CN113954658A

CN113954658A - Power system control method and power system of four-wheel-drive pure electric vehicle

Info

Publication number: CN113954658A
Application number: CN202111349436.8A
Authority: CN
Inventors: 刘力源; 王燕; 刘建康
Original assignee: FAW Group Corp
Current assignee: FAW Group Corp
Priority date: 2021-11-15
Filing date: 2021-11-15
Publication date: 2022-01-21
Anticipated expiration: 2041-11-15
Also published as: WO2023082843A1; CN113954658B

Abstract

The invention relates to the technical field of vehicles, and particularly discloses a power system control method and a power system of a four-wheel-drive pure electric vehicle, wherein the power system control method of the four-wheel-drive pure electric vehicle comprises the following steps: when the automobile runs, a first required torque M11 for driving the automobile to run is obtained, the maximum output torque of the first motor is M12, the sum of the maximum output torque of the first motor and the maximum output torque of the second motor is M13, the magnitude of M11, M12 and M13 is compared, if M11 is not more than M12, the first clutch is separated, the second clutch is separated, only the first motor outputs the torque, the second motor and the third motor are avoided, energy is saved, the automobile endurance mileage is prolonged, if M13 is not less than M11 and more than M12, the first clutch is combined, the second clutch is separated, the first motor, the second motor and the third motor output the torque at the same time, the use of the third motor can be avoided, the energy waste is reduced, and the automobile endurance mileage is prolonged.

Description

Power system control method and power system of four-wheel-drive pure electric vehicle

Technical Field

The invention relates to the technical field of vehicles, in particular to a power system control method and a power system of a four-wheel-drive pure electric vehicle.

Background

In order to pursue the pole braking force performance, the pure electric vehicle adopts a four-wheel drive configuration and carries two or three or even four motor systems; however, the actual use process of the user is not a pursuit of dynamic performance, the long endurance mileage is one of the main requirements of the user, and how to use a plurality of motors to meet the long endurance mileage is a problem to be solved by the patent. In order to meet the requirements of users on dynamic property and economy, the whole vehicle is required to carry more motor systems and set different driving modes, single or multiple motors are used for driving the vehicle to run through devices such as a second clutch, and the like, so that the requirements of the dynamic property and the long mileage are met.

For example, the prior patent with the application number of CN201620892065.6 discloses a power system of an electric vehicle and an electric vehicle with the same, wherein the power system of the electric vehicle adopts two motors, and is provided with a second clutch, a planetary gear and the like; the prior patent with the application number of CN202010214247.9 discloses a pure electric vehicle power driving system with a power separation device and a vehicle, wherein the pure electric vehicle power driving system with the power separation device comprises a main driving system, an auxiliary driving system, a main power separation device, an auxiliary power separation device and the like; the prior patent with the patent number of CN201721327830.0 discloses a four-drive power system and an electric vehicle, wherein the four-drive power system comprises two sets of power assemblies, and each set of power assembly comprises a motor, a motor controller, a speed reducer and the like. No specific control strategy is given in the above patent for how to distribute torque among multiple electric machines.

Therefore, a method for controlling a powertrain of a four-wheel-drive pure electric vehicle and a powertrain thereof are needed to solve the above problems.

Disclosure of Invention

The invention aims to: the power system control method and the power system of the four-wheel-drive pure electric vehicle are provided to reasonably distribute the output torque of each motor.

On one hand, the invention provides a control method of a power system of a four-wheel-drive pure electric vehicle, wherein the power system of the four-wheel-drive pure electric vehicle comprises a first motor, a second motor, a third motor, a power battery, a first clutch and a second clutch, the first motor is in transmission connection with a wheel end, the second motor is in selective transmission connection with the wheel end through the first clutch, the third motor is in selective transmission connection with the wheel end through the second clutch, the power battery is used for supplying power to the first motor, the second motor and the third motor, and the first motor, the second motor and the third motor can generate power and charge the power battery; the power system control method of the four-wheel-drive pure electric vehicle comprises the following steps:

acquiring the current working condition of the vehicle;

if the current working condition is a driving working condition, executing driving torque distribution, and treading an accelerator pedal of the automobile under the driving working condition;

said then performing a drive torque distribution comprises:

acquiring a first required torque M11 for driving the automobile to run;

respectively acquiring maximum output torques of the first motor, the second motor and the third motor, wherein the maximum output torque of the first motor is M12, and the sum of the maximum output torque of the first motor and the maximum output torque of the second motor is M13;

comparing the sizes of M11, M12, and M13;

if M11 is less than or equal to M12, the first clutch is disengaged, the second clutch is disengaged, only the first motor outputs torque, and the actual output torque of the first motor is equal to M11;

if M13 is more than or equal to M11 and more than M12, the first clutch is engaged, the second clutch is disengaged, the first motor and the second motor output torques simultaneously, and the sum of the actual output torque of the first motor and the actual output torque of the second motor is equal to M11;

if M11 > M13, the first clutch is engaged, the second clutch is engaged, the first motor, the second motor, and the third motor output torques simultaneously, and the sum of the actual output torque of the first motor, the actual output torque of the second motor, and the actual output torque of the third motor is equal to M11.

As a preferable technical scheme of the power system control method of the four-wheel-drive pure electric vehicle, the method for acquiring the first required torque for driving the vehicle comprises the following steps:

calculating the first wheel end required torque of the automobile according to the opening degree of an accelerator pedal, the speed and the change rate of the opening degree of the accelerator pedal;

calculating the maximum adhesive force of each wheel of the automobile according to the road adhesion parameters and the wheel pressure parameters, and calculating the second wheel end required torque for the running of the automobile according to the maximum adhesive force and the number of the wheels of the automobile;

the smaller value of the first wheel end demand torque and the second wheel end demand torque is taken as a first demand torque.

As a preferred technical solution of a power system control method of a four-wheel-drive pure electric vehicle, a method of respectively obtaining maximum output torques of the first motor, the second motor, and the third motor includes:

acquiring a first temperature of the first motor, a first voltage at an input end of the first motor, a maximum supply current of the first motor, and a maximum supply current of the first motor, wherein the maximum supply current of the first motor is inquired for a corresponding maximum output torque of the first motor from map1 among the first temperature, the first voltage, the first maximum supply current and the maximum output torque of the first motor according to the first temperature, the first voltage and the maximum supply current of the first motor;

acquiring a second temperature of the second motor, a second voltage at an input end of the second motor, a maximum supply current of the second motor, and a maximum supply current of the second motor, wherein the maximum output torque of the second motor is inquired correspondingly from map2 among the second temperature, the second voltage, the second maximum supply current and the maximum output torque of the second motor according to the second temperature, the second voltage and the maximum supply current of the second motor;

and acquiring a third temperature of the third motor, a third voltage at an input end of the third motor, a maximum supply current of the third motor, and a maximum output torque of the third motor, wherein the maximum supply current of the third motor is inquired from map3 between the third temperature, the third voltage, the third maximum supply current and the maximum output torque of the third motor according to the third temperature, the third voltage and the maximum supply current of the third motor.

As an optimal technical scheme of a power system control method of a four-wheel-drive pure electric vehicle, the power system control method of the four-wheel-drive pure electric vehicle further comprises the following steps:

if the current working condition is a braking working condition, executing braking torque distribution, and treading a brake pedal of the automobile under the braking working condition;

the brake torque distribution includes:

acquiring a second required torque M21 for braking the automobile;

respectively obtaining the maximum braking torque of the first motor, the second motor and the third motor, wherein the maximum braking torque of the first motor is M22; the sum of the maximum braking torque of the first electric machine and the maximum braking torque of the second electric machine is M23;

comparing the sizes of M21, M22, and M23;

if M21 is less than or equal to M22, the first clutch is separated, the second clutch is separated, and only the first motor is used for generating electricity to output braking torque;

if M23 is more than or equal to M21 and more than M22, the first clutch is engaged, the second clutch is disengaged, and the first motor and the second motor are simultaneously used for generating electricity to output braking torque;

if M21 > M23, the first clutch is engaged, the second clutch is engaged, and the first motor, the second motor and the third motor are simultaneously used for generating electricity to output braking torque;

as a preferable technical solution of the power system control method of the four-wheel-drive pure electric vehicle, the braking torque distribution further includes, after the first clutch is engaged and the second clutch is engaged:

calculating a sum of a maximum braking torque of the first motor, a maximum braking torque of the second motor, and a maximum braking torque of the third motor as M24;

comparing the sizes of M21 and M24;

if M21 > M24; the hydraulic brake mechanism is started to brake the wheel end.

On the other hand, the invention also provides a power system of the four-wheel-drive pure electric vehicle, which comprises a first motor, a second motor, a third motor, a power battery, a first clutch, a second clutch and a controller, wherein the first motor is in transmission connection with a wheel end, the second motor is in selective transmission connection with the wheel end through the first clutch, the third motor is in selective transmission connection with the wheel end through the second clutch, the power battery is used for supplying power to the first motor, the second motor and the third motor, and the first motor, the second motor and the third motor can generate power and charge the power battery;

the controller is used for implementing the power system control method of the four-wheel-drive pure electric vehicle in any one of the above schemes.

As a preferable technical scheme of a power system of the four-wheel-drive pure electric vehicle, the power battery comprises one or more of a lithium ion power battery, a flywheel energy storage battery system and a fuel battery system.

As a preferred technical scheme of a power system of the four-wheel-drive pure electric automobile, the first motor is in transmission connection with a rear axle, the second motor is in selective connection with the rear axle through the first clutch, and the third motor is in selective connection with a front axle through the second clutch.

As the preferable technical scheme of the power system of the four-wheel-drive pure electric vehicle, the power system of the four-wheel-drive pure electric vehicle also comprises a front speed reducer,

the second clutch is arranged between the third motor and the front speed reducer, and the front speed reducer is in transmission connection with the front axle; or the third motor is in transmission connection with the front speed reducer, and the second clutch is arranged between the front speed reducer and the front axle.

As a preferred technical scheme of a power system of a four-wheel-drive pure electric vehicle, the power system of the four-wheel-drive pure electric vehicle further comprises a rear speed reducer, the first motor is in transmission connection with the rear speed reducer, and the rear speed reducer is in transmission connection with the rear axle;

the second motor is selectively in transmission connection with the rear speed reducer through the first clutch.

The invention has the beneficial effects that:

the invention provides a power system control method and a power system of a four-wheel-drive pure electric vehicle, wherein the power system control method of the four-wheel-drive pure electric vehicle comprises the following steps: and when the current working condition is a running working condition, executing driving torque distribution. The driving torque distribution is executed by acquiring a first required torque M11 for driving the automobile to run, respectively acquiring maximum output torques of a first motor, a second motor and a third motor, wherein the maximum output torque of the first motor is M12, the sum of the maximum output torque of the first motor and the maximum output torque of the second motor is M13, comparing the magnitudes of the M11, the M12 and the M13, if M11 is less than or equal to M12, the first clutch is separated, the second clutch is separated, only the first motor outputs the torque, and the actual output torque of the first motor is equal to M11, so that the use of the second motor and the third motor is avoided, the energy waste caused by the fact that the self electric energy conversion efficiency of the second motor and the third motor cannot reach 100% is further reduced, and the endurance mileage of the automobile can be prolonged; if M13 is more than or equal to M11 and more than M12, the first clutch is combined, the second clutch is separated, the first motor and the second motor output torques simultaneously, and the sum of the actual output torque of the first motor and the actual output torque of the second motor is equal to M11, so that the use of a third motor can be avoided, the energy waste caused by the fact that the self electric energy conversion efficiency of the third motor cannot reach 100% can be further reduced, and the endurance mileage can be prolonged; if M11 > M13, the first clutch is engaged, the second clutch is engaged, the first motor, the second motor, and the third motor output torques simultaneously, and the sum of the actual output torque of the first motor, the actual output torque of the second motor, and the actual output torque of the third motor is equal to M11.

Drawings

FIG. 1 is a first structural schematic diagram of a four-wheel-drive pure electric vehicle power system in an embodiment of the invention;

fig. 2 is a schematic structural diagram ii of a four-wheel-drive pure electric vehicle power system in the embodiment of the invention.

In the figure:

1. a first motor; 2. a second motor; 3. a third motor; 4. a power battery;

51. a first clutch; 52. a second clutch;

61. a first motor controller; 62. a second motor controller; 63. a third motor controller; 64. a battery controller; 65. a vehicle control unit; 66. an electronic stability system;

7. a rear axle; 8. a rear retarder; 9. front axle, 10, front decelerator.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. Where the terms "first position" and "second position" are two different positions, and where a first feature is "over", "above" and "on" a second feature, it is intended that the first feature is directly over and obliquely above the second feature, or simply means that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or simply meaning that the first feature is at a lesser elevation than the second feature.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

As shown in fig. 1-2, the present embodiment provides a four-wheel drive pure electric vehicle power system, which includes a first motor 1, a second motor 2, a third motor 3, a power battery 4, a controller, a first clutch 51 and a second clutch 52, where the first motor 1 and the second motor 2 are both in transmission connection with a wheel end, the second motor 2 is in transmission connection with the wheel end selectively through the first clutch 51, the third motor 3 is in transmission connection with the wheel end selectively through the second clutch 52, the power battery 4 is used for supplying power to the first motor 1, the second motor 2 and the third motor 3, and the first motor 1, the second motor 2 and the third motor 3 can generate power and charge the power battery 4. The second electric machine 2 can be connected or disconnected by controlling the connection or disconnection of the first clutch, and the third electric machine 3 can be connected or disconnected by controlling the connection or disconnection of the second clutch 52. The power battery 4 comprises one or more of a lithium ion power battery, a flywheel energy storage battery system and a fuel battery system. The types of the first motor 1, the second motor 2 and the third motor 3 can be the same or different, and can be selected according to requirements.

As shown in fig. 1 and 2, the first electric machine 1 is in drive connection with the rear axle 7, the second electric machine 2 is selectively in drive connection with the rear axle 7 via a first clutch 51, and the third electric machine 3 is selectively in drive connection with the front axle 9 via a second clutch 52. When the first clutch is combined, the transmission of the second motor 2 can be switched into the rear axle 7; when the first clutch is disengaged, the second electric machine 2 can be disengaged and the drive connection to the rear axle 7 can be realized. When the second clutch 52 is combined, the transmission of the third motor 3 can be connected to the front axle 9; when the first clutch 51 is disengaged, the third electric machine 3 can be disengaged and the drive connection to the front axle 9 can be realized.

Optionally, as shown in fig. 1, the power system method of the four-wheel drive pure electric vehicle further includes a rear speed reducer 8, the first motor 1 is in transmission connection with the rear speed reducer 8, and the rear speed reducer 8 is in transmission connection with the rear axle 7; the second electric machine 2 is selectively in transmission connection with the rear retarder 8 via a first clutch 51. Wherein, first motor 1 and second motor 2 set up along the left and right direction interval of car to the output shaft coaxial line of first motor 1 and second motor 2 sets up.

Optionally, the power system of the four-wheel-drive pure electric vehicle further comprises a front speed reducer 10; as shown in fig. 1, the second clutch 52 is disposed between the third electric machine 3 and the front retarder 10, and the front retarder 10 is drivingly connected to the front axle 9. As an alternative, as shown in fig. 2, the third electric machine 3 is in transmission connection with the front retarder 10, and the second clutch 52 is arranged between the front retarder 10 and the front axle 9.

As an alternative, the first electric machine 1 and the second electric machine 2 are both in drive connection with the rear axle 7, and the third electric machine 3 is selectively in drive connection with the front axle 9 via a clutch. When the clutch is combined, the transmission of the third motor 3 can be switched into the front axle 9; when the clutch is disengaged, the third electric machine 3 can be disengaged and the drive connection to the front axle 9 can be realized. Preferably, the power system method of the four-wheel drive pure electric vehicle further comprises a front speed reducer 10, wherein the third motor 3 is selectively in transmission connection with an input gear of the front speed reducer 10 through a clutch, and an output gear of the front speed reducer 10 is in transmission connection with the front axle 9. The third motor 3 is in transmission connection with an input gear of a front speed reducer 10, and an output gear of the front speed reducer 10 is in selective transmission connection with a front axle 9 through a clutch.

The controller includes a first motor controller 61, a second motor controller 62, and a third motor controller 63. The first motor controller 61 is connected with the first motor 1 and the power battery 4, and the first motor controller 61 is used for controlling the current output from the power battery 4 to the first motor 1, so as to control the actual output torque of the first motor 1; meanwhile, the current input to the power battery 4 when the first motor 1 generates power can be controlled, and the braking torque generated by the first motor 1 can be further controlled. The second motor controller 62 is connected with the second motor 2 and the power battery 4, and the second motor controller 62 is used for controlling the current output from the power battery 4 to the second motor 2, so as to control the actual output torque of the second motor 2; meanwhile, the current input to the power battery 4 when the second motor 2 generates electricity can be controlled, and the braking torque generated by the second motor 2 can be further controlled. The third motor controller 63 is connected with the third motor 3 and the power battery 4, and the third motor controller 63 is used for controlling the current output from the power battery 4 to the third motor 3, so as to control the actual output torque of the third motor 3; meanwhile, the current input to the power battery 4 when the third motor 3 generates power can be controlled, and the braking torque generated by the third motor 3 can be further controlled. The output torque of the three motors is controlled, so that the magnitude of the output torque for driving the vehicle to run can be adjusted; by controlling the braking torques of the three motors, the magnitude of the braking torque for braking the vehicle can be adjusted.

The controller further comprises a battery controller 64, the battery controller 64 being connected to the power battery 4 and configured to estimate the maximum discharge power and the maximum Charge power of the power battery 4 based on the SOC (State of Charge) of the power battery 4, the voltage of the power battery 4 and the temperature of the power battery 4. The temperature of the power battery 4 can be collected by the temperature sensor connected to the battery controller 64, and the voltage of the power battery 4 can be collected by the voltage sensor connected to the power battery 4, and the obtaining of the SCO of the battery is prior art and will not be described herein again. Wherein, the voltage of the power battery 4 is the output voltage or the input voltage of the power battery 4.

The charging corresponding relation graph of the temperature of the power battery 4, the input voltage of the power battery 4, the SCO of the power battery 4 and the maximum charging power of the power battery 4 can be obtained through a large number of tests, and then the corresponding maximum charging power of the power battery 4 is inquired from the charging corresponding relation graph according to the obtained temperature of the power battery 4, the input voltage of the power battery 4 and the SOC of the power battery 4; similarly, the discharge correspondence map of the temperature of the power battery 4, the output voltage of the power battery 4, the SCO of the power battery 4, and the maximum discharge power of the power battery 4 may be obtained through a large number of tests, and then the amplified discharge power of the corresponding power battery 4 may be queried from the discharge correspondence map according to the obtained temperature of the power battery 4, the output voltage of the power battery 4, and the SOC of the power battery 4.

The maximum charging current of the power battery 4 can be calculated from the maximum charging power of the power battery 4 and the input voltage of the power battery 4. The maximum discharge current of the power battery 4 can be calculated by the maximum discharge power of the power battery 4 and the output voltage of the power battery 4. The maximum charging current may be shared among the first motor 1, the second motor 2, and the third motor 3 according to a first set ratio, so as to obtain the maximum charging current of the first motor 1, the maximum charging current of the second motor 2, and the maximum charging current of the third motor 3. The maximum discharge current can be distributed to the first motor 1, the second motor 2 and the third motor 3 according to a second set proportion, and then the maximum supply current of the first motor 1, the maximum supply current of the second motor 2 and the maximum supply current of the third motor 3 are obtained. Wherein, the first set proportion and the second set proportion can be set according to requirements. Taking the second set ratio as an example, the second set ratio may be a ratio between the rated output power of the first motor 1, the rated output power of the second motor 2, and the rated output power of the third motor 3.

The first motor controller 61 is also used to evaluate the maximum output torque of the first motor 1. Specifically, the first motor controller 61 obtains a first temperature of the first motor 1, a first voltage at an input end of the first motor 1, and a maximum supply current of the first motor 1, and the first motor controller 61 queries a corresponding maximum output torque of the first motor 1 from a map1 between the first temperature, the first voltage, the maximum supply current of the first motor 1, and the maximum output torque of the first motor 1 according to the first temperature, the first voltage, and the maximum supply current of the first motor 1. Among them, map1 can be obtained by a large number of experiments in the early stage. The first motor controller 61 may obtain the temperature of the first motor 1 through a temperature sensor connected to the first motor controller 61, and obtain the first voltage at the input terminal of the first motor 1 through a voltage sensor connected to the first motor controller 61.

The second motor controller 62 is also used to evaluate the maximum output torque of the second electric motor 2. Specifically, the second motor controller 62 obtains a second temperature of the second motor 2, a second voltage at the input end of the second motor 2, and a maximum supply current of the second motor 2, and the second motor controller 62 queries the corresponding maximum output torque of the second motor 2 from the map2 between the second temperature, the second voltage, the maximum supply current of the second motor 2, and the maximum output torque of the second motor 2 according to the second temperature, the second voltage, and the maximum supply current of the second motor 2. Among them, map2 can be obtained by a large number of experiments in the early stage. The second motor controller 62 may acquire the temperature of the second motor 2 through a temperature sensor connected to the second motor controller 62, and acquire the second voltage at the input terminal of the second motor 2 through a voltage sensor connected to the second motor controller 62.

The third motor controller 63 is used to evaluate the maximum output torque of the third motor 3. Specifically, the third motor controller 63 obtains the third temperature of the third motor 3, the third voltage at the input end of the third motor 3, and the maximum supply current of the third motor 3, and the third motor controller 63 queries the corresponding maximum output torque of the third motor 3 from the map3 between the third temperature, the third voltage, the maximum supply current of the third motor 3, and the maximum output torque of the third motor 3 according to the third temperature, the third voltage, and the maximum supply current of the third motor 3. Among them, map3 can be obtained by a large number of experiments in the early stage. The third motor controller 63 may obtain the temperature of the third motor 3 through a temperature sensor connected to the third motor controller 63, and obtain the third voltage at the input terminal of the third motor 3 through a voltage sensor connected to the third motor controller 63.

The first motor controller 61 is also used to evaluate the maximum braking torque of the first electric motor 1. The first motor controller 61 obtains a first temperature of the first motor 1, a first charging voltage at an output end of the first motor 1, and a maximum charging current of the first motor 1, and the first motor controller 61 queries a corresponding maximum braking torque of the first motor 1 from a map11 among the first temperature, the first charging voltage, the maximum charging current of the first motor 1, and the maximum braking torque of the first motor 1 according to the first temperature, the first charging voltage, and the maximum charging current of the first motor 1. Among them, map11 can be obtained by a large number of experiments in the early stage. The first motor controller 61 may acquire the first voltage at the output terminal of the first motor 1 through a voltage sensor connected to the first motor controller 61.

The second motor controller 62 is also arranged to evaluate the maximum braking torque of the second electric machine 2. The second motor controller 62 obtains the second temperature of the second motor 2, the second charging voltage at the output terminal of the second motor 2, and the maximum charging current of the second motor 2, and the second motor controller 62 queries the corresponding maximum braking torque of the second motor 2 from the map11 between the second temperature, the second charging voltage, the maximum charging current of the second motor 2, and the maximum braking torque of the second motor 2 according to the second temperature, the second charging voltage, and the maximum charging current of the second motor 2. Among them, map11 can be obtained by a large number of experiments in the early stage. The second motor controller 62 may acquire the second voltage at the output terminal of the second motor 2 through a voltage sensor connected to the second motor controller 62.

The third motor controller 63 is also arranged to evaluate the maximum braking torque of the third motor 3. The third motor controller 63 obtains the third temperature of the third motor 3, the third charging voltage at the output terminal of the third motor 3, and the maximum charging current of the third motor 3, and the third motor controller 63 queries the corresponding maximum braking torque of the third motor 3 from the map11 between the third temperature, the third charging voltage, the maximum charging current of the third motor 3, and the maximum braking torque of the third motor 3 according to the third temperature, the third charging voltage, and the maximum charging current of the third motor 3. Among them, map11 can be obtained by a large number of experiments in the early stage. The third motor controller 63 may acquire the third voltage at the output terminal of the third motor 3 through a voltage sensor connected to the third motor controller 63.

The controller also includes a vehicle control unit 65. The vehicle control unit 65 is connected to the first clutch and the second clutch 52, respectively, to control the engagement or disengagement of the first clutch and the second clutch 52, and further control whether the second motor 2 and the third motor 3 are involved in power transmission with the wheel ends.

The vehicle control unit 65 may also be configured to determine a current working condition of the vehicle, and when a brake pedal of the vehicle is stepped on, the vehicle control unit 65 may determine that the current vehicle is in the braking working condition; when the accelerator pedal of the vehicle is stepped, the vehicle control unit 65 may determine that the vehicle is currently in a driving condition, that is, the vehicle is moving forward or backing up. Specifically, taking the example of determining that the vehicle is in the braking condition, a position sensor may be disposed on the brake pedal, the position sensor may acquire the position information of the brake pedal, a corresponding chart of the position information and the opening degree of the brake pedal may be set in advance in the vehicle controller 65, the corresponding chart may be queried to acquire the opening degree of the brake pedal corresponding to the position information, and then whether the brake pedal is stepped on may be analyzed.

The vehicle control unit 65 may also calculate a first wheel end required torque of the vehicle according to the accelerator pedal opening, the vehicle speed, and the rate of change of the accelerator pedal opening. The vehicle speed can be acquired through a speed sensor, the change rate of the opening degree of an accelerator pedal, namely the change rate of the position of the accelerator pedal when the driver steps on the accelerator pedal, corresponds to the target acceleration which is expected to accelerate to the target vehicle speed at the current moment of the driver, and can be determined by the ratio of the opening degree of the accelerator pedal to the time for generating the opening degree of the accelerator pedal. A first relation graph of the accelerator pedal opening, the vehicle speed, and the rate of change of the accelerator pedal opening and the first wheel end demand torque may be preset in the vehicle control unit 65 in advance, and the first wheel end demand torque corresponding thereto may be acquired from the first relation graph according to the acquired accelerator pedal opening, vehicle speed, and rate of change of the accelerator pedal opening. The first map can be obtained by a large number of experiments in the early stage.

The controller further comprises an electronic stabilizing system 66, the electronic stabilizing system 66 is connected with the vehicle control unit 65, and the electronic stabilizing system 66 can calculate the maximum adhesive force of each wheel of the vehicle according to the road adhesion parameter and the wheel pressure parameter, and calculate the second wheel end required torque for vehicle running according to the maximum adhesive force and the number of the vehicle wheels. The adhesion parameters of the wheels can be represented by the slip rate of the automobile, and the slip rate of the automobile is the degree of slipping of the automobile. The electronic stability system 66 may obtain the actual rotation speed of the wheel through a rotation speed sensor connected to the electronic stability system, obtain the target vehicle speed of the vehicle by combining the diameter of the wheel, calculate the difference between the target vehicle speed and the actual vehicle speed, and calculate the ratio of the difference to the actual vehicle speed to be the slip ratio of the vehicle. The wheel pressure parameter is specifically the tire pressure, and can be obtained through a tire pressure sensor. In the electronic stability system 66, a relationship chart of the road adhesion parameter, the wheel pressure parameter, and the maximum adhesion force may be preset in advance, and the maximum adhesion force corresponding thereto may be queried from the relationship chart. It should be noted that it is prior art to calculate the second wheel end required torque for vehicle running according to the maximum adhesion and the number of vehicle wheels, and the description is omitted here.

It is understood that when the vehicle is running on a wet road surface, the driver performs the vehicle acceleration operation, and a phenomenon in which the wheels slip may occur. That is, the first wheel end demand torque is greater than the second wheel end demand torque at this time. If the slipping condition occurs, the vehicle controller 65 distributes the first wheel end required torque of the vehicle calculated according to the accelerator pedal opening, the vehicle speed and the change rate of the accelerator pedal opening to each motor, and the torque output by each motor matched with the motor output will cause the waste of energy. Meanwhile, this also indicates that the driving expectation of the driver is too high for the vehicle speed, and has a safety risk, and the driving expectation of the driver needs to be adjusted to be within a safety range. Therefore, in controlling the torque output by the motor, not only the first wheel end demand torque but also the second wheel end demand torque is considered. In this embodiment, the vehicle control unit 65 obtains the second wheel end required torque through the electronic stabilization system 66, and the vehicle control unit 65 compares the first wheel end required torque with the second wheel end required torque, and uses the smaller value of the first wheel end required torque and the second wheel end required torque as the first required torque. Therefore, the driving safety can be ensured, and the electric energy waste of the power battery 4 is reduced. Preferably, when the vehicle control unit 65 determines that the first wheel end required torque is greater than the second wheel end required torque, the vehicle control unit 65 controls the alarm device to give an alarm to remind the driver of paying attention to driving safety.

The vehicle control unit 65 is also connected to the first motor controller 61, the second motor controller 62, and the third motor controller 63, respectively, so that the vehicle control unit 65 can obtain the maximum output torque of the first motor 1, the maximum output torque of the second motor 2, and the maximum output torque of the third motor 3. The first required torque is M11, the maximum output torque of the first motor 1 is M12, the vehicle control unit 65 calculates the sum of the maximum output torque of the first motor 1 and the maximum output torque of the second motor 2, the sum of the maximum output torque of the first motor 1 and the maximum output torque of the second motor 2 is M13, and the vehicle control unit 65 compares the magnitudes of M11, M12 and M13; if M13 is greater than or equal to M11 > M12, it is indicated that the output torque provided by the first motor 1 cannot meet the driving expectation of the driver, and at least the first motor 1 and the second motor 2 are required to provide the output torque at the same time, so the vehicle controller 65 needs to control the first clutch to be engaged and the second clutch 52 to be disengaged so that the first motor 1 and the second motor 2 provide the output torque at the same time, and at this time, the third motor 3 does not need to be used, so as to reduce the load of the third motor 3 and improve the service life of the third motor 3; meanwhile, because the energy conversion efficiency of the motor is limited, 100% of electric energy cannot be converted into kinetic energy, energy waste exists only when the motor is used, and therefore the energy waste can be avoided by not using the third motor 3 at the moment, and the driving mileage of the automobile is prolonged. If M11 > M13, it is stated that only the first motor 1, the second motor 2, and the third motor 3 simultaneously provide output torque to meet the driver's expectation, so the vehicle controller 65 needs to control the first clutch to be engaged and the second clutch 52 to be engaged, and the first motor 1, the second motor 2, and the third motor 3 simultaneously provide output torque. If M11 is less than or equal to M12, it is indicated that the driving expectation of the driver can be met only by the first motor 1 providing the output torque, so the vehicle controller 65 needs to control the first clutch 51 to be disengaged and the second clutch 52 to be disengaged, and at this time, the second motor 2 and the third motor 3 do not need to be used, so that the loads of the second motor 2 and the third motor 3 are reduced, and the service lives of the second motor 2 and the third motor 3 are prolonged; meanwhile, because the energy conversion efficiency of the motor is limited, the energy waste can be avoided by not using the second motor 2 and the third motor 3, and the driving mileage of the automobile is prolonged.

Note that the sum of the maximum output torque of the first electric machine 1, the maximum output torque of the second electric machine 2, and the maximum output torque of the third electric machine 3 is larger than the first required torque in any one state.

The vehicle control unit 65 may also calculate a second required torque of the vehicle according to the brake pedal opening degree, the vehicle speed, and the change rate of the brake pedal opening degree. The change rate of the brake pedal opening, that is, the change rate of the brake pedal position when the driver steps on the brake pedal, corresponds to the target deceleration at which the driver expects deceleration to the target vehicle speed at the present time, and may be determined by the ratio of the brake pedal opening to the time during which the brake pedal opening is generated. A second relationship diagram of the brake pedal opening degree, the vehicle speed, and the rate of change of the brake pedal opening degree and the second required torque may be preset in advance in the vehicle controller 65, and the second required torque corresponding thereto may be acquired from the second relationship diagram according to the acquired brake pedal opening degree, vehicle speed, and rate of change of the brake pedal opening degree. The second map can be obtained by a large number of experiments in the early stage.

Under the braking condition, the vehicle control unit 65 may further obtain the maximum braking torque of the first motor 1, the maximum braking torque of the second motor 2, and the maximum braking torque of the third motor 3 from the first motor controller 61, the second motor controller 62, and the third motor controller 63, respectively. The second required torque is M21, the maximum braking torque of the first electric machine 1 is M22, and the vehicle control unit 65 calculates the sum of the maximum braking torque of the first electric machine 1 and the maximum braking torque of the second electric machine 2, and calculates the sum of the maximum braking torque of the first electric machine 1, the maximum braking torque of the second electric machine 2, and the maximum braking torque of the third electric machine 3. The sum of the maximum braking torque of the first motor 1 and the maximum braking torque of the second motor 2 is M23, and the sum of the maximum braking torque of the first motor 1, the maximum braking torque of the second motor 2, and the maximum braking torque of the third motor 3 is M24. The vehicle control unit 65 compares the sizes of M21, M22, and M23. If M21 > M23, it is stated that only the first motor 1, the second motor 2, and the third motor 3 simultaneously provide braking torque to meet the driver's expectation, so the vehicle controller 65 needs to control the first clutch 51 to be engaged and the second clutch 52 to be engaged, and the first motor 1, the second motor 2, and the third motor 3 simultaneously provide braking torque. If M21 is less than or equal to M22, it is indicated that the driving expectation of the driver can be met only by the first motor 1 providing the braking torque, so the vehicle controller 65 needs to control the first clutch 51 to be disengaged and the second clutch 52 to be disengaged, and at this time, the second motor 2 and the third motor 3 do not need to be used, so that the loads of the second motor 2 and the third motor 3 are reduced, and the service lives of the second motor 2 and the third motor 3 are prolonged; meanwhile, the self energy conversion efficiency of the motor is limited, so that the recovery efficiency of electric energy can be improved, and the driving mileage of the automobile is prolonged. If M23 is greater than or equal to M21 > M22, it is indicated that the braking torque provided by the first motor 1 cannot meet the driving expectation of the driver, and at least the first motor 1 and the second motor 2 are required to provide the braking torque at the same time, so the vehicle controller 65 needs to control the first clutch 51 to be combined and the second clutch 52 to be separated, so that the first motor 1 and the second motor 2 provide the braking torque at the same time, on the premise of ensuring normal braking of the vehicle, the use of the third motor 3 is avoided, so as to reduce the load of the third motor 3, and improve the service life of the third motor 3, and meanwhile, because the energy conversion efficiency of the third motor 3 is limited, the kinetic energy cannot be converted into electric energy by 100%, and energy waste exists as long as the use is carried out, so that the recovery efficiency of the electric energy can be improved without using the third motor 3, and the driving mileage of the vehicle can be prolonged. Preferably, the vehicle control unit 65 may continue to compare the sizes of M21 and M24, and when M21 > M24, indicating that the driver's driving expectations cannot be met even if the three motors simultaneously provide braking torque, then the hydraulic brake mechanism is activated to brake the wheel ends. Preferably, the hydraulic braking mechanism provides a braking torque equal to the difference between M21 and M24.

The embodiment also provides a power system control method of the four-wheel-drive pure electric vehicle, which is implemented by the power system of the four-wheel-drive pure electric vehicle. The control method of the power system of the four-wheel-drive pure electric vehicle comprises the following steps.

S10: acquiring the current working condition of the vehicle;

if the current working condition is a driving working condition, executing S20; if the current operating condition is the braking operating condition, S30 is executed.

S20: the driving torque distribution is performed.

S30: brake torque distribution is performed.

Executing the drive torque distribution includes:

s21: the first required torque M11 for driving the vehicle to travel is obtained.

The method for acquiring the first required torque for vehicle driving comprises the following steps:

the smaller value of the first wheel end demand torque and the second wheel end demand torque is taken as the first demand torque.

S22: the maximum output torques of the first motor 1, the second motor 2 and the third motor 3 are respectively obtained, and the maximum output torque of the first motor 1 is M12, and the sum of the maximum output torque of the first motor 1 and the maximum output torque of the second motor 2 is M13.

Specifically, the method of obtaining the maximum output torque of the first electric machine 1 includes: the method comprises the steps of obtaining a first temperature of a first motor 1, a first voltage of an input end of the first motor 1, a maximum supply current of the first motor 1 and a maximum supply current of the first motor 1, and inquiring the corresponding maximum output torque of the first motor 1 from map1 between the first temperature, the first voltage, the first maximum supply current and the maximum output torque of the first motor 1 according to the first temperature, the first voltage and the maximum supply current of the first motor 1.

The method of obtaining the maximum output torque of the second electric machine 2 includes: acquiring a second temperature of the second motor 2, a second voltage at an input end of the second motor 2, a maximum supply current of the second motor 2, and inquiring a corresponding maximum output torque of the second motor 2 from a map2 among the second temperature, the second voltage, the second maximum supply current, and the maximum output torque of the second motor 2 according to the second temperature, the second voltage, and the maximum supply current of the second motor 2;

the method of obtaining the maximum output torque of the third electric machine 3 includes: the third temperature of the third motor 3, the third voltage at the input end of the third motor 3, the maximum supply current of the third motor 3, and the maximum supply current of the third motor 3 are obtained, and the corresponding maximum output torque of the third motor 3 is queried from map3 between the third temperature, the third voltage, the third maximum supply current, and the maximum output torque of the third motor 3 according to the third temperature, the third voltage, and the maximum supply current of the third motor 3.

S23: size of M11, M12, and M13.

If M11 is less than or equal to M12, executing S24; if M13 is more than or equal to M11 and more than M12, executing S25; if M11 > M13, S26 is performed.

S24: the first clutch 51 is disengaged, the second clutch 52 is disengaged, only the first motor 1 outputs torque, and the actual output torque of the first motor 1 is equal to M11.

M11 is less than or equal to M12, which shows that the driving expectation of the driver can be met only by the first motor 1 providing the output torque, and the second motor 2 and the third motor 3 are not needed to be used.

S25: the first clutch 51 is engaged, the second clutch 52 is disengaged, the first motor 1 and the second motor 2 output torques simultaneously, and the sum of the actual output torque of the first motor 1 and the actual output torque of the second motor 2 is equal to M11.

M13 is more than or equal to M11 and more than M12, which indicates that the output torque provided by the first motor 1 cannot meet the driving expectation of the driver, and at least the first motor 1 and the second motor 2 are required to provide the output torque simultaneously, so that the vehicle controller 65 needs to control the first clutch 51 to be engaged and the second clutch 52 to be disengaged so that the first motor 1 and the second motor 2 provide the output torque simultaneously, and the third motor 3 is not required.

S26: the first clutch 51 is engaged, the second clutch 52 is engaged, the first motor 1, the second motor 2 and the third motor 3 output torques simultaneously, and the sum of the actual output torque of the first motor 1, the actual output torque of the second motor 2 and the actual output torque of the third motor 3 is equal to M11.

M11 > M13, which indicates that only the first motor 1, the second motor 2 and the third motor 3 simultaneously provide output torque to meet the driver's expectation, the vehicle controller 65 needs to control the first clutch 51 to be engaged and the second clutch 52 to be engaged, and the first motor 1, the second motor 2 and the third motor 3 simultaneously provide output torque.

The brake torque distribution includes:

s31: the second required torque M21 for vehicle braking is obtained.

Specifically, the second wheel end required torque of the automobile is calculated according to the change rates of the accelerator pedal opening, the vehicle speed and the brake pedal opening.

S32: respectively obtaining the maximum braking torque of the first motor 1, the second motor 2 and the third motor 3, wherein the maximum braking torque of the first motor 1 is M22; the sum of the maximum braking torque of the first electric machine 1 and the maximum braking torque of the second electric machine 2 is M23.

Wherein obtaining the maximum braking torque of the first electric machine 1 comprises: a first temperature of the first motor 1, a first charging voltage at an output terminal of the first motor 1, and a maximum charging current of the first motor 1 are obtained. According to the first temperature, the first charging voltage and the maximum charging current of the first motor 1, the corresponding maximum charging torque of the first motor 1 is inquired from the map11 between the first temperature, the first charging voltage, the maximum charging current of the first motor 1 and the maximum braking torque of the first motor 1.

Obtaining the maximum braking torque of the second electric machine 2 includes: a second temperature of the second motor 2, a second charging voltage of the output terminal of the second motor 2, and a maximum charging current of the second motor 2 are obtained. According to the second temperature, the second charging voltage and the maximum charging current of the second electric machine 2, the corresponding maximum charging torque of the second electric machine 2 is queried from the map21 between the second temperature, the second charging voltage, the maximum charging current of the second electric machine 2 and the maximum braking torque of the second electric machine 2.

Obtaining the maximum braking torque of the third electric machine 3 includes: a third temperature of the third motor 3, a third charging voltage of the output terminal of the third motor 3, and a maximum charging current of the third motor 3 are obtained. According to the third temperature, the third charging voltage and the maximum charging current of the third electric machine 3, the corresponding maximum charging torque of the third electric machine 3 is queried from the map31 between the third temperature, the third charging voltage, the maximum charging current of the third electric machine 3 and the maximum braking torque of the third electric machine 3.

S33: the sizes of M21, M22, and M23 were compared.

If M21 is less than or equal to M22, executing S34; if M23 is more than or equal to M21 and more than M22, executing S35; if M21 > M23, S36 is performed.

S34: the first clutch 51 is disengaged, the second clutch 52 is disengaged, and only the first motor 1 is used to generate electric power to output braking torque.

M21 is less than or equal to M22, which shows that the driving expectation of the driver can be met only by the first motor 1 providing the braking torque, and the second motor 2 and the third motor 3 are not needed to be used.

S35: the first clutch 51 is engaged, the second clutch 52 is disengaged, and the first motor 1 and the second motor 2 are simultaneously used to generate electricity to output a braking torque.

M23 is greater than or equal to M21 and greater than M22, which indicates that the braking torque provided by the first motor 1 cannot meet the driving expectation of the driver, and at least the first motor 1 and the second motor 2 are required to provide the braking torque at the same time, so that the vehicle controller 65 needs to control the first clutch 51 to be engaged and the second clutch 52 to be disengaged so that the first motor 1 and the second motor 2 provide the braking torque at the same time, and the third motor 3 is avoided being used on the premise of ensuring the normal braking of the vehicle.

S36: the first clutch 51 is engaged and the second clutch 52 is engaged and the first motor 1, the second motor 2 and the third motor 3 are simultaneously used to generate electricity to output the braking torque.

M21 > M23, which indicates that only the first electric machine 1, the second electric machine 2 and the third electric machine 3 simultaneously provide braking torque to meet the driver's expectation, the vehicle controller 65 needs to control the first clutch 51 to be engaged and the second clutch 52 to be engaged, and the first electric machine 1, the second electric machine 2 and the third electric machine 3 simultaneously provide braking torque.

S37: the sum of the maximum braking torque of the first electric machine 1, the maximum braking torque of the second electric machine 2, and the maximum braking torque of the third electric machine 3 is calculated as M24.

S38: comparing the sizes of M21 and M24; if M21 > M24; then S39 is executed; if M21 is less than or equal to M24, S10 is executed.

S39: the hydraulic brake mechanism is started to brake the wheel end.

M21 & gtM 24 shows that even if the braking torques are provided by the three motors at the same time, the driving expectation of the driver cannot be met, and the hydraulic braking mechanism is started to brake the wheel end.

In the control method of the power system of the four-wheel-drive pure electric vehicle, when only the first motor 1 and the second motor 2 are put into use to meet the driving requirement, the third motor 3 can be closed, so that the service life of the third motor 3 is shortened, the service life of the third motor 3 is prolonged, and meanwhile, the energy waste caused by the limitation of the self energy conversion efficiency of the third motor 3 can be avoided, and the endurance mileage is prolonged. When only first motor 1 comes into use and can satisfy the driving demand, can close second motor 2 and third motor 3, and then it is long to reduce second motor 2 and third motor 3's use, prolongs the life of second motor 2 and third motor 3, still can avoid the energy waste that second motor 2 and third motor 3 lead to because of self energy conversion efficiency limit simultaneously, extension continuation of the journey mileage.

It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A control method of a power system of a four-wheel-drive pure electric vehicle comprises the steps that the power system of the four-wheel-drive pure electric vehicle comprises a first motor (1), a second motor (2), a third motor (3), a power battery (4), a first clutch (51) and a second clutch (52), the first motor (1) is in transmission connection with a wheel end, the second motor (2) is selectively in transmission connection with the wheel end through the first clutch (51), the third motor (3) is selectively connected with the wheel end in a transmission way through the second clutch (52), the power battery (4) is used for supplying power to the first motor (1), the second motor (2) and the third motor (3), the first motor (1), the second motor (2) and the third motor (3) can generate electricity and charge the power battery (4); the control method of the power system of the four-wheel-drive pure electric vehicle is characterized by comprising the following steps:

acquiring the current working condition of the vehicle;

said then performing a drive torque distribution comprises:

acquiring a first required torque M11 for driving the automobile to run;

respectively acquiring the maximum output torques of the first motor (1), the second motor (2) and the third motor (3), wherein the maximum output torque of the first motor (1) is M12, and the sum of the maximum output torque of the first motor (1) and the maximum output torque of the second motor (2) is M13;

comparing the sizes of M11, M12, and M13;

if M11 is less than or equal to M12, the first clutch (51) is disengaged, the second clutch (52) is disengaged, only the first motor (1) outputs torque, and the actual output torque of the first motor (1) is equal to M11;

if M13 is more than or equal to M11 and more than M12, the first clutch (51) is engaged, the second clutch (52) is disengaged, the first motor (1) and the second motor (2) output torques simultaneously, and the sum of the actual output torque of the first motor (1) and the actual output torque of the second motor (2) is equal to M11;

if M11 > M13, the first clutch (51) is engaged, the second clutch (52) is engaged, the first electric machine (1), the second electric machine (2) and the third electric machine (3) output torques simultaneously, and the sum of the actual output torque of the first electric machine (1), the actual output torque of the second electric machine (2) and the actual output torque of the third electric machine (3) is equal to M11.

2. The powertrain control method of a four-wheel drive electric-only vehicle according to claim 1, wherein the method of obtaining the first required torque for vehicle travel comprises:

3. The powertrain control method of a four-wheel drive electric-only vehicle according to claim 1, wherein the method of obtaining the maximum output torque of the first electric machine (1), the second electric machine (2) and the third electric machine (3), respectively, comprises:

acquiring a first temperature of the first motor (1), a first voltage at an input end of the first motor (1), a maximum supply current of the first motor (1), and a maximum supply current of the first motor (1), wherein the maximum output torque of the first motor (1) is inquired according to the first temperature, the first voltage, and the maximum supply current of the first motor (1) from map1 among the first temperature, the first voltage, the first maximum supply current, and the maximum output torque of the first motor (1);

acquiring a second temperature of the second motor (2), a second voltage at an input end of the second motor (2), a maximum supply current of the second motor (2), and a maximum supply current of the second motor (2), wherein the maximum output torque of the second motor (2) is inquired according to the second temperature, the second voltage and the maximum supply current of the second motor (2) from map2 among the second temperature, the second voltage, the second maximum supply current and the maximum output torque of the second motor (2);

acquiring a third temperature of the third motor (3), a third voltage at an input end of the third motor (3), a maximum supply current of the third motor (3), and a maximum output torque of the third motor (3) corresponding to the maximum voltage, the third voltage, and the maximum supply current of the third motor (3) according to the third temperature, the third voltage, and the maximum supply current of the third motor (3), which are inquired from a map3 among the third temperature, the third voltage, the third maximum supply current, and the maximum output torque of the third motor (3).

4. The power system control method of the four-wheel-drive pure electric vehicle according to claim 1, characterized in that the power system control method of the four-wheel-drive pure electric vehicle further comprises:

the brake torque distribution includes:

acquiring a second required torque M21 for braking the automobile;

respectively acquiring the maximum braking torque of the first motor (1), the second motor (2) and the third motor (3), wherein the maximum braking torque of the first motor (1) is M22; the sum of the maximum braking torque of the first electric machine (1) and the maximum braking torque of the second electric machine (2) is M23;

comparing the sizes of M21, M22, and M23;

if M21 is less than or equal to M22, the first clutch (51) is separated, the second clutch (52) is separated, and only the first motor (1) is used for generating electricity to output braking torque;

if M23 is more than or equal to M21 and more than M22, the first clutch (51) is engaged, the second clutch (52) is disengaged, and the first motor (1) and the second motor (2) are simultaneously used for generating electricity to output braking torque;

if M21 > M23, the first clutch (51) is engaged, the second clutch (52) is engaged, and the first motor (1), the second motor (2), and the third motor (3) are simultaneously used to generate electricity to output braking torque.

5. The powertrain control method of a four-wheel drive electric-only vehicle according to claim 4, wherein the brake torque distribution further comprises, after engagement of the first clutch (51), engagement of the second clutch (52):

calculating the sum of the maximum braking torque of the first electric machine (1), the maximum braking torque of the second electric machine (2) and the maximum braking torque of the third electric machine (3) as M24;

comparing the sizes of M21 and M24;

if M21 > M24; the hydraulic brake mechanism is started to brake the wheel end.

6. A power system of a four-wheel-drive pure electric vehicle is characterized by comprising a first motor (1), a second motor (2), a third motor (3), a power battery (4), a first clutch (51), a second clutch (52) and a controller, the first motor (1) is in transmission connection with a wheel end, the second motor (2) is selectively in transmission connection with the wheel end through the first clutch (51), the third motor (3) is selectively connected with the wheel end in a transmission way through the second clutch (52) (5), the power battery (4) is used for supplying power to the first motor (1), the second motor (2) and the third motor (3), the first motor (1), the second motor (2) and the third motor (3) can generate electricity and charge the power battery (4);

the controller is used for implementing the power system control method of the four-wheel-drive pure electric vehicle as claimed in any one of claims 1 to 5.

7. The power system of a four-wheel drive electric vehicle according to claim 6, characterized in that the power battery (4) comprises one or more of a lithium ion power battery, a flywheel energy storage battery system, a fuel cell system.

8. The powertrain system of a four-wheel-drive electric vehicle according to claim 6, characterized in that the first electric machine (1) is in drive connection with the rear axle (7), the second electric machine (2) is selectively in drive connection with the rear axle (7) via the first clutch (51), and the third electric machine (3) is selectively in drive connection with the front axle (9) via the second clutch (52).

9. The powertrain system of a four-wheel-drive electric-only vehicle according to claim 8, characterized in that the powertrain system of a four-wheel-drive electric-only vehicle further comprises a front retarder (10);

the second clutch (52) is arranged between the third motor (3) and the front speed reducer (10), and the front speed reducer (10) is in transmission connection with the front axle (9); or,

the third motor (3) is in transmission connection with the front speed reducer (10), and the second clutch (52) is arranged between the front speed reducer (10) and the front axle (9).

10. The power system of the four-wheel-drive pure electric vehicle according to claim 8, characterized in that the power system of the four-wheel-drive pure electric vehicle further comprises a rear speed reducer (8), the first motor (1) is in transmission connection with the rear speed reducer (8), and the rear speed reducer (8) is in transmission connection with the rear axle (7);

the second motor (2) is selectively in transmission connection with the rear speed reducer (8) through the first clutch (51).