A parallel speed ratio control strategy determination method for a P2 architecture CVT hybrid transmission

Abstract

The present application relates to a kind of vehicle hybrid power system energy-saving control, especially to a kind of P2 architecture CVT hybrid transmission parallel speed ratio control strategy determination method used in vehicle hybrid power system energy-saving control.A kind of P2 architecture CVT hybrid transmission parallel speed ratio control strategy determination method, by positioning engine fuel consumption minimum drive curve based on pure engine driven vehicle operating condition, determine the most economical working speed of engine power generation based on engine pure power generation operating condition;According to the proportion of engine power generation power in engine total power, the optimal working speed is obtained by interpolating engine pure drive speed and engine pure power generation speed.The CVT speed ratio control strategy is designed by the method, decouples the optimal working speed of engine in the working condition of simultaneous driving and power generation of hybrid vehicle, the problem that transmission efficiency and motor power generation efficiency are simultaneously drawn by the optimal working speed of engine, guarantees the optimal speed ratio of the highest energy transmission efficiency in the parallel working condition of hybrid vehicle.

Description

Technical Field

[0001] This invention relates to an energy-saving control system for a vehicle hybrid power system, and more particularly to a method for determining the parallel speed ratio control strategy of a P2 architecture CVT hybrid transmission used in the energy-saving control of a vehicle hybrid power system. Background Technology

[0002] Single-motor or multi-motor hybrid systems based on CVT transmissions, while inheriting the advantages of continuously variable speed ratios of traditional CVT transmissions, add the control degree of freedom of motor charging and discharging torque (power). This allows the engine to not only change speeds but also change its operating torque, achieving dual-degree-of-freedom optimization of engine operating range speed and torque, thus improving fuel economy. However, while achieving excellent fuel economy, the variables for speed ratio optimization also increase. In addition to considering traditional engine fuel efficiency, factors such as transmission efficiency and the efficiency of motor power generation or power assist must also be considered, making the determination of the speed ratio strategy more complex. Summary of the Invention

[0003] This invention addresses the current situation in existing vehicle hybrid systems where the need to consider more optimization variables to improve fuel economy leads to a more complex determination of the speed ratio strategy. It provides a method for determining the parallel speed ratio control strategy of a P2 architecture CVT hybrid transmission, which can better guarantee the highest energy transfer efficiency under parallel operation of hybrid vehicles by optimizing the speed ratio strategy, thus ensuring the overall fuel economy of the vehicle.

[0004] To achieve the above-mentioned technical objectives, the specific technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: a method for determining the parallel speed ratio control strategy of a P2 architecture CVT hybrid transmission, comprising the following steps:

[0005] Step 1. Based on the engine fuel consumption characteristic data obtained from the engine bench test, create an engine thermal efficiency table;

[0006] Step 2. Based on the transmission efficiency data obtained from the CVT transmission bench test, create a table of average CVT transmission efficiency.

[0007] Step 3. Based on the engine thermal efficiency table formed in Step 1 and the CVT average transmission efficiency table formed in Step 2, multiply the efficiency at the same operating point to calculate the engine drive efficiency table, and draw the engine drive efficiency diagram based on the table data.

[0008] Step 4. Based on the drawn engine drive efficiency diagram, use the isopower lines to find the engine operating point with the highest engine drive efficiency under different engine power, and create the most economical drive curve of drive power-engine speed.

[0009] Step 5. Using vehicle speed and wheel-end torque demand as coordinates, create a wheel-end power demand table and an airspeed ratio table respectively. Take the power points in the power table as inputs, interpolate to find the most economical drive curve of the engine, and use the obtained engine speed as the numerator. Take the gearbox output shaft speed calculated from the vehicle speed value corresponding to the power point as the denominator. The fraction value is the speed ratio, which is filled into the corresponding position in the speed ratio table. After traversing, a drive speed ratio table is created.

[0010] Step 6. Based on the motor power generation efficiency data obtained from the P2 motor bench test, create a motor power generation efficiency table;

[0011] Step 7. Based on the engine thermal efficiency table formed in Step 1 and the motor power generation efficiency table formed in Step 6, calculate the engine power generation efficiency table by multiplying the efficiency at the operating point, and draw the engine power generation efficiency diagram based on the table data.

[0012] Step 8. Based on the drawn engine power generation efficiency diagram, use the isopower lines to find the engine operating point with the highest engine power generation efficiency under different engine power, and form the most economical power generation curve of power generation - engine speed.

[0013] Step 9. Using the actual vehicle speed and wheel-end torque requirements as inputs, interpolate and query the drive ratio table to obtain the target drive ratio. Using the power generation requirements as inputs, interpolate and query the most economical power generation curve to obtain the target power generation engine speed. Divide the speed by the gearbox output shaft speed to obtain the target power generation ratio. Using the power generation requirements as a factor of the engine's total power, interpolate the target drive ratio and the target power generation ratio to obtain the final calculated parallel target ratio.

[0014] Steps 1 to 5 are used to locate the engine's minimum fuel consumption drive curve. Based on the engine's pure power generation condition, steps 6, 7, and 8 determine the most economical operating speed for engine power generation. Then, based on the proportion of engine power generation in the engine's total power, the pure drive speed and pure power generation speed are interpolated to obtain the optimal operating speed. A CVT speed ratio control strategy is designed using this method, decoupling the problem of the engine's optimal operating speed affecting both transmission efficiency and motor power generation efficiency when hybrid vehicles are simultaneously driving and generating power. This ensures the optimal speed ratio with the highest energy transfer efficiency in parallel operation of the hybrid vehicle, thus guaranteeing the overall vehicle's fuel economy. By optimizing the speed ratio strategy, the optimal speed ratio with the highest energy transfer efficiency in parallel operation of the hybrid vehicle can be better guaranteed, ensuring the overall vehicle's fuel economy.

[0015] Preferably, in step 1, the engine fuel consumption characteristic data obtained from the engine bench test, namely engine speed Ne, engine output torque Te, and fuel consumption rate be, are converted into engine thermal efficiency ηe according to the following calculation formula ηe=1000*36000 / (44000*be), thus obtaining the engine speed-engine torque-engine thermal efficiency table.

[0016] Preferably, step 2 involves testing the transmission efficiency data obtained from the CVT transmission bench test, determining the transmission efficiency η1 at the test speed ratio i1, transmission input speed N1, and transmission input torque T1, where i1 is the first test speed ratio; and then checking the transmission efficiency η1 at the test speed ratio i1, transmission input speed N1, and transmission input torque T1.

[0017] Using the method described above, the transmission efficiency at a series of test speed ratios at operating points (N1, T1) was obtained, and the average transmission efficiency at that point was calculated using the following formula: η=(η1+η2+…+ηn) / n.

[0018] η = (η1 + η2 + ... + ηn) / n;

[0019] Where η is the average transmission efficiency, ηn is the transmission efficiency at the working point under the nth test speed ratio, and n is the number of test speed ratio samples for gearbox transmission efficiency.

[0020] Following the above method, after traversing the operating points, a table is generated showing the CVT input speed, CVT input torque, and CVT average transmission efficiency.

[0021] Preferably, in step 3, the engine thermal efficiency table from step 1 and the CVT average transmission efficiency table from step 2 are unified to the same speed and torque coordinate axis by interpolation. Under this same coordinate axis, the engine thermal efficiency and CVT transmission efficiency are multiplied to obtain the engine drive efficiency table, and the universal characteristic diagram of the engine drive efficiency is plotted.

[0022] Preferably, in step 4, a series of engine power Pi are set according to the engine power range, with m as the step size;

[0023] For a fixed engine power P, use the formula P=N*T / 9550 to calculate the engine torque at different speeds, and draw the engine speed-torque curve at that power, i.e. the engine isopower line. At the same time, look up the engine drive efficiency corresponding to each speed on the isopower line in the engine drive efficiency table in step 3 above.

[0024] Following the above method, draw a series of isopower lines of engine power Pi and find the corresponding engine drive efficiency. Extract the point with the highest engine drive efficiency on each isopower line. Connect a series of points with the lowest fuel consumption rate on the universal characteristic diagram of engine drive efficiency to form a smooth curve, thus creating the most economical drive curve of drive power-engine speed.

[0025] Preferably, in step 5, a two-dimensional table is created with vehicle speed and wheel-end torque as coordinates. The coordinate points on the two coordinate axes are orthogonal to form the wheel-end power demand. The table is filled into the previously created two-dimensional table to form the wheel-end power demand table.

[0026] Query the most economical drive curve of drive power-engine speed in step 4 using the wheel end demand power table point to obtain the target engine speed corresponding to the wheel end demand power point. With the engine speed as the numerator and the gearbox output shaft speed Nsec corresponding to the vehicle speed at the wheel end power point as the denominator, the fraction value is the speed ratio i corresponding to the engine's optimal drive efficiency speed at the wheel end demand power point.

[0027] Determine the maximum gear ratio imax and the minimum gear ratio imin of the CVT transmission. When the gear ratio i ≥ the maximum gear ratio imax, set the gear ratio i = imax; when the gear ratio i ≤ the minimum gear ratio imin, set the gear ratio i = imin; otherwise, set the gear ratio to i.

[0028] Calculate each required power in the wheel-end required power table using the method described above, and obtain a drive speed ratio table with vehicle speed and wheel-end required torque as the coordinate axes.

[0029] Preferably, in step 9, the target drive ratio ID is obtained by interpolating and querying the drive ratio table using the actual vehicle speed and wheel end torque requirements as inputs.

[0030] Using the power demand as input, the target power generation speed Nc is obtained by interpolating and querying the engine's most economical power generation curve;

[0031] Calculate the gearbox output shaft speed Nsec based on the vehicle speed, and the target power generation speed ratio ic = Nc / Nsec;

[0032] The power demand for power generation is Pcharge, the power demand at the wheel end is Pwheel, the interpolation factor is s=Pcharge / (Pcharge+Pwheel), and the final target speed ratio in parallel is ip=s*(ic-id)+id.

[0033] The vehicle speed mentioned above corresponds to the gearbox output shaft rotational speed Nsec, which is calculated as follows:

[0034] Nsec = V / (3.6*r)*(30 / pi)*ig;

[0035] In the above formula, V is the vehicle speed (km / h), r is the tire radius (m), pi is pi, and ig is the principal reduction ratio.

[0036] Preferably, the coordinate points on the two coordinate axes are orthogonal to form the required power at the wheel end, which is calculated as follows: Pwheel=V / (3.6*r)*Twheel;

[0037] In the above formula, V is the vehicle speed (km / h), r is the tire radius (m), and Twheel is the required torque at the wheel end (Nm).

[0038] The beneficial effects of this invention are: Based on the principle of optimal energy transfer efficiency, this invention uses simulation methods to optimize the speed ratio control strategy of hybrid CVT transmission, which reduces the work cycle of repeated real vehicle testing and speed ratio table optimization, and greatly improves work efficiency.

[0039] Based on the pure engine-driven vehicle operating condition, steps 1 to 5 are used to locate the engine's minimum fuel consumption drive curve. Based on the pure engine power generation operating condition, steps 6, 7, and 8 are used to determine the most economical operating speed for engine power generation. Then, based on the proportion of engine power generation in the total engine power, the pure engine drive speed and the pure engine power generation speed are interpolated to obtain the optimal operating speed. A CVT speed ratio control strategy is designed using this method, decoupling hybrid vehicles, especially P2 architecture CVT hybrid transmission vehicles, from the problem of the optimal engine operating speed affecting both transmission efficiency and motor power generation efficiency when driving and power generation occur simultaneously, due to the P2 motor and engine being coaxial and located at the front end of the CVT transmission's steel belt. This ensures the optimal speed ratio with the highest energy transfer efficiency in the parallel operation of the hybrid vehicle, thus guaranteeing the overall vehicle's fuel economy.

[0040] Meanwhile, the drive ratio table corresponding to the minimum fuel consumption curve of the engine under pure engine drive conditions can inherit the traditional fuel vehicle speed ratio calibration method matched with CVT transmission, which can effectively reduce the actual vehicle engineering calibration time and personnel training time, and save development costs. Attached Figure Description

[0041] Figure 1 This is a schematic diagram illustrating the steps of the method for determining the parallel speed ratio control strategy of the P2 architecture CVT hybrid transmission of the present invention.

[0042] Figure 2 This is a schematic diagram of the most economical engine drive curve in the method for determining the parallel speed ratio control strategy of the P2 architecture CVT hybrid transmission of the present invention.

[0043] Figure 3 This is a schematic diagram of the most economical power generation curve of the engine in the method for determining the parallel speed ratio control strategy of the P2 architecture CVT hybrid transmission of the present invention. Detailed Implementation

[0044] Figure 1 In the illustrated embodiment, a method for determining the parallel speed ratio control strategy of a P2 architecture CVT hybrid transmission includes the following steps:

[0045] Step 1. Based on the engine fuel consumption characteristic data obtained from the engine bench test, create an engine thermal efficiency table;

[0046] Step 2. Based on the transmission efficiency data obtained from the CVT transmission bench test, create a table of average CVT transmission efficiency.

[0047] Step 3. Based on the engine thermal efficiency table formed in Step 1 and the CVT average transmission efficiency table formed in Step 2, multiply the efficiency at the same operating point to calculate the engine drive efficiency table, and draw the engine drive efficiency diagram based on the table data.

[0048] Step 4. Based on the drawn engine drive efficiency diagram, use the isopower lines to find the engine operating point with the highest engine drive efficiency under different engine power levels, and create the most economical drive curve of drive power versus engine speed (see Table 1 below). Figure 2 );

[0049] Step 5. Using vehicle speed and wheel-end torque requirements as coordinates, create a wheel-end power requirement table and an airspeed ratio table respectively. Take the power points in the power table as input, interpolate to find the most economical engine drive curve, and use the obtained engine speed as the numerator. Take the gearbox output shaft speed calculated from the vehicle speed value corresponding to the power point as the denominator. The fraction value is the speed ratio, which is filled into the corresponding position in the speed ratio table. After traversing, a drive speed ratio table is created (see Table 2 below).

[0050] Step 6. Based on the motor power generation efficiency data obtained from the P2 motor bench test, create a motor power generation efficiency table;

[0051] Step 7. Based on the engine thermal efficiency table formed in Step 1 and the motor power generation efficiency table formed in Step 6, calculate the engine power generation efficiency table by multiplying the efficiency at the operating point, and draw the engine power generation efficiency diagram based on the table data.

[0052] Step 8. Based on the drawn engine power generation efficiency diagram, use isopower lines to find the engine operating point with the highest power generation efficiency under different engine power levels, forming the most economical power generation curve of power generation versus engine speed (see Table 3 below). Figure 3 );

[0053] Step 9. Using the actual vehicle speed and wheel-end torque requirements as inputs, interpolate and query the drive ratio table to obtain the target drive ratio. Using the power generation requirements as inputs, interpolate and query the most economical power generation curve to obtain the target power generation engine speed. Divide the speed by the gearbox output shaft speed to obtain the target power generation ratio. Using the power generation requirements as a factor of the engine's total power, interpolate the target drive ratio and the target power generation ratio to obtain the final calculated parallel target ratio.

[0054] Step 1 above uses the engine fuel consumption characteristic data obtained from the engine bench test, namely engine speed Ne, engine output torque Te, and fuel consumption rate be, to convert the engine fuel consumption rate into engine thermal efficiency ηe according to the following calculation formula ηe=1000*36000 / (44000*be), thus obtaining the engine speed-engine torque-engine thermal efficiency table.

[0055] Step 2 above uses the transmission efficiency data obtained from the CVT transmission bench test to test the transmission efficiency η1 at the test speed ratio i1, transmission input speed N1, and transmission input torque T1, where i1 is the first test speed ratio; find the transmission efficiency η1 at the test speed ratio i1, transmission input speed N1, and transmission input torque T1.

[0056] Using the method described above, the transmission efficiency at a series of test speed ratios at operating points (N1, T1) was obtained, and the average transmission efficiency at that point was calculated using the following formula: η=(η1+η2+…+ηn) / n.

[0057] η = (η1 + η2 + ... + ηn) / n;

[0058] Where η is the average transmission efficiency, ηn is the transmission efficiency at the working point under the nth test speed ratio, and n is the number of test speed ratio samples for gearbox transmission efficiency.

[0059] Following the above method, after traversing the operating points, a table is generated showing the CVT input speed, CVT input torque, and CVT average transmission efficiency.

[0060] In step 3 above, the engine thermal efficiency table from step 1 and the CVT average transmission efficiency table from step 2 are unified into the same speed and torque coordinate axis by interpolation. Under this same coordinate axis, the engine thermal efficiency and CVT transmission efficiency are multiplied to obtain the engine drive efficiency table, and the universal characteristic diagram of engine drive efficiency is plotted.

[0061] In step 4 above, the specific steps are as follows: Based on the engine's power range, a series of engine power Pi are set with a step size of m;

[0062] For a fixed engine power P, use the formula P=N*T / 9550 to calculate the engine torque at different speeds, and draw the engine speed-torque curve at that power, i.e. the engine isopower line. At the same time, look up the engine drive efficiency corresponding to each speed on the isopower line in the engine drive efficiency table in step 3 above.

[0063] Following the above method, draw a series of isopower lines of engine power Pi and find the corresponding engine drive efficiency. Extract the point with the highest engine drive efficiency on each isopower line. Connect a series of points with the lowest fuel consumption rate on the universal characteristic diagram of engine drive efficiency to form a smooth curve, thus creating the most economical drive curve of drive power-engine speed.

[0064] In step 5 above, the specific steps are as follows: Establish a two-dimensional table with vehicle speed and wheel-end torque as coordinates. The coordinate points on the two coordinate axes are orthogonal to form the wheel-end power demand. Fill in the previously established two-dimensional table to form the wheel-end power demand table.

[0065] The optimal driving efficiency curve of the engine and the driving power-engine speed at the wheel end demand power point in step 4) is obtained by querying the driving power-engine speed at the wheel end demand power point. The target engine speed corresponding to the wheel end demand power point is obtained by taking the engine speed as the numerator and the gearbox output shaft speed Nsec corresponding to the vehicle speed at the wheel end power point as the denominator. The fraction value is the speed ratio i corresponding to the engine's optimal driving efficiency speed at the wheel end demand power point.

[0066] Determine the maximum gear ratio imax and the minimum gear ratio imin of the CVT transmission. When the gear ratio i ≥ the maximum gear ratio imax, set the gear ratio i = imax; when the gear ratio i ≤ the minimum gear ratio imin, set the gear ratio i = imin; otherwise, set the gear ratio to i.

[0067] Calculate each required power in the wheel-end required power table using the method described above, and obtain a drive speed ratio table with vehicle speed and wheel-end required torque as the coordinate axes.

[0068] In step 9 above, the specific steps are as follows: using the actual vehicle speed and wheel end torque as inputs, interpolate and query the drive ratio table to obtain the target drive ratio ID;

[0069] Using the power demand for power generation as input, the engine's most economical power generation curve is interpolated to obtain the target power generation speed Nc; the gearbox output shaft speed Nsec is calculated based on the vehicle speed, and the target power generation speed ratio ic = Nc / Nsec;

[0070] The power demand for power generation is Pcharge, and the power demand at the wheel end is Pwheel.

[0071] Interpolation factor s = Pcharge / (Pcharge + Pwheel), and final parallel target speed ratio ip = s * (ic - id) + id.

[0072] The vehicle speed corresponds to the gearbox output shaft speed Nsec, which is calculated as follows:

[0073] Nsec = V / (3.6*r)*(30 / pi)*ig;

[0074] In the above formula, V is the vehicle speed (km / h), r is the tire radius (m), pi is pi, and ig is the principal reduction ratio.

[0075] The orthogonal coordinate points on the two coordinate axes form the required power at the wheel end, which is calculated as follows:

[0076] Pwheel = V / (3.6 * r) * Twheel;

[0077] In the above formula, V is the vehicle speed (km / h), r is the tire radius (m), and Twheel is the required torque at the wheel end (Nm).

[0078] Table 1 below shows the data for the most economical drive curve of drive power versus engine speed.

[0079]

[0080] The operating point, consisting of drive power and engine speed, corresponds to Figure 1 The most economical driving point is the inflection point on the curve. As shown in Table 1, the data in the second column (10kW, 980rpm) is... Figure 1 The second inflection point on the most economical drive curve lies on the 10kW constant power dashed line, with an x-axis value of 980rpm. This point indicates that if the engine outputs 10kW of drive power, the highest drive efficiency for the vehicle is achieved at 980rpm. (Observation...) Figure 1 It can be observed that this point is the furthest from the 0.29 engine drive efficiency line and the closest to the 0.3 engine drive efficiency line among all points on the 10kW power line.

[0081] Table 2 below shows the drive speed ratio table.

[0082] In Table 2, the horizontal axis represents the wheel-end torque requirement in Nm; the vertical axis represents the vehicle speed in km / h; the table values ​​represent the most economical drive ratio under the condition (power) where the vehicle speed and wheel-end torque requirement intersect; in this example, the gearbox ratio ranges from 0.4 to 2.4.

[0083]

[0084] Table 3 below shows the data for the most economical power generation curve of power generation versus engine speed:

[0085]

[0086] exist Figure 2 In the diagram, the solid contour lines represent the engine's constant drive efficiency, ranging from 0.2 to 0.32 in this example; the dashed contour lines represent the engine's constant power, ranging from 5 to 110 kW in this example; and the dotted lines represent the engine's most economical drive curve. On each engine's constant power line, a solid black dot indicates the operating point with the highest drive efficiency. Connecting all the solid dots on all the engine's constant power lines with a dotted line forms the engine's most economical drive curve.

[0087] exist Figure 3 In the diagram, the solid contour lines represent the engine's equal power generation efficiency lines, ranging from 0.24 to 0.335 in this example; the dashed contour lines represent the engine's equal power lines, ranging from 5 to 110 kW in this example; and the dotted lines represent the engine's most economical power generation curve. On each engine's equal power line, a black hollow dot indicates the operating point with the highest power generation efficiency. Connecting all the hollow dots on all the engine's equal power lines with a dotted line forms the engine's most economical power generation curve.

[0088] The above content and structure describe the basic principles, main features, and advantages of the product of this invention, which should be understood by those skilled in the art. The examples and descriptions above are merely illustrative of the principles of this invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for determining the parallel speed ratio control strategy of a P2 architecture CVT hybrid transmission, characterized in that... Includes the following steps: Step 1. Based on the engine fuel consumption characteristic data obtained from the engine bench test, create an engine thermal efficiency table; Step 2. Based on the transmission efficiency data obtained from the CVT transmission bench test, create a table of average CVT transmission efficiency. Step 3. Based on the engine thermal efficiency table formed in Step 1 and the CVT average transmission efficiency table formed in Step 2, multiply the efficiency at the same operating point to calculate the engine drive efficiency table, and draw the engine drive efficiency diagram based on the table data. Step 4. Based on the drawn engine drive efficiency diagram, use the isopower lines to find the engine operating point with the highest engine drive efficiency under different engine power, and create the most economical drive curve of drive power-engine speed. Step 5. Using vehicle speed and wheel-end torque demand as coordinates, create a wheel-end power demand table and an airspeed ratio table respectively. Take the power points in the power table as inputs, interpolate to find the most economical drive curve of the engine, and use the obtained engine speed as the numerator. Take the gearbox output shaft speed calculated from the vehicle speed value corresponding to the power point as the denominator. The fraction value is the speed ratio, which is filled into the corresponding position in the speed ratio table. After traversing, a drive speed ratio table is created. Step 6. Based on the motor power generation efficiency data obtained from the P2 motor bench test, create a motor power generation efficiency table; Step 7. Based on the engine thermal efficiency table formed in Step 1 and the motor power generation efficiency table formed in Step 6, calculate the engine power generation efficiency table by multiplying the efficiency at the operating point, and draw the engine power generation efficiency diagram based on the table data. Step 8. Based on the drawn engine power generation efficiency diagram, use the isopower lines to find the engine operating point with the highest engine power generation efficiency under different engine power, and form the most economical power generation curve of power generation - engine speed. Step 9. Using the actual vehicle speed and wheel-end torque requirements as inputs, interpolate and query the drive ratio table to obtain the target drive ratio. Using the power generation requirements as inputs, interpolate and query the most economical power generation curve to obtain the target power generation engine speed. Divide the speed by the gearbox output shaft speed to obtain the target power generation ratio. Using the power generation requirements as a factor of the engine's total power, interpolate the target drive ratio and the target power generation ratio to obtain the final calculated parallel target ratio. In step 9, the target drive ratio ID is obtained by interpolating and querying the drive ratio table using the actual vehicle speed and wheel end torque requirements as inputs. Using the power demand as input, the target power generation speed Nc is obtained by interpolating and querying the engine's most economical power generation curve; Calculate the gearbox output shaft speed Nsec based on the vehicle speed, and the target power generation speed ratio ic = Nc / Nsec; The power demand for power generation is Pcharge, the power demand at the wheel end is Pwheel, the interpolation factor is s=Pcharge / (Pcharge+Pwheel), and the final target speed ratio in parallel is ip=s*(ic-id)+id.

2. The method for determining the parallel speed ratio control strategy of the P2 architecture CVT hybrid transmission according to claim 1, characterized in that: Step 1, based on the engine fuel consumption characteristic data obtained from the engine bench test, namely engine speed Ne, engine output torque Te, and fuel consumption rate be, converts the engine fuel consumption rate into engine thermal efficiency ηe according to the calculation formula ηe=1000*36000 / (44000*be), and obtains the engine speed-engine torque-engine thermal efficiency table.

3. The method for determining the parallel speed ratio control strategy of the P2 architecture CVT hybrid transmission according to claim 1, characterized in that: Step 2, based on the transmission efficiency data obtained from the CVT transmission bench test, tests the transmission efficiency η1 at the speed ratio i1, transmission input speed N1, and transmission input torque T1, where i1 is the first test speed ratio. Using the above method, the transmission efficiency at a series of test speed ratios at operating points (N1, T1) was obtained, and the average transmission efficiency at that point was calculated using the formula η=(η1+η2+...+ηn) / n. Where η is the average transmission efficiency, ηn is the transmission efficiency at the working point under the nth test speed ratio, and n is the number of test speed ratio samples for gearbox transmission efficiency. Following the above method, after traversing the operating points, a table is generated showing the CVT input speed, CVT input torque, and CVT average transmission efficiency.

4. The method for determining the parallel speed ratio control strategy of the P2 architecture CVT hybrid transmission according to claim 1, characterized in that: In step 3, the engine thermal efficiency table from step 1 and the CVT average transmission efficiency table from step 2 are unified to the same speed and torque coordinate axis by interpolation. Under this same coordinate axis, the engine thermal efficiency and CVT transmission efficiency are multiplied to obtain the engine drive efficiency table, and the universal characteristic diagram of engine drive efficiency is plotted.

5. The method for determining the parallel speed ratio control strategy of the P2 architecture CVT hybrid transmission according to claim 1, characterized in that: In step 4, a series of engine power Pi are set according to the engine power range, with m as the step size; For a fixed engine power P, use the formula P=N*T / 9550 to calculate the engine torque at different speeds, and draw the engine speed-torque curve at that power, i.e. the engine isopower line. At the same time, look up the engine drive efficiency corresponding to each speed on the isopower line in the engine drive efficiency table in step 3 above. Following the above method, draw a series of isopower lines of engine power Pi and find the corresponding engine drive efficiency. Extract the point with the highest engine drive efficiency on each isopower line. Connect a series of points with the lowest fuel consumption rate on the universal characteristic diagram of engine drive efficiency to form a smooth curve, thus creating the most economical drive curve of drive power-engine speed.

6. The method for determining the parallel speed ratio control strategy of the P2 architecture CVT hybrid transmission according to claim 5, characterized in that: In step 5, a two-dimensional table is created with vehicle speed and wheel-end torque as coordinates. The coordinate points on the two coordinate axes are orthogonal to form the wheel-end power demand. The data is then filled into the previously created two-dimensional table to form the wheel-end power demand table. Query the most economical drive curve of drive power-engine speed in step 4 using the wheel end demand power table point to obtain the target engine speed corresponding to the wheel end demand power point. With the engine speed as the numerator and the gearbox output shaft speed Nsec corresponding to the vehicle speed at the wheel end power point as the denominator, the fraction value is the speed ratio i corresponding to the engine's optimal drive efficiency speed at the wheel end demand power point. Determine the maximum gear ratio imax and the minimum gear ratio imin of the CVT transmission. When the gear ratio i ≥ the maximum gear ratio imax of the transmission, set the gear ratio i = imax. When the gear ratio i ≤ the minimum gear ratio imin of the transmission, set the gear ratio i = imin; otherwise, set the gear ratio to i. Calculate each required power in the wheel-end required power table using the method described above, and obtain a drive speed ratio table with vehicle speed and wheel-end required torque as the coordinate axes.

7. The method for determining the parallel speed ratio control strategy of the P2 architecture CVT hybrid transmission according to claim 6, characterized in that: The vehicle speed mentioned corresponds to the gearbox output shaft speed Nsec. Nsec = V / (3.6*r)*(30 / pi)*ig; In the above formula, V is the vehicle speed (km / h), r is the tire radius (m), pi is pi, and ig is the principal reduction ratio.

8. The method for determining the parallel speed ratio control strategy of the P2 architecture CVT hybrid transmission according to claim 6, characterized in that: The coordinate points on the two coordinate axes are orthogonal, forming the required power at the wheel end, Pwheel = V / (3.6*r)*Twheel; In the above formula, V is the vehicle speed (km / h), r is the tire radius (m), and Twheel is the required torque at the wheel end (Nm).

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