A method of designing an electric drive system

Abstract

The application relates to a kind of electric drive system design methods, according to the driving condition data of whole vehicle to determine electric drive system parameter, and then the parameter value of the drive motor matched therewith can be determined, namely: according to the common driving condition of vehicle, the change relation of the demand torque, demand power of whole vehicle with time is calculated, and then the change relation of torque, power with speed is deduced, through statistical analysis method, torque-speed percentage distribution statistical data is obtained, the distribution frequency of drive motor operating point can be statistically analyzed, and the data point commonly used by drive motor is designed as the continuous operating point and high efficiency point of drive motor. By using the design method provided by the application, the economy of the whole vehicle is significantly improved under the premise of meeting the power demand of the whole vehicle, which helps to increase the driving range.

Description

Technical Field

[0001] This invention relates to the drive system of electric vehicles, and more specifically to a design method for an electric drive system. Background Technology

[0002] Currently, the design of electric drive systems for pure electric vehicles primarily considers overall vehicle dynamics. Based on vehicle dynamics evaluation indicators, such as maximum speed, maximum gradeability, and acceleration time, the rated and peak speeds, torques, and power requirements of the drive motor, as well as the number of gears and speed ratios of the transmission, are calculated using the vehicle driving force-driving resistance equation and the vehicle power balance equation. The rated power of the drive motor is mainly determined by the requirement for maximum speed; the peak power is determined by the maximum gradeability, the stable speed at which the maximum gradeability is climbed, and the acceleration time from 0 to 100 km / h; the rated torque is determined by the maximum gradeability and the stable speed at which the maximum gradeability is climbed; the peak torque is determined by the acceleration time from 0 to 100 km / h; and the peak speed is determined by the maximum speed.

[0003] After determining the above basic parameters, a performance redundancy coefficient is determined based on experience, typically between 1.1 and 1.2, to determine the parameters of the selected drive motor. Then, a drive motor with similar or identical performance is selected based on the product range provided by the motor supplier. To ensure the vehicle's overall power, motors with higher power and torque are generally selected, resulting in greater performance redundancy. Finally, a vehicle simulation model is built using the drive motor MAP (Motor Performance Map) to analyze the vehicle's economy. The simulation conditions are generally selected from the cyclic operating conditions in the "China Automotive Driving Conditions" (GB / T 38146 standard) to verify whether the selected drive motor and transmission meet the requirements for vehicle power and economy.

[0004] Existing design methods require first calculating drive motor parameters based on performance evaluation indicators, then selecting the drive motor, and finally verifying the vehicle's performance and economy using a vehicle simulation model. If the performance does not meet the vehicle's requirements, the process needs to be repeated. Therefore, existing design methods have long development cycles and involve a lot of repetitive work. These methods are essentially "passive" matching methods, considering fewer factors. Even if the drive motor's performance parameters theoretically meet the vehicle's performance evaluation indicators, it cannot guarantee that the system efficiency MAP matches the vehicle's requirements, and it can also affect the vehicle's economy. Summary of the Invention

[0005] This invention discloses an electric drive system design method that fully considers the different application scenarios and operating conditions of vehicles, resulting in varying torque and speed requirements for the drive motor. Compared to the "passive" matching design of existing technologies, this invention belongs to the "active" matching design. That is, based on the overall vehicle driving condition requirements, it uses mathematical statistical analysis to determine the distribution frequency of motor speed and torque under common operating conditions, and selects the region with the higher distribution frequency as the rated parameters of the drive motor. The drive motor matched by this method can balance the vehicle's power and economy.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] An electric drive system design method, comprising:

[0008] Acquire vehicle driving condition data, and calculate the required torque and required power at each moment based on the vehicle driving condition data, so as to obtain the data on the change of required torque and required power over time.

[0009] Based on the data on the change of demand torque over time, the data on the change of demand torque over speed can be calculated; based on the data on the change of demand power over time, the data on the change of demand power over speed can be calculated.

[0010] The system calculates the required torque value at each operating point at any given time, determines the maximum required torque, and defines the maximum required torque value as the maximum torque of the electric drive system. It also calculates the frequency distribution data of the required torque, sets the concentrated area of ​​this distribution data as the vehicle's commonly used operating point, and defines the required torque at this commonly used operating point as the rated torque of the electric drive system. Finally, the system calculates the required power value at each operating point at any given time, determines the maximum required power value, and defines the maximum required power value as the maximum power of the electric drive system. The system also calculates the frequency distribution data of the required power, sets the concentrated area of ​​this distribution data as the vehicle's commonly used operating point, and defines the required power at this commonly used operating point as the rated power of the electric drive system.

[0011] Statistical analysis of demand torque-speed frequency distribution data is conducted, and the region in the demand torque-speed frequency distribution data is identified as the system's efficient range. The speed and torque range of the system's efficient range are determined, and the speed and torque within this range are used as the demand speed and torque for vehicle design. Optimization is carried out in conjunction with vehicle dynamics evaluation indicators, economic evaluation indicators, and constraints to determine the number of gears and speed ratio of the transmission device.

[0012] Based on the determined maximum and rated torque requirements, the determined system efficiency range, and the determined speed ratio, the peak torque, rated torque, peak speed, and rated speed of the motor are determined. Then, combined with the determined rated power and peak power of the motor, the parameters of the electric drive system are determined.

[0013] Furthermore, the vehicle driving condition data refers to the relationship between vehicle speed and time.

[0014] Furthermore, the data on the relationship between vehicle speed and time can be obtained from the following standards: GB / T38146.1-2019 China Automotive Driving Cycle Part 1: Light Vehicles, GB / T 38146.2-2019 China Automotive Driving Cycle Part 2: Heavy Commercial Vehicles, the New European Driving Cycle, and the Globally Harmonized Light Vehicle Test Cycle.

[0015] Furthermore, the vehicle speed data in the overall vehicle driving condition data is converted to units. The original speed data is in km / h, which is converted to m / s using the following formula:

[0016]

[0017] In the above formula, u a The original vehicle speed data is shown, and u represents the vehicle speed data after conversion to units.

[0018] Furthermore, the required torque at each moment is calculated using the following formula:

[0019]

[0020] In the above formula, T0 represents the required torque at each operating point; T tq The torque of the drive motor is expressed in Nm; i g i0 represents the speed ratio of each gear in the transmission; i0 is the speed ratio of the main reducer; r is the rolling radius of the wheel, in meters; η T G is the transmission efficiency; m is the vehicle's weight in N; f is the vehicle's mass in kg; i is the rolling resistance coefficient; and C is the gradient. D A is the air resistance coefficient; A is the frontal area, in m². 2 δ is the rotational mass conversion factor; The acceleration of the vehicle, measured in m / s². 2 , Where u1 is the vehicle speed value at the previous moment and u2 is the vehicle speed value at the next moment; the operating point where the vehicle speed value is 0 and the acceleration is also 0 is defined as the stationary operating point of the vehicle, and the required torque value of the stationary operating point is set to 0.

[0021] Power demand P at each moment e Calculate using the following formula:

[0022]

[0023] Furthermore, when calculating the data on the variation of required torque with speed and the data on the variation of required power with speed, the data on the variation of required torque with time and the data on the variation of required power with time are combined respectively, and based on the relationship between time t and vehicle speed u in the vehicle driving condition data. a The corresponding relationship is given by the following formula: (vehicle speed u) a Converting to rotational speed n, we can then plot scatter plots of torque demand versus rotational speed and power demand versus rotational speed.

[0024]

[0025] Furthermore, when collecting the demand torque frequency distribution data, the demand torque value from 0 to the maximum value is evenly distributed in parts. The number of operating points within each torque distribution range is counted. The frequency of the operating points within the torque distribution range is obtained by dividing the number of operating points by the total number of operating points. Then, a demand torque frequency distribution map is drawn, and the area covering 90% of the distribution map is selected as the commonly used operating points of the vehicle.

[0026] When collecting statistical data on the frequency distribution of demand power, the demand power values ​​from 0 to the maximum value are distributed evenly in portions. The number of operating points within each power distribution range is counted. The frequency of the operating points within the power distribution range is obtained by dividing the number of operating points by the total number of operating points. Then, a demand power frequency distribution map is drawn, and the area covering 90% of the distribution map is selected as the commonly used operating points of the vehicle.

[0027] Furthermore, when statistically analyzing the demand torque-speed frequency distribution data, the demand torque value from 0 to the maximum value is evenly distributed in segments, and the speed n from 0 to the maximum speed is evenly distributed in segments. Using the demand torque interval as the vertical axis and the speed interval as the horizontal axis, each demand torque interval and speed interval segment constitutes a torque-speed distribution interval segment. The number of operating points within each torque-speed distribution interval segment is counted, and the frequency of each operating point within each interval is obtained by dividing the number of operating points by the total number of operating points. Then, a demand torque-speed frequency distribution statistical chart is plotted. The frequency distribution of operating points within each torque-speed distribution interval segment is represented in the distribution statistical chart according to frequency, using different symbols. The distribution of each symbol in the distribution statistical chart is observed, and the concentrated distribution area of ​​one type of symbol is selected as the system's high-efficiency zone.

[0028] Furthermore, the speed and torque range within the system's high-efficiency zone corresponds to the required speed and torque range for normal vehicle operation, thus allowing the determination of the speed and torque at the main reducer's output. According to the formula T0 = T... tq i g i0 and n0=n tq / i gi0 determines the required speed and torque of the vehicle, where n0 is the speed at the output of the main reducer, in r / min; n tq This refers to the speed of the drive motor, expressed in r / min.

[0029] The vehicle's performance is evaluated using maximum speed, maximum gradeability, and 0-100 km / h acceleration time as indicators of dynamic performance, and average energy consumption per 100 km as an indicator of economic performance. Constraints include a limited number of commonly used final drive ratios, maximum gear ratios, minimum gear ratios, and a limited number of gears for selected vehicle models. The transmission ratio i is used as the constraint. g With the speed ratio i0 of the main reducer as the optimization target, the speed ratio i of the transmission device is optimized. g Optimize the speed ratio i0 of the main reducer to obtain the number of gears and speed ratio i of the transmission device. g The speed ratio i0 with the main reducer.

[0030] This invention considers that different vehicle application scenarios and operating conditions result in varying torque and speed requirements for the drive motor. Existing design methods neglect these actual usage conditions, leading to significant redundancy in power parameter design and poor fuel economy. This invention determines the electric drive system parameters based on the vehicle's driving condition data, thereby determining the matching drive motor parameter values. Specifically, it first calculates the changes in the vehicle's required torque and power over time based on common driving conditions, then derives the changes in torque and power with speed. Through statistical analysis, it obtains torque-speed percentage distribution statistics, statistically analyzes the distribution frequency of the drive motor's operating points, and designs the commonly used data points of the drive motor as its continuous operating points and high-efficiency points. Using the design method provided by this invention, the overall vehicle's fuel economy is significantly improved while meeting the vehicle's power requirements, contributing to increased driving range. Attached Figure Description

[0031] Figure 1 This is a flowchart of the design method in an embodiment of the present invention;

[0032] Figure 2 This is a graph showing the change in required torque over time for a specific embodiment.

[0033] Figure 3 This is a scatter plot showing the required torque as a function of rotational speed in a specific embodiment.

[0034] Figure 4 This is a diagram showing the required torque frequency distribution for a specific embodiment;

[0035] Figure 5 This is a statistical diagram of the required torque-speed frequency distribution for a specific embodiment;

[0036] Figure 6This is a graph showing the power demand versus time for a specific embodiment.

[0037] Figure 7 This is a scatter plot showing the power requirement as a function of rotational speed in a specific embodiment.

[0038] Figure 8 This is a diagram showing the required power frequency distribution for a specific embodiment. Detailed Implementation

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0040] This embodiment discloses an electric drive system design method, mainly targeting the design of electric drive systems for pure electric vehicles. The aim is to select a drive motor and transmission device that match the electric drive system for the vehicle model to be developed. The electric drive system design method provided in this embodiment is as follows: Figure 1 As shown, it includes the following:

[0041] (1) Obtain vehicle driving condition data;

[0042] The acquired vehicle driving condition data is the vehicle speed u. a By analyzing the relationship between vehicle speed (in km / h) and time (in seconds), a curve showing the change in vehicle speed over time can be obtained. This data can be obtained from the following standards: GB / T 38146.1-2019 China Automotive Driving Cycle Part 1: Light Vehicles (CLTC), GB / T 38146.2-2019 China Automotive Driving Cycle Part 2: Heavy Commercial Vehicles (CHTC), the New European Driving Cycle (NEDC), and the Worldwide Harmonized Light Vehicles Test Cycle (WLTC).

[0043] When designing and developing vehicle models, the aforementioned standards, consistent with the model being developed, are selected, and the electric drive system parameters are designed based on the vehicle operating condition data provided in these standards. This embodiment uses the development of a 49-ton semi-trailer tractor and its matching power system as an example to illustrate the entire design process, selecting CHTC-HT operating condition data as the design basis.

[0044] (2) Vehicle speed unit conversion: Since the original vehicle speed data obtained in step (1) above is in km / h, in order to facilitate the following parameter calculations, the original vehicle speed data is converted to m / s. The unit conversion is performed according to the following formula:

[0045]

[0046] In the above formula, u a The original vehicle speed data is shown, and u represents the vehicle speed data after conversion to units.

[0047] (3) Calculation of required torque and required power at each moment:

[0048] (3-1) Based on the vehicle's driving condition data and the vehicle's driving force-driving resistance balance equation, the required torque T0 at each moment in the driving condition is calculated. The required torque T0 at each moment is calculated using the following formula:

[0049]

[0050] In the above formula, T tq The torque of the drive motor is expressed in Nm; i g i0 represents the speed ratio of each gear in the transmission system, which is either a reducer or a gearbox; r is the rolling radius of the wheel, in meters; η represents the speed ratio of each gear in the transmission system. T G is the transmission efficiency; m is the vehicle's weight in N; f is the vehicle's mass in kg; i is the rolling resistance coefficient; and C is the gradient. D A is the air resistance coefficient; A is the frontal area, in m². 2 δ is the rotational mass conversion factor; For the vehicle's acceleration, use the vehicle speed u converted from units in step (2), according to the formula... Perform the calculation; the result is in m / s. 2 Where u1 is the vehicle speed value at the previous moment and u2 is the vehicle speed value at the next moment. The operating point where the vehicle speed value is 0 and the acceleration is also 0 is defined as the stationary operating point of the vehicle, and the required torque value at the stationary operating point is set to 0.

[0051] (3-2) Based on the vehicle's driving condition data and the vehicle power balance equation, determine the required power P at each moment in the driving condition. e Calculate the required power P at each moment. e Calculate using the following formula:

[0052]

[0053] (4) Plot the curves of demand torque and demand power over time;

[0054] Based on the correspondence between the required torque T0 and time t at each moment in (3-1), a curve showing the change of required torque with time is plotted. The specific example given in this embodiment shows the curve of required torque changing with time as follows: Figure 2 As shown.

[0055] According to the power demand P at each moment in (3-2) eThe relationship between power demand and time t is plotted, and the curve of power demand changing with time is shown in the specific example given in this embodiment. Figure 6 As shown.

[0056] (5) Draw scatter plots of demand torque as a function of speed and demand power as a function of speed;

[0057] (5-1) Combining the torque demand curve with time in step (4), and based on the relationship between time and vehicle speed for the selected driving conditions in step (1), the vehicle speed u is calculated using the following formula. a The relationship with rotational speed n is used to convert vehicle speed to rotational speed, and then a scatter plot of the required torque versus rotational speed is plotted. The scatter plot of required torque versus rotational speed plotted in the specific example given in this embodiment is as follows: Figure 3 As shown.

[0058]

[0059] (5-2) Combining the power demand curve with time in step (4), and based on the relationship between time and vehicle speed for the selected driving condition in step (1), convert the vehicle speed to engine speed according to formula (4), and then plot a scatter plot of power demand versus engine speed. The scatter plot of power demand versus engine speed plotted in the specific example given in this embodiment is as follows: Figure 7 As shown.

[0060] (6) Draw the frequency distribution diagram of demand torque and the frequency distribution diagram of demand power;

[0061] (6-1) Calculate the required torque value at each operating point at each moment, and determine the maximum value T of the required torque. 0max The required torque value is increased from 0 Nm to the maximum value T. 0max The torque is evenly distributed into N1 parts, where N1 = 2, 3, 4, 5, ... The number of operating points within each torque distribution range is counted. The frequency of each operating point within that torque distribution range is obtained by dividing the number of operating points by the total number of operating points. This frequency distribution map of the required torque is then used to plot the torque frequency distribution. Since the required torque value is relatively large, the unit of the required torque is converted from Nm to kNm. The maximum required torque value T is then used. 0max The maximum torque of the electric drive system is determined. Due to the high frequency of torque distribution, the area covering 90% of the distribution map is selected as the vehicle's commonly used operating point, which is the rated torque of the electric drive system.

[0062] In a specific example, the demand torque frequency distribution diagram is as follows: Figure 4 As shown, for a 49-ton semi-trailer tractor under CHTC-HT conditions, the maximum torque of the electric drive system is determined to be 41.55 kNm; the operating point covering 90% of the area is 15.5 kNm, that is, the rated torque of the electric drive system is 15.5 kNm.

[0063] (6-2) Calculate the power demand value at each operating point at each moment, and determine the maximum power demand P. emax The power demand value is changed from 0kW to the maximum power demand value P. emax The power is evenly distributed into N² parts, where N² = 2, 3, 4, 5, ... The number of operating points within each power distribution range is counted. The frequency of each operating point within that power distribution range is obtained by dividing the number of operating points by the total number of operating points. This frequency distribution of the demand power is then used to plot the demand power frequency distribution map. The maximum demand power value P is then... emax The maximum power of the electric drive system is determined. Due to the high frequency of power distribution, the area covering 90% of the distribution map is selected as the vehicle's commonly used operating point, which is the rated power of the electric drive system.

[0064] In a specific example, the demand power frequency distribution diagram is as follows: Figure 8 As shown, for a 49-ton semi-trailer tractor under CHTC-HT operating conditions, after eliminating one abnormal power demand point, the maximum power of the electric drive system is determined to be 788kW; the operating point covering 90% of the area is 349kW, that is, the rated power of the electric drive system is 349kW.

[0065] (7) Draw a statistical graph of the frequency distribution of demand torque-speed;

[0066] The required torque is segmented according to the method of equal division of required torque in (6-1), that is, the required torque value ranges from 0 Nm to the maximum value T. 0max The torque is evenly distributed into N3 parts, where N3 = 2, 3, 4, 5, ... The speed n, from 0 r / min to the maximum speed, is evenly distributed into N4 parts, where N4 = 2, 3, 4, 5, ... Using the required torque range as the vertical axis and the speed range as the horizontal axis, each torque and speed range segment forms a torque-speed distribution interval. The number of operating points within each torque-speed distribution interval is counted. The frequency of each operating point within each interval is obtained by dividing the number of operating points by the total number of operating points. This frequency distribution is then used to plot the required torque-speed frequency distribution.

[0067] In a specific example, when plotting the demand torque-speed frequency distribution chart, the frequency distribution of operating points within each torque-speed distribution interval is represented in the distribution chart according to frequency level and using four different symbols (e.g., ...). Figure 5 (As shown). For example, Figure 5 In the diagram, data points with a distribution frequency ≤ 1.67% are represented by a diamond “◆”; data points with a distribution frequency > 1.67% and ≤ 3.33% are represented by a triangle “▲”; data points with a distribution frequency > 3.33% and ≤ 5.00% are represented by a box “■”; and data points with a distribution frequency > 5.00% are represented by a cross “×”. Observation Figure 5 The distribution of various symbols shows that the densely populated area of ​​the system's operation is marked with an "×". The area with a relatively concentrated distribution under this symbol is designated as the system's high-efficiency zone, thus determining the speed and torque range within this high-efficiency zone. Figure 5 In the study, the region of 350–450 r / min and 0–20 kNm was selected as the high-efficiency region of the system.

[0068] (8) Determine the speed ratio and number of gears;

[0069] The high-efficiency speed and torque range obtained in step (7) is the required speed and torque range for normal vehicle operation, i.e., the speed and torque at the output end of the main reducer. From (3-1), we know that T0 = T tq i g i0, and n0 = n tq / i g i0, where n0 is the speed at the output of the main reducer, in r / min; n tq The motor speed is measured in r / min. The torque and speed of the motor are obtained by increasing the torque and decreasing the speed through the transmission device and the main reducer.

[0070] The vehicle's performance is evaluated using maximum speed, maximum gradeability, and 0-100 km / h acceleration time as indicators of dynamic performance, and average energy consumption per 100 km as an indicator of economic performance. Constraints include a limited number of commonly used final drive ratios, maximum gear ratios, minimum gear ratios, and a limited number of gears for selected vehicle models. The transmission ratio i is used as the constraint. g With the speed ratio i0 of the main reducer as the optimization target, the speed ratio i of the transmission device is optimized. g Optimize the speed ratio i0 of the main reducer to obtain the number of gears and speed ratio i of the transmission device. g The speed ratio i0 with the main reducer.

[0071] (9) Determine the rated and peak torque and speed of the motor;

[0072] Based on the maximum required torque and rated required torque determined in (6-1), the system's high-efficiency range determined in step (7), and the transmission speed ratio i determined in step (8), g And the main reduction ratio i0, according to T tq =T0 / i g i0 and n tq =n0i g i0 determines the motor's peak torque, rated torque, peak speed, and rated speed.

[0073] (10) Determination of electric drive system parameters;

[0074] Step (7) determines the high-efficiency range of the motor; step (8) determines the number of gears and speed ratio of the transmission; step (9) determines the rated torque, peak torque, rated speed and peak speed of the motor; step (6-2) determines the rated power and peak power of the motor. Based on the above results, the parameters of the electric drive system are finally determined.

[0075] After completing the parameter design of the electric drive system according to the design method given above, the stator and rotor of the motor can be designed based on the determined parameters such as the high-efficiency range of the motor, rated torque, rated speed, rated power, peak torque, peak speed and peak power. This part can be carried out according to the existing design method. This part is not a technical improvement point of the present invention. Therefore, this embodiment omits this part.

[0076] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A design method for an electric drive system, characterized in that, include: Acquire vehicle driving condition data, and calculate the required torque and required power at each moment based on the vehicle driving condition data, so as to obtain the data on the change of required torque and required power over time. Based on the data on the change of demand torque over time, the data on the change of demand torque over speed can be calculated; based on the data on the change of demand power over time, the data on the change of demand power over speed can be calculated. The system calculates the required torque value at each operating point at any given time, determines the maximum required torque, and defines the maximum required torque value as the maximum torque of the electric drive system. It also calculates the frequency distribution data of the required torque, sets the concentrated area of ​​this distribution data as the vehicle's commonly used operating point, and defines the required torque at this commonly used operating point as the rated torque of the electric drive system. Finally, the system calculates the required power value at each operating point at any given time, determines the maximum required power value, and defines the maximum required power value as the maximum power of the electric drive system. The system also calculates the frequency distribution data of the required power, sets the concentrated area of ​​this distribution data as the vehicle's commonly used operating point, and defines the required power at this commonly used operating point as the rated power of the electric drive system. Statistical analysis of demand torque-speed frequency distribution data is conducted, and the region in the demand torque-speed frequency distribution data is identified as the system's efficient range. The speed and torque range of the system's efficient range are determined, and the speed and torque within this range are used as the demand speed and torque for vehicle design. Optimization is carried out in conjunction with vehicle dynamics evaluation indicators, economic evaluation indicators, and constraints to determine the number of gears and speed ratio of the transmission device. Based on the determined maximum required torque and rated required torque, the determined system high efficiency range, and the determined speed ratio, the peak torque, rated torque, peak speed, and rated speed of the motor are determined. Then, combined with the determined rated power and peak power of the motor, the parameters of the electric drive system are determined. The vehicle driving condition data is the data on the relationship between vehicle speed and time. The vehicle speed data in the overall vehicle driving condition data is converted to units. The original vehicle speed data is in km / h, which is converted to m / s using the following formula: ， In the above formula, u a The original vehicle speed data, u The vehicle speed data after unit conversion; The required torque at each moment is calculated using the following formula: ， In the above formula, T 0 represents the required torque at each operating point at any given time. T tq This refers to the torque of the drive motor, expressed in Nm. i g This refers to the speed ratio of each gear in the transmission device; i 0 is the speed ratio of the main reducer; r This is the wheel's rolling radius, in meters (m). η T For transmission efficiency; G This represents the vehicle's weight, expressed in Newtons (N). m Vehicle mass, in kg; f This is the rolling resistance coefficient; i Slope; C D This refers to the air drag coefficient; A The windward area is expressed in meters (m²). 2 ; δ This is the rotational mass conversion factor; The acceleration of the vehicle, measured in m / s². 2 , , in, u 1 represents the vehicle speed at the previous moment. u 2 represents the vehicle speed value at the next moment; the operating point where the vehicle speed value is 0 and the acceleration is also 0 is defined as the stationary operating point of the vehicle, and the required torque value of the stationary operating point is set to 0. Power required at every moment P e Calculate using the following formula: ； When calculating the data on torque demand versus speed and power demand versus speed, the data on torque demand versus time and power demand versus time are combined respectively, and the time is considered in the vehicle's driving condition data. t With vehicle speed u a The corresponding relationship is given by the following formula: vehicle speed u a Converted to speed n Then, scatter plots of torque demand versus speed and power demand versus speed can be plotted: ； When collecting data on the frequency distribution of demand torque, the demand torque values ​​from 0 to the maximum value are distributed evenly in portions. The number of operating points within each torque distribution range is counted. The frequency of the operating points within the torque distribution range is obtained by dividing the number of operating points by the total number of operating points. Then, a demand torque frequency distribution map is drawn, and the area covering 90% of the distribution map is selected as the commonly used operating points of the vehicle. When collecting statistical data on the frequency distribution of demand power, the demand power values ​​from 0 to the maximum value are distributed evenly in portions. The number of operating points within each power distribution range is counted. The frequency of the operating points within the power distribution range is obtained by dividing the number of operating points by the total number of operating points. Then, a demand power frequency distribution map is drawn, and the area covering 90% of the distribution map is selected as the commonly used operating points of the vehicle.

2. The electric drive system design method according to claim 1, characterized in that: The data on the relationship between vehicle speed and time can be obtained from the following standards: GB / T 38146.1-2019 China Automotive Driving Cycle Part 1: Light Vehicles, GB / T 38146.2-2019 China Automotive Driving Cycle Part 2: Heavy Commercial Vehicles, the New European Driving Cycle, and the Globally Harmonized Light Vehicle Test Cycle.

3. The electric drive system design method according to claim 1, characterized in that: When statistically analyzing the demand torque-speed frequency distribution data, the demand torque values ​​from 0 to the maximum value are evenly distributed in portions, and the speed is... n The torque and speed ranges from 0 to the maximum speed are evenly distributed. The torque range is plotted on the vertical axis and the speed range on the horizontal axis. Each torque and speed range segment constitutes a torque-speed distribution interval. The number of operating points in each torque-speed distribution interval is counted. The frequency of the operating points in each torque-speed distribution interval is obtained by dividing the number of operating points by the total number of operating points. Then, a torque-speed frequency distribution chart is plotted. The frequency distribution of operating points in each torque-speed distribution interval is represented in the distribution chart according to the frequency and different symbols. The distribution of each symbol in the distribution chart is observed. The concentrated distribution area of ​​one type of symbol is selected as the high-efficiency area of ​​the system.

4. The electric drive system design method according to claim 3, characterized in that: The speed and torque range within the system's high-efficiency zone corresponds to the required speed and torque range for normal vehicle operation, thus allowing determination of the speed and torque at the main reducer's output. According to the formula... T 0= T tq i g i 0 and n 0= n tq / i g i 0 can determine the required speed and torque of the vehicle, where, n 0 represents the speed at the output of the main reducer, in r / min. n tq This refers to the speed of the drive motor, expressed in r / min. The vehicle's performance is evaluated using maximum speed, maximum gradeability, and 0-100 km / h acceleration time as indicators of dynamic performance, and average energy consumption per 100 km as an indicator of economic performance. Constraints are set on a limited number of selected vehicle models, including common final drive ratios, maximum gear ratios, minimum gear ratios, and a limited number of gears. The transmission ratio is also considered. i g Speed ​​ratio of main reducer i 0 is the optimization target for the speed ratio of the transmission device. i g Speed ​​ratio of main reducer i Optimize 0 to obtain the number of gears and speed ratio of the transmission device. i g Speed ​​ratio of main reducer i 0.

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