Patent Description:
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to cargo transport vehicles such as semi-trailer vehicles and trucks, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as cars.

The braking system of a heavy duty vehicle is key to safe vehicle operation. The braking system not only limits vehicle velocity when needed, but also plays an important role in maintaining vehicle stability. For instance, if a left wheel of the vehicle runs over an icy area of the road, resulting in reduced friction and grip, while the corresponding right wheel runs on a non-slippery part of the road, then the braking system can be activated to compensate for and counteract the arisen slip situation.

A common approach for requesting a certain tyre force is to use torque control at the actuator level. However, such an approach has significant performance limitations. If a safety critical or excessive slip situation arises, then a relevant safety function (traction control, anti-lock brakes, etc.) steps in and requests a torque override in order to bring the slip back into control. A problem with this is that since the primary control of the actuator and the slip control are allocated to two different controllers, the latencies involved in the communication between them significantly limits the slip control performance.

A solution to the above approach may be to use a tyre model for converting a torque request into a wheel slip request. Thus, rather than to strive for a certain tyre force controlled at the actuator level, a faster control response may be obtainable by instead controlling the wheel slip, i.e. the rotational speed of the wheel. However, when multiple actuators act on the same wheel, also wheel slip requests may present problems. One example of such a problem may be on an axle that is connected to an electric machine and a friction brake. Another example is an axle where multiple electric machines (e.g. electric motors) are connected in parallel to the same axle. In these cases if a wheel slip request is to be followed, the allocation of requests between the multiple actuators must be done in a way that "fighting" between the actuators is avoided. For examples, if the three electric machines connected to the drive axle of the vehicle are simply all set to a motor speed request (corresponding to the requested wheel slip) it is very likely that the three electric machines would interfere with each other when the motor speed(s) come close to the target value. Thus, it would be desirable to use wheel slip control when multiple actuators act on a common wheel, wherein the above described drawbacks are at least partly mitigated.

Document <CIT> discloses a control device for an electric vehicle capable of stabilizing vehicle behaviour when performing slip control of drive wheels.

An object of the invention is to provide a method which alleviates the drawbacks of the prior art. This and other objects, which will become apparent in the following disclosure, are achieved by a method as defined in the accompanying independent claim <NUM>.

The present inventive concept is based on the realization that when two or more motion support devices, MSDs, (such as the above or other mentioned actuator combinations) are configured to provide torque to a common wheel of the vehicle (or to a common group of wheels, such as providing torque on an axle level), then the fighting/interfering between the MSDs may be avoided by controlling the MSDs to provide torque in a at least two different modes of operation. Thus, one or more MSDs may be controlled to provide torque in a first mode of operation, while the other MSD(s) may be controlled to provide torque in a second and/or further mode of the operation. For instance, one MSD may be controlled in a master mode of operation, while the other MSD(s) may be controlled in a slave mode of operation which is dependent on the master mode of operation. Different aspects and exemplary embodiments will be discussed in the following.

According to a first aspect of the present invention, there is provided a method for controlling wheel slip of a vehicle, wherein the vehicle comprises at least a first and a second motion support device, MSD, for providing torque to a common wheel of the vehicle, the method comprising:.

By having the first MSD and the second MSD provide torque in different modes of operation, even though performed simultaneously, the risk of interfering may be avoided when the MSDs come close to their target values associated with the received wheel torque request. There may be some other advantages, such that a more precise slip and torque control may be achieved at a given wheel simultaneously, and that a more precise slip control may be achieved while also achieving a desired distribution of torque and/or power across the MSDs providing energy efficiency improvements, reduced strain on individual MSDs etc..

The method presented in this disclosure may suitably be performed in an autonomous vehicle or in a driver-operated vehicle.

The inventive concept is not limited to only two MSDs, but may advantageously be implemented for three or more MSDs providing torque to a common wheel, or to a common group of wheels (such as on a common axle). The two or more MSDs may be of the same type, or of different types. Examples of conceivable MSDs that may be controlled in accordance with the present disclosure, include electric machines, such as electric motors; internal combustion engines, ICE; and friction brakes.

According to the invention, said first mode of operation is a speed control mode, wherein the method comprises sending a wheel speed request to the first MSD for controlling the rotational speed of the wheel. By applying a speed control mode, a fast and accurate slip control is achievable. Such speed control mode may be implemented for various types of MSDs, including electric machines, ICEs and friction brakes. The two former are exemplified in the following exemplary embodiment.

According to at least one exemplary embodiment, the first MSD is an electric machine or an internal combustion engine, ICE, wherein said first mode of operation is a speed control mode, wherein the method comprises sending a machine speed request to the first MSD for controlling the rotational speed of the first MSD. As above, this allows a fast and accurate slip control.

Thus, from the above it should be understood that the rotational speed of the machine itself may be controlled, or the rotational speed of the actual wheel may be controlled. The rotational speed of the machine may be different to the wheel speed (due to a gear box inbetween, etc.). An advantage of controlling the machine speed is where the MSD is a motor (such as electrical or ICE) that may be connected via shafts to the wheel. This is because the wheel speed signal may have some latency and or phase difference to the machine speed due to drive shaft stiffnesses, etc. Therefore, a control loop based on the machine speed may be more stable than a control loop based on the wheel speed.

According to the invention, said second mode of operation is a torque control mode, wherein the method comprises sending a torque request to the second MSD for controlling the torque of the second MSD. By controlling the first MSD to provide torque in a speed control mode, and controlling the second MSD to provide torque in a torque control mode, the risk of the MSDs fighting each other may be reduced. Furthermore, the response times may suitably be different. For instance, the speed control mode may have a faster control response time than the torque control mode.

According to at least one exemplary embodiment, the wheel is provided with a tyre for which a tyre model is provided, wherein, in the tyre model, longitudinal tyre force is represented as at least a function of longitudinal wheel slip, longitudinal wheel slip being dependent on rotational speed of the wheel and velocity of the vehicle, wherein the method comprises controlling the rotational speed based on said tyre model. Thus, a tyre model may advantageously be used to transform a torque request into a wheel slip request or a speed request. Thus, according to present disclosure, torque control latency may be avoided by providing the torque control at the same vehicle sub-system as the slip control. Such subsystems have relatively short response times compared to the vehicle control unit from which torque requests are traditionally sent. By using a tyre model in which a longitudinal tyre force is a function of at least the longitudinal wheel slip, a slip control sub-system can be used to provide a slip request which corresponds to a desired longitudinal force. Hereby, a fast response time is obtained.

It should be understood that although the tyre model, in its most basic form may be the longitudinal tyre force represented as only a function of longitudinal wheel slip, in at least some exemplary embodiments, other variables may also be included in the tyre model. For instance, the tyre model may also include other inputs, such as lateral wheel slip, vertical force on the tyre, etc..

It should also be understood that other exemplary embodiments may be implemented without a tyre model. For instance, the first MSD may be set in speed control mode with a speed calculated based on a longitudinal slip value (which may be constant or varied). In the case of a constant slip value being used that MSD would be trying to get to the maximum traction (or braking) setting, but would often be limited by the torque limitation that is also sent to the MSD. This is a simplified approach which does not require a tyre model, although exemplary embodiments with tyre models may be more accurate.

The longitudinal wheel slip may be a positive wheel slip or a negative wheel slip. During for instance acceleration, a positive propulsion slip may be obtained, i.e. the product of the rotational speed of the wheel and its radius is larger than the velocity of the vehicle in the direction of the wheel. During braking, a negative slip may be obtained, i.e. the product of the rotational speed of the wheel and its radius is lower than the velocity of the vehicle in the direction of the wheel.

According to at least one exemplary embodiment, in its conversion of the wheel torque request to the wheel rotational speed request, the control unit is configured to calculate a slip request based on the corrected function and to transform the slip request to the wheel rotational speed request using the slip formula: <MAT> where λ is the longitudinal wheel slip, where Rω is the rotational speed of the wheel, of which R is the wheel radius in meters and ω is the angular velocity of the wheel, and where vx, is the longitudinal speed of the wheel. Thus, the wheel rotational speed request is conveniently obtainable from the formula and the function of the tyre model.

Thus, λ is bounded between -<NUM> and <NUM> and quantifies how much the wheel is slipping with respect to the road surface. The control unit may suitably maintain information on vx, (in the reference frame of the wheel), while a wheel speed sensor may be used to determine ω.

According to at least one exemplary embodiment, the method further comprises.

Thus, the first MSD set to speed control mode "leads" the other MSDs. After a period of time (which is suitably long enough for a quasi-steady state to be reached between the first MSD and the wheel and road) the values of said selected control parameter is summed and then divided. It may be divided equally, but other rules may be applied in which each MSD receives its share of the summed value. It should be noted that the method does not need to necessarily wait for the first MSD to reach the target speed. Rather long enough time is allowed to pass so that the current applied torque on the first MSD does not exceed the speed request. For instance, there may be cases (on a dry road) where the first MSD will not reach the target speed at all, but the other MSD(s) should still (eventually) add torque to bring the overall wheel speed as close as possible to the target, or such that the total torque reaches a limit value.

It should also be understood that the received wheel rotational speed request may be met by controlling the rotational speed of the wheel or by controlling the rotational speed of the first MSD itself (any gear ratio etc. between the rotational speeds may thus be included in calculations and the conversion of the wheel torque request into the wheel rotational speed request).

The above selected control parameter may for instance be torque or power. This is reflected in the below disclosed exemplary embodiments.

According to at least one exemplary embodiment, said selected control parameter is torque, wherein said summarizing, dividing and sending comprises:.

The advantages are analogous to the above general disclosure of a control parameter.

According to at last one exemplary embodiment, said selected control parameter is power, wherein said summarizing, dividing and sending comprises:.

According to at least one exemplary embodiment, the method comprises, after a period of time, repeating said sequence of summarizing the values (e.g. torque or power), dividing the summed values, and sending a parameter request (e.g. torque request or power request) to the second MSD. Thus, the MSDs may be sent parameter requests based on their share of the total status. Time is allowed for the system to stabilise again, then the parameter statuses are read again and the sequence is repeated. If more than two MSDs act on the same wheel, for instance, three MSDs, than the first MSD may be operated in speed control mode, and the second and third MSDs may be controlled based on their share of the summed selected parameter value. When three MSDs are provided, the parameter split may be divided by three (however, other rules may be applied).

According to at least one exemplary embodiment, the method comprises dividing the value of the received wheel torque request between the first and the second MSDs based on a desired torque split, wherein said second mode of operation is a torque control mode, wherein the method comprises sending a torque request to the second MSD, wherein the first mode of operation is a speed control mode, wherein the method comprises sending a machine speed request to the first MSD, which machine speed request is selected based on the tyre model so as to provide the total value of the received wheel torque request. The dividing may be made based on a preferred torque split, i.e. the requested torque is not necessarily evenly divided. By dividing the value of the requested torque between the two or more MSDs, but letting one of MSDs work in speed control mode, while the other(s) work in torque control mode, fighting between the MSDs may be avoided. The one or more MSD:s that are in torque control mode may be regarded as providing a relatively rough baseline, while the first MSD (which is in speed control mode) may be regarded as providing the fine tuning for attaining the desired slip associated with the received wheel torque request. It should be noted that in this exemplary embodiment, the speed control mode does not necessarily need to have a faster response control loop than then torque control mode. The response time may thus be the same for both MSDs in this exemplary embodiment.

As have been mentioned various times in this disclosure, there may be more than two MSDs acting on the same wheel or on the same group of wheels. This is reflected in at least one exemplary embodiment, according to which the vehicle comprises a third MSD, for providing torque to said wheel, the method comprising controlling the third MSD in said second mode of operation, or in a third mode of operation which is different from the first and second modes of operation. Thus, in general, if there are three or more MSDs, the advantageous effects of avoiding fighting between the MSDs is obtainable even though the second and the third MSDs are controlled with the same mode of operation. For instance, the first MSD may be operated in speed control mode, and the second and third MSDs may be operated in torque control modes, in accordance with their share of a torque split. In some exemplary embodiments, the first MSD may be regarded as the master MSD, while the second and third MSDs may both be regarded as slave MSDs. Although the second and third MSDs may be controlled in the same mode of operation, in some exemplary embodiments they may be controlled in different modes of operation. For instance, in embodiments in which all MSDs are set to speed control modes, the first MSD may be set with a tight deadzone and fast control bandwidth, the second MSD may be set with an intermediate deadzone and a moderate control bandwidth, and the third MSD may be set with a large deadzone and a low control bandwidth.

It should be understood that in at least some exemplary embodiments the control modes for the different MSD:s may be switched over time. For instance, a specific MSD that is put in speed control could, over time, be swapped between available MSDs (e.g. if you have multiple identical electric machines, you could let them take turns at being the lead MSD).

According to a second aspect of the present invention, there is provided a computer program comprising program code means for performing the method according to the first aspect, including any embodiments thereof, when said program is run on a computer. The advantages of the computer program of the second aspect largely correspond to those of the first aspect, including any embodiments thereof.

According to a third aspect of the present invention, there is provided a computer readable medium carrying a computer program comprising program code means for performing the method according to the first aspect, including any embodiments thereof, when said program product is run on a computer. The advantages of the computer readable medium of the third aspect largely correspond to the advantages of the first aspect, including any embodiments thereof.

According to a fourth aspect of the present invention, there is provided a control unit for controlling wheel slip of a vehicle, wherein the vehicle comprises at least a first and a second motion support device, MSD, for providing torque to a common wheel of the vehicle, the control unit being configured to perform the method according to the first aspect. The advantages of the control unit of the fourth aspect largely correspond to the advantages of the first aspect, including any embodiments thereof.

The control unit may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit may also, or instead, include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where the control unit includes a programmable device such as the microprocessor, microcontroller or programmable digital signal processor mentioned above, the processor may further include computer executable code that controls operation of the programmable device.

According to a fifth aspect of the present invention, there is provided a vehicle comprising a control unit according to the fourth aspect wherein said first MSD is one of an electric machine, an ICE, and a brake actuator, wherein said second MSD is one of an electric machine and a brake actuator. The advantages of the vehicle of the fifth aspect largely correspond to the advantages of the first aspect, including any embodiments thereof.

Some exemplary embodiments (but not exhaustive) embodiments, include the following combinations of MSDs:.

<FIG> illustrates a vehicle <NUM> according to at least one exemplary embodiment of the invention. The exemplary illustration in <FIG> shows a tractor unit for towing a trailer unit (not shown), which together make up a semitrailer vehicle. However, the invention is applicable to other types of vehicles as well. For instance, the vehicle may be a different type of vehicle for cargo transport, such as a truck, or a truck with a dolly unit arranged to tow a trailer unit, etc.. It should furthermore be understood that the inventive concept is not limited to heavy duty vehicles, but may also be implemented in other vehicles, such as cars.

The illustrated vehicle <NUM> is supported on wheels <NUM>, some of which are driven wheels. Although the vehicle <NUM> in <FIG> only has four wheels <NUM>, the inventive concept is applicable to vehicles having more wheels, such as in the above-mentioned different types of vehicles.

Each wheel <NUM>, or at least a majority of the wheels, is associated with a respective wheel brake. This wheel brake may, e.g. be a pneumatically actuated disc brake or drum brake, but some aspects of the disclosure are also applicable to regenerative brakes which produce electrical power during vehicle retardation, and electrical machines able to slow down wheel rotational velocity upon request. The wheel brakes are controlled by a wheel end module (WEM), which may control applied braking force on at least one wheel <NUM> of a vehicle such as the vehicle <NUM> in <FIG>. Each WEM is communicatively coupled to a control unit (not shown in <FIG>), allowing the control unit to communicate with the WEM and thereby control vehicle braking. This control unit may potentially comprise a number of sub-units distributed across the vehicle <NUM>, or it may be a single physical unit. The control unit may e.g. allocate brake force between wheels to maintain vehicle stability.

It should be noted that in other exemplary embodiments, instead of, or in addition to having WEMs, there may be provided an axial control module (ACM). For instance, an ACM may be implemented in cases where the axle includes a machine that operates through a differential. Thus, although for simplicity, WEM will be discussed in connection with the description of the drawings, it should be understood that the corresponding functionality may be implemented by an ACM.

Each driven wheel <NUM> may be driven by a suitable electrical machine (such as an electrical motor, a combined motor/generator, etc.) or by an internal combustion engine, ICE, or a combination thereof. The electrical machine and/or ICE may drive more than one wheel, e.g. working across an open differential. In other exemplary embodiments, each driven wheel may be propelled by an individually associated electrical machine. In either case, the above-mentioned control unit may suitably be communicatively coupled to such electrical machines for allocating the propulsion force between wheels. A more detailed discussion of the above-discussed a control unit will follow in connection to the presentation of <FIG> and <FIG>.

As has been discussed in the Summary section of this disclosure, the general inventive concept concerns controlling wheel slip of a vehicle by controlling a first motion support device, MSD, to provide torque to the wheel in a first mode of operation, while controlling the second MSD to provide torque to the wheel in a second mode of operation which is different from the first mode of operation. Examples of configurations of motion support devices, MSDs, will now be discussed in connection with <FIG>.

<FIG> schematically illustrates some configurations in which the present invention may be implemented. As illustrated with solid lines, the present disclosure envisages controlling at least two MSDs <NUM>, <NUM> which act on the same wheel <NUM>. However, as illustrated with dashed lines, there may be more MSDs <NUM>, <NUM> acting on the same wheel <NUM> (in the drawing four MSDs are illustrated, however, it should be understood that the number of MSDs could be three, five or more). Furthermore, as illustrated with dashed line, there may be at least one further wheel <NUM>' on which the MSDs <NUM>-<NUM> act. Thus, the MSDs <NUM>-<NUM> may in some exemplary embodiments act on the same group of wheels <NUM>, <NUM>'. A vehicle for which the present inventive concept may be implemented, such as the vehicle <NUM> in <FIG>, may for instance have one or more MSDs <NUM>-<NUM> in the form of electric machines, in the form of ICEs, and/or in the form of brake actuators, which act on a common wheel <NUM> or a common group of wheels <NUM>, <NUM>'. Thus, some examples of combinations may be MSDs in the form of:.

<FIG> illustrates a control system <NUM> in which a control unit <NUM> according to at least one exemplary embodiment of the invention has been included. The control unit <NUM> may perform the inventive method discussed in this disclosure.

More specifically, in <FIG>, there is illustrated a control system <NUM> for a wheel <NUM>, here exemplified by the vehicle front axle left wheel. A wheel end module (WEM) <NUM> is arranged to control the wheel braking by a brake actuator <NUM>, i.e. a part of the brake system, here exemplified by a disc brake. As mentioned above, the WEM <NUM>, may be replaced by or complemented by an axle control module (ACM). The brake system may also comprise one or more electric machines (EM) <NUM>, and/or combinations of different brake actuators. The illustrated electric machine <NUM> may also be controlled to provide a propulsion force to the wheel <NUM>. The exemplified electric machine <NUM> may thus represents a first motion support device, MSD <NUM>, and the exemplified brake actuator <NUM> may represent a second motion support device, MSD <NUM>, or vice versa.

The WEM <NUM> is communicatively coupled to the control unit <NUM>, e.g. a vehicle motion management (VMM) system. Although the WEM <NUM> and the VMM <NUM> have been illustrated as two functionally separate entities, it should be understood that they may be structurally provided as one common entity. Thus, in some exemplary embodiments the WEM <NUM> and the VMM <NUM> are provided as one unit. In other exemplary embodiments, the WEM <NUM> and the VMM <NUM> may be structurally separated. It should also be understood that the VMM <NUM> may be distributed over several structural entities, some of which may be remote, e.g. off-board. For instance, some functionalities, such as calculations made by the VMM <NUM> may be cloud-based, wherein part of the VMM <NUM> may be provided at one or more remote servers, etc..

The control unit <NUM>, here embodied as the VMM <NUM>, may comprise or be operatively connected to a data storage <NUM>. The data storage <NUM> may thus be on-board the vehicle or off-board. <FIG> schematically illustrates a graph to depict that the data storage <NUM> may have a stored tyre model <NUM> for the tyre of the wheel <NUM>. As will be discussed in more detail in connection with <FIG>, in the tyre model <NUM>, longitudinal tyre force is represented as at least a function of longitudinal wheel slip. Longitudinal wheel slip is dependent on the rotational speed of the wheel <NUM> and the velocity of the vehicle. The rotational speed of the wheel <NUM> may be measured by a speed sensor <NUM> (see <FIG>). The measured rotational speed may be transmitted from the sensor <NUM> to the WEM <NUM>, by wireline or wireless. The velocity of the vehicle <NUM> may be measured by another sensor (not illustrated), such as a Hall-effect sensor, the measured velocity being obtainable by the VMM <NUM> and/or the WEM <NUM>.

The control unit <NUM>, here in the form of the VMM <NUM> may thus be used for controlling wheel slip of a vehicle, such as the vehicle <NUM> in <FIG>. The VMM <NUM> may be configured to perform the steps of the method according to the above mentioned first aspect of the invention, including any embodiments thereof. Thus, the VMM <NUM> may be configured to receive a wheel torque request and then, based on the received wheel torque request, the VMM <NUM> may control the first MSD <NUM> to provide torque to the wheel in a first mode of operation and to control the second MSD <NUM> to provide torque to the wheel in a second mode of operation which is different from the first mode of operation, wherein the controlling of the first MSD <NUM> and the second MSD <NUM> are, at least temporarily, performed simultaneously.

The VMM <NUM> may, of course, also be implemented in vehicles with other MSD configurations for controlling wheel slip. Such another exemplary configuration is illustrated in <FIG>, wherein three MSDs <NUM>, <NUM>', <NUM>" are illustrated in the form of a first electric machine (first MSD <NUM>), a second electric machine (second MSD <NUM>') and a third electric machine (third MSD <NUM>"). Thus, in this configuration illustrated in <FIG>, the VMM <NUM> may, for instance, control the first MSD <NUM> to provide torque to the wheel <NUM> in a first mode of operation, to control the second MSD <NUM>' to provide torque to the wheel <NUM> in a second mode of operation which is different from the first mode of operation, and to control the third MSD <NUM>" to provide torque to the wheel <NUM> in either the second or a third mode of operation which is different from both the first and the second modes of operation. The first MSD <NUM> and at least one of the second MSD <NUM>' and the third MSD <NUM>" may, at least temporarily, be controlled to provide torque simultaneously.

As already explained above, other configurations than the ones illustrated in <FIG> and <FIG> are of course conceivable, such as a configuration which includes an MSD in the form of an ICE.

The first mode of operation may be a speed control mode. Thus, in the example in <FIG>, the VMM <NUM> may thus send a wheel speed request to the first MSD <NUM> for controlling the rotational speed of the wheel <NUM>. Similarly, in the example in <FIG>, the VMM <NUM> may send a wheel speed request to the first MSD <NUM>. As already mentioned, although the first MSD <NUM> has been illustrated as an electric machine, in other exemplary embodiments it could be an ICE or a brake actuator. For instance, the VMM <NUM> may send a wheel speed request, e.g. via the WEM <NUM>, so as to control the rotational speed of the wheel <NUM> by means of a friction brake. In the case of the first MSD being an electric machine or an ICE, the VMM <NUM> may send either a wheel speed request of a machine speed request. A machine speed request may be used for controlling the rotational speed of the first MSD <NUM>. As explained previously in this disclosure, a control loop based on the machine speed may be more stable than a control loop based on the wheel speed.

The second mode of operation may, in at least some exemplary embodiments, be a torque control mode, wherein the VMM <NUM> sends a torque request to the second MSD <NUM>, <NUM>' (such as via the WEM <NUM>) for controlling the torque of the second MSD <NUM>, <NUM>'. For instance, in <FIG>, in which the second MSD <NUM> is illustrated in the form of a brake actuator, the brake actuator may be controlled to apply a certain torque to the wheel <NUM> (rather than controlled to obtain a certain wheel speed as discussed in the previous paragraph). In the case of the second MSD <NUM>' being an electric machine such as in <FIG> (or an ICE), the control parameter is the torque provided by the electric machine (rather than the rotational speed discussed in the previous paragraph).

The above explained examples are only a few ways in which fighting between MSDs may be avoided, by implementing the present inventive concept. Others being readily conceivable for the skilled person within the scope of the inventive concept.

For the above mentioned control of the rotational wheel speed or the control of rotational machine speed, a tyre model <NUM> may suitably be used, such as exemplified in <FIG>. As explained, the tyre of the wheel <NUM> may suitably be provided with a tyre model <NUM>, in which tyre model longitudinal tyre force Fx is represented as at least a function of longitudinal wheel slip A being dependent on rotational speed of the wheel and velocity of the vehicle.

<FIG> illustrates an example of a tyre model <NUM> in which tyre forces are represented as a function of longitudinal wheel slip. The longitudinal tyre force Fx is illustrated by the unbroken curve, while the lateral tyre force Fy is illustrated by the dashed curve. It should be noted that in this connection, longitudinal refers to a radial direction of the wheel <NUM>, specifically the radial direction which is parallel to the road surface and along which the wheel <NUM> is heading under normal conditions. The term lateral refers to a direction which is parallel to the wheel rotational axis. The longitudinal slip ratio, or simply longitudinal wheel slip, λ, is unitless, and may be expressed as: <MAT> where R is the wheel radius in meters, ω is the angular velocity of the wheel, and vx, is the longitudinal speed of the wheel (in the coordinate system of the wheel). Thus, A is bounded between -<NUM> and <NUM> and quantifies how much the wheel is slipping with respect to the road surface. During braking, vx > Rω, and thus the wheel slip is negative. During acceleration, vx < Rω, and thus the wheel slip is positive. The VMM <NUM> may maintain/obtain information on vx, (in the reference frame of the wheel), while the speed sensor <NUM> may be used to determine ω.

The VMM <NUM> may convert the received wheel torque request to a wheel rotational speed request based on the tyre model <NUM> stored in the data storage <NUM>. In some exemplary embodiments, the VMM <NUM> may initially only control the first MSD <NUM>, such that a rotational speed of the wheel <NUM> corresponding to the wheel rotational speed request is obtained, or such that the achieved rotational speed on the first MSD 116bdoes not reach the wheel rotational speed request and the applied torque is below a specified torque limit. Thus, initially only the first MSD <NUM> is controlled to provide torque to the wheel <NUM> in a first mode of operation. The second MSD <NUM>, <NUM>' is initially not controlled to provide torque to the wheel <NUM> in the second mode of operation.

The VMM <NUM> may then summarize the values of a selected control parameter present at the MSDs <NUM>, <NUM>, <NUM>', <NUM>" to obtain a summed value. Thus, in the example in <FIG> the values of the selected control parameter present at the first MSD <NUM> and the second MSD <NUM> are summed, while in the example in <FIG> the values of the selected control parameter present at the first MSD <NUM>, the second MSD <NUM>' and the third MSD <NUM>" are summed. The selected control parameter may, for instance, be the torques that are currently present at the different MSDs, or the selected parameter may, for instance, be the powers that are currently delivered by the different MSDs.

The VMM <NUM> may then divide the summed value between all the MSDs (i.e. in <FIG> between the first MSD <NUM> and the second MSD <NUM>; and in <FIG> between the first MSD <NUM>, the second MSD <NUM>' and the third MSD <NUM>") based on a desired value split. Thus, in the case of the selected control parameter being torque, then the division may be based on a desired torque split. In the case of the selected control parameter being power, then the division may be based on a desired power split. The VMM <NUM> may thus, based on the desired value split, assign a share of the summed value to the second MSD <NUM> (in <FIG>); or assign one share of the summed value to the second MSD <NUM>' and another share of the summed value to the third MSD <NUM>" (<FIG>). Having assigned a share to the second MSD <NUM>, <NUM>' (and third MSD <NUM>"), the VMM <NUM> may send a parameter request to the second MSD <NUM>, <NUM>' (and third MSD <NUM>") corresponding to its share of the summed value, while the first MSD <NUM> remains controlled in speed control mode. In case of the selected control parameter being torque, the parameter request may be a torque request. In case of the selected control parameter being power, the parameter request may be a power request.

Thus, according to the above, the VMM <NUM> may use a tyre model <NUM> to control the first MSD <NUM> to operate in a first mode of operation, namely in a speed control mode, and to calculate a parameter request based on current values of a selected control parameter present at the MSDs <NUM>, <NUM>, <NUM>', <NUM>", to control the second MSD <NUM>, <NUM>' (and third MSD <NUM>") in a second (and possibly a third) mode of operation. In this way, the first MSD <NUM> will be the master, which is used for setting the conditions for the other MSD(s) <NUM>, <NUM>' (<NUM>"), the slave(s), the control of the slave MSD(s) being dependent on its/their share of the summed value, which in turn is dependent on the torque applied to the wheel <NUM> by the first MSD <NUM> resulting from the speed control mode.

After a period of time, when the system has stabilized again, then the VMM <NUM> may repeat the sequence of summarizing the values, dividing the summed values, and sending a parameter request to the second MSD <NUM>, <NUM>' (and third MSD <NUM>").

In other exemplary embodiments, the VMM <NUM> may divide the value of the received wheel torque request between the first MSD <NUM> and the second MSD <NUM> based on a desired torque split (<FIG>), or between the first MSD <NUM>, the second MSD <NUM>' and the third MSD <NUM>" (<FIG>). The second mode of operation may in such cases be a torque control mode. Similarly, if the third MSD <NUM>" in <FIG> is operated in a third mode of operation, it may also be a torque control mode. In either case, the VMM <NUM> may send a torque request to the second MSD <NUM>, <NUM>' (and to the third MSD <NUM>"). Thus, in contrast to the previous example above, the second and third MSDs <NUM>, <NUM>', <NUM>" do not need to wait for the first MSD <NUM> to be controlled before they receive their shared value. Instead the second and third MSDs <NUM>, <NUM>', <NUM>" may be assigned their share independently of the first MSD <NUM>. The VMM <NUM> may therefore send a machine speed request to the first MSD <NUM> (speed control mode), which is selected based on the tyre model <NUM> such that the total value of the received wheel torque request is obtained. Thus, in this example, the first MSD <NUM> may be regarded as slave to the second (and third) MSD(s) <NUM>, <NUM>', <NUM>". In the case of <FIG>, when the wheel torque request is received by the VMM <NUM>, the capability of the electric machine (first MSD <NUM>) may be taken and subtracted from the total wheel torque request. The VMM <NUM> may send the remaining torque as a torque request to the brake actuator (second MSD <NUM>). To the electric machine (first MSD <NUM>), the VMM <NUM> may send the speed request corresponding to the wheel slip A (corresponding to the total torque, via the tyre model <NUM>).

The above are some examples of how fighting between MSDs may be avoided by having one MSD <NUM> in speed control mode, and the other MSD(s) <NUM>, <NUM>', <NUM>" in a different control mode such as a torque control mode. However, the first and second (and third) modes of operation may also be differentiated by different speed control modes. Thus, the VMM <NUM> may in at least some exemplary embodiments configure the first MSD <NUM> as a high bandwidth MSD having relatively short response time control loop and configuring the other MSD(s) <NUM>, <NUM>', <NUM>" as low bandwidth MSD(s) having relatively long response time control loop(s). Furthermore, the first MSD <NUM> may be configured with a relatively tight deadzone allowing the rotational speed of the first MSD <NUM> to deviate from the requested rotational speed by a relatively small value before correcting the rotational speed, and configuring the other MSD(s) <NUM>, <NUM>', <NUM>" with a relatively large deadzone allowing the rotational speed of the other MSD(s) <NUM>, <NUM>', <NUM>" to deviate from the requested speed by a relatively large value before correcting the rotational speed. By this differentiation in different modes of operation, i.e. different speed control modes, fighting between the MSDs may be avoided. Suitably, in the example of <FIG>, the third MSD <NUM>" is not only differentiated from the first MSD <NUM> as regards bandwidth and/or deadzone, but is also differentiated from the second MSD <NUM>'.

<FIG> schematically illustrates a method <NUM> according to at least one exemplary embodiment of the invention. Thus, there is provided a method <NUM> for controlling wheel slip of a vehicle, wherein the vehicle comprises at least a first and a second motion support device, MSD, for providing torque to a common wheel of the vehicle,
the method comprising:.

As can be readily understood from the previous discussions, in some exemplary embodiments step S2 may be initiated before step S3, in other exemplary embodiments step S3 may be initiated before step S2, and in further exemplary embodiments, steps S2 and S3 may be initiated simultaneously.

<FIG> schematically illustrates a control unit <NUM> according to at least one exemplary embodiment of the invention. In particular, <FIG> illustrates, in terms of a number of functional units, the components of a control unit <NUM> according to exemplary embodiments of the discussions herein. The control unit <NUM> may be comprised in the vehicle <NUM>, e.g. in the form of a VMM unit. Processing circuitry <NUM> may be 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.

Particularly, the processing circuitry <NUM> is configured to cause the control unit <NUM> to perform a set of operations, or steps, such as the method discussed in connection to <FIG> and exemplary embodiments thereof discussed throughout this disclosure. Thus, the processing circuitry <NUM> is thereby arranged to execute exemplary methods as herein disclosed.

The control unit may <NUM> further comprise an interface <NUM> for communications with at least one external device such as other controller(s) providing inputs/requests. As such, the interface <NUM> may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of ports for wireline or wireless communication.

Claim 1:
A method (<NUM>) for controlling wheel slip of a vehicle (<NUM>), wherein the vehicle comprises at least a first and a second motion support device, MSD (<NUM>, <NUM>, <NUM>', <NUM>", <NUM>, <NUM>, <NUM>, <NUM>), for providing torque to a common wheel (<NUM>) of the vehicle,
the method comprising:
receiving a wheel torque request,
based on the received wheel torque request:
• controlling the first MSD (<NUM>) to provide torque to the wheel in a first mode of operation,
• controlling the second MSD (<NUM>, <NUM>') to provide torque to the wheel in a second mode of operation which is different from the first mode of operation,
wherein said controlling of the first MSD and said controlling of the second MSD are, at least temporarily, performed simultaneously,
wherein said first mode of operation is a speed control mode, wherein the method comprises sending a wheel speed request to the first MSD (<NUM>) for controlling the rotational speed of the wheel (<NUM>),
wherein said second mode of operation is a torque control mode, wherein the method comprises sending a torque request to the second MSD (<NUM>, <NUM>') for controlling the torque of the second MSD (<NUM>, <NUM>').