Torque control method and device for electric four-wheel drive vehicle

Abstract

The application discloses a torque control method and device for an electric four-wheel drive vehicle. The method comprises the following steps: acquiring a required torque and a driving torque of the vehicle; determining whether the motor torque of a first motor of the vehicle has a torque zero-crossing stage in a process in which the total torque of the vehicle changes from the driving torque to the required torque; determining a torque zero-crossing interval corresponding to the torque zero-crossing stage; and controlling the output torque of the first motor to change at a first change rate and the output torque of a second motor to change at a second change rate in the torque zero-crossing interval, wherein the first change rate is smaller than the second change rate, and the overall change rate of the first change rate and the second change rate at the same time is a total torque change rate. The motor torque of the first motor is controlled to complete torque zero-crossing at a slow change rate, and the loss of the total torque change rate caused by the slow torque change rate of the first motor is compensated by the second motor, so that the engagement impact caused by torque zero-crossing is reduced, and the power response of the vehicle is ensured.

Description

Technical Field

[0001] This application relates to the field of electric vehicle technology, and in particular to a torque control method and device for an electric four-wheel drive vehicle. Background Technology

[0002] Due to the scarcity of oil and gas resources and the increasing prominence of environmental problems, electric vehicles, as a new generation of clean energy vehicles, are receiving more and more attention.

[0003] For electric vehicles, the power transmission is gear transmission. Due to limitations in gear manufacturing technology and cost, backlash is unavoidable between the meshing gear teeth. Furthermore, the power transmission system of electric vehicles (motor, gears, differential, wheels) lacks torque buffering devices similar to torsional vibration dampers and torque converters found in traditional vehicles. Therefore, during electric vehicle operation, when the motor torque switches between negative and positive torque, such as in tip-in mode (driving with 0% throttle coasting energy recovery or braking energy recovery), In the case of rapid acceleration (when the accelerator is pressed down), the motor torque switches from negative to positive. In the case of tip-out (when the accelerator is quickly released to regenerative braking or brake-induced energy recovery during acceleration or steady-speed driving), the motor torque switches from positive to negative. The motor torque crosses zero near zero torque, changing its direction. Simultaneously, the gear meshing surface changes. Due to gear backlash, this change in meshing surface causes meshing impact, affecting the vehicle's drivability. In electric four-wheel drive vehicles with dual motor drive systems (one drive motor on each axle), the torque of the front and rear axles crosses zero simultaneously at the same rate of change. Therefore, the impact felt by the driver is the combined effect of the front and rear axle impacts. Consequently, the meshing impact caused by torque zero-crossing is more pronounced in electric four-wheel drive vehicles.

[0004] Existing torque zero-crossing control strategies typically reduce engagement shock by limiting the rate of change of motor torque in the range near zero torque. However, this inevitably causes a delay in torque response, affecting the driving experience.

[0005] It is evident that the contradiction between the meshing shock caused by the torque crossing to zero and the torque response delay caused by limiting the torque crossing rate urgently needs to be resolved. Summary of the Invention

[0006] In view of this, this application provides a torque control method and device for an electric four-wheel drive vehicle, which resolves the contradiction between meshing shock caused by torque crossing zero and torque response delay caused by limiting the torque crossing zero rate by controlling the torque of the front and rear axle motors of the electric four-wheel drive vehicle.

[0007] The embodiments of this application disclose the following technical solutions:

[0008] On one hand, embodiments of this application provide a torque control method for an electric four-wheel drive vehicle, the method comprising:

[0009] Obtain the required torque and the vehicle's current driving torque;

[0010] If the torque of the first motor of the vehicle experiences a zero-crossing phase during the process of the vehicle's total torque changing from the driving torque to the required torque, the torque zero-crossing interval corresponding to the zero-crossing phase is determined; the existence of a torque zero-crossing phase includes the motor torque changing from positive torque to negative torque or from negative torque to positive torque; the upper and lower limits of the torque zero-crossing interval are the minimum driving torque of the rear axle motor of the vehicle and the minimum braking torque of the front axle motor of the vehicle, respectively; the first motor is either the front axle motor or the rear axle motor, and the second motor is either the front axle motor or the rear axle motor other than the first motor;

[0011] In the torque zero-crossing range, the output torque of the first motor is controlled to change at a first rate of change, and the output torque of the second motor is controlled to change at a second rate of change;

[0012] Wherein, the first rate of change is less than the second rate of change, and the overall rate of change of the first rate of change and the second rate of change at the same moment is the total torque rate of change; the total torque rate of change is obtained based on the required torque and the driving torque.

[0013] On the other hand, embodiments of this application provide a torque control device for an electric four-wheel drive vehicle, the device comprising an acquisition unit, a determination unit, and a control unit:

[0014] The acquisition unit is used to acquire the required torque and the vehicle's current driving torque.

[0015] The determining unit is configured to determine a torque zero-crossing interval corresponding to the torque zero-crossing stage if the motor torque of the first motor of the vehicle has a torque zero-crossing stage during the process of the total torque of the vehicle changing from the driving torque to the required torque; the existence of a torque zero-crossing stage includes the motor torque changing from positive torque to negative torque or from negative torque to positive torque; the upper and lower limits of the torque zero-crossing interval are the minimum driving torque of the rear axle motor of the vehicle and the minimum braking torque of the front axle motor of the vehicle, respectively; the first motor is the front axle motor or the rear axle motor, and the second motor is the motor other than the first motor among the front axle motor and the rear axle motor;

[0016] The control unit is configured to control the output torque of the first motor to change at a first rate of change and the output torque of the second motor to change at a second rate of change during the torque zero-crossing range; wherein the first rate of change is less than the second rate of change, and the overall rate of change of the first rate of change and the second rate of change at the same moment is the total torque rate of change; the total torque rate of change is obtained based on the required torque and the driving torque.

[0017] As can be seen from the above technical solution, during vehicle operation, the required torque and the vehicle's current driving torque are obtained. When it is determined that the torque of the vehicle's first motor has a torque zero-crossing stage during the process of the vehicle's total torque changing from the driving torque to the required torque, the torque zero-crossing interval corresponding to this stage is determined. Within this torque zero-crossing interval, the output torque of the first motor is controlled to change at a first rate of change, and the output torque of the second motor is controlled to change at a second rate of change. The first rate of change is less than the second rate of change, and the overall rate of change of the first and second rates at the same moment is the total torque change rate. In this way, by controlling the motor torque of the first motor to complete the torque zero-crossing at a slower rate of change, the meshing impact caused by the torque zero-crossing is mitigated. At the same time, the loss of the total torque change rate caused by its slower rate of change is compensated by the second motor. That is, at any given moment, the total torque change rate of the vehicle is kept constant. This total torque change rate is determined based on the required torque and the vehicle's current driving torque, thereby mitigating the meshing impact caused by the torque zero-crossing while ensuring the vehicle's power response. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A flowchart illustrating a torque control method for an electric four-wheel drive vehicle provided in this application embodiment;

[0020] Figure 2 A torque distribution diagram under driving conditions is provided for embodiments of this application;

[0021] Figure 3 A schematic diagram of torque distribution under driving conditions is provided for an embodiment of this application;

[0022] Figure 4 A torque distribution diagram under braking conditions is provided for an embodiment of this application;

[0023] Figure 5 A schematic diagram of torque distribution under braking conditions is provided for an embodiment of this application;

[0024] Figure 6 A schematic diagram illustrating torque change during the transition from energy recovery state to acceleration start-up state, provided as an embodiment of this application;

[0025] Figure 7 A schematic diagram illustrating the torque change during the transition from a constant speed driving state to an accelerated driving state, provided as an embodiment of this application;

[0026] Figure 8 A schematic diagram illustrating the torque change during the deceleration process from a constant speed driving state to an energy recovery state, provided for an embodiment of this application;

[0027] Figure 9 This is a structural diagram of a torque control device for an electric four-wheel drive vehicle provided in an embodiment of this application. Detailed Implementation

[0028] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0029] Figure 1 A flowchart illustrating a torque control method for an electric four-wheel drive vehicle provided in this application embodiment, the method comprising:

[0030] S101: Obtain the required torque and the vehicle's current driving torque.

[0031] The required torque and the vehicle's current driving torque are obtained. The required torque can be calculated based on vehicle speed, accelerator pedal opening, and brake pedal opening, while the current driving torque can be calculated based on the vehicle's current speed. The process of the vehicle's total torque changing from the driving torque to the required torque reflects the change in the vehicle's driving conditions.

[0032] S102: If the torque of the first motor of the vehicle has a zero-crossing stage during the process of the total torque of the vehicle changing from the driving torque to the required torque, determine the torque zero-crossing interval corresponding to the torque zero-crossing stage.

[0033] In the embodiments provided in this application, in the overall torque distribution of an electric four-wheel drive vehicle with a front axle motor and a rear axle motor, the rear axle motor is the main drive and the front axle motor is the main brake, wherein the braking state specifically refers to the energy recovery state of the electric four-wheel drive vehicle. For the rear axle motor, its maximum drive torque is ReTqMax, representing the maximum drive capability of the rear axle motor, and its minimum drive torque is PosTqMin, representing the minimum torque at the gear meshing surface of the rear axle motor. For the front axle motor, its maximum braking torque is FrTqMin, representing the maximum braking energy of the rear axle motor, and its minimum braking torque is NegTqMin, representing the minimum torque to ensure the gear meshing surface of the front axle motor.

[0034] During the process of the vehicle's total torque changing from the driving torque to the required torque, if the torque of the vehicle's first motor has a torque zero-crossing stage, the torque zero-crossing interval corresponding to this torque zero-crossing stage is determined; wherein, the existence of a torque zero-crossing stage includes the motor torque changing from positive torque to negative torque or the motor torque changing from negative torque to positive torque; the upper and lower limits of the torque zero-crossing interval are the minimum driving torque PosTqMin of the vehicle's rear axle motor and the minimum braking torque NegTqMin of the vehicle's front axle motor, respectively; the first motor is the front axle motor or the rear axle motor, and the second motor is the motor other than the first motor among the front axle motor and the rear axle motor.

[0035] S103: In the torque zero-crossing range, control the output torque of the first motor to change at a first rate of change, and control the output torque of the second motor to change at a second rate of change.

[0036] To mitigate the meshing shock caused by the rapid zero-crossing of motor torque, in this embodiment, during the torque zero-crossing interval, the output torque of the first motor is controlled to change at a first rate of change, and the output torque of the second motor is controlled to change at a second rate of change. The first rate of change is less than the second rate of change, and the overall rate of change of the first and second rates at any given moment is the total torque change rate, which is determined based on the required torque and the vehicle's current driving torque. Thus, by controlling the motor torque of the first motor during the torque zero-crossing phase to complete the torque zero-crossing at a slower rate, the meshing shock caused by the torque zero-crossing is mitigated. Simultaneously, the loss in the total torque change rate caused by the slower torque change rate is compensated by the second motor. That is, at any given moment, the total torque change rate of the vehicle is kept constant, and this total torque change rate, determined based on the required torque and the vehicle's current driving torque, ensures the vehicle's power response while mitigating the meshing shock caused by the torque zero-crossing.

[0037] Furthermore, the torque change range outside the first range is defined as the second range; the total torque change range identifies the range of change of the vehicle's total torque from the driving torque to the required torque; the first range is the torque zero-crossing range; in the second range, the output torque of the first motor is controlled to change at a third rate, and the output torque of the second motor is controlled to change at a fourth rate; wherein, the third rate of change is greater than the first rate of change, and the overall rate of change of the third and fourth rates of change at the same time is still the total torque change rate. After the motor torque of the motor with the torque zero-crossing stage completes the torque zero-crossing phase, it is controlled to output torque at a rate of change greater than the rate of change in the torque zero-crossing range, but at the same time, the overall rate of change of the motor torque of the two motors is still the total torque change rate, thereby ensuring the vehicle's power response.

[0038] Figure 2 A torque distribution diagram for driving conditions provided in an embodiment of this application:

[0039] Under driving conditions, if the required torque TqDmd is positive, the rear axle motor is prioritized for allocation. Specifically, if the required torque TqDmd is less than the maximum driving torque ReTqMax of the rear axle motor, the minimum braking torque NegTqMin is allocated as the output torque of the front axle motor, and the difference between the required torque and the minimum braking torque [TqDmd - NegTqMin] is allocated as the output torque of the rear axle motor. The minimum braking torque NegTqMin represents the minimum torque required to ensure the front axle motor's gears are engaged in gear braking contact. The advantage of this allocation is that in most driving conditions, with the rear axle driving, the front axle is always in gear braking contact contact. (This is especially important in Tip-out situations where the vehicle is under acceleration / deceleration.) When driving at high or steady speed, and quickly releasing the throttle to achieve coasting energy recovery or braking energy recovery, the front axle motor can directly bypass the torque zero-crossing process to generate braking torque, avoiding the transition process during torque zero-crossing. If the required torque TqDmd is greater than or equal to the maximum drive torque ReTqMax of the rear axle motor, then the output torque of the rear axle motor is allocated to the maximum drive torque ReTqMax, and the output torque of the front axle motor is the difference between the required torque and the maximum drive torque [TqDmd - ReTqMax]. That is, the rear axle motor outputs at maximum capacity, and the remaining required torque is supplemented by the front axle motor. Under the aforementioned driving conditions, the required torque of the vehicle is provided jointly by the output torque of the front axle motor and the output torque of the rear axle motor.

[0040] like Figure 3The diagram illustrates a torque distribution under driving conditions according to an embodiment of this application: When the required torque is less than the maximum driving torque of the rear axle motor, the minimum braking torque is always allocated as the output torque of the front axle motor, and the difference between the required torque and the minimum braking torque is used as the output torque of the rear axle motor. The minimum braking torque represents the minimum torque required to ensure that the gears of the front axle motor are engaged with the gear braking meshing surface. Under this type of driving condition, the rear axle is driven, and the front axle is always at the gear braking meshing surface. Therefore, when the vehicle is tip-out (when accelerating or driving at a steady speed, the throttle is quickly fully released to the coasting energy recovery or braking energy recovery state), the front axle motor can directly skip the torque zero-crossing process to generate braking torque, thus avoiding the transition process when the torque crosses zero.

[0041] Figure 4 A braking torque distribution diagram provided in an embodiment of this application:

[0042] Under braking conditions, if the required torque is a negative torque TqDmd, then the front axle motor is prioritized for allocation. Specifically, if the required torque TqDmd is greater than the maximum braking torque FrTqMin of the front axle motor, then the minimum drive torque PosTqMin is allocated as the output torque of the rear axle motor, and the difference between the required torque and the minimum drive torque [TqDmd - PosTqMin] is allocated as the output torque of the front axle motor. The minimum drive torque PosTqMin represents the minimum torque required to ensure gear engagement of the rear axle motor. The advantage of this allocation is that, under most braking conditions, the front axle brakes while the rear axle remains at the gear engagement surface. (Note: The last sentence about Tip-in (0) is incomplete and likely refers to a different topic.) When driving in regenerative braking or coasting mode with 100% throttle-over-charge, and rapidly pressing the accelerator, the rear axle motor can directly bypass the torque zero-crossing process to generate drive torque, avoiding the transition process during torque zero-crossing. If the required torque TqDmd is less than or equal to the maximum braking torque FrTqMin of the front axle motor, then the output torque of the front axle motor is allocated to the maximum braking torque FrTqMin, and the output torque of the rear axle motor is the difference between the required torque and the maximum braking torque [TqDmd - FrTqMin]. That is, the front axle motor outputs at its maximum capacity, and the remaining required torque is supplemented by the rear axle motor. Under the aforementioned braking conditions, the required torque of the vehicle is provided jointly by the output torque of the front axle motor and the output torque of the rear axle motor.

[0043] like Figure 5The diagram shown is a schematic of torque distribution under braking conditions provided in an embodiment of this application: When the required torque is greater than the maximum braking torque of the front axle motor, the minimum driving torque is always allocated as the output torque of the rear axle motor, and the difference between the required torque and the minimum driving torque is used as the output torque of the front axle motor. The minimum driving torque represents the minimum torque required to ensure that the gears of the rear axle motor are engaged with the gear drive meshing surface. Under this braking condition, the front axle brakes, and the rear axle is always in the gear drive meshing surface. When Tip-in (driving with 0% throttle coasting energy recovery or braking energy recovery, quickly pressing the accelerator), the rear axle motor can directly skip the torque zero crossing process to generate driving torque, avoiding the transition process when the torque crosses zero.

[0044] As Figure 3 and Figure 5 As shown, combined with the characteristic of electric four-wheel drive vehicles having two motors on the front and rear axles, the torque distribution method provided in this application allows the other axle to be on standby in the opposite direction when one axle of the vehicle is performing a driving / braking action, avoiding the torque zero-crossing process and achieving rapid torque response.

[0045] Specifically, such as Figure 6 The diagram shown is a schematic diagram of the change in total vehicle torque during the process from energy recovery state to acceleration start-up state (right side) and a schematic diagram of the change in torque of the front and rear axle motors of the vehicle (left side), provided in this application:

[0046] The vehicle's current required torque TqDmd1 is negative and greater than the maximum braking torque of the front axle motor. At this time, the minimum driving torque PosTqMin is allocated as the output torque of the rear axle motor, and the difference between the required torque and the minimum driving torque [TqDmd1-PosTqMin] is allocated as the output torque of the front axle motor. The minimum driving torque PosTqMin is the minimum positive torque, ensuring that the gear meshing surface of the rear axle motor is at the drive end, and this torque has a minimal impact on the vehicle's energy consumption.

[0047] During the running of a vehicle, when the driver presses the accelerator pedal, the demanded torque is TqDmd2, that is, the total torque of the vehicle is analyzed to change from TqDmd1 to TqDmd2, and the total torque change rate is TqRateDmd; if the demanded torque TqDmd2 is less than the maximum driving torque ReTqMax of the rear axle motor, the rear axle torque is controlled to change from PosTqMin to [TqDmd2-NegTqMin] at a slope of [TqRateDmd-TqRateFr], and simultaneously the output torque of the front axle motor is controlled to change from [TqDmd1-PosTqMin] to NegTqMin at a slope of TqRateFr, wherein the minimum braking torque NegTqMin is the minimum negative torque, which ensures that the gear meshing surface of the front axle motor is at the braking end, and this torque has extremely little influence on energy consumption. At any moment, the overall change of the output torque of the front axle motor and the output torque of the rear axle motor is the total torque change of the vehicle, which ensures that the total torque change completely follows the torque demand change during the whole torque response process.

[0048] In a possible implementation, when TqDmd2<ReTqMax*i, that is, when the demanded torque TqDmd2 is less than i times the maximum driving torque ReTqMax of the rear axle motor, the rear axle torque is controlled to change from PosTqMin to [TqDmd2-NegTqMin] at a slope of [TqRateDmd-TqRateFr], and simultaneously the output torque of the front axle motor is controlled to change from [TqDmd1-PosTqMin] to NegTqMin at a slope of TqRateFr. Wherein, ReTqMax is the maximum driving torque of the rear axle motor, representing the maximum output capacity of the rear axle motor; i is a calibratable coefficient, for example, i=0.8, which aims to leave a margin for control of larger demanded torque.

[0049] When the driver continues to press the accelerator pedal, the vehicle starts to accelerate, specifically as Figure 7 shown, which are a schematic diagram of a total vehicle torque change (on the right side) and a schematic diagram of torque changes of front and rear axle motors of the vehicle (on the left side) in a process from a uniform-speed driving state to an accelerated driving state provided by the present application:

[0050] The required torque is TqDmd3, meaning that the total torque of the vehicle changes from TqDmd2 to TqDmd3, and the rate of change of the total torque is TqRateDmd. If the required torque TqDmd3 is greater than the maximum driving torque ReTqMax of the rear axle motor, then it is determined that there is a torque zero-crossing stage in the process of the vehicle torque changing from TqDmd2 to TqDmd3. The torque zero-crossing interval corresponding to this torque zero-crossing stage is [NegTqMin, PosTqMin], that is, the upper limit and lower limit of the torque zero-crossing interval are the minimum driving torque of the rear axle motor and the minimum braking torque of the front axle motor, respectively. At this point, the motor torque changes in two stages. Specifically, the output torque of the front axle motor first changes from NegTqMin with a zero-crossing slope TqRateZeroX to PosTqMin, and then changes with a slope TqRateFr1 to [TqDmd3-ReTqMax]. Simultaneously, the output torque of the rear axle motor changes from [TqDmd2-NegTqMin] with a slope [TqRateDmd-TqRateFr] to ReTqMax; where TqRateFr is the real-time slope of the front axle motor's output torque. At any given moment, the overall rate of change of the output torque of the front axle motor and the rear axle motor is the rate of change of the vehicle's total torque, ensuring that the total torque change throughout the entire torque response process completely follows the torque demand change.

[0051] When the driver releases the accelerator pedal, the vehicle enters energy recovery mode, specifically as follows: Figure 8 The diagram shown is a schematic diagram (right side) illustrating the change in total vehicle torque during the deceleration process from a constant speed driving state to an energy recovery state, and a schematic diagram (left side) illustrating the change in torque of the front and rear axle motors of the vehicle, as provided in this application.

[0052] The required torque is TqDmd4, meaning the total vehicle torque changes from TqDmd3 to TqDmd4 at a rate of TqRateDmd. If the required torque TqDmd4 is greater than the maximum braking torque FrTqMin of the front axle motor, the output torque of the front axle motor changes in three stages: first from [TqDmd3-ReTqMax] with a slope TqRateFr2 to PosTqMin, and then with a zero-crossing slope TqRateZeroX to... NegTqMin, and finally changes according to the slope [TqRateDmd-TqRateRe] to [TqDmd4-PosTqMin], where TqRateRe is the real-time change slope of the output torque of the rear axle motor; at the same time, the output torque of the rear axle motor changes according to the slope [TqRateDmd-TqRateFr2] in the first segment mentioned above, and changes according to the slope TqRateRe2 to PosTqMin in the second and third segments mentioned above.

[0053] The above embodiments illustrate the torque change process under several typical operating conditions during vehicle operation. For other torque change scenarios, those skilled in the art can extrapolate from the above examples.

[0054] Figure 9 This application provides a structural diagram of a torque control device for an electric four-wheel drive vehicle, comprising an acquisition unit 901, a determination unit 902, and a control unit 903.

[0055] The acquisition unit 901 is used to acquire the required torque and the vehicle's current driving torque.

[0056] The determining unit 902 is configured to determine a torque zero-crossing interval corresponding to the torque zero-crossing stage if the motor torque of the first motor of the vehicle has a torque zero-crossing stage during the process of the total torque of the vehicle changing from the driving torque to the required torque; the existence of a torque zero-crossing stage includes the motor torque changing from positive torque to negative torque or from negative torque to positive torque; the upper and lower limits of the torque zero-crossing interval are the minimum driving torque of the rear axle motor of the vehicle and the minimum braking torque of the front axle motor of the vehicle, respectively; the first motor is the front axle motor or the rear axle motor, and the second motor is the motor other than the first motor among the front axle motor and the rear axle motor;

[0057] The control unit 903 is configured to control the output torque of the first motor to change at a first rate of change and the output torque of the second motor to change at a second rate of change in the torque zero-crossing range; wherein the first rate of change is less than the second rate of change, and the overall rate of change of the first rate of change and the second rate of change at the same moment is the total torque rate of change; the total torque rate of change is obtained based on the required torque and the driving torque.

[0058] In one possible implementation, the determining unit is further configured to determine the torque change range other than the first range in the total torque change range of the vehicle as the second range; the total torque change range identifies the range of change of the total torque of the vehicle from the driving torque to the required torque; the first range is the torque zero-crossing range; the control unit is further configured to control the output torque of the first motor to change at a third rate of change and control the output torque of the second motor to change at a fourth rate of change in the second range; wherein the third rate of change is greater than the first rate of change, and the overall rate of change of the third rate of change and the fourth rate of change at the same time is the total torque change rate.

[0059] Therefore, during vehicle operation, the required torque and the vehicle's current driving torque are obtained. When it is determined that the torque of the vehicle's first motor has a torque zero-crossing phase during the process of the vehicle's total torque changing from the driving torque to the required torque, the torque zero-crossing interval corresponding to this torque zero-crossing phase is determined. Within this torque zero-crossing interval, the output torque of the first motor is controlled to change at a first rate of change, and the output torque of the second motor is controlled to change at a second rate of change. The first rate of change is less than the second rate of change. The overall rate of change of the first and second rates at the same moment is the total torque change rate. In this way, by controlling the motor torque of the first motor to complete the torque zero-crossing at a slower rate of change, the meshing impact caused by the torque zero-crossing is mitigated. At the same time, the loss of the total torque change rate caused by its slower torque change rate is compensated by the second motor. That is, at any given moment, the total torque change rate of the vehicle is kept constant. This total torque change rate is determined based on the required torque and the vehicle's current driving torque, thereby mitigating the meshing impact caused by the torque zero-crossing while ensuring the vehicle's power response.

[0060] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to in the description of the method embodiments. The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0061] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0062] The foregoing has provided a detailed description of a torque control method and device for an electric four-wheel drive vehicle according to embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the method of this application. Furthermore, those skilled in the art will recognize that there will be changes in the specific implementation methods and application scope based on the method of this application. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A torque control method for an electric four-wheel drive vehicle, characterized in that, The method includes: Obtain the required torque and the vehicle's current driving torque; If the torque of the first motor of the vehicle experiences a zero-crossing phase during the process of the total torque of the vehicle changing from the driving torque to the required torque, the torque zero-crossing interval corresponding to the torque zero-crossing phase is determined; the existence of a torque zero-crossing phase includes the motor torque changing from positive torque to negative torque or from negative torque to positive torque; the upper and lower limits of the torque zero-crossing interval are the minimum driving torque of the rear axle motor of the vehicle and the minimum braking torque of the front axle motor of the vehicle, respectively; the first motor is either the front axle motor or the rear axle motor, and the second motor is either the front axle motor or the rear axle motor other than the first motor; wherein, the minimum driving torque of the rear axle motor is the minimum torque required to ensure that the gears of the rear axle motor engage the driving meshing surface, and the minimum braking torque of the front axle motor is the minimum torque required to ensure that the gears of the front axle motor engage the braking meshing surface; Under driving conditions, the required torque is a positive torque, and it is preferentially allocated to the rear axle motor. If the required torque is less than the maximum driving torque of the rear axle motor, the minimum braking torque of the front axle motor is allocated as the output torque of the front axle motor, and the difference between the required torque and the minimum braking torque of the front axle motor is used as the output torque of the rear axle motor. Under braking conditions, if the required torque is negative, the front axle motor is given priority. If the required torque is greater than the maximum braking torque of the front axle motor, the minimum driving torque of the rear axle motor is used as the output torque of the rear axle motor. The difference between the required torque and the minimum driving torque of the rear axle motor is used as the output torque of the front axle motor. In the torque zero-crossing range, the output torque of the first motor is controlled to change at a first rate of change, and the output torque of the second motor is controlled to change at a second rate of change; Wherein, the first rate of change is less than the second rate of change, and the overall rate of change of the first rate of change and the second rate of change at the same moment is the total torque rate of change; the total torque rate of change is obtained based on the required torque and the driving torque.

2. The method according to claim 1, characterized in that, Also includes: The torque variation range other than the first range on the total torque variation range of the vehicle is defined as the second range; the total torque variation range identifies the range of change of the total torque of the vehicle from the driving torque to the required torque; the first range is the torque zero-crossing range; In the second interval, the output torque of the first motor is controlled to change at a third rate of change, and the output torque of the second motor is controlled to change at a fourth rate of change; wherein, the third rate of change is greater than the first rate of change, and the overall rate of change of the third rate of change and the fourth rate of change at the same time is the total torque rate of change.

3. The method according to claim 1, characterized in that, Also includes: When the driving torque is negative, the required torque is positive, and the required torque is greater than the maximum driving torque of the rear axle motor of the vehicle, the front axle motor of the vehicle is determined to be the first motor.

4. The method according to claim 1, characterized in that, Also includes: When the driving torque is positive, the required torque is negative, and the required torque is less than the maximum braking torque of the front axle motor of the vehicle, the rear axle motor of the vehicle is determined to be the first motor.

5. The method according to claim 1, characterized in that, Also includes: When both the required torque and the driving torque are positive, and the required torque is greater than the maximum driving torque of the rear axle motor of the vehicle and the driving torque is less than the maximum driving torque of the rear axle motor of the vehicle, the front axle motor of the vehicle is determined to be the first motor.

6. The method according to claim 1, characterized in that, Also includes: When both the required torque and the driving torque are negative, and the required torque is less than the maximum braking torque of the front axle motor of the vehicle and the driving torque is greater than the maximum driving torque of the front axle motor of the vehicle, the rear axle motor of the vehicle is determined to be the first motor.

7. The method according to any one of claims 1-6, characterized in that, The required torque is obtained in the following way: Obtain the required torque calculated based on vehicle speed, accelerator pedal opening, and brake pedal opening.

8. The method according to any one of claims 1-6, characterized in that, The vehicle's current driving torque is obtained in the following way: Obtain the vehicle's current driving torque based on the vehicle's current speed.

9. A torque control device for an electric four-wheel drive vehicle, characterized in that, The device includes an acquisition unit, a determination unit, an allocation unit, and a control unit: The acquisition unit is used to acquire the required torque and the vehicle's current driving torque. The determining unit is used to determine the torque zero-crossing interval corresponding to the torque zero-crossing stage if the motor torque of the first motor of the vehicle has a torque zero-crossing stage during the process of the total torque of the vehicle changing from the driving torque to the required torque. The existence of the torque zero crossing stage includes the motor torque changing from positive torque to negative torque or from negative torque to positive torque; The upper and lower limits of the torque zero-crossing interval are the minimum driving torque of the rear axle motor and the minimum braking torque of the front axle motor of the vehicle, respectively; the first motor is either the front axle motor or the rear axle motor, and the second motor is either the front axle motor or the rear axle motor other than the first motor. The minimum driving torque of the rear axle motor is the minimum torque required to ensure that the gears of the rear axle motor engage with the driving meshing surface, and the minimum braking torque of the front axle motor is the minimum torque required to ensure that the gears of the front axle motor engage with the braking meshing surface. The allocation unit is configured to, under driving conditions, prioritize allocating the required torque to the rear axle motor if the required torque is positive, and if the required torque is less than the maximum driving torque of the rear axle motor, allocate the minimum braking torque of the front axle motor as the output torque of the front axle motor, and the difference between the required torque and the minimum braking torque of the front axle motor as the output torque of the rear axle motor. The allocation unit is further configured to, under braking conditions, prioritize allocating the front axle motor if the required torque is negative, and if the required torque is greater than the maximum braking torque of the front axle motor, allocate the minimum driving torque of the rear axle motor as the output torque of the rear axle motor, and the difference between the required torque and the minimum driving torque of the rear axle motor is used as the output torque of the front axle motor. The control unit is configured to control the output torque of the first motor to change at a first rate of change and the output torque of the second motor to change at a second rate of change in the torque zero-crossing range; wherein the first rate of change is less than the second rate of change, and the overall rate of change of the first rate of change and the second rate of change at the same moment is the total torque rate of change; the total torque rate of change is obtained based on the required torque and the driving torque.

10. The apparatus according to claim 9, characterized in that, The determining unit is further configured to determine the torque change range other than the first range on the total torque change range of the vehicle as the second range; the total torque change range identifies the range of change of the total torque of the vehicle from the driving torque to the required torque; the first range is the torque zero-crossing range; The control unit is further configured to control the output torque of the first motor to change at a third rate of change and the output torque of the second motor to change at a fourth rate of change in the second interval; wherein the third rate of change is greater than the first rate of change, and the overall rate of change of the third rate of change and the fourth rate of change at the same time is the total torque rate of change.

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