A Key Parameter Design Method for a Hydraulic Return Transmission System

Abstract

The present invention relates to the field of transmission equipment, and discloses a method for designing key parameters of a hydraulic return transmission system. The method includes: selecting key parameters to establish a decision vector; determining the control boundary of the displacement ratio; determining the value range of key design parameters; establishing a gear position matching relationship between the target vehicle and the hydraulic return transmission system according to the actual operation characteristics; establishing an objective function by using the integral mean value theorem; establishing and solving a multi-objective optimization model; determining and verifying the effectiveness of the hydraulic return transmission system and the selected key design parameters. This application comprehensively considers systematic key parameters such as the operation characteristics of the target vehicle, transmission efficiency, torque increase coefficient, working efficiency, shifting quality, and actual use quality, enabling the hydraulic return transmission system to be targeted to adapt to the complex operation conditions of different target engineering vehicles, giving play to the potential performance advantages of the hydraulic return transmission system, and improving the transmission performance of engineering vehicles to the greatest extent.

Description

Technical Field

[0001] The present invention relates to the field of transmission system design, and particularly to a method for designing key parameters of a hydraulic return transmission system. Background Art

[0002] The hydraulic return transmission system is a new type of transmission system, which belongs to a special form of the hydraulic mechanical two-flow transmission system. Generally, it is composed of a hydraulic return transmission device and a compound planetary gear power shift transmission in series. It can effectively make up for the disadvantages of low transmission efficiency and narrow high-efficiency area of the hydraulic torque converter while ensuring the power performance, and shows good application prospects in the fields of engineering vehicles such as bulldozers, loaders, and heavy transport vehicles. However, the hydraulic return transmission system does not yet have a systematic design system, and the method for designing the key parameters of the hydraulic return transmission system and its matching method with the target vehicle are also not clear. Standardizing and improving the design system of the hydraulic return transmission system is of great significance for promoting the wide application of the hydraulic return transmission system and improving the manufacturing level of engineering vehicles in China. Summary of the Invention

[0003] The present invention aims to provide a method for designing key parameters of a hydraulic return transmission system, so as to provide a systematic key parameter design scheme for the hydraulic return transmission system, enable the hydraulic return transmission system to adapt to the complex operating conditions of different target engineering vehicles in a targeted manner, and give play to the potential performance advantages of the hydraulic return transmission system.

[0004] The present invention realizes the above object through the following technical solutions: A method for designing key parameters of a hydraulic return transmission system, comprising the following steps:

[0005] (1) Select the overall transmission ratio i of the fixed-axis gears in the hydraulic return transmission device n , the characteristic constant k of each planetary row in the compound planetary gear power shift transmission n , the overall transmission ratio i of the central transmission and the final drive Z , and the shift displacement ratio ε of each gear n as key parameters, and establish a 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 return transmission mode;

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

[0008] (4) According to the actual operating characteristics of the target engineering vehicle, establish the gear matching relationship between the target vehicle and the hydraulic return transmission system;

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

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

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

[0012] Furthermore, in step (5), the establishment of the objective function includes:

[0013] Calculate the average efficiency of the hydraulic return drive device under the return drive model, and establish the objective function f representing the starting efficiency of the hydraulic return drive system 1 , that is In the formula, τ is the displacement ratio control interval of the pump-motor closed-loop system corresponding to the hydraulic return drive device in the return drive mode; η HMCS1 represents the transmission efficiency of the hydraulic return drive device in the return drive mode;

[0014] Establish the objective function f representing the transmission efficiency in the main load operation interval of the hydraulic return drive system 2 , that is In the formula, vn and vn-1 respectively represent the upper and lower limits of the theoretical vehicle speed in each load operation interval of the target vehicle; η mn is the transmission efficiency of the compound planetary gear power shift transmission in the nth gear;

[0015] Establish the objective function f representing the transmission efficiency in the non-load operation interval 3 , that is

[0016]

[0017] In the formula, η HMCS2 represents the transmission efficiency of the hydraulic return drive device in the shunt drive mode; χn and χn-1 respectively represent the upper and lower limits of the theoretical vehicle speed of each gear in the speed regulation interval corresponding to the return drive mode in the non-load operation interval; κn and κn-1 respectively represent the upper and lower limits of the theoretical vehicle speed of each gear in the speed regulation interval corresponding to the shunt drive mode in the non-load operation interval;

[0018] Establish the objective function for the displacement ratio control stroke during gear shifting as f 4 , that is In the formula, Δε k is the displacement ratio control stroke of the pump-motor closed-loop system when the hydraulic return drive system shifts gears between the kth and k+1st gears; m is the actual number of gears of the hydraulic return drive system;

[0019] Establish the objective function f representing the torque multiplication coefficient 5 , that is Wherein, K is the torque increasing coefficient of the hydraulic return drive system.

[0020] Further, in step (7), determine the key design parameters, including:

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

[0022] Construct a selection judgment matrix for the objective function using the 1-5 scale method;

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

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

[0025] Based on the principle of maximizing the score, select the key structural parameters indicated by the decision variables;

[0026] Calculate the maximum adhesion force F of the target vehicle a , that is Wherein, 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 the variable displacement hydraulic component and the fixed displacement hydraulic component, while ensuring that the maximum theoretical traction force of the target vehicle is not lower than the maximum adhesion force, and the maximum pressure difference of the pump-motor closed system is not higher than 350 bar;

[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 . From n p , i n and the rated speed of the engine, determine the transmission ratio distribution of each fixed-axis gear in the hydraulic return drive device.

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

[0030] Furthermore, in step (3), determine the value range of the key design parameters, comprehensively considering the specific configuration of the hydraulic return drive device and the transmission power, operating speed, and operating characteristics of the target vehicle.

[0031] Further, in step (4), a gear position matching relationship between the target vehicle and the hydraulic return drive system is established, and the return drive mode of the hydraulic return drive system can always cover the load operation range of the target construction vehicle.

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

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

[0034] Taking the hydraulic return drive system as the service object, the present invention comprehensively considers various factors such as vehicle operation characteristics, transmission efficiency, torque increase coefficient, working efficiency, shift quality, and actual use quality, and provides a systematic key parameter design scheme for the hydraulic return drive system, standardizing and improving the design system of the hydraulic return drive system. The design method of the present invention can enable the hydraulic return drive system to specifically adapt to the complex operation conditions of different target construction vehicles, exert the potential performance advantages of the hydraulic return drive system, and improve the transmission performance of the construction vehicle to the greatest extent. The present invention is of great significance for promoting the wide application of the hydraulic return drive system and improving the manufacturing level of construction vehicles in China. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings without creative efforts based on these drawings.

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

[0037] Figure 2 is the transmission principle diagram of the hydraulic return drive system of the embodiment of the present invention;

[0038] In the figure: i1 and i2 are the gear transmission ratios of each stage of PHAT; k1 to k4 are the planetary row characteristic constants of the planetary gear trains PG1 to PG4; B1 is the first gear brake, B2 is the second gear brake, C1 is the third gear clutch, C2 is the forward direction clutch, and B3 is the reverse direction brake.

[0039] Figure 3 is the Pareto optimal solution set of the key design parameters of the hydraulic return drive system of the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0041] The present invention provides a method for designing key parameters of a hydraulic return drive system, as Figure 1 shown, including the following steps:

[0042] (1) Comprehensively considering the influence of structural parameters on the operating characteristics, transmission efficiency, torque multiplication coefficient, working efficiency, and shifting quality of the target vehicle, select the overall fixed-axis gear transmission ratio i n in the hydraulic return drive device, the characteristic constants k n of each planetary row in the compound planetary gear power shift transmission, the overall transmission ratio i Z of the central drive and final drive, and the shifting displacement ratio ε n of each gear as key parameters, and establish a decision vector x = [i n k n i Z ε n .

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

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

[0045] (4) According to the actual operating characteristics of the target engineering vehicle, establish the gear matching relationship between the target vehicle and the hydraulic return drive system.

[0046] (5) Using the integral mean value theorem, calculate the average efficiency of the hydraulic return drive device under the return drive model, and establish an objective function f 1 representing the starting efficiency of the hydraulic return drive system, that is where τ is the displacement ratio regulation interval of the pump-motor closed-loop system corresponding to the hydraulic return drive device under the return drive mode; η HMCS1 represents the transmission efficiency of the hydraulic return drive device under the return drive mode.

[0047] (6) Establish an objective function f 2 representing the transmission efficiency of the main load operation interval of the hydraulic return drive system, that is where vn and vn-1 respectively represent the upper and lower limits of the theoretical vehicle speed of each load operation interval of the target vehicle; η mnIt is the transmission efficiency of the compound planetary gear power shift transmission in the nth gear.

[0048] (7) Establish the objective function f that characterizes the transmission efficiency in the unloaded operation range 3 , that is

[0049]

[0050] In the formula, η HMCS2 represents the transmission efficiency of the hydraulic return transmission device in the split transmission mode; χn and χn-1 respectively represent the upper and lower limits of the theoretical vehicle speeds of each gear in the speed regulation range corresponding to the return transmission mode in the unloaded operation range; κn and κn-1 respectively represent the upper and lower limits of the theoretical vehicle speeds of each gear in the speed regulation range corresponding to the split transmission mode in the unloaded operation range.

[0051] (8) In order to ensure the shifting quality, establish the objective function for characterizing the displacement ratio control stroke during the shifting process as f 4 , that is In the formula, Δε k is the displacement ratio control stroke of the pump-motor closed system when the hydraulic return transmission system shifts between the kth gear and the k+1th gear; m is the actual number of gears of the hydraulic return transmission system.

[0052] (9) Establish the objective function f that characterizes the torque increase coefficient 5 , that is In the formula, K is the torque increase coefficient of the hydraulic return transmission system.

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

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

[0055] (12) Use the 1-5 scale method to construct the selection judgment matrix of the objective function.

[0056] (13) Use the geometric mean method to calculate the weight coefficient w of each objective function from the selection judgment matrix.

[0057] (14) Normalize the absolute values of the Pareto solution set; establish the scoring function Score and sort the normalized calculation results of the Pareto solution set; in the formula, h i is the function value of the objective function f i after normalization.

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

[0059] (16) Calculate the maximum adhesion force F of the target vehicle a , that is where G a is the vehicle mass of the target vehicle; is the maximum adhesion coefficient of the target vehicle.

[0060] (17) Take the principle 1 that the maximum theoretical traction force of the target vehicle is not less than the maximum adhesion force; take the principle 2 that the maximum pressure difference of the pump - motor closed - loop system is not higher than 350 bar. Based on the above two principles, preliminarily determine the specifications of the variable - displacement hydraulic component and the fixed - displacement hydraulic component.

[0061] (18) 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 . From n p , i n and the rated speed of the engine, determine the transmission ratio distribution of each fixed - axis gear in the hydraulic return drive device.

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

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

[0064] To further illustrate the effectiveness of the key parameter design method and matching method of the hydraulic return drive system described in this article, the present invention takes a certain model of 160 - horsepower hydro - mechanical crawler dozer as the target vehicle, and takes the Figure 2 shown hydraulic return drive system as an example to design its key design parameters and match them with the target vehicle. The specific design process is as follows:

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

[0066] x = [k 1 k 2 k 3 i 1 i 2 i Z ε1 ε 2 (1)

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

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

[0069] From Figure 2 it can be known that the speed regulation characteristics of this hydraulic return transmission system are

[0070]

[0071] wherein, iHM1, iHM2, and iHM3 respectively represent the speed ratios of the 1st, 2nd, and 3rd gears of the hydraulic return transmission system; k1, k2, and k3 are the planetary row characteristic constants of the planetary rows PG1, PG2, and PG3 respectively.

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

[0073]

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

[0075] According to the mechanical design theory, the value range of the planetary row characteristic constant of a common planetary row is k ∈ [1.5, 4]. In the vehicle transmission system, the transmission ratio of a single - stage external - meshing 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 layout of the pump - motor closed - loop system is relatively flexible, and the center distance of the fixed - axis gears in the hydraulic return transmission device can be adjusted more freely. Therefore, it is considered 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 component is generally equal to the rated displacement of the fixed - displacement hydraulic component, and from Figure 2 it can be seen that the shown transmission systems all shift gears in the shunt transmission mode. Thus, the value range of ε1 and ε2 can be determined as ε1, ε2 ∈ [-1, 0].

[0079] Step 4: Establish the gear - position matching relationship.

[0080] Referring to relevant materials, in the typical cyclic operation conditions of a bulldozer (cutting soil - pushing soil - unloading soil - returning empty), cutting soil and pushing soil are the main load conditions of the bulldozer. In the horsepower range where the target bulldozer is located, the cutting speed (theoretical vehicle speed) of the bulldozer is generally 2.5 - 3 km / h; under heavy load conditions, the pushing and cutting speeds of the bulldozer are basically the same; under light load conditions, the pushing speed of the bulldozer is generally 5 - 6 km / h. In addition, at the rated engine speed, the upper limits of the theoretical driving speeds of the target bulldozer in gears 1, 2, and 3 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 first gear of the hydraulic return drive system as the cutting gear, the second gear as the transition gear, and the third gear as the soil transportation gear.

[0081] In order to ensure the highest transmission efficiency while enabling the return drive mode of the hydraulic return drive system to always cover the load operation range of the target construction vehicle, it is necessary to restrict the driving speed of the hydraulic return drive system, that is

[0082]

[0083] where \(v_1\) and \(v_3\) are the theoretical vehicle speeds of the first and third gears of the hydraulic return drive system, in km / h.

[0084] Step Five: Establish the objective function \(f_1\) representing the starting efficiency of the hydraulic return drive system.

[0085]

[0086] Step Six: Establish the objective function \(f_2\) representing the efficiency of the main load operation range of the hydraulic return drive system.

[0087]

[0088] Step Seven: Establish the objective function \(f_3\) representing the efficiency of the 3 - 5 km / h transition range of the hydraulic return drive system.

[0089]

[0090] where \(\lambda\) is the target displacement ratio of PHAT when shifting from the first gear to the second gear.

[0091]

[0092] Step Eight: Establish the objective function \(f_4\) representing the control stroke of the displacement ratio during the shifting process.

[0093]

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

[0095] Step Nine: Establish the objective function f5 representing the average torque increase coefficient.

[0096]

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

[0098]

[0099] Step Eleven: 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 Equation (14). Set the population size to 50 and the number of genetic generations to 200. The Pareto solution set of the multi-objective optimization model obtained by solving is as Figure 3 shown.

[0100] Step Twelve: Construct a selection judgment matrix for the objective function using the 1-5 scale method.

[0101] As Figure 3 can be seen, the optimal solutions of the objective functions f1 and f2 can converge to a very small range, which indicates that each group of decision vectors in the population can make PHAT have similar efficiency characteristics. In the Pareto optimal solution set of the 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 greater than the starting requirement of the target vehicle. Therefore, when estimating the weight coefficients of the objective functions using the analytic hierarchy process, the importance of f1, f2, and f5 should be weakened. Based on the above viewpoints, a selection judgment matrix for the objective function is constructed using the 1-5 scale method as shown in Table 1.

[0102] Table 1. Selection Judgment Matrix

[0103]

[0104]

[0105] Step Thirteen: Calculate the weight coefficients of each objective function by the analytic hierarchy process (geometric mean) as

[0106] [w1 w2 w3 w4 w5] = [0.072 0.072 0.436 0.305 0.115] (15)

[0107] Wherein, w1 to w5 are the weight coefficients of the objective functions f1 to f5 respectively.

[0108] Step 14: Normalize the absolute values of the Pareto solution set, and score and sort them using the scoring function S.

[0109]

[0110] In the formula, 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, finally determine that the partial structural parameters of PHAT are: k1 = 2.040; k2 = 1.868; k3 = 2.071; i1i2 = 2.800; iZ = 29.045; ε1 = -0.184; ε2 = -0.215.

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

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

[0114]

[0115] In the formula, Ga is the total vehicle mass of the target bulldozer; is the adhesion coefficient of the tracked vehicle. It can be known from the literature that on the dry clay road surface, the tracked vehicle generally has the maximum adhesion coefficient.

[0116] Since the total machine mass of the target bulldozer is 16740 kg, the maximum adhesion force of the target vehicle is about 147.65 kN.

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

[0118] In order to meet the functional requirements of the hydraulic return drive system, the present invention preliminarily selects the Rexroth A4VG series variable-displacement axial piston pumps and Rexroth A2FM fixed-displacement axial piston motors 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 components and the fixed-displacement hydraulic components 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 component remains at 75% of its rated speed, the variable-displacement hydraulic component has a high transmission efficiency at most displacements, and the pump-motor closed-loop system has a fast response speed. Therefore, the transmission ratios i1 and i2 are determined as

[0124]

[0125] where ners is the rated engine speed, in rpm (ners = 1850 rpm); nvrs is the rated speed of the variable-displacement hydraulic component, in rpm (nvrs = 2850 rpm).

[0126] So far, 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 verified by comparing the theoretical traction characteristics of the hydraulic return bulldozer and the target bulldozer.

[0127] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to 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; Establishing the objective function includes: 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; (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 (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.

3. 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.

4. 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.

5. 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.

6. 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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