Key parameter design method of hydraulic backflow transmission system

Abstract

The invention relates to the field of transmission equipment, and discloses a key parameter design method of a hydraulic backflow transmission system. The method comprises the following steps: selecting key parameters to establish decision vectors; determining a displacement ratio control boundary; determining the value range of the key design parameters; according to actual operation characteristics, establishing a gear matching relation between the target vehicle and the hydraulic backflow transmission system; establishing a target function by using an integral median theorem; establishing a multi-objective optimization model and solving; and determining and checking the effectiveness of the hydraulic backflow transmission system and the selected key design parameters. According to the method, systematic key parameters such as the operation characteristics, the transmission efficiency, the torque increasing coefficient, the working efficiency, the gear shifting quality and the actual use quality of the target vehicle are comprehensively considered, so that the hydraulic backflow transmission system can adapt to complex operation working conditions of different target engineering vehicles in a targeted mode, and the potential performance advantages of the hydraulic backflow transmission system are brought into play; and the transmission performance of the engineering vehicle is improved to the greatest extent.

Description

Technical Field

[0001] The invention relates to the field of transmission system design, and in particular to a key parameter design method for a hydraulic reflux transmission system. Background Art

[0002] The hydraulic return transmission system is a new type of transmission system, which is a special form of hydraulic mechanical dual-flow transmission system. It is generally composed of a hydraulic return transmission device and a compound planetary gear power shift transmission in series. It can effectively make up for the shortcomings of low transmission efficiency and narrow high-efficiency zone of the torque converter while ensuring power performance. It has shown good application prospects in the fields of engineering vehicles such as bulldozers, loaders, and heavy-duty transport vehicles. However, the hydraulic return transmission system does not yet have a systematic design system, and the key parameter design method of the hydraulic return transmission system and its matching method with the target vehicle are still unclear. Standardizing and improving the design system of the hydraulic return transmission system is of great significance to promoting the widespread application of the hydraulic return transmission system and improving the manufacturing level of engineering vehicles in my country. Summary of the invention

[0003] The present invention aims to provide a key parameter design method for a hydraulic reflux transmission system, and to provide a systematic key parameter design scheme for the hydraulic reflux transmission system, so that the hydraulic reflux transmission system can be specifically adapted to the complex operating conditions of different target engineering vehicles, and give full play to the potential performance advantages of the hydraulic reflux transmission system.

[0004] The present invention achieves the above-mentioned purpose through the following technical scheme: A key parameter design method of a hydraulic reflux transmission system comprises the following steps:

[0005] (1) Select the total transmission ratio i of the fixed axis gear in the hydraulic return transmission device n , the characteristic constant k of each planetary gear in the compound planetary gear power shift transmission n , central drive and final drive total transmission ratio i Z , the shift displacement ratio of each gear ε n As the key parameter, and establish the decision vector x = [i n k n i Z ε n ];

[0006] (2) Determine the displacement ratio control boundary of the pump-motor closed system in the recirculation transmission mode;

[0007] (3) Determine the value range of key design parameters;

[0008] (4) Establishing a gear matching relationship between the target vehicle and the hydraulic return transmission system based on the actual operating characteristics of the target engineering vehicle;

[0009] (5) Use the mean value theorem of integral to establish the objective function;

[0010] (6) Establish a multi-objective optimization model for the hydraulic reflux transmission system and solve it;

[0011] (7) Determine key design parameters and test effectiveness.

[0012] Furthermore, in step (5), an objective function is established, including:

[0013] The average efficiency of the hydraulic reflux transmission device under the reflux transmission model is calculated, and the objective function f1 that characterizes the starting efficiency of the hydraulic reflux transmission system is established, that is, Where, τ is the displacement ratio control range of the pump-motor closed system corresponding to the hydraulic reflux transmission device in the reflux transmission mode; η HMCS1 It indicates the transmission efficiency of the hydraulic reflux transmission device in the reflux transmission mode;

[0014] The objective function f2 that characterizes the transmission efficiency of the main load operation interval of the hydraulic reflux transmission system is established, that is, Where vn and vn-1 represent the upper and lower limits of the theoretical speed of the target vehicle in each load operation range respectively; η mn is the transmission efficiency of the compound planetary gear power shift transmission at the nth gear;

[0015] The objective function f3 that characterizes the transmission efficiency in the non-load operation interval is established, namely:

[0016]

[0017] Where η HMCS2 It represents the transmission efficiency of the hydraulic reflux transmission device in the split transmission mode; χn and χn-1 represent the upper and lower limits of the theoretical vehicle speed of each gear in the speed regulation range corresponding to the reflux transmission mode in the non-load operation range; κn and κn-1 represent the upper and lower limits of the theoretical vehicle speed of each gear in the speed regulation range corresponding to the split transmission mode in the non-load operation range;

[0018] The objective function f4 is established to characterize the displacement ratio control stroke during the gear shifting process, that is, In the formula, Δε k is the displacement ratio control stroke of the pump-motor closed system when the hydraulic reflux transmission system shifts between gear k and gear k+1; m is the actual gear number of the hydraulic reflux transmission system;

[0019] Establish the objective function f5 that represents the torque increase coefficient, that is, Where K is the torque increase coefficient of the hydraulic reflux transmission system.

[0020] Furthermore, in step (7), key design parameters are determined, including:

[0021] Solve the multi-objective optimization model and retain the Pareto optimal solution set;

[0022] The selection judgment matrix of the objective function is constructed using the 1-5 point scaling method;

[0023] The weight coefficient w of each objective function is calculated from the selection judgment matrix using the geometric mean method;

[0024] Normalize the absolute value of the Pareto solution set; establish a scoring function Score and sort the normalized calculation results of the Pareto solution set; where h i is the objective function f i The function value after normalization;

[0025] Based on the principle of maximizing the score, the key structural parameters shown by the decision variables are selected;

[0026] Calculate the maximum adhesion F of the target vehicle a ,Right now In the formula, G a is the vehicle mass of the target vehicle; is the maximum adhesion coefficient of the target vehicle;

[0027] Preliminarily determine the specifications of variable displacement hydraulic components and fixed displacement hydraulic components, and at the same time meet the requirements that the maximum theoretical traction of the target vehicle is not less than the maximum adhesion, and the maximum pressure difference of the pump-motor closed system is not higher than 350bar;

[0028] Take 75% of the rated speed of the variable displacement hydraulic component as the main operating speed n of the variable displacement hydraulic component p . By n p 、i n and the rated speed of the engine to determine the transmission ratio distribution of each fixed-axis gear in the hydraulic return transmission device.

[0029] Furthermore, in step (2), the displacement ratio control boundary of the pump-motor closed system in the reflux transmission mode is determined to ensure that the system always starts at a large displacement state, that is, the displacement ratio corresponding to the zero speed ratio |ε max |∈[0.9,1].

[0030] Furthermore, in step (3), the range of values ​​of key design parameters is determined, taking into account the specific configuration of the hydraulic reflux transmission device and the transmission power, operating speed, and operating characteristics of the target vehicle.

[0031] Furthermore, in step (4), a gear matching relationship between the target vehicle and the hydraulic reflux transmission system is established, and the reflux transmission mode of the hydraulic reflux transmission system can always cover the load operation range of the target engineering vehicle.

[0032] Specifically, in step (6), the multi-objective optimization model is solved, and a multi-objective optimization algorithm with constraint function is selected to solve the multi-objective optimization model.

[0033] In summary, the beneficial effects of the present invention are:

[0034] The present invention takes the hydraulic reflux transmission system as the service object, comprehensively considers the vehicle operation characteristics, transmission efficiency, torque increase coefficient, work efficiency, shift quality, actual use quality and other factors, and provides a systematic key parameter design scheme for the hydraulic reflux transmission system, standardizing and improving the design system of the hydraulic reflux transmission system. The design method described in the present invention enables the hydraulic reflux transmission system to adapt to the complex operating conditions of different target engineering vehicles in a targeted manner, give play to the potential performance advantages of the hydraulic reflux transmission system, and improve the transmission performance of engineering vehicles to the greatest extent. The present invention is of great significance to promoting the widespread application of the hydraulic reflux transmission system and improving the manufacturing level of engineering vehicles in my country. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 It is a calculation flow chart of the key parameter design method of the present invention;

[0037] Figure 2 is a transmission principle diagram of a hydraulic reflux transmission system according to an embodiment of the present invention;

[0038] In the figure: i1 and i2 are the gear ratios of each level of PHAT; k1~k4 are the planetary gear characteristic constants of the planetary gear system PG1~PG4 respectively; B1 is the 1st gear brake, B2 is the 2nd gear brake, C1 is the 3rd gear clutch, C2 is the forward direction clutch, and B3 is the reverse direction brake.

[0039] Figure 3 It is the Pareto optimal solution set of the key design parameters of the hydraulic reflux transmission system of the embodiment of the present invention. DETAILED DESCRIPTION

[0040] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0041] The present invention provides a key parameter design method for a hydraulic reflux transmission system, such as Figure 1 As shown, the following steps are included:

[0042] (1) Comprehensively consider the influence of structural parameters on the target vehicle's operating characteristics, transmission efficiency, torque increase coefficient, work efficiency, and shift quality, and select the total transmission ratio i of the fixed axis gear in the hydraulic reflux transmission device. n , the characteristic constant k of each planetary gear in the compound planetary gear power shift transmission n , central drive and final drive total transmission ratio i Z , the shift displacement ratio of each gear ε n As the key parameter, and establish the decision vector x = [i n k n i Z ε n ].

[0043] (2) Determine the displacement ratio control boundary of the pump-motor closed system under the recirculation transmission mode.

[0044] (3) Determine the value range of key design parameters.

[0045] (4) According to the actual operating characteristics of the target engineering vehicle, a gear matching relationship between the target vehicle and the hydraulic reflux transmission system is established.

[0046] (5) Using the integral mean value theorem, the average efficiency of the hydraulic reflux transmission device under the reflux transmission model is calculated, and the objective function f1 that characterizes the starting efficiency of the hydraulic reflux transmission system is established, namely: Where, τ is the displacement ratio control range of the pump-motor closed system corresponding to the hydraulic reflux transmission device in the reflux transmission mode; η HMCS1 Indicates the transmission efficiency of the hydraulic return transmission device in the return transmission mode.

[0047] (6) Establish the objective function f2 that characterizes the transmission efficiency of the main load operation interval of the hydraulic reflux transmission system, namely Where vn and vn-1 represent the upper and lower limits of the theoretical speed of the target vehicle in each load operation range respectively; η mn It is the transmission efficiency of the compound planetary gear power shift transmission in the nth gear.

[0048] (7) Establish the objective function f3 that represents the transmission efficiency in the non-load operation interval, namely

[0049]

[0050] Where η HMCS2 It represents the transmission efficiency of the hydraulic reflux transmission device in the diversion transmission mode; χn and χn-1 respectively represent the upper and lower theoretical speed limits of each gear in the speed regulation range corresponding to the reflux transmission mode in the non-load operating range; κn and κn-1 respectively represent the upper and lower theoretical speed limits of each gear in the speed regulation range corresponding to the diversion transmission mode in the non-load operating range.

[0051] (8) In order to ensure the shifting quality, the objective function f4 is established to characterize the displacement ratio control stroke during the shifting process, that is, In the formula, Δε k is the displacement ratio control stroke of the pump-motor closed system when the hydraulic reflux transmission system shifts between gear k and gear k+1; m is the actual number of gears of the hydraulic reflux transmission system.

[0052] (9) Establish the objective function f5 that represents the torque increase coefficient, that is, Where K is the torque increase coefficient of the hydraulic reflux transmission system.

[0053] (10) Integrate steps (1) to (9) to establish a multi-objective optimization model for the hydraulic reflux transmission system.

[0054] (11) Solve the above multi-objective optimization model and retain the Pareto optimal solution set.

[0055] (12) The 1 to 5 point scaling method is used to construct the selection judgment matrix of the objective function.

[0056] (13) The weight coefficient w of each objective function is calculated by the selection judgment matrix using the geometric mean method.

[0057] (14) Normalize the absolute value of the Pareto solution set; establish a scoring function Score and sort the normalized calculation results of the Pareto solution set; where h i is the objective function f i The normalized function value.

[0058] (15) Based on the principle of maximizing the score, the key structural parameters shown by the decision variables are selected.

[0059] (16) Calculate the maximum adhesion F of the target vehicle a ,Right now In the formula, G a is the vehicle mass of the target vehicle; is the maximum adhesion coefficient of the target vehicle.

[0060] (17) The maximum theoretical traction of the target vehicle is not less than the maximum adhesion as principle 1; the maximum pressure difference of the pump-motor closed system is not higher than 350 bar as principle 2. Based on the above two principles, the specifications of the variable displacement hydraulic components and the fixed displacement hydraulic components are preliminarily determined.

[0061] (18) Take 75% of the rated speed of the variable displacement hydraulic element as the main operating speed n of the variable displacement hydraulic element. p . By n p 、i n and the rated speed of the engine to determine the transmission ratio distribution of each fixed-axis gear in the hydraulic return transmission device.

[0062] (19) Verify the effectiveness of the hydraulic return drive system and selected key design parameters.

[0063] It should be noted that the system should always be started at a large displacement state, that is, the displacement ratio corresponding to the zero speed ratio |εmax|∈[0.9,1]; when determining the value range of key design parameters, the specific configuration of the hydraulic reflux transmission device and the transmission power, operating speed, operating characteristics and other factors of the target vehicle should be considered comprehensively; when establishing the gear matching relationship between the target vehicle and the hydraulic reflux transmission system, it must be ensured that the reflux transmission mode of the hydraulic reflux transmission system can always cover the load operation range of the target engineering vehicle.

[0064] In order to further illustrate the effectiveness of the key parameter design method and matching method of the hydraulic reflux transmission system described in this article, the present invention takes a certain model of 160 horsepower hydraulic mechanical crawler bulldozer as the target vehicle. Figure 2 Taking the hydraulic reflux transmission system shown in the figure as an example, its key design parameters are designed to match it with the target vehicle. The specific design process is as follows:

[0065] Step 1: Determine key design parameters. Figure 2 According to the structural characteristics of the transmission system shown, i1i2, k1, k2, k3, iZ, ε1, ε2 are selected as key structural parameters, and the decision vector x is established.

[0066] x=[k1 k2 k3 i1i2 i Z ε1ε2] (1)

[0067] Where iZ is the total transmission ratio of the bulldozer central drive and final drive; ε1 and ε2 are the shift displacement ratios of the 1st and 2nd gears of the hydraulic return drive system, respectively.

[0068] Step 2: Determine the displacement ratio control boundary of the pump-motor closed system in the recirculation transmission mode.

[0069] Depend on Figure 2 It can be seen that the speed regulation characteristics of the hydraulic reflux transmission system are:

[0070]

[0071] Wherein, iHM1, iHM2, iHM3 represent the 1st, 2nd, 3rd gear ratios of the hydraulic reflux transmission system respectively; k1, k2, k3 are the planetary gear characteristic constants of the planetary gears PG1, PG2, PG3 respectively.

[0072] From equations (2) to (4), it can be seen that the speed ratio of the hydraulic reflux transmission system is 0 when the displacement ratio ε = i1i2 / (1+k1). From this, the displacement ratio control boundary of the pump-motor system can be calculated as

[0073]

[0074] Step 3: Determine the value range of key design parameters.

[0075] According to mechanical design theory, the planetary gear characteristic constant of an ordinary planetary gear has a value range of k∈[1.5,4]. In a vehicle transmission system, the transmission ratio of a single-stage external gear is generally not greater than 2.8 and not less than 0.6. Therefore, the numerical relationship between i1, i2 and k1 can be expressed as

[0076]

[0077] It should be noted that the arrangement of the pump-motor closed system is relatively flexible, and the center distance of the fixed axis gear in the hydraulic reflux transmission device can be adjusted more freely. Therefore, it is believed that the values ​​of i1 and i2 can be appropriately expanded as needed.

[0078] In addition, in the hydraulic return transmission system, the maximum control displacement of the variable displacement hydraulic element is generally equal to the rated displacement of the fixed displacement hydraulic element, and Figure 2 The transmission systems shown all shift gears in the split transmission mode, from which the value range of ε1 and ε2 can be determined to be ε1, ε2∈[-1,0].

[0079] Step 4: Establish gear matching relationship.

[0080] According to the data, in the typical cyclic working conditions of the bulldozer (cutting soil-pushing soil-unloading soil-empty return), cutting soil and pushing soil are the main load conditions of the bulldozer. In the horsepower range where the target bulldozer is located, the soil cutting speed (theoretical vehicle speed) of the bulldozer is generally 2.5-3 km / h; under heavy load conditions, the bulldozing and cutting speeds of the bulldozer are basically the same; under light load conditions, the bulldozing speed of the bulldozer is generally 5-6 km / h. In addition, at the rated speed of the engine, the upper limits of the theoretical driving speed of the target bulldozer in the 1st, 2nd and 3rd gears are: 3.6 km / h, 6.3 km / h, and 10.5 km / h respectively. Based on the above analysis, the present invention believes that it is reasonable to use the 1st gear of the hydraulic return transmission system as the soil cutting gear, the 2nd gear as the transition gear, and the 3rd gear as the soil transport gear.

[0081] In order to ensure the highest transmission efficiency while making the reflux transmission mode of the hydraulic reflux transmission system always cover the load operation range of the target engineering vehicle, it is necessary to constrain the driving speed of the hydraulic reflux transmission system, that is,

[0082]

[0083] Wherein, v1 and v3 are the theoretical vehicle speeds of the 1st and 3rd gear of the hydraulic reflux transmission system, respectively, km / h.

[0084] Step 5: Establish the objective function f1 that characterizes the starting efficiency of the hydraulic reflux transmission system.

[0085]

[0086] Step 6: Establish the objective function f2 that characterizes the efficiency of the main load operation range of the hydraulic return transmission system.

[0087]

[0088] Step 7: Establish the objective function f3 that characterizes the efficiency of the hydraulic reflux transmission system in the transition range of 3 to 5 km / h.

[0089]

[0090] Where λ is the target displacement ratio of PHAT when shifting from first gear to second gear.

[0091]

[0092] Step 8: Establish an objective function f4 that characterizes the displacement ratio control stroke during the gear shifting process.

[0093]

[0094] Wherein, Δεk is the displacement ratio control stroke of the pump-motor closed system when the hydraulic return transmission system shifts between gear k and gear k+1; m is the number of gears of the hydraulic return transmission system, m=3.

[0095] Step 9: Establish the objective function f5 that characterizes the average torque increase coefficient.

[0096]

[0097] Step 10: Establish a multi-objective optimization model.

[0098]

[0099] Step 11: Solve the Pareto optimal solution set. The present invention uses the AGEMOEA multi-objective optimization algorithm to solve the multi-objective optimization model shown in formula (14). Set the population size to 50 and the genetic generation to 200, and solve the Pareto solution set of the multi-objective optimization model as follows: Figure 3 shown.

[0100] Step 12: Use the 1 to 5 point scaling method to construct the selection judgment matrix of the objective function.

[0101] Depend on Figure 3 It can be seen that the optimal solutions of objective functions f1 and f2 can converge to a very small range, which means that each group of decision vectors in the population can make PHAT have similar efficiency characteristics. In the Pareto optimal solution set of objective function f5, the minimum value of |f5| is 3.8, while the maximum torque increase coefficient of the target vehicle is 2.27, which is much larger than the starting requirement of the target vehicle. Therefore, when using the hierarchical analysis method to estimate the weight coefficient of the objective function, the importance of f1, f2, and f5 should be weakened. Based on the above viewpoints, the selection judgment matrix of the objective function is constructed using the 1-5 point scaling method as shown in Table 1.

[0102] Table 1. Selection judgment matrix

[0103]

[0104]

[0105] Step 13: The weight coefficients of each objective function are calculated by the hierarchical analysis method (geometric mean):

[0106] [w1 w2 w3 w4 w5]=[0.0720.0720.4360.3050.115] (15)

[0107] Where w1~w5 are the weight coefficients of objective functions f1~f5 respectively.

[0108] Step 14: Normalize the absolute value of the Pareto solution set, and use the scoring function S to score and sort.

[0109]

[0110] Where hi is the function value of the objective function fi after normalization; S is the score of each objective function.

[0111] Step 15: Based on the principle of the highest score, the final structural parameters of PHAT are determined as follows: k1=2.040; k2=1.868; k3=2.071; i1i2=2.800; iZ=29.045; ε1=-0.184; ε2=-0.215.

[0112] Step 16: Estimation of the maximum adhesion of the target vehicle.

[0113] The maximum adhesion Fa of the bulldozer can be expressed as

[0114]

[0115] Where Ga is the vehicle mass of the target bulldozer; is the adhesion coefficient of the tracked vehicle. According to the literature, tracked vehicles generally have the maximum adhesion coefficient on dry clay roads.

[0116] Since the target bulldozer has a total mass of 16740 kg, the maximum adhesion of the target vehicle is approximately 147.65 kN.

[0117] Step 17: Determine the specifications of variable displacement hydraulic components and fixed displacement hydraulic components.

[0118] In order to meet the functional requirements of the hydraulic reflux transmission system, the present invention preliminarily selects Rexroth A4VG series variable displacement axial piston pump and Rexroth A2FM fixed displacement axial piston motor as the main hydraulic components to form a pump-motor closed system.

[0119] Based on the selection principle of the pump and the motor and the structural parameter characteristics of i1i2=2.800, the present invention finally determines the performance parameters of the variable displacement hydraulic component and the fixed displacement hydraulic component as shown in Table 2.

[0120] Table 2 Pump-motor performance parameters of CLHS

[0121]

[0122] Step 18: Determine the transmission ratio distribution of each fixed-axis gear.

[0123] When the actual speed of the variable displacement hydraulic element is maintained at 75% of its rated speed, the variable displacement hydraulic element has a higher transmission efficiency at most displacements, and the pump-motor closed system has a faster response speed. Therefore, the transmission ratios i1 and i2 are determined as

[0124]

[0125] Wherein, ners is the rated speed of the engine, rpm (ners = 1850 rpm); nvrs is the rated speed of the variable displacement hydraulic element, rpm (nvrs = 2850 rpm).

[0126] At this point, the design of the key structural parameters of the hydraulic return transmission system and the matching of the hydraulic return transmission system with the target vehicle have been completed. The effectiveness of the selected key design parameters can be tested by comparing the theoretical traction characteristics of the hydraulic return bulldozer with those of the target bulldozer.

[0127] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A key parameter design method for a hydraulic reflux transmission system, characterized in that: The following steps are involved: (1) Select the total transmission ratio i of the fixed axis gear in the hydraulic return transmission device n , the characteristic constant k of each planetary gear in the compound planetary gear power shift transmission n , central drive and final drive total transmission ratio i Z , the shift displacement ratio of each gear ε n As the key parameter, and establish the decision vector x = [i n k n i Z ε n ]; (2) Determine the displacement ratio control boundary of the pump-motor closed system in the recirculation transmission mode; (3) Determine the value range of key design parameters; (4) Establishing a gear matching relationship between the target vehicle and the hydraulic return transmission system based on the actual operating characteristics of the target engineering vehicle; (5) Use the mean value theorem of integral to establish the objective function; (6) Establish a multi-objective optimization model for the hydraulic reflux transmission system and solve it; (7) Determine key design parameters and test effectiveness.

2. The key parameter design method of a hydraulic reflux transmission system according to claim 1 is characterized in that: In step (5), the objective function is established, including: The average efficiency of the hydraulic reflux transmission device under the reflux transmission model is calculated, and the objective function f1 that characterizes the starting efficiency of the hydraulic reflux transmission system is established, that is, Where, τ is the displacement ratio control range of the pump-motor closed system corresponding to the hydraulic reflux transmission device in the reflux transmission mode; η HMCS1 It indicates the transmission efficiency of the hydraulic reflux transmission device in the reflux transmission mode; The objective function f2 that characterizes the transmission efficiency of the main load operation interval of the hydraulic reflux transmission system is established, that is, Where vn and vn-1 represent the upper and lower limits of the theoretical speed of the target vehicle in each load operation range respectively; η mn is the transmission efficiency of the compound planetary gear power shift transmission at the nth gear; The objective function f3 that characterizes the transmission efficiency in the non-load operation interval is established, namely: Where η HMCS2 It represents the transmission efficiency of the hydraulic reflux transmission device in the split transmission mode; χn and χn-1 represent the upper and lower limits of the theoretical vehicle speed of each gear in the speed regulation range corresponding to the reflux transmission mode in the non-load operation range; κn and κn-1 represent the upper and lower limits of the theoretical vehicle speed of each gear in the speed regulation range corresponding to the split transmission mode in the non-load operation range; The objective function f4 is established to characterize the displacement ratio control stroke during the gear shifting process, that is, In the formula, Δε k is the displacement ratio control stroke of the pump-motor closed system when the hydraulic reflux transmission system shifts between gear k and gear k+1; m is the actual gear number of the hydraulic reflux transmission system; Establish the objective function f5 that represents the torque increase coefficient, that is, Where K is the torque increase coefficient of the hydraulic reflux transmission system.

3. The key parameter design method of a hydraulic reflux transmission system according to claim 1 is characterized in that: In step (7), key design parameters are determined, including: Solve the multi-objective optimization model and retain the Pareto optimal solution set; The selection judgment matrix of the objective function is constructed using the 1-5 point scaling method; The weight coefficient w of each objective function is calculated from the selection judgment matrix using the geometric mean method; Normalize the absolute value of the Pareto solution set; establish a scoring function Score and sort the normalized calculation results of the Pareto solution set; where h i is the objective function f i The function value after normalization; Based on the principle of maximizing the score, the key structural parameters shown by the decision variables are selected; Calculate the maximum adhesion F of the target vehicle a ,Right now In the formula, G a is the vehicle mass of the target vehicle; is the maximum adhesion coefficient of the target vehicle; Preliminarily determine the specifications of variable displacement hydraulic components and fixed displacement hydraulic components, and at the same time meet the requirements that the maximum theoretical traction of the target vehicle is not less than the maximum adhesion, and the maximum pressure difference of the pump-motor closed system is not higher than 350bar; Take 75% of the rated speed of the variable displacement hydraulic component as the main operating speed n of the variable displacement hydraulic component p . By n p 、i n and the rated speed of the engine to determine the transmission ratio distribution of each fixed-axis gear in the hydraulic return transmission device.

4. The key parameter design method of a hydraulic reflux transmission system according to claim 1 is characterized in that: In step (2), the displacement ratio control boundary of the pump-motor closed system in the reflux transmission mode is determined to ensure that the system always starts at a large displacement, that is, the displacement ratio |εmax|∈[0.9,1] corresponding to the zero speed ratio.

5. The key parameter design method of a hydraulic reflux transmission system according to claim 1 is characterized in that: In step (3), the value range of key design parameters is determined to meet the specific configuration of the hydraulic return transmission device, the transmission power, operating speed, and operating characteristics of the target vehicle.

6. The key parameter design method of a hydraulic reflux transmission system according to claim 1 is characterized in that: In step (6), the multi-objective optimization model is solved, and a multi-objective optimization algorithm with constraint function is selected to solve the multi-objective optimization model.

7. The key parameter design method of a hydraulic reflux transmission system according to claim 1 is characterized in that: In step (4), when establishing the gear matching relationship between the target vehicle and the hydraulic reflux transmission system, the reflux transmission mode of the hydraulic reflux transmission system always covers the load operation range of the target engineering vehicle.

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