Different Physical Properties of timing Belt Tooth Profiles

Trapezoidal Teeth:

Significant stress concentration effect: Load concentrates at the sharp corners on both sides of the tooth root, forming localized high-stress zones.

Crack initiation points: Under alternating loads, fatigue cracks readily form at these corners and propagate rapidly, leading to tooth failure.

Low material utilization: Substantial tooth material does not participate in effective load-bearing, constituting “dead weight.”

Arc Teeth/Parabolic Teeth (HTD, GT):

Smooth stress distribution: The smooth, continuous profile enables a fluid “streamlined” load distribution along the tooth contour without abrupt changes.

Exceptionally high root strength: The arcuate root functions like an arch bridge, converting radial forces into compressive stresses within the tooth body, significantly enhancing the bending fatigue limit.

High material utilization: The tooth profile aligns more closely with the principal stress trajectory, enabling more efficient material loading.Physical essence: Transitioning from stress singularities caused by geometric discontinuity to a state of uniform stress distribution through geometric continuity.
2. Meshing Dynamics and Impact Vibration

Trapezoidal Teeth:

“Wedge-in/Squeeze-out” Meshing: Collision occurs at the instant of tooth-to-groove contact, involving abrupt velocity changes.

Multi-tooth interference: Theoretically multi-tooth engagement, but due to tooth profile errors and elastic deformation, the actual effective number of engaged teeth is low, resulting in uneven load distribution.

Abundant excitation sources: Each entry and exit constitutes an impact, serving as a source of broadband vibration excitation.

Arc/Parabolic Teeth:

“Smooth Engagement-Disengagement” Meshing: Contact points move smoothly along the tooth profile with continuous velocity changes, significantly reducing impact acceleration.

Conjugate Meshing Optimization: Examples like GT tooth profiles achieve meshing trajectories closer to theoretical conjugate curves, enabling smooth power transmission.

Cleaner Vibration Spectrum: Primary vibration energy concentrates on the fundamental meshing frequency, facilitating resonance avoidance through design.

Physical Essence: Transitioning from discontinuous contact dynamics to quasi-conjugate continuous rolling contact reduces high-order harmonic excitation.

3. Contact Mechanics and Wear Mechanisms

Trapezoidal Teeth:

High specific pressure wear: Small contact area and high localized contact stress lead to severe adhesive wear and abrasive wear.

Wear patterns: Grooves often form in the middle of the tooth surface, with cracks appearing at the root corners.

Clearance deterioration: Tooth flank clearance rapidly increases after wear, causing a sharp decline in transmission accuracy.

Arc Teeth:

Low specific pressure, large contact area: Curved contact surfaces increase effective contact area and reduce surface contact stress.

Uniform wear distribution: Wear spreads more evenly across the entire tooth surface, maintaining better transmission accuracy throughout the service life.

Self-cleaning properties: Smooth tooth profiles resist foreign object entrapment.

Physical essence: By optimizing Hertzian contact stress distribution, wear shifts from localized to uniform wear.
4. Acoustic Performance of Synchronous Belts (Noise Generation Mechanisms)

Trapezoidal Teeth:

Air Pumping Effect: Rapid closure of tooth cavities during meshing compresses air, generating jet noise.

Structural Radiation Noise: Meshing impacts excite bending vibrations in the belt and pulleys, radiating mid-to-low frequency noise.

Typical Sound Pressure Level: Generally 3-8 dB(A) higher than arc teeth under identical operating conditions.

Arc/Parabolic Teeth:

Airflow Guidance Design: Tooth groove shape facilitates smoother airflow, reducing turbulence and pumping effects.

Reduced Impact Noise Sources: Smooth meshing significantly diminishes energy from primary excitation sources.

Lower High-Frequency Components: Smoother contact markedly reduces high-frequency “hissing” sounds caused by microscopic impacts.

Physical Essence: Suppresses noise at its source by reducing meshing impact energy and improving aerodynamic characteristics.

5. Transmission Accuracy and Stiffness Characteristics

Trapezoidal Teeth:

Large Backlash: Flank clearance is essential and increases rapidly with wear, leading to poor positioning accuracy.

Nonlinear Torsional Stiffness: A noticeable “free play” elastic range exists under light loads.

Thermal sensitivity: Pitch variations due to temperature changes significantly impact transmission accuracy.

Precision Arc Teeth (AT, GT):

Low preload sensitivity: Minimal backlash variation within reasonable preload ranges enables near-zero-backlash transmission.

High torsional stiffness: Optimized tooth profiles ensure tighter engagement within the wheel groove, enhancing resistance to elastic deformation.

Minimal synchronism error: Uniform load distribution across the multi-tooth engagement zone reduces the impact of cumulative pitch errors in the belt.

Physical principle: Enhances dynamic stiffness of the transmission system through interference-fit design and stiffness matching.
II. Quantitative Comparison of Key Performance Parameters for Timing Belts