WO2019190389A1

WO2019190389A1 - Method and system for propelling an electric vehicle

Info

Publication number: WO2019190389A1
Application number: PCT/SE2019/050281
Authority: WO
Inventors: Torbjörn Boxell
Original assignee: Scania Cv Ab
Priority date: 2018-03-29
Filing date: 2019-03-28
Publication date: 2019-10-03
Also published as: SE1850360A1; SE544431C2; DE112019000968T5

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 VEHICLE

Field of the invention

The present invention relates to vehicles, and in particular to a method and system for propelling an electric vehicle. The present invention also relates to a vehicle, as well 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/commercial vehicles, 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 with vehicle operation is consumption of energy, oftentimes in terms of consumption of fuel, for propulsion of the vehicle. The degree of utilization of heavy vehicles is often high, and with its associated fuel consumption, the cost of fuel may affect the profitability of the owner of the vehicle to a great extent.

In view of this, alternatives to the sole use of conventional combustion engine technology in a vehicle are increasingly being considered. For example, hybrid- electric vehicles are becoming increasingly more common. Vehicles of this kind comprise an electrical machine, which may be utilised to provide power for propelling the vehicle in combination with an internal combustion engine. Vehicles of this kind may have a drivetrain configuration similar to a conventional internal combustion engine 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 vehicles are equipped only with one or more electrical machines, and no internal combustion engine is present. Hence the power generation is solely obtained by one or more 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 may have a high degree of usability, and the vehicles may also be used e.g. by a driver for relatively long consecutive periods of time. Therefore, in addition to addressing energy consumption which may be carried out in a favourable manner e.g. using electric vehicles, efforts are also made to make the driving of the vehicle comfortable to the driver. Such driver comfortability may comprise e.g. economical aspects but may also comprise vehicle behaviour or safety when being driven.

Summary of the invention

It is an object of the present invention to provide a method and system that allows for a vehicle behaviour where electric vehicle behave in a manner that is expected by a driver, in particular in situations when going in a reverse direction of travel and/or in a forward 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 electric vehicle,

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 an electronically commutated electrical machine having a rotor and a stator, the stator comprising a stator winding comprising a plurality of circumferentially distributed electromagnets, the rotor being caused to rotate by magnetising the electromagnets, the electromagnets being magnetised according to predetermined magnetising patterns, a current magnetising pattern being switched from one pattern to another in dependence of a current rotational position of the rotor;

the method comprising, when the vehicle is manoeuvred in a state of low speed manoeuvring:

controlling the frequency at which magnetisation patterns are being switched, and/or controlling a magnitude of the current applied when magnetising the electromagnets, such that an acceleration of the electrical machine in response to a first 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 for storing energy to be used for powering the electrical machine.

According to embodiments of the invention, the energy store may be charged by regenerative braking using the electrical machine or another electrical machine of the vehicle.

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. The present invention relates to electric vehicles, where the vehicle is being powered and propelled by one or more electrical machines. Electric vehicles according to the invention may comprise a gearbox but this is not a general requirement since electrical machines may be operated from zero speed of rotation to a high speed of rotation while also being capable of delivering a high torque from zero speed of rotation. Still a gearbox may be present, e.g. in case the efficiency of the electrical machine vary in dependence of speed of rotation. The use of a gearbox may also allow operation of the electrical machine at more favourable speeds of rotation, and may increase the torque that is applied to the vehicle drive wheels. Furthermore, the torque 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 in general be operated in any direction of rotation while still providing the same properties e.g. in terms of efficiency, speed of rotation and deliverable torque. This, in turn, has as result that even if using a gearbox the need for a reverse gear no longer exist, since the reverse direction of travel of the vehicle may be accomplished by operating the electrical machine in a direction of rotation being opposite to the direction of rotation of the electrical machine that is utilised when travelling in the forward direction.

According to embodiments of the invention, the electrical machine is connected to one or more vehicle drive wheels through a gearbox, where the gearbox may have any from a plurality of configurations, for example, the gearbox may comprise one or two or more gears for propelling the vehicle. The gearbox may also comprise a neutral gear to allow the electrical machine or machines to be disconnected from the one or more vehicle drive wheels. However, the gearbox does not comprise a reverse 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 may allow the vehicle to be propelled in the same manner in regard of e.g. acceleration and speed of travel irrespective of whether the vehicle is moving in a forward or reverse direction of travel. This may not be desired, e.g. because oftentimes driver visibility in the rear direction is limited in comparison to the driver visibility in the forward direction of travel. According to the present invention, therefore, it is provided a method that may cause the vehicle to behave differently e.g. in dependence on whether the requested vehicle movement is a forward direction of travel or a reverse direction of travel.

In 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 controlled to be lower when going in a reverse direction in comparison to when going in a forward direction of travel. In this way, the vehicle may be caused to behave more like a vehicle comprising an internal combustion engine and a gearbox having a reverse gear. The invention may also be applied when low speed manoeuvring the vehicle in the forward direction.

With regard to the request for power, this may be an arbitrarily initiated request for power, i.e. in any manner a request for propelling power may be initiated. For example, power may be requested by driver manoeuvrable means for requesting power, such as an accelerator, but may also be e.g. a release of vehicle brakes since oftentimes a power is applied by the vehicle control system when brakes are released and the vehicle is in a state for being set in motion, such as e.g. by being in a 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 commutated electrical machine having a rotor and a stator, where rotation of the rotor may cause a vehicle drive wheel to rotate. The stator comprises a stator winding comprising a plurality 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, where each phase winding may comprise one or a plurality of electromagnets. These electromagnets may comprise a coil wound around a core being aligned in the radial direction. The electromagnets may be denoted stator poles. Furthermore, the poles/electromagnets may be configured to be magnetised such that, when magnetised, the magnetisation forms a magnet having north pole directed in a radial direction away from the rotor, and a south pole in a direction towards the rotor, or vice versa.

The electromagnets are magnetised according to predetermined magnetising patterns, where the magnetisation pattern may define the magnetisation of each electromagnet, where the desired magnetisation may be generated by applying a positive, a negative or a floating potential to the electromagnets, where this in general is accomplished by applying the voltage to stator terminals.

The stator may comprise at least three phase windings, each phase winding comprising 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, and the electromagnets attract magnets of the rotor to thereby cause a rotation of the rotor, 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 and also magnets of the rotor. When the rotor reaches and/or approaches a rotor position where it would be“locked” by the current magnetisation pattern, the magnetising pattern is switched to a subsequent pattern that causes the rotor to rotate a further portion of a revolution. A continuous switching of the magnetisation pattern may then keep the rotation in motion. If 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 selecting magnetisation 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 is manoeuvred in a state of low speed manoeuvring, such as when manoeuvred in a reverse direction of travel or when being low speed manoeuvred in the forward direction, the acceleration of the rotor, and hence the acceleration of the vehicle, may be controlled by controlling the frequency at which magnetisation patterns are being switched and/or controlling a magnitude of the current applied when magnetising the electromagnets according to a magnetisation pattern such that an acceleration of the electrical machine will be reduced in comparison to when the vehicle is not manoeuvred in the state of low speed manoeuvring, and e.g. is manoeuvred according to a state of general manoeuvring in the forward direction such as when manoeuvring the vehicle according to a state allowing speeds up to maximum speed of the vehicle.

In this way, maximum speed and/or acceleration of the vehicle can be limited in relation to standard/general travelling in the forward direction. For example, for a given accelerator position, the acceleration of the vehicle may be reduced, which may facilitate low speed manoeuvring, which thereby may reduce the risk for the vehicle moving in an unexpected manner e.g. when the vehicle is moving in the reverse direction.

In 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. Since the deliverable torque of the electrical machine is dependent on the applied current, a reduction only of the frequency at which the magnetisation patterns are switched, but maintaining the applied current unchanged, maximum torque may still be applied to the vehicle drive wheels by applying maximum current. Hence e.g. capabilities of performing vehicle starts on inclined surfaces may remain unchanged since full torque is available. Still the acceleration of the vehicle can be reduced by controlling the speed of the frequency at which the magnetisation patterns are switched.

Furthermore, the magnetic force being generated by the electromagnets, and thereby the 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 permanent magnets of the rotor. Therefore, an alternative method of reducing the acceleration of the 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 the switching pattern is changed is combined with a reduction of the current. This may be utilised to reduce energy consumption, since the reduced acceleration caused by controlling the frequency at which the switching pattern is changed may require lower currents, and by controlling the current to a level corresponding to a level required to provide the requested acceleration excess energy consumption can be reduced.

The acceleration of the electrical machine can be arranged to be reduced by reducing the frequency at which magnetisation patterns are being switched for at least one predetermined position of the driver controllable means when the vehicle is manoeuvred in a state of low speed manoeuvring in relation to the frequency at which magnetisation patterns are being switched for the same position of the driver controllable means when the vehicle is not manoeuvred in the state of low speed manoeuvring.

In addition, or alternatively, the acceleration of the electrical machine can be reduced by reducing the current being applied to the stator winding for at least one

predetermined position of the driver manoeuvrable means when the vehicle is manoeuvred in a state of low speed manoeuvring in relation to the current being 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 the driver manoeuvrable means is moved towards a second end position. In this way, the applied current may be controlled such that although being reduced 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.

Oftentimes the driver controllable means for requesting power is movable in a movement region between a first end position and a second end position. The frequency at which magnetisation patterns are being switched may be reduced for at least a portion of, or all of, the movement region of the driver controllable means when the vehicle is manoeuvred in a state of low speed manoeuvring in relation to when 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 least a portion of, or all of, the movement region may be reduced when the vehicle is manoeuvred 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 may have the advantage that a high torque can be applied to the vehicle drive wheel(s) at a low speed, which e.g. may be advantageous when the vehicle is being driven on an inclined surface. In principle, maximum torque may be applied to the drive wheels even when the vehicle is standing still, hence allowing use of the electrical machines also as a vehicle brake when the vehicle is standing still.

According to embodiments of the invention, the frequency at which magnetisation patterns are being switched, and/or the magnitude of the current applied when magnetising the electromagnets, is controlled such that an acceleration of the electrical machine in response to a first request for power using the driver

controllable means is reduced when the vehicle is manoeuvred in a state of low speed 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 reached. In this way, the vehicle may be allowed to behave as when going in the forward 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 be represented by a representation of the vehicle speed. For example, the rotor speed of 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 be determined, 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 reduced the vehicle is manoeuvred in a state of low speed manoeuvring in relation to when the vehicle is not manoeuvred in the state of low speed manoeuvring such that at most a predetermined vehicle speed is reached.

In this way, the vehicle may be allowed to behave as if being manoeuvred for general travel in the forward direction at first, but as soon as the vehicle speed reaches some predetermined speed the vehicle speed and/or acceleration can be arranged to be reduced in comparison to when the vehicle is manoeuvred for general travel in the forward 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 applied when magnetising the electromagnets is applied such that the applied current is reduced in relation to the applied current when the vehicle is not manoeuvred in the state of low speed manoeuvring for at least a first portion of the movement region of the driver controllable means for requesting power, stretching from no request for power towards the position for maximum request for power. For example, the current may be arranged to progressively increase as the driver manoeuvrable means is moved towards the second end position from the first end position. For example, the applied current may be controlled to increase progressively, i.e. non-linearly with a movement of the driver manoeuvrable means from the first end position towards the second end position. The applied current may be controlled such that although being reduced 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. The frequency at which magnetisation patterns are being switched may be controlled to only depend on rotor position. This in turn means that when maximum current is applied any speed of rotation of the electrical machines is available. Still low speed manoeuvring will be simplified since e.g. an accelerator needs to be depressed further 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 magnetisation patterns are switched and/or the magnitude of the current being applied to the stator winding, is controlled such that when the vehicle is manoeuvred in a state of low speed manoeuvring the frequency and/or magnitude of the current and/or vehicle speed at most corresponds to a percentage being less than 100% of the

frequency/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 suitable kind of means may be utilised, which may be movable in a movement region between 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 energy store into positive and negative voltages to be applied to the stator winding. The inverter 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 suitable states of low speed manoeuvring.

According to embodiments of the invention, states of low speed manoeuvring may be represented by different drive modes for propelling the vehicle. Such modes may include a mode for reduced speed manoeuvring of the vehicle, and a mode for standard travelling in the forward direction. For example, the mode for reduced speed manoeuvring of the vehicle may include a mode for reverse direction of travel, and/or a crawler mode for low speed manoeuvring in the forward direction. Hence, the control that has been discussed above for manoeuvring the vehicle in a state of low speed manoeuvring may be carried out when the vehicle is propelled in a drive mode for reduced speed manoeuvring of the vehicle, where the control may be carried out in relation to when the vehicle is being propelled according to a mode for standard travelling in the forward direction.

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

The invention may be carried out in a vehicle, and the invention also relates to a system corresponding to the method set forth above. The system is characterised in means carrying out features of the invention. Such means for carrying out features of the invention can consist of any suitable means, and the means can be specifically adapted to perform the features set forth in the system claim. Such means can consist 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 indicated in the detailed description of exemplary embodiments set out below and the attached drawings.

The vehicle may comprise a driver's seat for use by a driver when driving the vehicle, and the method according to the invention may arranged to be carried out when a driver is seated in the driver's seat while maneuvering the vehicle in a state of low speed manoeuvring.

Brief description of the drawings

Fig. 1 A illustrates a powertrain of an exemplary electric vehicle;

Fig. 1 B illustrates an example of a control unit/means in a vehicle control system;

Fig. 1 C 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.

Detailed description of exemplary embodiments

According to the following detailed description, embodiments of the invention are exemplified for a vehicle comprising drive modes. As has been explained above, the invention is applicable also for vehicles where no such drive modes are present, and where 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 and thereby control of the one or more electrical machines to be used. Fig. 1 A

schematically depicts a powertrain of an exemplary electric vehicle 100 according to embodiments of the invention. There exist electric vehicles of various kinds and designs. For example, the number of electrical machines being used for the propulsion of the vehicle may differ. According to the present, non-limiting, example of the invention, the powertrain of the electric vehicle 100 in Fig. 1 A comprises two electrical machines 101 , 102, which both are connected to a common shaft 104 forming a gearbox input shaft of a gearbox 103.

Electric vehicles of the disclosed kind may, but need not necessarily, comprise a gearbox, since electrical machines may be operated from zero speed of rotation to a high speed of rotation while also being capable of delivering a high torque from zero speed of rotation. Flowever, the efficiency of electrical machines may still be different for different speeds of rotation, and use of a gearbox may allow operation of the electrical machine(s) at more favourable speeds of rotation. Also, a gearbox may be utilised to increase the torque that is applied to the vehicle drive wheels in relation to the 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, but which differs from conventional gearboxes being used in conventional hybrid and non-hybrid vehicles comprising an internal combustion engine. According to the present example, the gearbox 103 comprises only two gears for providing two different gear ratios between the gearbox input shaft 104 and a gearbox output, which according to the present example is connected to, and represented by, a propeller 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 107 in case this is desired, e.g. to reduce the risk for the vehicle being accidentally and/or unintentionally set in motion. The gearbox does not comprise a reverse gear. Instead, when propelling the vehicle in the reverse direction, a gear is used that is also used for propelling the vehicle in the forward direction. Furthermore, in reality, the gearbox 103 may be e.g. bolted or other otherwise affixed to the electrical machines 101 , 102 e.g. to improve rigidity, and hence the separation of the components in fig. 1A are for illustration purposes only. As was mentioned, the gearbox 103 output is connected to a propeller shaft 107 which in a conventional manner propels the vehicle drive wheels 113, 114 via a final drive 108 and drive shafts 109a, 109b. However, the use of a gearbox is not a necessary feature according to the invention, but the invention may also be utilized in vehicles where e.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 controlling the electrical machines 101 , 102. Exemplary components of the drive system comprise an inverter drive 111 for controlling the electrical machines 101 , 102. An energy source, such as an energy store, e.g. consisting of one or more batteries 112 provides energy required for powering the electrical machines 101 , 102. A control unit/means 115 controls, inter alia, the inverter drive 111 to thereby control operation of the electrical machines 101 , 102. The control unit/means 115 may also be configured to control e.g. the gearbox 103 and/or other functions. The functionality may, 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 schematically shown in Fig. 1 C. The accelerator pedal 118 is movable within a movement region defined by two end positions P1 , P2, defining an angular range a. The accelerator pedal 118 position in the movement region can be determined, e.g. by means of a suitable sensor, such as, for example, a potentiometer or an angle sensor 119 or any other suitable kind of sensor which determines the current position of the accelerator pedal 118 in the movement region in which the accelerator pedal is movable. In principle, any position of the accelerator in the movement region may be detected using sensor means. When the accelerator pedal 118 is fully released, i.e. not manoeuvred by the driver, it is in a state of rest in position P1 , e.g. by means of a spring force, where position P1 represents no driver request for power from the electrical machines. Position P2 represents a fully depressed accelerator pedal and hence a driver request for full power, where any power between zero and full power may be requested by appropriately positioning the accelerator pedal at a

corresponding position between position P1 and position P2. Furthermore, the illustrated accelerator only represents an exemplary driver controllable means for requesting power, and any kind of suitable accelerator means may be utilised, such as e.g. a combined accelerator/decelerator, for as long as the means is movable in a movement 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 driver

controllable drive mode selector 116 for selecting a drive mode of the vehicle, such as selecting a direction of travel of the vehicle. For example, the driver controllable drive 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 the forward direction, e.g. when manoeuvring the vehicle with a high accuracy. The drive mods may also be selectable by the vehicle control system and hence need not be driver selected as in the present non-limiting example.

Fig. 2 discloses the electrical machine drive system of fig. 1 A 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. The energy 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. 2 also discloses a junction box 201 , which may be utilised to allow auxiliary equipment to be powered by the battery 112, e.g. via suitable conversion of the voltage if required. 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.

Inverter 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 various examples 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 prevent over voltages and/or short-circuiting, e.g. at system start up when e.g. capacitors may be essentially uncharged and thereby subjected to excessive currents. Such measures are known to the person skilled in the art and are therefore not disclosed further 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 torque and/or speed controlled by means of the inverter drive system. Inverter drives in general allow for rotational speed and torque control of the electrical machine by varying 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 electronically commutated machines, brushless DC electrical machines, and will be described more in detail below. The electrical machines 101 , 102 further have three phase windings 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 the electrical machines 101 , 102 using switches such as transistors 221 -226, where each phase 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 voltage so that both positive and negative voltages can be produced in the control of the electrical machines from the DC link voltage. The switches 221 -226 are controlled by control means, where the control signals may be generated based on requests from the control unit/means 115 to provide desired current/voltage pulses to the motor windings to obtain the desired control the speed and torque of the motor.

Inverter drives of the kind disclosed in fig. 2, and inverter drives in general and with regard 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- 236 being arranged anti-parallel to transistors 221 -226. The diodes 231 -236 will rectify the voltage induced in the stator e.g. during regenerative braking, and provide a rectified voltage on the DC link which may be utilised to charge the energy store 112. Further according to the present example, the electrical machines 101 , 102 are controlled by the same control signals and hence operate in synchronism.

An exemplary electrical machine 101 , which, as was mentioned, is an electronically commutated electrical machine, is schematically disclosed in fig. 4. The stator 406, according to the present example, comprises three phase windings U, V, W that are being individually controlled by the inverter drive 111 using the switches/transistors 221 -226. The inverter drive 111 is configured to selectively apply a positive voltage, a negative voltage or leave the terminal potential left floating by both switches of the associated 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 to phase winding U, a positive voltage is applied by closing switch 221 (thereby conducting) while switch 222 is open. Correspondingly, a negative voltage is applied by closing switch 222 while switch 221 is open. If both switches 221 -222 are left open, the terminal of phase winding U is left floating as mentioned. Through the use of a suitable switching of the switches, a controllable desired resulting average voltage amplitude of the stator terminal voltage can be obtained by controlling opening time, while the DC link/bus voltage still may remain essentially constant. In this 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 present example is attached to and/or forming the gearbox input shaft 104. The rotor comprises embedded permanent magnets 405 a-f. Each permanent magnet comprises a north (N) pole and a south (S) pole. Furthermore, each of the phase windings comprises six poles, in the present application also denoted electromagnets, being circumferentially distributed, e.g. evenly. For example, phase winding U comprises poles, electromagnets, U1 -U6. Correspondingly, phase winding V 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 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 phase winding, electromagnets may be formed in the stator windings and having a polarity which will attract poles of the permanent magnets 405a-f of the rotor 404. For example, according to the example of fig. 4, when a positive voltage is applied e.g. to the 'W terminal, and a negative voltage is applied to the 'U' terminal, the

electromagnets W1 -W6 of the W winding will form electromagnets having a north pole directed inwards towards the rotor, and a south pole directed outwards towards the exterior of the electrical machine 101. At the same time, the poles U 1 -U6 of the U terminal will form electromagnets having a south pole directed inwards towards the rotor 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 south poles of the embedded magnets 405a-f of the rotor. Correspondingly, the U windings will attract the north poles of the magnets of the rotor. This means that, in the example of fig. 4, the rotor will make a 20° rotation from the illustrated rotor position in a counter-clockwise direction, so that e.g. the north pole of magnet 405a will be aligned with the pole U1 of stator winding U instead of being aligned with pole W6 of stator winding W as is presently the situation in fig. 4. The south pole of magnet 405a, in turn, will become aligned with pole W6 of stator winding W. Correspondingly this applies to the north poles of magnets 405b-f and poles U2-U6 of stator winding U, 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. For example, the poles of winding V may be controlled such that the poles form a magnet having a south pole directed inwards towards the rotor, and a north pole directed outwards towards the exterior of the electrical machine 101 instead of the poles of winding W, which instead may be left unmagnetized. This will still accomplish the desired rotation. In general, with regard to inverters of the kind disclosed in fig. 2, it may be desirable to control the switches such that only one switch at a time changes state of the switch pairs 221-222, 223-224 and 225-226, respectively.

In order to further rotate the rotor, polarity and/or terminals being subjected to voltage can 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 the rotor, and a north pole directed outwards towards the exterior of the electrical machine 101. At the same time, e.g. the poles W1 -W6 of the W terminal may be controlled to form magnets having a south pole directed inward towards the rotor and a north pole outward towards the exterior of the device.

In this way, by suitably switching the voltage/current applied to the stator terminals to obtain desired magnetisation of the stator poles, the stator poles can be appropriately magnetized according to predetermined patterns, i.e. the ways in which

poles/electromagnets are to be magnetised in dependence of the rotor position to attract and repel the permanent magnets of the rotor to thereby obtain the desired rotation. For as long as the stator is kept magnetized according to a particular pattern, i.e. the poles are held at a certain magnetisation, e.g. according to the example of fig. 4, the rotor may be held in this position. Hence the speed of rotation can be controlled by changing the magnetisation pattern of the stator poles at a frequency 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, any number of intermediate patterns may be utilized, which may be applied in

dependence of the position of the rotor so that a smooth rotor motion is obtained. In case the above method is applied while applying a high current, the rotor motion may be jerky due to fast switches between rotor positions corresponding to magnetization patterns as the pattern is switched. Use of a plurality of intermediate patterns alleviates such behavior so that a smooth transition from one pattern to another is obtained 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 patterns to be used. The intermediate patterns may be configured such that a sinusoidal or trapezoidal voltage is applied to the stator winding. In case the current is reduced, the frequency at which magnetization patterns are switched will automatically be reduced, since the reduced current will have as result that the rotor moves slower, and the magnetization patterns are applied in dependence of rotor position. This also means that when the current is reduced, it is not required to use a plurality of intermediate patterns, since the reduced current in itself may ensure that the 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 to embodiments of the invention the winding is such that a positive voltage applied to a particular winding instead will form a magnet having a south pole directed inwards towards the rotor, and a north pole directed outwards towards the exterior of the electrical machine 101 and vice versa.

In 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 the permanent magnets of the rotor in relation to the stator poles, so that the appropriate magnetisation pattern to be generated by applying voltage to the stator terminals by the inverter drive can be applied in view of the current rotor position. In this way, changes of the polarity of the stator poles by changing polarity of the stator terminals can 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, such as one or more appropriate encoders being utilized to detect the rotational position of the 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 more absolute rotary encoders, one or more optical encoders, and/or one or more hall effect sensors to determine the rotational position, i.e. the positions of the permanent magnets 405a-f of the rotor 404, in relation to the stator poles.

It 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 example, with regard to an electrically commutated electrical machine, the stator may comprise any suitable number of stator poles, and other designs than a three-winding stator may also be utilised. For example, two or four or more windings, and each winding 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 be greater or lesser, where the magnetisation patterns being used to magnetise the stator may be adapted to the particular rotor/stator configuration. The adaption of the control in this manner is well within the skills of the person skilled in the art.

In addition to controlling the magnetisation of the stator poles/electromagnets, the amplitude of the current can be controlled to thereby also control the generated torque. A reduced torque will cause the rotor to rotate more slowly, and hence it will take a longer period of time reach the subsequent rotor position. Since the

magnetisation patterns are applied on the basis on rotor position, the speed of rotation is reduced even if the allowable frequency by which magnetisation patterns may be changed is not reduced. Flence the electrical machine can be controlled both with regard to speed of rotation and the amount of torque being generated which will impact 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 controlling the frequency at which magnetisation pattern of the stator poles is changed, and/or controlling the magnitude of the supplied current is utilized according to the invention in order to control the movement of the vehicle differently in dependence of whether the vehicle is going in a forward direction of motion or in a reverse direction of motion. Since the electromagnets of the stator can be magnetized in any desired manner, this also means that the direction of revolution of the rotor may be any desired direction. That is, counter-clockwise or clockwise. Because of this there is no need for any reverse gear in the gearbox, since the reverse operation can be controlled by appropriate magnetisation of the stator windings.

An exemplary method according to embodiments of the invention is disclosed in fig. 3 which 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 invention may be implemented in a computer program, which, when it is executed in a computer, instructs the computer to execute the method. The computer program is usually constituted by a computer program product stored on a non-transitory/non- volatile digital storage medium, in which the computer program is incorporated in the computer-readable medium of the computer program product. The computer- readable medium comprises a suitable memory, such as, for example: ROM (Read- Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically Erasable PROM), 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. The behaviour 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 electrical machines based on driver requests are, in general, controlled by control means such as e.g. a control system and/or a control unit. Control systems in modern vehicles commonly comprise communication bus systems comprising one or more

communication buses for linking a number of electronic control units (ECU's), or means or controllers, and various components located on the vehicle. Such a control system can comprise a large number of control units/means, and the responsibility for a specific function can be divided amongst more than one control unit. Vehicles of the shown type thus often comprise significantly more control units than the control unit/means 115 shown in fig. 1A, which is well known to the person skilled in the art within this technical field. For example, the gearbox 103 may be controlled by another control unit/means, and similarly various other functions of the vehicle may be controlled by control units/means as is known per se. The control units/means 115 of fig.1 A 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 a control unit/means, e.g. of the exemplified kind, this may hence be accomplished using 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 embodiments of the invention may also be implemented using a combination of a plurality of computer programs, which may be implemented in a same or different control units/means. A vehicle control system may also comprise only a single control unit/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 control unit/means 1 15 for controlling the electrical machine drive system.

The invention may, however, also be implemented in any other suitable control unit/means and/or combination of control units/means. The control of the electrical machines/inverter drive according to the invention will depend on signals being received from other control units/means and/or vehicle components, and it is generally the case that control units/means of the disclosed type are normally adapted to receive sensor signals from various parts of the vehicle 100. The control unit/means 1 15 will, for example, receive control signals representing the rotor/rotor magnet position, and further an indication of a requested direction of travel of the vehicle from drive mode selector 1 16, and request for power from the vehicle driver, e.g. requested using the accelerator 1 18. Control units/means of the illustrated type are 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 1 15) forming part of, or constituting, the vehicle control system is schematically shown in Fig. 1 B, wherein the control 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 signal processing (Digital Signal Processor, DSP) or a circuit having a predetermined specific function (Application Specific Integrated Circuit, ASIC). The computing unit 120 is connected to a memory unit 121 , which provides the processing unit 120, with e.g. the stored program code 126 and/or the stored data that the computing unit 120 requires to be able to perform calculations. The computing unit 120 is also arranged so 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 signals can comprise waveforms, impulses or other attributes that can be detected as information and can be converted into signals which can be processed by the computing unit 120. These signals may then be made available to the computing unit 120. The devices 123, 124 for transmission of output signals are arranged to convert signals received from the processing unit 120 in order to create output signals by, for example, modulating the signals, which can be transmitted to other parts of and/or systems of the vehicle. Each of the connections to the devices for receiving and transmitting input and output signals may comprise of one or more of a cable; a data bus, such as a CAN bus (Controller Area Network bus), a MOST bus (Media

Oriented Systems Transport), Ethernet, or any other bus configuration or combination of different data bus technologies, and/or a wireless connection. A person skilled in the art will appreciate that the claimed system, or part of the claimed system, may comprise the control unit/means 115 where means of the claimed system may comprise the computing unit 120.

An exemplary method 300 according to embodiments of the invention is illustrated in fig. 3. As was mentioned, according to the present example, the vehicle 100 comprises driver controllable means 118 for requesting power from the electrical machines 101 , 102. As was also mentioned above, these driver controllable means may e.g. be in the form of an accelerator 118, where the accelerator 118 may be depressed to request power from the electrical machines 101 , 102. The method 300 starts in step 301 where it is determined whether the drive mode selector 116 for selecting drive mode is set to a drive mode where speed is to be reduced. This drive mode may be the drive mode for reverse direction of travel, or the crawler mode for manoeuvring at low speed in the forward direction. The method 300 may remain in step 301 for as long as this is not the case, while the method may continue to step 302 when it is established that the driver has requested e.g.“reverse” or“ crawl” using drive mode selector 116. Manoeuvring of a vehicle in the reverse direction in general requires that the driver is more precautious since, for example, visibility may be limited in relation to when the vehicle is traveling in a forward direction. There may also 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 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 requested from the electrical machines 101 , 102 for a given driver request, which e.g. may be represented by the accelerator 118 position, is set to a response that differs from the response that would be obtained for a similar request for power in a situation where the driver instead has requested that the vehicle is to move in a forward direction of travel. For example, acceleration may be reduced.

In step 302 the power to be actually produced by the electrical machines 101 , 102 is set as a function of the selected drive mode, and also of the current accelerator position in accordance with a pedal position/power level dependency that has been set for travelling in the reverse direction or for crawler mode. That is, when e.g. a reverse direction of travel or crawler mode is selected, the power that is actually being requested by the electrical machines 101 , 102 in response to a request for power, such as e.g. a particular accelerator 118 position, will be different in comparison to when going in the forward direction of travel.

This may apply also to the situation when e.g. vehicle brakes are released but the accelerator has not been depressed. A request for power may be determined by determining whether the accelerator 118 is at least partially depressed. According to embodiments of the invention, the accelerator need not be depressed, but it may be sufficient to determine e.g. if the driver releases vehicle brakes, e.g. by releasing a brake pedal while the drive mode selector is set to a mode for propulsion of the vehicle. Oftentimes in such cases the vehicle starts moving in the selected direction of 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 is selected will be discussed below. The method may be ended in step 303, and the method may e.g. be continuously repeated to determine if the selected mode is still to be 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. It is also contemplated a method where the drive mode is determined, and suitable control is applied on the basis of the selected drive mode, where it can be

continuously determined which drive mode has been selected. Hence a method according 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 method according to fig. 3 may also be utilised e.g. if a parking state or neutral state has been selected using the selector for selecting a direction of travel, where the control of the electrical machines can be performed in accordance therewith, e.g. by requesting no power if no direction of travel has been selected.

With regard to the actual control of the electrical machines 101 , 102 in response to the request for power from the electrical machines 101 , 102, this may be

accomplished in various manners. For example, as was explained above, the speed of rotation of the electrical machines 101 , 102 may be determined by the speed at which 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 pattern to another, where, as was mentioned above, a plurality of intermediate patterns may be utilised. The faster the rotor is urged from one rotation position to a following rotation position defined by the subsequent magnetisation pattern, the faster the rotor will rotate.

Therefore, according to embodiments of the invention, the frequency at which magnetisation patterns are switched for a particular position of the accelerator may be reduced when the reverse direction of travel mode or crawler mode is requested.

In this way, if the driver depresses e.g. the accelerator 118 e.g. to a particular position, a change of magnetisation pattern at a higher frequency will be applied when the electrical machines 101 , 102 are controlled according to the control that has been defined for forward direction of travel mode in comparison to when the electrical machines 101 , 102 are controlled according to the control that has been defined e.g. for the reverse direction of motion. This further means that the vehicle acceleration may be lower for any given accelerator 118 position in the reverse direction control, or crawler control, in comparison to when the accelerator is similarly depressed when vehicle is being controlled according to the control defined for travelling in the forward direction. Thereby, the risk for the vehicle performing sudden and undesired high accelerations, and/or reaching undesirably high speeds, when travelling 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 illustrating the response 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-axis represents the response, e.g. in terms of acceleration or power being requested from the electrical machines 101 , 102, where“0” indicates no response being requested and MAX represents a situation where the vehicle control system requests maximum response from the electrical machines 101 , 102, i.e. maximum power/acceleration. The x-axis represents pedal position, where, in correspondence with figure 1 C, P1 represents a fully released pedal, and P2 a fully depressed accelerator 118.

The dotted line 501 represents the relationship between response being requested from the electrical machines 101 , 102 and accelerator position when the driver has selected a forward direction of travel. As can be seen from the figure, the actual request for power from the electrical machines increase with an increasingly depressed accelerator 118 pedal where a fully depressed accelerator essentially corresponds to a maximum response being requested from the electrical machines 101 , 102. The dotted line 501 is for illustration purposes only, and the relation between requested response and accelerator position e.g. need not be a straight line as in the present example, but may have any suitable relationship, and further need not necessarily increase all the way to a maximum response MAX_forw being requested.

The solid line 502 represents the relationship between power being requested from the electrical machines 101 , 102 and accelerator position when, instead, the driver has selected a reverse direction of travel or crawler mode. As can be seen from the figure, the actual request for response from the electrical machines increase with an increasingly depressed accelerator also in this case, but with the difference that a fully depressed accelerator, instead, corresponds to a considerably lower maximum response, MAX_reverse, being requested from the electrical machines 101 , 102. For example, the maximum response being requested from the electrical machines 101 , 102 when the reverse direction of travel is selected may be set to 50% of the maximum response being requested when the forward direction of travel is selected, or any other suitable higher or lower percentage. With regard to the illustrated request for response, the response is the combined power delivered by the two electrical machines 101 , 102. In fig. 5A, the y-axis could, instead, represent possible vehicle 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 vehicle possibly may be set in motion e.g. when vehicle brakes are released. As can also be seen from the figures, this requested response may be different for the different drive modes, and e.g. be reduced when reverse mode or crawler mode has been selected so that the vehicle may move slower in such a case. It is also to be noted that the power level being actually requested by the electrical machines when brakes are released but also accelerator is released may depend on e.g. current vehicle inclination and/or vehicle weight in order to provide the desired response. That is, the current being applied to the electrical machines may be different for different situations. A high vehicle weight, or an inclination, requires a higher current to obtain a 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 are switched, it may oftentimes be desirable to control the current in the same manner as when going in the forward direction. In this way it is still possible to obtain maximum torque by not reducing the current. That is, maximum current can be applied while the speed of rotation is reduced by the reduced frequency at which magnetisation patterns are switched. The maximum response, e.g. in terms of acceleration, that is delivered by the electrical machines is still reduced, since the maximum speed of rotation is reduced so that as a result the electrical machine at most will reach a predetermined speed of rotation, and thereby the vehicle will at most reach a corresponding predetermined vehicle speed.

However, when controlling the frequency at which magnetisation patterns are switched, it may oftentimes be desirable to simultaneously reduce the current, since a reduced current may still be sufficient to provide the desired vehicle acceleration. In this way, energy consumption can be reduced by not applying a higher current than is required to provide the desired acceleration. That is, the amplitude of the current being applied to the stator terminals, e.g. represented by the voltage amplitude being applied to the stator terminals, may be continuously controlled to precisely a level providing the desired response, thereby minimising excess energy consumption.

For example, the speed of rotation of the rotor and/or vehicle speed may be continuously determined to determine if the obtained response corresponds to the predetermined response. In this way it can be determined whether the applied current is insufficient, e.g. when the actual acceleration is below the predetermined acceleration. In such cases the current may be increased. Similarly, when the acceleration corresponds to the desired acceleration a reduction of the current may be attempted in an effort to improve energy consumption. This control may be continuously performed to maintain the current as close as possible at precisely the current that is required to obtain the desired control. For example, the actual rotor position may be compared with the expected rotor position, and this slip may be utilised 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 to changing the magnetisation pattern frequency, the current may instead be reduced for any accelerator position when the vehicle set for going in the reverse direction of travel in comparison to when a forward direction of travel has been selected.

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

Hence the lines 501 , 502 could alternatively represent frequency at which

magnetisation patterns are switched, and/or applied current. However, as was mentioned if the current is reduced, the available torque is also reduced, which may have to be taken into account e.g. if the vehicle is about to perform a movement on an inclined surface. As was mentioned above, in case the availability of a high torque is of essence, the reduction of the frequency at which magnetisation patterns are switched may be utilised in favour of reducing the current, since if the vehicle is heavily 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 progressively increase as the driver depresses the accelerator, so that sufficient torque to set the vehicle 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 I, and hence available torque. According to fig. 5B, instead of reducing the current throughout the movement region of the accelerator as exemplified above, the current is instead lower when a reduced speed mode is selected than the correspondingly applied current when the general forward direction mode is selected, dotted line 503, for a large portion of the accelerator movement region (P1 -P2), and high currents are only available when the accelerator has been depressed to a great extent, solid line 504. In this way, low speed control is facilitated to a great extent since high currents are only available at the end of the movement region of the accelerator, which thereby reduces the risk for undesired accelerations, since high acceleration may not be obtained unless the accelerator is depressed to a large extent because of

progressively 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 movement region of the accelerator. This example may according to embodiments of the invention be combined with a maximum allowed vehicle speed that imposes further restrictions regarding the current in case the vehicle reaches this maximum allowable speed.

According to embodiments of the invention, 100% of the deliverable

acceleration/torque from the electrical machines at a current speed is available at low vehicle speeds, but as vehicle speed increases, e.g. represented by the speed of rotation of the electrical machines, the possibility to request maximum vehicle acceleration may be limited, e.g. decreasingly, or alternatively the maximum allowable frequency at which the magnetisation pattern is switched may be limited as vehicle speed increases. Still the current may be controlled such that maximum torque is available while acceleration is limited. According to this embodiment, therefore, knowledge of vehicle speed is required, so that limitations can be imposed when the vehicle speed increases to thereby prevent the vehicle from reaching higher than a predetermined speed when going in the reverse direction, where the limit can be set e.g. as above. The vehicle speed may e.g. be derived from the electrical machine rotation speed or any other vehicle speed sensor used on the vehicle (e.g. ABS/EBS sensors, tachometer, output shaft speed sensor, GPS, etc).

According to embodiments of the invention described above, the vehicle may have a drive mode selector for selecting a mode for reduced speed travel both in the forward and the reverse direction. According to embodiments of the invention, the described solutions are applied when the driver selects a drive mode to specifically be used when moving only slowly in the forward or reverse direction, e.g. by selecting a mode being 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 ensured that a vehicle being propelled by one or more electrical machines will not exhibit the same acceleration and/or maximum speed when going in a reverse direction as when going in a forward direction in situations where a gearbox having a reverse gear is not being used.

Finally, the invention may also be utilised when the accelerator is released in case this is desired, so that e.g. the frequency at which magnetisation patterns are switched may be controlled according to any suitable profile to obtain a desired deceleration.

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

Claims

1. Method for 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 (101 , 102) being an electronically commutated electrical machine (101 , 102) 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 being characterised in, when the vehicle is manoeuvred in a state of low speed manoeuvring:

at least one of controlling the frequency at which magnetisation patterns are being switched and controlling a magnitude of the current applied when magnetising the electromagnets (U1-U6, V1 -V6, W1 -W6), such that an acceleration of the electrical machine (101 , 102) in response to a first 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.

2. Method 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 one predetermined position of driver controllable means (118) for actively requesting a propelling power from the electrical machine (101 , 102) when the vehicle 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. Method according to claim 1 or 2, further comprising:

reducing the acceleration of the electrical machine by reducing the current being applied to the stator winding (U, V, W) for at least one

predetermined position of driver manoeuvrable means (118) for actively requesting a propelling power from the electrical machine (101 , 102) when the vehicle 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.

4. Method according to any one of the claims 1 -3, wherein driver controllable means (118) for actively requesting a propelling power from the electrical machine (101 , 102) are movable in a movement region between a first end position (P1 ) and a second end position (P2), further comprising at least one of:

reducing the frequency at which magnetisation patterns are being switched for at least a portion of the movement region (P1 -P2) of the driver controllable means (118) when the vehicle 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, and

reducing 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 controllable means (118) when the vehicle 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.

5. Method according to any one of the claims 1 -4, further comprising:

at least one of controlling the frequency at which magnetisation patterns are being switched, and controlling the magnitude of the current applied when magnetising the electromagnets (U1-U6, V1 -V6, W1 -W6), such that an acceleration of the electrical machine (101 , 102) in response to a first request for power is reduced when the vehicle 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 only when a predetermined vehicle speed has been reached.

6. Method according to any one of the claims 1 -5, further comprising:

- determining a rotation position of the rotor, and - selecting a magnetisation pattern for magnetising the electromagnets (U1 - U6, V1-V6, W1 -W6) based on the rotation position of the rotor.

7. 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 a floating potential to the electromagnets.

8. Method 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 patterns are being switched and controlling a magnitude of the current being applied to the stator winding (U, V, W) such that at most a predetermined vehicle speed is reached.

9. Method according to any one of the claims 1 -8, wherein driver controllable means (118) for requesting power are movable in a movement region between a 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 the vehicle is manoeuvred in a state of low speed manoeuvring is reduced in relation to the applied current when the vehicle is not manoeuvred in the state of low speed manoeuvring for at least a first portion of the movement region, from the first position (P1 ) towards position (P2), of the driver controllable means for requesting power, the current being configured to progressively increase to maximum current with a movement towards the second position (P2).

10. Method according to any one of the claims 1 -9, the vehicle (100) further

comprising a gearbox comprising at least two gears, wherein:

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.

11. Method according to any one of the preceding claims, wherein the vehicle is manoeuvred in a state of low speed manoeuvring when a drive mode for reduced speed manoeuvring of the vehicle is selected.

12. Method according to claim 11 , wherein:

the drive mode for reduced speed manoeuvring of the vehicle is at least one 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 is

executed 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 by a computer, cause the computer to carry out the method according to any one of the claims 1 -12.

15. System for propelling an electric vehicle (100),

the vehicle (100) comprising:

the system being characterised in, when the vehicle is manoeuvred in a state of low speed manoeuvring:

means configured to control at least one of the frequency at which magnetisation patterns are being switched and a magnitude of the current applied when magnetising the electromagnets (U1 -U6, V1 -V6, W1-W6), such that an acceleration of the electrical machine (101 , 102) in response to a first 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.

16. Vehicle (100) comprising a system according to claim 14.