Technical field

The invention relates to a method and a control arrangement for starting an internal combustion engine. The invention also relates to a computer program, a computer- readable medium and a vehicle comprising such a control arrangement.

The following background description constitutes a description of the background to the invention, which does not necessarily have to constitute prior art.

One of the major global challenges today is reducing the negative impacts of road transportation on the environment due to greenhouse gas emissions. Moreover, in motor vehicles, such as cars, trucks and buses, the cost of fuel constitutes a significant expense for the vehicle's owner or user. This has led to an increased interest in vehicle electrification.

In general, hybrid vehicles are designed to provide improved energy economy compared to conventional vehicles powered solely by a combustion engine. Hybrid vehicles are equipped with at least two different power sources, such as an internal combustion engine and one or more electrical machines. Electric hybrid vehicles may be designed to be powered by an internal combustion engine, or at least one electrical machine at a time, or by a combination of the two (or more) power sources. For example, an electrical machine may provide additional power to assist an internal combustion engine when the vehicle is started from standstill, accelerating, or climbing a hill, and be used as only power source when vehicle load is light. The electrical machine may additionally be used for regenerative braking, thereby assisting the vehicle brakes while simultaneously recapturing energy from vehicle’s motion to generate electricity. The start of an internal combustion engine requires mechanical power to rotate a shaft of the internal combustion engine. When the outside temperature decreases, and thereby engine temperature, the mechanical energy required to start the internal combustion engine when cold may increase as e.g., the engine oil becomes more viscous making it more difficult to circulate, which in turn increases the mechanical power that is required to accomplish the start. At the same time, the energy that the battery system can deliver may decrease. The starting of an internal combustion engine during low temperatures may thereby become challenging.

It is an object of embodiments of the invention to alleviate or solve at least some of the drawbacks with the prior art.

Thus, it is an object to provide a solution for starting an internal combustion engine in a vehicle during conditions when sufficient power cannot be supplied by the vehicle’s starter motor.

According to a first aspect of the invention, aforementioned and further objectives are achieved through a method for starting an internal combustion engine of a vehicle, the vehicle comprising: a starter motor for starting the internal combustion engine, the starter motor being powered by a first battery system having a first voltage and a first battery, and an electrical machine being powered by a second battery system having a second voltage and a second battery, the second battery system being separated from the first battery system; the method comprising when a start of the internal combustion engine is initiated: determining that a propelling torque is to be applied to a rotational shaft of the internal combustion engine by both the starter motor and the electrical machine simultaneously; applying a first propelling torque to the rotational shaft of the internal combustion engine using the starter motor; and applying a second propelling torque to the rotational shaft of the internal combustion engine using the electrical machine, the applied first and second propelling torques together starting the internal combustion engine.

Starting an internal combustion engine may here relate to supplying an energy needed to rotate a crankshaft of the engine until ignition when the engine is able to operate on its own motion.

The vehicle’s electrical system may here comprise a first and a second battery system. The second battery system being separated from the first battery system may be understood as the two battery systems not being electrically connected when the vehicle is off and during normal vehicle operation. In that way one battery system may be used as auxiliary battery, supplying power to various accessories while the other mainly to supply power to the starter motor. Hereby, the risk of engine start failure due to power supply shortage is mitigated.

It may be determined that a propelling torque is to be applied to a rotational shaft of the internal combustion engine by both the starter motor and the electrical machine simultaneously, when a condition preventing normal combustion engine start, i.e. , by solely using the starter motor, is detected.

By applying the first and the second propelling torque to the rotational shaft of the internal combustion engine using the starter motor and the electrical machine, wherein the applied first and second propelling torques together start the internal combustion engine, a reliable engine start method is obtained. The power provided by the starter motor may be enhanced by applying additional power from the electrical machine when starting the engine. Ultimately, the size of the first battery system may be reduced as the need of dimensioning margins decreases. Hence, a cost-efficient solution is obtained with a reduced environmental impact.

In an embodiment of the invention, the determining that a propelling torque is to be applied to a rotational shaft of the internal combustion engine by both the starter motor and the electrical machine is based on a temperature of the internal combustion engine. Hereby, the engine start may be reliably performed in situations when power need increases and the risk of engine start failure due to power supply shortage is mitigated.

In an embodiment of the invention, the determining that a propelling torque is to be applied to a rotational shaft of the internal combustion engine by both the starter motor and the electrical machine is based on a charging level of the first battery system.

Hereby, the engine start may be reliably performed in situations when due to decreased charging level in the first battery system sufficient power cannot be supplied to start the internal combustion engine by means of the starter motor. Hence, the risk of engine start failure due to power supply shortage is mitigated.

In an embodiment of the invention, the method further comprises determining that a propelling torque is to be applied to a rotational shaft of the internal combustion engine by both the starter motor and the electrical machine when a temperature of the internal combustion engine is below a first temperature and/or the charging level of the first battery system is below a first charging level.

Hereby, the risk of engine start failure due to power supply shortage is mitigated.

In an embodiment of the invention, the vehicle further comprises means for transferring electrical energy between the first battery system and the second battery system, the method further comprising, based on a charging level of the first and/or second battery system: transferring electrical energy from the second battery system to the first battery system when applying the first propelling torque to the rotational shaft of the internal combustion engine using the starter motor.

Hereby, the power provided to the starter motor and thus the propelling torque to the engine may be increased. Hence increased efficiency is obtained.

In an embodiment of the invention, the vehicle further comprises a gearbox and a clutch arranged between the gearbox and the internal combustion engine, wherein applying the second propelling torque to the rotational shaft of the internal combustion engine comprises applying, by the electrical machine, the second propelling torque to the gearbox with the clutch being engaged.

The clutch being engaged is here equivalent to closed clutch when energy is transferred between the internal combustion engine and the gearbox of the vehicle.

By applying, by the electrical machine, the second propelling torque to the gearbox with the clutch being engaged, the power from the electrical machine will be transferred from the electrical machine to the engine.

In an embodiment of the invention, the vehicle further comprises a gearbox and a clutch arranged between the gearbox and the internal combustion engine, the method further comprising with the clutch being disengaged, accelerating, by the electrical machine, gearbox components interconnecting the electrical machine to the clutch prior to applying the first propelling torque by the starter motor, and following the acceleration of the interconnecting gearbox components, applying the second propelling torque to the rotational shaft of the internal combustion engine by connecting the gearbox to the internal combustion engine by engaging the clutch.

The clutch being disengaged is here equivalent to an open clutch when no energy is transferred between the internal combustion engine and the gearbox of the vehicle.

Hereby, when the electrical machine is activated with the clutch being disengaged, a torque will be applied to the gearbox building up a rotational power. The rotational power, also referred to as a moment of inertia, will be transferred to the engine once the clutch is engaged together with the propelling torque applied by the electrical engine. Hence an increased power may be transferred to the engine compared to the case when the power is supplied with the clutch engaged.

In an embodiment of the invention, the applying the propelling torque to a rotational shaft of the internal combustion engine by both the starter motor and the electrical machine further comprises: adapting the speed of rotation applied to the rotational shaft of the internal combustion engine by the electrical machine to the speed of rotation of the rotational shaft of the internal combustion engine applied by the starter motor.

Hereby, an efficient power is provided to the engine by both the starter motor and the electrical machine.

In an embodiment of the invention, the first voltage is different from the second voltage.

Hereby, a battery system powering a predetermined set of electrical components in the vehicle may be adapted to fit specific requirements put by the components, independent of the capability of other battery systems in the vehicle.

According to a second aspect, the invention relates to a control arrangement for starting an internal combustion engine of a vehicle, the vehicle comprising: a starter motor for starting the internal combustion engine, the starter motor being powered by a first battery system having a first voltage and a first battery, and an electrical machine being powered by a second battery system having a second voltage and a second battery, the second battery system being separated from the first battery system.

The control arrangement is configured to when a start of the internal combustion engine is initiated: determine that a propelling torque is to be applied to a rotational shaft of the internal combustion engine by both the starter motor and the electrical machine simultaneously; apply a first propelling torque to a rotational shaft of the internal combustion engine using the starter motor; and apply a second propelling torque to the rotational shaft of the internal combustion engine using the electrical machine, the applied first and second propelling torques together starting the internal combustion engine.

It will be appreciated that all the embodiments described for the method aspects of the invention are applicable also to at least one of the control arrangement aspects of the invention. Thus, all the embodiments described for the method aspects of the invention may be performed by the control arrangement, which may also be a control device, i.e. a device. The control arrangement and its embodiments have advantages corresponding to the advantages mentioned above for the methods and their embodiments.

According to a third aspect of the invention, aforementioned and further objectives are achieved through a vehicle comprising a control arrangement according to the second aspect.

According to a fourth aspect, the invention relates to a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to the first aspect.

According to a fifth aspect, the invention relates to a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to the first aspect.

The above-mentioned features and embodiments of the method, the control arrangement, the vehicle, the computer program, and the computer-readable medium, respectively, may be combined in various possible ways providing further advantageous embodiments.

Further advantageous embodiments of the method, the control arrangement, the vehicle, the computer program, and the computer-readable medium according to the present invention and further advantages with the embodiments of the present invention emerge from the detailed description of embodiments.

Brief description of the drawings

Embodiments of the invention will be illustrated in more detail below, along with the enclosed drawings, where similar references are used for similar parts, and where:

Figure 1 illustrates a vehicle in which embodiments of the invention may be implemented. Figure 2 shows a flow chart of a method for starting an internal combustion engine according to embodiments of the invention.

Figure 3 illustrates an electrical system of a vehicle in which embodiments of the invention may be implemented.

Figure 4 illustrates a non-limiting example of starting an internal combustion engine according to embodiments of the invention.

Figure 5 illustrates a non-limiting example of starting an internal combustion engine according to embodiments of the invention.

Figure 6 illustrates a control arrangement of the vehicle of Figure 1 according to embodiments of the invention.

Detailed description

The starting of an internal combustion engine in a vehicle requires an initial assistance to rotate the engine until a speed of rotation has been reached where the internal combustion engine is able to operate at its own motion. According to conventional solutions, an electrical motor such as a starter motor or another electrical motor in the vehicle may be used to rotate the engine’s crankshaft until the rotation is maintained by ignition of fuel. The electrical motor used to start the engine is in general powered by a battery system which may be dimensioned to provide a reliable energy source. However, the battery system also often needs to comply with other requirements related to cost, size and weight. For example, it may be desirable to keep down the cost, size, and weight of the battery system to provide a cost and energy efficient vehicle configuration.

In general, electrical machines used as starter motors may operate reliably during normal conditions when powered by relatively small batteries (e.g., ~50Ah). However, during situations when increased amount of power is required to start the engine, for example in low temperatures, such relatively small batteries may not be able to provide sufficient power. Cold starts, i.e., when the internal combustion engine has cooled substantially in relation to the running temperature, are more difficult than starting a vehicle that has been run recently. More effort is needed to rotate/turn over a cold engine for multiple reasons. For example, lower temperatures cause engine oil to become more viscous, making it more difficult to circulate the oil.

Another problem which may arise is that the battery system powering the starter motor has been drained such that the remaining energy level is not sufficient to start the internal combustion engine. Starting an internal combustion engine requires considerable power. The batteries are recharged during the operation of the internal combustion engine, however, during frequent start operations the energy level may drop, and sufficient power cannot be supplied.

It is an objective of the present invention to provide a method and a control arrangement for starting an internal combustion engine such that these problems are at least partly solved.

Figure 1 schematically illustrates an exemplary vehicle in which the embodiments of the present invention may be implemented. The vehicle 100 may be a heavy vehicle, such as a bus, or a truck.

The vehicle 100 comprises a plurality of electrical systems and subsystems. However, for simplicity only parts of the vehicle 100 that are associated with the proposed method are shown in Figure 1 .

The vehicle 100 comprises a powertrain 110, which in the shown embodiment comprises an internal combustion engine 101 , which in a conventional manner, via an output shaft 106, is connected to a gearbox 109 via a clutch 107 and a gearbox input shaft 108. Energy created in the internal combustion engine is transferred via the gearbox 109, a gearbox output shaft 112 and a final gear 113, e.g., a conventional differential and provides torque to one or more of the vehicles driving wheels.

In addition, the powertrain 110 includes a starter motor 102 for starting the internal combustion engine. The starter motor may be powered by a battery system 103 comprising at least one battery unit. Moreover, the powertrain 110 includes one or more electrical machines 104. The one or more electrical machines may be configured for driving drive wheels of the vehicle 100 and the vehicle 100 may thus for example be a so-called hybrid vehicle. Furthermore, the one or more electrical machines may be configured to transfer power to the internal combustion engine 101 via the gearbox 109, the gearbox input shaft 108, the clutch 107 and the output shaft 106. The one or more electrical machines 104 may be powered by one or more electric battery systems 105 each comprising at least one battery unit.

The vehicle 100 may also comprise one or several devices such as sensors 132, 134 for monitoring a temperature in one or more vehicle components and/or the ambient air temperature. For example, the temperature of the internal combustion engine 101 may be monitored. Moreover, the vehicle 100 may be configured to monitor, e.g. by means of one or more sensors 136, 138, a charging level of at least one battery unit of the one or more electric battery systems 103, 105, for example the battery units 307- 310 in Figure 3.

The internal combustion engine 101 , the starter motor 102 and the one or more electrical machines 104 may be controlled by the vehicle's control system via a control arrangement 120. The clutch 107, which may for example take the form of an automatically controlled clutch, and/or the gearbox 109, may also be controlled by means of one or more suitable control units, generally depicted as the control arrangement 120 in Figure 1. Thus, the control arrangement 120 may be distributed over several control units configured to control different parts of the vehicle 100. The control arrangement 120 may e.g. include a determining unit 121 , an applying unit 122, and an applying unit 123 arranged for performing the method steps of the disclosed invention as will be explained further on. The control arrangement 120 will be described in further detail in Figure 6.

The proposed solution will now be described with reference to Figure 2 which shows a flow chart of a method 200 for starting an internal combustion engine of a vehicle. The vehicle may be the vehicle 100 of Figure 1 .

As previously mentioned with reference to Figure 1 , the vehicle comprises a starter motor 102 for starting the internal combustion engine 101 , the starter motor 102 being powered by a first battery system 103 having a first voltage V1 and a first battery, and an electrical machine 104 being powered by a second battery system 105 having a second voltage V2 and a second battery, the second battery system 105 being separated from the first battery system 103. The first battery system 103 may, in other words, be isolated from the second battery system 105. Aspects of the vehicle’s electrical system will be explained in more detail with reference to Figure 3.

The method 200 is executed when a start of the internal combustion engine 101 is initiated and comprises steps 210 - 230.

In step 210 of Figure 2, it is determined that a propelling torque is to be applied to a rotational shaft of the internal combustion engine 101 by both the starter motor 102 and the electrical machine 104 simultaneously.

In step 220 of Figure 2, a first propelling torque is applied to the rotational shaft of the internal combustion engine 101 using the starter motor 102 .

In step 230 of Figure 2 a second propelling torque is applied to the rotational shaft of the internal combustion engine 101 using the electrical machine 104, the applied first and second propelling torques together starting the internal combustion engine 101.

Thus, in step 210 of method 200, it may be determined that a propelling torque is to be applied to a rotational shaft of the internal combustion engine 101 at least partly simultaneously by the starter motor 102 and the electrical machine 104.

The determining that a propelling torque is to be applied to a rotational shaft of the internal combustion engine 101 by both the starter motor 102 and the electrical machine 104 simultaneously, in step 210 of method 200, may comprise a determination that the vehicle’s starter motor 102 cannot supply sufficient power to start the internal combustion engine and thus that additional power is required.

The applying of a propelling torque by both the starter motor 102 and the electrical machine 104 simultaneously, may be understood as the propelling torque being applied at least partly overlapping by the starter motor 102 and the electrical machine 104. During such overlap, an enhanced power is transferred to the internal combustion engine compared to when a propelling torque is provided solely by one of the starter motor 102 and the electrical machine 104.

The method steps of method 200 as described herein do not necessarily need to be executed in the order illustrated. In one example, the first and the second propelling torque may be applied to the rotational shaft of the internal combustion engine 101 simultaneously. According to another example, the first propelling torque may be applied to the rotational shaft of the internal combustion engine 101 prior to applying the second torque, as long as the first and the second propelling torque are applied simultaneously during at least an overlapping time period. In similar manner, according to yet another example, the second propelling torque may be applied to the rotational shaft of the internal combustion engine 101 prior to applying the first torque, as long as the first and the second propelling torque are applied simultaneously during at least an overlapping time period.

By executing the steps 210 - 230 of the method 200, the start of the internal combustion engine is performed by at least partly simultaneously supplying power from the starter motor and the electrical motor. Thus, as previously described, the risk of engine start failure due to insufficient power supply is reduced since the effect of the power applied by the starter motor is increased by the simultaneous applying of power by the electrical machine.

Figure 3 illustrates a possible configuration of the electrical system in the vehicle 100 where the method and embodiments of the invention may be implemented.

In addition to the components already described with reference to Figure 1 , including the internal combustion engine 101 , the gearbox 109, the clutch 107 and the control arrangement 120, Figure 3 illustrates more in detail a possible implementation of the starter motor 102, the electrical machine 104 and the battery systems 103, 105 used to power the electrical components of the vehicle 100.

The starter motor 102 may, in one example, be mechanically connected to a rotational/crank shaft of the internal combustion engine 101 by means of a suitable gearing. When activated, the starter motor 102 may be configured to provide a propelling torque to rotate the engine’s rotational/crank shaft. The power for powering the starter motor 102 may be provided by a first battery system 103, comprising one or more batteries 309, 310 providing a first voltage V1 . When it is desired to start the internal combustion engine 101 , power from the battery system 103 is applied to the starter motor 102 enabling the starter motor to rotate the engine 101 . Thus, applying a propelling torque to the rotational shaft of the internal combustion engine 101 in step 220 in Figure 2 may be done when the starter motor 102 is activated by supplying power from the first battery system 103.

The battery system 103 may comprise one or more battery units 309, 310. Once the internal combustion engine 101 is running, the charge of the one or more battery units 309, 310 of the first battery system 103 may be sustained by, according to conventional solutions, converting mechanical energy generated by the engine into electrical energy. The battery system 103 may primary be used to power the vehicle’s starter motor. However, it may also be used to power various loads 301 such as various car accessories.

The electrical machine 104 may be a high voltage electrical machine, powered by the second battery system 105 via a high voltage converter 306. Thus, the electrical machine 104 may convert electrical energy, supplied from the second battery system 105 into mechanical energy applied to the drive line of the vehicle 100. The high voltage converter 306 may e.g., be configured to convert direct current voltage, DC voltage, supplied by the second battery system 105 to an alternating current voltage, AC voltage, required for powering the electrical machine 104. The electrical machine may be moreover operated, according to conventional methods, as an electric generator in a reverse flow of power converting mechanical energy into electrical energy which may be stored in the second battery system 105. Although only one electrical machine is illustrated in Figure 3, it should be understood that the vehicle 100 may comprise several electrical machines. In one example, the electrical machine 104 may be mechanically coupled with the gearbox 109 such that power from the electrical machine may be transferred via the gearbox 109, the gearbox input shaft 108, the clutch 107 and the output shaft 106 to the internal combustion engine 101. The electrical machine 104 may be activated when electrical energy is fed from the second battery system 105 enabling the electrical machine 104 to apply a torque to rotate the gearbox 109. When the clutch 107 is engaged, the torque applied by the electrical machine to the gearbox will be transferred to the vehicle’s internal combustion engine 101.

In another example, the electrical machine 104 may be mechanically coupled directly to the internal combustion engine 101 instead of being connected through other components such as the gearbox 109 and the clutch 107 and, when activated, provide propelling torque directly to the engine 101. Thus, applying a propelling torque to the rotational shaft of the internal combustion engine 101 in step 230 in Figure 2 may comprise the electrical machine 104 being activated by supplying power from the second battery system 105.

The electrical machine 104 may additionally be used as a generator for battery charging through regenerative braking recapturing energy from vehicle’s motion to generate electricity and helping to slow the vehicle. The second battery system 105 may comprise one or more battery units 307, 308 and have a second voltage V2. The second battery system 105 may be an auxiliary battery system used to power various loads 302 such as various car accessories.

As was previously mentioned with reference to Figure 2, the first and the second battery system 103, 105 may be separated from each other. As was also previously explained, the second battery system 105 being separated from the first battery system 103 may be understood as the two battery systems not being electrically connected to each other when the vehicle is turned off and during normal vehicle operation. In that way one battery system may be used as auxiliary battery, supplying power to various accessories while the other mainly supply power to the starter motor. Hereby, the risk of engine start failure due to power supply shortage is mitigated.

The vehicle may, in one example, comprise means 305 used for separating the first and the second battery system 103, 105. Such means may, for example, comprise a DC/DC converter. The DC/DC converter may furthermore be configured to connect the first and the second battery system 103, 105 and, when connected, to enable transferring of electrical energy between the two battery systems 103, 105 by converting the voltage of one battery system, e.g., the second voltage V2, to the voltage of the other battery system, e.g., to the first voltage V1 .

In an embodiment, the first voltage V1 is different from the second voltage V2.

In the non-limiting example in Figure 3, the first battery system 103 may comprise two series-connected 12 V, batteries 309, 310 providing a voltage of 24 V having a suitable capacity, such as e.g., 50Ah. The second battery system 105 may comprise two series- connected 24V batteries 307, 308 providing a voltage of 48V. As previously explained, by providing different voltage levels, a battery system powering a predetermined set of electrical components in the vehicle may be adapted to fit specific requirements of the components, independent of the capability of other battery systems in the vehicle.

In addition to the method steps 210 - 230 described with reference to Figure 2, the method 200 may, according to embodiments of the invention, comprise optional steps which are disclosed with reference to Figure 4 and Figure 5.

Figure 4 shows a flowchart of a method 400 according to embodiments of the invention. The method 400 is performed in a vehicle 100 comprising a gearbox 109 and a clutch 107 arranged between the gearbox 109 and the internal combustion engine 101 as explained with reference to Figurel .

In step 410 in Figure 4, a start of the vehicle’s internal combustion engine 101 is initiated. This may be done automatically or manually by the driver. The driver may, for example, turn a key or press a start button. Automatic start may be initiated by a control unit.

In step 420, which corresponds to step 210 in Figure 2, it is determined whether a propelling torque is to be applied to a rotational shaft of the internal combustion engine 101 by both the starter motor and the electrical machine simultaneously. If it is determined that the starter motor 102 will not be capable of supplying sufficient power for starting the internal combustion engine 101 , additional power will be needed from the electrical machine 104.

The determining in step 420 may, according to embodiments of the invention, be carried out prior to applying the first propelling torque in step 440 in Figure 4 and the second propelling torque in step 450 in Figure 4 to the rotational shaft of the internal combustion engine 101.

In one embodiment, the determining 420 may be based on a temperature T1 of the internal combustion engine 101.

As was previously explained, starting the internal combustion engine 101 at low temperatures may require increased energy. Cold starts require more power than starting of a vehicle that has been run recently. More effort is needed to rotate a cold engine for multiple reasons. For example, low temperatures may cause engine oil to become more viscous, making it more difficult to circulate the oil.

The engine temperature T1 may be obtained by means of any suitable sensor means 132 measuring a temperature of one of more engine components. Furthermore, the engine temperature may be estimated based on a temperature of the ambient air using e.g., theoretical thermal models of engine components, e.g., taking into account the time that has lapsed since the internal combustion engine was last turned off. The ambient air temperature may be obtained from e.g., one or more temperature sensors 134 or weather data of the current vehicle location.

In one embodiment it may be determined that a propelling torque is to be applied to a rotational shaft of the internal combustion engine 101 by both the starter motor 102 and the electrical machine 104 when a temperature T1 of the internal combustion engine 101 is below a first temperature.

The temperature T1 of the internal combustion engine may here relate to the actual temperature of the internal combustion engine 101 obtained from sensor data or determined according to the description above.

The first temperature may relate to a temperature threshold limit below which starting the internal combustion engine using the starter motor 102 is not considered to be possible. Such a temperature threshold limit may depend, e.g., on specifics of the internal combustion engine 101 , the starter motor 102 as well as the capacity and charging level of the battery system 103 powering the starter motor 102. The first temperature may be used as a reference which is suitable to compare the obtained temperature of the internal combustion engine T1 with at the time instance when an engine start is to be performed to determine if starting the engine with the starter motor alone is considered to be possible. The first temperature may be obtained by measuring or otherwise determining the performance of the starter motor 102 when powered by the battery system 103 and comparing with the amount of power needed to start the internal combustion engine 101 at different temperature levels. According to a non-limiting example, the first temperature may be any temperature below 0 °C, for example -10°C. Thus, when the temperature of the internal combustion engine 101 is below -10°C, it is determined that the starter motor 102 cannot provide sufficient power to start the internal combustion engine 101 and, consequently, that a propelling torque is to be applied to a rotational shaft of the internal combustion engine 101 by both the starter motor 102 and the electrical machine 104.

In one embodiment, the determining in step 420 may be based on a charging level of the first battery system 103. As was previously explained, the starting of an internal combustion engine 101 may require considerable power from the battery system 103 powering the starter motor 102. If the energy level of the first battery system 103 drops to a level where sufficient power cannot be supplied to start the internal combustion engine 101 , additional power may be needed to perform a successful engine start. The charging level of one or several batteries 309, 310 comprised in the first battery system 103 may be provided based on monitoring using for example a battery monitoring functionality in the vehicle.

In one embodiment it may be determined that that a propelling torque is to be applied to a rotational shaft of the internal combustion engine 101 by both the starter motor 102 and the electrical machine 104 when a temperature T1 of the internal combustion engine 101 is below a first temperature and/or the charging level of the first battery system 103 is below a first charging level.

The battery performance, e.g., in terms of the maximum deliverable power to power the starter motor may depend on the battery’s current charging level as well as the current temperature of the engine 101. For example, it may be possible to start an engine 101 using a starter motor 102 powered by a fully charged battery system 103 when the engine temperature is, for example, -5°C. However, if the charging level of the battery system 103 drops to a lower charging level, a start of the internal combustion engine at the temperature of -5°C may no longer be possible since the power that the battery may supply to the starter motor may not be sufficient. However, for higher temperatures an engine start may still be possible also when the charging level of battery system 103 is reduced. The temperature threshold for deciding whether to start the vehicle using the starter motor only or a combination of the starter motor and the electrical machine may hence be dependent also on the current charging level of at least the battery system 103. The first temperature and/or the first charging level may be obtained by measuring or otherwise determining the performance of the starter motor 102 when powered by the battery system 103 at different charging levels and comparing with the amount of power needed to start the internal combustion engine 101 at different temperature levels.

With further reference to step 420, if it is determined that torque is to be applied by both the starter motor and the electrical machine (Yes), the method continues to step 430, and if not (No), a conventional start of the internal combustion engine 101 is performed in step 480, by means of a starter motor 102.

According to the present example, the electrical machine 104 is arranged downstream the clutch and in step 430 the clutch is therefore engaged in case the clutch is not already engaged. Since, according to the present example, the electrical machine 104 is arranged downstream the gearbox, step 430 may also comprise a setting of the gearbox to a suitable gear that allows the desired speed of rotation of the internal combustion engine by means of the electrical machine 104.

In step 440, corresponding to the step 220 of method 200 in Figure 2, a first propelling torque is applied to the rotational shaft of the internal combustion engine 101 using the starter motor 102, as was previously described with reference to Figure 2.

In step 450 in Figure 4, corresponding to step 230 of method 200, a second propelling torque is applied to the rotational shaft of the internal combustion engine 101 using the electrical machine 104 as was previously described with reference to Figure 2.

Thus, in an embodiment, applying the second propelling torque to the rotational shaft of the internal combustion engine comprises applying, by the electrical machine 104, the second propelling torque to the gearbox 109 with the clutch being engaged. The applied power is hence transferred through the gearbox 109 and clutch 107 to the internal combustion engine 101 from the electrical machine 104.

In an optional step 460, in an embodiment, electrical energy from the second battery system 105 is transferred to the first battery system 103 when applying the first propelling torque to the rotational shaft of the internal combustion engine 101 using the starter motor 102. As previously explained with reference to Figure 3, the vehicle may comprise means 305 for transferring electrical energy between the first battery system 103 and the second battery system 105. Thus, the electrical energy may be transferred from the second battery system 105 to the first battery system 103 using, e.g., the DC/DC converter 305 converting the voltage from the second voltage level V2 to the first voltage level V1 to power the starter motor 102 and charge the first battery system 103. To transfer electrical energy, the first and the second battery system 103, 105 need to be electrically connected, e.g., by means of the DC/DC converter 305.

The transfer of energy in step 460 may be based on a charging level of the first and/or second battery system 103, 105.

The second battery system 105 may be used to assist the first battery system 103 during engine start, e.g., to increase the power that can be transferred to the internal combustion engine from the starting motor 102. Thus, electrical energy may be transferred from the second battery 105 system to the first battery system 103 when the charging level of the battery drops under a certain level.

In one example, the starter motor 102 may be powered by the battery system 103, 105 having the most power available, or otherwise being the most suitable to provide power, at the time when the engine start is carried out. In another example, the starter motor 102 may be powered by both battery systems 103, 105 simultaneously.

In an embodiment, applying the propelling torque to a rotational shaft of the internal combustion engine 101 by both the starter motor 102 and the electrical machine 105 in step 450 in Figure 4, further comprises, in step 470, adapting the speed of rotation applied to the rotational shaft of the internal combustion engine 101 by the electrical machine to the speed of rotation of the rotational shaft of the internal combustion engine 101 applied by the starter motor 102.

It may be the case that in order to provide maximum, or at least sufficiently high power to the internal combustion engine 101 , the speed of rotation of the starter motor 102 and the speed of rotation of the electrical machine 104 are synchronized by controlling the high voltage converter 306 using the control arrangement 120, such that the same speed of rotation is applied to the internal combustion engine from both starter motor 102 and the electrical machine 104. As previously explained in reference to Figure 3, the high voltage converter 306 supplies the electrical machine 104 with energy by converting DC voltage to AC voltage. In one example, the AC voltage required to power the electrical machine 104 is a three-phase alternating current. A person skilled in the art is aware of the fact that the speed of rotation of the electrical machine 104 may depend on the AC voltage frequency. The relation between the speed of rotation of the electrical machine 104 and the AC voltage frequency may be linear, as in synchronous motors, or non-linear due to slip, as in asynchronous motors. The rotational speed of the electrical machine 104 may be controlled by the control arrangement 120 controlling the frequency supplied by the high voltage converter 306, or by requesting a required propelling torque from the electrical machine 104, such that the rotational speed supplied by the electrical machine 104 to the internal combustion engine 101 is synchronized with the rotational speed supplied by the starter motor 102.

Turning to Figure 5, a flowchart of a further exemplary method 500 for starting an internal combustion engine 101 according to embodiments of the invention is shown.

The embodiment illustrated in fig. 5 may be performed during conditions, when the power supplied by the starter motor 102 together with the electrical machine 104 may still not be sufficient to properly start the engine 101. This may, for example, be the case when the battery system 105 powering the electrical machine 104 is low. The propelling torque applied by the electrical machine 104 to the engine 101 may then be increased by activating the electrical machine 104 with the clutch first being disengaged. Steps 510, 520, and 570 - 590 in Figure 5 correspond to steps 410, 420 and 460 - 480 of Figure 4 and have already been described with reference to Figure 4.

Thus, as previously explained with reference to Figure 4, in step 510 in Figure 5, corresponding to step 410 in Figure 4, a start of the vehicle’s internal combustion engine 101 is initiated.

In step 520, corresponding to step 420 in Figure 4, it is determined whether a propelling torque is to be applied to a rotational shaft of the internal combustion engine 101 by both the starter motor 102 and the electrical machine 104 simultaneously.

If it is determined that torque is to be applied by both the starter motor 102 and the electrical machine 104 (Yes), the method continues to step 530, and if not (No), a conventional start of the internal combustion engine 101 is performed in step 590, corresponding to step 480 in Figure 4, by means of the starter motor 102.

In step 530 the clutch 107 is disengaged instead of being engaged. It is still ensured that the gearbox is set to a suitable gear.

When the clutch 107 is disengaged, no propelling torque is applied to the rotational shaft of the internal combustion engine 101 by the electrical machine 104.

In step 540, in an embodiment, gearbox components interconnecting the electrical machine 104 to the clutch 107 (by the gearbox being set to a suitable gear) are accelerated by the electrical machine 104. In an embodiment, the gearbox components may be accelerated prior to applying, in step 550 in Figure 5 the first propelling torque by the starter motor 102.

In step 550 in Figure 5, corresponding to the step 440 of method 400 in Figure 4, the first propelling torque is applied to the rotational shaft of the internal combustion engine 101 using the starter motor 102, as was previously described with reference to Figure 4.

In step 560 in Figure 5, in an embodiment, following the acceleration of the gearbox components in step 540, the second propelling torque may be applied to the rotational shaft of the internal combustion engine 101. The second propelling torque may be applied by connecting the gearbox 109 and thereby the electrical machine 104 to the internal combustion engine 101 by engaging the clutch 107.

As previously explained, when the electrical machine 104 is activated with the clutch being disengaged, the gearbox components and possibly other components that are set in motion will inherently give rise to a moment of inertia in the rotating components. When the clutch 107 is closed, and the rotating parts are connected to the non-rotating, or at least slower rotating, internal combustion engine 101 , the moment of inertia gives rise to a torque attempting to accelerate the internal combustion engine 101. This torque may be substantial and is applied in addition to the torques applied by the starter motor 102 and electrical machine 104. Hence an increased power may be transferred to the engine compared to the case when the power is supplied with the clutch engaged which in turn may allow the internal combustion engine 101 to be properly started.

As previously explained with reference to Figure 4, in an optional step 570 in Figure 5, corresponding to step 460 in Figure 4, electrical energy from the second battery system 105 is transferred to the first battery system 103 when applying the first propelling torque to the rotational shaft of the internal combustion engine 101 using the starter motor 102.

In an optional step 580 in Figure 5, corresponding to the step 470 in Figure 4, the speed of rotation applied to the rotational shaft of the internal combustion engine 101 by the electrical machine 104 is adapted to the speed of rotation of the rotational shaft of the internal combustion engine 101 applied by the starter motor 102.

It should be noted that the method steps of methods 200, 400 and 500 as described herein do not necessarily need to be executed in the order illustrated. The steps may essentially be executed in any suitable order, for as long as the physical requirements and the information needed to execute each method step is available when the step is executed.

According to an aspect of the invention, a control arrangement 120 for starting an internal combustion engine 101 of a vehicle 100, is presented. The control arrangement 120 includes means 121 arranged for determining 210 that a propelling torque is to be applied to a rotational shaft of the internal combustion engine 101 by both the starter motor 102 and the electrical machine 104 simultaneously;

The control arrangement 120 further includes means 122 arranged for applying 220 a first propelling torque to a rotational shaft of the internal combustion engine 101 using the starter motor 102.

The control arrangement 120 further includes means 123 arranged for applying 230 a second propelling torque to the rotational shaft of the internal combustion engine 101 using the electrical machine 104, the applied first and second propelling torques together starting the internal combustion engine 101 .

The control arrangement 120, e.g. a device or a control device, according to the invention may be arranged for performing all of the above, in the claims, and in the herein described embodiments method steps. The control arrangement 120 is hereby provided with the above-described advantages for each respective embodiment.

The invention is also related to a vehicle 100 including the control arrangement 120.

Now turning to Figure 6 which illustrates the control arrangement 600/120, which may correspond to or may include one or more of the above-mentioned control units 121 , 122, 123 i.e. the control units performing the method steps of the disclosed invention. The control arrangement 600/120 comprises a computing unit 601 , which can be constituted by essentially any suitable type of processor or microcomputer, e.g. a circuit for digital signal processing such as Digital Signal Processor, DSP, or a circuit having a predetermined specific function such as Application Specific Integrated Circuit, ASIC. The computing unit 601 is connected to a memory unit 602 arranged in the control arrangement 600/120, which memory unit provides the computing unit 601 with, e.g., the stored program code and/or the stored data which the computing unit 601 requires to be able to perform computations. The computing unit 601 is also arranged to store partial or final results of computations in the memory unit 602.

In addition, the control arrangement 600/120 is provided with devices 611 , 612, 613, 614 for receiving and transmitting input and output signals. These input and output signals can contain waveforms, impulses, or other attributes which, by the devices 611 , 613 for the reception of input signals, can be detected as information and can be converted into signals which can be processed by the computing unit 601. These signals are then made available to the computing unit 601. The devices 612, 614 for the transmission of output signals are arranged to convert signals received from the computing unit 601 in order to create output signals by, e.g., modulating the signals, which can be transmitted to other parts of and/or systems in the vehicle 100.

Each of the connections to the devices for receiving and transmitting input and output signals can be constituted by one or more of a cable; a data bus, such as a Controller Area Network, CAN, bus, a Media Orientated Systems Transport, MOST, bus, or some other bus configuration; or by a wireless connection. A person skilled in the art will appreciate that the above-stated computer can be constituted by the computing unit 601 and that the above- stated memory can be constituted by the memory unit 602.

Control systems in modem vehicles commonly comprise communication bus systems consisting of one or more communication buses for linking a number of electronic control units, ECUs, or controllers, and various components located on the vehicle. Such a control system can comprise a large number of control units and the responsibility for a specific function can be divided amongst more than one control unit. Vehicles of the shown type thus often comprise significantly more control units than are shown in Figures 1 and 6, which is well known to the person skilled in the art within this technical field.

In a shown embodiment, the invention may be implemented by the one or more above mentioned control units 121 , 122 and 123. The invention can also, however, be implemented wholly or partially in one or more other control units already in the vehicle 100, or in some control unit dedicated to the invention.

Here and in this document, units are often described as being arranged for performing steps of the method according to the invention. This also includes that the units are designed to and/or configured to perform these method steps.

The one or more control units 121 , 122, 123 are in Figure 1 illustrated as separate units. These units may, however, be logically separated but physically implemented in the same unit or can be both logically and physically arranged together. These units may e.g. correspond to groups of instructions, which can be in the form of programming code, that are input into, and are utilized by a processor/computing unit 601 when the units are active and/or are utilized for performing its method step, respectively. The person skilled in the art will appreciate that a the herein described embodiments may also be implemented in a computer program, which, when it is executed in a computer, instructs the computer to execute the method. The computer program is usually constituted by a computer program product 603 stored on a non-transitory/non- volatile digital storage medium, in which the computer program is incorporated in the computer-readable medium of the computer program product. The computer-readable medium comprises a suitable memory, such as, e.g.: Read-Only Memory, ROM, Programmable Read-Only Memory, PROM, Erasable Programmable Read-Only Memory, EPROM, Flash memory, Electrically Erasable Programmable Read-Only Memory, EEPROM, a hard disk unit, etc. The invention is not limited to the above-described embodiments. Instead, the invention relates to, and encompasses all different embodiments being included within the scope of the independent claims.