the rotational speed of the electric machine 4, such that there is a difference in rotational speed over the clutch 12. That is, the rotational speed of the electric machine 4 may be controlled, such that a difference in rotational speed is obtained between the flywheel 12’ and the clutch disc 12”. The step of controlling s102 the rotational speed of the electric machine 4 suitably comprises to control the applied torque on the electric machine 4. The step of controlling s102 the rotational speed of the electric machine 4 may comprise braking the electric machine 4 and thus applying a negative torque on the electric machine 4. The rotational speed of the electric machine 4 may be controlled to be lower than the rotational speed of the combustion engine 2. The rotational speed of the electric machine 4 may be controlled to be lower than the idling speed of the combustion engine 2. The rotational speed of the electric machine 4 may be controlled to be close to the rotational speed of the combustion engine 2. If the slip amount (the difference in rotational speed) is too high the energy losses and the wear on the clutch disc 12” will be high. The rotational speed of the electric machine 4 may therefore be controlled, such that the difference in rotational speed between the flywheel 12’ and the clutch disc 12” is low enough to minimize the wear of the clutch disc 12” and to keep the energy losses low. The rotational speed of the electric machine 4 may thus be controlled to achieve a slip amount that minimizes the wear of the clutch disc 12”. However, if the slip amount is too small there is a risk for stickslip phenomenon to occur which is not desired. The rotational speed of the electric machine 4 may therefore be controlled, such that the slip amount is large enough to avoid stick-slip phenomenon in the clutch 12. The rotational speed of the electric machine 4 may be controlled to be within a range of 10-50 rpm lower than the idle speed of the combustion engine 2.

The method may be performed by means of the control arrangement 40 of the powertrain 3. The method may be referred to as a method for controlling a powertrain 3 to reduce noise while charging an energy storage device 30.

Figure 4 is a diagram of a version of a device 500. The control unit 42 and/or computer 44 described with reference to Figure 2 may in a version comprise the device 500. The term “link” refers herein to a communication link which may be a physical connection such as an optoelectronic communication line, or a nonphysical connection such as a wireless connection, e.g. a radio link or microwave link. The device 500 comprises a non-volatile memory 520, a data processing unit 510 and a read/write memory 550. The non-volatile memory 520 has a first memory element 530 in which a computer programme, e.g. an operating system, is stored for controlling the function of the device 500. The device 500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540.

There is provided a computer programme P which comprises routines for controlling a powertrain of a hybrid vehicle. The computer programme P comprises routines for controlling the clutch to a position enabling a predetermined torque to be transmitted from the combustion engine to the input shaft. The computer programme P comprises routines for controlling the rotational speed of the electric machine, such that the clutch is slipping. The computer programme P comprises routines for ensuring that no gear is engaged in the gearbox.

The programme P may be stored in an executable form or in a compressed form in a memory 560 and/or in a read/write memory 550.

Where the data processing unit 510 is described as performing a certain function, it means that the data processing unit 510 effects a certain part of the programme stored in the memory 560 or a certain part of the programme stored in the read/write memory 550.

The data processing device 510 can communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data processing unit 510 via a data bus 511. The read/write memory 550 is adapted to communicating with the data processing unit 510 via a data bus 514.

When data are received on the data port 599, they are stored temporarily in the second memory element 540. When input data received have been temporarily stored, the data processing unit 510 is prepared to effect code execution as described above.

Parts of the methods herein described may be effected by the device 500 by means of the data processing unit 510 which runs the programme stored in the memory 560 or the read/write memory 550. When the device 500 runs the programme, methods herein described are executed.

The foregoing description of the preferred embodiments of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to restrict the invention to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order best to explain the principles of the invention and its practical applications and hence make it possible for specialists to understand the invention for various embodiments and with the various modifications appropriate to the intended use.

Claims

1. A method for controlling a powertrain (3) of a hybrid vehicle (1), the powertrain (3) comprising: a combustion engine (2); an electric machine (4); a gearbox (6) comprising an input shaft (10) coupled to the electric machine (4); and a clutch (12) arranged to selectively transfer torque between the combustion engine (2) and the input shaft (10), the method comprising, when the vehicle (1) is at standstill and no gear is engaged in the gearbox (6): - controlling (s101) the clutch (12) to a position enabling a predetermined torque to be transmitted from the combustion engine (2) to the input shaft (10); and - controlling (s102) the rotational speed of the electric machine (4), such that the clutch (12) is slipping.

2. The method according to claim 1, wherein the powertrain (3) comprising an energy storage device (30) connected to the electric machine (4), wherein the predetermined torque corresponds to a power required to charge the energy storage device (30).

3. The method according to claim 1 or 2, wherein the rotational speed of the electric machine (4) is controlled to be lower than the rotational speed of the combustion engine (2).

4. The method according to any of the preceding claims, wherein the rotational speed of the electric machine (4) is controlled to be within a range of 10-50 rpm lower than the idling speed of the combustion engine (2).

5. The method according to any of the preceding claims, wherein the rotational speed of the electric machine (4) is controlled depending on the configuration of the clutch (12) and/or the predetermined torque to be transmitted.

6. The method according to any of the preceding claims, wherein the rotational speed of the electric machine (4) is controlled to avoid stick-slip phenomenon in the clutch (12).

7. A computer program (P) comprising instructions which, when the program is executed by a computer (44; 500), cause the computer (44; 500) to carry out the method according to any one of the preceding claims.

8. A computer-readable medium comprising instructions, which when executed by a computer (44; 500), cause the computer (44; 500) to carry out the method according to any one of claims 1-6.

9. A control arrangement (40) for controlling a powertrain (3) of a hybrid vehicle (1). the powertrain (3) comprising: a combustion engine (2); an electric machine (4); a gearbox (6) comprising an input shaft (10) coupled to the electric machine (4); and a clutch (12) arranged to selectively transfer torque between the combustion engine (2) and the input shaft (10), the control arrangement (40) comprising: - means for, when the vehicle (1) is at standstill and no gear is engaged in the gearbox (6), controlling the clutch (12) to a position enabling a predetermined torque to be transmitted from the combustion engine (2) to the input shaft (10); and - means for, when the vehicle (1) is at standstill and no gear is engaged in the gearbox (6), controlling the rotational speed of the electric machine (4), such that the clutch (12) is in a slipping state when the vehicle (1) is at standstill and no gear is engaged in the gearbox (6).

10. A powertrain (3) for a hybrid vehicle (1), comprising: a combustion engine (2); an electric machine (4); a gearbox (6) comprising an input shaft (10) coupled to the electric machine (4); and a clutch (12) arranged to selectively transfer torque between the combustion engine (2) and the input shaft (10), wherein the powertrain (3) further comprises a control arrangement (40) according to claim 9.

11. A vehicle (1) comprising a powertrain (3) according to claim 10.