Method of determining actuator brake torque limit

Abstract

The invention relates to a method of determining an actuator braking torque limit for a plurality of actuators (104), where each actuator (104) is operable to apply a braking torque on a wheel (102) of a vehicle (100), the method comprising: for each actuator (104), determining an actuator braking torque limit for each actuator (104); determining an actuator braking torque capability range based on the actuator-specific torque capacity and a current operating state of the actuator (104); determining, for each wheel (102) of the vehicle (100), a road condition braking torque capability range based on an estimated transverse wheel force acting on the wheel (102), an estimated coefficient of friction (218) between a tire surface of the wheel (102) and a road surface, and a vertical wheel force (220) acting on the wheel (102); and for each actuator (104), determining an actuator braking torque upper limit (228) and an actuator braking torque lower limit (230) based on the actuator braking torque capability range and the road condition braking torque capability range.

Description

Technical Field

[0001] The present invention relates to a method of determining actuator braking torque limits of a plurality of actuators. The present invention also relates to a vehicle motion management system connectable to a plurality of actuators. Although the present invention will be primarily directed to vehicles in the form of trucks, the present invention may also be applicable to other types of vehicles including actuators operable to apply braking torques on wheels of the vehicle, such as, for example, buses, work machines, trailers and other transport vehicles. Background Art

[0002] Electric propulsion of passenger vehicles is becoming a common solution to reduce the environmental impact of vehicles. Heavy vehicles such as trucks are also evolving to be able to provide electric propulsion. Electric propulsion systems include one or more electric machines that are operable to produce propulsion torque at one or more wheels of the vehicle. However, trucks are heavy and require relatively large batteries to achieve an acceptable driving range until the batteries must be recharged.

[0003] Electric vehicles also conventionally include foundation brakes, often also called service brakes, to ensure that the vehicle speed can be reduced as required. The foundation brakes can be based on friction for their operation and can be formed, for example, as disc brakes or drum brakes that can efficiently generate braking torque.

[0004] In order to regenerate as much electric power as possible, it is desirable to control the vehicle speed by utilizing the electric motor regenerated power, i.e. the braking operation. However, using only the electric motor to reduce the vehicle speed may not always be sufficient, and the foundation brakes must intervene, i.e. provide a brake blending action. However, if used excessively, friction brakes may experience a phenomenon known as brake fade, which is why friction brakes are not suitable for long-term use, such as may occur during long downhill driving. Brake fade is caused by heat accumulation on the braking surface and leads to a significant reduction in braking ability.

[0005] It is therefore desirable to improve the braking action of a vehicle, and in particular to correctly determine the torque limits of the various types of brakes, thereby taking greater advantage of the electric machine to brake the vehicle. Summary of the invention

[0006] It is therefore an object of the present invention to at least partially overcome the above mentioned drawbacks.

[0007] According to a first aspect, a method for determining actuator braking torque limits of multiple actuators is provided, wherein each actuator is operable to apply braking torque on a wheel of a vehicle, the method comprising: for each actuator, determining an actuator braking torque capacity range based on the actuator-specific torque capacity and the current operating state of the actuator; for each wheel of the vehicle, determining a road condition braking torque capacity range based on an estimated lateral wheel force acting on the wheel, an estimated friction coefficient between the tire surface of the wheel and the road surface, and a vertical wheel force acting on the wheel; and for each actuator, determining an actuator braking torque upper limit and an actuator braking torque lower limit based on the actuator braking torque capacity range and the road condition braking torque capacity range.

[0008] In the following text and throughout the description, the range limits are defined in terms of their minimum and maximum values ​​as absolute values. When comparing an upper limit to a lower limit, the upper limit is the value farthest from zero, while the lower limit is the value closest to zero. Since the braking torque itself is a negative value, the upper and lower limits in the following text should be interpreted as absolute values.

[0009] In addition, the actuator braking torque capacity range should be interpreted as being related to the dynamics of the actuator, i.e., the range of braking torques that the actuator is able to deliver based on the current operating state of the particular actuator. On the other hand, the road condition braking torque capacity range relates to the range of braking torques that can be obtained based on the coefficient of friction between the tire surface of the wheel and the road surface on which the vehicle can drive. As described above, the friction coefficient is an estimated parameter. The estimate can come from, for example, a camera and / or ambient temperature measurement, etc. Other friction estimation techniques can also be envisioned and applied by those skilled in the art. As described above, the lateral wheel force is also an estimated parameter, and an exemplary embodiment of such an estimate will be described in further detail below. According to an exemplary embodiment, the road condition braking torque capacity range can also be based on the wheel radius of the wheel.

[0010] Furthermore, the actuator-specific torque capacity should be interpreted as being hardware-dependent. Thus, different actuators have different torque capacities, and the actuator-specific torque capacity indicates how much torque a specific actuator is able to provide during braking. Thus, the actuator-specific torque capacity is a device specification of the actuator.

[0011] The present invention is based on the recognition that by determining the upper and lower limits of the braking torque of each actuator based on the range of the actuator braking torque capacity and the road condition braking torque capacity, a signal can be transmitted to the control distributor of the vehicle so that when the control distributor distributes the braking torque to the available individual actuators. The control distributor can accordingly preferentially distribute most of the braking torque to actuators in the form of motors without exceeding the braking torque limit of such motors in their current operating state. This will increase the power generated during braking, which in turn increases the operational driving distance of the vehicle. The signal transmitted to the control distributor will also reduce the risk of overheating of the actuators during braking, for example, and / or reduce the risk of distributing braking torque with a magnitude exceeding the upper and lower limits of the braking torque. Therefore, the control distributor will be able to distribute the total braking torque to multiple actuators to meet the total braking demand.

[0012] According to an exemplary embodiment, the current operating state of the actuator can be the braking torque level currently applied by the actuator. Therefore, based on the current braking torque level obtained by the actuator, the capability range of the actuator can be determined. The current braking torque level obtained by the actuator indicates how much additional braking torque the actuator can provide.

[0013] According to an exemplary embodiment, the method may further include determining a wheel slip value for each wheel of the vehicle and estimating the lateral wheel force based on a mapping model defining a relationship between the wheel slip and the lateral wheel force.

[0014] The mapping model is preferably based on predetermined characteristic values ​​of at least one wheel. The mapping model defines the relationship between wheel force and wheel slip. Wheel slip can also be recalculated as wheel speed, wherein the wheel speed can be defined relative to the ground and normalized, i.e. wheel slip, or defined as an absolute rotational speed. Thus, when defining the mapping model, lateral wheel force values ​​for a specific wheel speed or wheel slip value can be obtained.

[0015] The mapping model may be a fixed mapping model, and / or a mapping model that includes characteristics of an estimate of the relationship between wheel forces and wheel slip values. As another alternative, the mapping model may be parameterized based on other factors such as normal load on the tire, tire type, wear, friction, etc.

[0016] By estimating the lateral wheel forces based on the mapping model, the characteristics of the lateral wheel forces can be correctly estimated, ie it can be determined that the estimation is reliable.

[0017] Lateral wheel forces can also be estimated from vehicle state and road conditions, or measured.

[0018] According to an exemplary embodiment, the plurality of actuators may include: a first foundation brake operable to apply a braking torque on a first wheel; a second foundation brake operable to apply a braking torque on a second wheel; a third foundation brake operable to apply a braking torque on a third wheel; a fourth foundation brake operable to apply a braking torque on a fourth wheel; and a motor operable to apply a braking torque on the third wheel and the fourth wheel.

[0019] The first wheel and the second wheel are preferably a pair of front steering wheels of the vehicle, while the third wheel and the fourth wheel are a pair of rear wheels of the vehicle. In this case, the pair of front steering wheels are provided with foundation brakes, while the pair of rear wheels are also provided with foundation brakes and at least one motor to control braking. According to an exemplary embodiment, the motor can be connected to the third wheel and the fourth wheel via a differential coupling. A single motor thus propels and brakes the pair of rear wheels.

[0020] For example, the current operating state of the motor may be related to the current state of charge (SOC) level of the vehicle's energy storage system. In other words, the SOC level may be set as an indicator of how much braking torque the motor can provide.

[0021] According to an exemplary embodiment, the upper limit of the actuator braking torque of each of the first foundation brake and the second foundation brake may be a minimum value of an upper limit of the actuator braking torque capacity range and an upper limit of the road condition braking torque capacity range, and wherein the lower limit of the actuator braking torque of each of the first foundation brake and the second foundation brake may be the lower limit of the actuator braking torque capacity range.

[0022] Thereby, it is ensured that the actuator braking torque limits of the first foundation brake and the second foundation brake are not exceeded.

[0023] According to an exemplary embodiment, the upper limit of the actuator braking torque of the motor can be the minimum of the upper limit of the actuator braking torque capacity range and the braking torque corresponding to twice the lowest value of the upper limits of the road condition braking torque capacity range of the third wheel and the fourth wheel, and wherein the lower limit of the actuator braking torque of the motor can be the lower limit of the actuator braking torque capacity range.

[0024] The actuator braking torque limit of the electric machine can thereby be efficiently determined.

[0025] According to an exemplary embodiment, the upper limit of the actuator braking torque of each of the third foundation brake and the fourth foundation brake may be a minimum value of an upper limit of the actuator braking torque capacity range and an upper limit of the road condition braking torque capacity range minus an upper limit of the actuator braking torque of the motor, and wherein the lower limit of the actuator braking torque of each of the third foundation brake and the fourth foundation brake may be the lower limit of the actuator braking torque capacity range.

[0026] According to an exemplary embodiment, the method may further include receiving a signal indicating a requested braking torque for decelerating the vehicle; and determining a desired braking torque of the motor as a minimum of the requested braking torque and an actuator braking torque upper limit of the motor.

[0027] Therefore, the electric machine is utilized to the maximum extent during braking, either absorbing all braking torque, ie the requested braking torque, or, if the requested braking torque exceeds the electric machine's actuator upper limit, setting the electric machine's desired braking torque to its braking torque upper limit.

[0028] According to an exemplary embodiment, the method may further include determining a desired braking torque of each of the third foundation brake and the fourth foundation brake based on the requested torque, the desired braking torque of the motor, and an actuator braking torque upper limit of each of the third foundation brake and the fourth foundation brake, thereby determining a total braking torque of the foundation brakes of the third wheel and the fourth wheel.

[0029] According to an exemplary embodiment, the method may further include determining a desired braking torque of each of the first foundation brake and the third foundation brake based on the requested torque, the desired braking torque of the motor, the desired braking torque of each of the third foundation brake and the fourth foundation brake, and an actuator braking torque upper limit of each of the first foundation brake and the second foundation brake. If necessary, the foundation brakes of the first wheel and the second wheel may absorb the remaining portion of the braking request.

[0030] According to an exemplary embodiment, the method may further include determining a first axle pressure level experienced by a first axle connected to the first wheel and the second wheel, determining a second axle pressure level experienced by a second axle connected to the third wheel and the fourth wheel, and further determining a desired braking torque for each of the first foundation brake and the second foundation brake based on a pressure ratio between the first axle pressure level and the second axle pressure level.

[0031] The axle pressure ratio between the front axle and the rear axle is determined from this.

[0032] According to an exemplary embodiment, the method may further include comparing the torque request with the desired braking torque of the electric machine and the desired braking torque of each of the first, second, third, and fourth foundation brakes, and when the torque request exceeds the desired braking torque of the electric machine and the desired braking torque of each of the first, second, third, and fourth foundation brakes: determining an updated desired braking torque for each of the third and fourth foundation brakes based on the requested torque, the desired braking torque of the electric machine, the desired braking torque of each of the first and second foundation brakes, and an actuator braking torque upper limit for each of the third and fourth foundation brakes.

[0033] Therefore, in the case where the desired braking torque exceeds the braking torque absorbed by the first to fourth foundation brakes and the braking torque absorbed by the electric machine, the remaining braking torque is absorbed by the third foundation brake and the fourth foundation brake.

[0034] According to a second aspect, a vehicle motion management system for a vehicle is provided, which can be connected to multiple actuators, and the multiple actuators can be operated to apply braking torque to the wheels of the vehicle. The vehicle motion management system includes a processing circuit, and the processing circuit is configured to: for each actuator, determine the actuator braking torque capacity range based on the actuator-specific torque capacity and the current operating state of the actuator; for each wheel of the vehicle, determine the road condition braking torque capacity range based on the estimated lateral wheel force acting on the wheel, the estimated friction coefficient between the tire surface of the wheel and the road surface, and the vertical wheel force acting on the wheel; and for each actuator, determine the actuator braking torque upper limit and the actuator braking torque lower limit based on the actuator braking torque capacity range and the road condition braking torque capacity range.

[0035] The effects and features of the second aspect are largely similar to those described above in relation to the first aspect.

[0036] According to a third aspect, there is provided a computer program comprising program code means for performing the steps of any one of the embodiments described above in relation to the first aspect when the program is run on a computer.

[0037] According to a fourth aspect, there is provided a computer readable medium carrying a computer program, the computer program comprising program means for executing the steps of any one of the embodiments described above with respect to the first aspect when the program means is run on a computer.

[0038] The effects and features of the third and fourth aspects are largely similar to those described above with respect to the first aspect.

[0039] Further features and advantages will become apparent when studying the appended claims and the following description. Those skilled in the art will realize that different features can be combined to create embodiments other than those described in the following, without departing from the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The foregoing, as well as additional objects, features and advantages, will be better understood through the following illustrative and non-limiting detailed description of exemplary embodiments, in which:

[0041] Figure 1 is a lateral side view showing an exemplary embodiment of a vehicle in the form of a truck;

[0042] Figure 2 is a schematic diagram of a wheel motion management system according to an exemplary embodiment;

[0043] Figure 3 is a graph illustrating an exemplary embodiment of a model representing the relationship between wheel slip and lateral wheel force; and

[0044] Figure 4 is a flow chart of a method for determining an actuator braking torque limit according to an exemplary embodiment. DETAILED DESCRIPTION

[0045] The present invention will now be described more fully below with reference to the accompanying drawings, in which exemplary embodiments are shown. However, the present invention may 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 the sake of thoroughness and completeness. Throughout this specification, like reference numerals refer to like elements.

[0046] Specific reference Figure 1 , depicting a vehicle 100 in the form of a truck. The vehicle includes a plurality of wheels 102. Specifically, the vehicle 100 includes a pair of front wheels 120 (also referred to as a first wheel and a second wheel), a pair of rear wheels 130 (also referred to as a third wheel and a fourth wheel). The exemplary vehicle 100 also includes a pair of wheels 132 disposed between the pair of front wheels 120 and the pair of rear wheels 130, and a pair of wheels 134 disposed behind the pair of rear wheels 130. The following description will focus on describing the present invention in relation to the pair of front wheels 120 and the pair of rear wheels 130, but the present invention is equally applicable to actuators of other wheels.

[0047] like Figure 1As illustrated, a pair of front wheels 120 and a pair of rear wheels 130 each include at least one actuator 104. Specifically, a first wheel and a second wheel of the pair of front wheels 120 each include an actuator 104 in the form of a first foundation brake and a second foundation brake, of which only the first foundation brake 108 is shown. A second wheel and a third wheel of the pair of rear wheels 130 each include an actuator 104 in the form of a third foundation brake and a fourth foundation brake, of which only the third foundation brake 110 is shown. The vehicle 100 also includes an actuator 104 in the form of a motor 106. Figure 1 1 shows an example of an electric motor 106 operable to apply propulsion torque as well as braking torque on a pair of rear wheels 130. The electric motor 106 is preferably connected to the third wheel and the fourth wheel via a differential coupling, i.e. a single electric motor 106 is used for propulsion and braking of the pair of rear wheels 130. However, the present invention is also applicable to so-called wheel hub motors, in which each of the third wheel and the fourth wheel is provided with a separate electric motor to control propulsion and braking.

[0048] Thus, the motor 106 is arranged to provide tire forces, for example, to the wheels of the vehicle 100. Thus, the motor 106 may be adapted to generate propulsion torque and to be arranged in a regenerative braking mode for charging a battery (not shown) or other energy storage system of the vehicle 100. The motor may also generate braking torque without storing energy. For example, a brake resistor or the like may be used to dissipate excess energy from the motor during braking.

[0049] Furthermore, each of the actuators 104 is connected to a corresponding motion support system 300, which is arranged to control the operation of the actuator 104. Although the motion support system 300 is preferably a decentralized motion support system 300, a centralized implementation is also possible. Furthermore, it should be understood that some parts of the motion support system may be implemented using a processing circuit system remote from the vehicle, such as on a remote server that can be accessed from the vehicle via a wireless link. Furthermore, each motion support system 300 is connected to a vehicle motion management system 200 of the vehicle 100 via a data bus communication device 114 or the like. Thus, control signals may be transmitted between the vehicle motion management system 200 and the motion support system 300. The various parts of the vehicle motion management system 200 will be referred to below. Figure 2 Described in further detail.

[0050] The vehicle 100 optionally includes a wireless communication transceiver arranged to establish a radio link with a wireless network including a remote server. In this way, the control unit can access the remote server to upload and download data. It is worth noting that the vehicle 100 can store measurement data (such as the amount of regenerative energy generated by the motor 106 at various geographical locations along different vehicle routes) in local memory or in a remote server. The vehicle movement management system 200 can also query the remote server for information about the amount of regenerative energy previously experienced, and / or the temperature increase of various vehicle components along a given route.

[0051] The vehicle motion management system 200 may also be arranged to obtain data indicating the expected rolling resistance for a given route, either manually configured or remotely from a remote server. The rolling resistance of the vehicle 100 will affect the energy consumption of the vehicle as it traverses the route. For example, a gravel road may require more energy than a smoother asphalt highway. In addition, friction and air resistance may reduce the requirement for generating negative torque during downhill travel.

[0052] The vehicle motion management system 200 and the motion support system 300 may include a microprocessor, a microcontroller, a programmable digital signal processor, or another programmable device. The system may also or alternatively include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. In the case where the system includes a programmable device (such as the microprocessor, microcontroller, or programmable digital signal processor mentioned above), the processor may also include computer executable code that controls the operation of the programmable device.

[0053] As described above, the vehicle motion management system 200 is configured to transmit control signals to the motion support systems 300. In more detail, the control distributor of the vehicle motion management system 200 determines the braking torque level to be applied by each actuator 104 based on the torque request received by the vehicle motion management system 200 in order to obtain the desired braking action of the vehicle 100. In other words, the vehicle motion management system 200 determines the actuator braking torque limit of each of the actuators 104, and based on the determined actuator braking torque limit, the control distributor determines the optimized braking torque distribution to produce the desired braking action while generating as much electricity as possible through energy recovery from the motor 106. Subsequently, a signal is transmitted to each of the motion support systems 300, the signal indicating the torque level to be applied by the actuator of each motion support system 300. Now referring to Figure 2 1 and 2. The portions of the vehicle motion management system 200 are described below, wherein an actuator braking torque limit is determined for each actuator 104 controlled by a corresponding motion support system 300.

[0054] Figure 2is a schematic diagram of various parts of a vehicle motion management system 200 according to an exemplary embodiment. Specifically, Figure 2 The illustrated vehicle motion management system 200 includes an actuator capability module 202 , a road condition capability module 204 , an actuator limit module 206 , and the control distributor 208 described above.

[0055] The actuator capability module 202 is configured to determine an actuator braking torque capability range at the actuator level (i.e., for each actuator 104). The actuator braking torque capability range is based on the actuator-specific torque capacity and the current operating state of the actuator 210. The actuator-specific torque capacity is hardware-related and specifies how much torque a specific actuator 104 is able to provide during braking. On the other hand, the current operating state of the actuator is an indication of the braking torque level currently applied by the actuator 104. Once the actuator braking torque capability range is determined, the actuator capability module 202 transmits a signal indicating an upper limit 212 of the actuator braking torque capability range and a lower limit 214 of the actuator braking torque capability range to the actuator limit module 206.

[0056] The road condition capability module 204 is configured to determine a road condition braking torque capability range at the wheel level (i.e., for each wheel provided with an actuator 104). The road condition braking torque capability range is determined accordingly to find a braking torque range that can be applied by the actuator 104 to the corresponding wheel without exceeding the friction limit. The road condition braking torque capability range is based on an estimated lateral wheel force 216 acting on the wheel 102, an estimated friction coefficient 218 between the tire surface of the wheel 102 and the road surface, and a vertical wheel force 220 acting on the wheel 102. Reference will be made to Figure 3 A detailed example of how to estimate the lateral wheel force 216 is given. The friction coefficient 218 between the tire surface of the wheel 102 and the road surface can be determined by, for example, a camera and measured temperature. Figure 2 As illustrated, the road condition braking torque capacity range may also advantageously be based on the wheel radius of the wheel 102. Once the road condition braking torque capacity range is determined, the road condition capability module 204 transmits a signal to the actuator limit module 206 indicating an upper limit 224 of the road condition braking torque capacity range and a lower limit 226 of the road condition braking torque capacity range.

[0057] After receiving signals from the actuator capability module 202 and the road condition capability module 204, the actuator limit module 206 determines an actuator braking torque upper limit 228 and an actuator braking torque lower limit 230 for each actuator 104. Therefore, the actuator braking torque upper limit 228 and the actuator braking torque lower limit 230 are based on the actuator braking torque capacity range and the road condition braking torque capacity range, which will be further illustrated in detail below. Subsequently, the actuator braking torque upper limit 228 and the actuator braking torque lower limit 230 are transmitted to the control distributor 208, which distributes the braking torque to each actuator 104 based on the received braking torque request and transmits a signal to each actuator control system 300 so that each actuator control system 300 controls its actuator 104 accordingly.

[0058] The following is a detailed example describing how to determine Figure 1 The upper limit 228 and the lower limit 230 of the actuator braking torque of the different actuators 104 are shown in FIG. 2. In addition, and for the convenience of the reader's understanding, the actuator braking torque capacity range and the road condition braking torque capacity range of the different actuators 104 are defined as follows: the upper limit 212 of the actuator braking torque capacity range is also referred to as the actuator max , and the lower limit 214 of the actuator braking torque capacity range is also referred to as the actuator min The upper limit 224 of the road condition braking torque capacity range is also referred to as T max , and the lower limit 226 of the road condition braking torque capacity range is also referred to as T min In addition, the limit values ​​will be indexed with reference to their corresponding actuators according to: Index fl = first wheel, i.e. left front wheel, Index fr = the second wheel, i.e. the right front wheel, Index rl = the third wheel, i.e. the left rear wheel, Index rr = the fourth wheel, the right rear wheel, and Index em = motor.

[0059] The maximum braking torque T that the actuator 104 can apply to the corresponding wheel without exceeding the friction limit can be calculated according to the following formula (1): max .

[0060] in: R w is the wheel radius, μ is the estimated friction coefficient 218 between the tire surface of the wheel 102 and the road surface, F zis the vertical wheel force 220 acting on the wheel 102, and F y is the estimated lateral wheel force 216 acting on the wheel 102 .

[0061] In addition, for the first foundation brake 104 (ie, the foundation brake acting on the left front wheel), an actuator braking torque upper limit 228 and an actuator braking torque lower limit 230 (hereinafter also referred to as and ) can be determined according to equations (2) and (3):

[0062] For the second foundation brake 104 (ie, the foundation brake acting on the right front wheel), the actuator braking torque upper limit 228 and the actuator braking torque lower limit 230 (hereinafter also referred to as and ) can be determined according to equations (4) and (5):

[0063] In addition, the motor's actuator braking torque upper limit 228 and the actuator braking torque lower limit 230 (hereinafter also referred to as and ) can be determined according to equations (6) and (7):

[0064] For the left and right rear wheels, the following equations are used to determine .

[0065] In addition, for the third foundation brake 104 (ie, the foundation brake acting on the left rear wheel), the actuator braking torque upper limit 228 and the actuator braking torque lower limit 230 (hereinafter also referred to as and ) can be determined according to equations (8) and (9):

[0066] Similarly, for the fourth foundation brake 104 (ie, the foundation brake acting on the right rear wheel), the actuator braking torque upper limit 228 and the actuator braking torque lower limit 230 (hereinafter also referred to as and ) can be determined according to equations (10) and (11):

[0067] The reason why the upper limit of the actuator braking torque of the motor is included in equations (8) and (10) is that Figure 1 In the example illustrated, the electric motor is applying braking torque to the rear wheels.

[0068] Thus, the upper and lower braking torque limits of each actuator are determined. The above actuator braking torque limits calculated according to equations (2) to (11) are transmitted to the control distributor 208. The control distributor is configured to determine the vector describing the torque on each actuator The following equation is used to determine the vector Very useful.

[0069] First, the control distributor 208 receives a signal indicating a requested braking torque T of the vehicle 100. 请求 The desired braking torque of the motor 106 can be determined by equation (12):

[0070] The total braking torque (hereinafter referred to as T b,r ) can be determined by equation (13):

[0071] where F z,f is the axle pressure on the first axle connected to the pair of front wheels, and F z,r is the axle pressure on the second axle connected to the pair of rear wheels. In addition, and as can be seen from equation (13), the capacity of the motor has also been taken into account.

[0072] The total braking torque (hereinafter referred to as T b,f ) can be determined by equation (14):

[0073] To ensure that as much of the requested braking torque as possible is distributed among the actuators, an updated total braking torque (hereinafter referred to as T ) for the third and fourth wheels (ie, both the left and right rear wheels) may be determined by equation (15): b,r,upd When the torque request exceeds the desired braking torque of the electric machine and the desired braking torque of each of the first foundation brake, the second foundation brake, the third foundation brake, and the fourth foundation brake, T is used. b,r,upd .

[0074] The control distributor 208 can now set the distributed torque to:

[0075] As a precaution to ensure that the actuator limits are not exceeded, a check is preferably performed, and if any of the torques determined by equation (16) exceeds the actuator torque upper limit 228, the specified torque is set to correspond to the actuator torque upper limit 228, and the remaining torque is added to the actuator on the other side of the same axle. As an example, if the braking torque on the foundation brake 108 of a first wheel exceeds its actuator torque upper limit 228, the remaining torque will be added to the foundation brake 108 of a second wheel.

[0076] Reference now Figure 3 , which is a graph showing an exemplary embodiment of a model representing the relationship between wheel slip and lateral wheel force. Figure 3 The model shown may be used to estimate the lateral wheel forces 216 described above.

[0077] It can be seen that Figure 3 Model 350 is shown representing the relationship between the calculated longitudinal wheel slip and the estimated longitudinal wheel force values, while model 450 represents the relationship between the maximum available lateral wheel force for a given longitudinal wheel slip. Model 450 may also represent the lateral wheel force obtained for a given longitudinal wheel slip for a predetermined lateral slip angle of the tire. Vertical axis 340 represents the tire force generated between the surface supporting wheel 102 and the wheel, while horizontal axis 330 represents the longitudinal wheel slip of wheel 102 according to equation (17):

[0078] in: λ is the wheel slip of the wheel; ω w is the rotation speed of the wheel; R w is the wheel radius; and V x , w is the longitudinal speed of the wheel.

[0079] By calculating the wheel slip and using Figure 3 Using the model in , the lateral forces acting on the wheels can be determined.

[0080] In summary, now refer to Figure 4, which is a flow chart of a method for determining the actuator braking torque limits of the above-mentioned plurality of actuators 104. During operation of the vehicle 100, S1 an actuator braking torque capability range is determined. As described above, the actuator braking torque capability range is based on the torque capacity of the above-mentioned actuator-specific and the current operating state of the actuator. In addition, S2 a road condition braking torque capability range is determined. Also as described above, the road condition braking torque capability range is based on the estimated lateral wheel force 216 acting on the wheel 102, the estimated friction coefficient 218 between the tire surface of the wheel 102 and the road surface, and the vertical wheel force 220 acting on the wheel. The road condition braking torque capability range is also preferably based on the wheel radius 222 of the wheel. The actuator braking torque capability range and the road condition braking torque capability range are transmitted to the actuator limit module 206, thereby determining S3 an actuator braking torque upper limit 228 and an actuator braking torque lower limit 230 for each of the plurality of actuators 104 based on the actuator braking torque capability range and the road condition braking torque capability range.

[0081] It should be understood that the present disclosure is not limited to the embodiments described above and shown in the drawings; rather, those skilled in the art will recognize that many changes and modifications may be made within the scope of the appended claims.

Claims

1. A method of determining an actuator braking torque limit of a plurality of actuators, wherein each actuator is operable to apply a braking torque on a wheel of a vehicle, the method comprising: - for each actuator, determining (S1) an actuator braking torque capability range based on the actuator-specific torque capacity and the current operating state of said actuator; - determining (S2) a road condition braking torque capacity range for each wheel of the vehicle based on an estimated lateral wheel force acting on the wheel, an estimated friction coefficient between a tire surface of the wheel and a road surface, and a vertical wheel force acting on the wheel; as well as - for each actuator, determining ( S3 ) an actuator braking torque upper limit and an actuator braking torque lower limit based on the actuator braking torque capacity range and the road condition braking torque capacity range. 2 . The method of claim 1 , wherein the current operating state of the actuator is a braking torque level currently applied by the actuator.

3. The method according to any one of claims 1 or 2, further comprising: - determining a wheel slip value for each wheel of the vehicle, and - Estimating the lateral wheel force based on a mapping model defining the relationship between wheel slip and the lateral wheel force.

4. A method according to any one of the preceding claims, wherein the road condition braking torque capacity range is further based on the wheel radius of the wheel.

5. The method according to any one of the preceding claims, wherein the plurality of actuators comprises: a first foundation brake operable to apply a braking torque on a first wheel; a second foundation brake operable to apply a braking torque on a second wheel; a third foundation brake operable to apply a braking torque on a third wheel; a fourth foundation brake operable to apply a braking torque on a fourth wheel; and a motor operable to apply braking torque on the third wheel and the fourth wheel. 6 . The method of claim 5 , wherein the electric machine is connected to the third wheel and the fourth wheel via a differential coupling.

7. The method according to any one of claims 5 or 6, wherein the upper limit of the actuator braking torque of each of the first foundation brake and the second foundation brake is the minimum of: - an upper limit of the actuator braking torque capacity range and an upper limit of the road condition braking torque capacity range, and The actuator braking torque lower limit of each of the first foundation brake and the second foundation brake is a lower limit of the actuator braking torque capacity range.

8. The method according to any one of claims 5 to 7, wherein the upper limit of the actuator braking torque of the motor is the minimum of: - the upper limit of the actuator braking torque capability range, and - A braking torque corresponding to twice the smallest of: - the upper limit of the road condition braking torque capacity range of the third wheel and the fourth wheel, and The lower limit of the actuator braking torque of the motor is the lower limit of the actuator braking torque capacity range.

9. The method of claim 8, wherein the actuator braking torque upper limit of each of the third foundation brake and the fourth foundation brake is a minimum value of: - the upper limit of the actuator braking torque capacity range and the upper limit of the road condition braking torque capacity range minus the actuator braking torque upper limit of the motor, and The actuator braking torque lower limit of each of the third foundation brake and the fourth foundation brake is a lower limit of the actuator braking torque capacity range.

10. The method according to any one of claims 8 or 9, further comprising: - receiving a signal indicative of a requested braking torque for decelerating said vehicle; as well as - determining a desired braking torque of the electric machine as a minimum of the requested braking torque and the actuator braking torque upper limit of the electric machine.

11. The method according to claim 10, further comprising: - determining a desired braking torque for each of the third foundation brake and the fourth foundation brake based on the requested torque, the desired braking torque of the electric machine, and the actuator braking torque upper limit for each of the third foundation brake and the fourth foundation brake.

12. The method according to claim 11, further comprising: - determining a desired braking torque for each of the first foundation brake and the third foundation brake based on the requested torque, the desired braking torque of the electric machine, the desired braking torque for each of the third foundation brake and the fourth foundation brake, and an actuator braking torque upper limit for each of the first foundation brake and the second foundation brake.

13. The method according to claim 11, further comprising: - determining a first axle pressure level to which a first axle connected to said first wheel and said second wheel is subjected, - determining a second axle pressure level experienced by a second axle connected to the third wheel and the fourth wheel, and - determining the desired braking torque of each of the first foundation brake and the second foundation brake also based on a pressure ratio between the first axle pressure level and the second axle pressure level.

14. The method according to claim 13, further comprising: - comparing the torque request to the desired braking torque of the electric machine and the desired braking torque of each of the first, second, third, and fourth foundation brakes, and when the torque request exceeds the desired braking torque of the electric machine and the desired braking torque of each of the first, second, third, and fourth foundation brakes: - determining an updated desired braking torque for each of the third foundation brake and the fourth foundation brake based on the requested torque, the desired braking torque of the electric machine, the desired braking torque for each of the first foundation brake and the second foundation brake, and the actuator braking torque upper limit for each of the third foundation brake and the fourth foundation brake.

15. A vehicle motion management system for a vehicle, the vehicle motion management system connectable to a plurality of actuators operable to apply braking torque on wheels of the vehicle, the vehicle motion management system comprising processing circuitry configured to: - for each actuator, determining an actuator braking torque capability range based on the actuator-specific torque capacity and the current operating state of said actuator; - determining, for each wheel of the vehicle, a road condition braking torque capacity range based on an estimated lateral wheel force acting on the wheel, an estimated coefficient of friction between a tire surface of the wheel and a road surface, and a vertical wheel force acting on the wheel; and - For each actuator, determining an actuator braking torque upper limit and an actuator braking torque lower limit based on the actuator braking torque capacity range and the road condition braking torque capacity range.

16. A computer program comprising program code means for performing the steps of any one of claims 1 to 14 when said program is run on a computer.

17. A computer-readable medium carrying a computer program, the computer program comprising program means for executing the steps according to any one of claims 1 to 14 when the program means is run on a computer.

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