Power assembly, control method and electric vehicle

Abstract

The invention discloses a power assembly, a control method and an electric vehicle, and relates to the technical field of new energy automobiles. The power assembly comprises a motor controller and a driving motor, the motor controller comprises a three-phase bridge arm, three bridge arm midpoints of the three-phase bridge arm are used for being connected with a three-phase winding of the driving motor respectively, and in the process that the electric vehicle runs on the road surface with the adhesion coefficient smaller than a preset value, after the power assembly breaks down, the driving motor drives the three-phase winding to rotate. The motor controller circularly switches between an active short-circuit state and a full-tube-closing state in the process of controlling the driving motor to reduce the rotating speed, and the active short-circuit state refers to a state in which three upper bridge arms of the three-phase bridge arm are conducted and three lower bridge arms are disconnected or three upper bridge arms of the three-phase bridge arm are disconnected and three lower bridge arms are conducted; the fully-closed tube state refers to a state in which three upper bridge arms and three lower bridge arms of the three-phase bridge arms are all disconnected. According to the scheme, tire locking is avoided, slipping on a low-adhesion road surface is prevented, and the stability and safety of the electric vehicle are improved.

Description

Technical Field

[0001] This application relates to the field of electric vehicles, and more specifically, to a powertrain, a control method, and an electric vehicle. Background Technology

[0002] During the operation of an electric vehicle, the normal operation of the drive system is crucial; any malfunction can pose a serious threat to driver safety. Therefore, active protection is necessary when an electric vehicle malfunctions. When an electric vehicle experiences a system failure requiring high-voltage shutdown, the drive system enters active short-circuit (ASC) mode. During ASC, the drive motor generates significant braking torque, forcing a rapid decrease in speed to bring the vehicle to a stop. However, when an electric vehicle malfunctions on low-traction surfaces (such as icy, snowy, or slippery roads), the drive system's forced entry into ASC mode can cause the wheel speed to drop too quickly, potentially leading to wheel lock-up, instability, and fishtailing, resulting in a dangerous situation.

[0003] Therefore, how to control electric vehicles to safely enter an active short-circuit state on low-friction surfaces is a problem that needs to be solved. Summary of the Invention

[0004] This application provides a powertrain, a control method, and an electric vehicle. When the electric vehicle malfunctions while driving on a low-friction surface, the motor controller is intermittently activated to enter an active short-circuit state. The motor controller cycles between the active short-circuit state and the fully shut-off state. By forcing the electric vehicle to decelerate rapidly through the active short-circuit state, the tires are prevented from locking up, thus preventing skidding on low-friction surfaces and improving the stability and safety of the electric vehicle.

[0005] In a first aspect, this application provides a powertrain for an electric vehicle. The powertrain includes a motor controller and a drive motor. The motor controller includes three-phase bridge arms, with the midpoints of the three bridge arms respectively used to connect to the three-phase windings of the drive motor. During the electric vehicle's operation on a road surface with a coefficient of friction less than a preset value, before a powertrain failure, the motor controller outputs three-phase current to the drive motor to control the drive motor to drive the wheels of the electric vehicle. After a powertrain failure, the motor controller cycles between an active short-circuit state and a fully shut-off state while controlling the drive motor to reduce its speed. The active short-circuit state refers to a state where the three upper bridge arms of the three-phase bridge arm are conducting and the three lower bridge arms are disconnected, or the three upper bridge arms of the three-phase bridge arm are disconnected and the three lower bridge arms are conducting. The fully shut-off state refers to a state where both the three upper bridge arms and the three lower bridge arms of the three-phase bridge arm are disconnected.

[0006] The powertrain includes a motor controller and a drive motor. The motor controller comprises three-phase bridge arms, each containing two electronic switching devices connected in series. The midpoint of the bridge arm is the connection point between the two electronic switching devices. These electronic switching devices are composed of insulated-gate bipolar transistors and anti-parallel diodes, or other electronic components. Each phase bridge arm is divided into upper and lower bridge arms by its midpoint. One end of each of the three upper bridge arms is connected to one end of the power battery, and one end of each of the three lower bridge arms is connected to the other end of the power battery. The midpoint of each bridge arm is connected to the three-phase windings of the drive motor. During electric vehicle operation, when the powertrain is operating normally, the motor controller receives DC power from the power battery and converts it into three-phase AC power through the three-phase bridge arms to control the drive motor, thereby controlling the drive motor's output torque to drive the wheels of the electric vehicle.

[0007] Active short-circuit is a critical safety protection mechanism for the powertrain of electric vehicles. Its function is to protect high-voltage components and prevent dangerous conditions from escalating when system abnormalities occur. Active short-circuit works by controlling the three-phase bridge arms of the motor controller, creating a closed loop in the three-phase windings of the drive motor, isolating the drive motor from the high-voltage power battery. Specific implementation methods include upper bridge short-circuit and lower bridge short-circuit. Upper bridge short-circuit means connecting the three upper bridge arms and disconnecting the three lower bridge arms. Lower bridge short-circuit means disconnecting the three upper bridge arms and connecting the three lower bridge arms. When the motor controller operates in active short-circuit mode, it means controlling the motor controller to actively short-circuit. Active short-circuit mode is characterized by either the three upper bridge arms being connected and the three lower bridge arms being disconnected, or the three upper bridge arms being disconnected and the three lower bridge arms being connected. Active short-circuit mode completely isolates the drive motor, motor controller, and power battery, preventing fault energy from flowing back into the power battery, while providing a safe high-voltage disconnection environment for maintenance personnel.

[0008] When a powertrain malfunctions (e.g., high-voltage shutdown, system failure), to prevent back electromotive force from damaging the battery and motor controller and to achieve safe isolation of the high-voltage system, the powertrain will actively control the motor controller to enter an active short-circuit state. When the motor controller is in this active short-circuit state, the stator winding of the drive motor forms a closed-loop circuit with either the upper or lower arm of the motor controller. The drive motor operates as a generator, and the back electromotive force energy generated by the drive motor is released through the stator winding, resulting in a corresponding negative torque output by the drive motor, which brakes the electric vehicle. When the motor controller is in this active short-circuit state, the torque output by the drive motor at different speeds initially increases rapidly with increasing speed at low speeds, then decreases rapidly with increasing speed, and finally stabilizes at high speeds.

[0009] It should be understood that when other components of an electric vehicle malfunction, such as overvoltage, overcurrent, or overheating of the power battery, or when the electric vehicle is involved in a collision, the powertrain cannot continue to operate normally and needs to enter active short-circuit mode in a timely manner. This is also considered a powertrain malfunction.

[0010] The fully off state, also known as the three-phase open-circuit state, separates the motor controller and the drive motor by disconnecting all the switching transistors of the motor controller. When the motor controller operates in the fully off state, the energy on the drive motor side can only be passively rectified through the reverse diodes on the three-phase bridge arms. The drive motor operates in an open-circuit state and cannot feed energy back to the DC side. The rotor can only stop by mechanical damping, without generating additional torque or additional braking effect. The deceleration process of the wheels is affected by the friction of the road surface.

[0011] The coefficient of adhesion (COP) is the ratio of adhesion force to the normal pressure of the wheel, determined by the road surface and tires. A higher COP results in greater usable adhesion. When an electric vehicle travels on a surface with a COP lower than a preset value, its wheels are in a low-traction state, resulting in less wheel grip and a higher risk of slippage or wheel lock-up, leading to lower stability. If the powertrain malfunctions, the motor controller enters an active short-circuit state, causing the drive motor to output negative torque to brake the vehicle. However, when the drive motor speed is low, excessive negative torque can cause the wheel speed to drop too quickly, exceeding the adhesion limit and leading to wheel lock-up. This can cause the electric vehicle to lose direction and fishtail, posing a danger. Therefore, this needs to be controlled. After a powertrain malfunction, the motor controller cycles between active short-circuit and fully shut-off states while controlling the drive motor to reduce its speed. In active short-circuit mode, the drive motor generates a large negative torque, forcing the wheels to decelerate rapidly. In fully closed mode, the drive motor no longer generates negative torque, and the deceleration process of the wheels is affected by road friction. The deceleration process depends entirely on the road friction. Thus, the braking torque is dynamically adjusted according to the cyclic switching between active short-circuit mode and fully closed mode, simulating the working effect of an anti-lock braking system (ABS), thereby avoiding sudden changes in wheel speed and preventing tire lock-up.

[0012] It should be understood that the cyclic switching between active short-circuit state and fully off state of the motor controller means that the motor controller alternately enters the active short-circuit state and the fully off state. For example, the motor controller first enters the active short-circuit state and operates for a period of time, then switches from the active short-circuit state to the fully off state, operates in the fully off state for a period of time, then switches back from the fully off state to the active short-circuit state, and operates in the active short-circuit state again for a period of time, and so on. The motor controller alternates between the two states.

[0013] It should also be understood that the process of the drive motor reducing its speed refers to the period from when the drive motor begins to reduce its speed to when it stops reducing its speed, during which it cycles between an active short-circuit state and a fully off state. It does not mean that the reduction in drive motor speed will always be accompanied by this cycle of switching between active short-circuit and fully off states. The motor controller does not necessarily continuously switch between active short-circuit and fully off states while controlling the drive motor to reduce its speed. In one implementation, the motor controller will only perform this cycle of switching when certain conditions are met. Furthermore, the number of cycles is not fixed; it can cycle once or multiple times.

[0014] The preset values ​​are pre-calibrated based on real vehicle experiments and / or model calculations, or are pre-set by comprehensively considering the vehicle's requirements and performance.

[0015] According to the solution in this application, when an electric vehicle malfunctions while driving on a low-friction surface, the motor controller is intermittently activated to enter an active short-circuit state. The motor controller cycles between the active short-circuit state and the fully shut-off state. By forcing the speed of the drive motor to decrease rapidly through the active short-circuit state, the tires are prevented from locking up, thus preventing slippage on low-friction surfaces and improving the stability and safety of the electric vehicle.

[0016] In conjunction with the first aspect, in some implementations of the first aspect, after a powertrain failure, before the speed of the drive motor drops to a first preset speed, the motor controller operates in an active short-circuit state to reduce the speed of the drive motor.

[0017] Active short-circuit mode electrically disconnects the motor controller from the drive motor by short-circuiting all three phases of the drive motor. Without the control of the motor controller, the drive motor's characteristics are only affected by internal parameters and initial conditions after the controller operates in active short-circuit mode. When the motor controller operates in active short-circuit mode, the drive motor generates negative torque, which varies with speed. At low speeds, the negative torque output by the drive motor initially increases rapidly with increasing speed, then decreases rapidly with increasing speed, and tends to stabilize at high speeds.

[0018] When the speed of the drive motor is greater than the first preset speed, the motor controller operates in an active short-circuit state. The negative torque output by the drive motor is small. Even if the electric vehicle is driving on a low-friction surface, the negative torque on the wheels will not exceed the traction limit, and the wheels will not lock up. Therefore, the motor controller operates in an active short-circuit state to reduce the speed of the drive motor without switching to a fully shut-off state.

[0019] The first preset speed is pre-calibrated based on actual vehicle experiments and / or model calculations, or it is preset by comprehensively considering the needs and performance of the entire vehicle.

[0020] According to the solution of this application, when an electric vehicle malfunctions while driving on a low-friction surface, and the speed of the drive motor is high, the motor controller is controlled to operate in an active short-circuit state, forcing the speed of the drive motor to decelerate rapidly so that the electric vehicle can decelerate as quickly as possible, thereby improving the safety of the electric vehicle during deceleration and stopping due to an unexpected malfunction while driving on a low-friction surface.

[0021] In conjunction with the first aspect, in some implementations of the first aspect, after a powertrain failure, after the speed of the drive motor drops to less than or equal to a first preset speed, the motor controller cycles between an active short-circuit state and a fully shut-off state to allow the speed of the drive motor to continue to decrease.

[0022] When the speed of the drive motor decreases to less than or equal to the first preset speed, the motor controller operates in an active short-circuit state. The negative torque output by the drive motor is relatively large. When the electric vehicle is driving on a low-friction surface, the negative torque on the wheels may exceed the traction limit, causing the wheels to lock up. At this time, it is necessary to control the motor controller to cycle between the active short-circuit state and the fully shut-off state, so as to control the rate at which the speed of the drive motor decreases and prevent it from locking up too quickly.

[0023] According to the solution of this application, when an electric vehicle malfunctions while driving on a low-friction surface, and the speed of the drive motor is low, the motor controller switches cyclically between an active short-circuit state and a fully shut-off state. While the active short-circuit state forces the speed of the drive motor to decrease rapidly, the fully shut-off state is used to adjust the speed reduction rate, thereby preventing the tires from locking up, preventing slippage on low-friction surfaces, and improving the stability and safety of the electric vehicle.

[0024] In conjunction with the first aspect, in some implementations of the first aspect, after a powertrain failure, the motor controller cycles between an active short-circuit state and a fully shut-off state to reduce the speed of the drive motor to less than a second preset speed, and then the motor controller continues to operate in the active short-circuit state to further reduce the speed of the drive motor.

[0025] When the speed of the drive motor continues to decrease to less than the second preset speed, the negative torque output by the drive motor is small. Even if the electric vehicle is driving on a low-friction surface, the negative torque on the wheels will not exceed the traction limit, and the wheels will not lock up. Therefore, the motor controller operates in an active short-circuit state to reduce the speed of the drive motor, without having to switch to the fully shut-off state.

[0026] The second preset speed is pre-calibrated based on actual vehicle experiments and / or model calculations, or it is preset by comprehensively considering the needs and performance of the entire vehicle.

[0027] According to the solution of this application, when the speed of the drive motor has dropped below the second preset speed, the vehicle speed is also very low, and the wheels will not lock up. The motor controller is controlled to operate in an active short-circuit state to make the speed continue to decrease, thus ensuring safety and improving the stability and safety of the electric vehicle.

[0028] In conjunction with the first aspect, in some implementations of the first aspect, during the cyclic switching between the active short-circuit state and the fully shut-off state of the motor controller, the speed of the drive motor decreases when the motor controller is operating in the active short-circuit state, and the speed of the drive motor first increases and then decreases when the motor controller is operating in the fully shut-off state.

[0029] When the motor controller operates in active short-circuit mode, the stator winding of the drive motor forms a closed-loop circuit with the upper or lower bridge arm of the motor controller. The drive motor operates as a generator, and the back electromotive force energy generated by the drive motor is released through the stator winding. The drive motor outputs a corresponding negative torque, thereby reducing the speed of the drive motor. When the motor controller operates in fully off mode, the energy on the drive motor side can only be passively rectified through the reverse diodes on the three-phase bridge arm. The drive motor operates in open circuit mode and cannot feed energy back to the DC side. The rotor can only stop by mechanical damping, without generating additional torque or additional braking effect. The deceleration process of the wheels is affected by road friction. When the motor controller switches from active short-circuit mode to fully off mode, the speed of the drive motor will first increase briefly and then decrease. This is because the speed of the drive motor has decreased, but the speed of the electric vehicle is still relatively high. In the fully off state, the negative torque of the drive motor is released, and the drive motor is briefly in a free-rotation state. The speed will gradually match the speed of the electric vehicle, hence the brief increase in speed. Subsequently, the wheels are affected by road friction, and the speed of the drive motor continues to decrease.

[0030] According to the solution in this application, by switching between active short-circuit state and full shut-off state, tire lock-up can be effectively avoided on low-adhesion road surfaces, reducing safety risks such as sideslip and fishtailing. At the same time, it ensures the rapid deceleration performance of electric vehicles, maintains vehicle stability throughout the deceleration process, thereby shortening the braking distance and improving the safety and reliability of electric vehicles in complex road conditions.

[0031] In conjunction with the first aspect, in some implementations of the first aspect, during the cyclic switching between the active short-circuit state and the fully shut-off state of the motor controller, the speed of the drive motor decreases at a first rate during the operation of the motor controller in the active short-circuit state, and the speed of the drive motor first increases and then decreases at a second rate less than the first rate during the operation of the motor controller in the fully shut-off state.

[0032] When the motor controller operates in active short-circuit mode, the stator winding of the drive motor forms a closed-loop circuit with the upper or lower bridge arm of the motor controller. The drive motor operates as a generator, and the back electromotive force energy generated by the drive motor is released through the stator winding. The drive motor outputs a corresponding negative torque, thereby reducing the speed of the drive motor. When the motor controller operates in fully off mode, the energy on the drive motor side can only be passively rectified through the reverse diodes on the three-phase bridge arm. The drive motor operates in open-circuit mode and cannot feed energy back to the DC side. The rotor can only stop by mechanical damping, without generating additional torque or additional braking effect. The deceleration process of the wheels is affected by road friction. Therefore, the rate at which the drive motor speed decreases in the fully off mode is lower than the rate at which the motor controller decreases in the active short-circuit mode.

[0033] According to the solution in this application, by switching between active short-circuit state and full shut-off state, tire lock-up can be effectively avoided on low-adhesion road surfaces, reducing safety risks such as sideslip and fishtailing. At the same time, it ensures the rapid deceleration performance of electric vehicles, maintains vehicle stability throughout the deceleration process, thereby shortening the braking distance and improving the safety and reliability of electric vehicles in complex road conditions.

[0034] In conjunction with the first aspect, in some implementations of the first aspect, during the process of the motor controller cyclically switching between the active short-circuit state and the fully shut-off state, the motor controller operates in the active short-circuit state or the fully shut-off state according to the difference between the speed of the drive motor and the target speed, and the target speed gradually decreases over time.

[0035] When an electric vehicle is traveling on a low-friction surface, a powertrain failure requires the vehicle to enter an active short-circuit state to decelerate and stop. When the motor controller is in this active short-circuit state, the drive motor's speed decreases rapidly. However, an excessively rapid decrease in drive motor speed can cause wheel lock-up, leading to vehicle instability and skidding, resulting in a dangerous situation. Therefore, it is necessary to control the drive motor's speed to keep the wheel slip ratio within an ideal range to prevent lock-up or slippage.

[0036] The target speed is a speed change determined based on the performance and condition of the electric vehicle when decelerating on a low-friction surface, aiming to prevent instability and achieve rapid stopping. The gradual reduction of the target speed is based on the dynamic requirements during the vehicle's deceleration process.

[0037] According to the solution in this application, by real-time detection of the difference between the drive motor speed and the target speed and dynamically adjusting the operation to active short circuit or full shutdown state, the speed change is avoided, enabling the electric vehicle to effectively avoid tire lock-up on low-traction road surfaces, reducing safety risks such as sideslip and fishtailing, and improving the safety and reliability of the electric vehicle.

[0038] In conjunction with the first aspect, in some implementations of the first aspect, after a powertrain failure, when the difference between the target speed and the drive motor speed is greater than a first difference and the drive motor speed is less than the target speed, the motor controller switches to a fully shut-off state.

[0039] When the motor controller is operating in an active short-circuit state, the drive motor speed decreases rapidly under the influence of negative torque. When the difference between the target speed and the drive motor speed is greater than a first difference value, and the drive motor speed is less than the target speed, the actual speed of the drive motor differs significantly from the target speed, and is less than the target speed. This indicates that the actual speed changes faster than the target speed over time, and the speed may decrease too quickly, potentially causing wheel lock-up. In this situation, the motor controller needs to be switched to a fully off state to reduce the rate of decrease in drive motor speed and decrease the difference between the actual and target speeds.

[0040] According to the solution in this application, by real-time detection of the difference between the drive motor speed and the target speed and dynamic adjustment to operate in active short-circuit state or fully shut-off state, when the speed drops too quickly, it switches to fully shut-off state to effectively avoid tire lock-up on low-adhesion road surfaces, reduce safety risks such as sideslip and fishtailing, and improve the safety and reliability of electric vehicles.

[0041] In conjunction with the first aspect, in some implementations of the first aspect, after a powertrain failure, when the difference between the speed of the drive motor and the target speed is less than a second difference and the speed of the drive motor is greater than the target speed, the motor controller switches to active short-circuit operation.

[0042] When the motor controller is operating in a fully off state, the drive motor speed decreases slowly under the influence of friction. When the difference between the drive motor speed and the target speed is less than a second difference and the drive motor speed is greater than the target speed, the difference between the actual drive motor speed and the target speed is small, and it is greater than the target speed. This indicates that the rate of change of the actual speed over time is slower than the rate of change of the target speed over time, and there is a margin in the speed decrease, so the wheels will not lock up temporarily. At this time, it is necessary to switch the motor controller to active short-circuit operation, thereby increasing the rate of decrease of the drive motor speed and rapidly reducing the actual speed of the drive motor.

[0043] According to the solution in this application, by real-time detection of the difference between the speed of the drive motor and the target speed and dynamic adjustment to operate in active short-circuit state or fully shut-off state, when the difference between the speed and the target speed is small, the system switches to active short-circuit state to rapidly reduce the speed of the drive motor, thereby stopping the electric vehicle as soon as possible and improving the safety and reliability of the electric vehicle.

[0044] In conjunction with the first aspect, in some implementations of the first aspect, during the cyclic switching between an active short-circuit state and a fully shut-off state by the motor controller, the torque output by the drive motor fluctuates between negative torque and zero torque. The drive motor outputs negative torque when the motor controller is operating in the active short-circuit state, and zero torque when the motor controller is operating in the fully shut-off state; the negative torque is used to brake the wheels.

[0045] When the motor controller operates in an active short-circuit state, the stator winding of the drive motor forms a closed-loop circuit with the upper or lower arm of the motor controller. The drive motor operates as a generator, and the back electromotive force energy generated by the drive motor is released through the stator winding. The drive motor outputs a corresponding negative torque, which brakes the wheels of the electric vehicle. When the motor controller operates in a fully off state, the drive motor runs in an open circuit, does not generate additional torque, has zero output torque, and has no additional braking effect.

[0046] According to the solution in this application, by switching between active short-circuit state and full shut-off state, tire lock-up can be effectively avoided on low-adhesion road surfaces, reducing safety risks such as sideslip and fishtailing. At the same time, it ensures the rapid deceleration performance of electric vehicles, maintains vehicle stability throughout the deceleration process, thereby shortening the braking distance and improving the safety and reliability of electric vehicles in complex road conditions.

[0047] In conjunction with the first aspect, in some implementations of the first aspect, during the operation of the electric vehicle on a road surface with a coefficient of friction greater than a preset value, before a powertrain failure, the motor controller outputs three-phase current to the drive motor to control the drive motor to drive the wheels of the electric vehicle. After a powertrain failure, the motor controller continues to operate in an active short-circuit state to reduce the speed of the drive motor.

[0048] When electric vehicles travel on high-friction surfaces, their wheels have greater grip, making them less prone to slippage or lock-up, resulting in higher stability. If a powertrain malfunctions, the motor controller enters an active short-circuit state, causing the drive motor to output negative torque to brake the electric vehicle. This eliminates the need to switch to a fully shut-off state, allowing the drive motor to operate in an active short-circuit state more quickly.

[0049] According to the solution in this application, when an electric vehicle is driving on a high-adhesion road surface and the powertrain fails, it does not need to switch between active short-circuit state and full shutdown state. Instead, it always remains in active short-circuit state. Based on the change in the road adhesion coefficient, the control strategy is dynamically adjusted to bring the electric vehicle to a stop as soon as possible when there is no risk of locking up, thereby improving the safety and reliability of the electric vehicle.

[0050] In conjunction with the first aspect, in some implementations of the first aspect, the motor controller is used to adjust the target rotational speed according to the vehicle speed and wheel speed of the electric vehicle when the powertrain fails during the driving of the electric vehicle on a road surface with a coefficient of adhesion less than a preset value. The target rotational speed changes with the coefficient of adhesion of the road surface.

[0051] To prevent wheel lock-up during deceleration in electric vehicles, wheel slip ratio control is necessary. The motor controller obtains the drive motor speed via the resolver signal from the resolver sensor. The wheel speeds are calculated from the drive motor speed and the vehicle's gear ratio. Combining this with the wheel radius and the vehicle's speed, the slip ratio of each wheel can be determined. The target speed is determined based on the wheel slip ratios, and setting these target speeds allows for effective control of the wheel slip ratios. When the road surface adhesion coefficient changes, the wheel slip ratios also change, thus requiring a corresponding change in the target speed.

[0052] According to the scheme of this application, the target speed is dynamically adjusted based on the change of road surface adhesion coefficient and wheel slip ratio. The motor controller switches between active short circuit state and full shut-off state according to the target speed, avoiding excessive speed change. This enables electric vehicles to effectively avoid tire lock-up on low-adhesion road surfaces, reducing safety risks such as sideslip and fishtailing, and improving the safety and reliability of electric vehicles.

[0053] Secondly, this application provides a control method for an electric vehicle. The control method is used to control the electric vehicle to decelerate and stop after a powertrain failure during the electric vehicle's operation on a road surface with an adhesion coefficient less than a preset value. The powertrain includes a motor controller and a drive motor. The motor controller includes three-phase bridge arms, and the midpoints of the three bridge arms are respectively used to connect the three-phase windings of the drive motor. The control method includes, after the powertrain failure, controlling the motor controller to cyclically switch between an active short-circuit state and a fully shut-off state during the process of the drive motor reducing its speed. The active short-circuit state refers to a state in which the three upper bridge arms of the three-phase bridge arm are conducting and the three lower bridge arms are disconnected, or the three upper bridge arms of the three-phase bridge arm are disconnected and the three lower bridge arms are conducting. The fully shut-off state refers to a state in which both the three upper bridge arms and the three lower bridge arms of the three-phase bridge arm are disconnected.

[0054] In conjunction with the second aspect, in some implementations of the second aspect, when a powertrain failure occurs, the motor controller is first controlled to operate in an active short-circuit state to reduce the speed of the drive motor. Once the speed of the drive motor has decreased to a first speed value, the motor controller is controlled to cycle between the active short-circuit state and the fully shut-off state.

[0055] In conjunction with the second aspect, in some implementations of the second aspect, when the speed of the drive motor decreases to the second speed value, the motor controller is kept in an active short-circuit state to make the speed of the drive motor continue to decrease.

[0056] In conjunction with the second aspect, in some implementations of the second aspect, after a powertrain failure, when the difference between the speed of the drive motor and the target speed is greater than a first difference and the speed of the drive motor is less than the target speed, the motor controller is controlled to operate in an active short-circuit state; when the difference between the speed of the drive motor and the target speed is less than a second difference and the speed of the drive motor is greater than the target speed, the motor controller is controlled to operate in a fully shut-off state.

[0057] Thirdly, this application provides an electric vehicle including four wheels, a power battery, and a powertrain as described in the first aspect and its various implementations, the powertrain being used to receive power from the power battery to drive the four wheels.

[0058] Other beneficial effects can be found in the description of the first aspect, and will not be repeated here. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of an electric vehicle provided in an embodiment of this application;

[0060] Figure 2 This is a schematic diagram of the architecture of an electric vehicle provided in an embodiment of this application;

[0061] Figure 3 This is a schematic diagram of the powertrain provided in an embodiment of this application;

[0062] Figure 4 This is a schematic diagram illustrating the changes in the motor controller state and drive motor speed over time after a powertrain failure, as provided in an embodiment of this application.

[0063] Figure 5 This is a schematic diagram of the process of a motor controller cyclically switching between an active short-circuit state and a fully shut-off state, provided in an embodiment of this application.

[0064] Figure 6 This is a schematic diagram of controller interaction provided in an embodiment of this application;

[0065] Figure 7 This is a schematic diagram illustrating the changes in torque and speed of the drive motor of an electric vehicle over time during driving on a low-friction surface, according to an embodiment of this application.

[0066] Figure 8 This is a schematic diagram illustrating the change in torque and speed of the drive motor of an electric vehicle over time during its operation on a high-friction surface, as provided in an embodiment of this application. Detailed Implementation

[0067] The technical solutions in this application will now be described in conjunction with the accompanying drawings. The detailed descriptions and drawings of the following embodiments are used to exemplarily illustrate the principles of this application, but should not be used to limit the scope of this application; that is, this application is not limited to the described embodiments.

[0068] As the power source of an electric vehicle, the powertrain needs to enter active short circuit (ASC) mode to actively protect the powertrain when a system malfunctions. During ASC mode, the drive motor generates significant braking torque, forcing a rapid decrease in speed to bring the vehicle to a stop. However, when an electric vehicle malfunctions on low-traction surfaces (such as ice, snow, or slippery surfaces), the drive system forcibly entering ASC mode can cause the wheel speed to drop too quickly, potentially leading to wheel lock-up, instability, and fishtailing, resulting in a dangerous situation.

[0069] To address the aforementioned issues, this application provides a powertrain, a control method, and an electric vehicle. When an electric vehicle malfunctions while driving on a low-friction surface, the motor controller is intermittently activated in an active short-circuit state. The motor controller cycles between the active short-circuit state and the fully shut-off state. By forcing the electric vehicle to decelerate rapidly through the active short-circuit state, the tires are prevented from locking up, thus preventing skidding on low-friction surfaces and improving the stability and safety of the electric vehicle.

[0070] Figure 1 and Figure 2 This is a schematic diagram of the architecture of the electric vehicle 10 provided in the embodiments of this application.

[0071] like Figure 1 As shown, the electric vehicle 10 includes a vehicle controller 20, a power battery (not shown) and a powertrain 50. The powertrain 50 includes a motor controller 40 and a drive motor 30. The motor controller 40 is used to receive power from the power battery and output current to the drive motor 30 to control the drive motor 30 to output torque to drive the electric vehicle 10.

[0072] In one embodiment, the electric vehicle 10 has a distributed four-motor drive architecture, with the drive motors positioned beside the driving wheels and controlled by individual motor controllers 40. In another embodiment, the electric vehicle 10 also has a centralized drive motor architecture, where drive motors for driving two front wheels or two rear wheels are arranged together. There are one or more motor controllers 40. Each motor controller 40 corresponds one-to-one with a drive motor, or one motor controller 40 corresponds to multiple drive motors. The motor controllers 40 control the output torque of one or more drive motors to drive the electric vehicle 10.

[0073] In one embodiment, such as Figure 2 As shown in (a), the electric vehicle 10 has a distributed four-motor drive architecture, with the drive motors positioned beside the driving wheels and controlled by individual motor controllers. The electric vehicle 10 is also as follows... Figure 2 The centralized four-drive motor drive architecture shown in (b) has two drive motors for driving the two front wheels or the two rear wheels set together.

[0074] For example, the electric vehicle 10 includes four motor controllers: motor controller 41, motor controller 42, motor controller 43, and motor controller 44. The four motors include drive motor 31, drive motor 32, drive motor 33, and drive motor 34. Motor controller 41 controls drive motor 31 to drive wheel 51, motor controller 42 controls drive motor 32 to drive wheel 52, motor controller 43 controls drive motor 33 to drive wheel 53, and motor controller 44 controls drive motor 34 to drive wheel 54.

[0075] In one embodiment, the electric vehicle 10 still... Figure 2 The centralized drive motor architecture shown in (c) uses one drive motor to drive the two front wheels of the electric vehicle 10, and two drive motors to drive the two rear wheels of the electric vehicle 10 respectively.

[0076] In one embodiment, the various architectures mentioned above can also be combined, for example, the front drive adopts a distributed drive motor architecture and the rear drive adopts a centralized drive motor architecture.

[0077] The electric vehicle 10 also includes an accelerator pedal. The accelerator pedal is used to instruct the powertrain 50 to output drive torque to the wheels of the electric vehicle 10.

[0078] The accelerator pedal in this application is also called the power accelerator pedal or simply the accelerator pedal. The opening degree of the accelerator pedal indicates the amount of driving force required by the driver. The larger the opening degree of the accelerator pedal, the greater the driver's demand for driving force, and the greater the torque required from the drive motor. The powertrain controls the amount of current output to the drive motor based on the accelerator pedal opening degree so that the drive motor outputs the torque indicated by the accelerator pedal opening degree. A larger accelerator pedal opening degree results in a larger effective current value, thus a larger torque output by the drive motor; conversely, a smaller accelerator pedal opening degree results in a smaller effective current value, thus a smaller torque output by the drive motor. The driving torque output by the powertrain varies with the change in the accelerator pedal opening degree.

[0079] In one embodiment, each motor controller 40 is directly connected to the accelerator pedal and controls the corresponding drive motor 30 to output torque according to the torque signal output by the accelerator pedal.

[0080] In one embodiment, the vehicle controller 20 sends a torque signal to the motor controller 40 based on the opening degree of the accelerator pedal. The torque signal is used to indicate the torque indicated by the accelerator pedal opening degree.

[0081] The vehicle controller 20 connects to the sensors and actuators of the electric vehicle 10 and interacts with them via a controller area network (CAN) bus, Ethernet, local interconnect network (LIN) bus, high-speed fault-tolerant network protocol (FlexRay), or other types of connection methods.

[0082] In one embodiment, each motor controller 40 is connected to a resolver sensor. The resolver sensor is used to detect the rotational speed of the drive motor 30 controlled by the motor controller 40, and the motor controller 40 is used to receive signals from the resolver sensor. The resolver sensor can accurately detect the position, direction, and speed of the drive motor rotor, and is responsible for monitoring and extracting the rotational speed of the drive motor. It has a high sampling rate and is directly connected to the motor controller 40, resulting in short signal transmission time and higher stability.

[0083] Figure 3 This application provides a powertrain 50.

[0084] like Figure 3 As shown, the powertrain 50 includes a motor controller 40 and a drive motor 30. The motor controller 40 includes a three-phase bridge arm, and the midpoints of the three bridge arms are respectively used to connect the three-phase windings of the drive motor 30.

[0085] The motor controller 40 includes three-phase bridge arms, each of which includes two electronic switching devices connected in series. The midpoint of the bridge arm is the connection point between the two electronic switching devices. The electronic switching devices are composed of insulated-gate bipolar transistors and anti-parallel diodes, or other electronic components. Each phase bridge arm is divided into upper and lower bridge arms by the midpoint. One end of each of the three upper bridge arms is connected to one end of the power battery, and one end of each of the three lower bridge arms is connected to the other end of the power battery. The midpoint of each bridge arm is connected to the three-phase windings of the drive motor 30. During the operation of the electric vehicle 10, when the powertrain 50 is working normally, the motor controller 40 receives DC power from the power battery and converts it into three-phase AC power through the three-phase bridge arms to control the drive motor 30, thereby controlling the output torque of the drive motor 30 to drive the wheels of the electric vehicle 10.

[0086] During the driving of electric vehicle 10 on a road surface with a coefficient of adhesion less than a preset value, before the powertrain 50 fails, motor controller 40 outputs three-phase current to drive motor 30 to control drive motor 30 to drive the wheels of electric vehicle 10.

[0087] After the powertrain 50 fails, the motor controller 40 cycles between an active short circuit state and a fully shut-off state while controlling the drive motor 30 to reduce its speed. The active short circuit state refers to the state in which the three upper bridge arms of the three-phase bridge arm are conducting and the three lower bridge arms are disconnected, or the three upper bridge arms of the three-phase bridge arm are disconnected and the three lower bridge arms are conducting. The fully shut-off state refers to the state in which all three upper bridge arms and all three lower bridge arms of the three-phase bridge arm are disconnected.

[0088] Active short circuit is a key safety protection mechanism of the powertrain 50 in electric vehicles 10. Its function is to protect the safety of high-voltage components and prevent the escalation of dangerous operating conditions when system abnormalities occur. Active short circuit controls the three-phase bridge arms of the motor controller 40, causing the three-phase windings of the drive motor 30 to form a closed circuit, isolating the drive motor 30 from the high-voltage power battery. Specifically, it includes upper bridge short circuit and lower bridge short circuit. Upper bridge short circuit means turning on the three upper bridge arms of the three-phase bridge arm and turning off the three lower bridge arms. Lower bridge short circuit means turning off the three upper bridge arms of the three-phase bridge arm and turning on the three lower bridge arms. When the motor controller 40 is in active short circuit mode, it means controlling the motor controller 40 to actively short circuit. Active short circuit mode refers to a state where the three upper bridge arms of the three-phase bridge arm are turned on and the three lower bridge arms are turned off, or the three upper bridge arms of the three-phase bridge arm are turned off and the three lower bridge arms are turned on. The active short-circuit state can completely isolate the drive motor 30, motor controller 40 and power battery, prevent fault energy from flowing back into the power battery, and at the same time provide a safe high-voltage power-off environment for maintenance personnel.

[0089] When the powertrain 50 malfunctions (e.g., high-voltage shutdown, system failure), to prevent back EMF from damaging the power battery and motor controller 40 and to achieve safe isolation of the high-voltage system, the powertrain 50 will actively control the motor controller 40 to enter an active short-circuit state. When the motor controller 40 is in the active short-circuit state, the stator winding of the drive motor 30 forms a closed-loop circuit with the upper or lower bridge arm of the motor controller 40. The drive motor 30 operates as a generator, and the back EMF energy generated by the drive motor 30 is released through the stator winding. The drive motor 30 outputs a corresponding negative torque, which brakes the electric vehicle 10. When the motor controller 40 is in the active short-circuit state, the torque output by the drive motor 30 at different speeds initially increases rapidly with increasing speed at low speeds, then decreases rapidly with increasing speed, and tends to stabilize at high speeds.

[0090] It should be understood that when other components of the electric vehicle 10 malfunction, such as overvoltage, overcurrent, or overheating of the power battery, or when the electric vehicle 10 is involved in a collision, the powertrain 50 cannot continue to work normally and the powertrain 50 also needs to enter the active short-circuit mode in a timely manner. This is also considered as a malfunction of the powertrain 50.

[0091] The fully off state, also known as the three-phase open-circuit state, separates the motor controller 40 and the drive motor 30 by disconnecting all the switching transistors of the motor controller 40. When the motor controller 40 is in the fully off state, the energy on the drive motor 30 side can only be passively rectified through the reverse diodes on the three-phase bridge arm. The drive motor 30 operates in an open-circuit state, unable to feed energy back to the DC side. The rotor can only stop due to mechanical damping, without generating additional torque or providing additional braking effect. The deceleration of the wheels is affected by road friction.

[0092] The coefficient of adhesion is the ratio of adhesion force to the normal pressure of the wheel, determined by the road surface and tires. A higher coefficient of adhesion results in greater usable adhesion. When the electric vehicle 10 travels on a road surface with a coefficient of adhesion less than a preset value, its wheels are in a low-traction environment with low grip, making it prone to slippage or wheel lock-up, resulting in low stability. If the powertrain 50 malfunctions, the motor controller 40 enters an active short-circuit state, and the drive motor 30 outputs negative torque to brake the electric vehicle 10. However, when the drive motor 30's speed is low, the excessive negative torque output causes the wheel speed to drop too quickly, leading to the longitudinal force on the tires exceeding the adhesion limit, resulting in wheel lock-up and causing the electric vehicle 10 to become unstable and fishtail, posing a danger. Therefore, this needs to be controlled. After the powertrain 50 malfunctions, the motor controller 40 cycles between active short-circuit and fully shut-off states while controlling the drive motor 30 to reduce its speed. In the active short-circuit state, the drive motor 30 generates a large negative torque, forcing the wheels to decelerate rapidly. In the fully closed state, the drive motor 30 no longer generates negative torque, and the deceleration process of the wheels is affected by the road friction. The deceleration process depends entirely on the road friction. Thus, the braking torque is dynamically adjusted according to the cyclic switching between the active short-circuit state and the fully closed state, simulating the working effect of an anti-lock braking system (ABS), thereby avoiding sudden changes in wheel speed and preventing tire lock-up.

[0093] It should be understood that the cyclic switching between active short-circuit state and fully off state of the motor controller means that the motor controller alternately enters the active short-circuit state and the fully off state. For example, the motor controller first enters the active short-circuit state and operates for a period of time, then switches from the active short-circuit state to the fully off state, operates in the fully off state for a period of time, then switches back from the fully off state to the active short-circuit state, and operates in the active short-circuit state again for a period of time, and so on. The motor controller alternates between the two states.

[0094] It should also be understood that the process of the drive motor reducing its speed refers to the period from when the drive motor begins to reduce its speed to when it stops reducing its speed, during which it cycles between an active short-circuit state and a fully off state. It does not mean that the reduction in drive motor speed will always be accompanied by this cycle of switching between active short-circuit and fully off states. The motor controller does not necessarily continuously switch between active short-circuit and fully off states while controlling the drive motor to reduce its speed. In one implementation, the motor controller will only perform this cycle of switching when certain conditions are met. Furthermore, the number of cycles is not fixed; it can cycle once or multiple times.

[0095] The preset values ​​are pre-calibrated based on real vehicle experiments and / or model calculations, or are pre-set by comprehensively considering the vehicle's requirements and performance.

[0096] According to the solution of this application, when the electric vehicle 10 malfunctions while driving on a low-friction surface, the motor controller 40 is intermittently activated to enter an active short-circuit state. The motor controller 40 cycles between the active short-circuit state and the fully shut-off state. While forcing the speed of the drive motor 30 to decrease rapidly through the active short-circuit state, the tires are prevented from locking up, thus preventing slippage on the low-friction surface and improving the stability and safety of the electric vehicle 10.

[0097] Figure 4 This is a schematic diagram showing the state of the motor controller 40 and the speed of the drive motor 30 changing over time after a powertrain 50 malfunctions, according to an embodiment of this application.

[0098] In one embodiment, after a powertrain 50 failure, before the speed of the drive motor 30 drops to a first preset speed, the motor controller 40 operates in an active short-circuit state to reduce the speed of the drive motor 30.

[0099] The active short-circuit state electrically disconnects the motor controller 40 from the drive motor 30 by short-circuiting all three phases of the drive motor 30. Without the control of the motor controller 40, the characteristics of the drive motor 30 are only affected by internal parameters and initial conditions after the motor controller 40 operates in the active short-circuit state. After the motor controller 40 operates in the active short-circuit state, the drive motor 30 generates negative torque, and this negative torque varies with speed. At low speeds, the negative torque output by the drive motor 30 first increases rapidly with increasing speed, then decreases rapidly with increasing speed, and tends to stabilize at high speeds.

[0100] When the speed of the drive motor 30 is greater than the first preset speed, the motor controller 40 operates in an active short-circuit state. The negative torque output by the drive motor 30 is small. Even if the electric vehicle 10 is driving on a low-friction surface, the negative torque on the wheels will not exceed the traction limit and the wheels will not lock up. Therefore, the motor controller 40 operates in an active short-circuit state to reduce the speed of the drive motor 30 without switching to a fully shut-off state.

[0101] The first preset speed is pre-calibrated based on actual vehicle experiments and / or model calculations, or it is preset by comprehensively considering the needs and performance of the entire vehicle.

[0102] In one embodiment, after a powertrain 50 failure, after the speed of the drive motor 30 drops to less than or equal to a first preset speed, the motor controller 40 cycles between an active short-circuit state and a fully shut-off state to continue reducing the speed of the drive motor 30.

[0103] When the speed of the drive motor 30 decreases to less than or equal to the first preset speed, the motor controller 40 operates in an active short-circuit state. The negative torque output by the drive motor 30 is relatively large. When the electric vehicle 10 is driving on a low-friction surface, the negative torque on the wheels may exceed the traction limit, causing the wheels to lock up. At this time, it is necessary to control the motor controller 40 to cycle between the active short-circuit state and the fully shut-off state, so as to control the rate at which the speed of the drive motor 30 decreases, so that it does not lock up too quickly.

[0104] like Figure 4 As shown, before time t1, the speed of the drive motor 30 is greater than the first preset speed, and the motor controller 40 operates in an active short-circuit state to reduce the speed of the drive motor 30. After time t1, the speed of the drive motor 30 decreases to less than or equal to the first preset speed, and the motor controller 40 cycles between the active short-circuit state and the fully off state to continue reducing the speed of the drive motor 30.

[0105] In one embodiment, after a powertrain 50 malfunctions, the motor controller 40 cycles between an active short-circuit state and a fully shut-off state to reduce the speed of the drive motor 30 to less than a second preset speed. Then, the motor controller 40 continues to operate in the active short-circuit state to further reduce the speed of the drive motor 30.

[0106] When the speed of the drive motor 30 continues to decrease to less than the second preset speed, the negative torque output by the drive motor 30 is small. Even if the electric vehicle 10 is driving on a low-friction surface, the negative torque on the wheels will not exceed the friction limit and the wheels will not lock up. Therefore, the motor controller 40 operates in an active short-circuit state to reduce the speed of the drive motor 30 without having to switch to the fully shut-off state.

[0107] The second preset speed is pre-calibrated based on actual vehicle experiments and / or model calculations, or it is preset by comprehensively considering the needs and performance of the entire vehicle.

[0108] In another embodiment, after a powertrain 50 malfunctions, the motor controller 40 cycles between an active short-circuit state and a fully shut-off state to reduce the speed of the drive motor 30 to less than a second preset speed. After this, the motor controller 40 continues to operate in the fully shut-off state to further reduce the speed of the drive motor 30.

[0109] Figure 5 This is a schematic diagram illustrating the process of a motor controller 40 cyclically switching between an active short-circuit state and a fully shut-off state, as provided in an embodiment of this application.

[0110] In one embodiment, such as Figure 4 and Figure 5 As shown, during the cyclic switching between active short-circuit state and fully shut-off state, the motor controller 40 operates in active short-circuit state or fully shut-off state according to the difference between the speed of the drive motor 30 and the target speed, and the target speed gradually decreases over time.

[0111] When the electric vehicle 10 is traveling on a low-friction surface, if the powertrain 50 malfunctions, the electric vehicle 10 needs to enter an active short-circuit state to decelerate and stop. When the motor controller 40 is operating in the active short-circuit state, the speed of the drive motor 30 will decrease rapidly. However, if the speed of the drive motor 30 decreases too quickly, the wheels may lock up, causing the electric vehicle 10 to become unstable and fishtail, leading to a hazard. Therefore, it is necessary to control the speed of the drive motor 30 to keep the wheel slip ratio within an ideal range to prevent wheel lock-up or skidding.

[0112] The target speed is a speed change target determined based on the performance and state of the electric vehicle 10 when it decelerates on a low-friction surface, ensuring that instability will not occur and that the vehicle can stop as quickly as possible. The gradual reduction of the target speed is based on the dynamic requirements during the vehicle deceleration process.

[0113] In one embodiment, the motor controller 40 is used to adjust the target rotational speed according to the vehicle speed and wheel speed of the electric vehicle 10 when the powertrain 50 fails during the driving of the electric vehicle 10 on a road surface with a coefficient of adhesion less than a preset value. The target rotational speed changes with the coefficient of adhesion of the road surface.

[0114] To prevent wheel lock-up during deceleration, slip ratio control of the electric vehicle 10's wheels is necessary. The motor controller 40 obtains the rotational speed of the drive motor 30 via the resolver signal from the resolver sensor. The wheel rotational speed can be calculated using the drive motor 30's rotational speed and the electric vehicle 10's transmission ratio. Combining this with the wheel radius and the electric vehicle 10's speed, the slip ratio of each wheel can be obtained. The target rotational speed is determined based on the wheel slip ratio of the electric vehicle 10; setting the target rotational speed effectively regulates the wheel slip ratio. When the road surface adhesion coefficient changes, the wheel slip ratio also changes, and therefore the target rotational speed changes accordingly.

[0115] Figure 6 This is a schematic diagram of controller interaction provided in an embodiment of this application.

[0116] In one embodiment, such as Figure 6 As shown, the target speed and torque commands are sent from the vehicle controller to the motor controller 40, which then makes a judgment and controls the drive motor 30.

[0117] The vehicle controller can be a vehicle controller 20, or other controllers with computing capabilities such as a domain controller.

[0118] In one embodiment, after a powertrain 50 malfunctions, when the difference between the target speed and the speed of the drive motor 30 is greater than a first difference and the speed of the drive motor 30 is less than the target speed, the motor controller 40 switches to a fully shut-off state.

[0119] When the motor controller 40 is operating in an active short-circuit state, the speed of the drive motor 30 decreases rapidly under the influence of negative torque. When the difference between the target speed and the speed of the drive motor 30 is greater than a first difference and the speed of the drive motor 30 is less than the target speed, the actual speed of the drive motor 30 differs significantly from the target speed, and is less than the target speed. This indicates that the rate of change of the actual speed over time is faster than the rate of change of the target speed over time, and the speed may decrease too quickly, potentially causing the wheels to lock up. In this case, it is necessary to switch the motor controller 40 to a fully off state, thereby reducing the rate of decrease in the speed of the drive motor 30 and reducing the difference between the actual speed and the target speed of the drive motor 30.

[0120] like Figure 4 As shown, at times t3, t5, and t7, the difference between the target speed and the speed of the drive motor 30 is greater than the first difference and the speed of the drive motor 30 is less than the target speed, so the motor controller 40 switches to the fully shut-off state.

[0121] In one embodiment, after a powertrain 50 failure, when the difference between the speed of the drive motor 30 and the target speed is less than a second difference and the speed of the drive motor 30 is greater than the target speed, the motor controller 40 switches to active short-circuit operation.

[0122] When the motor controller 40 is operating in the fully off state, the speed of the drive motor 30 decreases slowly under the action of friction. When the difference between the speed of the drive motor 30 and the target speed is less than a second difference and the speed of the drive motor 30 is greater than the target speed, the difference between the actual speed of the drive motor 30 and the target speed is small, and it is greater than the target speed. This indicates that the rate of change of the actual speed over time is slower than the rate of change of the target speed over time, and there is a margin in the speed reduction, so the wheels will not lock up temporarily. At this time, it is necessary to switch the motor controller 40 to operate in the active short-circuit state, thereby increasing the rate of decrease of the speed of the drive motor 30, and the actual speed of the drive motor 30 decreases rapidly.

[0123] like Figure 4 As shown, at times t2, t4 and t6, the difference between the speed of the drive motor 30 and the target speed is less than the second difference and the speed of the drive motor 30 is greater than the target speed, so the motor controller 40 switches to active short-circuit operation.

[0124] In one embodiment, during the cyclic switching between the active short-circuit state and the fully shut-off state, the speed of the drive motor 30 decreases when the motor controller 40 is operating in the active short-circuit state, and increases and then decreases when the motor controller 40 is operating in the fully shut-off state.

[0125] When the motor controller 40 operates in the active short-circuit state, the stator winding of the drive motor 30 forms a closed-loop circuit with the upper or lower bridge arm of the motor controller 40. The drive motor 30 operates as a generator, and the back electromotive force energy generated by the drive motor 30 is released through the stator winding. The drive motor 30 outputs a corresponding negative torque, thereby reducing the speed of the drive motor 30. When the motor controller 40 operates in the fully off state, the energy on the drive motor 30 side can only be passively rectified through the reverse diodes on the three-phase bridge arm. The drive motor 30 operates in an open-circuit state and cannot feed energy back to the DC side. The rotor can only stop by mechanical damping, without generating additional torque or additional braking effect. The deceleration process of the wheels is affected by the road friction. When the motor controller 40 switches from the active short-circuit state to the fully off state, the speed of the drive motor 30 will first increase briefly and then decrease. This is because the speed of the drive motor 30 has decreased, but the speed of the electric vehicle 10 is still relatively high. In the fully shut-off state, the negative torque of the drive motor 30 is released, and the drive motor 30 is briefly in a free-rotation state. The speed will gradually match the speed of the electric vehicle 10, so the speed increases briefly. Subsequently, the wheels are subjected to the friction of the road surface, and the speed of the drive motor 30 continues to decrease.

[0126] In one embodiment, during the cyclic switching between the active short-circuit state and the fully shut-off state, the speed of the drive motor 30 decreases at a first rate when the motor controller 40 is operating in the active short-circuit state, and the speed of the drive motor 30 first increases and then decreases at a second rate less than the first rate when the motor controller 40 is operating in the fully shut-off state.

[0127] When the motor controller 40 operates in an active short-circuit state, the stator winding of the drive motor 30 forms a closed-loop circuit with either the upper or lower bridge arm of the motor controller 40. The drive motor 30 operates as a generator, and the back electromotive force energy generated by the drive motor 30 is released through the stator winding. The drive motor 30 outputs a corresponding negative torque, thereby reducing the speed of the drive motor 30. When the motor controller 40 operates in a fully off state, the energy on the drive motor 30 side can only be passively rectified through the reverse diodes on the three-phase bridge arm. The drive motor 30 operates in an open-circuit state and cannot feed energy back to the DC side. The rotor can only stop by mechanical damping, without generating additional torque or additional braking effect. The deceleration process of the wheels is affected by road friction. Therefore, the rate at which the speed of the drive motor 30 decreases in the fully off state is lower than the rate at which the motor controller 40 decreases in the active short-circuit state.

[0128] Figure 7 This is a schematic diagram showing the change of torque and speed output by the drive motor 30 over time when an electric vehicle 10 is traveling on a low-friction road surface, according to an embodiment of this application.

[0129] In one embodiment, such as Figure 7 As shown, during the cyclic switching between the active short-circuit state and the fully shut-off state, the torque output by the drive motor 30 fluctuates between negative torque and zero torque. The drive motor 30 outputs negative torque when the motor controller 40 is operating in the active short-circuit state, and zero torque when the motor controller 40 is operating in the fully shut-off state; the negative torque is used to brake the wheels.

[0130] When the motor controller 40 operates in an active short-circuit state, the stator winding of the drive motor 30 forms a closed-loop circuit with the upper or lower bridge arm of the motor controller 40. The drive motor 30 operates as a generator, and the back electromotive force energy generated by the drive motor 30 is released through the stator winding. The drive motor 30 outputs a corresponding negative torque, which brakes the wheels of the electric vehicle 10. When the motor controller 40 operates in a fully off state, the drive motor 30 operates in an open-circuit state, does not generate additional torque, has zero output torque, and has no additional braking effect.

[0131] Figure 8 This is a schematic diagram showing the change of torque and speed output by the drive motor 30 over time during the driving of an electric vehicle 10 on a high-friction road surface, according to an embodiment of this application.

[0132] In one embodiment, such as Figure 8 As shown, during the operation of the electric vehicle 10 on a road surface with a coefficient of friction greater than a preset value, before the powertrain 50 fails, the motor controller 40 outputs three-phase current to the drive motor 30 to control the drive motor 30 to drive the wheels of the electric vehicle 10. After the powertrain 50 fails, the motor controller 40 continues to operate in an active short-circuit state to reduce the speed of the drive motor 30.

[0133] When the electric vehicle 10 is driving on a high-friction surface, the wheels have greater grip, making it less prone to slippage or lock-up, resulting in higher stability. If the powertrain 50 malfunctions, the motor controller 40 enters an active short-circuit state, and the drive motor 30 outputs negative torque to brake the electric vehicle 10. It does not need to switch to a fully shut-off state and always remains in the active short-circuit state, thereby reducing the speed of the drive motor 30 more quickly.

[0134] This application provides a control method for an electric vehicle 10. The control method is used to control the electric vehicle 10 to decelerate and stop after a powertrain 50 malfunctions while the electric vehicle 10 is traveling on a road surface with a coefficient of friction less than a preset value. The control method is applied to the aforementioned powertrain 50 and electric vehicle 10.

[0135] The control method includes: after a powertrain 50 fails, the motor controller 40 cycles between an active short-circuit state and a fully shut-off state during the process of reducing the speed of the drive motor 30.

[0136] In one embodiment, when the powertrain 50 malfunctions, the motor controller 40 is first controlled to operate in an active short-circuit state to reduce the speed of the drive motor. Once the speed of the drive motor 30 drops to a first speed value, the motor controller 40 is controlled to cycle between the active short-circuit state and the fully shut-off state.

[0137] In one embodiment, when the speed of the drive motor 30 decreases to a second speed value, the motor controller 40 is controlled to continue operating in an active short-circuit state so that the speed of the drive motor 30 continues to decrease.

[0138] In one embodiment, after a powertrain 50 malfunctions, when the difference between the speed of the drive motor 30 and the target speed is greater than a first difference and the speed of the drive motor 30 is less than the target speed, the motor controller 40 is controlled to operate in an active short-circuit state; when the difference between the speed of the drive motor 30 and the target speed is less than a second difference and the speed of the drive motor 30 is greater than the target speed, the motor controller 40 is controlled to operate in a fully shut-off state.

[0139] The above control method can be applied to the aforementioned powertrain 50, and the relevant descriptions in the aforementioned powertrain 50 can also be used as control methods and applied to the electric vehicle 10, which will not be repeated here.

[0140] According to the solution of this application, when the electric vehicle 10 malfunctions while driving on a low-friction surface, the motor controller 40 is intermittently activated to enter an active short-circuit state. The motor controller 40 cycles between the active short-circuit state and the fully shut-off state. While forcing the speed of the drive motor 30 to decrease rapidly through the active short-circuit state, the tires are prevented from locking up, thus preventing slippage on the low-friction surface and improving the stability and safety of the electric vehicle 10.

[0141] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A powertrain for an electric vehicle, characterized in that, The powertrain includes a motor controller and a drive motor. The motor controller includes a three-phase bridge arm, and the midpoints of the three bridge arms are respectively used to connect the three-phase windings of the drive motor. During the electric vehicle's operation on a road surface with a coefficient of friction less than a preset value... Prior to a powertrain failure, the motor controller is used to output three-phase current to the drive motor to control the drive motor to drive the wheels of the electric vehicle; After the powertrain fails, the motor controller cycles between an active short-circuit state and a fully shut-off state while controlling the drive motor to reduce its speed. The active short-circuit state refers to a state where the three upper arms of the three-phase bridge arm are conducting and the three lower arms are disconnected, or the three upper arms of the three-phase bridge arm are disconnected and the three lower arms are conducting. The fully shut-off state refers to a state where both the three upper arms and the three lower arms of the three-phase bridge arm are disconnected.

2. The powertrain according to claim 1, characterized in that, After the powertrain fails, before the speed of the drive motor drops to a first preset speed, the motor controller operates in an active short-circuit state to reduce the speed of the drive motor.

3. The powertrain according to claim 1 or 2, characterized in that, After the powertrain fails, and after the speed of the drive motor drops to less than or equal to a first preset speed, the motor controller cycles between the active short-circuit state and the full shutdown state to continue reducing the speed of the drive motor.

4. The powertrain according to any one of claims 1-3, characterized in that, After the powertrain fails, the motor controller cycles between the active short-circuit state and the fully shut-off state to reduce the speed of the drive motor to less than a second preset speed. Then, the motor controller continues to operate in the active short-circuit state to further reduce the speed of the drive motor.

5. The powertrain according to any one of claims 1-4, characterized in that, During the cyclic switching between the active short-circuit state and the fully shut-off state, the speed of the drive motor decreases when the motor controller operates in the active short-circuit state, and increases and then decreases when the motor controller operates in the fully shut-off state.

6. The powertrain according to any one of claims 1-5, characterized in that, During the cyclic switching between the active short-circuit state and the fully shut-off state, the speed of the drive motor decreases at a first rate during the operation of the motor controller in the active short-circuit state, and the speed of the drive motor first increases and then decreases at a second rate less than the first rate during the operation of the motor controller in the fully shut-off state.

7. The powertrain according to any one of claims 1-6, characterized in that, During the cyclic switching between the active short-circuit state and the fully shut-off state, the motor controller operates in the active short-circuit state or the fully shut-off state according to the difference between the speed of the drive motor and the target speed, and the target speed gradually decreases over time.

8. The powertrain according to any one of claims 1-7, characterized in that, After the powertrain fails, when the difference between the target speed and the speed of the drive motor is greater than a first difference and the speed of the drive motor is less than the target speed, the motor controller switches to the fully shut-off state.

9. The powertrain according to any one of claims 1-8, characterized in that, After the powertrain fails, when the difference between the speed of the drive motor and the target speed is less than a second difference and the speed of the drive motor is greater than the target speed, the motor controller switches to the active short-circuit state.

10. The powertrain according to any one of claims 1-9, characterized in that, During the cyclic switching between the active short-circuit state and the fully shut-off state, the torque output by the drive motor fluctuates between negative torque and zero torque. The drive motor outputs negative torque during the operation of the motor controller in the active short-circuit state, and the drive motor outputs zero torque during the operation of the motor controller in the fully shut-off state. The negative torque is used to brake the wheels.

11. The powertrain according to any one of claims 1-10, characterized in that, During the operation of the electric vehicle on a road surface with a coefficient of adhesion greater than the preset value, Prior to a powertrain failure, the motor controller is used to output three-phase current to the drive motor to control the drive motor to drive the wheels of the electric vehicle; After the powertrain fails, the motor controller continues to operate in the active short-circuit state to reduce the speed of the drive motor.

12. The powertrain according to any one of claims 7-9, characterized in that, The motor controller is used for: When the electric vehicle is traveling on a road surface with a coefficient of adhesion less than a preset value, if the powertrain malfunctions, the target rotational speed is adjusted according to the vehicle speed and the wheel speed of the electric vehicle. The target rotational speed changes with the coefficient of adhesion of the road surface.

13. A control method for electric vehicles, characterized in that, The control method is used to control the electric vehicle to decelerate and stop after a powertrain failure during the electric vehicle's operation on a road surface with an adhesion coefficient less than a preset value. The powertrain includes a motor controller and a drive motor. The motor controller includes a three-phase bridge arm, and the midpoints of the three bridge arms are respectively used to connect the three-phase windings of the drive motor. The control method includes: After the powertrain fails, the motor controller switches between an active short-circuit state and a fully shut-off state during the process of reducing the speed of the drive motor. The active short-circuit state refers to the state in which the three upper bridge arms of the three-phase bridge arm are conducting and the three lower bridge arms are disconnected, or the three upper bridge arms of the three-phase bridge arm are disconnected and the three lower bridge arms are conducting. The fully shut-off state refers to the state in which both the three upper bridge arms and the three lower bridge arms of the three-phase bridge arm are disconnected.

14. The control method according to claim 13, characterized in that, The control method specifically includes: After a powertrain failure, if the difference between the speed of the drive motor and the target speed is greater than a first difference and the speed of the drive motor is less than the target speed, the motor controller is controlled to operate in the active short-circuit state; if the difference between the speed of the drive motor and the target speed is less than a second difference and the speed of the drive motor is greater than the target speed, the motor controller is controlled to operate in the fully shut-off state.

15. An electric vehicle, characterized in that, The electric vehicle includes four wheels, a power battery, and a powertrain as described in any one of claims 1-12, the powertrain being configured to receive power from the power battery to drive the four wheels.

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