A method and system for preventing overspeed of a motor of a pure electric commercial vehicle during downhill

Abstract

The application discloses a kind of pure electric commercial vehicle downhill motor anti-over-speed method and system, belong to automobile technical field, method includes following steps: real-time monitoring motor speed, whether current speed exceeds motor speed protection threshold is judged;If current speed exceeds the motor speed protection threshold, the threshold interval to which current speed belongs is judged;If current speed is in first threshold interval, then according to first preset rule request to limit motor output positive torque;If current speed is in second threshold interval, then according to second preset rule request motor output negative torque;If current speed is in third threshold interval, then according to third preset rule request motor output negative torque, and by vehicle braking system to exert air pressure braking force.The application prevents motor overspeed from source, actively adjusts control, power output is smooth, is not forced to cut off power, has no abrupt feeling, driving experience is better, and application range is wider.

Description

Technical Field

[0001] This invention relates to the field of automotive technology, and in particular to a method and system for preventing overspeeding of the motor in a pure electric commercial vehicle going downhill. Background Technology

[0002] As the "heart" of new energy vehicles, the electric motor plays a crucial role in their operation. However, in certain scenarios, the motor poses a risk of speeding. For example, when going downhill after climbing a steep hill, the driver may press the accelerator to accelerate quickly, causing the motor speed to rise rapidly and exceed the speed limit. Similarly, when starting with a heavy accelerator on a low-friction surface in a low gear, the motor may also quickly exceed the speed limit. A large number of motor speeding hazards affect the user's operational efficiency and safety, as well as the reputation and claims of car manufacturers. Therefore, in the current environment, preventing motor speeding has become an issue that cannot be ignored.

[0003] Against this backdrop, developing a practical and feasible strategy to prevent motor overspeeding is crucial for addressing the aforementioned issues. Secondly, it is also necessary to consider maintaining the existing motor infrastructure hardware without alterations to avoid the economic costs associated with hardware changes.

[0004] Some existing motor overspeed prevention solutions include an invention patent titled "Method for Preventing Motor Overspeed in Motor Vehicle Transmission System," which determines the maximum motor speed after vehicle slippage by using the road friction coefficient and the current load of the internal combustion engine. At this maximum speed, the motor is effectively decoupled from the transmission system to prevent overspeed. However, this method has a lag, requires vehicle slippage to trigger, and its estimation accuracy heavily relies on sensors, making it prone to misjudging slippage. Another invention patent, titled "Control System and Method for Preventing Motor Overspeed in Neutral Mode of Pure Electric Vehicles," utilizes battery energy recovery to consume reverse drag energy or forcibly consumes excess kinetic energy, thereby limiting motor speed and preventing overspeed. However, this patent has a narrow scope, only applicable to pure electric vehicles without a gearbox and with the motor directly connected to the main reducer, and relies on battery performance. In extreme scenarios, it cannot guarantee normal control. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for preventing motor overspeed in pure electric commercial vehicles going downhill. This aims to solve the problem of power loss caused by motor overspeed in current new energy commercial vehicles under heavy loads on steep slopes, in low-friction road conditions, and in parking power take-off scenarios. A method for redistributing the requested torque under different speed conditions is established. The vehicle controller receives the speed signal sent by the motor controller to identify the motor speed. Based on the motor's maximum speed and a set speed threshold range, the motor's operating status is confirmed, thereby allocating the required torque to the motor. It also confirms whether air braking is involved in the adjustment and control. Finally, the required torque is adjusted based on the speed. This method prevents motor overspeed from the source by actively adjusting and controlling the motor, resulting in smooth power output without forced power cut-off, abruptness, a better driving experience, and wider applicability.

[0006] In a first aspect, the present invention describes a method for preventing overspeeding of the motor of a pure electric commercial vehicle going downhill, comprising: Real-time monitoring of motor speed to determine whether the current speed exceeds the motor speed protection threshold N_pts; If the current speed exceeds the motor speed protection threshold, then determine the threshold range to which the current speed belongs: If the current speed is within the first threshold range, then the motor output positive torque is limited according to the first preset rule; If the current speed is within the second threshold range, then the motor is requested to output negative torque according to the second preset rule; If the current speed is within the third threshold range, the motor is requested to output negative torque according to the third preset rule, and the vehicle braking system applies air pressure power; wherein, when the speed does not exceed the maximum air pressure power speed threshold, the air pressure power increases linearly with the speed increase, and when the speed exceeds the maximum air pressure power speed threshold, the air pressure power remains at the maximum air pressure power. The upper limit of the first threshold interval is less than the lower limit of the second threshold interval, and the upper limit of the second threshold interval is less than the lower limit of the third threshold interval.

[0007] Preferably, the step of requesting to limit the positive torque output of the motor according to the first preset rule includes: obtaining and outputting the positive torque corresponding to the current speed on the first calibration curve or the second calibration curve; The step of requesting the motor to output negative torque according to the second preset rule includes: obtaining and outputting the negative torque corresponding to the current speed on the second calibration curve; The step of requesting the motor to output negative torque according to the third preset rule includes: obtaining and outputting the negative torque corresponding to the current speed on the motor's external characteristic curve.

[0008] Preferably, when the current rotational speed is within the first threshold range and does not exceed N_oat, the corresponding positive torque is obtained through the first calibration curve and the positive torque is output. When the current speed is within the first threshold range and exceeds N_oat, the corresponding positive torque is obtained through the second calibration curve and the positive torque is output. Wherein, N_oat is the motor peak speed N_max multiplied by the first preset ratio plus the motor forced upshift point speed N_pts.

[0009] Preferably, when the current speed exceeds N_oat, the vehicle controller sends a command to prohibit gear shifting.

[0010] Preferably, the calibration steps of the first calibration curve specifically include: The motor speed at the forced upshift point is used as the motor speed protection threshold N_pts, and the first calibration torque corresponding to N_pts is obtained. The point with the X-axis coordinate as N_pts and the Y-axis coordinate as the first calibration torque is set as point A; wherein, the first calibration torque is the positive torque corresponding to N_pts on the motor external characteristic curve. The peak motor speed N_max is multiplied by a first preset ratio and then the motor speed at the forced upshift point N_pts is used as N_oat. The second calibration torque corresponding to N_oat is obtained, and the point with N_oat on the X-axis and the second calibration torque on the Y-axis is set as point B. The second calibration torque is the positive torque corresponding to N_oat on the motor's external characteristic curve multiplied by a preset smoothing ratio. Substitute the X-axis and Y-axis coordinates of points A and B into y=k1 / x+b1 to calculate k1 and b1. Use y=k1 / x+b1 as the correspondence between the current speed and the corresponding positive torque output when the current speed is in the range of [N_pts, N_oat].

[0011] Preferably, the calibration steps for the second calibration curve specifically include: The peak motor speed N_max is multiplied by the second preset ratio and the motor forced upshift point speed N_pts is used as N_mcs. The third calibration torque corresponding to N_mcs is obtained. The point with the X-axis coordinate as N_mcs and the Y-axis coordinate as the third calibration torque is set as point C. The third calibration torque is the negative torque corresponding to N_mcs on the motor external characteristic curve. Substitute the X-axis and Y-axis coordinates of points B and C into y=k2x+b2 to calculate the undetermined coefficients k2 and b2. Use y=k2x+b2 as the correspondence between the current speed and the corresponding positive or negative output torque when the current speed is (N_oat, N_mcs). The rotational speed corresponding to the current torque = 0 is obtained by using y = k2x + b2 as N_ors, and [N_pts, N_ors] is used as the first threshold interval, and (N_ors, N_mcs) is used as the second threshold interval.

[0012] Preferably, during the application of pneumatic compression power by the vehicle braking system, the pneumatic compression power corresponding to the current speed is obtained through the pneumatic braking calibration curve.

[0013] Preferably, the calibration steps for the air brake calibration curve specifically include: The maximum air compression power speed threshold N_mbs is obtained by multiplying the motor peak speed N_max by the third preset ratio and adding the motor forced upshift point speed N_pts. The third threshold range of speed is [N_mcs, N_max]. The correspondence between the current speed and the required air compression power is defined as z=k3×x, where the current speed is within [N_mcs, N_mbs]. Here, k3 = the maximum air compression power that the vehicle braking system can apply / (N_mbs-N_mcs).

[0014] Preferably, if the current speed is within the second threshold range, the brake light is illuminated.

[0015] Secondly, the present invention discloses a downhill motor overspeed prevention system for pure electric commercial vehicles, comprising: The monitoring module is used to monitor the motor speed in real time and determine whether the current speed exceeds the motor speed protection threshold N_pts; The judgment module is used to determine the threshold range to which the current speed belongs if the current speed exceeds the motor speed protection threshold. If the current speed is within the first threshold range, then the motor output positive torque is limited according to the first preset rule; If the current speed is within the second threshold range, then the motor is requested to output negative torque according to the second preset rule; If the current speed is within the third threshold range, the motor is requested to output negative torque according to the third preset rule, and the vehicle braking system applies air pressure power; wherein, when the speed does not exceed the maximum air pressure power speed threshold, the air pressure power increases linearly with the speed increase, and when the speed exceeds the maximum air pressure power speed threshold, the air pressure power remains at the maximum air pressure power. The upper limit of the first threshold interval is less than the lower limit of the second threshold interval, and the upper limit of the second threshold interval is less than the lower limit of the third threshold interval.

[0016] Compared with the prior art, the present invention has the following advantages: This invention, through real-time monitoring and pre-control of the current rotational speed, intervenes in advance before the motor reaches the critical speed, fundamentally eliminating overspeeding without lag. Simultaneously, it employs multi-gradient motor speed regulation control, using a combination of power limitation, active anti-drag, and braking superposition to adjust in stages and prevent motor overspeeding. This method achieves smooth changes and gentle transitions in torque output through the setting of the first and second calibration curves and the inflection point N_oat, ensuring a smooth transition without jerking during vehicle operation and significantly improving ride comfort while maintaining safety. Finally, it deeply integrates the motor braking and air braking joint control mechanism to achieve a multi-layered, mutually redundant protection system, effectively improving the vehicle's safety redundancy and adaptability to different operating conditions. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a flowchart of one embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of a first calibration curve, a second calibration curve, and a schematic diagram of an air brake calibration curve, according to an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0022] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0023] It should be noted that any symbols and / or numbers present in the specification that are not marked in the accompanying drawings are not reference numerals.

[0024] Example 1 refer to Figure 1 , 2 As shown, this invention provides a method for preventing overspeeding of the motor of a pure electric commercial vehicle going downhill, comprising: 1. During vehicle operation, the current speed of the motor is monitored and determined in real time, and the vehicle controller identifies and reads the signals sent by the motor on the CAN line.

[0025] The current motor speed is pre-classified into intervals. The current motor speed is calibrated and set with thresholds by the vehicle controller. Three high speed intervals are set: the first threshold interval [N_pts, N_ors], the second threshold interval (N_ors, N_mcs), and the third threshold interval [N_mcs, N_max]. 2. Motor drive boundary limitations When the vehicle is under high voltage and driving normally, and the transmission is not shifting gears and the braking system is not requesting torque control, if the current speed of the motor exceeds the current speed protection threshold N_pts, it is determined whether the current speed range of the motor is within [N_pts, N_ors]. If it is within this range, the output torque of the motor is limited. Specific torque control curve shown Figure 2 The torque control curve uses the pre-calibrated first calibration curve and second calibration curve. The torque change corresponding to [N_pts, N_ors] follows the principle of slow first and then fast. In N_ors, the drive torque needs to be limited to 0. In this range, the torque calibration changes linearly with the speed. The vehicle controller issues commands to limit the positive drive torque output of the motor step by step. Two requirements must be met simultaneously: the positive drive torque output by the motor must not exceed the original external characteristics of the motor drive; after the boundary change inflection point N_oat, the vehicle controller sends a command to prohibit gear shifting. After applying control to the motor torque, the primary speed limiting protection is completed when the current motor speed is not in the range of [N_pts, N_ors]. 3. Active negative torque speed limiting If the motor fails to control its speed as expected after passing the primary speed limiting protection, and the current motor speed enters the second threshold range (N_ors, N_mcs), it actively requests the motor to output negative torque, as shown in the control curve. Figure 2 The second calibration curve corresponds to the interval (N_ors, N_mcs); and note that the brake light illuminates when the motor requests a negative torque.

[0026] 4. Active control of air brakes If the motor speed is not controlled as scheduled and the current speed of the motor enters the critical danger range of excessive speed, that is, the third threshold range [N_mcs, N_max], then control shall be carried out according to the following steps; When the motor's current speed reaches the set threshold range [N_mcs, N_max], it needs to actively request the motor to output negative torque, as shown in the control curve. Figure 2 At this time, the motor's active negative torque is requested according to the motor's external characteristic curve; When the current motor speed is greater than N_mcs, the vehicle braking system needs to be requested to apply air pressure. The air pressure braking force gradually increases with the increase of speed. The specific air pressure braking force is determined according to the air brake calibration curve. When the current speed reaches N_mbs, the air pressure braking force is requested to reach the maximum capacity of the braking system.

[0027] Figure 2 The diagram shows the first calibration curve, the second calibration curve, and the air brake calibration curve of the present invention; wherein, the horizontal axis represents the motor speed, and the vertical axis represents the torque / braking force. The calibration process is as follows: 1. First calibration curve The motor speed at the forced upshift point is used as the motor speed protection threshold N_pts, and the first rated torque corresponding to N_pts is obtained. The point with the X-axis coordinate as N_pts and the Y-axis coordinate as the first rated torque is set as point A; where the first rated torque is the positive torque corresponding to N_pts on the motor's external characteristic curve. The peak motor speed N_max is multiplied by a first preset ratio and then added to the motor's forced upshift point speed N_pts to obtain N_oat. The second calibration torque corresponding to N_oat is then obtained. The point where the X-axis coordinate is N_oat and the Y-axis coordinate is the second calibration torque is set as point B. The second calibration torque is the positive torque corresponding to N_oat on the motor's external characteristic curve multiplied by a preset smoothing ratio. In this embodiment, the first preset ratio is 2.5%-3.5%, preferably 3%. The smoothing ratio is 85-90%, preferably 90%.

[0028] Substitute the X-axis and Y-axis coordinates of points A and B into y=k1 / x+b1 to calculate k1 and b1. Use y=k1 / x+b1 as the correspondence between the current speed and the corresponding positive torque output when the current speed is in the range of [N_pts, N_oat].

[0029] 2. Second calibration curve The calibration steps for the second calibration curve specifically include: The peak motor speed N_max is multiplied by a first preset ratio and then added to the motor's forced upshift point speed N_pts to obtain N_oat. The second calibrated torque corresponding to N_oat is then obtained. The point where the X-axis coordinate is N_oat and the Y-axis coordinate is the second calibrated torque is set as point B. The second calibrated torque is the positive torque corresponding to N_oat on the motor's external characteristic curve multiplied by a preset smoothing ratio. In this embodiment, the first preset ratio is 2.5%-3.5%, preferably 3%. The smoothing ratio is 85-92%, preferably 90%. Setting the smoothing ratio achieves gradient control, preventing a noticeable speed limit as soon as the initial speed increases, avoiding frequent entry and exit from speed limits which would result in a poor driving experience, and providing a smoother ride.

[0030] The peak motor speed N_max is multiplied by a second preset ratio and then added to the motor's forced upshift point speed N_pts to obtain N_mcs. The third calibration torque corresponding to N_mcs is then obtained. The point where the X-axis coordinate is N_mcs and the Y-axis coordinate is the third calibration torque is set as point C. The third calibration torque is the negative torque corresponding to N_mcs on the motor's external characteristic curve. In this embodiment, the second preset ratio is 11%-13%, preferably 12%.

[0031] Substitute the X-axis and Y-axis coordinates of points B and C into y=k2x+b2 to calculate the undetermined coefficients k2 and b2. Use y=k2x+b2 as the correspondence between the current speed and the corresponding positive or negative output torque when the current speed is (N_oat, N_mcs).

[0032] 3. Air Brake Calibration Curve The peak motor speed N_max is multiplied by a third preset ratio, and then the motor's forced upshift point speed N_pts is added to obtain N_mbs. The formula k3 is calculated as: k3 = maximum air compression force that the vehicle braking system can apply / (N_mbs - N_mcs). The relationship between the current speed and the required air compression force when the current speed is within the range [N_mcs, N_mbs] is defined as z = k3 × x. In this embodiment, the third preset ratio is 19%-21%, preferably 20%.

[0033] Example 2 Taking the example of a driver speeding on a long downhill section of road, this article introduces how to prevent vehicle motors from speeding, following the example of... Figure 1 The flowchart shown is illustrated in the following specific implementation method: 1) At the beginning of a long downhill slope, the motor speed first exceeds the motor speed protection threshold N_pts. The vehicle controller recognizes that the speed is too high and directly limits the positive drive torque output of the motor according to the first and second calibration curves, cutting off the excess power supply, so that the motor speed increases slowly, suppressing the acceleration trend of the vehicle, suppressing the continuous increase of speed, and ensuring smooth driving without the application of braking force; 2) As the gradient continues, the vehicle speed and motor speed further increase, reaching the second threshold range (N_ors, N_mcs). At this point, limiting the positive torque can no longer control the speed. The vehicle controller cancels the positive drive torque, sends a request for negative torque, and outputs negative braking torque, following the second calibration curve. At this time, the electromagnetic drag effect of the motor is used to generate electric braking force, preventing the motor from further overspeeding. 3) If the slope is too steep, the motor speed will continue to spike into the third threshold range [N_mcs, N_max], entering the highest protection level. At this time, the negative torque requested by the overall control system is requested according to the motor's external characteristic curve. Simultaneously, the vehicle's braking system actively increases the braking air pressure, using a combination of electric and air braking to reduce the motor speed. Under the combined constraints of electromechanical coupling, the vehicle speed and motor speed gradually decrease when going downhill. 4) When the motor speed gradually decreases under the combined braking of electric braking and air braking, and the gradient gradually decreases, the motor speed decreases to the second threshold range (N_ors, N_mcs). At this time, the air braking of the whole vehicle is cancelled, and the vehicle controller still requests negative torque. The requested negative torque is requested according to the second calibration curve. At this time, only electric braking is used, so that the motor speed continues to decrease steadily. 5) When the motor speed decreases further and the motor speed is in the first threshold range [N_pts, N_ors], the vehicle controller cancels the negative torque request and sends positive torque to the vehicle. The requested torque is requested according to the torque calibration curve to continue to suppress the motor speed. 6) When the motor speed drops below N_pts and the speed leaves the first threshold range [N_pts, N_ors], the motor speed suppression is canceled. At this time, the requested torque follows the motor external characteristic curve, and the vehicle drives normally.

[0034] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0035] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preventing overspeeding of the motor of a pure electric commercial vehicle going downhill, characterized in that, Includes the following steps: Real-time monitoring of motor speed to determine whether the current speed exceeds the motor speed protection threshold N_pts; If the current speed exceeds the motor speed protection threshold, then determine the threshold range to which the current speed belongs: If the current speed is within the first threshold range, then the motor output positive torque is limited according to the first preset rule; If the current speed is within the second threshold range, then the motor is requested to output negative torque according to the second preset rule; If the current speed is within the third threshold range, the motor is requested to output negative torque according to the third preset rule, and the vehicle braking system applies air pressure power; wherein, when the speed does not exceed the maximum air pressure power speed threshold, the air pressure power increases linearly with the speed increase, and when the speed exceeds the maximum air pressure power speed threshold, the air pressure power remains at the maximum air pressure power. The upper limit of the first threshold interval is less than the lower limit of the second threshold interval, and the upper limit of the second threshold interval is less than the lower limit of the third threshold interval.

2. The method for preventing overspeeding of the downhill motor of a pure electric commercial vehicle according to claim 1, characterized in that, The step of requesting to limit the positive torque output of the motor according to the first preset rule includes: obtaining and outputting the positive torque corresponding to the current speed on the first calibration curve or the second calibration curve; The step of requesting the motor to output negative torque according to the second preset rule includes: obtaining and outputting the negative torque corresponding to the current speed on the second calibration curve; The step of requesting the motor to output negative torque according to the third preset rule includes: obtaining and outputting the negative torque corresponding to the current speed on the motor's external characteristic curve.

3. The method for preventing overspeeding of the downhill motor of a pure electric commercial vehicle according to claim 2, characterized in that, When the current speed is within the first threshold range and does not exceed N_oat, the corresponding positive torque is obtained through the first calibration curve and the positive torque is output. When the current speed is within the first threshold range and exceeds N_oat, the corresponding positive torque is obtained through the second calibration curve and the positive torque is output. Wherein, N_oat is the motor peak speed N_max multiplied by the first preset ratio plus the motor forced upshift point speed N_pts.

4. The method for preventing overspeeding of the downhill motor of a pure electric commercial vehicle according to claim 3, characterized in that, When the current speed exceeds N_oat, the vehicle controller sends a command to prohibit gear shifting.

5. The method for preventing overspeeding of the downhill motor of a pure electric commercial vehicle according to claim 3, characterized in that, The calibration steps for the first calibration curve specifically include: The motor speed at the forced upshift point is used as the motor speed protection threshold N_pts, and the first calibration torque corresponding to N_pts is obtained. The point with the X-axis coordinate as N_pts and the Y-axis coordinate as the first calibration torque is set as point A; wherein, the first calibration torque is the positive torque corresponding to N_pts on the motor external characteristic curve; The peak motor speed N_max is multiplied by a first preset ratio and then the motor speed at the forced upshift point N_pts is used as N_oat. The second calibration torque corresponding to N_oat is obtained, and the point with N_oat on the X-axis and the second calibration torque on the Y-axis is set as point B. The second calibration torque is the positive torque corresponding to N_oat on the motor's external characteristic curve multiplied by a preset smoothing ratio. Substitute the X-axis and Y-axis coordinates of points A and B into y=k1 / x+b1 to calculate k1 and b1. Use y=k1 / x+b1 as the correspondence between the current speed and the corresponding positive torque output when the current speed is in the range of [N_pts, N_oat].

6. The method for preventing overspeeding of the downhill motor of a pure electric commercial vehicle according to claim 5, characterized in that, The calibration steps for the second calibration curve specifically include: The peak motor speed N_max is multiplied by the second preset ratio and the motor forced upshift point speed N_pts is used as N_mcs. The third calibration torque corresponding to N_mcs is obtained. The point with the X-axis coordinate as N_mcs and the Y-axis coordinate as the third calibration torque is set as point C. The third calibration torque is the negative torque corresponding to N_mcs on the motor external characteristic curve. Substitute the X-axis and Y-axis coordinates of points B and C into y=k2x+b2 to calculate the undetermined coefficients k2 and b2. Use y=k2x+b2 as the correspondence between the current speed and the corresponding positive or negative output torque when the current speed is (N_oat, N_mcs). The rotational speed corresponding to the current torque = 0 is obtained by using y = k2x + b2 as N_ors, and [N_pts, N_ors] is used as the first threshold interval, and (N_ors, N_mcs) is used as the second threshold interval.

7. The method for preventing overspeeding of the downhill motor of a pure electric commercial vehicle according to claim 1, characterized in that, During the application of air compression power by the vehicle braking system, the air compression power corresponding to the current speed is obtained through the air brake calibration curve.

8. The method for preventing overspeeding of the downhill motor of a pure electric commercial vehicle according to claim 7, characterized in that, The calibration steps for the air brake calibration curve specifically include: The maximum air compression power speed threshold N_mbs is obtained by multiplying the motor peak speed N_max by the third preset ratio and adding the motor forced upshift point speed N_pts. The third threshold range of speed is [N_mcs, N_max]. The correspondence between the current speed and the required air compression power is defined as z=k3×x, where the current speed is within [N_mcs, N_mbs]. Here, k3 = the maximum air compression power that the vehicle braking system can apply / (N_mbs-N_mcs).

9. The method for preventing overspeeding of the downhill motor of a pure electric commercial vehicle according to claim 1, characterized in that, If the current speed is within the second threshold range, the brake lights will illuminate.

10. A downhill motor overspeed prevention system for pure electric commercial vehicles, characterized in that, include: The monitoring module is used to monitor the motor speed in real time and determine whether the current speed exceeds the motor speed protection threshold N_pts; The judgment module is used to determine the threshold range to which the current speed belongs if the current speed exceeds the motor speed protection threshold. If the current speed is within the first threshold range, then the motor output positive torque is limited according to the first preset rule; If the current speed is within the second threshold range, then the motor is requested to output negative torque according to the second preset rule; If the current speed is within the third threshold range, the motor is requested to output negative torque according to the third preset rule, and the vehicle braking system applies air pressure power; wherein, when the speed does not exceed the maximum air pressure power speed threshold, the air pressure power increases linearly with the speed increase, and when the speed exceeds the maximum air pressure power speed threshold, the air pressure power remains at the maximum air pressure power. The upper limit of the first threshold interval is less than the lower limit of the second threshold interval, and the upper limit of the second threshold interval is less than the lower limit of the third threshold interval.

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