Commercial vehicle gearbox center distance estimation method and device, gearbox and vehicle

Abstract

The invention belongs to the technical field of gearboxes for commercial vehicles, and particularly provides a commercial vehicle gearbox center distance estimation method and device, a gearbox and a vehicle. The method comprises the following steps that the structure of the gearbox is determined; comprising an integral structure and a combined structure. Constructing a center distance calculation initial model according to a gear meshing transmission principle; establishing a relationship between the gear calculation contact stress and the center distance by combining a center distance calculation initial model; performing parameter transformation on the initial center distance calculation model according to the relationship between the calculated contact stress and the center distance to obtain a final center distance calculation model; calculating the value of each parameter in the center distance calculation model according to the structure of the gearbox; and inputting the value of each parameter into a center distance calculation model to calculate the center distance of the gearbox. By constructing the center distance calculation model, the method can accurately and quickly estimate the center distance of the gearbox, the tedious trial and error process in a traditional method is avoided, the gearbox design efficiency and precision are improved, the product development period is shortened, and the development cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of commercial vehicle gearboxes, and in particular to a method and device for estimating the center distance of a commercial vehicle gearbox, a gearbox and a vehicle. Background Art

[0002] The gearbox center distance is the length of the common perpendicular segment between the axes of the two gears in a parallel axis gear pair. This parameter is crucial to the design of the gearbox because it not only determines the overall shape and size of the transmission, but also directly affects its cost-effectiveness. When the input and output torques are constant, the reduction of the center distance can significantly reduce the overall size of the gearbox, thereby reducing manufacturing costs. The determination of the center distance mainly depends on the gear with the largest torque multiplication factor (usually the first gear ratio), and once determined on the gearbox housing, it cannot be changed, so accurate prediction at the beginning of the design is particularly important.

[0003] At present, the evaluation of the gearbox center distance mainly relies on personal experience and comparison with existing similar gearboxes. Although this method is simple, it has obvious shortcomings. Due to the lack of scientific quantitative analysis and accurate data support, it often leads to large deviations in the initial estimation of the gearbox weight and cost.

[0004] Inaccurate center distance assessment may lead to multiple iterations and adjustments in the gearbox design process, which not only increases the design cycle and cost, but may also affect the final performance and quality of the product. Summary of the invention

[0005] In view of the problems existing in the gearbox center distance evaluation in the prior art, the present invention provides a method and device for estimating the gearbox center distance of a commercial vehicle, a gearbox and a vehicle.

[0006] In a first aspect, the technical solution of the present invention provides a method for estimating the center distance of a commercial vehicle gearbox, comprising the following steps: Determine the structure of the gearbox; including integral structure and combined structure; Construct an initial model for center distance calculation based on the gear meshing transmission principle; Combined with the initial model for center distance calculation, the relationship between gear contact stress and center distance is established; According to the relationship between the calculated contact stress and the center distance, the parameters of the initial center distance calculation model are transformed to obtain the final center distance calculation model; Calculating the values ​​of various parameters in the center distance calculation model according to the structure of the gearbox; Input the values ​​of each parameter into the center distance calculation model to calculate the gearbox center distance.

[0007] As a further limitation of the technical solution of the present invention, in the step of constructing an initial model for calculating the center distance according to the gear meshing transmission principle, the initial model for calculating the center distance is: ; , ; ; ; In the formula, is the center distance, is the pitch diameter of the first gear gear of the countershaft, is the pitch diameter of the first gear of the main shaft, is the pitch circle diameter of the first gear of the countershaft, is the pitch circle diameter of the first gear of the main shaft, is the meshing angle of the first gear pair end face, is the end face pressure angle of the first gear pair, It is the transmission ratio of the first gear pair.

[0008] As a further limitation of the technical solution of the present invention, the step of establishing the relationship between the gear contact stress and the center distance in combination with the initial model for center distance calculation includes: Gear contact stress calculation model derived from Hertz contact theory

[0009]

[0010] in, ; Combining the initial model for center distance calculation and the tangential force of the first gear of the countershaft, the relationship between the calculated contact stress and the center distance of the gear is obtained.

[0011]

[0012] In the formula, Calculate the contact stress for the first gear. is the load per unit length on the contact wire, is the Poisson's ratio of the countershaft first gear material, is the Poisson's ratio of the main shaft first gear material, is the elastic modulus of the material of the countershaft first gear, is the elastic modulus of the main shaft first gear material, is the comprehensive curvature radius of the meshing point on the meshing tooth surface, is the normal curvature radius of the countershaft first gear node, is the normal curvature radius of the main shaft first gear gear node, is the helix angle of the base circle of the first gear pair, is the secondary shaft torque, is the meshing tooth width of the first gear pair, is the material coefficient, is the node area coefficient, is the coincidence coefficient, is the roughness coefficient, is the lubrication speed coefficient, is the dynamic load coefficient.

[0013] As a further limitation of the technical solution of the present invention, in the step of performing parameter transformation on the initial center distance calculation model according to the relationship between the contact stress and the center distance to obtain the final center distance calculation model, the final center distance calculation model is:

[0014] In the formula, is the engine torque, is the transmission ratio of the constant mesh gear pair, is the safety factor, is the allowable contact stress.

[0015] As a further limitation of the technical solution of the present invention, the step of calculating the values ​​of the parameters in the center distance calculation model according to the structure of the gearbox includes: The material coefficient is calculated according to the elastic modulus of the material of the countershaft first gear, the elastic modulus of the material of the main shaft first gear and the transmission ratio of the first gear pair; Calculate the node area factor based on the end pressure angle and base circle helix angle; The end face meshing angle is calculated based on the backlash-free meshing condition of the variable displacement gear transmission.

[0016] As a further limitation of the technical solution of the present invention, the step of calculating the values ​​of the parameters in the center distance calculation model according to the structure of the gearbox also includes: The allowable contact stress value is set according to the gearbox structure, wherein the allowable contact stress value of the combined gearbox is smaller than the allowable contact stress value of the integral gearbox.

[0017] In a second aspect, the technical solution of the present invention provides a commercial vehicle gearbox center distance estimation device, including a structure determination unit, an initial model construction unit, a relationship establishment unit, a model transformation processing unit, a parameter acquisition unit and an execution unit; A structure determination unit, used to determine the structure of the gearbox; including an integral structure and a combined structure; An initial model building unit, used to build an initial model for center distance calculation according to the gear meshing transmission principle; A relationship building unit is used to build the relationship between the gear calculation contact stress and the center distance in combination with the initial model for center distance calculation; A model transformation processing unit is used to perform parameter transformation on the initial model for center distance calculation according to the relationship between the calculated contact stress and the center distance, so as to obtain a final center distance calculation model; A parameter acquisition unit, used to calculate the value of each parameter in the center distance calculation model according to the structure of the gearbox; The execution unit is used to input the values ​​of various parameters into the center distance calculation model to calculate the center distance of the gearbox.

[0018] As a further limitation of the technical solution of the present invention, the initial model for center distance calculation is: ; , ; ; ; In the formula, is the center distance, is the pitch diameter of the first gear gear of the countershaft, is the pitch diameter of the first gear of the main shaft, is the pitch circle diameter of the first gear of the countershaft, is the pitch circle diameter of the first gear of the main shaft, is the meshing angle of the first gear pair end face, is the end face pressure angle of the first gear pair, It is the transmission ratio of the first gear pair.

[0019] As a further limitation of the technical solution of the present invention, the gear contact stress calculation model is derived from the Hertz contact theory

[0020]

[0021] in, ; Combining the initial model for center distance calculation and the tangential force of the first gear of the countershaft, the relationship between the calculated contact stress and the center distance of the gear is obtained.

[0022]

[0023] In the formula, Calculate the contact stress for the first gear. is the load per unit length on the contact wire, is the Poisson's ratio of the countershaft first gear material, is the Poisson's ratio of the main shaft first gear material, is the elastic modulus of the material of the countershaft first gear, is the elastic modulus of the main shaft first gear material, is the comprehensive curvature radius of the meshing point on the meshing tooth surface, is the normal curvature radius of the countershaft first gear node, is the normal curvature radius of the main shaft first gear gear node, is the helix angle of the base circle of the first gear pair, is the secondary shaft torque, is the meshing tooth width of the first gear pair, is the material coefficient, is the node area coefficient, is the coincidence coefficient, is the roughness coefficient, is the lubrication speed coefficient, is the dynamic load coefficient.

[0024] As a further limitation of the technical solution of the present invention, the center distance calculation model is:

[0025] In the formula, is the engine torque, is the transmission ratio of the constant mesh gear pair, is the safety factor, is the allowable contact stress, is the meshing tooth width of the first gear pair, is the material coefficient, is the node area coefficient, is the coincidence coefficient, is the roughness coefficient, is the lubrication speed coefficient, is the dynamic load coefficient, is the pitch circle diameter of the first gear of the countershaft, is the meshing angle of the first gear pair end face, is the end face pressure angle of the first gear pair, It is the transmission ratio of the first gear pair.

[0026] As a further limitation of the technical solution of the present invention, the parameter acquisition unit is specifically used to calculate the material coefficient according to the elastic modulus of the material of the first gear of the secondary shaft, the elastic modulus of the material of the first gear of the main shaft and the transmission ratio of the first gear pair; calculate the node area coefficient based on the end face pressure angle and the base circle helix angle; calculate the end face meshing angle according to the backlash-free meshing condition of the shifted gear transmission; set the allowable contact stress value according to the gearbox structure, wherein the allowable contact stress value of the combined gearbox is less than the allowable contact stress value of the integral gearbox.

[0027] In a third aspect, the technical solution of the present invention provides a gearbox, which is a gearbox designed by the commercial vehicle gearbox center distance estimation method as described in the first aspect.

[0028] In a fourth aspect, the technical solution of the present invention further provides a vehicle, comprising the gearbox as described in the third aspect.

[0029] It can be seen from the above technical solutions that the present invention has the following advantages: by constructing a center distance calculation model, the method can accurately and quickly estimate the center distance of the gearbox, avoiding the tedious trial and error process in the traditional method, improving the efficiency and accuracy of the gearbox design, and helping to shorten the product development cycle and reduce development costs. Taking into account the different structures that may exist in the gearbox (integral and combined), the method of the present invention provides a flexible calculation framework that can adjust the calculation parameters according to different structural characteristics, ensuring the wide applicability and accuracy of the estimation results. Combined with the principle of gear meshing transmission, this method establishes a direct relationship between the calculated contact stress of the gear and the center distance, which helps to fully consider the force and wear conditions of the gear in the design stage, thereby optimizing the gear parameter design and improving the overall performance and life of the gearbox.

[0030] By accurately calculating the gearbox center distance, the spatial layout and matching accuracy of the internal components of the gearbox can be better controlled, the occurrence of failures caused by assembly errors or improper design can be reduced, and the reliability and stability of vehicle operation can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] 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, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 is a schematic flow chart of a method according to an embodiment of the present invention.

[0033] Figure 2 is the normal radius of curvature End face curvature radius Relationship diagram.

[0034] Figure 3 It is a diagram showing the b / d estimation of existing automobile transmissions.

[0035] Figure 4 is a schematic block diagram of an apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0037] like Figure 1 As shown, an embodiment of the present invention provides a method for estimating the center distance of a commercial vehicle gearbox, comprising the following steps: Step 1: Determine the structure of the gearbox; The gearbox is divided into integral structure and combined structure; different structure gearboxes have different working conditions. For example, the combined first gear is divided into high-speed area and low-speed area, which has a higher frequency of use and a lower standard value of allowable contact stress. Different structures are selected in different programs for separate consideration, which makes the calculation more accurate.

[0038] Step 2: Construct an initial model for center distance calculation based on the gear meshing transmission principle; It should be noted that, for the involute helical gear, the normal curvature radius of the base cylinder 101 at the node P in the meshing plane 102 is End face curvature radius Relationship Figure 2 shown.

[0039] Normal curvature radius ; Curvature radius of the node of the helical gear end face ; The relationship between the pitch circle diameter and the reference circle diameter:

[0040]

[0041] The relationship between gear ratio and diameter gives the transmission ratio of the first gear pair ; Calculation of the comprehensive curvature radius of the meshing point on the meshing tooth surface :

[0042] Positive pressure on tooth surface ; Determination of the total length L of the contact line: Total length of the contact line With gear width , Base circle helix angle , gear end face overlap , axial overlap When considering the influence of gear end face overlap and axial overlap, the relationship between them can be expressed by the following formula:

[0043] In the formula, It is called the coincidence coefficient. For the convenience of formula expression, it will be moved outside the square root in the calculation formula for contact stress value.

[0044] Since the contact line is tilted at an angle , so the total length of the contact line It can be determined according to the following formula based on the load-bearing tooth width;

[0045] Calculated load per unit length on the contact wire ; The basic expression of gear contact stress obtained from Hertz contact theory is:

[0046] The gear tooth manufacturing errors that affect the dynamic load of the gear are the base pitch error and the tooth profile error. The former affects the meshing and meshing process, and the latter affects the meshing process. In addition, the load distribution between the meshing teeth is not uniform. The tooth surface roughness grade and the state of the lubricating oil film between the tooth surfaces have a great influence on the tooth surface contact strength and bearing capacity of the gear. Therefore, when calculating the gear transmission strength, the dynamic load coefficient must also be introduced. .

[0047] According to the above formulas, the formula for calculating the contact stress of the gear is obtained:

[0048] According to the gear meshing transmission principle, the center distance value is always equal to the sum of the two pitch circle radii of the gear pair; , , The relationship between the pitch circle diameter and center distance of the first gear of the countershaft is: ; Step 3: Establish the relationship between the gear contact stress and the center distance by combining the initial model for center distance calculation; The tangential force of the first gear of the countershaft is calculated based on the following formula ; From the above formula, we can get the relationship between the contact stress and center distance of the first gear:

[0049] In the formula, Calculate the contact stress for the first gear. is the load per unit length on the contact wire, is the Poisson's ratio of the countershaft first gear material, is the Poisson's ratio of the main shaft first gear material, is the elastic modulus of the material of the countershaft first gear, is the elastic modulus of the main shaft first gear material, is the comprehensive curvature radius of the meshing point on the meshing tooth surface, is the normal curvature radius of the countershaft first gear node, is the normal curvature radius of the main shaft first gear gear node, is the helix angle of the base circle of the first gear pair, is the secondary shaft torque, is the meshing tooth width of the first gear pair, is the material coefficient, is the node area coefficient, is the coincidence coefficient, is the roughness coefficient, is the lubrication speed coefficient, is the dynamic load coefficient.

[0050] Step 4: Perform parameter transformation on the initial center distance calculation model according to the relationship between the calculated contact stress and the center distance to obtain the final center distance calculation model; Allowable contact stress of first gear ; Countershaft torque ; According to the above formula, the final center distance calculation formula is;

[0051] In the formula, is the engine torque, is the transmission ratio of the constant mesh gear pair, is the safety factor, is the allowable contact stress.

[0052] Step 5: Calculate the values ​​of various parameters in the center distance calculation model according to the structure of the gearbox; The material coefficient is calculated based on the following formula:

[0053] Usually a pair of gears are made of the same material, and the corresponding carburizing steel is usually ( , ); The node area coefficient is calculated based on the following formula:

[0054] According to the helical gear meshing principle, the end face pressure angle and base circle helix angle are calculated by the following formula:

[0055]

[0056] According to the backlash-free meshing condition of the variable gear transmission: the tooth thickness on one gear pitch circle is equal to the tooth width on the other gear pitch circle. Calculate the end face meshing angle :

[0057]

[0058]

[0059] in, Respectively For convenience, the involute function of different pressure angles has been listed in a table in the project for reference, and the relevant gear-related books or manuals are more convenient for the algorithm, which is obtained by numerical calculation method.

[0060] Calculation of point area coefficient: The node area coefficient is important for center distance calculation, and involves the selection of helix angle, pressure angle, and total transformation coefficient.

[0061] The contact stress and bending stress of the first gear are relatively large. According to the influence of pressure angle, helix angle and total transformation coefficient on gear stress. Considering the effect of axial force of helical gear on bearing, the helix angle is taken as , when the first gear is a straight gear A larger pressure angle can achieve better bending and contact strength, but a too large pressure angle can easily make the gear tooth tip too sharp and cause more noise. ; Positive displacement is beneficial to gear bending and contact strength, but too large displacement coefficient will make the gear tooth tip sharp, so =0.015 is more appropriate. Based on the above analysis, it is recommended to use the following numerical combination to calculate the node area coefficient, and the results are as follows: when =0.015 when =0.015 A confirmed actual value is used for the tooth width diameter ratio b / d. In order to reduce uneven tooth surface wear, a different value should be selected for each gear. Figure 3 The b / d estimation of existing automobile transmissions is given, based on Figure 3Combined with the previous statistical data, the tooth width diameter ratio of the countershaft first gear is selected as , contact coefficient helical gear , spur gear , roughness coefficient , lubrication coefficient , dynamic load coefficient , safety factor .

[0062] In actual transmission, due to the influence of the prime mover performance, the load will increase, thus affecting the bearing capacity of the gear. Therefore, the safety factor must be considered. If the safety factor is too large, the cost will increase, and if the safety factor is too small, the gear life will be affected.

[0063] According to previous data, the first-level contact stress allowable value : The first gear of the combined transmission main box is used in both high and low gears, so the number of cycles is large and the permissible contact stress is small. However, the first gear of the integral transmission is only used when starting or climbing, so the permissible contact stress can be large.

[0064] Combined gearbox ; Integral gearbox .

[0065] Step 6: Input the values ​​of each parameter into the center distance calculation model to calculate the gearbox center distance.

[0066] In the embodiment of the present invention, it is proposed to directly use the formula method to calculate the gear end face meshing angle, thereby calculating the node area coefficient, without manually querying from the chart, and the node area coefficient can be calculated more accurately and quickly. It is proposed that the large pressure angle and small helix angle of the first gear are more suitable for determining the center distance. The contact fatigue life is enhanced, the axial force of the gear is reduced, and the bearing life is enhanced.

[0067] like Figure 4 As shown, the technical solution of the present invention provides a commercial vehicle gearbox center distance estimation device, including a structure determination unit, an initial model construction unit, a relationship establishment unit, a model transformation processing unit, a parameter acquisition unit and an execution unit; A structure determination unit, used to determine the structure of the gearbox; including an integral structure and a combined structure; An initial model building unit, used to build an initial model for center distance calculation according to the gear meshing transmission principle; A relationship building unit is used to build the relationship between the gear calculation contact stress and the center distance in combination with the initial model for center distance calculation; A model transformation processing unit is used to perform parameter transformation on the initial model for center distance calculation according to the relationship between the calculated contact stress and the center distance, so as to obtain a final center distance calculation model; A parameter acquisition unit, used to calculate the value of each parameter in the center distance calculation model according to the structure of the gearbox; The execution unit is used to input the values ​​of various parameters into the center distance calculation model to calculate the center distance of the gearbox.

[0068] In some embodiments, the initial model for center distance calculation is: ; , ; ; ; In the formula, is the center distance, is the pitch diameter of the first gear gear of the countershaft, is the pitch diameter of the first gear of the main shaft, is the pitch circle diameter of the first gear of the countershaft, is the pitch circle diameter of the first gear of the main shaft, is the meshing angle of the first gear pair end face, is the end face pressure angle of the first gear pair, It is the transmission ratio of the first gear pair.

[0069] In some embodiments, the gear contact stress calculation model is derived from the Hertz contact theory.

[0070]

[0071] in, ; Combining the initial model for center distance calculation and the tangential force of the first gear of the countershaft, the relationship between the calculated contact stress and the center distance of the gear is obtained.

[0072]

[0073] In the formula, Calculate the contact stress for the first gear. is the load per unit length on the contact wire, is the Poisson's ratio of the countershaft first gear material, is the Poisson's ratio of the main shaft first gear material, is the elastic modulus of the material of the countershaft first gear, is the elastic modulus of the main shaft first gear material, is the comprehensive curvature radius of the meshing point on the meshing tooth surface, is the normal curvature radius of the countershaft first gear node, is the normal curvature radius of the main shaft first gear gear node, is the helix angle of the base circle of the first gear pair, is the secondary shaft torque, is the meshing tooth width of the first gear pair, is the material coefficient, is the node area coefficient, is the coincidence coefficient, is the roughness coefficient, is the lubrication speed coefficient, is the dynamic load coefficient.

[0074] In some embodiments, the center distance calculation model is:

[0075] In the formula, is the engine torque, is the transmission ratio of the constant mesh gear pair, is the safety factor, is the allowable contact stress, is the meshing tooth width of the first gear pair, is the material coefficient, is the node area coefficient, is the coincidence coefficient, is the roughness coefficient, is the lubrication speed coefficient, is the dynamic load coefficient, is the pitch circle diameter of the first gear of the countershaft, is the meshing angle of the first gear pair end face, is the end face pressure angle of the first gear pair, It is the transmission ratio of the first gear pair.

[0076] In some embodiments, the parameter acquisition unit is specifically used to calculate the material coefficient based on the elastic modulus of the material of the first gear of the secondary shaft, the elastic modulus of the material of the first gear of the main shaft, and the transmission ratio of the first gear secondary gear; calculate the node area coefficient based on the end face pressure angle and the base circle helix angle; calculate the end face meshing angle according to the backlash-free meshing condition of the shifted gear transmission; set the allowable contact stress value according to the gearbox structure, wherein the allowable contact stress value of the combined gearbox is smaller than the allowable contact stress value of the integral gearbox.

[0077] An embodiment of the present invention provides a gearbox, which is designed by the commercial vehicle gearbox center distance estimation method as described in the above embodiment.

[0078] An embodiment of the present invention further provides a vehicle, comprising the gearbox as described in the above embodiment.

[0079] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0080] An embodiment of a commercial vehicle gearbox center distance estimation device provided in an embodiment of the present invention belongs to the same inventive concept as the commercial vehicle gearbox center distance estimation method of the above-mentioned embodiments. For details not described in detail in the embodiment of the commercial vehicle gearbox center distance estimation device, reference can be made to the embodiment of the above-mentioned commercial vehicle gearbox center distance estimation method.

[0081] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A method for estimating the center distance of a commercial vehicle gearbox, characterized in that: The steps include: Determine the structure of the gearbox; including integral structure and combined structure; Construct an initial model for center distance calculation based on the gear meshing transmission principle; Combined with the initial model for center distance calculation, the relationship between gear contact stress and center distance is established; According to the relationship between the calculated contact stress and the center distance, the parameters of the initial center distance calculation model are transformed to obtain the final center distance calculation model; Calculating the values ​​of various parameters in the center distance calculation model according to the structure of the gearbox; Input the values ​​of each parameter into the center distance calculation model to calculate the gearbox center distance.

2. The commercial vehicle gearbox center distance estimation method according to claim 1, characterized in that: In the step of constructing the initial model for center distance calculation according to the gear meshing transmission principle, the initial model for center distance calculation is: ; ， ； ； ； In the formula, is the center distance, is the pitch diameter of the first gear gear of the countershaft, is the pitch diameter of the first gear of the main shaft, is the pitch circle diameter of the first gear of the countershaft, is the pitch circle diameter of the first gear of the main shaft, is the meshing angle of the first gear pair end face, is the end face pressure angle of the first gear pair, It is the transmission ratio of the first gear pair.

3. The commercial vehicle gearbox center distance estimation method according to claim 2, characterized in that: The steps of establishing the relationship between the contact stress and the center distance of the gear in combination with the initial model for center distance calculation include: Gear contact stress calculation model derived from Hertz contact theory in, ; Combining the initial model for center distance calculation and the tangential force of the first gear of the countershaft, the relationship between the calculated contact stress and the center distance of the gear is obtained. In the formula, Calculate the contact stress for the first gear. is the load per unit length on the contact wire, is the Poisson's ratio of the countershaft first gear material, is the Poisson's ratio of the main shaft first gear material, is the elastic modulus of the material of the countershaft first gear, is the elastic modulus of the main shaft first gear material, is the comprehensive curvature radius of the meshing point on the meshing tooth surface, is the normal curvature radius of the countershaft first gear node, is the normal curvature radius of the main shaft first gear gear node, is the helix angle of the base circle of the first gear pair, is the secondary shaft torque, is the meshing tooth width of the first gear pair, is the material coefficient, is the node area coefficient, is the coincidence coefficient, is the roughness coefficient, is the lubrication speed coefficient, is the dynamic load coefficient.

4. The commercial vehicle gearbox center distance estimation method according to claim 3, characterized in that: According to the relationship between contact stress and center distance, the initial center distance calculation model is transformed in parameters to obtain the final center distance calculation model. The final center distance calculation model is: In the formula, is the engine torque, is the transmission ratio of the constant mesh gear pair, is the safety factor, is the allowable contact stress.

5. The commercial vehicle gearbox center distance estimation method according to claim 4, characterized in that: The step of calculating the values ​​of the parameters in the center distance calculation model according to the structure of the gearbox includes: The material coefficient is calculated according to the elastic modulus of the material of the countershaft first gear, the elastic modulus of the material of the main shaft first gear and the transmission ratio of the first gear pair; Calculate the node area factor based on the end pressure angle and base circle helix angle; The end face meshing angle is calculated based on the backlash-free meshing condition of the variable displacement gear transmission.

6. The commercial vehicle gearbox center distance estimation method according to claim 5, characterized in that: The step of calculating the values ​​of the parameters in the center distance calculation model according to the structure of the gearbox also includes: The allowable contact stress value is set according to the gearbox structure, wherein the allowable contact stress value of the combined gearbox is smaller than the allowable contact stress value of the integral gearbox.

7. A device for estimating the center distance of a commercial vehicle gearbox, characterized in that: It includes a structure determination unit, an initial model building unit, a relationship establishment unit, a model transformation processing unit, a parameter acquisition unit and an execution unit; A structure determination unit, used to determine the structure of the gearbox; including an integral structure and a combined structure; An initial model building unit, used to build an initial model for center distance calculation according to the gear meshing transmission principle; A relationship building unit is used to build the relationship between the gear calculation contact stress and the center distance in combination with the initial model for center distance calculation; A model transformation processing unit is used to perform parameter transformation on the initial model for center distance calculation according to the relationship between the calculated contact stress and the center distance, so as to obtain a final center distance calculation model; A parameter acquisition unit, used to calculate the value of each parameter in the center distance calculation model according to the structure of the gearbox; The execution unit is used to input the values ​​of various parameters into the center distance calculation model to calculate the center distance of the gearbox.

8. The device for estimating the center distance of a commercial vehicle transmission according to claim 7, characterized in that: The parameter acquisition unit is specifically used to calculate the material coefficient according to the elastic modulus of the countershaft first gear material, the elastic modulus of the main shaft first gear material and the first gear gear ratio; calculate the node area coefficient based on the end face pressure angle and the base circle helix angle; Calculate the end face meshing angle according to the backlash-free meshing condition of the variable gear transmission; The allowable contact stress value is set according to the gearbox structure, wherein the allowable contact stress value of the combined gearbox is smaller than the allowable contact stress value of the integral gearbox.

9. A gearbox, characterized in that: The gearbox is a gearbox designed by the commercial vehicle gearbox center distance estimation method as described in any one of claims 1 to 6.

10. A vehicle, characterized in that: The vehicle comprises a transmission as claimed in claim 9.

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