SE1850360A1 - Method and system for propelling an electric vehicle - Google Patents

Abstract

The present invention relates to a method for propelling an electric vehicle (100),the vehicle (100) comprising:an electrical machine (101, 102) configured to selectively provide a controllable power for propelling at least one drive wheel (113, 114) of the vehicle (100), the electrical machine having a rotor (404) and a stator (406), the stator (406) comprising a stator winding (U, V, W) comprising a plurality of circumferentially distributed electromagnets (U1-U6, V1-V6, W1-W6), the rotor being caused to rotate by magnetising the electromagnets (U1-U6, V1-V6, W1-W6), the electromagnets (U1-U6, V1-V6, W1-W6) being magnetised according to predetermined magnetising patterns, a current magnetisation pattern being switched from one magnetisation pattern to another in dependence of a current rotational position of the rotor (404);the method comprising:controlling the frequency at which magnetisation patterns are being switched, and/or controlling a magnitude of the current applied when magnetising the electromagnets (U1-U6, V1-V6, W1-W6), such that, the vehicle is manoeuvred in a state of low speed manoeuvring, an acceleration of the electrical machine (101, 102) in response to a first request for power is reduced in relation to the response to said first request for power when the vehicle is not manoeuvred in the state of low speed manoeuvring.

Description

METHOD AND SYSTEM FOR PROPELLING AN ELECTRIC VEHICLEField of the invention The present invention relates to vehicles, and in particular to a method and systemfor propelling an electric vehicle. The present invention also relates to a vehicle, aswell as a computer program and a computer program product that implement the method according to the invention.Background of the invention With regard to vehicles in general, and at least to some extent heavy/commercialvehicles, such as trucks, buses and the like, fuel efficiency and reduction of exhaust emissions are important aspects of the overall vehicle performance.

This is often at least partly due to governmental concerns in pollution and air quality,e.g. in urban areas, which has also led to the adoption of various emission standards and rules in many jurisdictions.

Apart from governmental concerns, one of the main expenses associated withvehicle operation is consumption of energy, oftentimes in terms of consumption offuel, for propulsion of the vehicle. The degree of utilization of heavy vehicles is oftenhigh, and with its associated fuel consumption, the cost of fuel may affect theprofitability of the owner of the vehicle to a great extent. ln view of this, alternatives to the sole use of conventional combustion enginetechnology in a vehicle are increasingly being considered. For example, hybrid-electric vehicles are becoming increasingly more common. Vehicles of this kindcomprise an electrical machine, which may be utilised to provide power for propellingthe vehicle in combination with an internal combustion engine. Vehicles of this kindmay have a drivetrain configuration similar to a conventional internal combustionengine vehicle drive train configuration where one or more electrical machines and associated drive systems and possible energy stores have been added.

There are, however, also electric vehicles, i.e. non-hybrid vehicles. These vehiclesare equipped only with one or more electrical machines, and no internal combustionengine is present. Hence the power generation is solely obtained by one or more lO electrical machines, and where oftentimes the energy for powering the electrical machines is stored in an energy store such as one or more batteries.

With regard to commercial vehicles, such as e.g. city buses, vehicles of this kind mayhave a high degree of usability, and the vehicles may also be used e.g. by a driverfor relatively long consecutive periods of time. Therefore, in addition to addressingenergy consumption which may be carried out in a favourable manner e.g. usingelectric vehicles, efforts are also made to make the driving of the vehicle comfortableto the driver. Such driver comfortability may comprise e.g. economical aspects butmay also comprise vehicle behaviour or safety when being driven.

Summary of the invention lt is an object of the present invention to provide a method and system that allows fora vehicle behaviour where electric vehicle behave in a manner that is expected by adriver, in particular in situations when going in a reverse direction of travel and/or in aforward direction of travel at low speeds. This object is achieved by a method according to claim 1.

According to the present invention, it is provided a method for propelling an electricvehicle,the vehicle comprising: an electrical machine configured to selectively provide a controllable power for propelling at least one drive wheel of the vehicle, the electrical machine being anelectronically commutated electrical machine having a rotor and a stator, the statorcomprising a stator winding comprising a plurality of circumferentially distributedelectromagnets, the rotor being caused to rotate by magnetising the electromagnets,the electromagnets being magnetised according to predetermined magnetisingpatterns, a current magnetising pattern being switched from one pattern to another independence of a current rotational position of the rotor; the method comprising, when the vehicle is manoeuvred in a state oflow speed manoeuvring: controlling the frequency at which magnetisation patterns are beingswitched, and/or controlling a magnitude of the current applied when magnetising the lO electromagnets, such that an acceleration of the electrical machine in response to afirst request for power is reduced in relation to the response to the first request for power when the vehicle is not manoeuvred in the state of low speed manoeuvring.

According to embodiments of the invention, the vehicle comprises an energy store forstoring energy to be used for powering the electrical machine.

According to embodiments of the invention, the energy store may be charged byregenerative braking using the electrical machine or another electrical machine of thevehicle.

According to embodiments of the invention, the vehicle is a heavy commercial vehicle such as a truck or a bus.

According to embodiments of the invention, the electrical machine is an BLDC(Brushless DC) electrical machine.

As was mentioned above, vehicles may comprise various kinds of drivetrains. Thepresent invention relates to electric vehicles, where the vehicle is being powered andpropelled by one or more electrical machines. Electric vehicles according to theinvention may comprise a gearbox but this is not a general requirement sinceelectrical machines may be operated from zero speed of rotation to a high speed ofrotation while also being capable of delivering a high torque from zero speed ofrotation. Still a gearbox may be present, e.g. in case the efficiency of the electricalmachine vary in dependence of speed of rotation. The use of a gearbox may alsoallow operation of the electrical machine at more favourable speeds of rotation, andmay increase the torque that is applied to the vehicle drive wheels. Furthermore, thetorque being applied to the vehicle drive wheels may be increased using a gearbox,e.g. to provide a high torque when a heavy vehicle performs a start in an uphill.

However, as opposed to e.g. internal combustion engines, electrical machines may ingeneral be operated in any direction of rotation while still providing the sameproperties e.g. in terms of efficiency, speed of rotation and deliverable torque. This, inturn, has as result that even if using a gearbox the need for a reverse gear no longerexist, since the reverse direction of travel of the vehicle may be accomplished byoperating the electrical machine in a direction of rotation being opposite to the lO direction of rotation of the electrical machine that is utilised when travelling in theforward direction.

According to embodiments of the invention, the electrical machine is connected toone or more vehicle drive wheels through a gearbox, where the gearbox may haveany from a plurality of configurations, for example, the gearbox may comprise one ortwo or more gears for propelling the vehicle. The gearbox may also comprise aneutral gear to allow the electrical machine or machines to be disconnected from theone or more vehicle drive wheels. However, the gearbox does not comprise areverse gear, but the gear used for propulsion of the vehicle in the reverse direction of travel is a gear also being used for forward direction of travel.According to embodiments of the invention, no gearbox is utilised.

The possibility of operating the electrical machine in either direction of rotation mayallow the vehicle to be propelled in the same manner in regard of e.g. accelerationand speed of travel irrespective of whether the vehicle is moving in a forward orreverse direction of travel. This may not be desired, e.g. because oftentimes drivervisibility in the rear direction is limited in comparison to the driver visibility in theforward direction of travel. According to the present invention, therefore, it is provideda method that may cause the vehicle to behave differently e.g. in dependence onwhether the requested vehicle movement is a forward direction of travel or a reversedirection of travel. ln particular, acceleration and/or a maximum speed of the vehicle may be controlled to be lower when the vehicle is manoeuvred in a state of low speed manoeuvring.

For example, acceleration and/or a maximum speed of the vehicle may be controlledto be lower when going in a reverse direction in comparison to when going in aforward direction of travel. ln this way, the vehicle may be caused to behave morelike a vehicle comprising an internal combustion engine and a gearbox having areverse gear. The invention may also be applied when low speed manoeuvring thevehicle in the forward direction.

With regard to the request for power, this may be an arbitrarily initiated request forpower, i.e. in any manner a request for propelling power may be initiated. For lO example, power may be requested by driver manoeuvrable means for requestingpower, such as an accelerator, but may also be e.g. a release of vehicle brakes sinceoftentimes a power is applied by the vehicle control system when brakes arereleased and the vehicle is in a state for being set in motion, such as e.g. by being ina drive mode for setting the vehicle in motion. The request may also be performed in any other suitable manner.

According to the invention, the electrical machine is an electronically commutatedelectrical machine having a rotor and a stator, where rotation of the rotor may causea vehicle drive wheel to rotate. The stator comprises a stator winding comprising aplurality of circumferentially distributed electromagnets, where the rotor is caused to rotate by magnetising of the electromagnets.

The stator winding may comprise two or more, such as three, phase windings, whereeach phase winding may comprise one or a plurality of electromagnets. Theseelectromagnets may comprise a coil wound around a core being aligned in the radialdirection. The electromagnets may be denoted stator poles. Furthermore, thepoles/electromagnets may be configured to be magnetised such that, whenmagnetised, the magnetisation forms a magnet having north pole directed in a radialdirection away from the rotor, and a south pole in a direction towards the rotor, or vice versa.

The electromagnets are magnetised according to predetermined magnetisingpatterns, where the magnetisation pattern may define the magnetisation of eachelectromagnet, where the desired magnetisation may be generated by applying apositive, a negative or a floating potential to the electromagnets, where this ingeneral is accomplished by applying the voltage to stator terminals.

The stator may comprise at least three phase windings, each phase windingcomprising a plurality of circumferentially distributed electromagnets, where all electromagnets of a stator winding may be magnetised in the same way.

The magnetisation pattern being applied depends on the current rotor position, andthe electromagnets attract magnets of the rotor to thereby cause a rotation of therotor, where the rotation for a particular magnetisation pattern will be a portion of a full revolution, the portion depending on the number of electromagnets of the stator lO and also magnets of the rotor. When the rotor reaches and/or approaches a rotorposition where it would be “locked” by the current magnetisation pattern, themagnetising pattern is switched to a subsequent pattern that causes the rotor torotate a further portion of a revolution. A continuous switching of the magnetisationpattern may then keep the rotation in motion. lf the magnetisation of the electromagnets is not changed, the rotor may be held still in a locked position.

The method may comprise determining a rotation position of the rotor, and selectingmagnetisation pattern for magnetising the electromagnets based on the determined rotation position of the rotor.

According to embodiments of the invention, when the vehicle the vehicle ismanoeuvred in a state of low speed manoeuvring, such as when manoeuvred in areverse direction of travel or when being low speed manoeuvred in the fon/varddirection, the acceleration of the rotor, and hence the acceleration of the vehicle, maybe controlled by controlling the frequency at which magnetisation patterns are beingswitched and/or controlling a magnitude of the current applied when magnetising theelectromagnets according to a magnetisation pattern such that an acceleration of theelectrical machine will be reduced in comparison to when the vehicle is notmanoeuvred in the state of low speed manoeuvring, and e.g. is manoeuvredaccording to a state of general manoeuvring in the forward direction such as whenmanoeuvring the vehicle according to a state allowing speeds up to maximum speed of the vehicle. ln this way, maximum speed and/or acceleration of the vehicle can be limited inrelation to standard/general travelling in the forward direction. For example, for agiven accelerator position, the acceleration of the vehicle may be reduced, whichmay facilitate low speed manoeuvring, which thereby may reduce the risk for thevehicle moving in an unexpected manner e.g. when the vehicle is moving in the reverse direction. ln case the frequency at which the magnetisation patterns are switched is reduced,the rotor will rotate slower, since the rotor will only move to a position corresponding to a subsequent magnetisation pattern once the pattern is applied. lO Since the deliverable torque of the electrical machine is dependent on the appliedcurrent, a reduction only of the frequency at which the magnetisation patterns areswitched, but maintaining the applied current unchanged, maximum torque may stillbe applied to the vehicle drive wheels by applying maximum current. Hence e.g.capabilities of performing vehicle starts on inclined surfaces may remain unchangedsince full torque is available. Still the acceleration of the vehicle can be reduced bycontrolling the speed of the frequency at which the magnetisation patterns areswitched.

Furthermore, the magnetic force being generated by the electromagnets, and therebythe torque, will depend directly on the current being applied to the stator winding.Hence a lower current will result in a lower magnetic force attracting the permanentmagnets of the rotor. Therefore, an alternative method of reducing the acceleration ofthe rotor and thereby speed of rotation is to reduce the current being applied to the stator winding.

According to embodiments of the invention, the control of the frequency at which theswitching pattern is changed is combined with a reduction of the current. This may beutilised to reduce energy consumption, since the reduced acceleration caused bycontrolling the frequency at which the switching pattern is changed may require lowercurrents, and by controlling the current to a level corresponding to a level required toprovide the requested acceleration excess energy consumption can be reduced.

The acceleration of the electrical machine can be arranged to be reduced byreducing the frequency at which magnetisation patterns are being switched for atleast one predetermined position of the driver controllable means when the vehicle ismanoeuvred in a state of low speed manoeuvring in relation to the frequency atwhich magnetisation patterns are being switched for the same position of the drivercontrollable means when the vehicle is not manoeuvred in the state of low speed manoeuvring. ln addition, or alternatively, the acceleration of the electrical machine can be reducedby reducing the current being applied to the stator winding for at least onepredetermined position of the driver manoeuvrable means when the vehicle is manoeuvred in a state of low speed manoeuvring in relation to the current being lO applied for the same position when the vehicle is not manoeuvred in the state of low speed manoeuvring.

As is described below, the current may be arranged to progressively increase as thedriver manoeuvrable means is moved towards a second end position. ln this way, theapplied current may be controlled such that although being reduced in relation to theapplied current when going in the forward direction for e.g. most of the movementregion the current may still be allowed to progressively rise to maximum current as the second end position is reached.

Oftentimes the driver controllable means for requesting power is movable in amovement region between a first end position and a second end position. Thefrequency at which magnetisation patterns are being switched may be reduced for atleast a portion of, or all of, the movement region of the driver controllable meanswhen the vehicle is manoeuvred in a state of low speed manoeuvring in relation towhen the vehicle is not manoeuvred in the state of low speed manoeuvring.Alternatively, or in addition, the current being applied to the stator winding for at leasta portion of, or all of, the movement region may be reduced when the vehicle ismanoeuvred in a state of low speed manoeuvring in relation to when the vehicle is not manoeuvred in the state of low speed manoeuvring.

A low pattern switching frequency combined with high currents being supplied mayhave the advantage that a high torque can be applied to the vehicle drive wheel(s) ata low speed, which e.g. may be advantageous when the vehicle is being driven on aninclined surface. ln principle, maximum torque may be applied to the drive wheelseven when the vehicle is standing still, hence allowing use of the electrical machinesalso as a vehicle brake when the vehicle is standing still.

According to embodiments of the invention, the frequency at which magnetisationpatterns are being switched, and/or the magnitude of the current applied whenmagnetising the electromagnets, is controlled such that an acceleration of theelectrical machine in response to a first request for power using the drivercontrollable means is reduced when the vehicle is manoeuvred in a state of lowspeed manoeuvring in relation to the response when the vehicle is not manoeuvred in the state of low speed manoeuvring only when a first vehicle speed has been lO reached. ln this way, the vehicle may be allowed to behave as when going in theforward direction for as long as the vehicle speed is below a predetermined speed.The actual vehicle speed need not be determined, but the vehicle speed may berepresented by a representation of the vehicle speed. For example, the rotor speedof the electrical machine may be utilised as a representation of the vehicle speed.

According to embodiments of the invention, a vehicle speed of the vehicle may bedetermined, and the frequency at which magnetisation patterns are being switched,and/or a magnitude of the current being applied to the stator winding may be reducedthe vehicle is manoeuvred in a state of low speed manoeuvring in relation to whenthe vehicle is not manoeuvred in the state of low speed manoeuvring such that atmost a predetermined vehicle speed is reached. ln this way, the vehicle may be allowed to behave as if being manoeuvred for generaltravel in the forward direction at first, but as soon as the vehicle speed reaches somepredetermined speed the vehicle speed and/or acceleration can be arranged to bereduced in comparison to when the vehicle is manoeuvred for general travel in theforward direction, and the maximum allowable speed when going in reverse direction may also be limited as above.

According to embodiments of the invention, the magnitude of the current appliedwhen magnetising the electromagnets is applied such that the applied current isreduced in relation to the applied current when the vehicle is not manoeuvred in thestate of low speed manoeuvring for at least a first portion of the movement region ofthe driver controllable means for requesting power, stretching from no request forpower towards the position for maximum request for power. For example, the currentmay be arranged to progressively increase as the driver manoeuvrable means ismoved towards the second end position from the first end position. For example, theapplied current may be controlled to increase progressively, i.e. non-linearly with amovement of the driver manoeuvrable means from the first end position towards thesecond end position. The applied current may be controlled such that although beingreduced in relation to the applied current when going in the forward direction for e.g.most of the movement region the current may still be allowed to progressively rise to maximum current as the second end position is reached. lO lO The frequency at which magnetisation patterns are being switched may be controlledto only depend on rotor position. This in turn means that when maximum current isapplied any speed of rotation of the electrical machines is available. Still low speedmanoeuvring will be simplified since e.g. an accelerator needs to be depressedfurther to obtain the same power as is obtained by less depression when the vehicle is not in the state for low speed manoeuvring.

According to embodiments of the invention, the frequency at which magnetisationpatterns are switched and/or the magnitude of the current being applied to the statorwinding, is controlled such that when the vehicle is manoeuvred in a state of lowspeed manoeuvring the frequency and/or magnitude of the current and/or vehiclespeed at most corresponds to a percentage being less than 100% of thefrequency/magnitude/speed that is used when the vehicle is not in a state for low speed manoeuvring.

With regard to the driver manoeuvrable means for requesting power, any suitablekind of means may be utilised, which may be movable in a movement regionbetween two end positions where the position of the drive controllable means in the movement region may be determined for any position in the movement region.

Furthermore, an inverter drive may be utilised to convert a DC voltage of the energystore into positive and negative voltages to be applied to the stator winding. Theinverter drive may also be used to switch the DC voltage such that the mean voltage,and/or mean current, being applied to the stator winding can be controlled to a desired mean voltage/current.

With regard to states of low speed manoeuvring, such states may be any suitablestates of low speed manoeuvring.

According to embodiments of the invention, states of low speed manoeuvring may berepresented by different drive modes for propelling the vehicle. Such modes mayinclude a mode for reduced speed manoeuvring of the vehicle, and a mode forstandard travelling in the fon/vard direction. For example, the mode for reduced speedmanoeuvring of the vehicle may include a mode for reverse direction of travel, and/or a crawler mode for low speed manoeuvring in the fon/vard direction. lO ll Hence, the control that has been discussed above for manoeuvring the vehicle in astate of low speed manoeuvring may be carried out when the vehicle is propelled in adrive mode for reduced speed manoeuvring of the vehicle, where the control may becarried out in relation to when the vehicle is being propelled according to a mode forstandard travelling in the fon/vard direction.

The drive modes may be driver selectable and/or automatically selectable by thevehicle control system.

The invention may be carried out in a vehicle, and the invention also relates to asystem corresponding to the method set forth above. The system is characterised inmeans carrying out features of the invention. Such means for carrying out features ofthe invention can consist of any suitable means, and the means can be specificallyadapted to perform the features set forth in the system claim. Such means canconsist of one or more control units, one or more computer programs, or other electrical, mechanical and/or electromechanical elements or arrangements.

Further characteristics of the present invention and advantages thereof are indicatedin the detailed description of exemplary embodiments set out below and the attached drawings.

Brief description of the drawings Fig. 1A illustrates a powertrain of an exemplary electric vehicle; Fig. 1B illustrates an example of a control unit/means in a vehicle control system;Fig. 1C illustrates an exemplary accelerator of the vehicle of fig. 1A.

Fig. 2 illustrates an exemplary electrical machine drive system.

Fig. 3 illustrates an exemplary method according to embodiments of the invention.

Fig. 4 illustrates an exemplary electrical machine which may be utilised according to embodiments of the invention.

Figs. 5A-B illustrate exemplary control of the electrical machine when the vehicle is going in a reverse direction. lO 12 Detailed description of exemplary embodiments According to the following detailed description, embodiments of the invention areexemplified for a vehicle comprising drive modes. As has been explained above, theinvention is applicable also for vehicles where no such drive modes are present, andwhere instead states of low speed manoeuvring may be determined in other ways.For example, vehicle speed may be utilised to determine state of the vehicle andthereby control of the one or more electrical machines to be used. Fig. 1Aschematically depicts a powertrain of an exemplary electric vehicle 100 according toembodiments of the invention. There exist electric vehicles of various kinds anddesigns. For example, the number of electrical machines being used for thepropulsion of the vehicle may differ. According to the present, non-limiting, exampleof the invention, the powertrain of the electric vehicle 100 in Fig. 1A comprises twoelectrical machines 101, 102, which both are connected to a common shaft 104forming a gearbox input shaft of a gearbox 103.

Electric vehicles of the disclosed kind may, but need not necessarily, comprise agearbox, since electrical machines may be operated from zero speed of rotation to ahigh speed of rotation while also being capable of delivering a high torque from zerospeed of rotation. However, the efficiency of electrical machines may still be differentfor different speeds of rotation, and use of a gearbox may allow operation of theelectrical machine(s) at more favourable speeds of rotation. Also, a gearbox may beutilised to increase the torque that is applied to the vehicle drive wheels in relation tothe torque delivered by the electrical machine(s) to a higher torque than the deliverable torque of the electrical machines.

According to the present example, a gearbox 103 is, as mentioned, present, butwhich differs from conventional gearboxes being used in conventional hybrid andnon-hybrid vehicles comprising an internal combustion engine. According to thepresent example, the gearbox 103 comprises only two gears for providing twodifferent gear ratios between the gearbox input shaft 104 and a gearbox output,which according to the present example is connected to, and represented by, apropeller shaft 107. The gearbox 103 may further comprise a neutral gear so as to allow the electrical machines 101, 102 to be disconnected from the propeller shaft lO 13 107 in case this is desired, e.g. to reduce the risk for the vehicle being accidentallyand/or unintentionally set in motion. The gearbox does not comprise a reverse gear.lnstead, when propelling the vehicle in the reverse direction, a gear is used that isalso used for propelling the vehicle in the fon/vard direction. Furthermore, in reality,the gearbox 103 may be e.g. bolted or other otherwise affixed to the electricalmachines 101, 102 e.g. to improve rigidity, and hence the separation of thecomponents in fig. 1A are for illustration purposes only. As was mentioned, thegearbox 103 output is connected to a propeller shaft 107 which in a conventionalmanner propels the vehicle drive wheels 113, 114 via a final drive 108 and driveshafts 109a, 109b. However, the use of a gearbox is not a necessary featureaccording to the invention, but the invention may also be utilized in vehicles wheree.g. one or more drive wheels are propelled directly by the one or more electrical machines.

The vehicle 100 further comprises an electrical machine drive system for controllingthe electrical machines 101, 102. Exemplary components of the drive systemcomprise an inverter drive 111 for controlling the electrical machines 101, 102. Anenergy source, such as an energy store, e.g. consisting of one or more batteries 112provides energy required for powering the electrical machines 101, 102. A controlunit/means 115 controls, inter alia, the inverter drive 111 to thereby control operationof the electrical machines 101, 102. The control unit/means 115 may also beconfigured to control e.g. the gearbox 103 and/or other functions. The functionalitymay, however, also be divided among further control units/means. The gearbox 103 may, for example, comprise a planetary gear.

Furthermore, an exemplary accelerator 118 in the form of a pedal is schematicallyshown in Fig. 1C. The accelerator pedal 118 is movable within a movement regiondefined by two end positions P1, P2, defining an angular range oi. The acceleratorpedal 118 position in the movement region can be determined, e.g. by means of asuitable sensor, such as, for example, a potentiometer or an angle sensor 119 or anyother suitable kind of sensor which determines the current position of the acceleratorpedal 118 in the movement region in which the accelerator pedal is movable. ln principle, any position of the accelerator in the movement region may be detected lO 14 using sensor means. When the accelerator pedal 118 is fully released, i.e. notmanoeuvred by the driver, it is in a state of rest in position P1, e.g. by means of aspring force, where position P1 represents no driver request for power from theelectrical machines. Position P2 represents a fully depressed accelerator pedal andhence a driver request for full power, where any power between zero and full powermay be requested by appropriately positioning the accelerator pedal at acorresponding position between position P1 and position P2. Furthermore, theillustrated accelerator only represents an exemplary driver controllable means forrequesting power, and any kind of suitable accelerator means may be utilised, suchas e.g. a combined accelerator/decelerator, for as long as the means is movable in amovement region where the position of the drive controllable means in the movement region may be determined.

The vehicle 100 according to the present example also comprises a drivercontrollable drive mode selector 116 for selecting a drive mode of the vehicle, suchas selecting a direction of travel of the vehicle. For example, the driver controllabledrive mode selector 116 may comprise driver selectable directions of travel, e.g.“forward” and “reverse”. The selector may also comprise further options, such as e.g.“park” and/or “neutral” and a “crawler” mode for low speed manoeuvring in theforward direction, e.g. when manoeuvring the vehicle with a high accuracy. The drivemods may also be selectable by the vehicle control system and hence need not bedriver selected as in the present non-limiting example.

Fig. 2 discloses the electrical machine drive system of fig. 1A slightly more in detail.The energy store 112 is a direct current power supply, oftentimes a battery back,which may provide a relatively high voltage, e.g. in the order of 300-1000 V. Theenergy store may be arranged to be selectively connected to the inverter drive, e.g.via one or more circuit breakers 202 and/or other types of protective means. Fig. 2also discloses a junction box 201, which may be utilised to allow auxiliary equipmentto be powered by the battery 112, e.g. via suitable conversion of the voltage ifrequired. For example, the voltage used for powering the electrical machines 101,102 may be converted to, e.g., 24V, (or 12 V or 48V) for conventional 24 V (12V, 48V) applications, such as cooling fans or conventional vehicle electronics in general. lO lnverter drives, in general, use a DC link voltage, also known as DC bus voltage,from which of suitable frequency and amplitude are formed. There exist variousexamples of inverter drives, and the present invention is suitable for use with any inverter drive design providing the desired control of the electrical machine(s).

The system of fig. 2 may further comprise e.g. protection mechanisms to preventover voltages and/or short-circuiting, e.g. at system start up when e.g. capacitorsmay be essentially uncharged and thereby subjected to excessive currents. Suchmeasures are known to the person skilled in the art and are therefore not disclosedfurther in detail. Such measures also do not form part of the invention.

Electrical machines 101, 102 of the disclosed kind may be arranged to be torqueand/or speed controlled by means of the inverter drive system. lnverter drives ingeneral allow for rotational speed and torque control of the electrical machine byvarying e.g. amplitude and polarity of the voltage being fed to the stator winding terminals.

According to the present example, the electrical machines 101, 102 are electronicallycommutated machines, brushless DC electrical machines, and will be describedmore in detail below. The electrical machines 101, 102 further have three phasewindings configured to be individually controlled by associated switching means of the inverter drive 111.

The inverter drive 111 produces an AC electric current to drive each phase of theelectrical machines 101, 102 using switches such as transistors 221-226, where eachphase is connected between a switch pair 221-222; 223-224; and 225-226,respectively. Capacitors C1, C2, provide a ground potential at half the DC link voltageso that both positive and negative voltages can be produced in the control of theelectrical machines from the DC link voltage. The switches 221-226 are controlled bycontrol means, where the control signals may be generated based on requests fromthe control unit/means 115 to provide desired current/voltage pulses to the motorwindings to obtain the desired control the speed and torque of the motor. lnverter drives of the kind disclosed in fig. 2, and inverter drives in general and withregard to electric vehicles in particular, allows power to flow in both directions through the inverter. This is according to the present example made possible by diodes 231- lO 16 236 being arranged anti-parallel to transistors 221-226. The diodes 231-236 willrectify the voltage induced in the stator e.g. during regenerative braking, and providea rectified voltage on the DC link which may be utilised to charge the energy store112. Further according to the present example, the electrical machines 101, 102 arecontrolled by the same control signals and hence operate in synchronism.

An exemplary electrical machine 101, which, as was mentioned, is an electronicallycommutated electrical machine, is schematically disclosed in fig. 4. The stator 406,according to the present example, comprises three phase windings U, V, W that arebeing individually controlled by the inverter drive 111 using the switches/transistors221-226. The inverter drive 111 is configured to selectively apply a positive voltage, anegative voltage or leave the terminal potential left floating by both switches of theassociated switch pair being open, (i.e. non-conducting) to connection terminals 401,402, 403 of the phase windings U, V, W, respectively. For example, with regard tophase winding U, a positive voltage is applied by closing switch 221 (therebyconducting) while switch 222 is open. Correspondingly, a negative voltage is appliedby closing switch 222 while switch 221 is open. lf both switches 221-222 are leftopen, the terminal of phase winding U is left floating as mentioned. Through the useof a suitable switching of the switches, a controllable desired resulting averagevoltage amplitude of the stator terminal voltage can be obtained by controllingopening time, while the DC link/bus voltage still may remain essentially constant. lnthis way, the average current can also be controlled to thereby control the torque produced by the electrical machine 101.

The electrical machine 101 comprises a rotor 404, which, according to the presentexample is attached to and/or forming the gearbox input shaft 104. The rotorcomprises embedded permanent magnets 405 a-f. Each permanent magnetcomprises a north (N) pole and a south (S) pole. Furthermore, each of the phasewindings comprises six poles, in the present application also denotedelectromagnets, being circumferentially distributed, e.g. evenly. For example, phasewinding U comprises poles, electromagnets, U1-U6. Correspondingly, phase windingV comprises poles V1 -V6 and phase winding W comprises poles W1-W6. When a current/voltage is applied to one of the phase windings U, V, W, this voltage/current lO 17 is applied to all poles of the phase winding and a magnetic field is generated that magnetises the pole (electromagnet).

Hence, by appropriately applying a voltage to the poles/electromagnets of a phasewinding, electromagnets may be formed in the stator windings and having a polaritywhich will attract poles of the permanent magnets 405a-f of the rotor 404. Forexample, according to the example of fig. 4, when a positive voltage is applied e.g. tothe 'W' terminal, and a negative voltage is applied to the 'U' terminal, theelectromagnets W1-W6 of the W winding will form electromagnets having a northpole directed inwards towards the rotor, and a south pole directed outwards towardsthe exterior of the electrical machine 101. At the same time, the poles U1-U6 of the Uterminal will form electromagnets having a south pole directed inwards towards therotor and a north pole outwards towards the exterior of the device. The stator windings of the V terminal will be non-magnetized.

This, in turn, means that the poles W1-W6 of the W winding will attract the southpoles of the embedded magnets 405a-f of the rotor. Correspondingly, the U windingswill attract the north poles of the magnets of the rotor. This means that, in theexample of fig. 4, the rotor will make a 20° rotation from the illustrated rotor positionin a counter-clockwise direction, so that e.g. the north pole of magnet 405a will bealigned with the pole U1 of stator winding U instead of being aligned with pole W6 ofstator winding W as is presently the situation in fig. 4. The south pole of magnet405a, in turn, will become aligned with pole W6 of stator winding W. Correspondinglythis applies to the north poles of magnets 405b-f and poles U2-U6 of stator windingU, and the south poles of magnets 405b-f and poles W2-W6 of stator winding W,respectively. The exemplified control of the windings is for illustrative purposes only,and the windings may be controlled differently to accomplish the desired control. Forexample, the poles of winding V may be controlled such that the poles form a magnethaving a south pole directed inwards towards the rotor, and a north pole directedoutwards towards the exterior of the electrical machine 101 instead of the poles ofwinding W, which instead may be left unmagnetized. This will still accomplish thedesired rotation. ln general, with regard to inverters of the kind disclosed in fig. 2, it lO 18 may be desirable to control the switches such that only one switch at a time changesstate of the switch pairs 221-222, 223-224 and 225-226, respectively. ln order to further rotate the rotor, polarity and/or terminals being subjected to voltagecan be changed to cause the rotor to rotate a further 20° counter-clockwise rotation.This can be accomplished e.g. by applying terminal voltages such that the poles V1-V6 of the V winding form a magnet having a south pole directed inwards towards therotor, and a north pole directed outwards towards the exterior of the electricalmachine 101. At the same time, e.g. the poles W1-W6 of the W terminal may becontrolled to form magnets having a south pole directed inward towards the rotor and a north pole outward towards the exterior of the device. ln this way, by suitably switching the voltage/current applied to the stator terminals toobtain desired magnetisation of the stator poles, the stator poles can be appropriatelymagnetized according to predetermined patterns, i.e. the ways in whichpoles/electromagnets are to be magnetised in dependence of the rotor position toattract and repel the permanent magnets of the rotor to thereby obtain the desiredrotation. For as long as the stator is kept magnetized according to a particularpattern, i.e. the poles are held at a certain magnetisation, e.g. according to theexample of fig. 4, the rotor may be held in this position. Hence the speed of rotationcan be controlled by changing the magnetisation pattern of the stator poles at afrequency resulting in the desired speed of rotation of the rotor and thereby speed of movement of the vehicle.

For reasons of simplicity, the magnetisation has been disclosed as distinctive levels.This, however, need not be, and in general is not the case. For example, anynumber of intermediate patterns may be utilized, which may be applied independence of the position of the rotor so that a smooth rotor motion is obtained. lncase the above method is applied while applying a high current, the rotor motion maybe jerky due to fast switches between rotor positions corresponding to magnetizationpatterns as the pattern is switched. Use of a plurality of intermediate patternsalleviates such behavior so that a smooth transition from one pattern to another isobtained also when a high current is applied by utilizing intermediate patterns and where a high resolution of the rotor position, allows a plurality of intermediate lO 19 patterns to be used. The intermediate patterns may be configured such that asinusoidal or trapezoidal voltage is applied to the stator winding. ln case the currentis reduced, the frequency at which magnetization patterns are switched willautomatically be reduced, since the reduced current will have as result that the rotormoves slower, and the magnetization patterns are applied in dependence of rotorposition. This also means that when the current is reduced, it is not required to use aplurality of intermediate patterns, since the reduced current in itself may ensure thatthe rotor will not abruptly change position due to reduced torque.

Furthermore, as is apparent to a person skilled in the art, the north/south orientation,i.e. inwards or outwards, will depend on the winding, and hence according toembodiments of the invention the winding is such that a positive voltage applied to aparticular winding instead will form a magnet having a south pole directed inwardstowards the rotor, and a north pole directed outwards towards the exterior of theelectrical machine 101 and vice versa. ln order to ensure the desired operation e.g. to ensure a desired direction of rotation,it is required that the rotor position is known in order to determine the position of thepermanent magnets of the rotor in relation to the stator poles, so that the appropriatemagnetisation pattern to be generated by applying voltage to the stator terminals bythe inverter drive can be applied in view of the current rotor position. ln this way,changes of the polarity of the stator poles by changing polarity of the stator terminalscan be controlled to occur at a desired point in time to thereby obtain the desired rotor movement.

The rotor position can be determined using rotor position determining means, suchas one or more appropriate encoders being utilized to detect the rotational position ofthe rotor shaft. Such rotor position determining means is represented by 117 in fig.1A. For example, the rotor position determining means may comprise one or moreabsolute rotary encoders, one or more optical encoders, and/or one or more halleffect sensors to determine the rotational position, i.e. the positions of the permanentmagnets 405a-f of the rotor 404, in relation to the stator poles. lt is to be understood that the electrical machine 101 of fig. 4 is for illustrative purposes only, and that the electrical machine may be of various designs. For lO example, with regard to an electrically commutated electrical machine, the stator maycomprise any suitable number of stator poles, and other designs than a three-windingstator may also be utilised. For example, two or four or more windings, and eachwinding may have any suitable number of electromagnets may be utilised.Furthermore, the rotor may comprise any suitable number of permanent magnets,where the number of magnets need not equal the number of stator poles but may begreater or lesser, where the magnetisation patterns being used to magnetise thestator may be adapted to the particular rotor/stator configuration. The adaption of thecontrol in this manner is well within the skills of the person skilled in the art. ln addition to controlling the magnetisation of the stator poles/electromagnets, theamplitude of the current can be controlled to thereby also control the generatedtorque. A reduced torque will cause the rotor to rotate more slowly, and hence it willtake a longer period of time reach the subsequent rotor position. Since themagnetisation patterns are applied on the basis on rotor position, the speed ofrotation is reduced even if the allowable frequency by which magnetisation patternsmay be changed is not reduced. Hence the electrical machine can be controlled bothwith regard to speed of rotation and the amount of torque being generated which willimpact acceleration of the rotor and thereby speed of rotation of the rotor.

The described control of the speed of rotation of the electrical machine by controllingthe frequency at which magnetisation pattern of the stator poles is changed, and/orcontrolling the magnitude of the supplied current is utilized according to the inventionin order to control the movement of the vehicle differently in dependence of whetherthe vehicle is going in a forward direction of motion or in a reverse direction ofmotion. Since the electromagnets of the stator can be magnetized in any desiredmanner, this also means that the direction of revolution of the rotor may be anydesired direction. That is, counter-clockwise or clockwise. Because of this there is noneed for any reverse gear in the gearbox, since the reverse operation can becontrolled by appropriate magnetisation of the stator windings.

An exemplary method according to embodiments of the invention is disclosed in fig. 3which will be discussed below. The person skilled in the art will appreciate that a method for controlling the electrical machines of the vehicle according to the present lO 21 invention may be implemented in a computer program, which, when it is executed ina computer, instructs the computer to execute the method. The computer program isusually constituted by a computer program product stored on a non-transitory/non-volatile digital storage medium, in which the computer program is incorporated in thecomputer-readable medium of the computer program product. The computer-readable medium comprises a suitable memory, such as, for example: ROIVI (Read-Only l\/lemory), PROIVI (Programmable Read-Only l\/lemory), EPROIVI (ErasablePRONI), Flash memory, EEPROIVI (Electrically Erasable PRONI), a hard disk unit,etc., and be arranged in or in connection with a control unit/system/means,whereupon the computer program is executed by the control unit/system/means. Thebehaviour of the electrical machines can thus be controlled by modifying parameters using the instructions of the computer program.

A plurality of the functions of a vehicle, such as controlling one or more electricalmachines based on driver requests are, in general, controlled by control means suchas e.g. a control system and/or a control unit. Control systems in modern vehiclescommonly comprise communication bus systems comprising one or morecommunication buses for linking a number of electronic control units (ECU's), ormeans or controllers, and various components located on the vehicle. Such a controlsystem can comprise a large number of control units/means, and the responsibilityfor a specific function can be divided amongst more than one control unit. Vehicles ofthe shown type thus often comprise significantly more control units than the controlunit/means 115 shown in fig. 1A, which is well known to the person skilled in the artwithin this technical field. For example, the gearbox 103 may be controlled by anothercontrol unit/means, and similarly various other functions of the vehicle may becontrolled by control units/means as is known per se. The control units/means 115 offig.1A may hence communicate with other control units/means via the communication bus system.

When a method according to embodiments of the invention is implemented in acontrol unit/means, e.g. of the exemplified kind, this may hence be accomplishedusing a computer program stored on storage means of the control unit/means and being executed by executing means of the control unit/means. A method according to lO 22 embodiments of the invention may also be implemented using a combination of aplurality of computer programs, which may be implemented in a same or differentcontrol units/means. A vehicle control system may also comprise only a single controlunit/means carrying out the various control system functions of the vehicle.

The present invention can be implemented in any suitable control unit/control means,and, according to the illustrated example, the invention is implemented in controlunit/means 115 for controlling the electrical machine drive system.

The invention may, however, also be implemented in any other suitable controlunit/means and/or combination of control units/means. The control of the electricalmachines/inverter drive according to the invention will depend on signals beingreceived from other control units/means and/or vehicle components, and it isgenerally the case that control units/means of the disclosed type are normallyadapted to receive sensor signals from various parts of the vehicle 100. The controlunit/means 115 will, for example, receive control signals representing the rotor/rotormagnet position, and further an indication of a requested direction of travel of thevehicle from drive mode selector 116, and request for power from the vehicle driver,e.g. requested using the accelerator 118. Control units/means of the illustrated typeare also usually adapted to deliver control signals to various parts and components of the vehicle, e.g. to the inverter drive.

An exemplary control unit/means (the control unit/means 115) forming part of, orconstituting, the vehicle control system is schematically shown in Fig. 1B, wherein thecontrol unit/means comprise a computing unit 120, which can comprise, for example,any suitable type of processor or microcomputer, such as a circuit for digital signalprocessing (Digital Signal Processor, DSP) or a circuit having a predeterminedspecific function (Application Specific Integrated Circuit, ASlC). The computing unit120 is connected to a memory unit 121, which provides the processing unit 120, withe.g. the stored program code 126 and/or the stored data that the computing unit 120requires to be able to perform calculations. The computing unit 120 is also arrangedso as to store partial or final results of computations in the memory unit 121.

Furthermore, the control unit/means 115 is provided with devices 122, 123, 124, 125 for receiving and transmitting input and output signals. These input and output lO 23 signals can comprise waveforms, impulses or other attributes that can be detected asinformation and can be converted into signals which can be processed by thecomputing unit 120. These signals may then be made available to the computing unit120.The devices 123, 124 for transmission of output signals are arranged to convertsignals received from the processing unit 120 in order to create output signals by, forexample, modulating the signals, which can be transmitted to other parts of and/orsystems of the vehicle. Each of the connections to the devices for receiving andtransmitting input and output signals may comprise of one or more of a cable; a databus, such as a CAN bus (Controller Area Network bus), a l\/IOST bus (l\/lediaOriented Systems Transport), Ethernet, or any other bus configuration or combinationof different data bus technologies, and/or a wireless connection. A person skilled inthe art will appreciate that the claimed system, or part of the claimed system, maycomprise the control unit/means 115 where means of the claimed system maycomprise the computing unit 120.

An exemplary method 300 according to embodiments of the invention is illustrated infig. 3. As was mentioned, according to the present example, the vehicle 100comprises driver controllable means 118 for requesting power from the electricalmachines 101, 102. As was also mentioned above, these driver controllable meansmay e.g. be in the form of an accelerator 118, where the accelerator 118 may bedepressed to request power from the electrical machines 101, 102. The method 300starts in step 301 where it is determined whether the drive mode selector 116 forselecting drive mode is set to a drive mode where speed is to be reduced. This drivemode may be the drive mode for reverse direction of travel, or the crawler mode formanoeuvring at low speed in the forward direction. The method 300 may remain instep 301 for as long as this is not the case, while the method may continue to step302 when it is established that the driver has requested e.g. “reverse” or “ crawl”using drive mode selector 116. l\/lanoeuvring of a vehicle in the reverse direction ingeneral requires that the driver is more precautious since, for example, visibility maybe limited in relation to when the vehicle is traveling in a forward direction. There mayalso be times when the available space surrounding the vehicle is limited, and low speed manoeuvring with higher precision being desirable also when the vehicle is lO 24 going in the forward direction, for which reason embodiments of the invention may be utilised when e.g. a crawler mode has been selected.

Therefore the response, e.g. in terms of acceleration/power being actually requestedfrom the electrical machines 101, 102 for a given driver request, which e.g. may berepresented by the accelerator 118 position, is set to a response that differs from theresponse that would be obtained for a similar request for power in a situation wherethe driver instead has requested that the vehicle is to move in a forward direction oftravel. For example, acceleration may be reduced. ln step 302 the power to be actually produced by the electrical machines 101, 102 isset as a function of the selected drive mode, and also of the current acceleratorposition in accordance with a pedal position/power level dependency that has beenset for travelling in the reverse direction or for crawler mode. That is, when e.g. areverse direction of travel or crawler mode is selected, the power that is actuallybeing requested by the electrical machines 101, 102 in response to a request forpower, such as e.g. a particular accelerator 118 position, will be different incomparison to when going in the forward direction of travel.

This may apply also to the situation when e.g. vehicle brakes are released but theaccelerator has not been depressed. A request for power may be determined bydetermining whether the accelerator 118 is at least partially depressed. According toembodiments of the invention, the accelerator need not be depressed, but it may besufficient to determine e.g. if the driver releases vehicle brakes, e.g. by releasing abrake pedal while the drive mode selector is set to a mode for propulsion of thevehicle. Oftentimes in such cases the vehicle starts moving in the selected directionof travel, i.e. the electrical machines are controlled to apply some torque to the drive wheels.

Exemplary controls when e.g. a reverse direction of travel or crawler mode isselected will be discussed below. The method may be ended in step 303, and themethod may e.g. be continuously repeated to determine if the selected mode is still tobe applied. Similarly, parallel methods may be utilised to determine whether e.g.another drive mode, e.g. a forward direction of travel mode, has been selected. lt is also contemplated a method where the drive mode is determined, and suitable lO control is applied on the basis of the selected drive mode, where it can becontinuously determined which drive mode has been selected. Hence a methodaccording to fig. 3 may be utilised for the control irrespective of direction of travel,where changes in the request for direction of travel is accounted for. The methodaccording to fig. 3 may also be utilised e.g. if a parking state or neutral state hasbeen selected using the selector for selecting a direction of travel, where the controlof the electrical machines can be performed in accordance therewith, e.g. byrequesting no power if no direction of travel has been selected.

With regard to the actual control of the electrical machines 101, 102 in response tothe request for power from the electrical machines 101, 102, this may beaccomplished in various manners. For example, as was explained above, the speedof rotation of the electrical machines 101, 102 may be determined by the speed atwhich the magnetisation pattern of the magnetisation of the stator poles is switched,i.e. the speed at which the magnetisation is switched from one magnetisation patternto another, where, as was mentioned above, a plurality of intermediate patterns maybe utilised. The faster the rotor is urged from one rotation position to a followingrotation position defined by the subsequent magnetisation pattern, the faster the rotor will rotate.

Therefore, according to embodiments of the invention, the frequency at whichmagnetisation patterns are switched for a particular position of the accelerator maybe reduced when the reverse direction of travel mode or crawler mode is requested.ln this way, if the driver depresses e.g. the accelerator 118 e.g. to a particularposition, a change of magnetisation pattern at a higher frequency will be appliedwhen the electrical machines 101, 102 are controlled according to the control thathas been defined for forward direction of travel mode in comparison to when theelectrical machines 101, 102 are controlled according to the control that has beendefined e.g. for the reverse direction of motion. This further means that the vehicleacceleration may be lower for any given accelerator 118 position in the reversedirection control, or crawler control, in comparison to when the accelerator is similarlydepressed when vehicle is being controlled according to the control defined for travelling in the forward direction. Thereby, the risk for the vehicle performing sudden lO 26 and undesired high accelerations, and/or reaching undesirably high speeds, whentravelling in the reverse direction of motion or performing precision manoeuvring in the forward direction may be reduced.

An exemplary control is illustrated in fig. 5A, which shows a graph i||ustrating theresponse that the vehicle control system requests from the electrical machines 101,102 in response to a driver request for power using the accelerator. The y-axisrepresents the response, e.g. in terms of acceleration or power being requested fromthe electrical machines 101, 102, where “0” indicates no response being requestedand l\/lAX represents a situation where the vehicle control system requests maximumresponse from the electrical machines 101, 102, i.e. maximum power/acceleration.The x-axis represents pedal position, where, in correspondence with figure 1C, P1represents a fully released pedal, and P2 a fully depressed accelerator 118.

The dotted line 501 represents the relationship between response being requestedfrom the electrical machines 101, 102 and accelerator position when the driver hasselected a forward direction of travel. As can be seen from the figure, the actualrequest for power from the electrical machines increase with an increasinglydepressed accelerator 118 pedal where a fully depressed accelerator essentiallycorresponds to a maximum response being requested from the electrical machines101, 102. The dotted line 501 is for illustration purposes only, and the relationbetween requested response and accelerator position e.g. need not be a straight lineas in the present example, but may have any suitable relationship, and further neednot necessarily increase all the way to a maximum response l\/lAX_forw being requested.

The solid line 502 represents the relationship between power being requested fromthe electrical machines 101, 102 and accelerator position when, instead, the driverhas selected a reverse direction of travel or crawler mode. As can be seen from thefigure, the actual request for response from the electrical machines increase with anincreasingly depressed accelerator also in this case, but with the difference that afully depressed accelerator, instead, corresponds to a considerably lower maximumresponse, l\/lAX_reverse, being requested from the electrical machines 101, 102. For example, the maximum response being requested from the electrical machines 101, lO 27 102 when the reverse direction of travel is selected may be set to 50% of themaximum response being requested when the forward direction of travel is selected,or any other suitable higher or lower percentage. With regard to the illustratedrequest for response, the response is the combined power delivered by the twoelectrical machines 101, 102. ln fig. 5A, the y-axis could, instead, represent possiblevehicle speed. Furthermore, according to the example of figs. 5A-B, there is a non-zero request for response also when the accelerator is released, so that the vehiclepossibly may be set in motion e.g. when vehicle brakes are released. As can also beseen from the figures, this requested response may be different for the different drivemodes, and e.g. be reduced when reverse mode or crawler mode has been selectedso that the vehicle may move slower in such a case. lt is also to be noted that thepower level being actually requested by the electrical machines when brakes arereleased but also accelerator is released may depend on e.g. current vehicleinclination and/or vehicle weight in order to provide the desired response. That is, thecurrent being applied to the electrical machines may be different for differentsituations. A high vehicle weight, or an inclination, requires a higher current to obtaina torque that provides the same response as when the vehicle weight is lower or the vehicle is on a level surface.

Furthermore, when controlling the frequency at which magnetisation patterns areswitched, it may oftentimes be desirable to control the current in the same manner aswhen going in the forward direction. ln this way it is still possible to obtain maximumtorque by not reducing the current. That is, maximum current can be applied whilethe speed of rotation is reduced by the reduced frequency at which magnetisationpatterns are switched. The maximum response, e.g. in terms of acceleration, that isdelivered by the electrical machines is still reduced, since the maximum speed ofrotation is reduced so that as a result the electrical machine at most will reach apredetermined speed of rotation, and thereby the vehicle will at most reach acorresponding predetermined vehicle speed.

However, when controlling the frequency at which magnetisation patterns areswitched, it may oftentimes be desirable to simultaneously reduce the current, since a reduced current may still be sufficient to provide the desired vehicle acceleration. ln lO 28 this way, energy consumption can be reduced by not applying a higher current thanis required to provide the desired acceleration. That is, the amplitude of the currentbeing applied to the stator terminals, e.g. represented by the voltage amplitude beingapplied to the stator terminals, may be continuously controlled to precisely a levelproviding the desired response, thereby minimising excess energy consumption.

For example, the speed of rotation of the rotor and/or vehicle speed may becontinuously determined to determine if the obtained response corresponds to thepredetermined response. ln this way it can be determined whether the appliedcurrent is insufficient, e.g. when the actual acceleration is below the predeterminedacceleration. ln such cases the current may be increased. Similarly, when theacceleration corresponds to the desired acceleration a reduction of the current maybe attempted in an effort to improve energy consumption. This control may becontinuously performed to maintain the current as close as possible at precisely thecurrent that is required to obtain the desired control. For example, the actual rotorposition may be compared with the expected rotor position, and this slip may beutilised e.g. to calculate the current vehicle weight and/or inclination, which then may be used in the control of the current.

Furthermore, according to embodiments of the invention, as an alternative tochanging the magnetisation pattern frequency, the current may instead be reducedfor any accelerator position when the vehicle set for going in the reverse direction oftravel in comparison to when a forward direction of travel has been selected.

As discussed above, the reduction of the applied current will reduce the torqueproduced by the electrical machine, which will render the rotor motion slower whenmoving from one magnetisation pattern position to the next. Since the magnetisationpatterns are applied on the basis of rotor position, this will have as result that thefrequency at which the magnetisation patterns are switched is reduced as aconsequence. Vehicle acceleration and achievable speed is dependent on the torquebeing produced by the electrical machine, and thereby acceleration so that thevehicle may be controlled to at most will reach a predetermined speed and/oracceleration. Thereby, the desired result may be obtained by only reducing the applied current. Furthermore, the applied current as a function of accelerator position lO 29 may e.g. be progressive as is also exemplified below. This further facilitates lowspeed manoeuvring since the accelerator needs to be depressed even further to obtain higher torques.

Hence the lines 501, 502 could alternatively represent frequency at whichmagnetisation patterns are switched, and/or applied current. However, as wasmentioned if the current is reduced, the available torque is also reduced, which mayhave to be taken into account e.g. if the vehicle is about to perform a movement onan inclined surface. As was mentioned above, in case the availability of a high torqueis of essence, the reduction of the frequency at which magnetisation patterns areswitched may be utilised in favour of reducing the current, since if the vehicle isheavily loaded a high torque may be required, and frequency control may make use of full torque.

Alternatively, as is described below, the current may be arranged to progressivelyincrease as the driver depresses the accelerator, so that sufficient torque to set thevehicle in motion in a desired manner will be obtained by sufficiently depressing the accelerator.

Fig. 5B illustrates a further embodiment of the invention, where the x-axis represents,similar to fig. 5A, the accelerator position. The y-axis represents the applied current l,and hence available torque. According to fig. 5B, instead of reducing the currentthroughout the movement region of the accelerator as exemplified above, the currentis instead lower when a reduced speed mode is selected than the correspondinglyapplied current when the general fon/vard direction mode is selected, dotted line 503,for a large portion of the accelerator movement region (P1-P2), and high currents areonly available when the accelerator has been depressed to a great extent, solid line504. ln this way, low speed control is facilitated to a great extent since high currents areonly available at the end of the movement region of the accelerator, which therebyreduces the risk for undesired accelerations, since high acceleration may not beobtained unless the accelerator is depressed to a large extent because ofprogressively increasing current as in the disclosed example. Hence accurate low speed control is facilitated since the response is reduced for a large part of the lO movement region of the accelerator. This example may according to embodiments ofthe invention be combined with a maximum allowed vehicle speed that imposesfurther restrictions regarding the current in case the vehicle reaches this maximumallowable speed.

According to embodiments of the invention, 100% of the deliverableacceleration/torque from the electrical machines at a current speed is available at lowvehicle speeds, but as vehicle speed increases, e.g. represented by the speed ofrotation of the electrical machines, the possibility to request maximum vehicleacceleration may be limited, e.g. decreasingly, or alternatively the maximumallowable frequency at which the magnetisation pattern is switched may be limited asvehicle speed increases. Still the current may be controlled such that maximumtorque is available while acceleration is limited. According to this embodiment,therefore, knowledge of vehicle speed is required, so that limitations can be imposedwhen the vehicle speed increases to thereby prevent the vehicle from reachinghigher than a predetermined speed when going in the reverse direction, where thelimit can be set e.g. as above. The vehicle speed may e.g. be derived from theelectrical machine rotation speed or any other vehicle speed sensor used on thevehicle (e.g. ABS/EBS sensors, tachometer, output shaft speed sensor, GPS, etc).

According to embodiments of the invention described above, the vehicle may have adrive mode selector for selecting a mode for reduced speed travel both in the forwardand the reverse direction. According to embodiments of the invention, the describedsolutions are applied when the driver selects a drive mode to specifically be usedwhen moving only slowly in the forward or reverse direction, e.g. by selecting a modebeing different from normal travel in the forward direction, such as a manoeuvring/ranging mode.

The present invention, consequently, provides a solution where it can be ensuredthat a vehicle being propelled by one or more electrical machines will not exhibit thesame acceleration and/or maximum speed when going in a reverse direction as whengoing in a forward direction in situations where a gearbox having a reverse gear is not being used. 31 Finally, the invention may also be utilised when the accelerator is released in casethis is desired, so that e.g. the frequency at which magnetisation patterns areswitched may be controlled according to any suitable profile to obtain a desired deceleration.

The present invention is not limited to the above described embodiments. lnstead,the present invention relates to, and encompasses all different embodiments being comprised within the scope of the independent claims.

Claims (1)

1. Claims Method for method for propelling an electric vehicle (100), the vehicle (100) comprising: an electrical machine (101, 102) configured to selectively provide acontrollable power for propelling at least one drive wheel (113, 114) of thevehicle (100), the electrical machine (101, 102) being an electronicallycommutated electrical machine (101, 102) having a rotor (404) and a stator(406), the stator (406) comprising a stator winding (U, V, W) comprising aplurality of circumferentially distributed electromagnets (U1-U6, V1 -V6, W1-W6), the rotor being caused to rotate by magnetising the electromagnets (U1-U6, V1-V6, W1-W6), the electromagnets (U1-U6, V1-V6, W1-W6) beingmagnetised according to predetermined magnetising patterns, a currentmagnetisation pattern being switched from one magnetisation pattern toanother in dependence of a current rotational position of the rotor (404); the method being characterised in, when the vehicle is manoeuvred ina state of low speed manoeuvring: at least one of controlling the frequency at which magnetisation patternsare being switched and controlling a magnitude of the current applied whenmagnetising the electromagnets (U1-U6, V1 -V6, W1-W6), such that anacceleration of the electrical machine (101, 102) in response to a first requestfor power is reduced in relation to the response to the first request for power when the vehicle is not manoeuvred in the state of low speed manoeuvring. l\/lethod according to claim 1, further comprising:reducing the acceleration of the electrical machine by reducing the frequency at which magnetisation patterns are being switched for at least onepredetermined position of driver controllable means (118) for activelyrequesting a propelling power from the electrical machine (101, 102) when thevehicle is manoeuvred in a state of low speed manoeuvring in comparison to when the vehicle is not manoeuvred in the state of low speed manoeuvring. 3. l\/lethod according to claim 1 or 2, further comprising: reducing the acceleration of the electrical machine by reducing the lOcurrent being applied to the stator winding (U, V, W) for at least onepredetermined position of driver manoeuvrable means (118) for activelyrequesting a propelling power from the electrical machine (101, 102) when thevehicle is manoeuvred in a state of low speed manoeuvring in comparison to when the vehicle is not manoeuvred in the state of low speed manoeuvring. _ Method according to any one of the claims 1-3, wherein driver controllable means (118) for actively requesting a propelling power from the electricalmachine (101, 102) are movable in a movement region between a first endposition (P1) and a second end position (P2), further comprising at least oneof:reducing the frequency at which magnetisation patterns are beingswitched for at least a portion of the movement region (P1-P2) of the drivercontrollable means (118) when the vehicle is manoeuvred in a state of lowspeed manoeuvring in comparison to when the vehicle is not manoeuvred inthe state of low speed manoeuvring, andreducing the current being applied to the stator winding (U, V, W) for at least a portion of the movement region (P1-P2) of the driver controllablemeans (118) when the vehicle is manoeuvred in a state of low speedmanoeuvring in comparison to when the vehicle is not manoeuvred in the state of low speed manoeuvring. _ l\/lethod according to any one of the claims 1-4, further comprising: at least one of controlling the frequency at which magnetisation patternsare being switched, and controlling the magnitude of the current applied whenmagnetising the electromagnets (U1-U6, V1 -V6, W1-W6), such that anacceleration of the electrical machine (101, 102) in response to a first requestfor power is reduced when the vehicle is manoeuvred in a state of low speedmanoeuvring in comparison to when the vehicle is not manoeuvred in the stateof low speed manoeuvring only when a predetermined vehicle speed hasbeen reached. _ l\/lethod according to any one of the claims 1-5, further comprising: - determining a rotation position of the rotor, and lO- selecting a magnetisation pattern for magnetising the electromagnets (U1-U6, V1 -V6, W1-W6) based on the rotation position of the rotor. Method according to any one of the claims 1-6, wherein: -the magnetisation pattern defining the magnetisation of each electromagnet,the magnetisation being generated by applying a positive, a negative or af|oating potential to the electromagnets. l\/lethod according to any one of the claims 1-7, further comprising: determining a representation of a vehicle speed of the vehicle (100),and at least one of controlling the frequency at which magnetisation patternsare being switched and controlling a magnitude of the current being applied tothe stator winding (U, V, W) such that at most a predetermined vehicle speedis reached. l\/lethod according to any one of the claims 1-8, wherein driver controllablemeans (118) for requesting power are movable in a movement region betweena first end position (P1) and a second end position (P2), further comprising:controlling the magnitude of the current applied when magnetising the electromagnets (U1-U6, V1 -V6, W1 -W6), such that the applied when thevehicle is manoeuvred in a state of low speed manoeuvring is reduced inrelation to the applied current when the vehicle is not manoeuvred in the stateof low speed manoeuvring for at least a first portion of the movement region,from the first position (P1) towards position (P2), of the driver controllablemeans for requesting power, the current being configured to progressivelyincrease to maximum current with a movement towards the second position(P2). l\/lethod according to any one of the claims 1-9, the vehicle (100) furthercomprising a gearbox comprising at least two gears, wherein: the gear used for propulsion of the vehicle in the reverse direction oftravel is a gear also being used for forward direction of travel. lO 11.l\/lethod according to any one of the preceding claims, wherein the vehicle ismanoeuvred in a state of low speed manoeuvring when a drive mode for reduced speed manoeuvring of the vehicle is selected. 12. l\/lethod according to claim 11, wherein:the drive mode for reduced speed manoeuvring of the vehicle is at leastone of a mode for travelling in the reverse direction and a crawler mode for low speed manoeuvring in the forward direction of travel. 13. Computer program comprising instructions which, when the program isexecuted by a computer, cause the computer to carry out the method according to any one of the preceding claims. 14. Computer-readable medium comprising instructions which, when executed bya computer, cause the computer to carry out the method according to any oneof the claims1-15. System for propelling an electric vehicle (100), the vehicle (100) comprising: an electrical machine (101, 102) configured to selectively provide acontrollable power for propelling at least one drive wheel (113, 114) of thevehicle (100), the electrical machine (101, 102) being an electronicallycommutated electrical machine (101, 102) having a rotor (404) and a stator(406), the stator (406) comprising a stator winding (U, V, W) comprising aplurality of circumferentially distributed electromagnets (U1-U6, V1 -V6, W1-W6), the rotor being caused to rotate by magnetising the electromagnets (U1-U6, V1-V6, W1-W6), the electromagnets (U1-U6, V1-V6, W1-W6) beingmagnetised according to predetermined magnetising patterns, a currentmagnetisation pattern being switched from one magnetisation pattern toanother in dependence of a current rotational position of the rotor (404); the system being characterised in, when the vehicle is manoeuvred ina state of low speed manoeuvring: means configured to control at least one of the frequency at whichmagnetisation patterns are being switched and a magnitude of the currentapplied when magnetising the electromagnets (U1-U6, V1 -V6, W1-W6), suchthat an acceleration of the electrical machine (101, 102) in response to a firstrequest for power is reduced in relation to the response to the first request for power when the vehicle is not manoeuvred in the state of low speedmanoeuvring. 16.Vehicle (100) comprising a system according to claim 14.