SE539371C2

SE539371C2 - A method for starting an internal combustion engine in a parallel hybrid powertrain and a vehicle comprising such a hybrid drive powertrain

Info

Publication number: SE539371C2
Application number: SE1550567A
Authority: SE
Inventors: Sunden Fredrik; Nilsson Mattias
Original assignee: Scania Cv Ab
Priority date: 2015-05-05
Filing date: 2015-05-05
Publication date: 2017-08-22
Also published as: DE102016005413A1; SE1550567A1

Description

A method for starting an internal combustion engine in a parallel hybrid powertrain and a vehicle comprising such a hybrid drive powertrain.

TECHNICAL FIELD The present invention relates to a method for starting an internal combustion engine in a parallel hybrid powertrain according to the preamble of claim 1. The invention also relates to a vehicle comprising such a hybrid powertrain according to claim 9, a computer program for starting an internal combustion engine according to claim 10 and a computer program product comprising program code according to claim 11.

BACKGROUND Hybrid vehicles comprise a primary propulsion means such as an internal combustion engine and a secondary propulsion means such as an electric machine. In a parallel hybrid powertrain the primary propulsion means and the secondary propulsion means may operate in parallel to simultaneously drive the vehicle or the propulsion means may operate to drive the vehicle one at a time. The electric machine is equipped with at least one energy storage such as electrochemical energy storage for storing electrical energy and a control unit to control the flow of electrical energy between the energy storage and the electric machine. The electric machine may thus alternately operate as a motor and a generator, based on the operating condition of the vehicle. When the vehicle is braking, the electric machine generates electrical energy, which is stored in the energy storage. This is usually called regenerative braking, which means that the vehicle is braking by means of the electric machine and the internal combustion engine. The stored electrical energy may be utilized later for the propulsion of the vehicle.

Under certain operating conditions it is desirable to turn off the internal combustion engine, for example in order to save fuel and to avoid cooling of the internal combustion engine exhaust gas aftertreatment system. When a torque increase to the hybrid powertrain is needed or when the energy storage must be recharged, the internal combustion engine must start quickly and efficiently.

Document US 2013/0231813 A1 discloses a method for starting an internal combustion engine in a hybrid powertrain wherein the electric machine is decelerated to substantially a standstill, the clutch is at least partially engaged and the electric machine is accelerated in order to accelerate the internal combustion engine. Decelerating the electric machine is time consuming and such a method is thus inefficient. The document also discloses a method for starting the internal combustion engine where, while the gearbox is in a neutral state, the electric machine is controlled to a constant speed and the clutch is at least partly engaged. Such a method may cause wear of the clutch.

SUMMARY OF THE INVENTION Despite known solutions in the field, there is a need to develop a method for starting an internal combustion engine in a parallel hybrid powertrain, which is quick and reliable and which minimizes the wear of the clutch.

An object of the present invention is thus to achieve a method for starting an internal combustion engine in a parallel hybrid powertrain, which minimizes the wear of the clutch.

Another object of the invention is to achieve a method for starting an internal combustion engine in a parallel hybrid powertrain, which is quick and reliable.

A further object of the invention is to achieve a method for starting an internal combustion engine in a parallel hybrid powertrain, which maintains the comfort of the vehicle passengers.

Another object of the present invention is to achieve a vehicle with a parallel hybrid powertrain comprising an internal combustion engine, wherein the internal combustion engine may be started according to a new and advantageous method.

Another object of the present invention is to achieve a new and advantageous computer program for starting an internal combustion engine in a parallel hybrid powertrain.

The herein mentioned objects are achieved by a methodcharacterized bythe features in the characterizing part of claim 1.

The herein mentioned objects are also achieved by a vehiclecharacterized bythe features in the characterizing part of claim 10.

The herein mentioned objects are also achieved by a computer program for starting an internal combustion enginecharacterized bythe features in the characterizing part of claim 11.

The herein mentioned objects are also achieved by a computer program product for starting an internal combustion enginecharacterized bythe features in the characterizing part of claim 12.

According to an aspect of the present invention a method for starting an internal combustion engine in a parallel hybrid powertrain is provided. The parallel hybrid powertrain comprises an electric machine, a clutch arranged between the electric machine and the internal combustion engine and a gearbox with an input shaft connected to the electric machine and the clutch. The method comprises the steps of: a) controlling the electric machine, such that the torque provided by the electric machine is gradually decreased to zero; b) disengaging an engaged gear; c) controlling the clutch to provide a gradually increased clutch torque; d) controlling the electric machine to provide a gradually increased electric machine torque, such that there is a substantially constant offset between the clutch torque and the electric machine torque, wherein the electric machine torque is lower than the clutch torque; and e) starting combustion in the internal combustion engine.

When the internal combustion engine is turned off in the parallel hybrid powertrain, the electric machine solely provides the output torque of the powertrain to a drive shaft arranged in connection to the gearbox and the driving wheels. A gear in the gearbox is engaged and the clutch is disengaged. The clutch is connected to the crank shaft of the internal combustion engine and the input shaft and thus the electric machine. The input shaft of the gearbox extends through the electric machine and is thus connected to the gearbox at one end and the clutch at the other end. When the electric machine provides the output torque, the input shaft rotates and the crank shaft is still.

When a decision to start the internal combustion engine has been made, the electric machine is controlled, such that the electric machine torque is gradually decreasing to zero. The decrease of electric machine torque will have substantially no effect on the speed of the electric machine and thus neither on the input shaft speed. When the electric machine no longer provides any torque, the forces acting on the engaged gear are reduced to zero. The previously engaged gear may thereby easily be disengaged. When the gear is disengaged and the gearbox thereby is in a neutral state the clutch is controlled to provide a gradually increased clutch torque. This means that the clutch is controlled to a partly engaged state and thereby slips. The crank shaft will thus start rotating and a clutch torque is thereby transferred to the internal combustion engine. The provided clutch torque will thus affect the speed of the internal combustion engine. By allowing the clutch to slip, the crank shaft will have a braking effect on the input shaft connected to the electric machine. The provided clutch torque and the electric machine torque are thus counteracting. The electric machine is controlled to provide a gradually increased electric machine torque, such that there is a substantially constant offset between the clutch torque and the electric machine torque, wherein the electric machine torque is lower than the clutch torque. By controlling the electric machine to provide a lower torque than the provided clutch torque the electric machine speed will gradually decrease and the internal combustion engine speed will gradually increase. At one stage the electric machine speed and the internal combustion engine speed will be identical and the clutch will thus slip into a substantially engaged state. By controlling the electric machine torque and the clutch torque such that the electric machine speed and the internal combustion engine speed converges the wear and tear of the clutch is minimized. Also, since the clutch slips into an engaged state without having to decrease the electric machine torque to zero, a quick and efficient method for starting an internal combustion engine is achieved.

When the clutch is engaged the clutch torque is zero and the electric machine speed and the internal combustion engine speed are the same. The electric machine is then preferably controlled such that the internal combustion engine reaches a predetermined internal combustion engine speed, whereby the combustion in the internal combustion engine is started and the internal combustion engine is thereby started. The predetermined speed at which the combustion in the internal combustion engine is controlled to start is suitably an idling speed.

The torque provided by the electric machine is preferably increased by increasing the current and thus the power supplied to the electric machine. Thus, the torque provided by the electric machine is preferably decreased by decreasing the current and thus the power supplied to the electric machine.

The internal combustion engine, the clutch, the electric machine and the gearbox are arranged in connection to a control unit. The control unit is adapted to control the internal combustion engine, the clutch, the electric machine and the gearbox, for example for starting the internal combustion engine. A computer may be connected to the control unit.

According to an aspect of the invention the offset between the clutch torque and the electric machine torque is between 150-250 Nm, preferably 200 Nm. The clutch torque may be increased with between 4000-6000 Nm/s, preferably 5000 Nm/s.

According to an aspect of the invention the partly engaged state of the clutch is adaptively determined. Clutch discs in general will change over time due to heat, wear and tear. The clutch stage corresponding to a specific provided clutch torque might therefore change over time. By monitoring the provided clutch torque the stage corresponding to the specific clutch torque may be adaptively determined. This way, it is ensured that sufficient torque is provided to start the internal combustion engine. The provided clutch torque is preferably monitored by the control unit.

The method steps c) and d) may be performed substantially simultaneously. Alternatively, the step d) may be initiated sometime after the initiation of step c).

According to an aspect of the invention the method comprises the further steps of: f) disengaging the clutch; g) engaging a requested gear; and h) engaging the clutch.

When the internal combustion engine is started the clutch is engaged and the gearbox is still in a neutral state. The crank shaft of the internal combustion engine and the input shaft have the same rotational speed. This makes it convenient to shift gear. The electric machine torque is therefore decreased to zero and the clutch is thus easily disengaged. The requested gear is subsequently engaged. The requested gear may be a new gear or the same gear as before the start of the internal combustion engine. The internal combustion engine is thereafter controlled, such that the internal combustion engine speed is synchronized with the electric machine speed and the clutch is controlled to an engaged state. The internal combustion engine may thereby provide output torque to the drive shaft and thus at least partly propels the vehicle. When the clutch is engaged and the internal combustion engine is providing output torque, the torque provided by the electric machine may be reduced or maintained depending on the operating situation. According to an aspect of the invention the method further comprises the step to reduce the electric machine torque to zero, whereby the internal combustion engine solely provides output torque and the electric machine may operate as a generator. Alternatively, the method comprises the further step to maintain the electric machine torque or reduce it to a level different from zero. This way, both the internal combustion engine and the electric machine may provide output torque to the drive shaft or the internal combustion engine may be used to drive units arranged on the internal combustion engine, such as compressor units or air conditioning units.

Preferably, the step g) to engage a requested gear includes synchronizing the input shaft speed with a target speed for the requested gear by means of the electric machine. This way, the requested gear may easily be engaged.

According to an aspect of the invention, a computer program is provided, wherein said computer program comprises programme code for causing an electronic control unit or another computer connected to the electronic control unit to perform the steps according to the herein mentioned method for starting an internal combustion engine.

According to an aspect of the invention a computer programme product is provided, comprising a programme code stored on a computer-readable medium for performing the method steps according to the herein mentioned method for starting an internal combustion engine, when said computer programme is run on an electronic control unit or another computer connected to the electronic control unit.

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 the invention is 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 parallel hybrid powertrain according to an embodiment of the invention; Figure 3a illustrates a flow chart for a method for starting an internal combustion engine according to an embodiment of the invention; Figure 3b illustrates a flow chart for a method for starting an internal combustion engine according to an embodiment of the invention; Figure 4 illustrates diagrams of torque and speed variations during a method for starting an internal combustion engine according to an embodiment of the invention;Figure 5 schematically illustrates a control unit or computer according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 schematically shows a side view of a vehicle 1 which comprises a parallel hybrid powertrain 2 according to an embodiment of the invention. The hybrid powertrain 2 comprises an internal combustion engine 4 and an electric machine 14 connected to a gearbox 6. The gearbox 6 is also connected to the driving wheels 8 of the vehicle 1, through a drive shaft 10.

Figure 2 schematicallyshows a parallel hybrid powertrain 2 in a vehicle 1 according to an embodiment of the invention. The powertrain 2 comprises an internal combustion engine 4, a clutch 12, an electric machine 14 and a gearbox 6. The clutch 12 is arranged between the internal combustion engine 4 and the electric machine 14 and is connected to the crankshaft 16 of the internal combustion engine 4 and an input shaft 17 of the gearbox 6. The input shaft 17 of the gearbox 6 thus extends through the electric machine 14.An output shaft of the gearbox 6, the drive shaft 10, is connected to the driving wheels 8 of the vehicle 1. Only two driving wheels 8 are illustrated in Figure 2, however, any number of driving wheels 8 may be driven by the hybrid powertrain 2 within the scope of the invention.

The internal combustion engine 4, the clutch 12, the electric machine 14 and the gearbox 6 are arranged in connection to a control unit 18. The control unit 18 is adapted to control the internal combustion engine 4, the clutch 12, the electric machine 14 and the gearbox 6, for example for starting the internal combustion engine 4 while the vehicle 1 is propelled by the electric machine 14. A computer 20 may be connected to the control unit 18.

In order to drive the driving wheels 8 and thus propel the vehicle 1, the internal combustion engine 4 and/or the electric machine 14 generates a torque which is transferred via the gearbox 6 to the drive shaft 10. The torque on the drive shaft 10, called output torque, is the torque that propels the vehicle 1. When the internal combustion engine 4 provides output torque on the drive shaft 10 and propels the vehicle 1, the clutch 12 is engaged and a gear is engaged. The electric machine 14 may in this case either provide additional output torque on the drive shaft 10 or it may operate as a generator. In some situations it may be desirable to turn off the internal combustion engine 4 and propel the vehicle 1 by means of the electric machine 14. For instance, in order to save fuel and to avoid cooling of the internal combustion engine 4 exhaust gas afterfreatment system. In these situations the clutch 12 is disengaged and a gear is engaged. When, however, the internal combustion engine 4 is needed again it is important that it can be started in a quick and efficient way.

Figure 3a shows a flowchart for a method for starting an internal combustion engine 4 in a parallel hybrid powertrain 2 according to an embodiment of the invention. The parallel hybrid powertrain 2 is configured as described in Figure 2. The method comprises the step a) to control the electric machine 14, such that the torque Te provided by the electric machine 14 is gradually decreased to zero (see Figure 4). The method further comprises the step b) to disengage an engaged gear and step c) to control the clutch 12 to provide a gradually increased clutch torque Tc. The method further comprises the step d) to control the electric machine 14 to provide a gradually increased electric machine torque Te, such that there is a substantially constant offset between the clutch torque Tc and the electric machine torque Te, wherein the electric machine torque Te is lower than the clutch torque Tc. At the subsequent step e) the combustion in the internal combustion engine 4 is started and the internal combustion engine is thus started. Torque and speed variations during the method for starting an internal combustion 4 engine are shown in Figure 4.

When the internal combustion engine 4 is turned off in the parallel hybrid powertrain 2, the electric machine 14 solely provides the output torque on the drive shaft 10. A gear in gearbox 6 is engaged and the clutch 12 is disengaged. When the electric machine 14 provides the output torque, the crankshaft 16 is still and the input shaft 17 is rotating.

The control unit 18 preferably controls the electric machine 14, such that the electric machine torque Te is decreased to zero; controls the disengagement of the engaged gear; controls the clutch 12 to provide a gradually increased clutch torque Tc; controls the electric machine 14 to provide a gradually increased electric machine torque Te, lower than the clutch torque Tc and controls the internal combustion engine 4 such that it is ignited.

In step a) the electric machine 14 is suitably controlled such that the torque Te provided by the electric machine 14 is gradually decreased to zero by decreasing the current and thus the power supplied to the electric machine 14. When the electric machine 14 no longer provides any torque Te, the forces acting on the engaged gear are reduced to zero. The previously engaged gear may thereby easily be disengaged.

Preferably, the step c) to control the clutch 12 to provide a gradually increased clutch torque Tc includes controlling the clutch 12 to a partly engaged state. This means that the clutch 12 will slip and the crank shaft 16 will thus start rotating and a clutch torque Tc is thereby transferred to the internal combustion engine 4. The provided clutch torque Tc will thus affect the speed nice of the internal combustion engine 4. By allowing the clutch 12 to slip, the crank shaft 16 will have a braking effect on the input shaft 17 connected to the electric machine 14. The electric machine speed ne will thereby be decreased.

The partly engaged stage of the clutch 12 is preferably adaptively determined. Clutch discs in general will change over time due to heat, wear and tear. The clutch stage corresponding to a specific provided clutch torque Tc might therefore change over time. By monitoring the provided clutch torque Tc the stage corresponding to the specific clutch torque Tc may be adaptively determined. This way, it is ensured that sufficient torque is provided to start the internal combustion engine 4. The provided clutch torque Tc is preferably monitored by the control unit 18.

Preferably, in step d) the electric machine 14 is controlled to provide a gradually increased electric machine torque Te, such that there is a substantially constant offset of 200 Nm between the clutch torque Tc and the electric machine torque Te. By controlling the electric machine 14 to provide a lower torque Te than the provided clutch torque Tc the electric machine speed ne will gradually decrease and the internal combustion engine speed nice will gradually increase. At one stage the electric machine speed ne and the internal combustion engine speed nice will be identical and the clutch 12 will thus slip into a substantially engaged state.

When the clutch 12 is engaged the electric machine speed ne and the internal combustion engine speed nice are the same and the electric machine 14 is providing the torque. The electric machine 14 is then preferably controlled such that the internal combustion engine 4 reaches a predetermined internal combustion engine speed nice whereby the combustion in the internal combustion engine 4 is started and the internal combustion engine 4 is thereby started. The predetermined speed nice at which the combustion in the internal combustion engine 4 is controlled to start is suitably an idling speed.

Figure 3b shows a flowchart for a method for starting an internal combustion engine 4 in a parallel hybrid powertrain 2 according to an embodiment of the invention. The method comprises the steps described in Fig. 3a and the further steps of f) disengaging the clutch 12; g) engaging a requested gear; and h) engaging the clutch 12.

When the internal combustion engine 4 is started the clutch 12 is engaged and the gearbox 6 is still in a neutral state. The electric machine torque Te is suitably decreased to zero and the internal combustion engine 4 thus provides the torque. This makes it convenient to shift gear. The crank shaft 16 of the internal combustion engine 4 and the input shaft 17 have the same rotational speed and the clutch 12 is thus easily disengaged in step f).

A new gear, or the same gear as before the start of the internal combustion engine 4, is engaged in step g). Preferably, the step g) to engage a requested gear includes synchronizing the input shaft speed with a target speed for the requested gear by means of the electric machine. This way, the requested gear may easily be engaged.

The clutch 12 is subsequently controlled to an engaged state in step h). The step h) preferably includes controlling the internal combustion engine 4 to the same rotational speed nice as the electric machine speed ne before engaging the clutch 12. The internal combustion engine 4 may thereby provide output torque to the drive shaft 10 and thus at least partly propels the vehicle 1. When the clutch 12 is engaged and the internal combustion engine 4 is providing output torque, the torque Te provided by the electric machine 14 may be reduced or maintained depending on the operating situation. According to an aspect of the invention the method further comprises the step to reduce the electric machine torque Te to zero, whereby the internal combustion engine solely provides output torque and the electric machine may operate as a generator. Alternatively, the method comprises the further step to maintain the electric machine torque or reduce it to a level different from zero. This way, both the internal combustion engine and the electric machine may provide output torque to the drive shaft or the internal combustion engine may be used to drive units arranged on the internal combustion engine, such as compressor units or air conditioning units.

Figure 4 shows diagrams of the torque and speed variations during a method for starting an internal combustion engine 4 according to an embodiment of the invention. The method for starting an internal combustion engine 4 is described in Figure 3a-3b and is here further illustrated by diagrams over the torque and speed variations over time.

The top diagram shows the torque variations over time measured in seconds. The upper solid curve represents the electric machine torque Te and the lower dashed curve represents the clutch torque Tc. The bottom diagram shows the speed variation over time measured in seconds where the solid line represents the electric machine speed ne and the dashed curve represents the internal combustion engine speed nice- When the vehicle 1 is propelled by the electric machine 14 the electric machine speed ne is different from zero and the internal combustion engine speed nice is zero provided that the clutch 12 is disengaged. The electric machine 14 provides a torque Te and since the clutch 12 is disengaged, the clutch torque Tc is zero. The time ti represents the time when the start of the internal combustion engine 4 is initiated. At the time ti, the electric machine 14 is controlled such that the electric machine torque Te is gradually decreased to zero. The electric machine speed ne is substantially the same while the electric machine torque Te is decreased. At the time t2, the electric machine torque Te has reached zero, the engaged gear is disengaged and the clutch 12 is controlled to provide a gradually increased clutch torque Tc. The electric machine 14 is also controlled to provide a gradually increased electric machine torque Te, such that there is a constant offset between the clutch torque Tc and the electric machine torque Te, wherein the electric machine torque Te is lower than the clutch torque Tc.

As described in Figure 3a-3b the clutch torque Tc and the electric machine torque Te are counteracting. Since the clutch torque Tc is greater than the electric machine torque Te, the clutch torque Tc has a braking effect on the electric machine speed ne which is gradually decreased. The clutch torque Tc will at the same time affect the crank shaft 16 of the internal combustion engine 4 and the internal combustion engine speed nice will thereby gradually increase. Due to the offset between the electric machine torque Te and the clutch torque Tc, the electric machine speed ne and the internal combustion engine speed nice will eventually coincide. At this point, represented by t3, the clutch 12 has slipped into a substantially engaged state and the clutch torque Tc is thereby zero.

When the clutch 12 is engaged the electric machine 14 is controlled such that the internal combustion engine 4 reaches a predetermined internal combustion engine speed nice whereby the combustion in the internal combustion engine 4 is started and the internal combustion engine 4 is thereby started. The predetermined speed nice at which the combustion in the internal combustion engine 4 is controlled to start is suitably an idling speed.

When the internal combustion engine 4 is started the clutch 12 is engaged and the gearbox 6 is still in a neutral state. In order to engage a gear the electric machine torque Te is decreased to zero and the clutch 12 is thus easily disengaged at a time t4. The electric machine 14 is then controlled to synchronize the electric machine speed ne with the speed for the requested gear. The electric machine speed ne reaches the speed for the requested gear at a time t5and the requested gear is engaged. The internal combustion engine 4 is then controlled, such that the internal combustion engine speed nice is synchronized with the electric machine speed ne at a time t6and the clutch 12 is controlled to an engaged state.

Figure 5 is a diagram of a version of a device 500. The control unit 18 and/or computer 20 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 non-physical 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 starting an internal combustion engine in a parallel hybrid powertrain. The computer programme P comprises routines for controlling the electric machine such that the electric machine torque is gradually decreased to zero. The computer programme P comprises routines for disengaging an engaged gear. The computer programme P comprises routines for controlling the clutch to provide a gradually increased clutch torque. The computer programme P comprises routines for controlling to electric machine to provide a gradually increased electric machine torque, such that there is a substantially constant offset between the clutch torque and the electric machine torque, wherein the electric machine torque is lower than the clutch torque reducing the clutch torque. The computer programme P comprises routines for starting the combustion in the internal combustion engine. The computer programme P comprises routines for disengaging the clutch, engaging a requested gear and engaging the clutch.

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 starting an internal combustion engine (4) in a parallel hybrid powertrain (2) comprising an electric machine (14), a clutch (12) arranged between the electric machine (14) and the internal combustion engine (4) and a gearbox (6) with an input shaft (17) connected to the electric machine (14) and the clutch (12), characterized by the steps of: a) controlling the electric machine (14), such that the torque (Te ) provided by the electric machine (14) is gradually decreased to zero; b) disengaging an engaged gear; c) controlling the clutch (12) to provide a gradually increased clutch torque (Tc ); d) controlling the electric machine (14) to provide a gradually increased electric machine torque (Te ), such that there is a substantially constant offset between the clutch torque (Tc ) and the electric machine torque (Te ), wherein the electric machine torque (Te ) is lower than the clutch torque (Tc ); and e) starting combustion in the internal combustion engine (4).

2. A method according to claim 1, characterized in that the offset between the clutch torque (Tc ) and the electric machine torque (Te ) is between 150-250 Nm.

3. A method according to claim 1 or 2, characterized in that the clutch torque (Tc ) and the electric machine torque (Te ) are counteracting.

4. A method according to any of the preceding claims, characterized in that the step c) includes controlling the clutch (12) to a partly engaged state.

5. A method according to claim 4, characterized in that the partly engaged state of the clutch (12) is adaptively determined.

6. A method according to any of the preceding claims, characterized in that step c) and d) are performed substantially simultaneously.

7. A method according to any of the preceding claims, characterized by the further steps of: f) disengaging the clutch (12); g) engaging a requested gear; and h) engaging the clutch (12).

8. A method according to claim 7, characterized in that the step g) includes synchronizing the input shaft speed with a target speed for the requested gear by means of the electric machine (14).

9. A vehicle with a parallel hybrid powertrain (2), characterized in that the powertrain (2) comprises an internal combustion engine (4) which is started according to the method in any of the claims 1-8.

10. A computer program (P), wherein said computer program comprises programme code for causing an electronic control unit (18; 500) or another computer (20; 500) connected to the electronic control unit (18; 500) to perform the steps according to any of the claims 1-8.

11. A computer programme product comprising a programme code stored on a computer-readable medium for performing the method steps according to any of claims 1-8, when said computer programme is run on an electronic control unit (18; 500) or another computer (20; 500) connected to the electronic control unit (18; 500).