阅读说明：本技术 用于控制车辆的方法和设备 (Method and apparatus for controlling vehicle ) 是由 C·查兹柯密斯 P·格鲁伯 A·索尔尼奥蒂 M·沙阿 M·巴斯汀 于 2018-04-26 设计创作，主要内容包括：公开了一种控制车辆的方法,所述方法包括以下步骤：考虑到车辆的操作极限,基于初始基准偏航力矩和总车轮扭矩需求来确定饱和基准偏航力矩；基于所述饱和基准偏航力矩来确定所述电动车辆的多个车轮中的每个车轮的初始扭矩分配；对于所述多个车轮中的每个车轮,检查所述车轮的初始扭矩分配是否超过所述车轮相应的车轮扭矩极限。响应于确定第一车轮的初始扭矩分配超过相应的车轮扭矩极限,并且在确定所述车辆相同侧的第二车轮的初始扭矩分配小于相应的车轮扭矩极限时,通过增加到第二个车轮的扭矩分配来修正初始扭矩分配。然后可以控制所述电动车辆,以将已修正的扭矩分配施加到所述多个车轮。还公开了用于控制车辆的设备。(Disclosed is a method of controlling a vehicle, the method including the steps of: determining a saturated reference yaw moment based on the initial reference yaw moment and the total wheel torque demand in view of operating limits of the vehicle; determining an initial torque distribution for each of a plurality of wheels of the electric vehicle based on the saturated reference yaw moment; for each of the plurality of wheels, checking whether an initial torque distribution for the wheel exceeds a respective wheel torque limit for the wheel. The initial torque distribution is modified by increasing the torque distribution to a second wheel in response to determining that the initial torque distribution for the first wheel exceeds the corresponding wheel torque limit and upon determining that the initial torque distribution for a second wheel on the same side of the vehicle is less than the corresponding wheel torque limit. The electric vehicle may then be controlled to apply the corrected torque distribution to the plurality of wheels. An apparatus for controlling a vehicle is also disclosed.)

1. A method of controlling a vehicle, the method comprising:

determining a saturated reference yaw moment based on the initial reference yaw moment and the total wheel torque demand in view of operating limits of the vehicle;

determining an initial torque distribution for each of a plurality of wheels of the electric vehicle based on the saturated reference yaw moment;

for each of the plurality of wheels, checking whether an initial torque distribution for the wheel exceeds a respective wheel torque limit for the wheel;

in response to determining that an initial torque distribution for a first wheel of the plurality of wheels exceeds a respective wheel torque limit for the first wheel and that an initial torque distribution for a second wheel of the plurality of wheels on the same side of the vehicle as the first wheel is less than a respective wheel torque limit for the second wheel, modifying the initial torque distribution by increasing the torque distribution to the second wheel and controlling the electric vehicle to apply the modified torque distribution to the plurality of wheels.

2. The method of claim 1, wherein the initial torque distribution is determined based on a vertical load on each of the plurality of wheels.

3. The method of claim 2, wherein the initial torque distribution on the side of the electric vehicle is determined by distributing torque to the plurality of wheels on the side of the electric vehicle in proportion to the respective vertical loads on the wheels.

4. The method of any one of the preceding claims, wherein determining the saturated reference yaw moment comprises:

determining, for the total wheel torque request, whether the reference yaw moment exceeds a maximum yaw moment or a minimum yaw moment defined by the operational limits; and

in response to determining that the reference yaw moment exceeds the maximum yaw moment or the minimum yaw moment, setting a limit of the saturated reference yaw moment to the maximum yaw moment or the minimum yaw moment, respectively.

5. The method of any preceding claim, wherein the operating limits of the electric vehicle are determined based on a maximum torque and a minimum torque applicable to each wheel of the electric vehicle, the operating limits comprising:

a maximum yaw moment obtainable by applying the maximum torque to a first plurality of wheels on one side of the electric vehicle and the minimum torque to a second plurality of wheels on an opposite side of the electric vehicle;

a minimum yaw moment obtainable by applying the minimum torque to the first plurality of wheels and the maximum torque to the second plurality of wheels;

a maximum total wheel torque that can be obtained by applying the maximum torque to each wheel of the electric vehicle; and

a minimum total wheel torque that can be achieved by applying the minimum torque to each wheel of the electric vehicle.

6. A computer readable storage medium arranged to store computer program instructions, characterized in that the computer program instructions, when executed, perform the method of any of the preceding claims.

7. An apparatus for controlling a vehicle, characterized in that the apparatus comprises:

a vehicle control unit configured to control the electric vehicle;

a torque distribution unit configured to: determining a saturated reference yaw moment based on an initial reference yaw moment and a total wheel torque demand, and determining an initial torque distribution for each of a plurality of wheels of the electric vehicle based on the saturated reference yaw moment, taking into account operating limits of the vehicle;

a wheel torque limit checking unit configured to check, for each of the plurality of wheels, whether an initial torque distribution for the wheel exceeds a respective wheel torque limit for the wheel; and

a torque redistribution unit for redistributing the torque,

wherein, in response to determining that an initial torque distribution of a first wheel of the plurality of wheels exceeds a respective wheel torque limit of the first wheel and determining that an initial torque distribution of a second wheel of the plurality of wheels on the same side of the vehicle as the first wheel is less than a respective wheel torque limit of the second wheel, the torque redistribution unit is configured to modify the initial torque distribution by adding a torque distribution to the second wheel and to control the vehicle control unit to apply the modified torque distribution to the plurality of wheels.

8. The apparatus of claim 7, wherein the torque distribution unit is configured to determine the initial torque distribution based on a vertical load on each of the plurality of wheels.

9. The apparatus of claim 8, wherein the torque distribution unit is configured to determine an initial torque distribution on a side of the electric vehicle by distributing torque to the plurality of wheels on the side of the electric vehicle in proportion to respective vertical loads on the wheels.

10. An apparatus according to claim 7, 8 or 9, characterized in that the torque distribution unit is configured to determine the saturated reference yaw moment by determining whether the reference yaw moment exceeds a maximum yaw moment or a minimum yaw moment defined by the operational limits for the total wheel torque demand; and in response to determining that the reference yaw moment exceeds the maximum yaw moment or the minimum yaw moment, setting a limit of the saturated reference yaw moment to the maximum yaw moment or the minimum yaw moment, respectively.

11. The apparatus according to any one of claims 7 to 10, wherein the torque distribution unit is configured to determine an operation limit of the electric vehicle based on a maximum torque and a minimum torque applicable to each wheel of the electric vehicle, the operation limit including:

a maximum yaw moment obtainable by applying the maximum torque to a first plurality of wheels on one side of the electric vehicle and the minimum torque to a second plurality of wheels on an opposite side of the electric vehicle;

a minimum yaw moment obtainable by applying the minimum torque to the first plurality of wheels and the maximum torque to the second plurality of wheels;

a maximum total wheel torque that can be obtained by applying the maximum torque to each wheel of the electric vehicle; and

a minimum total wheel torque that can be achieved by applying the minimum torque to each wheel of the electric vehicle.

12. An apparatus for controlling a vehicle, characterized in that the apparatus comprises:

one or more processors; and

computer readable memory arranged to store computer program instructions that, when executed by the one or more processors, cause the one or more processors to:

determining a saturated reference yaw moment based on the initial reference yaw moment and the total wheel torque demand in view of operating limits of the vehicle;

determining an initial torque distribution for each of a plurality of wheels of the electric vehicle based on the saturated reference yaw moment;

for each of the plurality of wheels, checking whether an initial torque distribution for the wheel exceeds a respective wheel torque limit for the wheel;

in response to determining that an initial torque distribution of a first wheel of the plurality of wheels exceeds a respective wheel torque limit of the first wheel and determining that an initial torque distribution of a second wheel of the plurality of wheels on the same side of the vehicle as the first wheel is less than a respective wheel torque limit of the second wheel, correcting the initial torque distribution by adding a torque distribution to the second wheel and controlling the electric vehicle to apply the corrected torque distribution to the plurality of wheels.

13. The apparatus of claim 12, wherein the computer program instructions are configured to determine the initial torque distribution based on a vertical load on each of the plurality of wheels.

14. The apparatus of claim 13, wherein the computer program instructions are configured to determine an initial torque distribution on a side of the electric vehicle by distributing torque to a plurality of wheels on the side of the electric vehicle in proportion to respective vertical loads on the wheels.

15. An apparatus as claimed in claim 12, 13 or 14, wherein the computer program instructions are configured to determine the saturated reference yaw moment by:

determining, for the total wheel torque request, whether the reference yaw moment exceeds a maximum yaw moment or a minimum yaw moment defined by the operational limits; and

in response to determining that the reference yaw moment exceeds the maximum yaw moment or the minimum yaw moment, setting a limit of the saturated reference yaw moment to the maximum yaw moment or the minimum yaw moment, respectively.

16. The apparatus of any one of claims 12 to 15, wherein the computer program instructions are configured to determine operating limits for the electric vehicle based on a maximum torque and a minimum torque applicable to each wheel of the electric vehicle, the operating limits comprising:

a maximum yaw moment obtainable by applying the maximum torque to a first plurality of wheels on one side of the electric vehicle and the minimum torque to a second plurality of wheels on an opposite side of the electric vehicle;

a minimum yaw moment obtainable by applying the minimum torque to the first plurality of wheels and the maximum torque to the second plurality of wheels;

a maximum total wheel torque that can be obtained by applying the maximum torque to each wheel of the electric vehicle; and

a minimum total wheel torque that can be achieved by applying the minimum torque to each wheel of the electric vehicle.

17. A vehicle, characterized in that it comprises a device according to any one of claims 7 to 16.

18. The vehicle of claim 17, characterized in that the vehicle is an electric vehicle.

Technical Field

The present invention relates to controlling a vehicle, such as an electric vehicle. More particularly, the present invention relates to a method and apparatus for determining a torque distribution for a plurality of wheels of a vehicle.

Background

Electric vehicles are known in which each wheel of the vehicle has its own dedicated electric motor. This arrangement allows the wheels of the vehicle to be driven independently of each other and allows different torques to be applied to each wheel. The process of determining how to distribute the available torque among the wheels is referred to as torque distribution.

Various torque distribution methods are known. For example, torque may be distributed to different wheels in order to optimize tire force (tire forces). However, the computational effort to accomplish this may be too large and the optimization process must be done in real time.

The invention has been made in such a situation.

Disclosure of Invention

According to a first aspect of the present invention, there is provided a method of controlling a vehicle, the method comprising: determining a saturated reference yaw moment based on the initial reference yaw moment and the total wheel torque demand in view of operating limits of the vehicle; determining an initial torque distribution for each of a plurality of wheels of the electric vehicle based on the saturated reference yaw moment; for each of the plurality of wheels, checking whether an initial torque distribution for the wheel exceeds a respective wheel torque limit for the wheel; in response to determining that an initial torque distribution for a first wheel of the plurality of wheels exceeds a respective wheel torque limit for the first wheel and determining that an initial torque distribution for a second wheel of the plurality of wheels on the same side of the vehicle as the first wheel is less than a respective wheel torque limit for the second wheel, modifying the initial torque distribution by increasing the torque distribution to the second wheel and controlling the electric vehicle to apply the modified torque distribution to the plurality of wheels.

In some embodiments according to the first aspect, the initial torque distribution is determined based on a vertical load on each of the plurality of wheels. For example, in one embodiment according to the first aspect, the initial torque distribution on the electric vehicle side is determined by distributing torque to the plurality of wheels on the electric vehicle side in proportion to the respective vertical loads on the wheels.

In some embodiments according to the first aspect, determining the saturated reference yaw moment comprises: determining, for the total wheel torque request, whether the reference yaw moment exceeds a maximum yaw moment or a minimum yaw moment defined by the operational limits; and in response to determining that the reference yaw moment exceeds the maximum yaw moment or the minimum yaw moment, rating the limit of the saturated reference yaw moment as the maximum yaw moment or the minimum yaw moment, respectively.

In some embodiments according to the first aspect, the operating limits of the electric vehicle are determined based on a maximum torque and a minimum torque applicable to each wheel of the electric vehicle, the operating limits comprising: maximum yaw moment, minimum yaw moment, maximum total wheel torque, and minimum total wheel torque. The maximum yaw moment may be obtained by applying the maximum torque to a first plurality of wheels on one side of the electric vehicle and the minimum torque to a second plurality of wheels on an opposite side of the electric vehicle; the minimum yaw moment may be obtained by applying the minimum torque to the first plurality of wheels and applying the maximum torque to the second plurality of wheels; the maximum total wheel torque may be obtained by applying the maximum torque to each wheel of the electric vehicle; the minimum total wheel torque may be obtained by applying the minimum torque to each wheel of the electric vehicle.

According to a second aspect of the present invention, there is provided a computer readable storage medium arranged to store computer program instructions which, when executed, perform a method according to the first aspect.

According to a third aspect of the present invention, there is provided an apparatus for controlling a vehicle, the apparatus comprising: a vehicle control unit, a torque distribution unit, a wheel torque limit checking unit, and a torque redistribution unit. The vehicle control unit is configured to control the electric vehicle; the torque distribution unit is configured to determine a saturated reference yaw moment based on an initial reference yaw moment and a total wheel torque demand, taking into account operational limits of the vehicle, and determine an initial torque distribution for each of a plurality of wheels of the electric vehicle based on the saturated reference yaw moment; the wheel torque limit checking unit is configured to check, for each of the plurality of wheels, whether an initial torque distribution of the wheel exceeds a respective wheel torque limit for the wheel; wherein, in response to determining that an initial torque distribution of a first wheel of the plurality of wheels exceeds a respective wheel torque limit of the first wheel and determining that an initial torque distribution of a second wheel of the plurality of wheels on the same side of the vehicle as the first wheel is less than a respective wheel torque limit of the second wheel, the torque redistribution unit is configured to modify the initial torque distribution by adding a torque distribution to the second wheel and to control the vehicle control unit to apply the modified torque distribution to the plurality of wheels.

In some embodiments according to the third aspect, the torque distribution unit is configured to determine the initial torque distribution based on a vertical load on each of the plurality of wheels. For example, in one embodiment according to the third aspect of the present invention, the torque distribution unit is configured to determine the initial torque distribution on the electric vehicle side by distributing torque to the plurality of wheels on the electric vehicle side in proportion to the respective vertical loads on the wheels.

In some embodiments according to the third aspect, the torque distribution unit is configured to determine the saturated reference yaw moment by determining, for the total wheel torque demand, whether the reference yaw moment exceeds a maximum yaw moment or a minimum yaw moment defined by the operational limits; and in response to determining that the reference yaw moment exceeds a maximum yaw moment or a minimum yaw moment, setting a limit of the saturated reference yaw moment to the maximum yaw moment or the minimum yaw moment, respectively.

In some embodiments according to the third aspect, the torque distribution unit is configured to determine operating limits of the electric vehicle based on a maximum torque and a minimum torque applicable to each wheel of the electric vehicle, the operating limits including: maximum yaw moment, minimum yaw moment, maximum total wheel torque, and minimum total wheel torque. The maximum yaw moment may be obtained by applying the maximum torque to a first plurality of wheels on one side of the electric vehicle and the minimum torque to a second plurality of wheels on an opposite side of the electric vehicle; the minimum yaw moment may be obtained by applying the minimum torque to the first plurality of wheels and applying the maximum torque to the second plurality of wheels; the maximum total wheel torque may be obtained by applying the maximum torque to each wheel of the electric vehicle; the minimum total wheel torque may be obtained by applying the minimum torque to each wheel of the electric vehicle.

According to a fourth aspect of the present invention, there is provided an apparatus for controlling a vehicle, the apparatus comprising: one or more processors and computer readable memory. The computer readable memory is arranged to store computer program instructions that, when executed by the one or more processors, cause the one or more processors to determine a saturated reference yaw moment based on an initial reference yaw moment and a total wheel torque demand, taking into account operational limits of the vehicle; determining an initial torque distribution for each of a plurality of wheels of the electric vehicle based on the saturated reference yaw moment; for each of the plurality of wheels, checking whether an initial torque distribution for the wheel exceeds a respective wheel torque limit for the wheel; in response to determining that an initial torque distribution for a first wheel of the plurality of wheels exceeds a respective wheel torque limit for the first wheel and that an initial torque distribution for a second wheel of the plurality of wheels on the same side of the vehicle as the first wheel is less than a respective wheel torque limit for the second wheel, modifying the initial torque distribution by increasing to the torque distribution for the second wheel and controlling the electric vehicle to apply the modified torque distribution to the plurality of wheels.

In some embodiments according to the fourth aspect, the computer program instructions are configured to cause the initial torque distribution to be determined based on a vertical load on each of the plurality of wheels. For example, in one embodiment according to the fourth aspect of the present invention, the computer program instructions are configured such that the initial torque distribution on one side of the electric vehicle is determined by distributing torque to a plurality of wheels on that side of the electric vehicle in proportion to respective vertical loads on the wheels.

In some embodiments according to the fourth aspect, the computer program instructions are configured to determine the saturated reference yaw moment by: determining, for the total wheel torque request, whether the reference yaw moment exceeds a maximum yaw moment or a minimum yaw moment defined by the operational limits; and in response to determining that the reference yaw moment exceeds a maximum yaw moment or a minimum yaw moment, setting a limit of the saturated reference yaw moment to the maximum yaw moment or the minimum yaw moment, respectively.

In some embodiments according to the fourth aspect, the computer program instructions are configured to determine operating limits of the electric vehicle based on a maximum torque and a minimum torque applicable to each wheel of the electric vehicle, the operating limits comprising: maximum yaw moment, minimum yaw moment, maximum total wheel torque, and minimum total wheel torque. The maximum yaw moment may be obtained by applying the maximum torque to a first plurality of wheels on one side of the electric vehicle and the minimum torque to a second plurality of wheels on an opposite side of the electric vehicle; the minimum yaw moment may be obtained by applying the minimum torque to the first plurality of wheels and applying the maximum torque to the second plurality of wheels; the maximum total wheel torque may be obtained by applying the maximum torque to each wheel of the electric vehicle; the minimum total wheel torque may be obtained by applying the minimum torque to each wheel of the electric vehicle.

According to a fifth aspect of the present invention, there is provided a vehicle comprising the apparatus of the third or fourth aspect. In some embodiments according to the fifth aspect, the vehicle is an electric vehicle.

Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 illustrates an electric vehicle according to an embodiment of the present invention;

FIG. 2 illustrates the yaw moment experienced by an electric vehicle when different levels of torque are applied on opposite sides of the vehicle, according to an embodiment of the present invention;

FIG. 3 illustrates symbols used throughout this document to refer to certain vehicle sizes and the components of forces acting on the vehicle;

FIG. 4 illustrates operational boundaries of a vehicle defined by maximum and minimum yaw moments and maximum and minimum wheel torques in accordance with an embodiment of the present invention;

FIG. 5 illustrates a change in operational boundaries due to a reduction in maximum wheel torque of either the front right-hand tire or the rear right-hand tire;

FIG. 6 illustrates a change in operational boundaries due to a reduction in maximum wheel torque for either the left hand front tire or the left hand rear tire;

fig. 7 is a flowchart illustrating a method of controlling an electric vehicle according to an embodiment of the present invention;

FIG. 8 is a flow chart illustrating a method for determining whether to modify the initial torque distribution according to an embodiment of the present invention;

FIG. 9 is a flow chart illustrating a method of correcting an initial torque distribution when the torque distribution for any wheel will exceed an operational limit in accordance with an embodiment of the present invention; and

fig. 10 schematically illustrates the structure of a control unit for controlling an electric vehicle according to an embodiment of the present invention.

Detailed Description

In the following detailed description, certain exemplary embodiments of the present invention are shown and described, simply by way of illustration. As will be realized by those skilled in the art, the described embodiments can be modified in various different ways, all without departing from the scope of the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. Like reference numerals refer to like elements throughout the specification.

Referring now to fig. 1, an electric vehicle according to an embodiment of the invention is illustrated. In the present embodiment, the vehicle 100 comprises four wheels 101, 102, 103, 104 and four electric motors 111, 112, 113, 114, each arranged to independently drive a respective one of the wheels 101, 102, 103, 104 via a gearbox 115 and an axle 116. The wheels are arranged as a pair of front wheels 101, 102 and a pair of rear wheels 103, 104. However, in other embodiments, other numbers of wheels and other arrangements are possible. In some embodiments, additional axles may be provided, and/or the vehicle may include an odd number of wheels, e.g., a pair of rear wheels and a single front wheel.

The wheels that can be driven by the motor may be referred to as "driven wheels". In addition to a plurality of driven wheels, in some embodiments of the invention, the vehicle may further include one or more non-driven wheels that are not connected to the motor, but are free to rotate due to contact with the road surface during movement of the vehicle. For example, in another embodiment of the invention, the front wheels may be non-driven wheels, while only the rear wheels may be driven by the motor, or vice versa.

The plurality of motors 111, 112, 113, 114 may be controlled to exert a yaw moment on the electric vehicle 100. Here, "yaw" is used in its conventional sense to refer to rotation of the vehicle about a vertical axis. For example, the plurality of motors 111, 112, 113, 114 may be controlled to apply a higher torque to one side wheel of the vehicle 100 than to the other side wheel of the vehicle 100. The result is that the vehicle 100 is subjected to a greater acceleration force on the side to which the higher torque is applied. Therefore, the vehicle 100 is subjected to a moment about the vertical axis. This moment may be referred to as a yaw moment and the vertical axis may be referred to as a yaw axis.

FIG. 2 illustrates the yaw moment M experienced by the electric vehicle 100 when different levels of torque are applied on opposite sides of the vehicle 100_z,HL. In FIG. 2, T_w,rrRepresents the torque, T, applied to the right rear wheel 104_w,lrRepresenting the torque, T, applied to the left rear wheel 103_w,rfIndicates the torque, T, applied to the right front wheel 102_w,lfIndicating the torque applied to the left front wheel 101. T is_w,rRepresenting the total torque applied to the wheels 102, 104 on the right hand side of the vehicle 100. T is_w,lRepresenting the total torque applied to the wheels 101, 103 on the left hand side of the vehicle 100. T is_w,modRepresenting the total torque applied to the four wheels 101, 102, 103, 104 of the vehicle 100.

With continued reference to fig. 1, the vehicle 100 further includes: a yaw rate sensor 120 and a control unit 130. The yaw rate sensor 120 is arranged to measure the yaw rate of the vehicle 100, and the control unit 130 is configured to determine a reference yaw rate r_refAnd a yaw rate measurement value r obtained by the yaw rate sensor 120, based on the reference yaw rate r_refTo determine a reference yaw moment M of the vehicle 100_Z. The control unit 130 is further configured to base the reference yaw moment M_ZAnd total wheel torque request T_w,modDetermines a torque distribution defining the torque to be applied to each of the plurality of wheels 101, 102, 103, 104, and controls the plurality of motors 111, 112, 113, 114 to distribute the determined torque to the plurality of wheels 101, 102, 103, 104.

Yaw rate is the angular velocity of rotation about the yaw axis, usually expressed in degrees per second or radians per second. Yaw rate sensor 120 may be any suitable type of yaw rate sensor, such as a piezoelectric sensor or a micromechanical sensor. Examples of suitable yaw rate sensors are known in the art, and a detailed description of the operation of yaw rate sensor 120 will not be provided herein to avoid obscuring the concepts of the present invention.

Depending on the embodiment, the control unit 130 may be implemented in hardware, for example using an Application Specific Integrated Circuit (ASIC) or a Field Programmable Gate Array (FPGA), or may be implemented in software. In the present embodiment, a software implementation is used, and the control unit 130 comprises a processing unit 131 and a computer readable memory 132, the computer readable memory 132 being arranged to store computer program instructions executable by the processing unit 131 to determine the reference yaw rate. The processing unit 131 may include one or more processors.

The control unit 130 is configured to determine a reference yaw rate based on the steering angle δ and the vehicle speed V, and to adjust according to the value of the rear wheel slip angle β r that has been obtained,rear wheel slip angle beta_rThe current measured offset of the vehicle from the rear axle is described. Depending on the embodiment, the rear wheel slip angle may be measured at a point in line with the rear axle 116, or may be derived from a measurement of the slip angle at a distance from the rear axle 116, for example in some embodiments, a current value of the slip angle may be obtained by deriving an estimated slip angle based on a measurement of one or more other physical quantities, rather than measuring the slip angle directly. For example, an estimated slip angle is derived based on the current steering angle, yaw rate, lateral acceleration, and forward acceleration.

Fig. 3 illustrates symbols used to refer to certain vehicle sizes and the components of the forces exerted on the vehicle 100. Throughout this document the following definitions are used:

beta is the angle of departure at the center of gravity of the vehicle

β_rRear wheel slip angle

u-forward velocity component

v ═ lateral velocity component

V-vehicle actual speed

r-yaw rate of vehicle

a is the distance between the front axle and the center of gravity of the vehicle

b is the distance between the rear axle and the center of gravity of the vehicle

d_fSemi-wheelbase (front)

d_rSemi-wheelbase (rear)

d-average track half (d)_f+d_r)/2

R-wheel radius

In this embodiment, the following notation convention is employed: defining a yaw moment or rate that is positive for a counterclockwise rotation (i.e., turning the vehicle to the left); defining a clockwise rotation (i.e., turning the vehicle to the right) as a negative yaw moment or rate. It should be understood that if the opposite sign convention is employed, the equations disclosed herein may be modified as desired. It should also be understood that the equations disclosed herein are equations for a four-wheel vehicle in which each wheel can be independently driven, and if the vehicle includes a different number of driven wheels, the equations can be modified as needed.

The control unit 130 may take into account certain operating limits of the vehicle 100 when allocating available torque to the wheels of the vehicle 100. In the present embodiment, the operation limits, referred to as a maximum wheel torque limit and a minimum wheel torque limit, are determined based on a maximum torque and a minimum torque that can be applied to each wheel of the electric vehicle 100. The torque limit for any given wheel depends on factors such as the maximum and minimum torques that can be applied by the motor, and the wheel operating conditions. The wheel operating conditions may be defined in terms of various parameters including, but not limited to, the coefficient of friction between the wheels and the road surface, the slip ratio (slip ratio), and the vertical load. The operating limits are defined according to boundaries determined by the following parameters:

maximum yaw moment M_z,maxThe maximum yaw moment M can be obtained by applying the maximum torque to the wheels on one side of the electric vehicle and the minimum torque to the wheels on the opposite side of the electric vehicle_z,max；

Minimum yaw moment M_z,minThe minimum yaw moment M may be obtained in the opposite direction to the maximum yaw moment by applying the minimum torque to one side wheel and the maximum torque to the opposite side wheel_z,min；

Maximum total wheel torque T_w,maxThe maximum total wheel torque T may be obtained by applying the maximum torque to each wheel of the electric vehicle_w,max(ii) a And

minimum total wheel torque T_w,minThe minimum total wheel torque T may be obtained by applying the minimum torque to each wheel of the electric vehicle_w,min。

Maximum yawing moment M_z,maxThe maximum yaw moment M is the maximum yaw moment in the positive direction (i.e., the vehicle turns left), when the minimum torque is applied to the wheels on the left-hand side of the vehicle 100 and the maximum torque is applied to the wheels on the right-hand side of the vehicle 100_z,maxThe following will occur:

total wheel torque T when said maximum yaw moment is applied_w,Mz,maxComprises the following steps:

T_w,Mz,max＝T_w,rf,max+T_w,rr,max+T_w,lf,min+T_w,lr,min

minimum yaw moment M_z,minThe minimum yaw moment M is the maximum yaw moment in the negative direction (i.e., the vehicle turns to the right), when the minimum torque is applied to the wheels on the right hand side of the vehicle 100 and the maximum torque is applied to the wheels on the left hand side of the vehicle 100_z,minThe following will occur:

total wheel torque T when the minimum yaw moment is applied_w,Mz,minComprises the following steps:

T_w,Mz,min＝T_w,rf,min+T_w,rr,min+T_w,lf,max+T_w,lr,max

maximum wheel torque T_w,maxIs the maximum total torque that can be applied to all wheels of the vehicle 100, as follows:

T_w,max＝T_w,rf,max+T_w,rr,max+T_w,lf,max+T_w,lr,max

a yaw moment M generated on the vehicle 100 when the maximum torque is applied to each wheel_z,Tw,maxIs derived from the following formula:

similarly, the minimum wheel torque T_w,minIs the minimum total torque that can be applied to all wheels of the vehicle 100, as follows:

T_w,min＝T_w,rf,min+T_w,rr,min+T_w,lf,min+T_w,lr,min

a yaw moment M generated on the vehicle 100 when the minimum torque is applied to each wheel_z,Tw,minIs derived from the following formula:

in FIG. 4, the maximum yaw moment M is plotted_z,maxAnd minimum yaw moment M_z,minAnd maximum wheel torque T_w,maxAnd minimum wheel torque T_w,minThe operation boundary of the vehicle in the present embodiment is defined. The graph in fig. 4 illustrates the operational boundaries under nominal conditions. The boundary may move with changes in the vehicle conditions, for example during cornering, the shape defined by the operational boundary may change due to changes in vertical load, motor limit, and/or coefficient of friction at the wheels. In this embodiment, all four motors 111, 112, 113, 114 are capable of applying the same maximum torque, and are capable of applying equal levels of tractive effort and braking torque. That is, the maximum torque that can be applied to each wheel is equal in magnitude and opposite in sign to the minimum torque that can be applied to that wheel, i.e., T_w,max＝-T_w,min. Further, in the present embodiment, the front-half track width df is equal to the rear-half track width dr. Thus, since the torque on one side of the vehicle is equal in magnitude and opposite in sign to the total torque on the opposite side of the vehicle, the moment M is at maximum yaw_z,maxAnd minimum yaw moment M_z,minTotal wheel torque T_w,Mz,max、T_w,Mz,minAre all equal to zero. Thus, the point (T)_w,Mz,max,M_z,max) And (T)_w,Mz,min,M_z,min) Are all located on the y-axis, i.e. line T_w＝0。

Similarly, in the present embodiment, when the maximum wheel torque T is applied_w,maxOr minimum wheel torque T_w,minThe total yaw moment at time is equal to zero because equal torque is applied on both sides of the vehicle 100. Thus, in FIG. 4, the point (T)_w,max,M_z,Tw,max) And (T)_w,min,M_z,Tw,min) Are all located on the x-axis, i.e. line M_z＝0。

The importance of the operating limits can be further explained with reference to fig. 5 and 6. Fig. 5 illustrates how the operating limits change when the maximum torque that can be applied to either of the right hand side wheels 102, 104 is reduced, for example due to a failure of one of the right hand side motors 112, 114. Fig. 6 illustrates how the operating limits change when the maximum torque that can be applied to either of the left hand wheels 101, 103 is reduced, for example due to a failure of one of the left hand motors 111, 113. When maximum wheel torque T is applied_w,maxWhen the torque capacity of a wheel is reduced, an imbalance is created, resulting in a net positive or negative moment M_z,Tw,max. A reduction in the maximum torque of one wheel also results in a reduction in the maximum yaw moment that can be applied. For example, if the reduction occurs at one of the right hand wheels 102, 104, the maximum yaw moment M that can be applied in a positive direction_z,maxAnd decreases. Similarly, if the reduction occurs at one of the left hand side wheels 101, 103, then the maximum yaw moment M that can be applied in a negative direction_z,minAnd decreases.

Referring now to fig. 7, a flowchart illustrating a method of controlling an electric vehicle is illustrated, in accordance with an embodiment of the present invention. The flowchart illustrates the steps performed by the control unit 130.

In step S701, the control unit 130 sets the reference yaw rate r_refAnd determining a reference yaw moment M_z,HLSo as to track said reference yaw rate r_ref. The control unit 130 also calculates the total wheel torque request T_w,modAnd steering angle delta from the driver. The reference yaw moment M may be set according to the current operating conditions of the electric vehicle_z,HLAnd total wheel torque request T_w,mod. For example, in some embodiments, the control unit 130 may automatically adjust the total wheel torque request T when a large yaw rate error is detected_w,mod。

In the present embodiment, it is preferred that,the control unit 130 is configured to set the reference yaw rate r based on the steering angle δ and the vehicle speed V_refAnd is adjusted according to the value of the rear wheel slip angle β r that has been obtained. Reference yaw rate r_refIs the yaw rate deemed appropriate for the vehicle handling characteristics and current friction conditions of the wheels. For example, the control unit 130 may set a higher reference yaw rate for a lower rear wheel slip angle, and may set a lower reference yaw rate for a higher rear wheel slip angle.

In other embodiments, the set reference yaw rate r may be used in step S701_refIrrespective of the rear wheel slip angle beta_r. For example, in another embodiment, the reference yaw rate r may be determined based on an estimated coefficient of friction between the tire and the road surface_refAlternatively, any other suitable method may be used to determine the reference yaw rate r_ref. Setting a reference yaw rate r_refAnd a reference yaw moment M_z,HLAre known in the art, and a detailed description of alternative methods will not be provided herein to avoid obscuring the inventive concepts. For example, in another embodiment, the reference yaw rate r_refCan be determined using a method similar to that disclosed in "Bosch ESP Systems:5 Yeast of Experimental", van Zanten, A., SAE technical paper 2000-01-1633,2000, doi:10.4271/2000-01-1633 ", wherein vehicle parameters including wheel base and characteristic speed are considered, and r is determined based on vehicle speed and steering angle_ref。

Next, in step S702, the control unit 130 determines the dynamic saturation reference yaw moment M in consideration of the operation limit_z,HL,sat. Dynamic saturated reference yawing moment M_z,HL,satIs the maximum yaw moment that can be achieved in the direction of the reference yaw moment while still meeting the total wheel torque requirement T_w,mod. In the present embodiment, a dynamic saturated reference yaw moment M is defined_z,HL,satThe following were used:

in other embodimentsTo account for the safety factor, an upper limit of the saturated reference yaw moment may be set at a certain percentage of the maximum or minimum yaw moment. For example, in some embodiments, a saturated reference yaw moment may be set to an upper limit of 0.9M in the positive direction_z,max,Tw,modAnd an upper limit of the saturated reference yaw moment is set to 0.9M in the negative direction_z,min,Tw,mod。

Once the saturated reference yaw moment M is obtained_z,HL,satThen, in step S703, the control unit 130 determines the total wheel torque that can be applied to each side of the vehicle 100 so as to generate the saturated reference yaw moment M_z,HL,satAnd satisfies the total wheel torque demand T_w,modThe following are:

wherein, T_w,lIs the total wheel torque on the left hand side of the vehicle 100, and T_w,rIs the total wheel torque on the right hand side of the vehicle 100.

Next, in step S704, the control unit 130 determines an initial torque distribution for each of the plurality of wheels on each side of the vehicle 100 according to the torque distribution criteria. In the present embodiment, the control unit 130 takes the vertical load on each of the plurality of wheels as a torque distribution criterion. In other embodiments, different criteria may be used to determine how to distribute torque between the wheels on one side of the vehicle 100. In other embodiments, examples of alternative criteria that may be used in step S704 for distributing torque include, but are not limited to, tire operating load, tire deflection loss, and minimization of driveline power input.

For example, the control unit 130 may be configured to estimate the vertical load on each wheel based on information about the vehicle weight, suspension geometry and/or driving conditions. When the vehicle 100 turns, the vertical load of the wheels on the outer side of the corner will increase, and the vertical load of the wheels on the inner side of the corner will decrease. Also, during acceleration or braking, the vertical load will change. In addition, the vertical load will vary due to the aerodynamic characteristics of the vehicle 100, e.g., aerodynamic front lift (aerodynamic nose lift) may reduce the vertical load of the front wheels. The control unit 130 may be pre-programmed with the necessary information to estimate the vertical load of each wheel.

In the present embodiment, once the control unit 130 determines the vertical load of each wheel, for example by estimating the vertical load as described above or by receiving measurement values from sensors, the control unit 130 determines each wheel T_w,lf、T_w,lr、T_w,rf、T_w,rrThe initial torque distribution of (c) is as follows:

here, T_w,lfFor the initial torque distribution, T, of the left front wheel_w,lrFor the initial torque distribution of the left rear wheel, T_w,rfFor the initial torque distribution, T, of the right front wheel_w,rrIs the initial torque distribution for the right rear wheel. Similarly, F_z,lfVertical load of the left front wheel, F_z,lrFor vertical loading of the left rear wheel, F_z,rfVertical load of the right front wheel, F_z,rrIs the vertical load of the right rear wheel. In this manner, the total wheel torque on one side of the vehicle 100 is distributed among the wheels on that side in proportion to the corresponding vertical loads.

Next, in step S705, the control unit 130 checks whether the initial torque distribution of each of the plurality of wheels 101, 102, 103, 104 would exceed the wheel torque limit corresponding to that wheel. A wheel may be said to be "saturated" if its initial torque distribution exceeds its wheel torque limit.

If any of the wheels is found to be saturated, it is determined in step S705 that the initial torque distribution cannot actually be achieved. If this is the case, in step S706, the control unit 130 corrects the initial torque distribution by attempting to redistribute the excess torque originally distributed to the saturated wheels to one or more unsaturated wheels on the same side of the vehicle 100. In the event that one or more wheels are in saturation, the torque redistributed in step S706 may ensure that the modified torque distribution still provides a total wheel torque on the side of the vehicle 100 that is as close as possible to the total wheel torque required on the side of the vehicle 100, and that the total wheel torque on both sides is as close as possible to the total wheel torque requirement. This in turn ensures that the achieved yaw moment is as close as possible to the saturated reference yaw moment M_z,HL,sat. In step S707, the control unit 130 controls the electric vehicle 100 to apply the corrected torque distribution to the plurality of wheels 101, 102, 103, 104.

In contrast, the prior art torque distribution methods do not redistribute the excess torque to the other wheels. This may result in the actual total wheel torque being significantly less than the required total wheel torque demand when the wheels are in saturation. As an example, if there is a vertical load of 4000N at each wheel and a total wheel torque demand of 2000Nm at the left hand side of the vehicle 100, then torque is initially distributed in proportion to the vertical load in step S704, and the initial torque distribution for the left front wheel 101 and the left rear wheel 103 is 1000Nm each. If the individual wheel torque limits for the front left wheel 101 and the rear left wheel 103 are 400Nm and 2200Nm, respectively, then a conventional torque distribution method without torque redistribution would result in 400Nm of wheel torque being applied to the front left wheel 101 and 1000Nm of wheel torque being applied to the rear left wheel 103. This will result in a total wheel torque 1400Nm at the left hand side of the vehicle 100, which is less than 2000Nm for the total wheel torque demand at the left hand side. Conversely, when the front left wheel 101 is found to be in saturation, 600Nm of excess torque can be redistributed to the rear left wheel 103 by redistributing the torque in step S706, thereby ensuring that a total wheel torque demand of 2000Nm at the left hand side of the vehicle 100 is still achieved.

Under certain operating conditions, the total wheel torque demand requested by the driver of the vehicle 100 may not be met while also achieving the saturated reference yaw moment M_z,HL,sat. For example, if one or more wheels on one side of the vehicle 100 are in a saturated condition, there may be a situation where the reserve torque capacity at the unsaturated wheel is insufficient to redistribute all of the excess torque of the saturated wheel. In that case, the total wheel torque on that side of the vehicle will be less than the total wheel torque demand on that side of the vehicle, and the resulting yaw moment will be compared to the saturated reference yaw moment M_z,HL,satDifferent. In some embodiments of the invention this may be done by correcting the total wheel torque request T when a large yaw rate error is detected, i.e. when the error between the measured yaw rate and the reference yaw rate exceeds a certain threshold value_w,modTo solve the problem. For example, the total wheel torque request T may be calculated prior to calculating the torque distribution_w,modReduced from the driver demand level to ensure that the saturated reference yaw moment M can still be achieved_z,HL,sat。

On the other hand, if no wheel saturation is found in step S705, the control unit 130 directly proceeds to step S707 and controls the electric vehicle 100 to apply the initial torque distribution to the plurality of wheels 101, 102, 103, 104. This avoids unnecessarily expending processing power and system resources to correct the torque distribution when the initial torque distribution is acceptable.

Referring now to FIG. 8, a flowchart illustrating a method for determining whether to modify an initial torque split is illustrated, in accordance with an embodiment of the present invention. During step S705 of the flowchart shown in fig. 7, the steps illustrated in fig. 8 may be performed. However, in other embodiments, a different method may be used in step S705 instead of the method shown in fig. 8.

First, in step S801,the control unit 130 checks whether each wheel is saturated by comparing the initial torque distribution of each wheel with the individual wheel torque limits of that wheel. A wheel is said to be saturated if its initial torque distribution exceeds its wheel torque limit. For example, when T_w,lf＞T_w,lf,maxWhen it is time, the left front wheel is saturated.

If in step S801 it is found that the initial torque distribution for a wheel exceeds the torque limit for that wheel, then in step S802 the wheel is marked as "saturated", for example by setting the value of the boolean flag to "true" in association with that wheel. In step S803, the control unit 130 checks whether all the wheels have been checked. If not, the control unit repeats steps S801 and S802 until all wheels have been checked.

Then, in step S804, the control unit checks the state of the flag set in step S802 to determine whether any wheel saturation is found. If none of the wheels is saturated, the process directly continues to step S707 and the motors 111, 112, 113, 114 are controlled to distribute a respective initial torque to each wheel 101, 102, 103, 104.

On the other hand, if any wheel is found to be saturated in step S804, the control unit proceeds to step S706 and calculates a corrected torque distribution. FIG. 9 is a flow chart illustrating a method of correcting an initial torque distribution when the torque distribution for any wheel will exceed an operational limit in accordance with an embodiment of the present invention. The steps shown in fig. 9 may be performed during step S706 of the flowchart shown in fig. 7. However, in other embodiments, a different method may be used in step S706 instead of the method shown in fig. 9.

To avoid confusion, the corrected torque distribution for a particular wheel is referred to hereinafter as a 2-stage torque distribution (designated by subscript L)₂Labeled) and the initial torque split for a particular wheel is referred to hereinafter as the level 1 torque split (by subscript L)₁A marker).

The process shown in fig. 9, starting in step S901, is performed by selecting one of the saturated wheels and checking the same side as the selected wheelIs also saturated. If all wheels on one side of the vehicle are saturated, the control unit 130 proceeds to step S902 and decreases the wheel torque distribution on that side to meet the individual wheel torque limit. In the present embodiment, in step S902, the L of each wheel on the side of the vehicle is adjusted by₂The torque distribution is set equal to the respective wheel torque limits to modify the torque distribution. In other embodiments, L may be₂The torque distribution is set below the respective wheel torque limit, for example, set at 90% of the wheel torque limit.

On the other hand, if it is found in step S901 that not all the wheels on one side are saturated, in the present embodiment, the surplus torque that has been distributed to the saturated wheels is redistributed to any of the unsaturated wheels on the same side of the vehicle. This ensures that the total wheel torque on that side is as close as possible and ideally equal to the total wheel torque demand on that side. In the present embodiment, the torque is redistributed in step S903.

In step S903, the control unit 130 distributes the excess torque of the saturated wheel to the unsaturated wheel on the same side. In step S903, L of the wheel is saturated, similarly to step S902₂The torque distribution is set equal to the individual wheel torque limit for that wheel.

For example, if the front left wheel 101 is saturated and there is reserve torque capacity on the rear left wheel 103 (i.e., the rear left wheel 103 is not saturated), T will be_w,lf,L2Set equal to the individual wheel torque limit T of the left front wheel 101_w,lf,max. In this example, this causes the amount of unallocated torque on the left side of the vehicle to be equal to T_w,lf,sat－T_w,lf,max. Thus, in this embodiment, L of the left rear wheel 103₂The torque split is set equal to the left total wheel torque demand and the wheel torque limit (T) of the left front wheel 101_w,lf,sat－T_w,lf,max) So that the total torque on the left side of the vehicle is equal to the total wheel torque demand on the left hand side.

In the case of towing, the final L is determined for one side of the vehicle (e.g., left hand side)₂The process of torque distribution can be summarizedThe following is concluded:

in the case of braking, L ends up₂The torque split can be summarized as follows:

wherein T is the case when none of the left-hand wheels is saturated_w,lf,L2＝T_w,lf,L1And T_w,lr,L2＝T_w,lr,L1Initial L indicating that all wheels remain₁And (4) torque distribution.

Once the final L has been determined on one side of the vehicle₂Torque distribution, the control unit 130 checks whether the torque distribution on both sides of the vehicle 100 has been processed in step S904. If so, the process proceeds to step S707, and the control unit 130 controls the electric vehicle 100 to set the final L₂The torque distribution is applied to the wheels 101, 102, 103, 104.

On the other hand, if the other side has not been processed, the control unit 130 checks the state of the flag of the other side wheel of the vehicle 100 to see whether any wheel on the other side is saturated in step S905. If any wheel on the other side is saturated, the control unit 130 returns to step S901 and repeats setting of L on the other side of the vehicle₂And (5) torque distribution. If none of the wheels on the other side are saturated, the control unit 130 maintains the initial L on that side of the vehicle₁Torque is distributed, and proceeds to step S707 as before.

A method such as that illustrated in fig. 9 may be used to redistribute excess torque from a saturated wheel to other wheels of the vehicle having spare torque capacity on the same side of the vehicle so that the total wheel torque demand may still be achieved.

Referring now to fig. 10, a structure of a control unit for controlling an electric vehicle is schematically illustrated according to an embodiment of the present invention. The diagram shown in fig. 10 is intended to convey an understanding of the flow of information within the device and the operations performed. It should be understood that the architecture shown in fig. 10 is provided for illustrative purposes only and should not be construed to imply a particular physical layout or functional separation between physical components. For example, some of the elements shown in FIG. 10 may be implemented in hardware, while other elements may be implemented in software.

In this embodiment, the apparatus is configured to receive a total torque request T_w,totAnd control inputs 1000 in the form of steering angle delta, and sensor inputs from sensor system 1010. In the present embodiment, the sensor input includes a rear wheel slip angle β_rVehicle speed V, lateral acceleration a_yLongitudinal acceleration a_xAnd the measured yaw rate r. In other embodiments, different sensor inputs may be provided depending on the method used to calculate the reference yaw moment and the required parameters. The apparatus further comprises a reference yaw rate setting unit 1020, the reference yaw rate setting unit 1020 being configured to set a reference yaw rate r based on the steering angle δ and the vehicle speed V_refAnd according to the obtained rear wheel slip angle beta_rAnd (6) adjusting.

The apparatus further comprises a reference yaw moment setting unit 1030, the reference yaw moment setting unit 1030 being configured to set a reference yaw rate r based on the reference yaw rate r_refAnd the error between the measured yaw rate r and the total wheel torque request T_w,totAccording to the reference yaw rate r_refTo set a reference yaw moment M_z. In the present embodiment, the reference yaw moment setting unit 1030 includes a feedback-plus-feedforward yaw rate tracking controller 1031 configured to receive a signal including a vehicle speed V, a longitudinal acceleration a, and a feedback-plus-feedforward yaw rate tracking controller 1031_xAnd a feed forward input of steering angle delta. In other embodiments, feedback control alone may be used rather than the inverse as in the present embodimentFeed-forward and feed-forward control to set the reference yaw moment. The input parameters may be selected according to the selected control algorithm.

The apparatus further comprises a vehicle control unit 1040, the vehicle control unit 1040 being configured to distribute torque to different wheels of the vehicle 100, and a vehicle control unit 1050 controlling the electric vehicle 100 to apply the determined torque distribution to the plurality of wheels 101, 102, 103, 104.

Although embodiments of the present invention are described with respect to electric vehicles, it should be understood that the principles disclosed herein may be readily applied to other types of vehicles capable of controlling the level of torque applied to different wheels, such as vehicles using gasoline, diesel, LPG (liquefied petroleum gas), or hybrid systems.

Although certain embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that many changes and modifications may be made without departing from the scope of the invention as defined in the appended claims.