Types and characteristics of tooth clutches
A tooth clutch is a mechanical clutch that transmits or disconnects power through meshing between teeth. It consists of two half-clutches with teeth on their end faces. The active half-clutch is fixedly connected to the shaft, while the driven half-clutch is slidingly connected to the shaft via a guide key. Disengagement is achieved by axial movement of the driven end. Tooth clutches have the characteristics of simple structure, high torque transmission, and no relative slip after engagement. They are widely used in transmission systems in machine tools, automobiles, construction machinery, and other fields. Depending on the tooth shape, tooth direction, number of teeth, and operating conditions, tooth clutches can be divided into various types, each with its own unique structural characteristics and applicable scenarios.
Dog clutches can be categorized by tooth profile: rectangular, triangular, trapezoidal, and serrated. These clutches differ significantly in torque transmission, engagement smoothness, and CNC machining difficulty. Rectangular tooth clutches feature rectangular teeth with the top and bottom teeth parallel to the axis. This simplifies manufacturing and provides a large tooth contact area. They can transmit high torque (up to 10,000 Nm or more), but they also experience significant engagement shock. They are suitable for low-speed engagement ( <100 rpm ), such as in stamping machine clutches. Triangular tooth clutches feature an isosceles triangle tooth profile with a 30°-60° tooth angle . These sharp top teeth facilitate centering, provide smooth engagement, and minimize shock. However, their tooth root strength is low, resulting in lower torque transmission (typically <5,000 Nm ). They are suitable for medium-speed , light-load applications, such as the feed mechanism of small machine tools. Trapezoidal clutches feature an isosceles trapezoidal tooth profile with a profile angle of 20°-30° . They offer high tooth root strength, strong load-bearing capacity, and self-centering properties, resulting in smooth engagement and disengagement. They transmit torques ranging from 500 to 20,000 N · m and are the most widely used type, suitable for applications such as machine tool spindles and automotive transmissions. Sawtooth clutches feature a sawtooth-like tooth profile with a 3°-8° inclination angle on the one-way load-bearing tooth surface and a 20°-30° inclination angle on the non-load-bearing surface . They can transmit high one-way torques (up to 30,000 N · m ) but cannot withstand reverse torque, making them suitable for unidirectional transmission applications such as crane hoist mechanisms.
Dog clutches can be categorized by tooth orientation: spur, helical, and helical. Different tooth orientations affect the clutch’s engagement performance and axial force. Spur tooth clutches have teeth parallel to the axis, requiring precise alignment of the tooth grooves during engagement. This eliminates axial forces, resulting in a simple structure and easy manufacturing. However, this is susceptible to stiff impact between the teeth during engagement, making them suitable for manual operation or low-speed automatic engagement. Helical tooth clutches have teeth at an angle of 10°-20° to the axis. This generates an axial force component during engagement, enabling automatic clutch engagement, reducing impact and ensuring a smoother engagement process. However, this axial force increases wear on the guide key, requiring enhanced lubrication. These clutches are suitable for medium-speed automatic engagement transmissions, such as those in textile machinery. Helical tooth clutches have a helical tooth orientation and linear contact between the tooth surfaces, resulting in smoother engagement and greater torque transmission. However, these clutches are complex to manufacture and expensive to manufacture. They are suitable for high-speed, heavy-load applications (speeds > 1000 rpm , torques > 10,000 N · m ), such as propulsion systems for large ships.
Categorized by tooth count, dog clutches typically have 3-60 teeth. The number of teeth affects the clutch’s engagement precision and transmission smoothness. Clutches with a low tooth count ( 3-6 teeth) have large tooth profiles and high root strength, enabling high torque transmission. However, they suffer from low indexing accuracy and difficulty aligning the teeth during engagement. These clutches are suitable for heavy-duty applications where indexing accuracy is not a priority, such as crusher transmission systems. Clutches with a medium tooth count ( 8-20 teeth) have a moderate tooth profile, ensuring a certain torque transmission range ( 5000-15000 N· m ) while maintaining good indexing accuracy (within ± 1° ). They are suitable for most general-purpose machinery, such as machine tool spindles. Clutches with a high tooth count ( 25-60 teeth) have a small tooth profile, high indexing accuracy (within ± 0.5° ), and smooth engagement. However, they suffer from low root strength and low torque transmission ( <5000 N · m ). These clutches are suitable for precision transmissions and indexing mechanisms, such as the indexing tables of CNC machine tools.
Dog clutches can be categorized by operating conditions, either dry or wet, with different types tailored to suit varying lubrication and environmental requirements. Dry dog clutches operate without lubrication, offering a simple structure and low cost. However, they suffer from rapid tooth wear and a short lifespan. They are suitable for low-speed, light-load, and intermittent operation, such as in the transmission mechanisms of hand tools. Wet dog clutches operate in an oil bath, creating a lubricating film between the teeth. This reduces friction, wear, and lifespan, while also minimizing engagement shock and noise. They are suitable for high-speed, heavy-load, and continuous operation, such as in automotive transmissions and hydraulic machinery. Special types of dog clutches also exist, such as safety dog clutches (which provide overload protection by causing tooth slip when torque exceeds a set value) and synchronized dog clutches (which incorporate a synchronizer to ensure the driving and driven ends rotate at the same speed during engagement). These specialized clutches offer unique advantages in specific applications, expanding the scope of dog clutch applications.
The advantages of dog clutches can be summarized as follows: compact structure, high torque transmission, no slip after engagement, high transmission efficiency (over 98%), and low cost. Disadvantages include a slight impact during engagement, limited engagement at low speeds or when the vehicle is stopped, susceptible tooth surface wear, and high requirements for installation concentricity (generally ≤ 0.1mm). In practical applications, the appropriate dog clutch type should be selected based on factors such as the torque transmission, speed, engagement frequency, and operating environment. Attention should also be paid to the shaft fit accuracy (typically H7/k6), tooth surface hardness (58-62 HRC after carburizing and quenching), and lubrication method to ensure clutch life and reliability. With advances in material technology and manufacturing processes, new dog clutches employ high-strength alloys (such as 20CrNi2MoA) and precision CNC machining techniques, further improving load capacity and service life, expanding their application in high-end equipment.
