A method for obtaining PV value eccentric load distribution of differential planetary gear sliding bearing

Abstract

The present invention discloses a method for obtaining the PV value eccentric load distribution of a differential planetary gear sliding bearing, which belongs to the field of design and verification of the thermal load-bearing capacity of vehicle differentials. The present invention adopts a combined model of a Timoshenko beam and a finite number of clearance bearings to simulate the load distribution of the differential planetary pin hole, and then uses an analytical method to calculate its pressure distribution and PV value distribution based on the calculated load distribution, thereby solving the problems of complex modeling, difficult convergence, and cumbersome data post-processing brought about by the use of traditional three-dimensional solid finite element contact algorithms. The present invention can save a lot of computing time and R&D costs, and solve key data that cannot be tested by experiments. This provides an effective basis for the design and optimization of the thermal load-bearing capacity of differential gears, and also lays the foundation for achieving high efficiency and high power density of automobile differential assemblies.

Description

Technical Field

[0001] The present invention belongs to the field of design and verification of thermal load capacity of vehicle differentials, and in particular to a method for obtaining PV value eccentric load distribution of differential planetary gear sliding bearings. Background Art

[0002] Currently, the primary mode of differential failure in electric vehicles is severe adhesion caused by sliding friction between the planetary gears and the pins, leading to adhesion, tearing, or fracture of the planetary components. As electric vehicles demand ever-increasing power density in their electric drive systems, the geometric dimensions of the differential assembly have barely increased. The rotational friction between the planetary gears and the pins in the differential is equivalent to a hydrodynamic sliding bearing. However, this bearing lacks an oil filling port. Under high-speed, heavy-load differential operating conditions, it is virtually impossible to form a lubricating film, resulting in a starved lubrication state. This condition can cause adhesion failure even after a short duration.

[0003] In order to check the thermal load-bearing capacity of the sliding bearing in advance during the design stage, its PV value (the product of the bearing pressure P and the speed V) is generally calculated. Under the action of the meshing force of the planetary gears, the sliding bearing will be overloaded during operation. If the axial distribution of the load in the bearing shell is unclear, the PV value calculated using uniform load is obviously inconsistent with the actual situation, because bonding first occurs in the local area with the largest PV value, and then quickly spreads to the entire bearing shell.

[0004] Finite element analysis is a commonly used method to accurately calculate the load distribution and PV value distribution of the planetary gear pinhole mating surface under the action of gear meshing forces. However, the differential assembly has a high number of high-pair contacts (point-line contacts) during operation, making it difficult to achieve equilibrium convergence during static finite element iterations, and the calculation results are cumbersome to process. If the concept of finite element analysis can be applied to simplify the problem into a semi-analytical method for rapid iterative solution, it will significantly improve the technology of differential design and PV value calculation, reduce the number of experiments, and improve R&D efficiency. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem of calculating the bonding load capacity of the pin hole of the differential planetary gear, overcome the disadvantages of the traditional finite element method such as long simulation time, difficult convergence, and cumbersome data processing, and provide a method for obtaining the PV value eccentric load distribution of the differential planetary gear sliding bearing.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for obtaining PV value eccentric load distribution of a differential planetary gear sliding bearing comprises the following steps:

[0008] (1) Establish a differential gear model in the transmission system analysis software based on the differential design parameters; at the same time, establish the Timoshenko beam model of the planetary pin shaft, left and right half shafts, main reducer gear shaft, and gear blank;

[0009] (2) establishing a geometric model of the differential housing, dividing it into finite elements, and then importing it into the transmission system analysis software for assembly with the differential gear;

[0010] (3) Assemble the planetary gears to the planetary pins, and assemble the left and right half-shaft gears to the left and right half-shafts respectively to achieve meshing;

[0011] (4) A virtual planet carrier is built on the differential case. The axial position of the virtual planet carrier is the center of the planet pin hole. The planet pin shaft and planet gear are converted into planetary components and assembled on the virtual planet carrier.

[0012] (5) The rotating sliding contact between the planetary gear and the planetary pin is equivalent to a sliding bearing. The sliding bearing is discretized into m parts along the axial direction using the slicing method. A radial clearance bearing unit is established at each discretized sliding bearing, and a total of m clearance bearing units are established.

[0013] At the same time, the radial clearance value of each bearing is set to the actual fit clearance between the pin and the hole;

[0014] (6) Establish the left and right bearing units of the differential housing according to the actual bearing model, set the boundary constraints of the outer rings of the left and right bearing units, and ground the outer rings of the bearings or connect them to the gearbox housing;

[0015] (7) Determine and set the load condition based on the actual differential working condition of the vehicle, input the load to the main reduction gear position of the differential case in the transmission system analysis software, and output the differential load to the left and right half shafts;

[0016] (8) Perform static calculation in the transmission system analysis software, set the convergence conditions, and extract the radial load Fr of each of the m clearance bearings after iterative balance. i , calculate the average contact pressure p of each clearance bearing according to the sliding bearing theory i , the average contact pressure p i The eccentric load distribution in the planetary pin hole can be obtained by drawing a curve along the axial direction;

[0017] p i =Fr i / (D·L i ), i=1~m (1)

[0018] Where D is the inner diameter of the bearing, L i is the length of the stiffness bearing;

[0019] (9) Obtain the p of the planetary pin hole m sliding contact pairsi v-value:

[0020] p i v=π·n p ·Fr i / (60L i ), i=1~m (3)

[0021] Among them, n p is the rotation speed of the planetary gear; v is the relative sliding linear velocity between the pin hole and the pin shaft;

[0022] The p of the sliding contact pair i The v value is plotted into a curve along the axial direction to obtain the eccentric load distribution of the PV value in the planetary pin hole.

[0023] Furthermore, the method further includes step (10), wherein (10) calculating the load uneven distribution coefficient K in the planetary pin hole p and PV value unevenness coefficient K pv , load unevenness coefficient K p for:

[0024]

[0025] PV value unevenness coefficient K pv for:

[0026]

[0027] Furthermore, in step (9), the speed n of the planetary gear is calculated based on the speed difference between the two half-shaft gears under the vehicle differential working condition. p , based on the planetary gear speed n p The relative sliding linear velocity v between the pin hole and the pin shaft is obtained as:

[0028] v=π·D·n p / 60 (2).

[0029] Furthermore, the transmission system analysis software in step (1) is Romax or MASTA.

[0030] Furthermore, the transmission system analysis software in step (1) is an arbitrary solver having Timoshenko beam elements, clearance bearing elements and three-dimensional solid elements.

[0031] Furthermore, in step (2), the node density of the beam is set to have an aspect ratio less than 0.1.

[0032] Furthermore, in step (5), m is greater than or equal to the pin hole length L, and the unit of the pin hole length L is mm.

[0033] Furthermore, in step (8), the convergence conditions are set as force less than or equal to 1 N and displacement less than or equal to 0.05 μm.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The method for obtaining the PV value distribution of the planetary gear sliding bearing of the automobile differential of the present invention is used to simulate and calculate the degree of eccentricity of the planetary gear pin hole under different loads when the differential gear is in an eccentric differential working condition, and obtain the load distribution and PV value distribution, as well as the load unevenness coefficient and PV value unevenness coefficient. The method of the present invention can save a lot of computing time compared to traditional finite element methods, and obtain the thermal bearing capacity parameters of the differential pin hole that are consistent with the test results. By studying the distribution law of the PV value along the axial direction, the influence of different eccentricity degrees on the thermal bearing capacity and contact lubrication characteristics is revealed, which provides an effective reference basis for the design and optimization research of the thermal bearing capacity of the differential gear, and also lays the foundation for the automobile differential assembly to achieve high efficiency and high power density. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a flow chart of a method for obtaining PV value eccentric load distribution of a differential planetary gear sliding bearing according to the present invention;

[0037] Figure 2 A geometric model of a differential assembly, which is the subject of the calculation method of the present invention;

[0038] Figure 3 Discretize the sliding contact pair slices and establish m clearance bearing models for the present invention;

[0039] Figure 4 is the radial load distribution curve in the calculation result of the present invention, wherein, Figure 4 (a) is the force distribution diagram of the left pin hole, Figure 4 (b) is the force distribution diagram of the right pin hole. Figure 4 (c) is the pressure distribution diagram of the left pin hole, Figure 4 (d) is the pressure distribution diagram of the right pin hole;

[0040] Figure 5 is the PV value distribution curve in the calculation result of the present invention, wherein, Figure 5 (a) is the PV value distribution diagram of the left pin hole, Figure 5 (b) is the PV value distribution diagram of the right pin hole. DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the solutions of 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 embodiments described 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 making creative efforts should fall within the scope of protection of the present invention.

[0042] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0043] The present invention is described in further detail below with reference to the accompanying drawings:

[0044] See also Figure 1 , Figure 1 This is a flow chart of the present invention, a method for obtaining the PV value eccentric load distribution of a differential planetary gear sliding bearing, and the implementation steps are as follows:

[0045] (1) Establish a mathematical model of the differential gear pair in the transmission system analysis software Romax based on the differential design parameters;

[0046] (2) Establish the Timoshenko beam model of the planetary pin shaft, left and right half shafts, main reducer gear shaft, and gear blank and set the node density of the beam solution to an aspect ratio less than 0.1;

[0047] (3) Use UG software to build the geometric model of the differential housing, divide the mesh into a finite element model, and then export it into a Nastran (.dat / .bdf) format file, and then import it into the Romax model to replace the main reduction gear shaft;

[0048] (4) Assemble the planetary gears and half-shaft gears to the planetary pins and half-shafts respectively to achieve correct meshing;

[0049] (5) Create a virtual planet carrier on the differential housing, with the axial position at the center of the planet pin hole, and convert the planet pins and planet gears into planetary components and assemble them to the correct position on the virtual planet carrier;

[0050] (6) The rotating sliding contact between the planetary gear and the planetary pin is equivalent to a sliding bearing. The sliding bearing is discretized into m parts along the axial direction using the slicing method, so that m is greater than or equal to the pin hole length L (unit: mm). A radial clearance bearing unit is established at each small segment. A total of m clearance bearings need to be established, and the radial clearance (play) value of each bearing is set to the actual fit clearance between the pin and the hole;

[0051] (7) Establish the left and right bearing units of the differential housing according to the actual bearing model, and set the boundary constraints of the outer ring of the bearing. The outer ring can be grounded or connected to the gearbox housing;

[0052] (8) Determine and set the load conditions to be solved based on the actual differential working conditions of the vehicle, where the system input load is at the main reduction gear position of the differential case, and the differential output load is located at the left and right half shafts respectively;

[0053] (9) Set the convergence conditions as force less than or equal to 1N and displacement less than or equal to 0.05μm, perform static calculation, and extract the radial load Fr of each of the m clearance bearings after iterative balance. i (i = 1 ~ m), calculate the average contact pressure p of each short clearance bearing according to the sliding bearing theory i :

[0054] p i =Fr i / (D·L i ), i=1~m (1)

[0055] Where D is the inner diameter of the bearing, L i is the length of the clearance bearing, and by plotting it into a curve along the axial direction, the eccentric load distribution in the planetary pin hole can be obtained;

[0056] (10) According to the speed difference between the two half-shaft gears under the vehicle differential working condition, calculate the speed n of the planetary gear p , then the relative sliding linear velocity between the pin hole and the pin shaft can be obtained as:

[0057] v=π·D·n p / 60 (2)

[0058] (11) Calculate the PV value of the planetary pin hole m sliding contact pairs, which can be calculated by formula (3):

[0059] p i v=π·n p ·Fr i / (60L i ), i=1~m (3)

[0060] By plotting it into a curve along the axial direction, the eccentric load distribution of the PV value in the planetary pin hole can be obtained;

[0061] (12) Calculate the load uneven distribution coefficient in the planetary pin hole.

[0062] The load unevenness factor is:

[0063]

[0064] The PV value unevenness coefficient is:

[0065]

[0066] Example

[0067] See also Figure 2 , Figure 2 This is the geometric model of the differential assembly, which is the calculation object of the present invention. The differential assembly mainly consists of two planetary gears, two axle gears, a planetary pin, and a differential housing. The number of planetary gear teeth is 8, the number of axle gear teeth is 11, the module is 6.2mm, the pin diameter is 20mm, and the differential housing ball diameter is 90mm.

[0068] See also Figure 3 , Figure 3 Discretize the slices of the planetary gear pinhole and pin shaft sliding contact pair and create m clearance bearing models. In this example, the pinhole length is 22 mm, which is divided into 22 equal parts. Therefore, 23 clearance bearings are created, and the initial clearance is set to 0.1 mm. If the pinhole has a bulge, the clearance value can also be set according to the reshaping curve.

[0069] Set the load condition to 4000Nm for the differential housing torque (wheel end torque), 500rpm for the single-side planetary gear speed under the differential condition, set the iterative convergence conditions to force less than or equal to 1N and displacement less than or equal to 0.05mm, and then solve the calculation. The results are as follows: Figure 4 and Figure 5 See also Figure 4 , Figure 4 is the radial load distribution curve in the calculation result of the present invention, wherein, Figure 4 (a) is the force distribution diagram of the left pin hole, Figure 4 (b) is the force distribution diagram of the right pin hole. Figure 4 (c) is the pressure distribution diagram of the left pin hole, Figure 4 (d) is the pressure distribution diagram of the right pin hole; see Figure 5 , Figure 5 is the PV value distribution curve in the calculation result of the present invention, wherein, Figure 5 (a) is the PV value distribution diagram of the left pin hole, Figure 5 (b) is the PV value distribution diagram of the right pin hole.

[0070] This invention uses a combined model of a Timoshenko beam and a finite number of clearance bearings to simulate the load distribution of the differential planetary pinhole. Based on the calculated load distribution, analytical methods are used to calculate the pressure distribution and PV value distribution. This solves the problems associated with traditional three-dimensional solid finite element contact algorithms, such as complex modeling, difficult convergence, and cumbersome data post-processing. This invention can significantly save computing time and R&D costs, and can address critical data that cannot be measured experimentally. This provides an effective basis for the design and optimization of the thermal load capacity of differential gears and lays the foundation for achieving high efficiency and high power density in automotive differential assemblies.

[0071] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for obtaining the PV value eccentric load distribution of a differential planetary gear sliding bearing, characterized in that: The following steps are involved: (1) Establish a differential gear model in the transmission system analysis software based on the differential design parameters; at the same time, establish the Timoshenko beam model of the planetary pin shaft, left and right half shafts, main reducer gear shaft, and gear blank; (2) establishing a geometric model of the differential housing, dividing it into finite elements, and then importing it into the transmission system analysis software for assembly with the differential gear; (3) Assemble the planetary gears to the planetary pins, and assemble the left and right half-shaft gears to the left and right half-shafts respectively to achieve meshing; (4) A virtual planet carrier is built on the differential case. The axial position of the virtual planet carrier is the center of the planet pin hole. The planet pin shaft and planet gear are converted into planetary components and assembled on the virtual planet carrier. (5) The rotational sliding contact between the planetary gear and the planetary pin is equivalent to a sliding bearing, and the sliding bearing is discretized into m parts along the axial direction using a slicing method. A radial clearance bearing unit is established at each discretized sliding bearing, and a total of m clearance bearing units are established; At the same time, the radial clearance value of each bearing is set to the actual fit clearance between the pin and the hole; (6) Establish the left and right bearing units of the differential housing according to the actual bearing model, set the boundary constraints of the outer rings of the left and right bearing units, and ground the outer rings of the bearings or connect them to the gearbox housing; (7) Determine and set the load condition based on the actual differential working condition of the vehicle, input the load to the main reduction gear position of the differential case in the transmission system analysis software, and output the differential load to the left and right half shafts; (8) Perform static calculation in the transmission system analysis software, set the convergence conditions, and extract the radial load Fr of each of the m clearance bearings after iterative balance. i , according to the sliding bearing theory, calculate the average contact pressure p of each clearance bearing i , the average contact pressure p i The eccentric load distribution in the planetary pin hole can be obtained by drawing a curve along the axial direction; p i =Fr i / (D·L i ),i=1~m (1) Where D is the inner diameter of the bearing, L i is the length of the stiffness bearing; (9) Obtain the p of the planetary pin hole m sliding contact pairs i v-value: p i v=π·n p ·Fr i / (60L i ),i=1~m (3) Among them, n p is the rotation speed of the planetary gear; v is the relative sliding linear velocity between the pin hole and the pin shaft; The p of the sliding contact pair i The v value is plotted into a curve along the axial direction to obtain the eccentric load distribution of the PV value in the planetary pin hole.

2. The method for obtaining the PV value eccentric load distribution of a differential planetary gear sliding bearing according to claim 1, characterized in that: The step (10) is also included, wherein the load uneven distribution coefficient K in the planetary pin hole is calculated. p and PV value unevenness coefficient K pv , load unevenness coefficient K p for: PV value unevenness coefficient K pv for:

3. The method for obtaining the PV value eccentric load distribution of a differential planetary gear sliding bearing according to claim 1, characterized in that: In step (9), the speed n of the planetary gear is calculated based on the speed difference between the two half-shaft gears under the vehicle differential working condition. p , based on the planetary gear speed n p The relative sliding linear velocity v between the pin hole and the pin shaft is obtained as: v=v·D·n p / 60 (2)。 4. The method for obtaining the PV value eccentric load distribution of a differential planetary gear sliding bearing according to claim 1, characterized in that: The transmission system analysis software in step (1) is Romax or MASTA.

5. The method for obtaining the PV value eccentric load distribution of a differential planetary gear sliding bearing according to claim 1, characterized in that: The transmission system analysis software in step (1) is an arbitrary solver having Timoshenko beam units, clearance bearing units and three-dimensional solid units.

6. The method for obtaining the PV value eccentric load distribution of a differential planetary gear sliding bearing according to claim 1, characterized in that: In step (2), the node density of the beam solution is set to an aspect ratio less than 0.

1.

7. The method for obtaining the PV value eccentric load distribution of a differential planetary gear sliding bearing according to claim 1, characterized in that: In step (5), m is greater than or equal to the pin hole length L, and the unit of the pin hole length L is mm.

8. The method for obtaining the PV value eccentric load distribution of a differential planetary gear sliding bearing according to claim 1, characterized in that: In step (8), the convergence conditions are set as force less than or equal to 1 N and displacement less than or equal to 0.05 μm.

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