Torque-rate limited control of electric machines on vehicles

Abstract

A computer-implemented control system (300, 500, 600) for controlling at least one electric machine, EM, (180, 210, 340) on a heavy-duty vehicle (100), the computer-implemented control system comprising processing circuitry arranged to configure a torque-rate limit for controlling the EM (180, 210, 340) during braking, where the torque-rate limit for controlling the EM during braking is equal to or smaller than a torque-rate limit associated with a service brake, SB, system (220, 230, 240) of the heavy-duty vehicle (100), receive a request for negative acceleration (areq), and control the EM (180, 210, 340) to apply a negative torque in response to the request for negative acceleration (areq) at a rate below the configured torque-rate limit for controlling the EM during braking.

Description

[0001] TORQUE-RATE LIMITED CONTROL OF ELECTRIC MACHINES ON VEHICLES

[0002] TECHNICAL FIELD

[0003] This disclosure relates generally to control of heavy-duty vehicles such as trucks, buses, and heavy construction equipment. In particular aspects, the disclosure relates to torque-rate limited control of electric machines on heavy-duty vehicles during braking in order to, among other things, reduce tyre wear and maintain service brake functionality.

[0004] Although the disclosure may be described with respect to a particular vehicle, the disclosure is not restricted to any particular vehicle or vehicle type.

[0005] BACKGROUND

[0006] A heavy-duty vehicle, such as a truck or a bus, often comprises a plurality of different motion support devices (MSD), i.e., actuators such as propulsion devices, steering actuators, active suspension systems and brakes that can be used to control the motion of the vehicle. Electric machines that can be used for both propulsion and braking are becoming more and more common also on heavy-duty vehicles. Electric machines respond very quickly to requests for applied torque, which means that they can be used to control vehicle motion at high bandwidth. This is an advantage if, e.g., it is desired to control wheel slip of the vehicle with high accuracy and low latency.

[0007] It is desired to integrate control of these electric machines in the overall motion control of heavy-duty vehicles in an efficient manner.

[0008] SUMMARY

[0009] The present disclosure relates generally to control systems and methods for control of electric machines in heavy-duty vehicles. Some of the techniques disclosed herein may be described in terms of a computer system and / or as methods performed by the computer system.

[0010] There is disclosed a computer-implemented control system for controlling at least one electric machine (EM) on a heavy-duty vehicle. The computer-implemented control system comprises processing circuitry arranged to configure a torque-rate limit for controlling the EM during braking, where the torque-rate limit for controlling the EM during braking is equal to or smaller than a torque-rate limit associated with a service brake (SB) system of the heavy-duty vehicle. In other words, the torque-rate limit for controlling the EM during braking is configured in dependence of the torque-rate limit or capability of the SB system in order to balance the two. The processing circuitry is also configured to receive a request for negative acceleration, and to control the EM to apply a negative torque in response to the request for negative acceleration at a rate at or below the configured torque-rate limit for controlling the EM during braking. This way the high bandwidth actuation capability of the EM is suppressed a bit in order to reduce the jerk which can lead to increased tyre wear. The reduction in generated wheel force during braking is compensated for by the SB system on the vehicle, which compensation distributes wheel force over the axles of the vehicle. A reduction in tyre wear is obtained as a result of the torque-rate limitation, which is an advantage. The torque rate limitation imposed on the EM may correspond to a vehicle acceleration of about 0.1g per second or so, where g is the Earth gravity acceleration number, i.e., about 9.81 m / s2. The processing circuitry can also be arranged to configure respective torque-rate limits for controlling a plurality of EMs on the heavy-duty vehicle during braking, i.e., the techniques disclosed herein are also applicable to systems comprising more than one EM, and to systems comprising more than one EM driven axle. The processing circuitry is preferably also arranged to suspend the torque-rate limit for controlling the EM during braking in case the vehicle is performing a situation avoidance maneuver or an emergency braking operation, in order to not jeopardize vehicle safety.

[0011] According to some aspects, the torque-rate limit for controlling the EM during braking is implemented at least in part as a low-pass filter applied to a torque request associated with the EM on the heavy-duty vehicle during braking. This low-pass filter can be implemented at reasonable computational complexity and is easily configured, which is an advantage.

[0012] According to other aspects, the torque-rate limit for controlling the EM during braking is implemented as part of a control allocation function of the heavy-duty vehicle. This allows for more fine-grained control of the actuation on the vehicle, such as coordination between different motion support devices on the vehicle. The torque-rate limit for controlling the EM during braking can for instance be represented in the control allocation function as a capability constraint associated with the EM. This way the techniques disclosed herein can be integrated into existing control allocation architectures as a software update, which is an advantage. The torque-rate limit associated with the SB system can be obtained at least in part as a predetermined parameter. However, certain advantages can be obtained by adjusting the torquerate limit associated with the SB system during operation based on a monitored response by the SB system to an actuation request. A suitable balance between the EM and SB systems can also be determined by practical experimentation.

[0013] According to some aspects, the processing circuitry is furthermore arranged to maintain an SB usage record indicative of past actuation by the SB system of the heavy-duty vehicle, and to trigger actuation of the SB system in case the SB usage record does not satisfy a usage acceptance criterion. This way SB functionality is maintained since the SB devices will be exercised regularly, i.e., as soon as the usage record does not satisfy the usage acceptance criterion. It is an advantage that the SB system is used regularly, since this allows the system to detect malfunction in the SB system, which would otherwise perhaps go unnoticed. Hence, by ensuring that the SB system is exercised regularly, it is kept in working condition and also diagnosed regularly for faults. The processing circuitry is preferably arranged to predict future use of the SB system based on a future route of the heavy-duty vehicle, and to postpone actuation of the SB system even if the SB usage record does not satisfy the usage acceptance criterion in case of a to predicted future use of the SB system. This way the exercising of the SB system is better optimized and not performed unnecessarily often. The usage acceptance criterion may comprise, e.g., a time period since last use, a required duty cycle of use, a minimum amount of torque to be applied by the SB system to count as use, and so on.

[0014] According to some aspects, the processing circuitry is arranged to modify the torque-rate limit for controlling the EM during braking based on a state of charge (SoC) of an electrical energy storage system (ESS) of the heavy-duty vehicle. This allows for optimization of ESS charge, such that SB exercising is more often performed when the energy from regenerative braking is not needed.

[0015] According to some aspects, the torque-rate limits for controlling the plurality of EMs during braking are adjusted to even out applied tyre forces of the heavy-duty vehicle. Thus, tyre wear is more evenly distributed over the wheels of the vehicle. The processing circuitry can also be arranged to estimate tyre wear associated with the wheels on the heavy-duty vehicle, and to adjust the torque-rate limit for controlling the EM based on the estimated tyre wear. According to some aspects, the processing circuitry is arranged to control the EM to generate positive propulsion torque and the SB system to generate negative braking torque in response to detecting build-up of rust in the SB system. This way SB exercising can be performed without affecting the overall motion by the vehicle, which is an advantage.

[0016] The different techniques and features of the computer system discussed herein may also be described as corresponding methods, associated with the same advantages. The above aspects, accompanying claims, and / or examples disclosed herein above and later below may be suitably combined with each other as would be apparent to anyone of ordinary skill in the art.

[0017] 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. There are also disclosed herein control units, computer systems, computer readable media, and computer program products associated with the above discussed technical benefits.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] With reference to the appended drawings, below follows a more detailed description of aspects of the disclosure cited as examples.

[0020] Figure 1 illustrates an example heavy-duty vehicle,

[0021] Figure 2 schematically illustrates an electric machine and service brakes on a vehicle,

[0022] Figure 3 illustrates some example motion support devices on a heavy-duty vehicle,

[0023] Figure 4 is a graph that exemplified torque-rate limited control of an electric machine,

[0024] Figure 5 shows aspects of an example vehicle motion control system,

[0025] Figure 6 is a schematic diagram of an exemplary computer system,

[0026] Figure 7 is a flow chart illustrating methods, and

[0027] Figure 8 shows an example computer program product.

[0028] DETAILED DESCRIPTION

[0029] The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness. Like reference character refer to like elements throughout the description. Aspects set forth below represent the necessary information to enable those skilled in the art to practice the disclosure.

[0030] Figure 1 illustrates an example heavy-duty vehicle 100, here in the form of a truck comprising a tractor 110 and a trailer 120. The tractor 110 of the vehicle 100 comprises two front wheels 101 of a steered front axle and a set of rear wheels 102 on rear tractor axles. The trailer 120 also comprises wheels 103 that support it on the road surface 104. One or more tractor rear axles, and / or one or more trailers axles may also be steered axles.

[0031] A heavy-duty vehicle may be defined in some cases as a freight vehicle of more than 3.5 metric tons or as a passenger transport vehicle of more than 8 seats. A heavy-duty vehicle may also be defined as a vehicle with a frontal area that is larger than 45 square feet, which is about 4.18 square meters. The teachings herein are particularly suitable for use with semi-trailer type vehicles such as that shown in Figure 1 and rigid trucks, including rigid trucks with dollies and one or more trailers.

[0032] The vehicle 100 comprises a computer-implemented control system that is arranged to estimate vehicle motion relative to the road surface 104 and / or in a global reference system. The control system implements one or more control functions that control vehicle motion based at least in part on the estimated vehicle motion. This control system may comprise one or more control units 130 distributed over the vehicle or centralized at one place. Each vehicle control unit 130 may comprise one or more processor devices. A processor device may be distributed over several spatially separated units or centralized in one place. The control system, or parts thereof, may be arranged to communicate via wireless link 140 to a wireless access point 150, such as a radio base station of a cellular access network or the like. Thus, the vehicle control system may communicate with one or more remote servers 160 implementing data repositories, remote processing resources, and the like, in order to exchange data and perform various computation tasks. The computer-implemented control system may be referred to as, or form part of, a system for vehicle motion management (VMM). A higher layer control system may use the VMM system to obtain a desired motion by the vehicle 100. The higher layer control system may be referred to as a traffic situation management (TSM) system, and may comprise both a manual driver interface, advanced driver assistance (ADAS) functions, as well as autonomous drive (AD) capability. An example computer-implemented control system will be discussed below in connection to Figure 6.

[0033] Generally, herein, various forms of data signals and messages are transmitted between functions, internal to some processing circuitry or in between physically separated processing devices. These signals and messages are often referred to in terms of data indicative of a given parameter or data item. It is appreciated that the term “data indicative of’ is to be construed broadly to mean, e.g., the actual value, an approximation of the value, or an abstraction of the value. The data can for instance be represented using a varying number of bits in a digital message or transmitted in analog form. A given value may also be represented using an abstraction or code, such as a discrete value in a given predefined range.

[0034] The example vehicle 100 comprises an electrical energy storage system (ESS) 170 arranged to power an electric machine 180 capable of generating both propulsion and braking torque, i.e., both positive and negative torque, on the frontmost rear axle, as illustrated in Figure 1. A heavy- duty vehicle generally comprises several actuators, collectively referred to herein as motion support devices (MSD). The MSDs of a vehicle may comprise one or more combustion engines, electric machines, steering actuators, brake systems, active suspension systems, and so on. A heavy-duty vehicle, such as the vehicle 100, is normally over-actuated, which means that a given motion by the vehicle can be obtained by a number of different actuator motion request combinations. Steering can, for instance, be achieved by actuating a power steering system, and also by differential braking on the two sides of the vehicle. An active suspension system can also be used to obtain a certain curvature by the vehicle 100. A global motion request issued, e.g., by a driver or by an autonomous control system forming part of the TSM function of the vehicle 100, for a given overall vehicle motion behavior can therefore be satisfied in a number of different ways, some good and some not so good in terms of cost, where the cost function may involve aspects such as component wear, energy expenditure, and passenger convenience.

[0035] To brake the vehicle 100, braking torque must be generated by the wheels 101, 102, 103. This braking torque results in longitudinal tyre forces Fxthat decelerates the vehicle. In case the tyre forces are localized as high tyre forces on one axle, then tyre wear will be large on this axle. It is preferred to distribute tyre forces over the wheels of the vehicle, since this results in a decrease in tyre wear. The schematic graph at the bottom of Figure 1 illustrates the case of unevenly applied braking torques as a dashed line 190 and more evenly applied braking torques as the solid lines 191. A particular focus of the techniques disclosed herein is to allocate MSD requests such that tyre wear is reduced. Another focus of at least some of the techniques disclosed herein is to maintain the function of the service brakes, i.e., the disc brakes or the drum brakes on the vehicle 100. A third focus of the techniques disclosed herein is to provide regular SB system functional diagnostics.

[0036] Figure 2 schematically illustrates an electric machine 210 (EM) and service brakes (SB) 220, 230, 240 on a vehicle unit, such as the tractor 110 in Figure 1. The service brakes may comprise disc brakes and / or drum brakes. The EM 210 can be used for both propulsion and braking, but only actuates one of the tractor axles, in this case via a differential 215. Hence, the torque applied by the EM 210 generates wheel force only on some of the wheels on the tractor. EMs are capable of relatively high bandwidth actuation, i.e., the applied torque by the EM 210 can be changed much more quickly compared to legacy combustion engine drive units and more quickly than most service brakes. This means that the EM is often used extensively to control the motion of the vehicle, especially if more advanced wheel slip control systems are implemented as part of the vehicle motion control system, while the service brakes are used less frequently, since they are slower. This, in turn, means that more tyre force is generated by the wheels on the EM actuated wheel axle compared to the wheels on the other axles, which leads to uneven tyre wear, where the wheels actuated by the EM are worn down more than the other wheels on the vehicle. Thus, if nothing is done, the situation with uneven wheel forces illustrated in Figure 1 is obtained, where the EM axle bears most of the braking burden. This is especially true for the jerk part of braking, seen when brakes are applied at high torque-rate, i.e., where braking torque develops fast. Also, since the service brakes 220, 230, 240 are used less frequently (since most of the braking is handled by the EM), the service brakes may suffer from build-up of rust which is detrimental to performance. To alleviate these issues, it is desired to optimize the brake blending between service brakes and electric machine, i.e., the allocation of actuator control requests sent to the EM and to the service brakes. Torque-rate is a rate of change in applied torque by an actuator. The unit of torque-rate is Nm / s (Newton meters per second), although torque-rate can also be given in an equivalent acceleration change of a vehicle unit as function of time. A torque-rate limit applied during braking is a limit on how fast the negative torque changes, i.e., how fast the brakes are applied to develop braking force. An actuator having a torque-rate limit that is larger than some other actuator is capable of applying braking torque faster than the other actuator, thus achieving a larger applied torque in the same amount of time. The example 250 in Figure 2 illustrates an example torque-rate limit 251 as the dashed line. The solid line torque curve 252 develops at a rate below the torque-rate limit 251, i.e., slower, while the dash-dotted torque curve 253 develops at a rate above the torque-rate limit 251, i.e., faster.

[0037] Brake blending between SBs and EMs on a heavy-duty vehicle can be achieved in a straightforward manner by limiting the rate of applied torque by the EM during braking to be below a torque-rate associated with the SBs. This means that the SBs are forced into action during a braking event, since the EM 210 is no longer fast enough to accommodate most of the motion requests issued by the VMM system. This in turn means that the wheel forces will be more evenly distributed over the wheels of the vehicle.

[0038] Figure 3 schematically illustrates example control system 300 for controlling a wheel 102 on the vehicle 100 to generate a longitudinal wheel tyre Fxby some example MSDs here comprising a friction brake 330 (such as a disc brake or a drum brake) and an electric machine 340. The friction brake 330 and the propulsion device 340 are examples of wheel torque generating devices, which can be controlled by one or more MSD control units 330. The control can be based on measurement data obtained from, e.g., a wheel speed sensor (WS) 360 in combination with data from one or more inertial measurement units (IMU) 370 and optionally also based on data from other vehicle state sensors, such as radar sensors, lidar sensors, and vision-based sensors such as camera sensors and infra-red detectors. The EM 340 may be used to perform slip control of the wheel 102, which means that the EM 340 will modulate applied torque at high bandwidth to obtain a desired difference between wheel speed and wheel speed over ground. This will, however, result in that the wheel 102 will generate a higher wheel force compared to wheels only actuated by friction brakes, unless a torque-rate limitation is imposed on the EM, as proposed herein. A traffic situation management (TSM) function 310 such as an advanced driver assistance system (ADAS) or an autonomous drive (AD) system may plan the driving operation of the vehicle 100 with a time horizon of 10 seconds or so. Alternatively, a human driver generates the higher layer control commands of the vehicle control system 300. This time period corresponds to, e.g., the time it takes for the vehicle 100 to negotiate a curve or the like. The vehicle maneuvers, planned and executed by the TSM function 310, can be associated with acceleration profiles areq and curvature profiles creq which describe a desired target vehicle velocity in the vehicle forward direction and turning to be maintained for a given maneuver. The TSM function 310 continuously requests the desired acceleration profiles areq and steering angles (or curvature profiles creq) from a vehicle motion management (VMM) system 320 which performs force allocation to meet the requests from the TSM function in a safe and robust manner. Force allocation will be discussed in more detail below in connection to Figure 5. The force allocation is translated into MSD request signals that are sent to the different MSDs on the vehicle 100, via the MSD control unit or units 330.

[0039] The VMM function 320 comprises an MSD torque-rate limiting function 325. The purpose of this torque-rate limiting function is to limit the bandwidth at which the EM is used to generate negative torque, i.e., limit the speed at which braking force is applied to the wheel 102. The torque-rate limitation slows down the EM during braking, which forces actuation by the friction brakes in order to satisfy the acceleration profile areq requested by the TSM function 310. Since the friction brakes on the vehicle 100 are now used in combination with the EM during retardation of the vehicle, even if they are not strictly needed given the specifications of the EM in terms of torque-rate capability, the tyre wear is more evenly distributed over the axles on the vehicle, which is an advantage.

[0040] According to some aspects a torque-rate limitation is applied also during propulsion. However, in this case the reduction in MSD capability cannot be compensated for by the SB system.

[0041] Figure 4 shows a graph 400 of longitudinal acceleration axvs time t. A request for negative acceleration is issued around time t = 1, shown in Figure 4 as a dash-dotted line. The EM would be able to apply negative torque with very small delay and at a high magnitude torquerate to accommodate the entirety or at least a majority of this request, but because of the torquerate limitation function 325, the amount of actuation by the EM is reduced as illustrated in the Figure by the solid line. The discrepancy between acceleration request and EM actuation is filled up by the SB system on the vehicle during an initial time period 410, as illustrated by the dashed line. Thus, the tyre wear resulting from the negative acceleration request is distributed over the axles on the vehicle, which evens out tyre wear in a desired manner.

[0042] The torque-rate limitation imposed on the EM may be somewhere in a range of 0.1g-0.2g, where g is the gravity acceleration (approximately 9.81 m / s2). The torque-rate limitation of most SB systems is on the order of 0.5g or so.

[0043] Note also that the SB actuation is maintained over an additional time period 420. This maintained SB actuation is performed in order to exercise the SBs in order to maintain SB functionality. This actuation removes rust and other undesired surface coatings from the SB system. This actuation also acts as a test to check if the SB system is operational.

[0044] Figure 5 schematically illustrates functionality 500 for controlling the vehicle 100 by some example MSDs here comprising brake actuators, propulsion actuators, and power steering, with respective controllers collectively referred to herein as MSD control 330. The control functionality illustrated in Figure 5 is based on control allocation, where an MSD coordination function allocates requests to the different available MSDs on the vehicle in order to satisfy a motion request from a higher layer TSM function 310.

[0045] Each wheel 101, 102, 103 on the vehicle 100 has a longitudinal velocity component vxand a lateral velocity component vy(in the coordinate system of the wheel or in the coordinate system of the vehicle, depending on implementation). There is a longitudinal tyre force Fxand a lateral tyre force Fy, and also a normal force Fzacting on the wheel. Unless explicitly stated otherwise, the tyre forces are defined in the coordinate system of the wheel, i.e., the longitudinal force is directed in the rolling plane of the wheel, while the lateral tyre force is directed normal to the rolling plane of the wheel. The MSD request signals are generated at least in part to obtain a desired set of tyre forces from the different wheels on the tractor 110 and the trailer 120.

[0046] The VMM system 320 operates with a time horizon of about 1 second or so, and continuously transforms the acceleration profiles areq and curvature profiles creq from the TSM function 310 into MSD motion requests 531, 532, 533 for controlling vehicle motion functions, actuated by the different MSDs of the vehicle 100 which report back capabilities and status information 534, 535, 536 to the VMM function 320, which in turn may be used as constraints in the MSD coordination function 570.

[0047] The VMM system 320 performs vehicle state or motion estimation 550, i.e., the VMM system 320 continuously determines a vehicle state s as function of time t comprising positions, speeds, accelerations, and articulation angles of the different units in the vehicle combination by monitoring operations using various sensors 540 arranged on the vehicle 100, often but not always in connection to the MSDs. The vehicle state at a future time instant can also be predicted by a state prediction function 555. This vehicle state prediction function may be realized by a vehicle model having a vehicle state which can be extrapolated into a predicted vehicle state, given a current vehicle state, and optionally also given the current vehicle motion request.

[0048] The result of the state estimation 550 and optionally also the state prediction 555, i.e., the estimated vehicle state s at one or more time instants, is input to a force generation module 560 which determines the required global forces V=[Vi, V2] for the different vehicle units to cause the vehicle 100 to move according to the requested acceleration and curvature profiles areq, creq, and to behave according to the desired vehicle behavior. This example has two vehicle units. More vehicle units are possible, and also a single vehicle unit, e.g., in case the vehicle is a rigid truck or a passenger car. The required global force vector V is input to the MSD coordination function 570 which allocates tyre forces and coordinates other MSDs such as steering and suspension. The coordination by the MSD coordination function is advantageously performed by taking the MSD capabilities into account.

[0049] The MSD coordination function outputs an MSD control allocation for the i :th wheel, which may comprise any of a torque Ti, a longitudinal wheel slip Xi, a wheel rotational speed Oi, and / or a wheel steering angle 5i. The coordinated MSDs then together provide the desired lateral Fy and longitudinal Fx forces on the vehicle units, as well as the required moments Mz, to obtain the desired motion by the vehicle combination 100. Thus, according to some aspects of the present disclosure, the VMM system 320 manages both force generation and MSD coordination, i.e., it determines what forces that are required at the vehicle units in order to fulfil the requests from the TSM function 310, for instance to accelerate the vehicle according to a requested acceleration profile requested by TSM and / or to generate a certain curvature motion by the vehicle also requested by TSM. The forces may comprise e.g., yaw moments Mz, longitudinal forces Fxand lateral forces Fy, as well as different types of torques to be applied at different wheels. The forces are determined such as to generate the vehicle behavior which is expected by the TSM function in response to the control inputs generated by the TSM function 310.

[0050] To give an example of how an MSD coordination function 570 might operate, consider a control problem where x = [x^ x^ ... , xN] is a vector of MSD motion requests, v is a vector that represents a desired set of global vehicle forces to be generated, B is a control effectiveness matrix, and xdis a vector of desired MSD motion requests. The vector of desired motion requests may, e.g., comprise a default actuator state associated with the smallest energy consumption or the like. The MSD coordination problem can then be cast as x* = arg subject to Xi < x < xu

[0051] Where Wxand Wvare weighting matrices, y is a tuning parameter, and xt< x < xuare constraints imposed on the MSD coordination optimization problem. The constraints xtand xumay at least in part be determined based on the torque-rate limitation functions discussed herein. In this way the MSD coordination function 570 is generally constrained in its allocation of motion requests to the different MSDs.

[0052] The torque-rate limitation techniques discussed herein can be implemented by a torque-rate limitation function 325. This function ensures that the rate at which braking torque is applied by the EM does not go above the configured braking torque-rate limitation of the control system 500. This can be done, e.g., by setting constraints on applied torque for use in the MSD coordination function 570.

[0053] The computer-implemented control systems 300, 500, 600 discussed herein are generally suitable for controlling at least one EM 180, 210, 340 on a heavy-duty vehicle 100 in order to reduce tyre wear on the wheels of at least one axle driven by the EM. The computer- implemented control system comprises processing circuitry arranged to configure a torque-rate limit for controlling the EM 180, 210, 340 during braking, where the torque-rate limit for controlling the EM is equal to or smaller than a torque-rate limit associated with an SB system 220, 230, 240 of the heavy-duty vehicle 100, where the torque-rate limit associated with the SB system is obtained from local memory, determined during execution, or obtained from an external source. This means that a request for retardation of the heavy-duty vehicle 100, i.e., a request for braking, is normally fulfilled by actuation of both the SB system and the EM, and not just by the EM 180, 210, 340 which evens out tyre forces over the axles of the vehicle 100 and thus also tyre wear. The torque-rate limit associated with the SB system can be obtained as a pre-determined parameter and / or estimated in real-time by monitoring the response by an SB device to an actuation request. The torque rate limit of the SB system may, e.g., correspond to about 0.5g or so. The response by the SB system to a braking request can be monitored, e.g., by a WS sensor 360 and / or by an IMU 370 that measures acceleration by the vehicle. This way the actual torque-rate limit of an SB device or an SB system can be estimated.

[0054] The processing circuitry is arranged to receive a request for negative acceleration areq, e.g., from a TSM function 310 or from a driver as discussed above, and to control the EM 180, 210, 340 to apply a negative torque in response to the request for negative acceleration areq at a rate below the configured torque-rate limit for controlling the EM during braking. Thus, the SB system is also actuated in order to accommodate the request for negative acceleration areq, since the EM braking operation has been slowed down to a point where the SB system becomes fast enough to contribute to the braking operation. This evens out the tyre wear over the different axles of the vehicle, which is an advantage.

[0055] The torque-rate limit for controlling the EM 180, 210, 340 during braking can be implemented as a low-pass filter, sometimes also referred to as an averaging filter, applied to a torque request associated with the EM 180, 210, 340 on the heavy-duty vehicle 100 during a braking operation. The parameters of this low-pass filter can be adjusted to obtain a larger or a smaller torque-rate limit. The torque-rate limit for controlling the EM 180, 210, 340 may also be implemented as part of a control allocation function 570 of the heavy-duty vehicle 100, as discussed above in connection to Figure 5, e.g., as a dedicated rate limitation function that determines the torque-rate limitation to use for a given maneuver and / or based on the operating scenario. In this case it may be advantageous to represent the torque-rate limit for controlling the EM 180, 210, 340 as a capability constraint associated with the EM 180, 210, 340, as discussed above. Notably, the torque-rate limitation that is applied during braking is preferably suspended in case the vehicle is performing some sort of emergency maneuver, such as a situation avoidance maneuver or an emergency braking maneuver. Thus, the vehicle control system applies the torque-rate limitation selectively such that it doesn’t have an impact on the maneuverability of the vehicle in critical driving scenarios. For instance, if a warning flag has been raised by the vehicle control system indicative of a hazard or malfunction, then the torque-rate limitation may be removed immediately in order to not have a detrimental effect on the controllability of the vehicle.

[0056] The processing circuitry may furthermore be arranged to maintain an SB usage record indicative of past actuation by the SB system 220, 230, 240 of the heavy-duty vehicle 100, and to trigger actuation of the SB system 220, 230, 240 in case the SB usage record does not satisfy a usage acceptance criterion. This way the condition of the SB system can be maintained through regular use of the SB system, which mitigates problems related to build-up of rust in the brake system. The usage acceptance criterion may, e.g., comprise a minimum amount of use-time in a day or a week, or in some other time period. The usage acceptance criterion may also comprise a requirement on applied torque by the SB system on the different axles of the vehicle. The processing circuitry can also be arranged to predict future use of the SB system 220, 230, 240 based on a future route of the heavy-duty vehicle 100, and to postpone actuation of the SB system even if the SB usage record does not satisfy the usage acceptance criterion in case of a to predicted future use of the SB system. According to some aspects, the processing circuitry is arranged to control the EM 180, 210, 340 to generate positive torque and the SB system 220, 230, 240 to generate negative torque in response to detecting build-up of rust in the SB system 220, 230, 240. This way the SB system can be kept fully functional despite most of the negative torque actuation being performed by the EM.

[0057] The processing circuitry may be arranged to modify the torque-rate limit for controlling the EM 180, 210, 340 based on a state of charge (SoC) of an electrical energy storage system (ESS) of the heavy-duty vehicle. This way the tyre wear rate can be traded off against state of charge of the ESS 170 on the heavy-duty vehicle 100. In case the batteries are almost empty more braking torque can be generated by the EM, at the expense of an increase in tyre wear. Less torque can be applied using the EM in case the ESS 170 has more charge, thus reducing tyre wear. The processing circuitry can also be arranged to configure respective torque-rate limits for controlling a plurality of EMs 180, 210, 340 on the heavy-duty vehicle 100. The torque-rate limits for controlling the plurality of EMs can then be adjusted to even out applied tyre forces of the heavy-duty vehicle 100.

[0058] According to some aspects, the processing circuitry is arranged to estimate tyre wear associated with the wheels on the heavy-duty vehicle 100, and to adjust the torque-rate limit for controlling the EM 180, 210, 340 based on the estimated tyre wear. In case the estimated tyre wear indicates uneven wear, then the torque-rate limitation can be adjusted to mitigate this uneven tyre wear and make it more even. If the wheels driven by the EM are worn faster than the other wheels, then the torque-rate limitation should be decreased to reduce the wear on the EM- driven axle, and vice versa.

[0059] FIG. 6 is a schematic diagram of a computer system 600 for implementing examples disclosed herein. The computer system 600 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 600 may be connected (e.g., networked) to other machines in a LAN, an intranet, an extranet, or the Internet. While only a single device is illustrated, the computer system 600 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, a 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.

[0060] The computer system 600 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 600 may include processing circuitry 602 (e.g., processing circuitry including one or more processor devices or control units), a memory 604, and a system bus 606. The computer system 600 may include at least one computing device having the processing circuitry 602. The system bus 606 provides an interface for system components including, but not limited to, the memory 604 and the processing circuitry 602. The processing circuitry 602 may include any number of hardware components for conducting data or signal processing or for executing computer code stored in memory 604. The processing circuitry 602 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 602 may further include computer executable code that controls operation of the programmable device.

[0061] The system bus 606 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 604 may be one or more devices for storing data and / or computer code for completing or facilitating methods described herein. The memory 604 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 604 may be communicably connected to the processing circuitry 602 (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 604 may include non-volatile memory 608 (e.g., read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), etc.), and volatile memory 610 (e.g., random-access memory (RAM)), or any other medium which can be used to carry or store desired program code in the form of machineexecutable instructions or data structures, and which can be accessed by a computer or other machine with processing circuitry 602. A basic input / output system (BIOS) 612 may be stored in the non-volatile memory 608 and can include the basic routines that help to transfer information between elements within the computer system 600.

[0062] The computer system 600 may further include or be coupled to a non-transitory computer- readable storage medium such as the storage device 614, 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 614 and other drives associated with computer- readable media and computer-usable media may provide non-volatile storage of data, data structures, computer-executable instructions, and the like.

[0063] 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 614 and / or in the volatile memory 610, which may include an operating system 616 and / or one or more program modules 618. All or a portion of the examples disclosed herein may be implemented as a computer program 620 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 614, which includes complex programming instructions (e.g., complex computer-readable program code) to cause the processing circuitry 602 to carry out actions described herein. Thus, the computer-readable program code of the computer program 620 can comprise software instructions for implementing the functionality of the examples described herein when executed by the processing circuitry 602. In some examples, the storage device 614 may be a computer program product (e.g., readable storage medium) storing the computer program 620 thereon, where at least a portion of a computer program 620 may be loadable (e.g., into a processor) for implementing the functionality of the examples described herein when executed by the processing circuitry 602. The processing circuitry 602 may serve as a controller or control system for the computer system 600 that is to implement the functionality described herein.

[0064] The computer system 600 may include an input device interface 622 configured to receive input and selections to be communicated to the computer system 600 when executing instructions, such as from a keyboard, mouse, touch-sensitive surface, etc. Such input devices may be connected to the processing circuitry 602 through the input device interface 622 coupled to the system bus 606 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 600 may include an output device interface 624 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 600 may include a communications interface 626 suitable for communicating with a network as appropriate or desired.

[0065] 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.

[0066] Figure 7 is a flow chart illustrating methods that correspond to the different technical features of the computer system and the vehicles discussed herein. The flow chart illustrates a computer- implemented method for controlling at least one EM 180, 210, 340 on a heavy-duty vehicle 100. The method comprises configuring SI, by a computer-implemented control system comprising processing circuitry, a torque-rate limit for controlling the EM 180, 210, 340 during braking, where the torque-rate limit for controlling the EM during braking is equal to or smaller than a torque-rate limit associated with an SB system 220, 230, 240 of the heavy-duty vehicle 100, receiving S2, by the by a computer-implemented control system, a request for negative acceleration areq, and controlling S3, by the by a computer-implemented control system, the EM 180, 210, 340 to apply a negative torque in response to the request for negative acceleration areq at a rate at or below the configured torque-rate limit for controlling the EM during braking.

[0067] The various technical features of the processing circuitry discussed above can be incorporated into the disclosed method as optional method parts.

[0068] Figure 8 illustrates a computer readable medium 810 carrying a computer program comprising program code means 820 for performing the methods illustrated in Figure 10 and the techniques discussed herein, when said program product is run on a computer. The computer readable medium and the code means may together form a computer program product 800.

[0069] The operational steps described in any of the exemplary aspects herein are described to provide examples and discussion. The steps may be performed by hardware components, may be embodied in machine-executable instructions to cause a processor to perform the steps, or may be performed by a combination of hardware and software. Although a specific order of method steps may be shown or described, the order of the steps may differ. In addition, two or more steps may be performed concurrently or with partial concurrence.

[0070] 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, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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 inventive concepts being set forth in the following claims.

Claims

CLAIMS1. A computer-implemented control system (300, 500, 600) for controlling at least one electric machine, EM, (180, 210, 340) on a heavy-duty vehicle (100), the computer- implemented control system comprising processing circuitry arranged to configure a torque-rate limit for controlling the EM (180, 210, 340) during braking, where the torque-rate limit for controlling the EM during braking is equal to or smaller than a torque-rate limit associated with a service brake, SB, system (220, 230, 240) of the heavy-duty vehicle (100), receive a request for negative acceleration (areq), and control the EM (180, 210, 340)to apply a negative torque in response to the request for negative acceleration (areq) at a rate at or below the configured torque-rate limit for controlling the EM during braking.

2. The computer-implemented control system (300, 500, 600) according to claim 1, where the torque-rate limit for controlling the EM (180, 210, 340) during braking is implemented at least in part as a low-pass filter applied to a torque request associated with the EM (180, 210, 340) on the heavy-duty vehicle (100) during braking.

3. The computer-implemented control system (300, 500, 600) according to claim 1 or 2, where the torque-rate limit for controlling the EM (180, 210, 340) during braking is implemented as part of a control allocation function (570) of the heavy-duty vehicle (100).

4. The computer-implemented control system (300, 500, 600) according to claim 3, where the torque-rate limit for controlling the EM (180, 210, 340) during braking is represented in the control allocation function as a capability constraint associated with the EM (180, 210, 340).

5. The computer-implemented control system (300, 500, 600) according to any previous claim, where the torque-rate limit associated with the SB system is obtained at least in part as a pre-determined parameter.

6. The computer-implemented control system (300, 500, 600) according to any previous claim, where the torque-rate limit associated with the SB system is adjusted during operation based on a monitored response by the SB system to an actuation request.

7. The computer-implemented control system (300, 500, 600) according to any previous claim, where the processing circuitry is furthermore arranged to maintain an SB usage record indicative of past actuation by the SB system (220, 230, 240) of the heavy-duty vehicle (100), and to trigger actuation of the SB system (220, 230, 240) in case the SB usage record does not satisfy a usage acceptance criterion.

8. The computer-implemented control system (300, 500, 600) according to claim 7, where the processing circuitry is arranged to predict future use of the SB system (220, 230, 240) based on a future route of the heavy-duty vehicle (100), and to postpone actuation of the SB system even if the SB usage record does not satisfy the usage acceptance criterion in case of a to predicted future use of the SB system.

9. The computer-implemented control system (300, 500, 600) according to any previous claim, where the processing circuitry is arranged to modify the torque-rate limit for controlling the EM (180, 210, 340) during braking based on a state of charge, SoC, of an electrical energy storage system, ESS, of the heavy-duty vehicle.

10. The computer-implemented control system (300, 500, 600) according to any previous claim, where the processing circuitry is arranged to configure respective torque-rate limits for controlling a plurality of EMs (180, 210, 340) on the heavy-duty vehicle (100) during braking.

11. The computer-implemented control system (300, 500, 600) according to claim 10, where the torque-rate limits for controlling the plurality of EMs during braking are adjusted to even out applied tyre forces of the heavy-duty vehicle (100).

12. The computer-implemented control system (300, 500, 600) according to any previous claim, where the processing circuitry is arranged to estimate tyre wear associated with the wheels on the heavy-duty vehicle (100), and to adjust the torque-rate limit for controlling the EM (180, 210, 340) based on the estimated tyre wear.

13. The computer-implemented control system (300, 500, 600) according to any previous claim, where the processing circuitry is arranged to control the EM (180, 210, 340) to generate positive propulsion torque and the SB system (220, 230, 240) to generate negative braking torque in response to detecting build-up of rust in the SB system (220, 230, 240).

14. The computer-implemented control system (300, 500, 600) according to any previous claim, where the processing circuitry is arranged to suspend the torque-rate limit for controlling the EM (180, 210, 340) during braking in case the vehicle (100) is performing a situation avoidance maneuver or an emergency braking operation.

15. A computer-implemented method for controlling at least one electric machine, EM, (180, 210, 340) on a heavy-duty vehicle (100), the method comprising configuring (SI), by a computer-implemented control system comprising processing circuitry, a torque-rate limit for controlling the EM (180, 210, 340) during braking, where the torquerate limit for controlling the EM during braking is equal to or smaller than a torque-rate limit associated with a service brake, SB, system (220, 230, 240) of the heavy-duty vehicle (100), receiving (S2), by the by a computer-implemented control system, a request for negative acceleration (areq), and controlling (S3), by the by a computer-implemented control system, the EM (180, 210, 340) to apply a negative torque in response to the request for negative acceleration (areq) at a rate at or below the configured torque-rate limit for controlling the EM during braking.

16. A computer program product comprising program code for performing, when executed by the processing circuitry, the method of claim 15.

17. A non-transitory computer-readable storage medium comprising instructions, which when executed by processing circuitry, cause the processing circuitry to perform the method of claim 15.

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