This article focuses on the design and calculation of modified helical cylindrical gears, especially in the context of electric vehicle window regulators. It discusses the importance of gear modification, the methods of determining gear parameters, and the impact of different parameters on gear performance. Through detailed analysis and examples, it provides a comprehensive understanding of the design and application of modified gears.
1. Introduction
Gears play a crucial role in mechanical transmission systems. In some cases, especially when dealing with small gears with a modulus of 1 mm and a small number of teeth, modified gears are often required to ensure proper operation. In electric vehicle window regulators, the gears need to have good meshing performance and reliability to ensure the smooth operation of the window.
2. Gear Modification Basics
2.1 Reasons for Gear Modification
When the number of teeth of a gear is small, such as less than 12 in the case of a modulus of 1 mm, root cutting may occur during the gear cutting process. Root cutting will weaken the strength of the gear teeth and reduce the quality of gear transmission. To avoid this problem, gear modification is necessary.
| Gear Type | Minimum Number of Teeth to Avoid Root Cutting |
|---|---|
| External meshing spur gear (when , , , ) | 17 |
| External meshing spur gear (when , , , ) | 14 (actual minimum can be 12) |
2.2 Principles of Gear Modification
Gear modification is achieved by moving the gear tooth profile. By adjusting the position of the cutting tool relative to the workpiece center, gears with the same modulus and tooth profile angle but different tooth thicknesses and root heights can be cut. This effectively reduces the non-involute part of the gear root and adds an involute tooth surface at the tooth tip.
3. Electric Vehicle Window Regulator Structure and Gear Application
3.1 Structure of Electric Vehicle Window Regulator
The electric vehicle window regulator mainly consists of a DC motor, a worm shaft, left and right gear-wormwheel assemblies, a large gear, a spline shaft, and a sheave. The DC motor drives the worm shaft to rotate. When the worm shaft rotates clockwise, the right worm engages with the right gear-wormwheel assembly to drive the window to rise; when it rotates counterclockwise, the left worm engages with the left gear-wormwheel assembly to drive the window to fall.
3.2 Gear Application in Window Regulator
In the window regulator, the left and right gears and the large gear are helical cylindrical gears. The meshing of these gears needs to be stable to ensure the smooth operation of the window. The gears need to have appropriate parameters to avoid problems such as root cutting and ensure sufficient strength.
4. Determination of Gear Parameters
4.1 Observation and Measurement of Gears
4.1.1 Gear Tooth Number and Root Cutting Judgment
The left and right gears in the window regulator have 8 teeth each. According to the gear design theory, when the number of teeth is small, root cutting is likely to occur. By comparing the tooth shape of the gears with that of non-modified gears, it can be qualitatively determined that the left and right gears are modified gears.
4.1.2 Measurement of Gear Parameters
To further determine the properties of the gears, the tooth tip circle diameter and the center distance between the gears need to be measured. By comparing the measured values with the theoretical values of non-modified gears, it can be clearly seen that the left and right gears and the large gear in the window regulator have undergone modification.
| Parameter | Measured Value (Sample) | Theoretical Value (Non-modified) |
|---|---|---|
| Right gear tooth tip circle diameter | 111.86 | 10.88 |
| Large gear tooth tip circle diameter | 147.44 | 147.55 |
| Center distance between left and right gears and large gear | 27.80 | 26.96 |
4.2 Selection of Gear Modification Methods
4.2.1 Types of Gear Modification
There are mainly two types of gear modification: height modification and angle modification. For height modification, the meshing center distance is equal to the non-modified meshing center distance , and the sum of the modification coefficients . For angle modification, the meshing center distance is different from .
4.2.2 Selection Criteria
In the window regulator, since the measured center distance and the non-modified center distance (), angle modification is adopted. Angle modification can be further divided into positive angle modification and negative angle modification, which can be distinguished according to the values of the modification coefficients of the two meshing gears.
5. Geometric Calculation of Modified Helical Cylindrical Gears
5.1 Calculation of Minimum and Maximum Modification Coefficients
5.1.1 Minimum Modification Coefficient to Avoid Root Cutting
When and , the minimum modification coefficient to avoid root cutting is . For gears with , . When allowing a slight root cutting, the minimum modification coefficient is .
5.1.2 Maximum Modification Coefficient to Avoid Tooth Tip Sharpening
With the increase of the modification coefficient, the tooth shape gradually becomes sharp. When , , and , the maximum modification coefficient is obtained through lookup tables. The modification coefficient should satisfy . If the selected modification coefficient exceeds , the tooth tip width needs to be checked.
5.2 Calculation of Geometric Parameters of Modified Gears
5.2.1 Calculation of Non-modified Gear Geometric Parameters
Taking the non-modified helical cylindrical gears in the window regulator as an example, with , , , , , , and , the following parameters can be calculated:
- Transverse module:
- Transverse tooth profile angle: ,
- Tooth tip height:
- Tooth total height:
- Pitch circle diameter: ,
- Non-modified meshing center distance:
- Transverse (pitch circle) meshing angle: ,
5.2.2 Calculation of Modified Gear Geometric Parameters
Based on the measured center distance of the modified gears in the window regulator, the following parameters can be calculated:
- Normal total modification coefficient:
- Transverse center distance variation coefficient:
- Normal center distance variation coefficient:
- Normal tooth tip height reduction coefficient:
- Tooth tip height: ,
- Tooth tip circle diameter: ,
- Tooth total height:
- Transverse meshing module:
- Pitch circle diameter: ,
- Base circle helix angle: ,
- Base circle diameter: ,
6. Design of Modified Helical Cylindrical Gears
The design of modified helical cylindrical gears mainly relies on the measurement data of samples and the center distance data of the installation holes of the gears in the gear box and gear cover. At the same time, the modulus, number of teeth, and large diameter data of the sample gears are also used for calculation. The design of large modified gears and left and right modified gears needs to consider various factors to ensure that the gears can meet the requirements of the transmission system.
7. Conclusion
In the design and manufacture of gears, especially for small gears with a modulus of 1 mm and a small number of teeth, gear modification is an important method to ensure gear performance. In electric vehicle window regulators, the correct design and calculation of modified gears can ensure the smooth operation of the window and improve the reliability of the system. Through the determination of gear parameters and the selection of appropriate modification methods, the quality of gear transmission can be effectively improved. Future research can focus on further optimizing the design method of modified gears and exploring new materials and manufacturing processes to improve the performance of gears.
In the above article, the relevant content is organized and expounded in detail. The use of tables helps to clearly show the data and calculation results, making the article more readable. At the same time, the content is mainly discussed from the aspects of gear modification principles, application in window regulators, parameter determination, and geometric calculation, which provides a comprehensive understanding of the design and calculation of modified helical cylindrical gears.进入 AI 阅读
