Enhancing Machinery Efficiency: Motor Speed Reducers in Action (Ⅱ)

In this article, we will focus on introducing the concept, advantages, and disadvantages of gear transmission, while also providing a detailed overview of four main types: involute cylindrical gear transmission, bevel gear transmission, worm gear transmission, and planetary gear systems.


Gear transmission is a common and vital method of power transfer, extensively applied in various industrial equipment and mechanical systems. It ensures precise power transfer, control, and application. Building upon the foundational knowledge we gained from the previous article, this piece emphasizes the importance of motor reducers and their role in speed reduction and torque amplification. In this article, we will focus on introducing the concept, advantages, and disadvantages of gear transmission, while also providing a detailed overview of four main types: involute cylindrical gear transmission, bevel gear transmission, worm gear transmission, and planetary gear systems.

**Three Core Concepts of Gear Transmission**

At the heart of gear transmission lies the engagement between gears, which facilitates the transfer of power and motion. To gain a deeper understanding of how gear transmission works, it's essential to grasp the following three key concepts:

1. Backlash: Backlash refers to the amount of play or movement in one gear when another gear is fixed. Backlash exists to accommodate factors such as gear manufacturing precision errors, installation center distance errors, high-temperature expansion, and material expansion, ensuring that gear transmission doesn't get stuck under various conditions.

※ The backlash is directly related to the backlash of the transmission chain. Calculation formula:

2. Contact Ratio: Contact ratio reflects the number of gear pairs simultaneously engaged during the operation of a pair of gears. A higher contact ratio indicates that more gear pairs are involved in engagement simultaneously, which helps reduce stress on individual teeth, enhancing transmission safety and smoothness.

3. Slip Ratio in Gear Transmission:Slip ratio indicates the relative sliding on the tooth surface of a gear pair during operation. A higher slip ratio can lead to tooth surface wear and adhesion, reducing transmission efficiency and affecting the lifespan of gear transmission.

Advantages and Disadvantages of Gear Transmission


- Compact Structure: Gear transmission components are typically arranged compactly, suitable for engineering applications with limited space.

- Reliability: Gear transmission design and manufacturing undergo precise calculations and testing, resulting in high reliability and exceptional stability.

- High Efficiency: Compared to other transmission methods like belt drive, gear transmission usually offers higher efficiency, converting more input power into output power.

- Longevity: Gear transmissions often have a long lifespan, especially with proper maintenance and lubrication.

- Constant Transmission Ratio: Once gear transmission is designed and manufactured, its transmission ratio remains constant, unaffected by external factors, suitable for a wide range of power and speed requirements.

However, gear transmission also has some drawbacks:

- Higher Manufacturing and Installation Costs: Gear transmission typically requires more cost and labor for manufacturing and installation compared to other transmission methods, including precise gear machining and accurate gearbox installation.

- High Contact Forces: Under high loads and speeds, gear transmission can generate high contact forces, potentially leading to surface wear and damage. Adequate lubrication is crucial to reduce this wear.

- Vibration and Noise at Low Precision: If gear transmission manufacturing precision is low, it can result in vibration and noise, affecting machine performance and workplace noise levels.

**Four Primary Types of Gear Transmission**

This article will also provide in-depth insights into the first two primary types of gear transmission:

Involute Cylindrical Gear Transmission: This type of gear transmission is characterized by involute gears, known for their high contact ratio and excellent load-carrying capacity. It's commonly employed in high-precision applications to reduce vibrations and noise.

1. Involute: In involute cylindrical gear transmission, the involute is a unique tooth profile. It forms a dynamic straight line, which, when rolled along a fixed circle (base circle), traces the involute curve on the base circle's surface. The design of involute gears offers distinct advantages, enabling smooth power transfer and noise reduction.

2. Module: Module is an artificially set parameter used to determine the size of gears.

- For involute spur gears, mn=mt.

- For involute helical gears, mn=mtcosβ.

- Helical gears provide higher contact ratios but introduce axial forces; herringbone gears can address this issue.

3. Undercutting: During the manufacturing of involute gears, if the number of teeth on a gear is too low, the gear's top teeth may cut off a portion of the involute tooth profile at the root of the wheel, known as undercutting.

- To prevent undercutting, it's generally required that Z1+Z2≥2Zmin=34. Smaller gears (Z1) can have fewer teeth than Zmin and use positive profile shift to reduce the mechanism's size, improve load-carrying capacity, and enhance wear resistance.

4. Profile Shift: Profile shift is a method to alter the shape of gear teeth by adjusting the relative position of the cutting tool to the gear being processed. This technique has multiple applications, including avoiding gear undercutting, adjusting gear center distances for different conditions, and enhancing gear load-carrying capacity.

5. Profile Tangent: Profile tangent is closely related to the tooth profile of involute gears. It refers to the tangent to the base circle, which must also be the normal line on both sides of the gear tooth profile. This feature is crucial for ensuring proper gear engagement.

Bevel Gear Transmission: Bevel gear transmission utilizes bevel gears and is suitable for applications requiring torque transfer and changes in motion direction.

- Hypoid Gear: Hypoid gear is a special type of bevel gear characterized by its base circle tangentially touching the base circle of a 2nd-degree conical gear. The gear profile projects onto the hypoid's conical surface, creating an approximate gear shape. Unfolding the hypoid gear results in two partially circular gears, contributing to the improved performance of bevel gear transmission.

- Equivalent Number of Teeth: Equivalent number of teeth is a method for calculating parameters of bevel gear transmission. It approximates the hypoid gear profile as incomplete spur gears and then completes them as spur gears. The calculation of equivalent number of teeth is Z_v = Z / cos(δ), where δ represents the angular pitch cone angle.

Worm Gear Transmission: Worm gear transmission is an efficient method suitable for applications requiring significant speed reduction, such as agitators and conveyors in the mechanical industry.
Planetary Gear Systems: Planetary gear systems are complex gear transmission systems typically comprising multiple gears and shafts. They are used to achieve intricate transmission ratios and motion control.

In summary, gear transmission plays a critical role in mechanical engineering, offering advantages like compact structure, high efficiency, and long lifespan. However, precise manufacturing and maintenance are essential to ensure optimal performance. Understanding various types of gear transmission aids engineers in selecting the best transmission method for their applications. In the next article, we will delve into the concepts of worm gear transmission and planetary gear systems while providing key recommendations for selection and application.

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