What is inner gear ring?

What is inner gear ring?

The inner ring gear is a kind of annular mechanical transmission component, with dense tooth grooves distributed on the inner side, and power transmission and speed conversion are realized by meshing with external gears or planetary gears. Its structure is divided into two kinds of drum teeth and straight teeth, the drum tooth design can improve the angular displacement bearing capacity and torque transmission efficiency, and the materials are mostly wear-resistant engineering plastics, metals or composite materials, which have the characteristics of high precision, low noise and long life. It is widely used in the field of industrial equipment transmission system, automobile gearbox and precision machinery, such as forging machinery, industrial robot joints, etc., with the advantages of small size, high transmission efficiency and strong adaptability, and is an indispensable core component in modern equipment manufacturing.

Inner ring gear features

As the core component of high-efficiency transmission, the characteristics of the internal gear ring can be summarized into the following five dimensions:

1. Structural design advantages

Adopting a closed transmission structure with annular cogging and external gear meshing, the drum tooth design can absorb shaft offset (allowable ±1° angular displacement), and the impact resistance is increased by more than 30% compared with straight teeth

Precision tooth shaping (ISO 6-7 accuracy) ensures smooth engagement and transmission errors within ±15μm

2. Breakthrough in material properties

Metal ring gear: high-strength alloy steel (20CrMnTi) has been carburized and quenched, with a tooth surface hardness of HRC58-62 and a wear life of more than 100,000 hours

Non-metallic ring gears: Glass-reinforced nylon 66 (GF30) has a density of only 1.3 g/cm³ and a self-lubricating coefficient of 0.12, resulting in a 40% weight reduction and maintenance-free

3. Optimization of transmission efficiency

Transmission efficiency of more than 98.5% (planetary drive system), 18% energy saving compared to belt drive

The torque density is up to 250 N・m/cm³ (metal ring gear), and 1200 N・m torque can be transmitted in a space of φ150 mm

4. Adaptability to working conditions

The operating temperature range is -40°C~+180°C, which meets the needs of cold and hot environments

The dynamic response time is < 50ms, which is suitable for precision control scenarios such as AGV robots

Salt spray corrosion resistance up to 1000 hours (neutral salt spray test) for offshore equipment

5. Modular design trends

Integrated design: The bearing housing, sealing structure and ring gear are integrated to reduce assembly errors

Quick-change interfaces: 70% reduction in service time thanks to standardized flange connections

Smart ring gears: Built-in temperature/stress sensors for predictive maintenance

These characteristics make the inner gear ring play a key role in the motor reducer of new energy vehicles (such as the Tesla Model 3 adopts a double inner gear ring structure), wind power speed increasing box (carrying 1.5MW torque), aerospace (resistant to -200°C cryogenic environment) and other fields, and its development direction is evolving in the direction of higher power density, lower noise (<65dB), and longer maintenance-free intervals (more than 8 years).

How the inner ring gear works

The working principle of the inner gear ring is based on the theory of gear meshing transmission, the core of which is the transmission of power and motion through the precise meshing of the inner cogging and the external or planetary gears, and the specific mechanism can be divided into the following four levels:

1. Basic meshing mechanism

Tooth shape matching: The inner gear ring adopts an involute tooth profile (pressure angle 20°±2°) to form a conjugate meshing with the external gear, and the contact point moves along the normal direction of the tooth surface to ensure the smooth transmission of force.

Modulus-to-digital coordination: The tooth pitch (p=πm) is strictly consistent with the modulus of the external gear, so as to achieve no backlash or controllable backlash meshing (sidelash 0.05-0.2mm) to avoid shock and vibration.

Contact stress distribution: The contact stress on the tooth surface is calculated by the Hertzian formula (σ_H=0.418√(F/(bρ))), and the drum tooth design reduces the contact stress by 25% and prolongs the life.

2. Transmission mode analysis

Fixed shaft transmission: when the inner gear ring is fixed, the external gear rotates to drive the planetary wheel to rotate to achieve deceleration and torque increase (transmission ratio i=1+z_ inside/z_outside).

Turnover transmission: When the inner ring gear is used as a follower, it forms a differential motion with the planetary wheel, which is applied to the differential to achieve the speed difference between the left and right wheels.

Composite transmission: Multiple sets of inner gear ring combinations, such as a dual-clutch gearbox, enable a quick shift response in less than 0.2 seconds.

3. Impact of key parameters

Gear ratio: The difference in the number of teeth determines the transmission ratio (i=z_ / (z_ inside ±z_ outside)), e.g. i=3 when z_ inside = 72 and z_ outside = 24.

Helix angle: β=8°-15° helical tooth design increases the degree of coincidence to 1.5-2.0 and reduces noise by 3-5dB.

Displacement coefficient: Positive displacement (x=+0.5) improves root strength, negative displacement (x=-0.3) improves meshing performance.

4. Dynamic response characteristics

Inertia matching: The moment of inertia of the inner ring gear should be matched with the drive motor (J=0.5mR²) to avoid resonance frequency offset.

Lubrication mechanism: Lubrication with oil mist lubrication (flow rate 5-15 L/min) or solid lubricating coating (MoS₂ thickness 3-5 μm) reduces the coefficient of friction to less than 0.08.

Temperature compensation: The coefficient of thermal expansion of the ring gear (α=11.5×10⁻⁶/°C) is compensated by preload to ensure the meshing stability at high temperatures.

Taking the automotive planetary gearbox as an example, when the inner gear ring is fixed, the input power of the sun gear drives the planetary gear to rotate, and the output speed of the planetary carrier is 1/(1+z_ /z_ sun) of the sun gear), achieving 3-5 times deceleration; When the inner ring gear rotates, it can be continuously variable by adjusting its speed. This design allows the inner ring gear to transmit torque of up to 5000N・m while maintaining a transmission efficiency of ≥96%, making it a core element of modern powertrains.

Precautions for application

1. Installation alignment: It is necessary to ensure accurate alignment with internal gear rings, gears and other components to avoid local wear or abnormal noise on the tooth surface caused by eccentricity.

2. Lubrication management: select appropriate lubricants (such as gear oil) and replenish or replace them regularly to prevent dry friction and aggravation of wear on the tooth surface.

3. Load and speed matching: avoid long-term overload or overspeed operation, which can easily lead to fatigue fracture or plastic deformation of the tooth surface beyond the rated parameters.

4. Material adaptability: select materials with corresponding strength and wear resistance (such as carburized steel) according to working conditions, and pay attention to the influence of heat treatment process (quenching, nitriding, etc.) on performance.

5. Environmental protection: In humid, dusty or corrosive environments, it is necessary to strengthen sealing protection to prevent rust or foreign matter from invading and damaging the tooth surface.

6. Dynamic balance: dynamic balance test is required when rotating at high speed to reduce the impact of vibration on transmission stability.

7. Maintenance cycle: Regularly check the tooth surface wear, cracks and tooth root fatigue, and repair or replace the damaged parts in time.

8. Fixing reliability: ensure that bolts, keyways and other connection structures are tightened to avoid transmission failure caused by loosening.

Inner gear ring supplier

LTZC provides inner gear ring. If you are looking for a supplier of  inner gear ring, please contact us for the latest quotation.