Automotive Plastic Gears Reduce Gear Meshing Vibration and Noise with High Damping Performance

One of the sources of noise and vibration that needs to be addressed to comply with noise regulations and improve in-vehicle comfort is the engine room. For example, to suppress vibrations from the engine, a balance shaft may be used. However, when metal gears are used in balance shafts, vibration and noise are easily generated during gear meshing, making additional countermeasures necessary. Resonac proposes plastic gears as an effective solution for reducing vibration and noise generated during gear meshing.

Solution

More than 10 dB Noise Reduction at 2,000 rpm through High Damping Performance

Secondary balance shaft gears in automotive engines operate at twice the engine speed, and therefore metal gears made of carbon steel are commonly used to ensure durability and reliability. However, vibration and noise generated by metal-to-metal gear meshing remain a key challenge.

Resonac' KM-9100 is plastic gears manufactured by vacuum injection molding using a highly heat-resistant polyaminoamide resin (Tg ≥ 215°C) reinforced with aramid fibers. By damping vibration at the gear meshing interface, the plastic gear significantly reduces noise. In particular, testing has demonstrated a noise reduction of more than 10 dB at 2,000 rpm, which corresponds to the typical operating rotational speed range.

Lightweighting and Superior Vibration Damping

Replacing metal gears with plastic gears offers not only vibration reduction but also significant weight savings. One commonly used material is PEEK (poly ether ether ketone) reinforced with glass fibers (GF). While PEEK is a thermoplastic resin with low elasticity and certain damping properties, the type and amount of reinforcing fibers that can be added are limited.

In contrast,KM-9100 uses a thermosetting polyaminoamide resin, allowing a high loading of aramid fibers (AF), which provide excellent damping performance. As a result, KM-9100 exhibits shorter vibration transmission time and higher damping performance than metal gears and glass-fiber-reinforced PEEK gears.

Vibration Damping Performance

• Test Conditions:
• [Test Method] Vibration test using an impact hammer and accelerometer to measure damping behavior (internal testing)
• [Specimen Size] L105 × W25 × T5 mm

Features

50% Weight Reduction Compared to Steel Gears

The resin used in these gears has approximately one-sixth the density of steel. By replacing steel with resin, significant weight reduction can be achieved at the gear level. This also enables downsizing of drive motors, contributing to overall system weight reduction.

Example: Weight reduction achieved by adopting KM-9100 plastic balancer gears

• Note: Actual weight reduction depends on the resin-to-metal component ratio.

Continuous Operation at Oil Temperatures up to 130°C

KM-9100 maintains its performance without deformation or degradation even at oil temperatures of 130°C. It has been adopted and supplied for balance shaft gears in engine rooms and motor reduction gears for over 25 years.

• Note: As of October 2025

Reinforcement That Does Not Damage Mating Gears

When combining gears made from different materials, such as resin and metal, damage or chipping at the meshing interface can be a concern. Because KM-9100 uses organic fibers as reinforcement, it does not damage mating gears—even when paired with unhardened metal gears.

Updated: April 28, 2026

Need More Information?

Full technical specifications, featuring comparisons of Tg and vibration damping performance, can be found in our detailed report.

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