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 a rechargeable battery, or to a brake resistor which dissipates the electrical energy as heat. Electrical machines are normally associated with a limited braking torque capability, and the energy dissipation capability is limited. An other example of prior art <CIT>.

<CIT> discloses a type of vehicle brake arrangement based on a combination of an electric machine and an eddy current brake. This arrangement is able to generate more torque compared to the electric machine alone.

<CIT> discloses a vehicle braking system comprising an eddy current braking device arranged to receive current from an electrical machine arranged for regenerative braking, and a controller means arranged to control the amount of current to be provided to the eddy current braking device and the amount of current to be provided to an energy storage means in dependence of at target deceleration value of the vehicle and an energy absorption capability of the energy storage means.

<CIT> discloses a wheel drive unit comprising an electric machine and an eddy current brake, wherein both the electric machine and the eddy current brake can be used for braking.

However, there is a continuing need for further improvements in braking arrangements for heavy duty vehicles which are able to provide sufficient braking torque, also for extended periods of time, which are not susceptible to brake fading.

The present invention is defined by the attached independent claims. Other preferred embodiments may be found in the dependent claims. The present application discloses a braking arrangement (<NUM>, <NUM>) for decelerating a heavy duty vehicle (<NUM>), the arrangement comprising a control unit (<NUM>), at least one electric machine (<NUM>, <NUM>) arranged for regenerative braking, an electrical energy absorption device (<NUM>, <NUM>, <NUM>), an eddy current braking device (<NUM>, <NUM>), and a power distribution network (<NUM>) arranged to connect the electric machine (<NUM>, <NUM>) to the energy absorption device (<NUM>, <NUM>, <NUM>) and to the eddy current braking device (<NUM>, <NUM>), wherein the control unit (<NUM>) is configured to distribute regenerated electrical power from the electric machine (<NUM>, <NUM>) between the energy absorption device (<NUM>, <NUM>, <NUM>) and the eddy current braking device (<NUM>, <NUM>) by the power distribution network (<NUM>) in dependence of a target deceleration value of the heavy duty vehicle (<NUM>), wherein the control unit (<NUM>) is also configured to control the distribution of regenerated electrical power from the electric machine (<NUM>, <NUM>) between the energy absorption device (<NUM>, <NUM>, <NUM>) and the eddy current braking device (<NUM>, <NUM>) in dependence of an energy absorption capability of the energy absorption device (<NUM>, <NUM>, <NUM>), characterized in that the control unit (<NUM>) is configured to control the distribution of regenerated electrical power from the electric machine (<NUM>, <NUM>) between the energy absorption device (<NUM>, <NUM>, <NUM>) and the eddy current braking device (<NUM>, <NUM>) such that a constant baseline torque level is generated by the eddy current braking device, the torque applied by the electric machine being modulated to control wheel slip at a desired wheel slip level. Furthermore the present application discloses a method performed by a control unit (<NUM>) for decelerating a heavy duty vehicle (<NUM>), the method comprising obtaining (S1) a deceleration request indicative of a desired braking torque, determining (S2) if regenerative braking by an electric machine (<NUM>, <NUM>) associated with a braking torque capability is sufficient to meet the deceleration request, applying (S3) braking torque by a combination of the electric machine (<NUM>, <NUM>) and an eddy current braking device (<NUM>, <NUM>) powered by the electric machine (<NUM>, <NUM>) if the regenerative braking capability of the electric machine (<NUM>, <NUM>) is not sufficient to meet the deceleration request, and distributing the regenerated electrical power produced by the regenerative braking capability between an energy absorption device (<NUM>, <NUM>, <NUM>) and the eddy current braking device (<NUM>, <NUM>) such that a constant baseline torque level is generated by the eddy current braking device, the torque applied by the electric machine being modulated to control wheel slip at a desired wheel slip level.

<FIG> illustrates an example vehicle combination <NUM> for cargo transport. The vehicle combination <NUM> comprises a truck or towing vehicle <NUM> configured to tow a first trailer unit <NUM> in a known manner, e.g., by a fifth wheel connection <NUM>. To extend the cargo transport capability of the vehicle combination <NUM>, a dolly vehicle <NUM> can be connected to the rear of the first trailer <NUM> via a drawbar. This dolly vehicle can then tow a second trailer <NUM>, thus increasing the cargo transport capacity of the vehicle combination.

Each of the vehicle units <NUM>, <NUM>, <NUM>, <NUM> comprise means for generating negative torque, i.e., a braking torque to decelerate the vehicle combination <NUM>.

A dolly vehicle <NUM> is traditionally a passive vehicle comprising no driven or steerable axles, and with a relatively short wheelbase. It has recently been shown that self-powered dolly vehicles may provide both increased fuel efficiency and maneuverability. This type of self-powered dolly vehicle comprises an on-board energy source, such as a battery, super-capacitor or a fuel cell stack, and at least one pair of driven wheels. Some self-powered dolly vehicles may also be steerable.

Both the truck <NUM> and the self-powered steerable dolly vehicle <NUM>, and potentially also one or more of the trailer units <NUM>, <NUM> may comprise electric machines for propulsion and regenerative braking. However, most regenerative electric brakes are not capable of generating enough braking torque to perform hard braking, such as may be required during an emergency maneuver or the like, where accelerations on the order of -<NUM> to -<NUM> may be required. A heavy-duty vehicle such as the vehicle <NUM> therefore normally comprises friction brakes to complement the regenerative braking by the electric machine.

However, as mentioned above, 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. This rather complicated braking system drives cost and also requires extensive servicing.

It is most advantageous to be able to generate high braking torque by a self-powered dolly vehicle unit. This is because the dolly vehicle unit <NUM> can act as an anchor to brake the heavy duty vehicle <NUM>, and also to reduce overshoot by the second trailer <NUM> during hard turning, e.g., during evasive maneuvering. Thus, the techniques disclosed herein are particularly suitable for use with self-powered dolly vehicle units <NUM>.

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>.

<FIG> shows a braking arrangement <NUM> for decelerating a heavy duty vehicle <NUM>. The arrangement comprises a control unit <NUM> and least one electric machine <NUM>, <NUM> arranged for regenerative braking. The arrangement further comprises an electrical energy absorption device <NUM>, an eddy current braking device <NUM>, <NUM>, and a power distribution network <NUM> arranged to connect the electric machine <NUM>, <NUM> to the energy absorption device <NUM>, and to the eddy current braking device <NUM>, <NUM>. The control unit <NUM> is configured to distribute regenerated electrical power from the electric machine <NUM>, <NUM> between the energy absorption device <NUM> and the eddy current braking device <NUM>, <NUM> by the power distribution network <NUM> in dependence of a target deceleration value of the heavy duty vehicle <NUM>.

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.

The control unit <NUM> can also be configured to control various functions in addition to power distribution, such as steering. It may be equipped with a communication interface <NUM> arranged for communication with other units comprised in the vehicle <NUM>. This control unit will be discussed in more detail below in connection to <FIG>.

The electric machine <NUM>, <NUM> is arranged to generate a torque T1l, T1r, T2l, T2r around the wheel axle and thereby control the rotation of the wheel <NUM>. To achieve deceleration of the vehicle, a negative torque T1l, T1r, T2l, T2r may be generated by the electric machine <NUM>, <NUM> through regenerative braking. A negative torque can also be generated by the eddy current braking device <NUM>, <NUM>.

With reference also to <FIG>, an eddy current braking device <NUM>, <NUM> comprises at least one electrically conductive component <NUM>, which may be in the shape of a disc, and at least one magnet <NUM>, <NUM>. To increase the ability to generate negative torque, and to improve heat dissipation ability, the eddy current braking device <NUM>, <NUM> may comprise a plurality of electrically conductive discs <NUM> attached to a wheel axle <NUM> for generating braking torque. <FIG> shows an example of such an eddy current braking device with a plurality of electrically conductive discs <NUM>. However, a single disc is of course sufficient for generating braking torque by the eddy current braking device. More than one magnet can of course also be used with one or more respective electrically conductive discs.

The electrically conductive discs are made from an electrically conductive material, which is herein considered to be a material with an electric conductivity similar to that of a metal, substantially an electric conductivity above <NUM> Siemens / m. Optionally, the electrically conducting material may be a metal that reacts weakly to magnetic fields, such as copper or aluminum.

The electrically conductive disc or discs <NUM> are arranged such that when an axle <NUM> to which the eddy current braking device <NUM>, <NUM> is attached is rotating, the electrically conductive disc or discs <NUM> are also rotating. This may for example be accomplished by attaching the conductive disc <NUM> directly to the axle <NUM>, or via some form of gear arrangement.

The at least one magnet <NUM>, <NUM> comprises an electromagnet with a conductive coil and optionally also a core comprising a ferri- or ferromagnetic material, for example iron, permalloy, or ferrite. When an electric current is run through the conductive coils a magnetic field is generated in and around the coil according to Ampère's law. The core concentrates the magnetic flux, thereby producing a stronger magnetic field.

The at least one magnet <NUM>, <NUM> is arranged such that when the eddy current brakes are engaged the electrically conducting disc <NUM> is exposed to the magnetic field between the two magnetic poles, with the field lines of the magnetic field substantially perpendicular to the surface of the disc <NUM>. As an example, the magnet <NUM>, <NUM> could be a magnetic circuit, i.e. an electromagnet where the core is shaped to form a loop, and the electrically conductive disc <NUM> could be inserted into an air gap of the magnetic circuit. As another example, two magnets <NUM>, <NUM> could be arranged with the north pole of the first magnet and the south pole of the second magnet facing each other, with the electrically conductive disc <NUM> inserted between the north and south pole.

When the axle <NUM> is rotating and the eddy current braking device <NUM>, <NUM> is engaged, the magnetic field generated by the magnet <NUM>, <NUM> induces eddy currents in the moving electrically conductive disc <NUM> as predicted by Faraday's law of induction. Said eddy currents generate a magnetic field that counteracts the magnetic field generated by the magnet, thereby creating a drag force on the electrically conducting disc <NUM>. The electrons forming part of the induced eddy currents are subject to an electrical resistance when moving through the electrically conductive disc <NUM>, causing some of the energy of the moving electrons to be dissipated as heat. Through this mechanism, the kinetic energy of the electrically conductive disc <NUM> is converted into heat.

When the eddy current braking device <NUM>, <NUM> is not engaged, the electrically conductive disc <NUM> is not exposed to a magnetic field from the magnet <NUM>, <NUM>. If the magnet <NUM>, <NUM> is an electromagnet, the strength of the generated magnetic field depends on the electric current being passed through the conductive coil. In a situation when the eddy current braking device <NUM>, <NUM> is not engaged, the strength of this electric current may be substantially zero. Thus, advantageously, when the eddy current brakes are not engaged, no drag resistance or the like is experienced. This is a major benefit compared to standard service brakes (friction brakes such as disc brakes and drum brakes) which are usually associated with some residual applied brake pad force due to not releasing correctly when not applied, generating rolling resistance and heat.

<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>.

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 the eddy current braking device and the electric machine must be dimensioned to provide a combined negative torque to support use cases <NUM> and hard braking according to use case <NUM>.

It is appreciated that the vehicle <NUM> will, most likely, comprise several electric machines and eddy current braking devices which will be coordinated to meet torque requirements.

As previously described, the electric power used to generate the electric current in the conductive coil may be regenerated electric power from the electric machine <NUM>, <NUM>.

However, the electric power used to generate the electric current could also come from an energy storage device such as a battery or a super-capacitor.

An electrical energy absorption device <NUM>, <NUM>, <NUM> can for example be a device that stores electrical energy, such as a rechargeable battery <NUM> or a super-capacitor. An electrical energy absorption device <NUM>, <NUM>, <NUM> can also be a device that dissipates electrical energy, such as a resistor <NUM> which converts the electrical energy to heat without providing any useful effect such as braking or energy storage. An electrical energy absorption device <NUM>, <NUM>, <NUM> may also be a combination of devices that store electrical energy and devices that dissipate electrical energy.

<FIG> further illustrates the braking arrangement described above from a functional perspective. The control unit <NUM> is arranged to send a braking request to the electric machine <NUM>, <NUM> via a communication interface <NUM>. During regenerative braking, the electric machine <NUM>, <NUM> generates electric power which is transmitted to the distribution network <NUM> via a power interface <NUM>.

The distribution network is arranged to distribute the generated electric power between the eddy current braking device <NUM>, <NUM> and an energy absorption device <NUM>, <NUM>, <NUM> over two respective power distribution interfaces <NUM>, <NUM> in dependence of input received from the control unit <NUM> over a control interface <NUM>. The control unit <NUM> is arranged to obtain an energy absorption capability of the energy absorption device <NUM>, <NUM>, <NUM> over interface <NUM> and a braking and energy dissipation capacity of the eddy current braking device <NUM>, <NUM> over interface <NUM>, and modify the input to the distribution network <NUM> in dependence of these parameters.

As an example, if a large deceleration value of the vehicle <NUM> is required, the corresponding required negative torque may exceed what can be generated by the electric machine <NUM>, <NUM> alone. A larger fraction of the regenerated electric power may then be directed to the eddy current braking device <NUM>, <NUM>, which will in turn generate a negative torque, resulting in a larger total negative torque than that produced by the electric machine <NUM>, <NUM> alone. This way a very strong braking force can be generated, which is an advantage.

As another example, if the capacity of the energy absorption device <NUM>, <NUM>, <NUM> is insufficient to absorb the regenerated electric power, a larger fraction of the regenerated electric power may be directed to the eddy current braking device <NUM>, <NUM> even if the required torque could be produced solely by the electric machine <NUM>, <NUM>. Directing the regenerated electric power to the eddy current braking device <NUM>, <NUM> will result in an additional negative torque being generated by the eddy current braking device <NUM>, <NUM>. This serves both to dissipate the excess regenerated electric power and to decrease the negative torque that needs to be produced by the electric machine <NUM>, <NUM>, resulting in less electric power being regenerated. This way the specification and requirements imposed on the peak energy absorption capability of the energy absorption device can be relaxed, which is an advantage.

Thus, the control unit <NUM> may be configured to control the distribution of regenerated electrical power from the electric machine <NUM>, <NUM> between the energy absorption device <NUM>, <NUM>, <NUM> and the eddy current braking device <NUM>, <NUM> in dependence of an energy absorption capability of the energy absorption device <NUM>, <NUM>, <NUM>.

An energy absorption capability of the energy absorption device <NUM>, <NUM>, <NUM> may indicate a maximum amount of energy that the energy absorption device <NUM>, <NUM>, <NUM> can absorb without sustaining damage. An energy absorption capability of an energy absorption device <NUM>, <NUM>, <NUM> may also indicate a maximum rate of energy absorption by the energy absorption device <NUM>, <NUM>, <NUM>, or a combination of a maximum amount of energy that can be absorbed and a maximum rate at which it can be absorbed.

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 a resistor <NUM>, an energy absorption capability may be determined by the power rating of the resistor <NUM>, i.e. the amount of power that can be dissipated via the resistor <NUM> 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 resistor will have a smaller energy absorption capability compared to a cool un-used 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, thus the energy absorption capability may also range over a time span of months or even years.

The energy absorption device may comprise a rechargeable battery <NUM>, and the control unit <NUM> may configured to control the distribution of regenerated electrical power from the electric machine <NUM>, <NUM> between the rechargeable battery <NUM> and the eddy current braking device <NUM>, <NUM> in dependence of a state of charge, SOC, of the rechargeable battery <NUM>. In particular, a larger fraction of the regenerated electrical power may be directed to the rechargeable battery <NUM> if the state of charge, SOC, is low. Conversely, if the state of charge, SOC, is high or the battery is fully charged, a larger fraction of the regenerated electrical power may be directed to the eddy current braking device <NUM>, <NUM>.

Also, the energy absorption device may comprise a resistor <NUM> configured to dissipate excess electrical energy from the electric machine <NUM>, <NUM> and to regulate a voltage level of the braking arrangement. That is, the electrical resistance of the resistor <NUM> may be selected such that a voltage experienced by other components of the braking arrangement, e.g. the eddy current braking device <NUM>, <NUM> or the energy absorption device <NUM>, <NUM>, <NUM>, is kept at a desired value.

With reference to <FIG>, the braking torque capability level Tcap of the electric machine <NUM>, <NUM> may generally correspond to a torque level that is sustainable over an extended period of time. An extended period of time could in this context be <NUM> seconds or more. Thus, a sustainable torque level may e.g. depend on a capacity of the cooling system of the electric machine <NUM>, <NUM>.

However, the electric machine <NUM>, <NUM> is also normally associated with a peak braking torque level Tpeak above a braking torque capability level of the electric machine. This peak braking torque level can be maintained by the electric machine for a limited duration of time. The control unit <NUM> may then be configured to request a braking torque level from the electric machine <NUM>, <NUM> between the peak braking torque level and the braking torque capability level to decelerate the heavy duty vehicle. A limited duration of time could for example be <NUM> seconds or less.

Applying a braking torque above Tcap will result in the generation of additional electric power. Optionally, the control unit may be arranged to distribute the additional electric power to the eddy current braking device <NUM>, <NUM>. In addition to the braking torque generated by the electric machine, a braking torque will then be generated by the eddy current braking device, resulting in a high total braking torque. For example, the total peak braking torque Tpeak may approach four times the total continuous maximum braking torque of the electric machine, though only for the limited amount of time during which a braking torque above Tcap can be sustained. This may for example be useful for emergency braking.

<FIG> comprises a graph <NUM> illustrating braking torque as a function of the angular velocity of the wheel axle <NUM>. At low to moderate angular velocities, braking torques up to the braking torque capability level Tcap can be applied for an extended period of time, and braking torques up to the peak braking torque level Tpeak can be applied for a limited time. At high angular velocities, the electric machine <NUM>, <NUM> may become unable to sustain the braking torque, leading to a decrease in braking torque with increasing angular velocity as seen in <FIG>.

A consequence of this decrease is that less electric power is regenerated, meaning that less electric power from the electric machine <NUM>, <NUM> is available to power the eddy current braking device <NUM>, <NUM>. According to aspects, the braking arrangement <NUM>, <NUM> may be arranged to power the eddy current braking device <NUM>, <NUM> from a different energy source at high angular velocities of the wheel axle <NUM>. This energy source may for example be a battery <NUM> or a super-capacitor. According to other aspects, the braking arrangement <NUM>, <NUM> may also be arranged to power the eddy current braking device from a different energy source if the function of the electric machine <NUM>, <NUM> becomes impaired.

According to aspects, the control unit <NUM> may be arranged to perform a vehicle motion management function comprising force generation and motion support device, MSD, coordination.

<FIG> schematically illustrates functionality <NUM> for controlling a wheel <NUM> by some example motion support device (MSDs) here comprising the electric machine <NUM> and the eddy current brake <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. An example vehicle motion support device control system is also shown in <FIG>.

A traffic situation management (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 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. The TSM function <NUM> continuously requests the desired acceleration profiles areq and curvature profiles creq from a vehicle motion management (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.

Acceleration profiles and curvature profiles may also be obtained from a driver of the heavy duty vehicle via normal control input devices such as a steering wheel, accelerator pedal and brake pedal. The source of said acceleration profiles and curvature profiles is not within scope of the present disclosure and will therefore not be discussed in more detail herein.

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 <NUM>, <NUM> 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 <NUM> (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 <NUM>.

A tyre model, exemplified in <FIG>, can be used to translate between a desired longitudinal tyre 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 tyre 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. In "<NPL> covers the fundamentals of tyre models. 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.

For instance, the VMM function <NUM> keeps track of the state of charge of the electrical energy system (ESS) of the vehicle, i.e., the traction batteries or the fuel cell system as well as the current state of any brake resistors, and determines how to best meet braking torque requirements by the electric machines and by the eddy current braking devices. The VMM directs electrical energy to the eddy current brakes if this is favorable in a given situation, and to the ESS otherwise.

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 tyre road contact patch.

With reference to <FIG>, the inverse tyre 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 <NUM>. The MSD controllers report back capabilities <NUM>-<NUM> 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 <NUM> maintains information on vx (in the reference frame of the wheel), while a wheel speed sensor or the like can be used to determine ωx (the rotational velocity of the wheel).

In order for a wheel (or tyre) to produce a wheel force, slip must occur. For smaller slip values the relationship between slip and generated force are approximately linear, where the proportionality constant is often denoted as the slip stiffness of the tyre. A tyre <NUM> is subject to a longitudinal force Fx, a lateral force Fy, and a normal force Fz. The normal force Fz is key to determining some important vehicle properties. For instance, the normal force to a large extent determines the achievable lateral tyre force Fy by the wheel since, normally, Fy ≤ µ Fz, where µ is a friction coefficient associated with a road friction condition. The maximum available lateral force for a given lateral slip can be described by the so-called Magic Formula as described in "<NPL>.

According to aspects, slip control during endurance braking can be improved by simultaneously using several types of braking, i.e. what is known as brake blending. As an example, the control unit <NUM> may be configured to control the distribution of regenerated electrical power from the electric machine <NUM>, <NUM> between the energy absorption device <NUM>, <NUM>, <NUM> and the eddy current braking device <NUM>, <NUM> such that a constant baseline torque level is generated by the eddy current braking device <NUM>, <NUM>. The torque applied by the electric machine can then be modulated to control wheel slip at a desired wheel slip level. With the eddy current braking device <NUM>, <NUM> generating a baseline torque level, the electric machine <NUM>, <NUM> can be used to control wheel slip with low latency.

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. Normally, a retarder or engine brake is used to provide endurance braking. However, the disclosed braking arrangements are possible to design so the endurance braking is supported without need for additional retarders, friction brakes, or the like.

To guarantee vehicle downhill gradeability, the eddy current braking device and the electric machine are 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 also arranged to distribute the regenerated energy to the eddy current braking device when the energy absorption capability of the energy absorption device is depleted. The eddy current braking device is dimensioned to absorb this energy level. Thus, vehicle downhill gradeability is guaranteed.

The electric machine <NUM>, <NUM>, the eddy current braking device <NUM>, <NUM>, and the power distribution network <NUM> may be integrally formed in a single wheel end module. Such a wheel end module may comprise an output port for feeding electrical energy to the energy absorption device <NUM>, <NUM>, <NUM>.

The wheel end module may also comprise a control port by which it can be connected to the control unit <NUM>. The control unit <NUM> may then be arranged to send e.g. a torque request or a wheel slip request as described above to the wheel end module together with an energy absorption capability of an energy absorption device <NUM>, <NUM>, <NUM> that is external to the wheel end module. Within the wheel end module, the requested torque or wheel slip can then be generated by the electric machine <NUM>, <NUM> and the eddy current braking device <NUM>, <NUM> in such a way that the electrical energy fed to the energy absorption device <NUM>, <NUM>, <NUM> does not exceed the energy absorption capability.

According to aspects, the electric machine <NUM>, <NUM> may be an axial flux electric machine. In contrast to a radial flux electric machine, in which the stator forms a substantially cylindrical shell concentric with the substantially circular rotor and the magnetic flux is directed radially between the rotational axis of the rotor and the stator, the magnetic flux in an axial flux electric machine is directed along the rotational axis of the rotor. Both the rotor and the stator in an axial flux electric machine may be thought of as discs, placed next to each other with the axis of rotation of the rotor perpendicular to both discs. During operation, the magnetic flux between rotor and stator will then be parallel to the axis of rotation. Optionally, more than one stator may be used. Axial flux electric machines may be associated with higher power densities and a less complicated manufacturing process compared to radial flux electric motors.

There is also herein disclosed a heavy duty vehicle unit <NUM>, <NUM>, <NUM>, <NUM> comprising a braking arrangement <NUM>, <NUM> as described above.

The flowchart in <FIG> shows a method, performed by a control unit <NUM>, for decelerating a heavy duty vehicle <NUM>. The method comprises obtaining S1 a deceleration request indicative of a desired braking torque and determining S2 if regenerative braking by an electric machine <NUM>, <NUM> associated with a braking torque capability is sufficient to meet the deceleration request. The method further comprises applying S3 a braking torque by a combination of the electric machine <NUM>, <NUM> and an eddy current braking device <NUM>, <NUM> powered by the electric machine <NUM>, <NUM> if the regenerative braking capability of the electric machine <NUM>, <NUM> is not sufficient to meet the deceleration request.

As an example, a deceleration request may be obtained from a traffic situation management (TSM) function as described above. As another example, the deceleration request may be obtained via pedal inputs from the driver.

When a braking torque is applied using both the electric machine <NUM>, <NUM> and the eddy current braking device <NUM>, <NUM>, the eddy current braking device <NUM>, <NUM> may be powered directly by the electric machine <NUM>, <NUM>. That is, as regenerative braking by the electric machine <NUM>, <NUM> results in the generation of electric power, some of this electric power is directed to power the conductive coil of the electromagnet comprised n the eddy current braking device <NUM>, <NUM>.

Using the electric machine <NUM>, <NUM> and the eddy current braking device <NUM>, <NUM> in combination, it is possible to generate higher braking torques than using the electric machine <NUM>, <NUM> alone. For example, the method may also comprise controlling S4 the electric machine <NUM>, <NUM> to generate a braking torque above the braking capability of the electric machine for a limited duration of time to meet the deceleration request. The additional electrical power generated during this time can be used to directly power the eddy current braking device <NUM>, <NUM>, which results in a substantial increase of the total braking torque.

The method may also comprise that the braking capability of the electric machine <NUM>, <NUM> is determined S21 in dependence of an energy absorption capability of an energy absorption device <NUM>, <NUM>, <NUM>.

An energy absorption device <NUM>, <NUM>, <NUM> may be a device that dissipates electric energy into heat, such as a resistor <NUM>, or a device that stores electric energy, such as a battery <NUM>. An energy absorption capability of a resistor <NUM> may be determined by its power rating, i.e. how much power it can dissipate without overheating or sustaining damage. The energy absorption capability of a battery <NUM> may be determined by a difference between the current state of charge of the battery <NUM> and the maximum charge.

If the energy absorption capability of the energy absorption device is large, e.g. if the state of charge of the battery <NUM> is low, it can absorb a larger amount of regenerated electric power from the electric machine <NUM>, <NUM> and the braking capability may thus be higher. If the battery is close to its maximum charge, the braking capability may be lower as the regenerated electric power cannot be absorbed by the battery <NUM>.

There is also herein disclosed a control unit <NUM> comprising processing circuitry <NUM> configured to perform a method as described above, and a computer program <NUM> comprising program code means for performing a method as previously described when said program is run on a computer or on processing circuitry <NUM> of a control unit (<NUM>.

<FIG> schematically illustrates, in terms of a number of functional units, the components of a control unit <NUM> according to embodiments of the discussions and methods disclosed herein. This control unit <NUM> may be comprised in a vehicle unit <NUM>, <NUM>, <NUM>, e.g., in the form of a vehicle motion management (VMM) unit configured to perform force allocation and the like. 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.

The control unit <NUM> may further comprise an interface <NUM> for communications with at least one external device, such as an electric machine or a gearbox.

Claim 1:
A braking arrangement (<NUM>, <NUM>) for decelerating a heavy duty vehicle (<NUM>), the arrangement comprising a control unit (<NUM>), at least one electric machine (<NUM>, <NUM>) arranged for regenerative braking, an electrical energy absorption device (<NUM>, <NUM>, <NUM>), an eddy current braking device (<NUM>, <NUM>), and a power distribution network (<NUM>) arranged to connect the electric machine (<NUM>, <NUM>) to the energy absorption device (<NUM>, <NUM>, <NUM>) and to the eddy current braking device (<NUM>, <NUM>), wherein the control unit (<NUM>) is configured to distribute regenerated electrical power from the electric machine (<NUM>, <NUM>) between the energy absorption device (<NUM>, <NUM>, <NUM>) and the eddy current braking device (<NUM>, <NUM>) by the power distribution network (<NUM>) in dependence of a target deceleration value of the heavy duty vehicle (<NUM>), wherein the control unit (<NUM>) is also configured to control the distribution of regenerated electrical power from the electric machine (<NUM>, <NUM>) between the energy absorption device (<NUM>, <NUM>, <NUM>) and the eddy current braking device (<NUM>, <NUM>) in dependence of an energy absorption capability of the energy absorption device (<NUM>, <NUM>, <NUM>), characterized in that the control unit (<NUM>) is configured to control the distribution of regenerated electrical power from the electric machine (<NUM>, <NUM>) between the energy absorption device (<NUM>, <NUM>, <NUM>) and the eddy current braking device (<NUM>, <NUM>) such that a constant baseline torque level is generated by the eddy current braking device, the torque applied by the electric machine being modulated to control wheel slip at a desired wheel slip level.