WO2015106772A1

WO2015106772A1 - A control method and propulsion system in a hybrid vehicle

Info

Publication number: WO2015106772A1
Application number: PCT/EP2014/000137
Authority: WO
Inventors: Martin KÄRVERUD
Original assignee: Volvo Truck Corporation
Priority date: 2014-01-20
Filing date: 2014-01-20
Publication date: 2015-07-23

Abstract

The invention relates to control method for a propulsion system (102) in a hybrid vehicle (101). The propulsion system (102) comprises an Internal Combustion Engine (ICE) (103) and an Electric Machine (EM) (105) wherein said ICE (103) and EM (105) are configured to be mechanically connected to traction wheels (108) and at least a clutch (104) between the ICE (103) and the traction wheels (108). The control method comprising an ICE shut down algorithm when slowing down the vehicle speed to a speed lower than an idle speed comprising the steps of: - Maintaining the ICE (103) drivingly connected to its traction wheels (108) while the speed of the vehicle (101, 201, 301) is lowered to a speed below ICE idle speed and - Cutting off the injection of fuel into the ICE (103) before the ICE engine speed reaches zero while the ICE still is connected to its associated traction wheels (108).

Description

A control method and propulsion system in a hybrid vehicle

TECHNICAL FIELD OF THE INVENTION

The invention relates to a system and a method for drivetrain control for hybrid vehicles comprising an Internal combustion engine and an electric machine for propulsion of a vehicle. The invention is in particular directed to the control of the vehicle propulsion units when the vehicle is slowed down or stopped.

BACKGROUND OF THE INVENTION

Electric hybrid vehicles, i.e. a vehicle comprising an Internal Combustion Engine (ICE) and an Electric

Machine (EM), e.g. an electric motor being able to use as a generator as well, are well known in the art. One main goal for electric hybrids is to use the different propulsion sources, i.e. the ICE and the EM, in an energy efficient way and control these units to

cooperate properly in order to reduce fuel consumption and emissions from the exhaust.

Hybrids may be of different kinds such as parallel hybrids or series hybrids or a mixture of these kinds. In general, series hybrids are designed such that there is no mechanical connection between the ICE and the EM which is designed to propel the vehicle. The output shaft of the ICE is connected to a generator which generates electricity in order to power the EM which in turn provides propulsion force to traction wheels of the vehicle. For this kind of vehicles is there thus no possibility to provide traction force directly

(mechanically) from the ICE to the traction wheels. In another kind of electric hybrids, parallel hybrids, is the ICE mechanically connected with the EM. In a common used configuration is the output shaft of the ICE connected to an input shaft of the EM via a clutch. An output shaft of the EM is connected to the traction wheels via a gearbox. However, also other

configurations of a parallel hybrid is possible, e.g. may the gearbox be located between the ICE and the EM even though this configuration not is as common as the configuration described above.

There may also be hybrids which have an ICE

mechanically connected to a first driven axle having a first pair of driven wheels and a second driven axle powered by an EM, alternatively replacing the second driven axle with one or several EM directly coupled to each driven wheel.

In the configurations described above is the ICE intended to provide traction force to the traction wheels during at least some occasions, e.g. when driving at a relative constant speed on a high way is the hybrid in general only using the ICE. In city traffic, when there in general are frequent slowdowns or stops at relative low speeds is there in general an alternating use of the ICE and the EM in order to optimize fuel consumption. By controlling ' the different power sources (ICE and EM) according to present (and anticipated) conditions and being able to start and shut down the different power sources at the right occasions and in the right manner when slowing down or stopping may the vehicle be driven economically. In DE 10 2007 055 742 is described a method for

controlling a hybrid powertrain when shutting down the ICE. The ICE may be shut down while being connected to the EM and may thus be slowed down in an efficient way. An advantage compared to allowing the engine to slow down by its own is that undesired vibrations may be avoided as the ICE is slowing down at low Revolutions Per Minute (RPM) . Further documents describing shut down of an ICE in a hybrid is for example disclosed in US 2009 / 271 057; US 8,210,294; US 2012 / 016 573; or US 2006 / 030 979.

There are thus a number of different ways known for how to control shut down of an ICE in a hybrid. However, there is still a need for improvement in controlling the cooperation of the different power sources in a hybrid and how to control shut down of the ICE in order to improve fuel efficiency and avoid undesired

vibrations from low speed revelations of the ICE when stopping or slowing down.

DESCRIPTION OF THE INVENTION

An object of the invention is to provide a control system for a hybrid vehicle comprising an Internal Combustion Engine (ICE) and an Electric Machine (EM) which may shut down the ICE in a fuel efficient way when the vehicle is slowed down or stopped.

The invention is directed to the kind of hybrids which have mechanical connection between the ICE and a driven axle, i.e. for those kind of hybrids in which the ICE is drivingly connected to one (or several) driven axles and is in particular suitable for parallel hybrids and hybrids having the ICE and an EM drivingly connected to different driven wheels. Hence, both the ICE and the EM are configured to be mechanically connected to and able to provide a traction torque to traction wheels. There is also at least a clutch provided in the mechanical connection of the ICE to its associated traction wheels. By engaging or disengaging the clutch the ICE may switch between being drivingly connected and disconnected from its associated traction wheels. The control method comprises an ICE shut down algorithm which is intended to be used when the vehicle slows down to a speed lower than an idle speed of the ICE. The retardation of the vehicle may thus be controlled by recuperation, i.e. running the EM in generator mode and charging the battery, with fuel cut off to the ICE from the start of the retardation. The ICE shut down control algorithm comprises the steps of:

I. Maintaining the ICE connection to traction wheels while the speed of the vehicle is lowered to a speed corresponding to a speed of the ICE below its idle speed. Hence, it is intended that the engine speed will be forced to reduce its speed quicker due to its maintained connection to the powertrain and the wheels while the vehicle speed is slowed down below the idle speed. This will enable the ICE to reduce its speed with reduced undesired vibrations and/or noise.

II. Cutting off the injection of fuel into the ICE before the engine speed reaches zero while the ICE still is connected to traction wheel. Hence, the fuel injection may be cut off above or below the idle speed while the vehicle is retarding or start to retard while the ICE still is drivingly connected to its associated traction wheels. By cutting off the fuel may it be possible to reduce the overall fuel consumption and reduce emissions from the vehicle. In addition, in those cases the engine is connected to a generator, e.g. if connected to a reversible EM which may work as a generator, may kinetic energy of the moving parts of the ICE be regenerated.

The ICE shut down algorithm is intended to be used primarily when there is a complete stop of the vehicle and the vehicle decelerates more or less continuously until the vehicle is at standstill. In these cases is thus the connection of the ICE to the traction wheels in general maintained until the vehicle is at

standstill. As will be further exemplified below, there may be certain occasions when it is desired to

disengage the connection of the ICE to the driven axle, e.g. if the retardation rate of the vehicle is slow or slowing down drastically or if it is indicated that the vehicle will continue to travel at a speed below a speed corresponding to engine idle speed. In this case will the engine thus be allowed to be slowed down due to internal friction and/or other braking mechanisms. In order to be able to use the system efficiently is it further desired to control the braking system

adequately and the braking may be controlled by a braking allocating system. The braking system may for example include retarder, engine brake, exhaust brake or regenerative braking using the EM as a generator and service brakes. In dependence of braking demand and relevant parameters, e.g. braking time, engine

temperature, brake temperatures and State Of Charge (SOC) of a battery may the appropriate braking

allocation be made. In addition, there is of course also the braking from internal friction of the

powertrain and the engine which also will be used.

The disconnection of the ICE from the traction wheels may be made in different ways. In those instances the ICE is drivingly connected to the driven axle via the EM is there often a clutch between the ICE and EM. The ICE could thus be disconnected from the traction wheels by disengaging the clutch between the ICE and EM resulting in a disconnected ICE and a still connected EM. Hence, in this case, will the disengagement of the clutch result in a maintained connection of the EM to the driven axle while the ICE is disconnected. In most cases, when the ICE is disconnected, is there a desire to have the EM connected. To have the EM connected will provide for the benefit of making a quick response to a desired acceleration request as well as being prepared to be used as a generator in regenerative braking. An object of the ICE shut down algorithm engine is to save fuel and improve fuel efficiency. It is thus desired to cut off the fuel injection as early as possible in order to save fuel. Hence, it may be desired to cut off the fuel injection even before the engine idle speed has been reached if there is

identified there will be a stop of the vehicle or reduction of the speed to a speed below engine idle speed. However, even if there is an indication it is desired to make a stop of the vehicle, a cut off of the fuel injection to the ICE may lead to a rather abrupt braking if the vehicle speed is too high and cause an inconvenient sudden slow down for passenger and cause undesired wear of the engine. In order to reduce the braking effect, and allowing the shutdown at a higher speed, could the gearbox be controlled to shift up a gear or even shift up to highest gear, when the engine shut down algorithm is intended to be used and the fuel injection is cut off. In other cases may it be desired to cut off the fuel at a speed below the engine idle speed also. Hence, the fuel injection cut off may be set in a wide variety of ranges depending on the prevailing circumstances but is in general thought to be made at an engine speed above the idle speed of the ICE.

As briefly mentioned above, there may be certain occasions when the ICE shut down algorithm not is suitable to use the whole way unto standstill. The ICE shut down algorithm may thus further comprise the feature of at least partly disconnecting the ICE from the traction wheels if the vehicle is travelling at a speed corresponding to a speed below engine idle speed at certain occasions, e.g. if the vehicle has

travelled, or there is an indication the vehicle will travel, at a speed below a speed corresponding to engine idle speed for a certain time or distance. This could for example be the case if the vehicle speed is reduced due to a traffic jam and ends up in slowly moving cue.

The ICE shut down algorithm may be controlled to be performed when there is an indication that the vehicle will reduce its speed to standstill. There may

optionally be a further prerequisite that there is an indication that the vehicle will be at standstill for a predetermined time. Hence, the feature of using an expected stop condition for selecting to use the ICE shut down algorithm may be used. However, as previously described above, there may be occasions when there is no longer a desire to stop the vehicle. This may for example be the case when it is first indicated that a complete stop is expected but it is later indicated that the vehicle no longer is expected to stop or the stop is expected later on. In practice, this could be the case for a public

transportation bus which usually make a stop at a bus stop but skips the stop. The bus decelerates to a speed below the idle speed of the engine in order to stop and the ICE shut down algorithm is activated. However, due to an indication that no passengers will get off the bus and no persons are waiting at the bus stop to get on, the driver no longer desires to stop. This may thus also be a case wherein the earlier described feature of disconnecting the ICE from the traction wheels when the vehicle is travelling at a speed corresponding to a speed below engine idle speed may be used and the EM may easier be used to accelerate the bus.

There may of course be further control algorithms for the vehicle which may be used together with the ICE shut down algorithm. There may for example also be an ICE idle algorithm also intended to be used when slowing down the vehicle speed to a speed lower than an idle speed of the vehicle. The ICE idle algorithm comprises the steps of;

I. Disengaging the ICE connection to the traction wheels while the speed of the vehicle is lowered to a speed corresponding to a speed of the ICE below its idle speed. In case the ICE and the EM are drivingly connected to the same driven axle is the ICE in general connected to the driven axle upstream of the EM, i.e. the EM is located in between the ICE and the driven axle. If there is a clutch located in between the ICE and the EM will a disengagement of this clutch thus

disconnect the ICE from the EM as well as the driven axle. The EM will thus still be engaged with the driven axle after disengagement of the clutch in this configuration and the ICE be disconnected .

Maintaining the fuel injection to the ICE in order to maintain the ICE running, e.g. at idle speed, while the speed of the vehicle is reduced to a speed corresponding to a speed of the ICE below its idle speed. In this arrangement will there thus be a continuously feed of fuel to the ICE. Even though there is a continuous fuel consumption may this strategy be advantageous in view of overall fuel efficiency in certain cases. For instance, in cases when a si.op. or the time- when driving the vehicle at a speed corresponding to a speed below engine idle speed is expected to be rather short and the ICE torque is desired soon again, may the consumption of fuel due to ICE stop and start be greater than if the engine is run at idle speed. It may also be possible to use the engine for other purposes than propelling the vehicle while running, e.g. for generating electricity if it may selectively be connected to a generator. The control method may thus select between to use the ICE shut down or the ICE idle algorithm in dependence of vehicle related parameters and/or expected near future driving patterns .

The ICE idle algorithm is thus intended to be used when there is a desire to keep the ICE running at low speeds or standstill. However, the conditions may change and it may be estimated due to change in parameters that there is a desire to shut down the ICE, e.g. in order to save fuel. The ICE idle algorithm may thus further comprises the step of cutting off the fuel injection to the ICE. In case there is a clutch in between the ICE and EM it could be engaged such that the ICE may be slowed down and stopped in a controlled manner,

otherwise it may simply be allowed to slow down

naturally. This action could be performed when there is a desire to stop the ICE when the vehicle reaches standstill or have been at standstill for a certain time and/or the vehicle is expected to be at standstill exceeding a certain time limit.

It has been described above that the ICE shut down and ICE idle algorithms may be selected when the vehicle is, or intended to be, decelerated to a vehicle speed below a speed corresponding to engine idle speed. The selection between the ICE shut down algorithm and the ICE idle algorithm may be made due to a multitude of different criteria and may for example be made in dependence of if there is an expectation to reach standstill or not. In case this criteria is used for selection between the different algorithms is it implied that the ICE shut off algorithm should be used if a standstill is expected. It may also be the case that the strategy to be chosen is dependent on an estimated time at standstill and in this case is the most obvious selection to use the ICE shut down

algorithm if the standstill is expected to be above a certain time limit. However, there may be overriding criteria, e.g. the need for the engine running due to a low SOC (State Of Charge) or having a lot of power consuming auxiliaries running desiring the ICE to be running such that power may be provided and thus indicating that the ICE idle algorithm should be used. In general, provided that there is no urgent need for any function of the vehicle, is the overriding criteria for selecting the desired algorithm the expected fuel efficiency for the respective algorithms when the vehicle is reducing its speed, below ICE idle speed.

Since an important criteria for minimizing the fuel consumption for a vehicle with frequent accelerations and decelerations for stopping and starting the vehicle is to know when a stop or slow driving condition (below engine idle speed) is expected and for how long the stop/slow driving condition will last is it important to be able to predict future driving conditions

including an expected stop and/or an expected time for standstill. This may be predicted based on info

provided by a navigational device, e.g. GPS combined with map data. Such a map may include features such as where stop signs and/or traffic lights are located. The predicted driving pattern may also be based on

empirically collected or preprogrammed driving data for a certain route including predetermined stops, e.g. for a bus route or a garbage truck collecting route. By using this data it may be estimated when it is

beneficial, e.g. in view of optimized fuel consumption, when to use either of the ICE shut down or idle

algorithm. The ICE shut down algorithm could for example be used for scheduled stops or scheduled stops above a certain time limit when this algorithm is considered to be best.

As previously discussed, there may be further

parameters in addition to fuel consumption, which may be used for selecting when to use the ICE shut down algorithm. These parameters may for example be State Of Charge (SOC) of a battery or energy storage unit, brake pedal actuation and/or ICE or EM temperature.

The control system is intended to be used on a

multitude of different hybrid configurations which uses an ICE and EM. One beneficial system in which it may be used is a system wherein the propulsion system is designed such that the ICE and EM form part of the same powertrain and thus may propel the same traction wheels. The system may be configured such that an output shaft of the ICE is connected to an input shaft of the EM via a clutch. Furthermore, an output shaft of the EM is connected to a driven axle. In this

configuration may thus the driven axle be mechanically powered by either the ICE or EM. The configuration also allows the ICE to be disconnected from the driven axle by disengaging the clutch in between the ICE and EM. To be noted, the clutch could be a part of a more

sophisticated arrangement, e.g. a part of a gearbox and need not to be a simple clutch. The invention is further directed to a hybrid

propulsion system comprising an Electronic Control Unit (ECU) in order to control the propulsion system

comprising the ICE and EM. By ECU is meant either a single processor or a group of processors working together in order to perform the desired control of the system. As previously described, the ICE and EM are configured to be mechanically connected to and able to provide a traction torque to traction wheels. There is also at least a clutch provided in the mechanical connection of the ICE to its associated traction wheels such that said ICE may switch between being drivingly connected and disconnected from its associated traction wheels. The ECU is connected to said clutch, ICE and EM in order to control them. The ECU is programmed to selectively perform an ICE shut down algorithm when slowing down the vehicle speed to a speed lower than an idle speed of the vehicle. The ICE shut down algorithm programmed onto the ECU comprises the steps of:

- Maintaining the ICE connection to traction wheels while the speed of the vehicle is lowered to a speed corresponding to a speed of the ICE below its idle speed, and

- Cutting off the injection of fuel into the engine before the engine speed reaches zero while the ICE still is connected to traction wheels.

The propulsion system may further be designed such that the ICE and EM form part of the same powertrain. Such an arrangement could for example have an output shaft of the ICE connected to an input shaft of the EM via a clutch and a driven axle connected to an output shaft of the EM via a gearbox. The clutch may either be just a clutch or be a part of a more sophisticated

arrangement. By having such an arrangement, it will be possible to disconnect the ICE from the driven axle by disengaging the clutch in between said ICE and EM.

There may of course be further clutches in the

arrangement, e.g. between the EM and the driven axle. A gearbox could also be relocated to be placed upstream of the EM, between the ICE and EM, instead of as suggested first.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a schematic view of a first hybrid

vehicle configuration suitable for the present invention .

Fig. 2 shows a schematic view of a second hybrid

vehicle configuration suitable for the present invention .

Fig. 3 shows a schematic view of a third hybrid

vehicle configuration suitable for the present invention

DETAILED DESCRIPTION OF THE DRAWINGS

In figure 1 is a schematic view of a hybrid vehicle 101 shown. The hybrid vehicle 101 is provided with a powertrain 102 which comprises an Internal Combustion Engine (ICE) 103, a clutch 104, an Electric Machine (EM) 105, a gearbox 106 and a driven axle 107 connected to a pair of traction wheels 108 a, b. The hybrid vehicle further comprises a non-driven axle 109

provided with a pair of wheels 110 a, b. The driven axle 108 is connected to an output shaft of the EM 105 via the gearbox 106. An input shaft of the EM 105 is connected to the ICE 103 via the clutch 104. The powertrain 102 is further connected to an Electronic Control Unit (ECU) 111 which is intended to control the relevant parts of the powertrain 102.

The ECU may thus be programmed to control the

powertrain as desired. The ECU 111 may also be

connected to relevant sensors or other control units wherefrom it may collect relevant data for the control of the powertrain, e.g. engine speed of the ICE, clutch positions (engaged/disengaged), present gear selection, State Of Charge (SOC) of the battery, exhaust emissions etc. Hence, the ECU 111 will be provided with the relevant data for controlling the powertrain. The ECU 111 will thus be programmed to perform an ICE engine shut down algorithm which will be executed dependent on input data and threshold values and/or look up tables for relevant parameters. If the criteria for executing the ICE engine shut down algorithm are fulfilled, the ECU 111 will control the powertrain 102 to maintain the ICE 103 connection to traction wheels 108 a, b while the speed of the vehicle is lowered to a speed

corresponding to a speed of the ICE below its idle speed. This may for example be the case when it is expected that the vehicle 101 will make a stop. In case there should be no other overriding function indicating that the ICE 103 should be disconnected from the traction wheels 108 a, b the ICE 103 will stay

connected to the traction wheels 108 a, b until the vehicle 101 stops. Hence, the ICE 103 will be forced to slow down by the braking action of the vehicle and its connection to the powertrain 102 and EM 105 will also make it possible to reduce undesired vibrations and/or noise. In addition, the kinetic energy, or inertia, of the moving parts of the ICE 103 may be used for

regenerating energy in the EM 105, if it may be used as a generator, to be stored in an accumulator 112

connected to the EM 105.

The ECU 111 is further programmed to cut off the injection of fuel into the ICE 103 before the engine speed reaches zero. By cutting off the fuel may it be possible to reduce the overall fuel consumption and reduce emissions from the vehicle. The fuel may be cut off at an appropriate stage, e.g. when the engine speed of the ICE 103 reaches its idle speed.

An appropriate end criteria for the ICE shut down algorithm may be when the vehicle has reached

standstill. The ECU 111 may in this case prepare the vehicle for take off, e.g. by disengaging the clutch 104 such that the vehicle may start by using the EM 105 as the propulsive force when taking off.

The configuration described herein can be changed while still being within the scope of the invention. For example, in an alternative embodiment could the gearbox 106 and the EM 105 switch positions. Another

alternative embodiment could be to have two gearboxes, a main gearbox and a range gear, and replace the gearbox 106 for the range gear and replace the clutch 104 with a main gearbox.

In figures 2 and 3 are described two further

embodiments of the present invention which have an ICE connected to a first pair of driven wheels and an EM connected to another, second pair of wheels. In figure 2 is thus described a possible configuration of a hybrid powertrain 202a, 202b of a hybrid vehicle 201. In this embodiment is an ICE 203 drivingly connected to a driven axle 207 comprising a pair of traction wheels 208 a, b via a gearbox 206. A first electric machine (EMI) 205a is connected to a second driven axle 209 having attached a second pair of driven wheels 210 a, b thereto. The ICE 203 is also attached to a second electric machine (EM2) 205b which may be used as a generator in order to charge an accumulator or battery 212 which also is connected to the EMI 205a such that EMI is powered and may provide traction force to the second driven axle 209. The propulsion units, the ICE 203 and the. EMI 205a, are drivingly connected to different driven axles 207, 209 and not drivingly connected to each other. The ICE 203 is connected to its associated driven axle 207 via a clutch 204 located between the second electric machine EM2 205b and the ICE 203.

In figure 3 is described still another possible

configuration of a hybrid powertrain 302a, 302b of a hybrid vehicle 301 which has a basic structure similar to the one described in figure 2. Also in this

embodiment comprises the hybrid vehicle 301 an ICE 303 drivingly connected to a driven axle 307, comprising a pair of traction wheels 308 a, b, via a gearbox 306 and an electric machine (EMI) 305 is connected to a second driven axle 309 having attached a second pair of driven wheels 310 a, b thereto. The propulsion units, the ICE 303 and the EMI 305, are drivingly connected to

different driven axles 307, 309 and not drivingly connected to each other. The ICE 303 is connected to its associated driven axle 307 via a clutch 304. Also these configurations may be modified with

rearrangement of clutches and or gearboxes. It may als be possible to replace the electric machine connected to a driven axle for a pair of wheel motors which are connected to one traction wheel each.

In the above examples has it only been shown that each of the propulsion units are connected to a single driven axle. They could of course be connected to two or more driven axles also.

Hence, there may be several hybrid systems and

configurations for which the present invention may be used as long as there is an ICE which may be drivingly connected and disconnected from being used to provide mechanical, propulsive force to a driven axle.

Claims

A control method for a propulsion system

(102,202,302) in a hybrid vehicle (101,201,301), said propulsion system ( 102 , 202 , 302 ) comprising an Internal Combustion Engine (ICE) (103,203,303) and an Electric Machine (EM) (105, 205, 305) wherein said ICE (103,203,303) and EM (105, 205, 305) are configured to be mechanically connected to and able to provide a traction torque to traction wheels (108, 208, 210, 308, 310) and at least a clutch (104, 204, 304) provided in the mechanical connection of said ICE (103,203,303) to its associated traction wheels (108, 208, 308) such that said ICE (103,203,303) may switch between being drivingly connected and disconnected from its associated traction wheels (108, 208, 308), said control method comprising an ICE shut down algorithm when slowing down the vehicle speed to a speed lower than an idle speed of the vehicle (101,201,301) comprising the steps of:

- Maintaining the ICE (103,203,303) drivingly connected to its associated traction wheels (108, 208, 308) while the speed of the vehicle (101, 201, 301) is lowered to a speed corresponding to a speed of the ICE (103,203,303) below its idle speed, characterized in that

- the injection of fuel into the ICE (103,203,303) is cut off before the ICE engine speed reaches zero while the ICE still is connected to its associated traction wheels (108, 208, 308).

2. A control method according to claim 1

characterized in that said connection of the ICE (103, 203, 303) to the traction wheels (108, 208, 308) is maintained until the vehicle is at

standstill.

A control method according to claim 1

characterized in that said control method

comprises the feature of cutting off the fuel injection to the ICE (103, 203, 303) at an engine speed above the idle speed of the ICE.

A control method according to any previous claim, characterized in that said ICE shut down algorithm further comprises the feature of at least partly disconnecting the ICE (103, 203, 303) from the associated traction wheels (108, 208, 308) if the vehicle (101, 201, 301) is travelling at a speed corresponding to a speed below ICE engine idle speed and the vehicle (101, 201, 301) has travelled, or there is an indication the vehicle will continue to travel, at a speed below a speed corresponding to ICE engine idle speed.

A control method according to any previous claim, characterized in that said shut down algorithm is performed when there is an indication that the vehicle (101, 201, 301) will reduce its speed to standstill .

A method according to claim 5,

characterized in that said shut down algorithm is performed when there is an indication that the vehicle (101, 201, 301) will be at standstill for a predetermined time. A method according to any previous claim,

characterized in that said control method

comprises in addition to said ICE shut down algorithm an ICE idle algorithm to be used when slowing down the vehicle speed to a speed lower than an idle speed of the vehicle (101, 201, 301), said control method selecting in dependence of vehicle related parameters and/or expected near future driving patterns between using said ICE shut down or said ICE idle algorithm, said ICE idle algorithm comprises the steps of:

- Disengaging the ICE (103, 203, 303) from being drivingly connected to its associated traction wheels (108, 208, 308) and, when applicable, to the EM (105, 205b) while the speed of the vehicle (101, 201, 301) is lowered to a speed

corresponding to a speed of the ICE (103, 203, 303) below its idle speed,

- maintaining the fuel injection to the ICE (103, 203, 303) in order to maintain the ICE running, e.g. at idle speed, while the speed of the vehicle (101, 201, 301) is reduced to a speed

corresponding to a speed of the ICE (103, 203, 303) below its idle speed.

A control method according to claim 7,

characterized in that said ICE idle algorithm further comprises the step of cutting off the fuel injection to the ICE (103, 203, 303) and, when applicable, engaging said ICE with the EM (105, 205b) when there is a desire to stop the ICE provided that the vehicle (101, 201, 301) reaches standstill or have been at standstill for a certain time and/or the vehicle is expected to be at standstill exceeding a certain time limit.

. A control method according to claim 7 or 8,

characterized in that said selection between said ICE shut down algorithm and said ICE idle

algorithm is made in dependence of if there is an expectation to reach standstill and/or the

expected time for a standstill and/or an expected fuel efficiency for the respective algorithms when the vehicle (101, 201, 301) is reducing its speed below ICE idle speed.

10. A control method according to any previous

claim, characterized in that an expected stop and/or an expected time for standstill is based on info provided by a navigational device, e.g. GPS combined with map data, and/or driving data for a certain route including predetermined stops, e.g. for a bus route or a garbage truck collecting route, such that the ICE engine shut down

algorithm is used for scheduled stops or scheduled stops above a certain time limit.

11. A method according to any previous claims,

characterized in that said ICE shut down

algorithm is selected in dependence of State Of

Charge (SOC) of a battery or energy storage unit, brake lever pressure and/or ICE or EM

temperature .

12. A method according to any previous claim,

characterized in that said propulsion system is designed such that said ICE (103, 203) and EM (105, 205b) form part of the same powertrain and an output shaft of the ICE is connected to an input shaft of the EM via a clutch (104, 204) and an output shaft of the EM (105, 205b) is

connected to the driven axle (107, 207) such that the ICE (103, 203) may be disconnected from the driven axle (107, 207) by disengaging the clutch (104, 204) in between said ICE (103, 203) and EM (105, 205b) .

. A propulsion system (102, 202, 302) for a hybrid vehicle (101, 201, 301) comprising an Internal Combustion Engine (ICE) (103, 203, 303) and an . Electric Machine (EM) (105, 205, 305) wherein said ICE and EM are configured to be mechanically connected to and able to provide a traction torque to traction wheels (108,208, 210, 308, 310) and at least a clutch (104, 204, 304) provided in the mechanical connection of said ICE (103, 203, 303) to its associated traction wheels (108, 208, 308) such that said ICE may switch between being drivingly connected and at least partly

disconnected from its associated traction wheels (108, 208, 308), said propulsion system further comprising an Electronic Control Unit (ECU) (111, 211, 311), connected to said clutch (104, 204, 304), ICE (103, 203, 303) and EM (105, 205, 305), programmed to selectively perform an ICE shut down algorithm when slowing down the vehicle speed to a speed lower than an idle speed of the vehicle (101, 201, 301) wherein said ICE shut down

algorithm comprises the steps of:

- Maintaining the ICE (103, 203, 303) drivingly connected to traction wheels (108, 208, 308) while the speed of the vehicle (101, 201, 301) is lowered to a speed corresponding to a speed of the ICE below its idle speed, and

- Cutting off the injection of fuel into the ICE (103, 203, 303) before the ICE engine speed reaches zero while the ICE (103, 203, 303) still is connected to traction wheels.

A propulsion system (102, 202) according to claim 13, characterized in that said propulsion system

(102, 202) is designed such that said ICE (103, 203) and EM (105, 205b) form part of the same powertrain and an output shaft of the ICE (103, 203) is connected to an input shaft of the EM

(105, 205b) via said clutch (104, 204) and an output shaft of the EM is connected to the driven axle (107, 207) such that the ICE may be

disconnected from the driven axle (107, 207) by disengaging the clutch (104, 204) in between said ICE and EM.