Patent Description:
A heavy-duty vehicle, such as a truck or semi-trailer vehicle, normally comprises a service brake system based on friction brakes. Friction brakes, such as disc brakes or drum brakes, are highly efficient in generating braking torque. However, if the friction brakes are used too intensively, a phenomenon referred to as brake fading may occur, which is why friction brakes are not suitable for prolonged periods of use that may, e.g., occur when driving downhill for an extended period of time. Brake fading is caused by a build-up of heat in the braking surfaces and leads to significantly reduced braking capability. To avoid brake fading, heavy-duty vehicles often comprise auxiliary brakes capable of endurance braking, such as engine brakes and various retarder systems.

An electric machine can also be used to slow down a vehicle. The electric machine may then act as a generator which converts the kinetic energy from the vehicle into electrical energy. This electrical energy can be fed to an energy storage system (ESS) such as a rechargeable battery or the like, resulting in an overall increase in energy efficiency of the vehicle. Surplus energy from regenerative braking can also be fed to a brake resistor where it is converted into heat.

Electric machines (EM) do not suffer from brake fading, but since the combined energy absorption capability of the ESS and any brake resistors is limited, the electric machine may still not be able to perform endurance braking for prolonged periods of time. Thus, either additional means for braking need to be installed in the vehicle, or the requirements on the electrical energy system of the vehicle must be over-dimensioned to support endurance braking, which is undesired.

<CIT> discloses an EM design where the output current from the EM during regenerative braking can be adjusted by displacing the rotor axially relative to the stator. <CIT> instead proposes to change the magnetic properties of the rotor in an EM to adjust its output current during regenerative braking. However, despite the work done so far, there is a continuing need for improvements in order to realize the full potential of electrically powered heavy-duty vehicles. <CIT> discloses an electric machine with a magnetic circuit control device capable of synthetically improving motor efficiency and motor performance by making the magnetic circuit as a variable structure and controlling the magnetic circuit suited with operation condition.

It is an object of the present disclosure to provide improved electric machines and also improvements in the control of electric machines which facilitate robust and efficient endurance braking by heavy-duty vehicles. This object is at least in part obtained by an electric machine for a heavy-duty vehicle. The electric machine comprises a stator and a rotor separated by an air gap, where the stator comprises a stator reconfiguration device arranged to modify a magnetic property of the material in the stator. The stator is arranged to be mechanically reconfigurable by the stator reconfiguration device to allow control of magnetic flux in the air gap.

This configuration allows a control unit arranged external to the electric machine to adjust the power losses of the electric machine (EM) to a desired power loss setting. If there is ample room in an energy storage system (ESS), then the power losses can be reduced down to a minimum in order to, e.g., recuperate as much energy as possible during braking. However, if the energy storage system is about to reach full state of charge, then the power losses can be increased in order to reduce the energy output from the electric machine during braking. The mechanical arrangements disclosed herein can be adjusted regularly by an actuator controlled by a control unit. The stator is preferably axially fixed with respect to the rotor. This allows for a more robust actuator arrangement which can be used to adjust power losses in the electric machine in a more reliable manner compared o the case where the stator is arranged movable in the axial direction with respect to the rotor.

This proposed electric machines allow for regulating the output energy during endurance braking by a heavy-duty vehicle dynamically to match the energy absorption capabilities of the energy storage system of the vehicle. Thus, the endurance capability of the vehicle is extended, which is an advantage. The regulation of efficiency level can be performed in real-time, or in a predictive manner to ensure that both current and future endurance braking capability of the vehicle is satisfactory.

If the ESS is in a state where it can absorb energy then the EM is configured to output current which can be used, e.g., to replenish batteries in the ESS. However, if the ESS is not able to absorb maximum output current from the EM in some vehicle motion scenario, then the energy output from the EM can be reduced by increasing the power loss level at which the EM is operating, which then instead increases the heat generation in the EM. It is an advantage to be able to adjust EM energy output in this manner to facilitate endurance braking, since the energy absorption demands on other vehicle components can be reduced, leading to a less complicated and more cost-effective overall vehicle energy system. Also, since the efficiency level of the EM is modulated in dependence of driving scenario, there is no significant performance penalty on the energy efficiency of the vehicle. According to the invention, the stator reconfiguration device comprises a first section and second sections formed in different materials, where the different materials have different magnetic permeability properties, such that an orientation of the stator reconfiguration device relative to the stator influences the magnetic property of the stator. This way of controlling the magnetic flux in the air gap has been shown to be particularly effective and can be realized in a mechanically robust manner with reasonably low cost, which is an advantage. The first section can for instance be formed in a material with high magnetic permeability such as soft magnetic composite or laminated magnetic steel, and where the second section which is formed in a low magnetic permeability material such as copper or aluminum.

According to aspects, the stator reconfiguration device is a rod extending in a longitudinal direction axially along the stator, where the rod is axially divided into first and second sections, and where the two sections are associated with different magnetic permeabilities. The stator reconfiguration device can then be rotatably mounted about the longitudinal axis to allow control of the magnetic flux in the air gap by rotation of the stator reconfiguration device. This version of the stator reconfiguration device is also relatively easy to implement in a reliable and robust manner and has been found to yield good results in terms of magnetic flux control.

According to aspects, the stator reconfiguration device is a rod extending in a longitudinal direction axially along the stator, where the rod is divided into first and second sections by a plane extending transversal to the longitudinal direction of the rod, where the two sections are associated with different magnetic permeabilities, and where the stator reconfiguration device is slidably mounted in the axial direction relative to the stator to allow control of magnetic flux in the air gap by longitudinal displacement of the rod. This is an alternative to the options discussed above and associated with the same advantages.

According to the invention, the stator reconfiguration device comprises one or more conduits for passing a cooling medium through the stator reconfiguration device. These conduits improve the cooling capacity of the electric machine, and therefore allows for higher currents to pass through the components of the electric machine. The high currents, in turn, means that more power loss can be supported, which is an advantage.

According to aspects, the stator reconfiguration device comprises at least a first section and a second section formed in different materials, where the different materials have respective high and low relative magnetic permeability properties, and where the one or more conduits are arranged in the section associated with the low magnetic permeability property. This way the conduits are arranged where they are needed the most, i.e., in a location where heat generation can be expected.

According to aspects the electric machine comprises a stator geometry control unit arranged to control the orientation of the stator reconfiguration device based on a received control signal.

There are also disclosed herein vehicle control units, vehicles, and methods associated with the above-mentioned advantages.

The skilled person realizes that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention, which is defined by the appended claims.

<FIG> illustrates an example heavy-duty vehicle <NUM> for cargo transport. The vehicle combination <NUM> comprises a truck or towing vehicle configured to tow a trailer unit in a known manner, e.g., by a fifth wheel connection. Herein, a heavy-duty vehicle is taken to be a vehicle designed for the handling and transport of heavier objects or large quantities of cargo. However, a heavy-duty vehicle could also be a vehicle designed for use in construction, mining operations, and the like. It is appreciated that the techniques and devices disclosed herein can be applied together with a wide variety of electrically powered vehicle units, not just that exemplified in <FIG>. In particular, the techniques disclosed herein are also applicable to, e.g., rigid trucks and multi-trailer electric heavy-duty vehicles comprising one or more dolly vehicle units.

The vehicle <NUM> is an electrically powered vehicle comprising one or more electric machines (EM) <NUM>. The one or more EMs are arranged to generate both positive and negative torque, i.e., to provide both propulsion and braking of the vehicle <NUM>. The vehicle <NUM> also comprises an energy storage system (ESS) <NUM> configured to power the one or more EMs. The ESS <NUM> may comprise a battery pack and potentially also a fuel cell (FC) stack arranged to generate electrical energy from a hydrogen storage tank on the vehicle <NUM> (not shown in <FIG>). The ESS optionally also comprises a brake resistance arranged to dissipate surplus energy which the electrical energy storage devices on the vehicle <NUM> cannot accommodate.

A vehicle control unit <NUM> is arranged to monitor and control various vehicle operations and functions. The vehicle control unit is, e.g., arranged to monitor and control the ESS <NUM> as well as the one or more EMs <NUM>, and optionally also the operation of the FC stack. The vehicle control unit <NUM> may also comprise higher layer control functions such as vehicle route planning and may have access to geographical data comprising height profiles of different planned vehicle routes and the like, as well as positioning data indicating a current location of the vehicle <NUM>, which can be determined from, e.g., a global positioning system (GPS) receiver.

The vehicle <NUM> optionally comprises a wireless communications transceiver arranged to establish a radio link <NUM> to a wireless network <NUM> comprising a remote server <NUM>. This way the control unit <NUM> may access the remote server <NUM> for uploading and downloading data such as the geographical data mentioned above comprising height profiles of different planned vehicle routes. Notably, the vehicle <NUM> may store measurement data such as amounts of regenerated energy by the one or more EMs <NUM> at various geographical locations an along different vehicle routes in local memory or at the remote server <NUM>. The vehicle control unit <NUM> may also query the remote server for information about previously experienced amounts of regenerated energy, and/or temperature increases in various vehicle components along a given route, by the same vehicle or by some other vehicle having travelled along (parts of) the same route.

The vehicle control unit <NUM> may furthermore be arranged to obtain data indicative of an expected rolling resistance for a given route, either from manual configuration or remotely from the remote server <NUM>. The rolling resistance of the vehicle <NUM> will affect the energy consumption of the vehicle as it traverses a route. For instance, a gravel road is likely to require more energy compared to a more smooth asphalt freeway. Also, friction and air resistance will reduce the requirements on generating negative torque during downhill driving.

It is required to be able to brake the vehicle <NUM> as it travels down steep long hills and the like, where friction brakes risk onset of brake fading. The EMs <NUM> on the vehicle <NUM> may, as mentioned above, be used to generate braking torque. Electrical energy from the EMs generated during braking can then be fed to the ESS as long as the ESS can absorb the power, resulting in recuperated energy and a more energy efficient vehicle operation, which is an advantage. However, when the batteries of the ESS are fully charged, no more energy can be absorbed. Furthermore, there may be a limit on maximum current or voltage that can be fed to the batteries of the ESS when charging. If the batteries in the ESS cannot accept all of the output energy from the electric machines, surplus energy can be fed to the brake resistor which then dissipates the surplus energy as heat. However, a brake resistor also has a maximum amount of power it can absorb since it will eventually get too hot. Furthermore, there is normally a peak power capability of the brake resistor, i.e., there may be a limit on maximum current or voltage that can be fed to the brake resistor.

If the battery pack on the vehicle <NUM> is fully charged and the brake resistor has reached a maximum allowable temperature, there is no safe way of dispersing power generated from the electric machine during braking. This problem can be alleviated somewhat by over-dimensioning the brake resistor, but this solution is not desired since it drives both cost and component footprint.

The magnetic flux through a surface is the surface integral of the normal component of the magnetic field B over that surface. It is usually denoted Φ or ΦB. The SI unit of magnetic flux is the Weber (Wb; in derived units, volt-seconds), and the CGS unit is the Maxwell.

Magnetic permeability is a measure of magnetization that a material obtains in response to an applied magnetic field. Permeability is typically represented by the Greek letter µ. The reciprocal of magnetic permeability is magnetic reluctivity. In SI units, permeability is measured in Henries per meter (H/m), or equivalently in Newtons per ampere squared (N/A<NUM>). The permeability constant µ<NUM>, also known as the magnetic constant or the permeability of free space, is the proportionality between magnetic induction and magnetizing force when forming a magnetic field in a classical vacuum. A closely related property of materials is magnetic susceptibility, which is a dimensionless proportionality factor that indicates the degree of magnetization of a material in response to an applied magnetic field.

An electrical motor is normally designed for operation at maximum efficiency, i.e., minimum power loss, meaning that maximum output power is generated during regenerative braking in order to recuperate as much energy as possible during downhill driving. However, there are techniques available for increasing the power losses incurred in the EM in a controlled manner during operation, which allows the power loss in the EM to be adjusted to a desired level. An electric machine used to generate braking torque which is operated in a less energy efficient mode of operation will generate more heat and less output current compared to an electric machine that is operated at maximum efficiency.

The generated torque by an EM is a function of the cross product between the current vector of the EM and the magnetic flux in the air gap formed between stator and rotor. It is therefore possible to adjust generated torque by altering the magnetic flux in the air gap. This adjustment of magnetic flux can be achieved by mechanically modifying the geometry of the EM, whereby the power losses in the EM can be manipulated. <CIT> disclosed an EM design where the output current from the EM during regenerative braking can be adjusted by displacing the rotor axially relative to the stator. This axial adjustment has an impact on the magnetic flux in the air gap formed between stator and rotor, and therefore represents a way to adjust the power loss of the EM during operation. However, it is relatively complicated to robustly offset the stator and rotor axially in this manner. <CIT> instead proposed to change the magnetic properties of the rotor in an EM to adjust its output current during regenerative braking. However, since the rotor is not stationary, control of its internal components in this manner is also rather complicated, and most likely also associated with an increased cost.

The present disclosure instead proposes to adjust the geometry of the stator in order to change its magnetic properties during operation, and in this way control the power losses in the EM. There are at least two possibilities for mechanically modifying the magnetic properties of the stator: Increasing the stator and/or rotor losses by increasing the eddy currents in the EM, which can be achieved by changing parts of the stator structure from laminated steel (or soft magnetic composite) to solid steel, and/or changing the magnetic flux in the stator. A reduction in the magnetic flux needs then to compensated with higher current to achieve the same torque and increasing the current results in higher power losses. Thus, by making parts of the stator flexible, the power losses in the EM can be manipulated in close to real-time.

Apart from mechanically modifying the magnetic properties of the stator, it has also been realized that there is a control freedom associated with electric machines which allow most electric machines to be operated at a reduced efficiency. The general principles of such sub-optimal energy efficiency electric machine control are described in, e.g., <CIT> and also in <CIT>.

In addition to presenting techniques for modifying the magnetic properties of the stator during EM operation, the present disclosure also builds on the previous work in the prior art by providing a control mechanism and a communications interface which allows the vehicle control unit <NUM> to balance electrical current output from the EM <NUM> during regenerative braking with a temperature increase in the EM during braking. In essence, the control unit <NUM> is, by the proposed technique, able to balance EM temperature increase with ESS energy absorption capability during extended periods of down-hill driving, thereby providing an improved endurance braking capability for the heavy-duty vehicle <NUM> and thus a reduced need for over dimensioning the components of the vehicle <NUM>. The control signaling between the vehicle control unit and the one or more electric machines on the vehicle is versatile and allows for an efficient and robust control of the electric vehicle propulsion system. According to a preferred implementation, the control unit <NUM> also balances the current output of the EM during driving in a predictive manner. For instance, suppose a route involves an initial flat stretch of road followed by a long downhill section. The control unit may then mechanically and/or electrically configure the EM in an energy inefficient mode of operation to consume more power during the drive on the flat stretch of the route, in order to ensure sufficient endurance braking capability during the long downhill part of the route.

It is appreciated that the configuration of EM efficiency level is equivalent to the configuration of a power loss level of the EM. As will be explained in the following, the techniques disclosed herein are applicable also when no torque is generated by the EM, in which case a definition of efficiency may be cumbersome. Thus, herein, a power loss level is the same thing as an efficiency level, although the term power loss level is preferred when discussing EM operation involving zero torque.

<FIG> illustrates an example vehicle propulsion system <NUM> comprising an EM <NUM>, an ESS <NUM> and a vehicle control unit <NUM>. The EM <NUM> here comprises an EM control unit <NUM> arranged to control the operation of an inverter <NUM> which drives the electric machine. The EM is associated with an EM temperature <NUM>, which may relate to, e.g., a temperature of the stator windings and/or to other components in the EM. It is appreciated that the different components of an electric machine are associated with a specification regarding maximum temperatures. If those temperatures are exceeded, then the respective EM components risk malfunction or will at least suffer an increased wear. The EM control unit <NUM> is arranged to communicate with the vehicle control unit <NUM> over a control interface <NUM>. Various control messages may be exchanged over this interface <NUM>. For instance, the vehicle control unit <NUM> may use the interface <NUM> to configure a degree of efficiency, or a power loss level of the EM subsystem <NUM>. The EM sub-system <NUM> may also use the interface <NUM> to report back capabilities to the vehicle control unit <NUM>. Thus, advantageously, if the vehicle propulsion system comprises more than one EM, or even more than one EM subsystem, such as different EM subsystems on different vehicle units, then the vehicle control unit <NUM> may communicate with the EM subsystems and balance regenerative braking efficiency in dependence of their respective capabilities and energy absorption capabilities of the vehicle ESS <NUM>.

The EM subsystem <NUM> may, as mentioned above, be operated at varying degrees of efficiency, using either mechanical adjustments in the EM or variation in the control of the EM drive circuit. An EM used for propulsion of a vehicle <NUM> is normally operated at maximum efficiency, which means that a maximum output current always results from applying negative torque, in order to recuperate as much energy as possible. However, as explained in <CIT> and <CIT>, the currents in the stator windings of the EM can be controlled such that this efficiency is reduced significantly. Furthermore, it has been realized that this efficiency can be controlled by the control unit <NUM> in real time, or at least close to real time, in dependence of the energy efficiency capability of the EM <NUM> and in dependence of the energy absorption capability of the ESS <NUM>. This way the control unit <NUM> can obtain both an energy efficient operation by the vehicle <NUM> by maximizing energy efficiency as long as the ESS <NUM> is able to absorb the generated output current during regenerative braking, and also an increased capability of endurance braking if needed, by reducing the efficiency of the EM <NUM>, i.e., increasing the EM power loss, thereby reducing output energy from the EM during regenerative braking and instead raising the internal temperature of the EM <NUM>. In fact, a power loss can even be configured at zero torque, in which case the EM start to act like a brake resistance which dissipates energy from the ESS.

In addition to the control of currents in the stator windings of the EM, it is also possible to mechanically modify a magnetic property of the stator by means of an actuator. This actuator control is indicated as a stator geometry control unit <NUM> connected to the EM control unit <NUM> in <FIG>.

Advantageously, an EM where the efficiency level is configurable in this manner also comprises a higher capacity cooling system, such as an oil-based cooling system with a sufficiently sized heat exchanger and fan. The higher the cooling capacity of the EM, the less power efficient it can be for longer periods of time. In fact, with a sufficiently dimensioned cooling system, the EM can be designed to provide endurance braking for an unlimited duration of time, at least for certain vehicle maximum load and the like. The endurance braking capability of the EM can be further increased if the techniques involving stator geometry reconfiguration is combined with the techniques involving control of stator winding currents. By balancing the two methods of EM power loss control, the rate of temperature increases in the EM for a given braking torque can be reduced.

The cooling of the EM can also be adjustable, e.g., by adjusting a fan speed or flow rate of cooling liquid to provide additional cooling when the EM is configured in an energy inefficient mode of operation, i.e., at high power loss. Thus, according to some aspects, the control unit <NUM> is configured to control a variable cooling <NUM> of the EM <NUM> in dependence of the efficiency level at which the EM is configured, such that increased cooling is performed when the EM is operated in an energy inefficient mode of operation, that is, at a high power loss setting. Advantageously, this cooling system can be combined with the mechanism for modify the magnetic properties of the stator, as will be discussed in more detail below. The variable cooling <NUM> of the EM <NUM> can also be configured to operate in a predictive manner. This means that the variable cooling system is operated in anticipation of an increase in temperature, e.g., if it is known that an endurance braking function of the vehicle <NUM> will be used in the near future, since there is a long downhill section of road up ahead of the vehicle along its planned route.

The ESS <NUM> of the vehicle propulsion system <NUM> comprises a battery pack <NUM> connected to an optional brake resistor <NUM> for dissipating surplus energy. An optional FC stack <NUM> is also indicated as comprised in the ESS <NUM>. The ESS <NUM> is associated with a state of charge (SoC) <NUM> indicating, e.g., how much charge that is currently carried by the battery pack. Of course, one or more components of the ESS <NUM> may also be associated with a temperature <NUM>, where it is appreciated that some components may risk permanent damage or at least temporarily reduced function is overheated. The temperature of the brake resistor <NUM> can be expected to vary with surplus energy. If it is used to dissipate large amounts of energy, then it may reach critical temperatures, which is of course undesired. The FC stack <NUM> is normally difficult to turn off and re-start since it takes time to do this without damaging the FC stack. Thus, it is preferred to always generate some power by the FC stack <NUM>, even if the ESS is close to full SoC and the vehicle is driving downhill. One advantage of the techniques disclosed herein is that the efficiency level of the EM subsystem <NUM> can be configured at a constant power loss value corresponding to the minimum output power from the FC stack, thus compensating for the energy contribution by the FC stack.

An electric machine, such as the EM <NUM>, comprises a stator and a rotor which are separated by an air gap, where the rotor is arranged to rotate together with the motor axle. Herein, the motor axle will be generally used as reference axis, and its extension direction will be referred to as the axial direction, denoted as A in the Figures. The EMs considered herein have stators which are axially fixed with respect to the rotor, i.e., the EMs discussed herein are different from the type of EMs discussed in <CIT> where the rotor is axially displaced relative to the stator in order to control the efficiency of the electric machine.

The stators of the herein disclosed EMs comprise one or more stator reconfiguration devices which are arranged to modify a magnetic property of the stator. Thus, the EMs differ from those discussed in <CIT> where it is proposed to change the magnetic properties of the rotor instead of the stator to adjust EM efficiency and/or power loss level.

The stator <NUM> in the current proposal is mechanically reconfigurable by the stator reconfiguration device to allow control of magnetic flux in the air gap. This means that an actuator is used to change the physical orientation of the stator reconfiguration device relative to the stator, and thereby change the power loss level of the EM. This mechanical reconfiguration of the stator can advantageously be combined with control of the stator winding currents in order to obtain an even better control of the power loss in the EM.

The electric machine <NUM> may, as shown in <FIG>, comprise a stator geometry control unit <NUM> arranged to control the physical orientation of the stator reconfiguration device based on a received control signal <NUM>. This control signal <NUM> will then determine the current energy efficiency, i.e., the current power loss level at which the EM <NUM> is operating.

The EM <NUM> preferably also comprises a temperature sensor <NUM> arranged to measure a temperature of the stator reconfiguration device. Thus, the EM control unit <NUM> may report current temperatures up to the vehicle control unit <NUM>, which may adapt its control of the vehicle <NUM> in dependence of the temperatures of the stator reconfiguration devices on the vehicle <NUM>. By allowing a controlled increase in temperature, more current can be allowed to flow, which results in increased power loss.

<FIG> show two example stator reconfiguration devices <NUM>, <NUM> which can be used to mechanically modify a magnetic property of the stator in the EM <NUM>, e.g., its magnetic permeability in a certain place or the tendency for eddy currents to be generated at some location in the stator. The stator reconfiguration devices are arranged to be at least partially embedded into the stator, where they may affect the magnetic flux in the stator. <FIG> shows an example EM <NUM> comprising a plurality of stator reconfiguration devices arranged axially (A) in the stator.

Without loss in generality, each of the stator reconfiguration devices <NUM>, <NUM> comprises two different materials denoted M1 and M2, with different respective magnetic permeabilities, where it is appreciated that more than two materials can be used in the stator reconfiguration devices. This means that a stator reconfiguration device can be moved relative to the stator, and in this way change the magnetic properties of the stator, which in turn will have an impact on the power loss in the EM <NUM>. The stator reconfiguration device <NUM> in <FIG> is arranged to be rotated about its longitudinal axis, as indicated by the arrow R, which will change the material configuration in the stator if the rotation is performed relative to the stator, i.e., with the stator in a fixed position. Depending on the angle of rotation, a given material will be presented to one side. Put differently, the stator reconfiguration device <NUM> is in the form of a rod extending in a longitudinal direction axially A along the stator. The rod is divided axially into first and second sections, where the two sections are associated with different magnetic permeabilities, and where the stator reconfiguration device <NUM> is rotatably mounted about the longitudinal axis to allow control of the magnetic flux in the air gap by rotation of the stator reconfiguration device <NUM>.

The stator reconfiguration device <NUM> in <FIG> is instead divided transversally to its longitudinal axis, such that the first material M1 forms one end of the rod and the other material M2 forms the opposite end of the rod. With this configuration, the axial position of the stator reconfiguration device <NUM> relative to the stator will affect the magnetic properties of the stator, and thus impact the power loss in the EM <NUM>. In other words, the stator reconfiguration device <NUM> can be slided back and forth in the axial direction, in order to change the magnetic properties of the stator. In other words, the stator reconfiguration device <NUM> may also be formed as a rod extending in the longitudinal direction axially A along the stator, where the rod is divided into first and second sections by a plane extending transversal to the longitudinal direction of the rod, and where the two sections are associated with different magnetic permeabilities. The stator reconfiguration device <NUM> can be slidably mounted in the axial direction A relative to the stator <NUM> to allow control of magnetic flux in the air gap by longitudinal displacement of the rod.

Generally, the stator reconfiguration devices <NUM>, <NUM> disclosed herein may comprise first and second sections formed in different materials M1, M2, where the different materials have different magnetic permeability properties, such that an orientation of the stator reconfiguration device <NUM>, <NUM> relative to the stator influences the magnetic property of the stator. The first section can be formed in a material with high magnetic permeability such as soft magnetic composite or laminated magnetic steel, and the second section can be formed in a low magnetic permeability material such as copper or aluminum. Of course, other high permeability materials are known, as well as other low permeability materials. By at least partially embedding a stator reconfiguration device into the stator, it can be used to control the magnetic flux in the air gap between stator and rotor.

It is appreciated that the stator reconfiguration device <NUM> need not be shaped as a cylinder, since it does not rotate but slide relative to the stator. A rectangular cross section shape would also be possible for instance, or any cross section shape which allows the stator reconfiguration device <NUM> to slide axially relative to the stator.

<FIG> and <FIG> illustrate a practical example <NUM> of how the stator reconfiguration device <NUM> can be used to change the magnetic properties of the stator. <FIG> illustrates an EM comprising a stator <NUM> and a rotor <NUM> separated by an air gap <NUM>, where a stator reconfiguration device <NUM> has been embedded into the stator radially outwards from the motor axle. The stator reconfiguration device <NUM> has been arranged rotatably embedded into the stator outer hull, where about half of the rod is inside the hull of the stator <NUM>, and about half of the rod is outside the hull. Now, by rotating the stator reconfiguration device about its longitudinal axis, as indicated by the arrow R in <FIG> and <FIG>, the rod will present a different material to the stator interior. In <FIG> the high magnetic permeability material M1 is presented towards the interior of the stator <NUM>, while in <FIG> the low magnetic permeability material M2 is instead presented towards the interior of the stator <NUM>. The effect on the magnetic flux in the air gap can be seen in the Figures from the insert scales: the magnetic flux in the air gap <NUM> is notably higher when the high magnetic permeability material M1 is presented towards the stator interior by the stator reconfiguration device <NUM> compared to when the material M2 is facing the interior of the stator.

Of course, the same effect can also be obtained if the stator reconfiguration device <NUM> is used instead and slided axially with respect to the stator, such that different magnetic permeability materials are embedded into the stator.

<FIG> shows the stator reconfiguration device from <FIG> without magnetic flux strength, and with flux direction indicated by the arrows.

As shown in <FIG>, the stator reconfiguration device <NUM>, <NUM> may also comprise one or more conduits <NUM> for passing a cooling medium through the stator reconfiguration device. These cooling conduits allow for an efficient cooling of the EM since they are arranged close to the location where heat will be generated when the EM is operating in an inefficient mode of operation associated with high power loss. The cooling conduits are preferably formed in the low magnetic permeability material M2, where the need for cooling is the highest. In other words, the stator reconfiguration device <NUM>, <NUM> comprises first and second sections formed in different materials M1, M2, where the different materials have respective high and low relative magnetic permeability properties, and where the one or more conduits are arranged in the section associated with the low magnetic permeability property.

Although the EM <NUM> comprising the stator reconfiguration devices <NUM>, <NUM> provides advantages in its own right, additional benefits can be obtained if the variable power loss features of the EM is controlled by the vehicle control unit <NUM> in a way which fully exploits its possibilities. Towards this end, with reference also to <FIG>, there is disclosed herein a vehicle control unit <NUM>, <NUM> for controlling an EM <NUM> of a heavy-duty vehicle <NUM>. The EM comprises a stator <NUM> and a rotor <NUM> separated by an air gap <NUM>, where the stator <NUM> comprises a stator reconfiguration device <NUM>, <NUM> as discussed above arranged to modify a magnetic property of the stator, whereby the stator <NUM> is mechanically reconfigurable by the stator reconfiguration device <NUM>, <NUM> to allow control of magnetic flux in the air gap. The heavy-duty vehicle <NUM> also comprises an energy storage system (ESS) <NUM> as shown in <FIG>, connected to the EM <NUM>.

With reference to the flow chart in <FIG>, the control unit <NUM>, <NUM> comprises processing circuitry <NUM> configured to obtain S1 an energy absorption capability of the ESS <NUM>, determine S2 an amount of regenerated energy by the EM <NUM> during braking, and configure S3 an efficiency level of the EM <NUM> in dependence of the energy absorption capability of the ESS <NUM> and the amount of regenerated energy by the EM <NUM> during braking, at least in part by reconfiguring the stator reconfiguration device <NUM>, <NUM>.

According to some aspects, the processing circuitry <NUM> is configured to predict S22 an amount of regenerated energy from the EM <NUM> based on a planned route of the vehicle <NUM>, and to control the stator reconfiguration device <NUM>, <NUM> in dependence of the predicted amount of regenerated energy. <FIG> illustrates an example <NUM> of a height profile along a planned vehicle route (shown as a solid line). The dashed line in <FIG> illustrates an expected SoC along the same route for a nominal value of configured electric machine efficiency, i.e., a given orientation of the stator reconfiguration device. It can be seen that the SoC decreases in uphill sections of the route and increases in downhill sections of the route. At the end of this route the expected SoC exceeds <NUM>%, which is undesired. This can be avoided by using the techniques of the present disclosure, i.e., by proactively increasing the power losses in the electric machine, whereby energy is instead converted into heat inside the EM subsystem instead of being output from the EM subsystem as electrical current. The expected SoC in <FIG> may be determined from the current energy absorption capability of the ESS and the expected energy generation from regenerative braking. The estimated energy generation (in Joules and/or Watts) from regenerative braking in a given driving scenario for different power loss configurations can be tabulated beforehand by experimentation and/or mathematical analysis which may involve computer simulation. However, additional advantages can be obtained if the energy generation in different operating conditions is logged, perhaps in collaboration with other vehicle via the remote server <NUM>. This way the accuracy of the estimated amount of energy that can be expected from regenerative braking in different driving conditions and with different energy efficiency settings of the EM systems on the vehicle <NUM> can be improved. For instance, if a given vehicle driving down a hill having a certain slope and carrying a given amount of cargo generates a certain amount of energy, then this amount and the driving conditions can be written to memory, and optionally communicated to the remote server <NUM>. The next time the vehicle drives down a similar slope carrying a similar load, the estimate of generated energy will be more accurate. The vehicle may also download relevant data from the remote server <NUM> indicative of an expected behavior of the EM along some given route. Interpolation can of course be used to estimate energy generation for a scenario which resembles some already experienced scenarios. This way the estimate of the regenerative amount of energy for different configurations of electric machine energy efficiency is further improved since more data will be available.

The rolling resistance can, as mentioned above, also have an effect on the energy consumption of the EM as the vehicle <NUM> traverses a route. The rolling resistance can often be accurately predicted based on information related to the road properties, such as if the road is a gravel road or a smooth freeway. The rolling resistance is also at least partly a property of the vehicle <NUM>, and its tyres.

Interestingly, the vehicle may upload the "ESS SoC profile" <NUM> corresponding to travelled routes to the remote server <NUM>. The remote server <NUM> can then store this information, an make it available for other vehicles. Thus, a vehicle planning a transport mission can query the remote server <NUM> to see if an ESS SoC profile is available for the planned route. If this is the case, then the vehicle can download the SoC profile from the remote server and use this SoC profile to plan EM efficiency level configuration for the duration of the route. his ensures that the vehicle maintains an endurance braking capability for the entire route.

According to some aspects, the processing circuitry <NUM> is configured to send S32 a control signal comprising a requested power loss level to an EM control unit <NUM> arranged to control the position of the stator reconfiguration device <NUM>, <NUM> in dependence of the requested power loss level.

According to some other aspects, the processing circuitry <NUM> is configured to receive S34 a power loss capability report from the EM control unit <NUM>.

<FIG> shows a flow chart which summarizes some of the methods discussed herein. There is disclosed a method performed in a vehicle control unit <NUM> for controlling an electric machine (EM) <NUM> of a heavy-duty vehicle <NUM> which comprises an energy storage system (ESS) <NUM> connected to the EM <NUM>. The method comprises obtaining S1 an energy absorption capability of the ESS <NUM>. This energy absorption capability of the ESS is likely to vary over time, and can be monitored by the control unit <NUM>, e.g., by determining S11 a state of charge (SoC) <NUM> of a battery pack comprised in the ESS <NUM>, by determining S12 a temperature of the battery pack comprised in the ESS <NUM>, and/or determining S13 a temperature <NUM> of a brake resistor <NUM> comprised in the ESS <NUM>. The relationship between energy absorption capability and these different parameters can be pre-configured at the factory when the vehicle <NUM> is assembled, e.g., as a look-up table or the like in a memory accessible from the control unit <NUM>, and/or regularly provided as part of a software update. Energy absorption capability in terms of power may be limited by an upper power limit which depends on the design of the ESS, i.e., the rating of the components comprised in the ESS. The capability of the ESS in terms of power is normally also dependent on temperature. For instance, brake resistance temperature impacts energy absorption capability negatively, since a very hot braking resistance may not be able to absorb very much energy until it has cooled down again. The energy absorption capability in terms of energy amount is often a linear function of state of charge, where a nearly fully charged battery pack cannot absorb so much energy, and a nearly empty battery pack is able to absorb a significant amount of energy.

A retarder is a device used to augment some of the functions of primary friction-based braking system, usually on heavy-duty vehicles. Retarders serve to slow vehicles down or maintain a steady speed while traveling down a hill and help prevent the vehicle from "running away" by accelerating down the hill. They are not usually capable of bringing vehicles to a standstill, as their effectiveness diminishes as vehicle speed lowers. They are instead used as an additional "assistance" to slow vehicles, with the final braking done by a conventional friction braking system or a brake system based on electric machines. As the friction brake will be used less, particularly at higher speeds, their service life is increased. The braking capability of a retarder system is a function of the state of the retarder, such as its temperature. The method may furthermore comprise determining S14 a state, such as a temperature or other metric indicative of a braking capability, of a retarder system arranged to provide a braking torque to prevent acceleration by the heavy-duty vehicle <NUM>. Various retarder systems are known, such as water retarders and oil retarders.

An increased accuracy in determining the energy absorption capability of the ESS can be obtained if the behavior of the ESS is monitored during vehicle operation, and the dependence between energy absorption capability and vehicle component state is recorded. For instance, the effect of temperature on the behavior of the ESS can be monitored and a record of energy absorption capability can be maintained, which can then be consulted if an energy absorption capability is to be determined in the future. Data related to energy absorption capability of the ESS can also be communicated to the remote server <NUM>, which may then construct a model of ESS energy absorption capability to be shared with other vehicles of the same type or comprising the same type of ESS.

The method also comprises determining S2 an amount of regenerated energy by the EM <NUM> during braking. The amount of energy regenerated by the EM <NUM> during braking can of course be determined simply by measuring S21 the amount of regenerated energy by the EM <NUM>. However, it is also possible to predict S22 the amount of regenerated energy from the EM <NUM> based on a planned route of the vehicle <NUM>.

The methods may also comprise determining S23 a maximum amount of regenerated energy by the EM <NUM> based on a vehicle load and an endurance braking requirement of the vehicle <NUM>. The vehicle <NUM> may, e.g., be required to be able to limit speed when driving downhill for longer distances, i.e., the vehicle may be associated with an endurance braking capability requirement. This requirement together with a minimum energy absorption capability of the vehicle ESS can be translated into a maximum allowable efficiency of the electric machines on the vehicle. The required longitudinal torque can be expressed as <MAT> where mGCW is the vehicle gross combination weight, ax,req is the required retardation, CdAf is the product of air drag coefficient Cd and vehicle front area Af, ρair represents air density, vx is the vehicle speed, g is the gravitational constant, Cr is rolling resistance, and s is a slope percentage between <NUM> and <NUM>. Using this equation, e.g., the required torque for a planned route can be obtained for nominal value of air resistance (or air drag coefficient, front area etc.). The required torque can in turn be used to determine the energy generation during downhill sections. In case the energy absorption capability of the ESS goes below the required level and/or if the capability of the EM in terms of minimum efficiency increases, then the vehicle control unit <NUM> may trigger a warning signal, or even prevent vehicle operation.

The method also comprises configuring S3 a power loss level or an efficiency level of the EM <NUM> in dependence of the energy absorption capability of the ESS <NUM> relative to the amount of regenerated energy by the EM <NUM> during braking. This may, e.g., be achieved by configuring S31 the efficiency level of the EM <NUM> as a D/Q setpoint determined under constraints of a desired motor torque and power loss level, as was discussed in, e.g., <CIT> and <CIT>, and/or by mechanically configuring the stator reconfiguration devices discussed above in connection to <FIG> and <FIG>. In this way, the vehicle control unit <NUM> balances the efficiency level of the electric machines on the vehicle <NUM> such that the amount of regenerated energy during downhill driving does not exceed the energy absorption capabilities of the vehicle ESS. As discussed above, the efficiency level of the EM <NUM> may be expressed in terms of a power loss in absolute or relative terms. An absolute measure of power loss may, e.g., be measured in Watts (W), while a relative power loss level may be measured, e.g., in terms of a percentage with respect to maximum efficiency. It is appreciated that the techniques disclosed herein are applicable also when no torque is generated by the EM, where the EM still can be configured to draw power from the ESS.

The technique of configuring a power loss level or an efficiency level of the EM <NUM> in dependence of the energy absorption capability of the ESS <NUM> may involve a model and a calculation method to optimize the power losses of a permanent magnet synchronous electric machine with respect to some target performance criteria. The adjustment of efficiency level of an electric machine is a generally known technique and will therefore not be discussed in detail herein. We instead refer to examples from the literature for more details and implementation examples, e.g., <CIT> and <CIT>.

The example circuit model and calculation method provide separation of the power losses associated with the winding power loss and core power losses for a machine, for different dc voltages and axle speeds. The algorithm calculates the current set-points in direct and quadrature dimension (id, iq) that provides a certain power loss for a given torque request, dc voltage Udc, maximum current Imax and axle speed ω.

The electric machine model is represented by the circuit model shown in <FIG>. This model is an extension to the model provided by <NPL>. The model comprises a leakage inductance Lλ, a mutual inductance: Lm, and two resistances r and rc, where resistance r is associated with the Cu-losses (electric machine variable losses) and the resistance rc is associated with the core losses in the electric machine. There is also a back-EMF denoted here by e which is associated with the permanent magnetic flux of the electric machine. The voltage v is the applied voltage from the inverter, i.e., the motor drive circuit. Generally, below, subscript d denotes direct dimension and subscript q denotes quadrature dimension. Electric machine axle speed is denoted by ω and ψ generally denotes flux.

The corresponding state space equation for machine state x = (imd, imq, id, iq), with respect to the circuit model in <FIG>, is given by following expression, <MAT> where (imd, imq) denotes direct and quadrature components of the current related to the mutual inductance Lm, (id, iq) denotes direct and quadrature components of the current set-point, e = ωψm, ψm is permanent magnet flux, and where the matrices in the synchronous to angular frequency dq-framework yields: <MAT> <MAT> <MAT>.

The electric torque T is given by the equation below, where ψδ denotes the airgap flux. Considering a machine with salient poles, the combination of setpoint currents id and iq provides a degree of freedom to minimize the power loss in the machine for a certain torque. Here considering a three phase machine with pole number n.

For a permanent magnet synchronous machine with salient poles, there are at least two degrees of freedom in choice of current references. Hence, it is possible to find a current reference vector that minimizes the power loss in each working point of operation unless operating on the boundary. The steady state power losses are defined in the following relation which also is the objective function for the optimization. <MAT> where <MAT>.

Hence, for a certain torque set-point Tsp(ω, Udc) in terms of the motor axle speed ω and the voltage Udc behind the inverter, and a minimum power loss set-point psp, the optimization problem to be solved can be represented as minx f(x) subject to <MAT> <MAT> <MAT> where lb and ub are lower and upper bounds which can be configured according to any constraints in place on the EM state. The non-linear non-equality constraints yield for motor mode of operation <MAT> and the non-linear equality constraints are given by <MAT> where <MAT> and <MAT>.

<FIG> shows an example signaling diagram which illustrates the disclosed methods in terms of signaling over the interface <NUM> between vehicle control unit <NUM> and the EM subsystem control unit <NUM>. In this example, the EM subsystem control unit first reports a power loss capability to the vehicle control unit. Based on the capabilities of the EM sub-system the vehicle control unit <NUM> then uses the interface <NUM> to the EM control unit <NUM> to set a desired power loss. This configuration is then acknowledged by the EM control unit by means of a power loss status message. In this example, the temperature of the electric machine then increases. To protect the components of the EM subsystem from overheating, a new lower power loss capability is reported to the vehicle control unit over the interface. This new capability report may result in an updated power loss setting by the vehicle control unit. Of course, the vehicle control unit <NUM> may respond to the new capability report in other ways. For instance, the vehicle control unit <NUM> may perform a different force allocation over the different vehicle motion support devices in order to reduce the torque requests on the EM subsystem reporting a reduced power loss capability. This way the vehicle control unit <NUM> can also balance energy dissipation over the whole vehicle combination. <FIG> illustrates an example operation of the signaling interface <NUM>, shown in <FIG>, for exchanging data between the vehicle control unit <NUM> and the EM control unit <NUM>, i.e., a signaling interface arranged to carry a request from the vehicle control unit 130to the EM control unit <NUM> indicating a desired efficiency level for operation by the EM.

The interface between the vehicle control unit <NUM> and the EM subsystem <NUM>, comprising the EM control unit <NUM>, deserves some special attention. To allow full flexibility in configuring different efficiency levels of the EM, while at the same time maintaining a robust and safe vehicle operation, the methods may comprise sending S32 a requested power loss from the vehicle control unit <NUM> to the EM control unit <NUM>. This requested power loss may, as noted above, conveniently be defined relative to a nominal efficiency level or relative to some maximum obtainable efficiency level. <FIG> shows an example <NUM> where the desired power loss has been configured at 5kW. It is noted that this power loss is maintained for a wide range of desired motor torques and motor speeds. In fact, it is noted that the EM subsystem is even able to sustain a power loss at zero generated torque. In other words, the EM subsystem may also assume a role similar to a braking resistance which can be used to dissipate energy even if no torque is generated by the electric machine.

The methods disclosed herein optionally also comprise sending S33 a power loss status report from the EM control unit <NUM> to the vehicle control unit <NUM>. This power loss status report may comprise information such as, e.g., a current setting of power loss, allowing the vehicle control unit to verify that a requested power loss is actually in effect. As mentioned above, the EM control unit may also be configured to send S34 a power loss capability report to the vehicle control unit <NUM>, thus informing the vehicle control unit <NUM> about what ranges of power losses that can be supported currently. This capability report may also comprise a prediction regarding a time period during which a current power loss can be sustained. This prediction can, e.g., be based on a rate of increase in temperature of the electric machine, and possibly also on past experiences during similar operating conditions, of which data has been stored in memory. In other words, the power loss capability report is optionally determined S35 based on a temperature level of the EM <NUM>.

With reference to <FIG>, most FC stacks <NUM> should, for durability reasons, not be stopped and re-started frequently. Hence it is desired that the FC stack <NUM> provides a minimum power output even if the power is not needed for propulsion. To allow for this constant generation of energy even when the ESS is fully charged, the method may comprise configuring S36 the efficiency level of the EM <NUM> in dependence of a minimum power output of an FC stack <NUM> in the vehicle <NUM>.

The efficiency level of an electric machine is often a function of axle speed. Therefore, the method may also comprise configuring S37 a gear ratio associated with a transmission of the heavy-duty vehicle <NUM> in order to adjust the efficiency level of the EM.

<FIG> schematically illustrates, in terms of a number of functional units, the components of a control unit such as the ECU <NUM>. The control unit may implement one or more of the above discussed functions of the TSM, VMM and/or the MSD control function, according to embodiments of the discussions herein. The control unit is configured to execute at least some of the functions discussed above for control of a heavy-duty vehicle <NUM>. Processing circuitry <NUM> is provided using any combination of one or more of a suitable central processing unit CPU, multiprocessor, microcontroller, digital signal processor DSP, etc., capable of executing software instructions stored in a computer program product, e.g., in the form of a storage medium <NUM>. The processing circuitry <NUM> may further be provided as at least one application specific integrated circuit ASIC, or field programmable gate array FPGA.

In other words, <FIG> schematically illustrates a vehicle control unit <NUM> for controlling an electric machine <NUM> of a heavy-duty vehicle <NUM>, where the heavy-duty vehicle comprises an energy storage system <NUM> connected to the EM <NUM>. The control unit <NUM> comprises processing circuitry <NUM> configured to obtain S1 an energy absorption capability of the ESS <NUM>, determine S2 an amount of regenerated energy by the EM <NUM> during braking, and configure S3 an efficiency level of the EM <NUM> in dependence of the energy absorption capability of the ESS <NUM> and the amount of regenerated energy by the EM <NUM> during braking.

Claim 1:
An electric machine (<NUM>) for a heavy-duty vehicle (<NUM>),
the electric machine comprising a stator (<NUM>) and a rotor (<NUM>) separated by an air gap (<NUM>),
where the stator (<NUM>) comprises a stator reconfiguration device (<NUM>, <NUM>) arranged to modify a magnetic property of the stator, where the stator reconfiguration device (<NUM>, <NUM>) comprises first and second sections formed in different materials (M1, M2), where the different materials have different magnetic permeability properties, such that an orientation of the stator reconfiguration device (<NUM>, <NUM>) relative to the stator (<NUM>) influences the magnetic property of the stator,
wherein the stator (<NUM>) is arranged to be mechanically reconfigurable by the stator reconfiguration device (<NUM>, <NUM>) to allow control of magnetic flux in the air gap,
characterized in that
the stator reconfiguration device (<NUM>, <NUM>) comprises one or more conduits (<NUM>) for passing a cooling medium through the stator reconfiguration device.