A computer system and a computer -implemented method for controlling an articulated tractor-trailer combination

Abstract

A computer system for controlling an articulated tractor-trailer combination, the computer system comprising processing circuitry configured to determine, based on a received brake request and an estimated value of the road friction (µest), a brake force distribution between motor or engine braking of the tractor, and service braking of the trailer. The processing circuitry is configured to control a torque (Tqtractor) to be applied by the motor or engine in accordance with the determined brake force distribution, determine, independently of the estimated value of the road friction (µest), a longitudinal wheel slip limit for wheels of said drive axle, translate the determined longitudinal wheel slip limit to a wheel speed limit for said wheels of said drive axle of the tractor. If the wheel speed of the wheels of said drive axle have reached a speed value below the wheel speed limit, then the motor or engine is controlled so that the wheel speed is returned to a speed value above the wheel speed limit.

Description

A COMPUTER SYSTEM AND A COMPUTER -IMPLEMENTED METHOD FOR CONTROLLING AN ARTICULATED TRACTORTRAILER COMBINATIONTECHNICAL FIELD[1] The disclosure relates generally to articulated tractor-trailer combinations. In particular aspects, the disclosure relates to a computer system and a computer-implemented method for controlling an articulated tractor-trailer combination. The disclosure also relates to a heavy-duty vehicle comprising such a computer system. The disclosure further relates to a computer program product and a non-transitory computer-readable storage medium, by means of which said computer-implemented method may be performed. The disclosure can be applied to various different heavy-duty vehicles. For instance, in an articulated tractortrailer combination to which the disclosure is applied, the tractor may be in the form of a truck, bus, or construction equipment, among other vehicle types. Although the disclosure may be described with respect to a particular vehicle, the disclosure is not restricted to any particular vehicle.BACKGROUND[2] Many heavy-duty vehicles are provided with one or more safety systems such as electronic stability control (ESC) and / or anti-lock braking system (ABS). For tractor-trailer combinations, regenerative braking of the drive axle of the tractor may cause lateral instability during slippery driving situations. This may therefore cause the ESC and / or ABS systems to become activated, resulting in a less predictable behaviour of the vehicle from a driver perspective. This may lead to less recuperated energy, not only due to the ESC / ABS interventions, but also because the driver may decide to simply disable the regenerative braking functionality.SUMMARY[3] According to a first aspect of the disclosure, there is provided a computer system for controlling an articulated tractor-trailer combination, the computer system comprising processing circuitry configured to:- receive a brake request,- determine or receive an estimated value of the road friction (piest) relative to at least one tire of a drive axle of the tractor,- determine, based on the received brake request and the estimated value of the road friction (jiest), a brake force distribution between: i) motor or engine braking of the tractor, and ii) service braking of the trailer,- control a torque (Tqtmctor) to be applied by the motor or engine in accordance with the determined brake force distribution,- determine, independently of the estimated value of the road friction (jiest), a longitudinal wheel slip limit for wheels of said drive axle,- translate the determined longitudinal wheel slip limit to a wheel speed limit for said wheels of said drive axle of the tractor, and wherein upon determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, the processing circuitry is configured to control the motor or engine so that the wheel speed of the wheels of said drive axle is returned to a speed value above the wheel speed limit.The first aspect of the disclosure may, in general terms, seek to improve the conditions for regenerating energy in a tractor-trailer combination. In particular the first aspect of the disclosure may seek to solve the occasional conflicting problem of regenerative braking at the cost of lateral instability during slipper driving situations. A technical benefit may include that, by combining a brake force distribution based on estimated available friction force with wheel slip-based “safety net” limits, regenerative braking is enabled while maintaining satisfactory lateral stability.[4] Thus, by determining a preliminary brake force distribution based on an estimated value of the road friction, the risk of lateral instability may be reduced. However, in case the friction force is not sufficiently well estimated, the “safety net” provided by the defined wheel slip limits may be used for correction in order to further reduce the risk of lateral instability. Hereby, the advantage of regenerative braking may be maintained while reducing the risk of lateral instability.[5] It should be noted that, even though the teachings of the present disclosure may advantageously be implemented for a battery electric vehicle in connection with regenerative braking, other implementations are also conceivable. For instance, the teachings of the present disclosure may be implemented in connection with engine braking of a vehicle propelled by an internal combustion engine.[6] The torque (Tqtractor) controlled to be applied by the motor or engine of the heavy- duty vehicle may be a first torque. The processing circuitry may control a second torque to be applied to the trailer, in order to achieve the determined brake force distribution between the motor or engine braking of the tractor on the one hand, and the service braking of the trailer on the other hand.[7] The longitudinal wheel slip limit for the wheels of the drive axle may be determined in various conceivable manner. Parameters that may be taken into account for defining the longitudinal wheel slip limit include the mass of the trailer, the mass of the tractor, the load carried by the tractor-trailer combination, the speed of the tractor-trailer combination, the inclination of the road on which the tractor-trailer combination is travelling. Furthermore, the longitudinal wheel slip limit may suitably be dynamically changed based on an estimated lateral force (Fyest). For instance, if the tractor is under heavy steering, for example when driving through a curve, then the lateral force (Fyest) may increase, and therefore the magnitude of (in absolute numbers) the longitudinal wheel slip limit may suitably be reduced. Another example may be when the vehicle is driving in a downhill slope, especially in a curve so that the trailer is pushing from behind in an angle. The trailer may then be pushing the tractor from behind, increasing the risk of lateral instability and therefore the magnitude of the longitudinal wheel slip limit may suitably be reduced.[8] Any tyre may have a certain tyre model in which tyre forces are represented as a function of longitudinal wheel slip. It should be noted that in this connection, longitudinal refers to a radial direction of the wheel, specifically the radial direction which is parallel to the road surface and along which the wheel is heading under normal conditions. The longitudinal slip ratio, or simply longitudinal wheel slip, A, is unitless, and may be expressed as:where R is the wheel radius in meters, co is the angular velocity of the wheel, and vx, is the longitudinal speed of the wheel (in the coordinate system of the wheel). In practice vxmay for example be found by using sensors measuring non-driven wheel speeds. Thus, A is bounded between -1 and 1 and quantifies how much the wheel is slipping with respect to the road surface. During braking, vx> Rco, and thus the wheel slip is negative. During acceleration, vx< Rco, and thus the wheel slip is positive. The processing circuitry may obtain information on vx, (in the reference frame of the wheel), while a wheel speed sensor may be used to determine co.[9] In a tyre model, the longitudinal tyre force Fxhas an initial steep rise from zero up to a maximum of the curve. Although the rise is not perfectly constant it may be approximated by a gradient. The part of the curve where the steep rising is interrupted is the slip limit. In other words, past the slip limit, a higher angular velocity will not result in much higher longitudinal force. Thus, by controlling an electric machine to perform regenerative braking to the wheel slip limit (i.e. to the limit where it provides a desired effect), an efficient energy recovery may be achieved without compromising on the provision of an adequate braking force (negative torque). Thus, rather than passing the wheel slip limit, which would only increase the wheel slip without providing any additional braking force, other brake actuators, such as service brakes on the trailer may then be applied for further reducing the speed of the heavy-duty vehicle. Reduced longitudinal wheel slip also allows for higher lateral force. With high long wheel slip, there may be lateral instability.

[0010] The road friction (pest) may, for example, be determined using any known procedure, such as using a sensor (such as a camera) for monitoring the condition of the ground on which the tractor is travelling.

[0011] Optionally in some examples, including in at least one preferred example, the processing circuitry may further be configured to:- based on the estimated value of the road friction (gest), determine a road friction force, and- determine said brake force distribution so that the brake force on the drive axle of the tractor is limited to not exceed said road friction force. A technical benefit may include that this reduces the risk of applying too much force on the drive axle which could result in lateral instability.

[0012] Optionally in some examples, including in at least one preferred example, said brake request may be generated by a driver of the tractor releasing the accelerator pedal. Atechnical benefit may include that such a brake request may suitably be used in relation to regenerative braking of the tractor, for example when running downhill, in order to ensure that a relatively large amount of energy is regenerated when retardation of the tractor-trailer combination is requested.

[0013] Optionally in some examples, including in at least one preferred example, said brake request may be a pure regenerative brake request or a pure engine brake request. A pure regenerative brake request may advantageously be implemented for battery electric vehicles (BEV). A pure engine brake request may advantageously be implemented for an internal combustion engine (ICE) vehicle, in particular a diesel vehicle.

[0014] Optionally in some examples, including in at least one preferred example, said brake request may be configured to receive said estimated value of the road friction (pest) from a friction estimator device, wherein, upon said determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, the processing circuitry is further configured to send a feedback message to the friction estimator device to enable the friction estimator device to update said estimated value of the road friction (gest). A technical benefit may include that in this way the estimation may be improved for future brake requests, and thus the risk of lateral instability may be further reduced.

[0015] The updating of the estimated value may, in some examples, be implemented by adaptation of a global self-learning model (e.g. machine learning algorithm). The global selflearning model may be updated in order to improve the correlation between future friction estimations and desired wheel speed values (i.e. above the wheel speed limit) based on such future friction estimations.

[0016] Optionally in some examples, including in at least one preferred example, the computer system may further comprise said friction estimator device. A technical benefit may include that the computer system can conveniently update the friction estimator device, as has for example been discussed above, or as will be further discussed below. The friction estimator device may, for example, be or include a camera-based device for classifying the road surface. In some examples, the friction estimator device may be or include a processor which executes an algorithm that uses wheel forces, loads, etc.

[0017] Optionally in some examples, including in at least one preferred example, said friction estimator device may be configured to reset or override the updated estimated valueof the road friction (|iest) based on one of:- a calculation by the friction estimator device resulting in an estimation deviating from the updated estimated value by at least a predetermined amount,- a predefined time period having elapsed since the estimated value was updated,- wheel slip values determined for tractor during propulsion, wherein the wheel slip values exceed a predetermined sliding threshold,- wheel slip values on drive axle determined during braking, wherein the wheel slip values exceed a predetermined sliding threshold,- wheel slip values determined for trailer, wherein the wheel slip values exceed a predetermined sliding threshold.A technical benefit may include that, because the estimated value may have been updated based on certain temporary conditions, which may no longer be valid, the friction estimator device may suitably reset or override the updated estimated value to better reflect current conditions.

[0018] Optionally in some examples, including in at least one preferred example, the friction estimator device may be configured to update said estimated value of the road friction (piest) based on feedback data received from detected ABS (Anti-lock Braking System) control. A technical benefit may include that the updating of the estimated value is based on a more holistic approach, enabling an even more accurate updating of the estimated value.

[0019] Optionally in some examples, including in at least one preferred example, the friction estimator device may be configured to calculate said estimated value of the road friction (pest) based on information about a longitudinal tire force (Fx) and a drive axle load force (Fz). A technical benefit may include that values of these forces may be conveniently obtained. The longitudinal tire force Fxmay be obtained from the motor torque status, which can be converted to the longitudinal tire force Fx. The drive axle load force Fzcan be obtained by a load sensor. The processing circuitry may thus be configured to receive information about the forces Fxand Fz. Suitably, wheel slip control may be used as a trigger for friction estimation calculation based on Fx / Fz. In other words, when the wheel speed of the drive axle is controlled to return to the speed value above the wheel speed limit (as discussed above), such wheel slip control may suitably be used to trigger a friction estimation calculation, and possibly an updating of the previously estimated value if the friction estimation calculation provides a result which deviates from the previously estimated value by a predefined amount.

[0020] Optionally in some examples, including in at least one preferred example, said estimated value of the road friction (pest) is selected from one of a plurality of predetermined discrete values. A technical benefit may include that an estimated value may be provided in a simple manner. Another benefit may include that, in case a friction estimator device is unavailable, a friction estimation may still be made, although possibly less accurate.

[0021] Optionally in some examples, including in at least one preferred example, each one of said predetermined discrete values is associated with a respective road or environmental condition, such as dry asphalt road, wet asphalt road, snowy road, icy road, etc. Such conditions may be detected by different sensors as known in the art. For instance, thermal IR detectors or acoustic sensors may be used for detecting wet asphalt; ice sensors; temperature sensors, etc may be implemented for determining the different road and / or environmental conditions. A technical benefit may include that such easily identifiable conditions may be used for determining an associated estimated value. The number of discrete values may be appropriately selected. For instance, in some examples the discrete values could be: p = { 1, 0.7, 0.5, 0.3, 0.1 }The processing circuity may, for instance, use an algorithm which starts by assuming p = 1. In case of a need for wheel slip control intervention (controlling the wheel speed to return to a speed value above the wheel speed limit), then the processing circuitry may shift to p = 0.7. If there is again a wheel slip control intervention, then there may be another shift to p = 0.5, and so on. This is, of course, just one illustrative example of how the updates of discrete estimated values may be provided. Another example would, for instance, to make an initial guess by the processing circuitry based on the ambient temperature. In order to avoid getting stuck with a low friction estimate, which implies restrictive regenerative brake force limits, the friction estimation could be moved up by resetting or overriding the estimated value as discussed above.

[0022] Optionally in some examples, including in at least one preferred example, upon said determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, the processing circuitry is further configured to cause the currently selected predetermined discrete value to be updated to another one of said predetermined discrete values. A technical benefit may include, that although a predetermined or limited number ofdiscrete values are available for providing an estimated value of the road friction (pest), the value selection may be repeatedly executed and updated, for example allowing the processing circuitry to operate in accordance with one of the above examples (or in accordance with any other appropriate updating strategies).

[0023] According to a second aspect of the disclosure, there is provided a heavy-duty vehicle in the form of an articulated tractor-trailer combination, the heavy-duty vehicle comprising the computer system of the first aspect, including any examples thereof. The second aspect of the disclosure may seek to address the corresponding matters as discussed in relation to the first aspect. Furthermore, technical benefits of the second aspect may largely correspond to those discussed in relation to the first aspect, including any examples thereof.

[0024] According to a third aspect of the disclosure, there is provided a computer- implemented method for controlling an articulated tractor-trailer combination, the method comprising:- receiving, by processing circuitry of a computer system, a brake request,- determining or receiving, by the processing circuitry, an estimated value of the road friction (pest) relati ve to at least one tire of a drive axle of the tractor,- determining, by the processing circuitry, based on the received brake request and the estimated value of the road friction (pest), a brake force distribution between: i) motor or engine braking of the tractor, and

[0025] ii) service braking of the trailer,- controlling, by the processing circuitry, a torque (Tqtractor) to be applied by the motor or engine in accordance with the determined brake force distribution,- determining, by the processing circuitry, independently of the estimated value of the road friction (pest), a longitudinal wheel slip limit for wheels of said drive axle,- translating, by the processing circuitry, the determined longitudinal wheel slip limit to a wheel speed limit for said wheels of said drive axle of the tractor, and- upon determination that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, controlling, by the processing circuitry, the motor or engine so that the wheel speed of the wheels of said drive axle is returned to a speed value above the wheel speed limit.The third aspect of the disclosure may seek to address the corresponding matters as discussedin relation to the first aspect. Furthermore, technical benefits of the third aspect may largely correspond to those discussed in relation to the first aspect, including any examples thereof.

[0026] In the following, a number of examples of the computer-implemented method of the third aspect are listed. The examples correspond to respective examples of the computer system of the first aspect. Technical benefits and variations discussed above in relation to the first aspect may therefore also be applicable to the respective examples of the third aspect.

[0027] Optionally in some examples, including in at least one preferred example, the method may further comprise:- based on the estimated value of the road friction (pest), determining, by the processing circuitry, a road friction force, and- determining, by the processing circuitry, said brake force distribution so that the brake force on the drive axle of the tractor is limited to not exceed said road friction force

[0028] Optionally in some examples, including in at least one preferred example, said brake request may be generated by a driver of the tractor releasing the accelerator pedal.

[0029] Optionally in some examples, including in at least one preferred example, said brake request may be a pure regenerative brake request or a pure ending brake request.

[0030] Optionally in some examples, including in at least one preferred example, may further comprise:- receiving, by the processing circuitry, said estimated value of the road friction (pest) from a friction estimator device, and- upon said determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, sending, by the processing circuitry, a feedback message to the friction estimator device to enable the friction estimator device to update said estimated value of the road friction (gest).

[0031] Optionally in some examples, including in at least one preferred example, the method may further comprise:- controlling, by the processing circuitry, said friction estimator device to reset or override the updated estimated value of the road friction (pest) based on one of:- a calculation by the friction estimator device resulting in an estimation deviating from the updated estimated value by at least a predetermined amount,- a predefined time period having elapsed since the estimated value was updated,- wheel slip values determined for tractor during propulsion, wherein the wheel slip values exceed a predetermined sliding threshold,- wheel slip values on drive axle determined during braking, wherein the wheel slip values exceed a predetermined sliding threshold,- wheel slip values determined for trailer, wherein the wheel slip values exceed a predetermined sliding threshold.

[0032] Optionally in some examples, including in at least one preferred example, the method may further comprise:- controlling, by the processing circuitry, the friction estimator device to update said estimated value of the road friction (pest) based on feedback data received from detected ABS (Anti-lock Braking System) control.

[0033] Optionally in some examples, including in at least one preferred example, the method may further comprise:- controlling, by the processing circuitry, the friction estimator device to calculate said estimated value of the road friction (pest) based on information about a longitudinal tire force (Fx) and a drive axle load force (Fz).

[0034] Optionally in some examples, including in at least one preferred example, said estimated value of the road friction (pest) is selected from one of a plurality of predetermined discrete values.

[0035] Optionally in some examples, including in at least one preferred example, each one of said predetermined discrete values is associated with a respective road or environmental condition, such as dry asphalt road, wet asphalt road, snowy road, icy road.

[0036] Optionally in some examples, including in at least one preferred example, the method may further comprise:- upon said determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, causing, by the processing circuitry, the currently selected predetermined value to be updated to another one of said predetermined values.

[0037] According to a fourth aspect of the disclosure, there is provided a computer program product comprising program code for performing, when executed by the processing circuitry, the method of the third aspect, including any examples thereof.

[0038] According to a fifth aspect of the disclosure, there is provided non-transitory computer-readable storage medium comprising instructions, which when executed by the processing circuitry, cause the processing circuitry to perform the method of the third aspect, including any examples thereof.

[0039] The disclosed aspects, examples (including any preferred examples), and / or accompanying claims may be suitably combined with each other as would be apparent to anyone of ordinary skill in the art. Additional features and advantages are disclosed in the following description, claims, and drawings, and in part will be readily apparent therefrom to those skilled in the art or recognized by practicing the disclosure as described herein.

[0040] There are also disclosed herein computer systems, control units, code modules, computer-implemented methods, computer readable media, and computer program products associated with the above discussed technical benefits.BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Examples are described in more detail below with reference to the appended drawings.

[0042] FIG. 1 schematically illustrates a heavy-duty vehicle according to one example of this disclosure.

[0043] FIG. 2 is a block diagram illustrating an implementation according to one example of this disclosure.

[0044] FIG. 3 is a block diagram illustrating an implementation according to another example of this disclosure.

[0045] FIG. 4 is a block diagram illustrating an implementation according to yet another example of this disclosure.

[0046] FIG. 5 is a block diagram illustrating the general teachings of this disclosure, in accordance with a further example.

[0047] FIG. 6 is a flow chart of an exemplary method of controlling an articulated tractor-trailer combination, in accordance with one example of this disclosure.

[0048] FIG. 7 is a flow chart of other exemplary methods of this disclosure.

[0049] FIG. 8 is a schematic diagram of an exemplary computer system for implementing examples disclosed herein, according to an example.DETAILED DESCRIPTION

[0050] The detailed description set forth below provides information and examples of the disclosed technology with sufficient detail to enable those skilled in the art to practice the disclosure.

[0051] The present disclosure solves problems related to energy recuperation in heavy- duty vehicles. As explained previously in this disclosure, a problem that may occur during regenerative braking of a drive axle of a tractor in a tractor-trailer combination is that this may cause lateral instability during slippery driving situations, which in turn may result in less predictable behaviour (from a driver’s perspective) due to ESC and / or ABS systems becoming activated. This may lead to less recuperated energy, not only due to the ESC / ABS interventions, but also because the driver may decide to simply disable the regenerative braking functionality. However, according to this disclosure, regenerative braking is enabled while maintaining satisfactory lateral stability because a brake force distribution, based on estimated available friction force, is combined with wheel slip-based control (the latter part of the combination thus presenting a “safety net” functionality).

[0052] FIG. 1 schematically illustrates a vehicle 1 according to one example of this disclosure. More specifically, the illustrated vehicle l is a heavy-duty vehicle combination which comprises an articulated tractor-trailer combination. Thus, the heavy-duty vehicle includes a tractor 2 pulling a trailer 4. The tractor 2 has three wheel axles 6, 8, 10, each one of the wheel axles 6, 8, 10 having at least one left wheel and at least one right wheel. In this example, the tractor 2 has a front axle 6 and two rear axles 8, 10. One of the rear axles 8, 10 may be a lift axle. It should be understood that the teachings of this disclosure may also be implemented for vehicles without any lift axle. Additionally, the teachings of the present disclosure are not limited to a particular vehicle propulsion system, i.e., the teachings herein may be implemented for vehicles propelled by electric motors (such as battery electric vehicles, BEV), or vehicle propelled by internal combustion engines, fuel cells, hybrid systems, etc. Furthermore, the teachings of the present disclosure may be implemented for driver-operated vehicles and for autonomous (self-driving) vehicles. In, for example the case of a BEV, the propulsion system may comprise a single electric motor or several electric motors. For instance, one or more electric motors may be arranged at the hub of a wheel.

[0053] In the illustration in FIG. 1, the longitudinal direction (X) is in the right-to-left direction (or vice versa). In other words, when the heavy-duty vehicle is driving forwardly or reversing along a straight road segment, it will be travelling in the longitudinal direction (X). The vertical direction (Z) is generally a direction perpendicular to the ground on which the vehicle stands. The lateral direction (F) is perpendicular to the geometrical plane of the drawing figure, and thus perpendicular to the longitudinal direction (X) and the vertical direction (Z). The longitudinal direction (X) may also be referred to as a direction coinciding or being parallel with the roll axis of the vehicle, the lateral direction (F) may also be referred to as a direction coinciding or being parallel with the pitch axis, and the vertical direction (Z) may also be referred to as a direction coinciding or being parallel with the yaw axis.

[0054] FIG. 2 is a block diagram illustrating an implementation according to one example of this disclosure. Three main blocks are illustrated in FIG. 2. A first main block 20 represents the braking hardware of the tractor-trailer combination. Within the first main block 20 there is represented a trailer service brake 22 and a motor 24 of a drive axle of the tractor. A second main block 30 represents a first function of a processing circuitry for safe and regenerative brake force distribution. Within the second main block 30 there is a torque limit estimation block 32 and a brake force distribution block 34. A third main block 40 represents a safety net function of the processing circuitry. Within the third main block 40 there is a longitudinal wheel slip limit generation block 42 and a wheel slip control block 44.

[0055] FIG. 2 illustrates an example of how a processing circuitry of a computer system may be used for controlling a tractor-trailer combination. In particular, the processing circuitry is configured to receive a brake request Fxreq. The brake request Fxreqmay, for example, be a pure regenerative brake request, or it may be generated by a driver of the tractor releasing the accelerator pedal. In this example, the brake request Fxreqis received by the brake force distribution block 34. The processing circuitry may also be configured to receive an estimated value of the road friction / j.est relative to at least one tire of a drive axle of the tractor. In this example, the estimated value of the road frictionest is received by the torque limit estimation block 32.

[0056] As illustrated in FIG. 2, the estimated value of the road friction .est may suitably be provided to the torque limit estimation block 32, which based on the estimated value determines brake torque limit for brake force distribution on the drive axle. In FIG. 2, this is illustrated by a torque limit Tqjtmbeing provided from the torque limit estimation block 32 tothe brake force distribution block 34. Other input parameters that the processing circuitry may take into account, (and as illustrated here as inputs to the torque limit estimation block 32) may include an estimated lateral force Fyest and a vertical drive axle load force Fz. For instance, if the tractor is under heavy steering, for example when driving through a curve, then the lateral force Fyest may increase, and therefore the allowable torque range provided to the brake force distribution block 34 may be dynamically changed.

[0057] Based on the received brake request Fxreqand the estimated value of the road frictionest, the processing circuitry determines a brake force distribution between the motor braking of the tractor and service braking of the trailer. In particular, the processing circuitry is configured to control a torque to be applied by the motor in accordance with the determined brake force distribution. This is illustrated by a torque command Tqtractor being sent from the brake force distribution block 34 to the motor 24 of the drive axle of the tractor. Furthermore, FIG. 2 illustrates that a torque command Trailer is sent from the brake force distribution block 34 to the trailer service brakes 22. Hereby the brake force is distributed by providing braking torque to the tractor on the one hand, and to the trailer on the other hand.

[0058] The processing circuitry is further configured to use its safety net function in the third main block 40, including slip limit generation block 42 and the wheel slip control block 44 therein. In particular, the processing circuitry is configured to determine, independently of the estimated value of the road frictionest, a longitudinal wheel slip limit for wheels of said drive axle. This is illustrated in FIG. 2 by using the longitudinal tire force Fxwheei (i. e. , not the brake request Fxreqwhich is also a value in the longitudinal direction), the estimated lateral force FyeSt and the vertical drive axle load force Fzas input to the slip limit generation block 42. Based on these pieces of input the processing circuitry may determine a longitudinal wheel slip limit. This is illustrated by a longitudinal wheel slip value Slipxiimbeing provided from the slip limit generation block 42 to the wheel slip control block 44. The processing circuitry is further configured to translate the determined longitudinal wheel slip limit to a wheel speed limit for the wheels of the drive axle of the tractor. This is illustrated by a speed value Speedhm being provided from the wheel slip control block 44 to the motor 24 of the drive axle of the tractor.

[0059] If the processing circuitry determines that the applied torque Tqtractor to the motor 24 of the drive axle of the tractor has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, the processing circuitry is configured tocontrol the motor 24 so that the wheel speed of the wheels of said drive axle is returned to a speed value above the wheel speed limit. Functionally, this control would be associated with the wheel slip control block 44 in FIG. 2. Hereby, although a good lateral stability may be achievable by the second main block 30 controlling the brake force distribution based on an estimated value of the road frictionest, the additional functionality of the safety net provided by the third main block 40 improves the possibilities of good lateral stability even more. Thus, the teachings of this disclosure allow for the possibility of good regenerative braking without compromising on lateral stability.

[0060] FIG. 3 is a block diagram illustrating an implementation according to another example of this disclosure. FIG. 3 illustrates that the processing circuitry may be configured to receive the estimated value of the road frictionest from a friction estimator device 50. This is illustrated in FIG. 3 by the estimated value of the road frictionest being provided by the friction estimator device 50 to the torque limit estimation block 32. As further illustrated in FIG. 3, the friction estimator device 50 may be configured to calculate said estimated value of the road friction uest based on information about the longitudinal tire force Fxwheei and the vertical drive axle load force Fz.

[0061] Furthermore, as illustrated in FIG. 3, upon determination by the processing circuitry that the applied torque Tqtractor to the motor 24 of the drive axle of the tractor has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, the processing circuitry may be further configured to send a feedback message 52 to the friction estimator device 50 to enable the friction estimator device 50 to update said estimated value of the road frictionThis is illustrated in FIG. 3 by the wheel slip control block 44 providing the feedback message 52 to the friction estimator device 50. In other words, when the processing circuitry is actively performing wheel slip control to bring the wheel speed back to a speed value above the wheel speed limit, then such active controlling may trigger feedback information to the friction estimator device 50, so that also the brake force distribution can be updated based on the updated estimated value of the road friction .est.

[0062] It should be understood that, in at least some examples, the illustrated friction estimator device 50 may form part of the same computer system as the one that the processing circuitry forms part of. Furthermore, the friction estimator device 50 may beconfigured to reset or override the updated estimated value of the road friction pest as has already been described previously in this disclosure.

[0063] FIG. 4 is a block diagram illustrating an implementation according to yet another example of this disclosure. In particular, FIG. 4 illustrates that in addition to, or as an alternative to, the wheel slip control triggered feedback message 52 (as discussed in relation to FIG. 3), the friction estimator device 50 may be configured to update the estimated value of the road frictionestbased on feedback data 54 received from detected ABS (Anti-lock Braking System) control. In the example in FIG. 4, when ABS control is active on the trailer service brake 22, feedback is provided to the friction estimator device 50.

[0064] FIG. 5 is a block diagram illustrating the general teachings of this disclosure, in accordance with a further example. In particular, FIG. 5 illustrates a computer system 60 for controlling an articulated tractor-trailer combination, the computer system 60 comprising processing circuitry 70 configured to:- receive a brake request Fxreq,- determine or receive an estimated value of the road frictionest relative to at least one tire of a drive axle of the tractor,- determine, based on the received brake request and the estimated value of the road friction est, a brake force distribution between: i) motor or engine braking of the tractor, and ii) service braking of the trailer- control a torque Tqtractor to be applied by the motor or engine in accordance with the determined brake force distribution,- determine, independently of the estimated value of the road frictionest, a longitudinal wheel slip limit for wheels of said drive axle,- translate the determined longitudinal wheel slip limit to a wheel speed limit for said wheels of said drive axle of the tractor, and wherein upon determination by the processing circuitry 70 that the applied torque Tqtractor has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, the processing circuitry 70 is configured to control the motor or engine so that the wheel speed Speeds of the wheels of said drive axle is returned to a speed value above the wheel speed limit.

[0065] FIG. 6 is a flow chart of an exemplary method 100 of controlling an articulated tractor-trailer combination, in accordance with one example of this disclosure. In particular, FIG. 6 illustrates a computer-implemented method 100 for controlling an articulated tractortrailer combination, the method comprising:- receiving, (SI), by processing circuitry of a computer system, a brake request,- determining or receiving (S2), by the processing circuitry, an estimated value of the road friction relative to at least one tire of a drive axle of the tractor,- determining (S3), by the processing circuitry, based on the received brake request and the estimated value of the road friction, a brake force distribution between: i) motor or engine braking of the tractor, and ii) service braking of the trailer,- controlling (S4), by the processing circuitry, a torque to be applied by the motor or engine in accordance with the determined brake force distribution,- determining (S5), by the processing circuitry, independently of the estimated value of the road friction, a longitudinal wheel slip limit for wheels of said drive axle,- translating (S6), by the processing circuitry, the determined longitudinal wheel slip limit to a wheel speed limit for said wheels of said drive axle of the tractor, and- upon determination that the applied torque has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, controlling (S7), by the processing circuitry, the motor or engine so that the wheel speed of the wheels of said drive axle is returned to a speed value above the wheel speed limit.

[0066] FIG. 7 is a flow chart of other exemplary methods 200 of this disclosure. In particular, FIG. 7 illustrates that in addition to the acts (S1-S7) performed by the processing circuitry in FIG. 6, it is illustrated in FIG. 7 that the processing circuitry may perform one or more extra acts (SX). For instance, such extra acts (SX) may include one or more of:- determining a road friction force, and determining said brake force distribution so that the brake force on the drive axle of the tractor is limited to not exceed said road friction force;- sending a feedback message to a friction estimator device in case speed value of the wheels of the drive axle are below the wheel speed limit so as to update the estimated value of the road friction;- controlling the friction estimator device to reset or override the updated estimated value ofthe road friction,- and any other acts or functions discussed elsewhere in this disclosure.

[0067] FIG. 8 is a schematic diagram of an exemplary computer system for implementing examples disclosed herein, according to an example. FIG. 8 is a schematic diagram of a computer system 800 for implementing examples disclosed herein. The computer system 800 is adapted to execute instructions from a computer-readable medium to perform these and / or any of the functions or processing described herein. The computer system 800 may be connected (e.g., networked) to other machines in a LAN (Local Area Network), LIN (Local Interconnect Network), automotive network communication protocol (e.g., FlexRay), an intranet, an extranet, or the Internet. While only a single device is illustrated, the computer system 800 may include any collection of devices that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. Accordingly, any reference in the disclosure and / or claims to a computer system, computing system, computer device, computing device, control system, control unit, electronic control unit (ECU), processor device, processing circuitry, etc., includes reference to one or more such devices to individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. For example, control system may include a single control unit or a plurality of control units connected or otherwise communicatively coupled to each other, such that any performed function may be distributed between the control units as desired. Further, such devices may communicate with each other or other devices by various system architectures, such as directly or via a Controller Area Network (CAN) bus, etc.

[0068] The computer system 800 may comprise at least one computing device or electronic device capable of including firmware, hardware, and / or executing software instructions to implement the functionality described herein. The computer system 800 may include processing circuitry 802 (e.g., processing circuitry including one or more processor devices or control units), a memory 804, and a system bus 806. The computer system 800 may include at least one computing device having the processing circuitry 802. The system bus 806 provides an interface for system components including, but not limited to, the memory 804 and the processing circuitry 802. The processing circuitry 802 may include any number of hardware components for conducting data or signal processing or for executing computer code stored in memory 804. The processing circuitry 802 may, for example,include a general-purpose processor, an application specific processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a circuit containing processing components, a group of distributed processing components, a group of distributed computers configured for processing, or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. The processing circuitry 802 may further include computer executable code that controls operation of the programmable device.

[0069] The system bus 806 may be any of several types of bus structures that may further interconnect to a memory bus (with or without a memory controller), a peripheral bus, and / or a local bus using any of a variety of bus architectures. The memory 804 may be one or more devices for storing data and / or computer code for completing or facilitating methods described herein. The memory 804 may include database components, object code components, script components, or other types of information structure for supporting the various activities herein. Any distributed or local memory device may be utilized with the systems and methods of this description. The memory 804 may be communicably connected to the processing circuitry 802 (e.g., via a circuit or any other wired, wireless, or network connection) and may include computer code for executing one or more processes described herein. The memory 804 may include non-volatile memory 808 (e.g., read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), etc.), and volatile memory 810 (e.g., randomaccess memory (RAM)), or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a computer or other machine with processing circuitry 802. A basic input / output system (BIOS) 812 may be stored in the non-volatile memory 808 and can include the basic routines that help to transfer information between elements within the computer system 800.

[0070] The computer system 800 may further include or be coupled to a non-transitory computer-readable storage medium such as the storage device 814, which may comprise, for example, an internal or external hard disk drive (HDD) (e.g., enhanced integrated drive electronics (EIDE) or serial advanced technology attachment (SATA)), HDD (e.g., EIDE or SATA) for storage, flash memory, or the like. The storage device 814 and other drivesassociated with computer-readable media and computer-usable media may provide nonvolatile storage of data, data structures, computer-executable instructions, and the like.

[0071] Computer-code which is hard or soft coded may be provided in the form of one or more modules. The module(s) can be implemented as software and / or hard-coded in circuitry to implement the functionality described herein in whole or in part. The modules may be stored in the storage device 814 and / or in the volatile memory 810, which may include an operating system 816 and / or one or more program modules 818. All or a portion of the examples disclosed herein may be implemented as a computer program 820 stored on a transitory or non-transitory computer-usable or computer-readable storage medium (e.g., single medium or multiple media), such as the storage device 814, which includes complex programming instructions (e.g., complex computer-readable program code) to cause the processing circuitry 802 to carry out actions described herein. Thus, the computer-readable program code of the computer program 820 can comprise software instructions for implementing the functionality of the examples described herein when executed by the processing circuitry 802. In some examples, the storage device 814 may be a computer program product (e.g., readable storage medium) storing the computer program 820 thereon, where at least a portion of a computer program 820 may be loadable (e.g., into a processor) for implementing the functionality of the examples described herein when executed by the processing circuitry 802. The processing circuitry 802 may serve as a controller or control system for the computer system 800 that is to implement the functionality described herein.

[0072] The computer system 800 may include an input device interface 822 configured to receive input and selections to be communicated to the computer system 800 when executing instructions, such as from a keyboard, mouse, touch-sensitive surface, etc. Such input devices may be connected to the processing circuitry 802 through the input device interface 822 coupled to the system bus 806 but can be connected through other interfaces, such as a parallel port, an Institute of Electrical and Electronic Engineers (IEEE) 1394 serial port, a Universal Serial Bus (USB) port, an IR interface, and the like. The computer system 800 may include an output device interface 824 configured to forward output, such as to a display, a video display unit (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)). The computer system 800 may include a communications interface 826 suitable for communicating with a network as appropriate or desired.

[0073] The operational actions described in any of the exemplary aspects herein are described to provide examples and discussion. The actions may be performed by hardware components, may be embodied in machine-executable instructions to cause a processor to perform the actions, or may be performed by a combination of hardware and software. Although a specific order of method actions may be shown or described, the order of the actions may differ. In addition, two or more actions may be performed concurrently or with partial concurrence.

[0074] Example 1 : A computer system for controlling an articulated tractor-trailer combination, the computer system comprising processing circuitry configured to:- receive a brake request,- determine or receive an estimated value of the road friction (gest) relative to at least one tire of a drive axle of the tractor,- determine, based on the received brake request and the estimated value of the road friction (gest), a brake force distribution between: i) motor or engine braking of the tractor, and ii) service braking of the trailer,- control a torque (Tqtractor) to be applied by the motor or engine in accordance with the determined brake force distribution,- determine, independently of the estimated value of the road friction (gest), a longitudinal wheel slip limit for wheels of said drive axle,- translate the determined longitudinal wheel slip limit to a wheel speed limit for said wheels of said drive axle of the tractor, and wherein upon determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, the processing circuitry is configured to control the motor or engine so that the wheel speed of the wheels of said drive axle is returned to a speed value above the wheel speed limit.

[0075] Example 2: The computer system of example 1, wherein the processing circuitry is further configured to- based on the estimated value of the road friction (gest), determine a road friction force, and- determine said brake force distribution so that the brake force on the drive axle of the tractor is limited to not exceed said road friction force.

[0076] Example 3: The computer system of any one of examples 1-2, wherein said brake request is generated by a driver of the tractor releasing the accelerator pedal.

[0077] Example 4: The computer system of any one of examples 1-2, wherein the brake request is a pure regenerative brake request or a pure engine brake request.

[0078] Example 5: The computer system of any one of examples 1-4, wherein the processing circuitry is configured to receive said estimated value of the road friction (pest) from a friction estimator device, wherein, upon said determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, the processing circuitry is further configured to send a feedback message to the friction estimator device to enable the friction estimator device to update said estimated value of the road friction (gest).

[0079] Example 6: The computer system of example 5, further comprising said friction estimator device.

[0080] Example 7: The computer system of example 6, wherein said friction estimator device is configured to reset or override the updated estimated value of the road friction (pest) based on one of:- a calculation by the friction estimator device resulting in an estimation deviating from the updated estimated value by at least a predetermined amount,- a predefined time period having elapsed since the estimated value was updated,- wheel slip values determined for tractor during propulsion, wherein the wheel slip values exceed a predetermined sliding threshold,- wheel slip values on drive axle determined during braking, wherein the wheel slip values exceed a predetermined sliding threshold- wheel slip values determined for trailer, wherein the wheel slip values exceed a predetermined sliding threshold.

[0081] Example 8: The computer system of any one of examples 6-7, wherein the friction estimator device is configured to update said estimated value of the road friction (pest) based on feedback data received from detected ABS (Anti-lock Braking System) control.

[0082] Example 9: The computer system of any one of examples 6-8, wherein said friction estimator device is configured to calculate said estimated value of the road friction (pest) based on information about a longitudinal tire force (Fxwheei) and a drive axle load force (Fz).

[0083] Example 10: The computer system of any one of examples 1-8, wherein said estimated value of the road friction (pest) is selected from one of a plurality of predetermined discrete values.

[0084] Example 11 : The computer system of example 10, wherein each one of said predetermined discrete values is associated with a respective road or environmental condition, such as dry asphalt road, wet asphalt road, snowy road, icy road.

[0085] Example 12: The computer system of any one of examples 10-11, wherein, upon said determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, the processing circuitry is further configured to cause the currently selected predetermined discrete value to be updated to another one of said predetermined discrete values.

[0086] Example 13: A heavy-duty vehicle in the form of an articulated tractor-trailer combination, the heavy-duty vehicle comprising the computer system of any one of examples 1-12.

[0087] Example 14: A computer-implemented method for controlling an articulated tractor-trailer combination, the method comprising:- receiving, by processing circuitry of a computer system, a brake request,- determining or receiving, by the processing circuitry, an estimated value of the road friction (pest) relative to at least one tire of a drive axle of the tractor,- determining, by the processing circuitry, based on the received brake request and the estimated value of the road friction (pest), a brake force distribution between: i) motor or engine braking of the tractor, and ii) service braking of the trailer- controlling, by the processing circuitry, a torque (Tqtractor) to be applied by the motor or engine in accordance with the determined brake force distribution,- determining, by the processing circuitry, independently of the estimated value of the road friction (pest), a longitudinal wheel slip limit for wheels of said drive axle,- translating, by the processing circuitry, the determined longitudinal wheel slip limit to a wheel speed limit for said wheels of said drive axle of the tractor, and- upon determination that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, controlling, bythe processing circuitry, the motor or engine so that the wheel speed of the wheels of said drive axle is returned to a speed value above the wheel speed limit.

[0088] Example 15: The method of example 14, further comprising:- based on the estimated value of the road friction (gest), determining, by the processing circuitry, a road friction force, and- determining, by the processing circuitry, said brake force distribution so that the brake force on the drive axle of the tractor is limited to not exceed said road friction force.

[0089] Example 16: The method of any one of examples 14-15, wherein said brake request is generated by a driver of the tractor releasing the accelerator pedal.

[0090] Example 17: The method of any one of examples 14-15, wherein said brake request is a pure regenerative brake request or a pure ending brake request.

[0091] Example 18: The method of any one of examples 14-17, further comprising:- receiving, by the processing circuitry, said estimated value of the road friction (pest) from a friction estimator device, and- upon said determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, sending, by the processing circuitry, a feedback message to the friction estimator device to enable the friction estimator device to update said estimated value of the road friction (gest).

[0092] Example 19: The method of example 18, further comprising:- controlling, by the processing circuitry, said friction estimator device to reset or override the updated estimated value of the road friction (pest) based on one of:- a calculation by the friction estimator device resulting in an estimation deviating from the updated estimated value by at least a predetermined amount,- a predefined time period having elapsed since the estimated value was updated,- wheel slip values determined for tractor during propulsion, wherein the wheel slip values exceed a predetermined sliding threshold,- wheel slip values on drive axle determined during braking, wherein the wheel slip values exceed a predetermined sliding threshold,- wheel slip values determined for trailer, wherein the wheel slip values exceed a predetermined sliding threshold.

[0093] Example 20: The method of any one of examples 18-19, further comprising:- controlling, by the processing circuitry, the friction estimator device to update said estimated value of the road friction (pest) based on feedback data received from detected ABS (Anti-lock Braking System) control.

[0094] Example 21 : The method of any one of examples 18-20, further comprising:- controlling, by the processing circuitry, the friction estimator device to calculate said estimated value of the road friction (pest) based on information about a longitudinal tire force (Fx) and a drive axle load force (Fz).

[0095] Example 22: The method of any one of examples 14-21, wherein said estimated value of the road friction (pest) is selected from one of a plurality of predetermined discrete values.

[0096] Example 23 : The method of example 22, wherein each one of said predetermined discrete values is associated with a respective road or environmental condition, such as dry asphalt road, wet asphalt road, snowy road, icy road.

[0097] Example 24: The method of any one of example 22-23, further comprising:- upon said determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, causing, by the processing circuitry, the currently selected predetermined value to be updated to another one of said predetermined values.

[0098] Example 25: A computer program product comprising program code for performing, when executed by the processing circuitry, the method of any of examples 14-24.

[0099] Example 26: A non-transitory computer-readable storage medium comprising instructions, which when executed by the processing circuitry, cause the processing circuitry to perform the method of any of examples 14-24.

[0100] The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises,” “comprising,” “includes,” and / or “including” when used herein specify the presence of stated features, integers, actions, steps, operations, elements, and / orcomponents, but do not preclude the presence or addition of one or more other features, integers, actions, steps, operations, elements, components, and / or groups thereof.

[0101] It will be understood that, although the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the present disclosure.

[0102] Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element to another element as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

[0103] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0104] It is to be understood that the present disclosure is not limited to the aspects described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the present disclosure and appended claims. In the drawings and specification, there have been disclosed aspects for purposes of illustration only and not for purposes of limitation, the scope of the disclosure being set forth in the following claims.

Claims

ClaimsWhat is claimed is:

1. A computer system for controlling an articulated tractor-trailer combination, the computer system comprising processing circuitry configured to:- receive a brake request,- determine or receive an estimated value of the road friction (pest) relative to at least one tire of a drive axle of the tractor,- determine, based on the received brake request and the estimated value of the road friction (gest), a brake force distribution between: i) motor or engine braking of the tractor, and ii) service braking of the trailer,- control a torque (Tqtractor) to be applied by the motor or engine in accordance with the determined brake force distribution,- determine, independently of the estimated value of the road friction (pest), a longitudinal wheel slip limit for wheels of said drive axle,- translate the determined longitudinal wheel slip limit to a wheel speed limit for said wheels of said drive axle of the tractor, and wherein upon determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, the processing circuitry is configured to control the motor or engine so that the wheel speed of the wheels of said drive axle is returned to a speed value above the wheel speed limit.

2. The computer system of claim 1, wherein the processing circuitry is further configured to:- based on the estimated value of the road friction (pest), determine a road friction force, and- determine said brake force distribution so that the brake force on the drive axle of the tractor is limited to not exceed said road friction force.

3. The computer system of any one of claims 1-2, wherein said brake request is generated by a driver of the tractor releasing the accelerator pedal.

4. The computer system of any one of claims 1-2, wherein the brake request is a pure regenerative brake request or a pure engine brake request.

5. The computer system of any one of claims 1-4, wherein the processing circuitry is configured to receive said estimated value of the road friction (pest) from a friction estimator device, wherein, upon said determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, the processing circuitry is further configured to send a feedback message to the friction estimator device to enable the friction estimator device to update said estimated value of the road fri ction (gest).

6. The computer system of claim 5, further comprising said friction estimator device.

7. The computer system of claim 6, wherein said friction estimator device is configured to reset or override the updated estimated value of the road friction (pest) based on one of:- a calculation by the friction estimator device resulting in an estimation deviating from the updated estimated value by at least a predetermined amount,- a predefined time period having elapsed since the estimated value was updated,- wheel slip values determined for tractor during propul sion, wherein the wheel slip values exceed a predetermined sliding threshold,- wheel slip values on drive axle determined during braking, wherein the wheel slip values exceed a predetermined sliding threshold,- wheel slip values determined for trailer, wherein the wheel slip values exceed a predetermined sliding threshold.

8. The computer system of any one of claims 6-7, wherein the friction estimator device is configured to update said estimated value of the road friction (pest) based on feedback data received from detected ABS (Anti-lock Braking System) control.

9. The computer system of any one of claims 6-8, wherein said friction estimator device is configured to calculate said estimated value of the road friction (pest) based on informationabout a longitudinal tire force (FXWheei) and a drive axle load force (Fz).

10. The computer system of any one of claims 1-8, wherein said estimated value of the road friction (pest) is selected from one of a plurality of predetermined discrete values.

11. The computer system of claim 10, wherein each one of said predetermined discrete values is associated with a respective road or environmental condition, such as dry asphalt road, wet asphalt road, snowy road, icy road.

12. The computer system of any one of cl aims 10-11, wherein, upon said determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, the processing circuitry is further configured to cause the currently selected predetermined discrete value to be updated to another one of said predetermined discrete values.

13. A heavy-duty vehicle in the form of an articulated tractor-trailer combination, the heavy-duty vehicle comprising the computer system of any one of claims 1-12.

14. A computer-implemented method for controlling an articulated tractor-trailer combination, the method comprising:- receiving, by processing circuitry of a computer system, a brake request,- determining or receiving, by the processing circuitry, an estimated value of the road friction (|iest) relative to at least one tire of a drive axle of the tractor,- determining, by the processing circuitry, based on the received brake request and the estimated value of the road friction (pest), a brake force distribution between: i) motor or engine braking of the tractor, and ii) service braking of the trailer,- controlling, by the processing circuitry, a torque (Tqtractor) to be applied by the motor or engine in accordance with the determined brake force distribution,- determining, by the processing circuitry, independently of the estimated value of the road friction (pest), a longitudinal wheel slip limit for wheels of said drive axle, ,- translating, by the processing circuitry, the determined longitudinal wheel slip limit to awheel speed limit for said wheels of said drive axle of the tractor, and- upon determination that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, controlling, by the processing circuitry, the motor or engine so that the wheel speed of the wheels of said drive axle is returned to a speed value above the wheel speed limit.

15. The method of claim 14, further comprising:- based on the estimated value of the road friction (pest), determining, by the processing circuitry, a road friction force, and- determining, by the processing circuitry, said brake force distribution so that the brake force on the drive axle of the tractor is limited to not exceed said road friction force.

16. The method of any one of claims 14-15, wherein said brake request is generated by a driver of the tractor releasing the accelerator pedal.

17. The method of any one of claims 14-15, wherein said brake request is a pure regenerative brake request or a pure ending brake request.

18. The method of any one of claims 14-17, further comprising:- receiving, by the processing circuitry, said estimated value of the road friction (pest) from a friction estimator device, and- upon said determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, sending, by the processing circuitry, a feedback message to the friction estimator devi ce to enable the friction estimator device to update said estimated value of the road friction (pest).

19. The method of claim 18, further comprising:- controlling, by the processing circuitry, said friction estimator device to reset or override the updated estimated value of the road friction (pest) based on one of:- a calculation by the friction estimator device resulting in an estimation deviating from the updated estimated value by at least a predetermined amount,- a predefined time period having elapsed since the estimated value was updated,- wheel slip values determined for tractor during propul sion, wherein the wheel slip values exceed a predetermined sliding threshold,- wheel slip values on drive axle determined during braking, wherein the wheel slip values exceed a predetermined sliding threshold,- wheel slip values determined for trailer, wherein the wheel slip values exceed a predetermined sliding threshold.

20. The method of any one of claims 18-19, further comprising:- controlling, by the processing circuitry, the friction estimator device to update said estimated value of the road friction (pest) based on feedback data received from detected ABS (Anti-lock Braking System) control.

21. The method of any one of claims 18-20, further comprising:- controlling, by the processing circuitry, the friction estimator device to calculate said estimated value of the road friction (pest) based on information about a longitudinal tire force (Fx) and a drive axle load force (Fz).

22. The method of any one of claims 14-21, wherein said estimated value of the road friction (pest) is selected from one of a plurality of predetermined discrete values.

23. The method of claim 22, wherein each one of said predetermined discrete values is associated with a respective road or environmental condition, such as dry asphalt road, wet asphalt road, snowy road, icy road.

24. The method of any one of claims 22-23, further comprising:- upon said determination by the processing circuitry that the applied torque (Tqtractor) has caused the wheel speed of the wheels of said drive axle to reach a speed value below the wheel speed limit, causing, by the processing circuitry, the currently selected predetermined value to be updated to another one of said predetermined values.

25. A computer program product comprising program code for performing, when executed by the processing circuitry, the method of any of claims 14-24.

26. A non-transitory computer-readable storage medium comprising instructions, which when executed by the processing circuitry, cause the processing circuitry to perform the method of any of claims 14-24.

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