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 not capable of prolonged periods of use which may occur when driving downhill for an extended period of time. If the friction brakes are used too intensively, a phenomenon referred to as brake fading may occur. 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.

Electric machines can also be used to brake a vehicle, i.e., to generate braking torque. The electric machine then acts as a generator which converts the kinetic energy from the vehicle into electrical energy. This electrical energy can be fed to an electrical energy storage system (ESS) such as a rechargeable battery, or to a brake resistor which dissipates the electrical energy as heat.

Electric machines do not suffer from brake fading, but since the total energy absorption capability of the ESS and brake resistor 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> describes an example of such a vehicle type.

There is a continuing need for further improvements in braking arrangements for heavy-duty vehicles. It is also desired to simplify control of the ESS system on the vehicle.

It is an object of the present disclosure to provide improvements in braking arrangements for heavy-duty vehicles. This object is at least in part obtained by a method for adapting air resistance of a heavy-duty vehicle. The vehicle comprises at least one electric machine arranged for regenerative braking, one or more energy absorption devices arranged to receive energy from the at least one electrical machine during regenerative braking, and a variable air resistance arrangement arranged to provide a range of different air resistances of the vehicle. The method comprises: obtaining a current energy absorption capability of the one or more energy absorption devices; obtaining an expected energy generation from regenerative braking during a planned route of the vehicle and during a nominal value of air resistance of the vehicle; determining a desired air resistance of the vehicle from the range of different air resistances of the vehicle based on the current energy absorption capability and the expected energy generation; and causing adaption of the variable air resistance arrangement according to the desired air resistance.

It is desirable to be able to control the energy generation from regenerative braking, especially during extended periods of downhill sections of a planned route. The variable air resistance arrangement can be adapted to increase or decrease an actual energy generation from regenerative braking during the planned route (relatively to the expected energy generation). If the actual air resistance is changed from a nominal value, more or less negative torque is required from the at least one electric machine to provide the same braking torque to slow down the vehicle. Thus, the present disclosure improves braking and regenerative energy management by arranging a range of different air resistances of the vehicle in dependent of different scenarios. For example, if a surplus of energy is expected, e.g., more than what is required to fully charge a battery, the air resistance may be increased, while air resistance can be reduced down to a minimum in case of an energy shortage in the battery. Furthermore, the range of different air resistances of the vehicle reduces the need for over dimensioning the energy absorption devices and/or the need for additional braking means required for endurance braking.

According to aspects the desired air resistance is larger than or equal to the nominal value if the expected energy generation is larger than or equal to the current energy absorption capability. According to other aspects, the desired air resistance is lower than or equal to the nominal value if the expected energy generation is lower than or equal to the current energy absorption capability.

According to aspects, the variable air resistance arrangement comprises any of: a variable suspension of the vehicle, a variable spoiler arranged on the vehicle, and a variable deflector arranged on the vehicle. The variable spoiler and the variable suspension may already be present on existing heavy-duty vehicles. In that case, minimum alterations are required on existing vehicles to implement the disclosed method. The variable deflector may provide additional variable air resistance if desired.

According to aspects, one of the one or more energy absorption devices is an electronic storage system (ESS). In that case, the method may further comprise obtaining a current state of charge (SoC) of the ESS. Then, the desired air resistance of the vehicle may be determined based on the current energy absorption capability, the expected energy generation, and the current SoC.

According to aspects, the desired air resistance is larger than or equal to the nominal value if the SoC is larger than or equal to a predetermined threshold. If, e.g., the battery is empty it may be desirable to decrease the desired air resistance to increase the actual energy generation. According to further aspects, the desired air resistance is lower than or equal to the nominal value if the SoC is lower than or equal to a predetermined threshold. There is also disclosed herein a computer program comprising program code means for performing any of the steps discussed above when said program is run on a computer or on processing circuitry of an electronic control unit (ECU).

There is also disclosed herein a computer readable medium carrying a computer program comprising program code means for performing any of the steps discussed above when said program product is run on a computer or on processing circuitry of an ECU.

There is also disclosed herein an ECU for adapting air resistance of a heavy-duty vehicle. The vehicle comprises at least one electric machine arranged for regenerative braking, one or more energy absorption devices arranged to receive energy from the at least one electrical machine during regenerative braking, and a variable air resistance arrangement arranged to generate a range of different air resistances of the vehicle. The ECU is arranged to: obtain a current energy absorption capability of the one or more energy absorption devices; obtain an expected energy generation from regenerative braking during a planned route of the vehicle and during a nominal value of air resistance of the vehicle; determine a desired air resistance of the vehicle based on the current energy absorption capability and the expected energy generation; and causing adaption of the variable air resistance arrangement according to the desired air resistance.

There is also disclosed herein a vehicle comprising the ECU according to the discussion above.

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 claims of the present invention.

<FIG> illustrates an example heavy-duty vehicle combination <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. Each of the vehicle units may comprise means for generating negative torque, i.e., a braking torque to decelerate the vehicle combination <NUM>. The vehicle combination <NUM> comprises wheels <NUM>, <NUM>, and <NUM>. The combination further comprises an ESS <NUM> such as a rechargeable battery and an electronic control unit <NUM> for, i. , controlling motion of the vehicle combination. The vehicle <NUM> may furthermore comprise a fuel cell stack configured to generate electrical power from a hydrogen storage tank.

Herein, a heavy-duty vehicle <NUM> is taken to be a vehicle designed for the handling and transport of heavier objects or large quantities of cargo. As an example, a heavy-duty vehicle could be a semi-trailer vehicle, or a truck as described above. As another example, a heavy-duty vehicle could 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 those exemplified in <FIG>. Thus, the techniques disclosed herein are also applicable to, e.g., rigid trucks and also multi-trailer electric heavy-duty vehicles comprising one or more dolly vehicle units.

The truck, and potentially also the trailer unit, comprise one or more electric machines <NUM>, <NUM>, <NUM> for propulsion and regenerative braking, such as axial flux electric machines. The electric machine then acts as a generator which converts the kinetic energy from the vehicle into electrical energy. This electrical energy can be fed to one or more energy absorption devices, which can be an electrical energy storage system (ESS) such as a rechargeable battery or super capacitor. An electrical energy absorption device can also be a device that dissipates electrical energy, such as a brake resistor which converts the electrical energy to heat without providing any useful effect such as braking or energy storage. An electrical energy absorption device may also be a combination of devices that store electrical energy and devices that dissipate electrical energy.

A heavy-duty vehicle such as the vehicle <NUM> normally comprises friction brakes to complement the regenerative braking by the electric machine. However, 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. Thus, an endurance braking system, such as an engine brake or hydraulic brake system for prolonged periods of braking may be required in addition to the regenerative brakes and the friction brakes.

Electric machines do not suffer from brake fading, but since the total energy absorption capability of the ESS and brake resistor 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.

Referring back to <FIG>, the electric machines <NUM>, <NUM>, <NUM> are connected to an ESS. Electrical energy from the electric machine generated during braking is fed to the ESS as long as the ESS can absorb the power. When the ESS is fully charged, no more energy can be absorbed by it. Furthermore, there may be a limit on maximum current or voltage that can be fed to the ESS when charging. If the ESS cannot accept all energy from the electric machine, surplus energy can be fed to a brake resistor which dissipates the surplus energy as heat. A braking system may therefore comprise a switch, which is arranged to distribute the generated electrical energy from the electric machine to the ESS and/or brake resistor. However, the brake resistor 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.

A fuel cell stack is normally associated with some minimum level of energy output and cannot easily be turned off. This minimum level of power output will also contribute to energy surplus during extended periods of downhill driving.

If the battery is fully charged and if the brake resistor has reached a maximum allowable temperature, there is no safe way of dispersing the power generated from the electric machine during braking. In that case, regenerative braking must stop. This problem can be alleviated somewhat by over-dimensioning the brake resistor, but that may not be sufficient in a really long slope, e.g. For this reason, additional braking means, such as friction brakes, are required. They may also be required since, as mentioned, electrical machines normally have limited peak braking torque capability. Friction brakes, however, risk onset of brake fading when the vehicle travels down steep long hills and the like. Alternatively, or in combination of, additional braking means can comprise an eddy current brake. However, it may be desirable to add even further additional braking means or reduce the requirements of the additional braking means.

Consequently, there is a need for further improvements in braking arrangements for heavy-duty vehicles which can provide sufficient braking torque, also for extended periods of time. It is also desired to simplify control of the regenerative energy system on the vehicle. It is desirable to be able to control the energy generation from regenerative braking, especially during extended periods of downhill sections of a planned route. Energy generation can include energy rate (i.e., power) and total energy during the planned route.

The present disclosure improves braking and energy management by allowing the vehicle to be configured with a range of different air resistances, where the air resistance is configurable in dependence of different operating scenarios. The present disclosure aims to predict how much energy that can be expected from regenerative braking over a coming time period of, say, e.g., a few minutes to a few hours. A vehicle motion management (VMM) function keeps track of the current energy absorption capability of one or more energy absorption devices of the vehicle, including ESS, braking resistances, eddy current brakes etc. A traffic situation management (TSM) function and higher layers in a vehicle control stack keeps track of future sections of road which need to be travelled along the planned route. The VMM then adapts the air resistance according to scenario, such as an extended downhill section. If a surplus of energy is expected, then the VMM will increase air resistance, while air resistance will be reduced down to a minimum in case of an energy shortage.

More specifically, there is disclosed herein a method for adapting air resistance of a heavy-duty vehicle <NUM>, as illustrated in <FIG>. The vehicle comprises at least one electric machine <NUM>, <NUM>, <NUM> arranged for regenerative braking, one or more energy absorption devices <NUM> arranged to receive energy from the at least one electrical machine during regenerative braking, and a variable air resistance arrangement <NUM>, <NUM>, <NUM> arranged to provide a range of different air resistances of the vehicle. The method comprises: obtaining S1 a current energy absorption capability of the one or more energy absorption devices <NUM>; obtaining S3 an expected energy generation from regenerative braking during a planned route of the vehicle and during a nominal value of air resistance of the vehicle <NUM>; determining S4 a desired air resistance of the vehicle <NUM> from the range of different air resistances of the vehicle based on the current energy absorption capability and the expected energy generation; and adapting S5 the variable air resistance arrangement <NUM>, <NUM>, <NUM> according to the desired air resistance.

Air resistance, also called drag, is a force which tends to slow the movement of a vehicle through air. The force acts in a direction opposite to the movement direction of the vehicle and increases as the vehicle moves faster. The air resistance of a vehicle can be approximated by
<MAT>
where Cdrag is a drag coefficient, <IMG> is the density of the air, A is a cross sectional area of the vehicle, and v is the speed of the vehicle. In general, the variable air resistance arrangement is some sort of arrangement for changing the air resistance, e.g., by adapting the area of the vehicle or by adapting the drag coefficient. In particular, the variable air resistance arrangement may comprise any of: a variable suspension <NUM> of the vehicle, a variable spoiler <NUM> arranged on the vehicle <NUM>, and a variable deflector <NUM> arranged on the vehicle. Other arrangements are also possible. A spoiler on a vehicle is typically some sort of deflector, e.g., a narrow plate arranged along the roof, arranged to reduce a tendency of the vehicle to lift off the road at high speeds. The orientation of the spoiler can be changed for changing air resistance, e.g., by changing the angle the spoiler in respect to the forward direction of the vehicle. More generally, the variable air resistance arrangement can be any type of adaptable air deflector, such as a flap arranged on the side of the vehicle. The variable suspension of the vehicle may be used to change the clearance underneath the vehicle, which in turn affects the air resistance of the vehicle.

Adapting the variable air resistance arrangement <NUM>, <NUM>, <NUM> according to the desired air resistance means to change a setting of the arrangement, such as an angle of a spoiler or deflector, or a clearance height. If the variable air resistance arrangement comprises a plurality of adaptable elements, multiple settings may result in the same air resistance. In that case, the method may comprise selecting the combination of settings that improves a secondary objective, such as minimizing turbulence.

According to aspects, the energy absorption capability of the energy absorption device <NUM> includes a maximum amount of energy that the energy absorption device <NUM>, <NUM> can absorb to reach a desired energy level, e.g., the maximum capacity of a battery. The energy absorption capability can also include a maximum rate of energy absorption by the energy absorption device <NUM>, <NUM>, i.e., a maximum power. As mentioned, the VMM function may keep track of the current energy absorption capability. The current energy absorption capability may also be obtained from other systems or functions.

For a battery <NUM>, an energy absorption capability may be determined by the difference between the current state of charge of the battery <NUM> and the maximum charge of the battery <NUM>. For example, it the battery is fully charged, the energy absorption capability may be zero. For a brake resistor, an energy absorption capability may be determined by the power rating of the brake resistor, i.e., the amount of power that can be dissipated via the brake resistor without causing it to overheat or become damaged. It is appreciated that the energy absorption capability of a device can vary over time, both short-term and long-term. For instance, an already overheated brake resistor will have a smaller energy absorption capability compared to a cool un-used brake resistor, causing variation over time-spans such as tens of minutes or even tens of seconds. A new battery often has better energy absorption capabilities compared to an older more worn battery. The energy absorption capability may also range over a time span of months or even years.

The TSM function and higher layers may keep track of the planned route, i.e., one or more sections of road that the vehicle will traverse, such as a downhill section. Using that, the expected energy generation from regenerative braking during the planned route of the vehicle can be determined. The expected energy generation may also be obtained from other systems or functions.

The expected energy generation is determined for a nominal value of air resistance of the vehicle <NUM>. Preferably, the nominal value is a predetermined value of air resistance in the range of different air resistances of the vehicle that the variable air resistance arrangement <NUM>, <NUM>, <NUM> is arranged to generate. In that case, the nominal value may, e.g., be the lowest value of air resistance in the range, or a value in the middle of the range. If the nominal value is in the middle of the range, the variable air resistance arrangement <NUM>, <NUM>, <NUM> can be adapted to increase or decrease the actual energy generation from regenerative braking during the planned route. If the actual air resistance is changed, more or less negative torque is required from the at least one electric machine <NUM>, <NUM>, <NUM> to provide the same braking torque to slow down the vehicle. These relationships may be determined and tabulated from practical experiments involving different vehicle types. The relationships may also be at least partly determined from analytical analysis and/or computer simulation.

The desired air resistance of the vehicle <NUM> is the actual air resistance that increase or decrease the actual energy generation from regenerative braking compared to the expected energy generation for the nominal value of air resistance. If the actual air resistance should increase or decrease depends on the scenario. Thus, the desired air resistance is determined based on the current energy absorption capability and the expected energy generation. The desired air resistance can be determined by the VMM function, or by other means.

The estimated energy generation (in Joules and/or Watts) from regenerative braking in a given driving scenario for different air resistance 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. This way the estimate of how much energy that can be expected from regenerative braking can be improved in accuracy. For instance, if a given vehicle drives 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. The next time the vehicle drives down a similar slope carrying a similar load, the estimate of generated energy will be more accurate. Interpolation can of course be used to estimate energy generation for a scenario which resembles some already experienced scenarios. The gathered data about regenerated energy in different driving conditions and with different air resistance configurations can also be shared with other vehicles, e.g., via a remote server. This way the estimate of the regenerative amount of energy is further improved since more data will be available.

The desired air resistance may be larger than or equal to the nominal value if the expected energy generation is larger than or equal to the current energy absorption capability. For example, if a surplus of energy is expected, the desired air resistance will be increased compared to the nominal value. If, e.g., the battery <NUM> is half full and the expected energy generation exceeds the energy required to fully charge the battery, the desired air resistance will be increased to reduce the actual energy generation. In another example, the desired air resistance is increased to reduce the actual energy generation because a brake resistor is anticipated to heat up too quickly otherwise. It is understood that the vehicle may also be complemented with additional braking means if the increased air resistance is not enough to reduce the actual energy generation sufficiently. Furthermore, the desired air resistance may be lower than or equal to the nominal value if the expected energy generation is lower than or equal to the current energy absorption capability.

If one of the one or more energy absorption devices <NUM> is an electronic storage system (ESS), the method may further comprise obtaining S2 a current state of charge (SoC) of the ESS <NUM>. In that case, the desired air resistance of the vehicle <NUM> is determined S51 based on the current energy absorption capability, the expected energy generation, and the current SoC.

The desired air resistance may be larger than or equal to the nominal value if the SoC is larger than or equal to a predetermined threshold. If, e.g., the battery <NUM> is empty or only charged up to a level well below full charge, it may be desirable to decrease the desired air resistance to increase the actual energy generation. Furthermore, the desired air resistance may be lower than or equal to the nominal value if the SoC is lower than or equal to a predetermined threshold.

There is also disclosed herein an electronic control unit (ECU) <NUM> for adapting air resistance of a heavy-duty vehicle <NUM>. The vehicle comprises at least one electric machine <NUM>, <NUM>, <NUM> arranged for regenerative braking, one or more energy absorption devices <NUM> arranged to receive energy from the at least one electrical machine during regenerative braking, and a variable air resistance arrangement <NUM>, <NUM>, <NUM> arranged to generate a range of different air resistances of the vehicle. The ECU is arranged to: obtain a current energy absorption capability of the one or more energy absorption devices <NUM>; obtain an expected energy generation from regenerative braking during a planned route of the vehicle <NUM> and during a nominal value of air resistance of the vehicle <NUM>; determine a desired air resistance of the vehicle <NUM> based on the current energy absorption capability and the expected energy generation; and adapt the variable air resistance arrangement <NUM>, <NUM>, <NUM> according to the desired air resistance.

Any of the TSM function and the VMM function may be performed by the ECU <NUM> or by one or more separate units.

There is also disclosed herein a vehicle <NUM> comprising the ECU <NUM> according to the discussion above.

<FIG> schematically illustrates functionality <NUM> for controlling one or more wheels <NUM>, <NUM>, <NUM> by some example motion support devices (MSDs), here comprising at least the electric machine <NUM>, <NUM>, <NUM> and the variable air resistance arrangement <NUM>, <NUM>, <NUM>. The control is based on, e.g., measurement data obtained from vehicle sensors <NUM> such as wheel speed sensors, global positioning system (GPS) sensors, radar sensors, lidar sensors, and also vision-based sensors such as camera sensors and infra-red detectors.

The control may also be based on topological data indicating a height profile of a planned route. This topological data together with an estimated gross cargo weight can be used to determine a need for braking the heavy duty vehicle <NUM> along the route.

A TSM function <NUM> plans driving operation with a time horizon of, e.g., <NUM> seconds or so. This time frame corresponds to, e.g., the time it takes for the vehicle <NUM> to negotiate a curve. The time horizons can be much longer, however, such as in the order of hours. The vehicle maneuvers, planned and executed by the TSM, can be associated with acceleration profiles areq and curvature profiles creq which describe a desired vehicle velocity and turning for a given maneuver. An example acceleration profile areq comprises the target deceleration value required to transverse a downhill section of the road. The TSM function <NUM> continuously requests the desired acceleration profiles areq and curvature profiles creq from a VMM function <NUM> which performs force allocation to meet the requests from the TSM in a safe and robust manner. The VMM function continuously feeds back capability information to the TSM function detailing the current capability of the vehicle in terms of, e.g., forces, maximum velocities, and accelerations which can be generated.

The VMM function <NUM> operates with a time horizon of about <NUM> second or so, and continuously transforms the acceleration profiles areq and curvature profiles creq into control commands for controlling vehicle motion functions, actuated by the different MSDs of the vehicle <NUM> which in turn report back capabilities to the VMM function <NUM>. The different capabilities are used by the VMM function as constraints in the vehicle control.

The VMM function <NUM> performs vehicle state or motion estimation <NUM>, i.e., the VMM function <NUM> continuously determines a vehicle state s comprising positions, speeds, accelerations, and articulation angles of the different units in the vehicle combination by monitoring operations using various sensors <NUM> arranged on the vehicle <NUM>, often but not always in connection to the MSDs.

The result of the motion estimation <NUM>, i.e., the estimated vehicle state s, is input to a force generation module <NUM> which determines the required global forces and moments Fx Fy Mz, V=[V<NUM>, V<NUM>, V<NUM>], and for the different vehicle units to cause the vehicle <NUM> to move according to the requested acceleration and curvature profiles areq, creq. The required global force vector V is input to an MSD coordination function <NUM> which allocates wheel forces and also coordinates other MSDs such as steering and suspension. The coordinated MSDs then together provide the desired lateral Fy and longitudinal Fx forces on the vehicle units, as well as the required moments Mz, to obtain the desired motion by the vehicle combination <NUM>.

By determining vehicle unit motion using, e.g., global positioning systems, vision-based sensors, wheel speed sensors, radar sensors and/or lidar sensors, and translating this vehicle unit motion into a local coordinate system of a given wheel (in terms of, e.g., longitudinal and lateral velocity components), it becomes possible to accurately estimate wheel slip in real time by comparing the vehicle unit motion in the wheel reference coordinate system to data obtained from the wheel speed sensor arranged in connection to the wheel.

A tire model can be used to translate between a desired longitudinal tire force Fxi for a given wheel i and an equivalent wheel slip λi for the wheel. Wheel slip λ relates to a difference between wheel rotational velocity and speed over ground and will be discussed in more detail below. Wheel speed ω is a rotational speed of the wheel, given in units of, e.g., rotations per minute (rpm) or angular velocity in terms radians/second (rad/sec) or degrees/second (deg/sec). A tire model is a model of wheel behavior which describes wheel force generated in longitudinal direction (in the rolling direction) and/or lateral direction (orthogonal to the longitudinal direction) as function of wheel slip. See, e.g., chapter <NUM> where the relationship between wheel slip and longitudinal force is discussed.

To summarize, the VMM function <NUM> manages both force generation and MSD coordination, i.e., it determines what forces that are required at the vehicle units in order to fulfil the requests from the TSM function <NUM>, for instance to accelerate the vehicle according to a requested acceleration profile requested by TSM and/or to generate a certain curvature motion by the vehicle also requested by TSM. The forces may comprise e.g., yaw moments Mz, longitudinal forces Fx and lateral forces Fy, as well as different types of torques to be applied at different wheels.

According to aspects, the TSM <NUM> function optionally complemented by higher control layers keep track of future downhill sections of road which need to be traversed. Thus, the vehicle may determine, e.g., how many height-meters which must be descended and ascended along a given route. This data together with data indicating, e.g., gross cargo weight can be used to determine an estimated amount of energy which will be regenerated during downhill sections of the route to be travelled by the vehicle <NUM>. The vehicle control system may, as mentioned above, be pre-configured with data indicating how much energy that can be expected to be generated for a given driving scenario, i.e., per unit of time for a given degree of slope and for different vehicle loads. This data may also be dynamically obtained or refined over time, by measuring an actual amount of regenerated energy for different downhill driving conditions. The data can then be used to predict an amount of regenerated energy from a future downhill driving scenario. This predicted amount of regenerated energy can then be compared to the estimated energy absorption capability of the vehicle, and the air resistance property of the vehicle can be adapted accordingly.

For example, suppose air resistance can be configured in ten different settings ranging from <NUM>-<NUM>, where <NUM> is the least amount of air resistance and <NUM> is the most amount of air resistance. Suppose further that the vehicle energy absorption capability is X Joules, and that the vehicle is about to travel down a hill with a given slope for a given distance. The vehicle can then consult its database where estimates of regenerated energy for each of the ten different air resistances are tabulated for similar driving conditions, and thus pick a suitable air resistance configuration for the planned route.

As another example, consider a planned route having a given height profile. The vehicle can then predict a SoC for the planned route based on the height profile. If this SoC exceeds a capacity of the ESS, then the vehicle air resistance can be increased for key portions of the route to avoid occurrences of a SoC above capacity.

An example of a height profile along a route is shown in <FIG> as a solid line. The dashed line shows expected SoC along the same route for a nominal value of air resistance. 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 method of the present disclosure. The planned route of the disclosed method can be the whole route in <FIG>, sections of the route in <FIG>, or a combination of both. If the planned route is the whole route in the figure, a single desired air resistance may be determined to keep the SoC below fully charged. If the planned route comprises one or more sections of the route in the figure, different desired air resistances may be determined for the different sections. Optionally, the determined air resistance for each section may be determined based on the current section and future sections.

The expected SoC in <FIG> may be determined from the current energy absorption capability of the one or more energy absorption devices <NUM> and the expected energy generation from regenerative braking. The expected energy generation can be obtained from a known torque behavior of the at least one electric machine <NUM>, <NUM>, <NUM>. An example of torque versus motor speed (in revolutions per minute, rpm) is shown in <FIG>. The relationship between required torque and different scenarios is discussed in more detail below. The VMM function <NUM> keeps track of the current energy absorption capability of the vehicle, including braking resistances, eddy current brakes, battery SoC, etc. The VMM can then determine how to best adapt the variable air resistance to increase or decrease the actual energy generation from regenerative braking during the planned route.

The interface between VMM and MSDs capable of delivering torque to the vehicle's wheels has, traditionally, been focused on torque-based requests to each MSD from the VMM without any consideration towards wheel slip. However, this approach has significant performance limitations. In case a safety critical or excessive slip situation arises, then a relevant safety function (traction control, anti-lock brakes, etc.) operated on a separate control unit normally steps in and requests a torque override in order to bring the slip back into control. The problem with this approach is that since the primary control of the actuator and the slip control of the actuator are allocated to different electronic control units (ECUs), the latencies involved in the communication between them significantly limits the slip control performance. Moreover, the related actuator and slip assumptions made in the two ECUs that are used to achieve the actual slip control can be inconsistent and this in turn can lead to sub-optimal performance.

Significant benefits can be achieved by instead using a wheel speed or wheel slip-based request on the interface between VMM and the MSD controller, thereby shifting the difficult actuator speed control loop to the MSD controllers, which generally operate with a much shorter sample time compared to that of the VMM function. Such an architecture can provide much better disturbance rejection compared to a torque-based control interface and thus improves the predictability of the forces generated at the tire road contact patch.

With reference to <FIG>, the inverse tire model block <NUM> translates the required wheel forces Fxi, Fyi determined for each wheel, or for a subset of wheels, by the MSD coordination block <NUM> into equivalent wheel speeds ωwi or wheel slips λi. These wheel speeds or slips are then sent to the respective MSD controllers. The MSD controllers report back capabilities which can be used as constraints in, e.g., the MSD coordination block <NUM>.

Longitudinal wheel slip λ may, in accordance with SAE J670 (SAE Vehicle Dynamics Standards Committee January <NUM>, <NUM>) be defined as <MAT> where R is an effective wheel radius in meters, ωx is the angular velocity of the wheel, and vx is the longitudinal speed of the wheel (in the coordinate system of the wheel). Thus, λ is bounded between -<NUM> and <NUM> and quantifies how much the wheel is slipping with respect to the road surface. Wheel slip is, in essence, a speed difference measured between the wheel and the vehicle. Thus, the herein disclosed techniques can be adapted for use with any type of wheel slip definition. It is also appreciated that a wheel slip value is equivalent to a wheel speed value given a velocity of the wheel over the surface, in the coordinate system of the wheel. The VMM <NUM> and optionally also the MSD control units, maintains information on vx (in the reference frame of the wheel), while a wheel speed sensor or the like can be used.

Vehicle downhill gradeability relates to the ability of a heavy-duty vehicle to drive down long hills at constant cruising speed. The air resistance and the rolling resistance from the road decelerates the vehicle, while the gravitational pull on the vehicle provides accelerating force. To guarantee vehicle downhill gradeability, the electric machine, the variable air resistance arrangement <NUM>, <NUM>, <NUM>, and other possible additional braking means can be dimensioned to support a constant cruising speed, e.g., somewhere between <NUM>-<NUM>/h, during extended downhill driving. To design for downhill gradeability means that the electric machine is dimensioned to provide a continuous negative torque level at a given level and at a given air resistance range, and also arranged to distribute the regenerated energy to one or more energy absorption devices. The energy absorption devices are dimensioned to absorb these energy levels. Thus, vehicle downhill gradeability may be guaranteed, at least for a range of driving conditions.

<FIG> illustrates four use cases <NUM> which a heavy-duty vehicle <NUM> must be able to operate in. The vehicle <NUM> must be able to start in slopes <NUM> (startability), even if the vehicle <NUM> is heavily loaded and the road friction is not ideal. The vehicle must also be able to negotiate even steeper slopes at constant velocity <NUM>, e.g., <NUM>/h (positive gradeability). Downhill gradeability performance <NUM> is perhaps even more important, which means that the vehicle <NUM> must be able to limit speed when driving downhill for longer distances (endurance braking). Finally, acceleration and braking capability implies that peak torque requirements, both on positive and on negative torque, must be met by the vehicle MSDs.

The required longitudinal torque can be expressed as <MAT> where mGCW is the vehicle gross combination weight, ax,req is the required acceleration (which is zero or very small for use cases <NUM>, <NUM> and <NUM>), 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 uphill driving positive torque scenarios, the terms <MAT> and gCrmGCW must be overcome by the propulsion MSDs, while in downhill scenarios the terms instead help to brake the vehicle <NUM>. This means that the electric machine must be dimensioned to support positive torque sufficient for use cases <NUM> and <NUM>, while the combination of electric machine and other possible additional braking means must be dimensioned to provide a combined negative torque to support use cases <NUM> and hard braking according to use case <NUM>.

<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.

Claim 1:
A method for adapting air resistance of a heavy-duty vehicle (<NUM>), the vehicle comprising at least one electric machine (<NUM>, <NUM>, <NUM>) arranged for regenerative braking, one or more energy absorption devices (<NUM>) arranged to receive energy from the at least one electrical machine during regenerative braking, and a variable air resistance arrangement (<NUM>, <NUM>, <NUM>) arranged to provide a range of different air resistances of the vehicle, wherein the method comprises:
obtaining (S1) a current energy absorption capability of the one or more energy absorption devices (<NUM>); characterized in that
obtaining (S3) an expected energy generation from regenerative braking during a planned route of the vehicle and during a nominal value of air resistance of the vehicle (<NUM>);
determining (S4) a desired air resistance of the vehicle (<NUM>) from the range of different air resistances of the vehicle based on the current energy absorption capability and the expected energy generation; and
causing adaptation (S5) of the variable air resistance arrangement (<NUM>, <NUM>, <NUM>) according to the desired air resistance.