A method for designing the play of a ball bearing of an electric drive system

Abstract

This invention discloses a clearance design method for ball bearings in electric drive systems, belonging to the field of mechanical structure design technology. It aims to solve the technical problems of low clearance matching accuracy, insufficient bearing reliability, and poor end-product quality consistency caused by insufficient coupling of key influencing factors such as machining discreteness, ball-raceway contact deformation, and foreign object intrusion in existing designs. This invention is fully adaptable to the application scenarios of the automotive industry, including large-scale bearing production, varying processing levels among multiple suppliers, and complex and variable load spectra. It can accurately output the matching scheme between shaft diameter tolerance zone and bearing clearance, significantly improving the consistency between design and actual production. It is applicable to the clearance and fit design of core components such as deep groove ball bearings in electric drive transmission systems of new energy vehicles, and has strong engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of mechanical structure design technology, specifically relating to a method for designing the clearance of ball bearings in an electric drive system. Background Technology

[0002] Deep groove ball bearings are core components of electric drive systems in new energy vehicles. Their clearance and fit parameters have a decisive impact on the overall operating performance of the machine. Excessive clearance can easily induce abnormal NVH (noise, vibration, and harshness) such as excessive vibration, compromising the smoothness of system operation. Insufficient clearance will exacerbate frictional heat generation, leading to abnormal temperature rise, rotational jamming, and in severe cases, even machine shutdown. A reasonable clearance design not only enables a more uniform load distribution on the bearing but also significantly extends its service life, providing a crucial guarantee for the reliability of the electric drive system.

[0003] Currently, the design of ball bearing clearance and fit in the industry mostly relies on analysis of assembly stress and temperature rise factors, which is difficult to adapt to the complex operating conditions and production characteristics of new energy electric drive systems. This results in three major technical defects: First, insufficient adaptability to operating conditions. The dynamic impact of Hertzian contact deformation of the ball and raceway on the actual clearance is not quantified for variable load conditions such as starting, acceleration, and braking of electric drive systems, leading to a large deviation between the designed clearance and the actual working clearance. Second, the risk of foreign objects such as metal shavings and dust encroaching on the clearance space is not assessed in conjunction with the cleanliness level of the transmission lubrication circuit. The reserved clearance is prone to early jamming failure after being occupied by foreign objects. Third, the manufacturing discreteness is ignored. In multi-supplier mass production, although key dimensions such as shaft diameter and bearing inner diameter meet the tolerance standards, there is random discreteness. The existing design does not establish a correlation model between discreteness and clearance consistency, resulting in the actual product clearance qualification rate not matching the design, and the stability of the final product quality is difficult to guarantee.

[0004] Therefore, it is urgent to construct a fully coupled design method that integrates processing discreteness, contact deformation, and foreign object intrusion to achieve precise design of clearance and fit, and improve the operating performance and quality consistency of bearings in electric drive systems. Summary of the Invention

[0005] The purpose of this invention is to provide a clearance design method for ball bearings in electric drive systems, aiming to solve problems such as low clearance matching accuracy and poor bearing reliability caused by insufficient coupling of machining offset, contact deformation and foreign object intrusion in existing designs.

[0006] To achieve the above objectives, the clearance design method for ball bearings in the electric drive system of the present invention adopts the following technical solution:

[0007] Step 1: Determine the machining pass rate of each structural parameter, material parameter, working condition parameter, tolerance parameter, temperature parameter, shaft diameter and bearing inner diameter.

[0008] Step 2: Calculate the nominal interference fit based on the tolerances of the bearings and shafts, as well as the temperature rise of each component. d a and actual over-excess d.

[0009] Step 3: Calculate the reduction in interference caused by the load based on the bearing dimensions, the radial force applied, and the rated static load. d F Based on the dimensions of the shaft and bearings and the temperature, calculate the reduction in interference caused by the temperature rise. D T The necessary overshoot is determined by the sum of the two.

[0010] Step 4: Calculate the surface stress p of the mating surfaces based on the dimensions and material parameters of the shaft and bearing. m Raceway diameter expansion D i and the maximum stress p in the circumferential direction max .

[0011] Step 5: Using knowledge of normal distribution, construct a mapping relationship between the machining mean offset and the pass rate, and calculate the actual machining mean values ​​ms and mi of shaft diameter and bearing inner diameter under different pass rates.

[0012] Step 6: Calculate the installation clearance based on the actual machining average values ​​ms and mi of the shaft and shaft diameter, as well as the standard deviation. f .

[0013] Step 7: Calculate the clearance change caused by temperature difference based on the bearing's internal dimensional parameters and material parameters. T .

[0014] Step 8: Based on the installation clearance f and the change in clearance caused by temperature rise T Calculate effective clearance .

[0015] Step 9: Based on the bearing mechanical analysis, obtain the average contact deformation distribution under each operating condition. Calculate the equivalent contact deformation over the entire bearing lifespan using a weighted average method based on the proportion of operating conditions. F .

[0016] Step 10: Estimate the diameter d of the foreign object based on the filter membrane diameter required for cleanliness control. fo .

[0017] Step 11: Determine the optimal range of working clearance, then take into account the diameter of the foreign object and the magnitude of contact deformation to calculate the optimal range of effective clearance.

[0018] Step 12: Using the maximum stress p in the circumferential direction max The boundary condition is that the actual interference is greater than the necessary interference. Adjust the shaft diameter tolerance zone or clearance until the effective clearance falls within the calculated optimal range and meets the boundary condition.

[0019] The advantages of the design method of this invention are:

[0020] 1. By quantitatively linking the statistical characteristics of the machining pass rate with the dimensional mean offset, the bearing fit and clearance are upgraded from traditional static design to a dynamic process-performance precise linkage mode, which significantly improves the consistency between the design scheme and actual production.

[0021] 2. Based on the actual working environment of the electric drive system and combined with the system cleanliness control requirements, clearance design is carried out to effectively reduce the risk of bearing damage caused by foreign object intrusion;

[0022] 3. The method of calculating equivalent contact deformation based on load spectrum provides a more scientific basis for the precise design of bearing clearance. Attached Figure Description

[0023] Figure 1 This represents the normal distribution of shaft diameter dimensions at different yield rates, assuming consistent machining stability.

[0024] Figure 2 This describes the dimensional and structural relationship between the bearing, shaft, and housing bore. Detailed Implementation

[0025] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. It should be noted that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] Please see Figures 1-2 The following is a detailed explanation of the technical solution of the present invention, taking the 6207 deep groove ball bearing for the motor shaft of a DHT system as an example. Symbol explanation: s represents shaft, b represents bearing, h represents seat hole, i and o represent inner and outer rings respectively, min represents lower tolerance limit, and max represents upper tolerance limit.

[0027] Step 1: Determine the machining pass rate of each structural parameter, material parameter, working condition parameter, tolerance parameter, temperature parameter, shaft diameter and bearing inner diameter;

[0028] The shaft of a certain motor is made of 40Cr, with an outer diameter of ds and an inner diameter of d0. The drive end is supported by a 6207 bearing with a precision grade of 0. The bearing housing is made of aluminum alloy with an outer diameter of Do. The inner ring is required to have a tight fit with the shaft, and the outer ring is required to have a loose fit with the housing.

[0029] The following conditions are known: the elastic modulus E, Poisson's number e, and coefficient of thermal expansion α of each part material; the inner and outer diameters d and D of the bearing, the width B, and the inner and outer raceway diameters d i and d o and the diameter D w The maximum radial force F that the bearing can withstand under the durability load spectrum r Rated static load C or The ideal machining pass rate for shaft diameter and bearing inner diameter is 99.7%. If the tolerance zone half-width is A, then the standard deviation σ = A / 3. The actual machining pass rates for shaft diameter and bearing inner diameter are 98% and 97% respectively, with unchanged machining stability. Assuming the shaft diameter tolerance is m6 and the bearing clearance is... 0, determine the recommended clearance range that prevents slippage of the bearing inner ring and ensures that installation will not cause cracking.

[0030] Step 2: Calculate the nominal interference fit based on the tolerances of the bearings and shafts, as well as the temperature rise of each component. d a and actual over-excess d;

[0031] ;

[0032] .

[0033] Step 3: Calculate the reduction in interference caused by the load based on the bearing dimensions, the radial force applied, and the rated static load. d F Based on the dimensions of the shaft and bearings and the temperature, calculate the reduction in interference caused by the temperature rise. D T The necessary interference is determined by the sum of the two. C;

[0034] ;

[0035] .

[0036] Step 4: Calculate the surface stress p of the mating surfaces based on the dimensions and material parameters of the shaft and bearing. m Raceway diameter expansion D i and the maximum stress p in the circumferential direction max ;

[0037] ;

[0038] ;

[0039] ;

[0040] In the formula, k = d / d i k0 = d0 / d, K1 and K2 are material-related parameters that can be found in various bearing literature and reference books.

[0041] Step 5: Using knowledge of the normal distribution, construct a mapping relationship between the processing mean offset and the pass rate. Since this relationship is a transcendental equation about the offset and has no analytical solution, construct the error function as follows:

[0042] ;

[0043] In the formula, σ is the cumulative distribution function of the standard normal distribution, P0 is the actual processing pass rate, and assuming that σ remains constant (processing stability is consistent), the Brent method can be used to iteratively solve for ms=35.02mm and mi=34.992.

[0044] Step 6: Calculate the installation clearance based on the actual machining average values ​​ms and mi of the shaft and shaft diameter, as well as the standard deviation. f , ;

[0045] In the formula, m f and σ f These are the mean and standard deviation of the clearance after installation, calculated using the following formulas:

[0046] .

[0047] Step 7: Calculate the clearance change caused by temperature difference based on the bearing's internal dimensional parameters and material parameters. T ;

[0048] .

[0049] Step 8: Based on the installation clearance f and the change in clearance caused by temperature rise T Calculate effective clearance ;

[0050] .

[0051] Step 9: Obtain the average contact deformation distribution under the k-th working condition based on bearing mechanical analysis. F , k The equivalent contact deformation over the entire life cycle of a bearing is calculated using a weighted average method based on the proportion of operating time. F .

[0052] ;

[0053] In the formula, δ j It is the elastic contact deformation of the j-th rolling element, α j Z is the contact angle of the j-th rolling element, and Z is the number of balls;

[0054] ;

[0055] In the formula, w k It represents the duration percentage of the k-th operating condition, and n is the total number of operating conditions. The durability load spectrum of a certain DHT system is calculated to be 8µm.

[0056] Step 10: Estimate the diameter d of the foreign object based on the filter membrane diameter required for cleanliness control. fo =10um.

[0057] Step 11: Assuming the optimal range of working clearance is [-10,0]um, the effective clearance range is calculated to be [-8,2]um using the following formula;

[0058] .

[0059] Step 12: As shown in the following formula, limit the maximum stress p in the circumferential direction using linear programming. max =200MPa, effective interference is greater than necessary interference, shift the tolerance zone of clearance, and finally confirm that the minimum design clearance is within the range of [11,20]um;

[0060] .

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0062] The parts of this invention not described in detail are prior art.

Claims

1. A method for designing the clearance of a ball bearing in an electric drive system, characterized in that: Includes the following steps: Step 1: Determine the structural parameters, material parameters, operating condition parameters, tolerance parameters, temperature parameters, shaft diameter, and bearing inner diameter machining pass rate of the bearing; Step 2: Calculate the nominal interference fit based on the tolerances of the bearings and shafts, as well as the temperature rise of each component. d a and actual over-excess d; Step 3: Calculate the reduction in interference caused by the load based on the bearing dimensions, the radial force applied, and the rated static load. d F Based on the dimensions of the shaft and bearings and the temperature, calculate the reduction in interference caused by the temperature rise. D T The necessary interference is determined by the sum of the two. C; Step 4: Calculate the surface stress p of the mating surfaces based on the dimensions and material parameters of the shaft and bearing. m Raceway diameter expansion D i and the maximum stress p in the circumferential direction max ; Step 5: Using the normal distribution related knowledge, a mapping relationship between the machining mean offset and the qualified rate is constructed, and the actual machining mean m of the shaft diameter and the bearing inner diameter under different qualified rates is calculated s and m i ; Step 6: Based on the actual average machining value m of the shaft and shaft diameter s and m i and standard deviation calculation of installation clearance f ; Step 7: Calculate the clearance change caused by temperature difference based on the bearing's internal dimensional parameters and material parameters. T ; Step 8: Based on the installation clearance f and the change in clearance caused by temperature rise T Calculate effective clearance ; Step 9: Based on the bearing mechanical analysis, obtain the average contact deformation distribution under each operating condition. Calculate the equivalent contact deformation over the entire bearing lifespan using a weighted average method based on the proportion of operating conditions. F ; Step 10: Estimate the diameter d of the foreign object based on the filter membrane diameter required for cleanliness control. f ; Step 11: Determine the optimal range of working clearance, then take into account the diameter of the foreign object and the magnitude of contact deformation to calculate the optimal range of effective clearance; Step 12: Using the maximum stress p in the circumferential direction max The boundary condition is that the actual interference is greater than the necessary interference. Adjust the shaft diameter tolerance zone or clearance until the effective clearance falls within the calculated optimal range and meets the boundary condition.

2. The clearance design method for a ball bearing in an electric drive system according to claim 1, characterized in that: The nominal interference in step 2 d a and actual over-excess d is calculated according to the following formula: ； 。 3. The clearance design method for a ball bearing in an electric drive system according to claim 1, characterized in that: The reduction in interference caused by the load in step 3. d F The decrease in interference caused by temperature rise D T Calculate using the following formula: ； ； In the formula: F r C represents the maximum radial force that the bearing can withstand. or B represents the rated static load; B represents the width.

4. The clearance design method for a ball bearing in an electric drive system according to claim 1, characterized in that: In step 4, the surface stress p m Raceway diameter expansion D i and the maximum stress p in the circumferential direction max It can be calculated using the following formula: ； ； ； In the formula: k = d / d i k0 = d0 / d, K1 and K2 are material-related parameters.

5. The clearance design method for a ball bearing in an electric drive system according to claim 1, characterized in that: In step 5, the normal distribution is used to construct a mapping relationship between the processing mean offset and the pass rate. This relationship is a transcendental equation about the offset, which has no analytical solution. Therefore, the error function is constructed as follows: ； In the formula, Let P0 be the cumulative distribution function of a standard normal distribution, P0 be the actual processing pass rate, and σ remain constant. The Brent method is used to iteratively solve for m. s and m i ; In step 6, the actual machining average value m of the shaft diameter and bearing inner diameter is used. s and m i Get installation clearance f The calculation formula is as follows: ； In the formula, m △f and σ △f These are the mean and standard deviation of the clearance after installation. The relevant calculation formulas are shown in the table below: 。 6. The clearance design method for a ball bearing in an electric drive system according to claim 1, characterized in that: The change in clearance in step 7 T The calculation is performed using the following formula: ； In step 8, based on the installation clearance f and the change in clearance caused by temperature rise T Calculate effective clearance ; 。 7. The clearance design method for a ball bearing in an electric drive system according to claim 1, characterized in that: Equivalent contact deformation in step 9 F The calculation is performed using the following formula: ; In the formula, δ j It is the elastic contact deformation of the j-th rolling element, α j Z is the contact angle of the j-th rolling element, and Z is the number of balls; ; In the formula, w q It represents the percentage of time for the q-th working condition, and n is the total number of working conditions.

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