Automotive Internal Gear – Multi-Material, M0.15-M2.2 OEM

Automotive internal gears provide compact parallel shaft transmission drives with considerable speed reduction. An internal gear is a gear with its teeth cut in the internal surface of a cylinder and meshes with external spur gears — and in the context of the automotive drivetrain, the internal ring gear is the element that makes every planetary transmission stage in the automatic gearbox work. Internal gears enable a velocity change without a directional change — which would otherwise require an idler gear with classic external spur gears, adding one more shaft, two more bearings, and additional housing bores to the gearbox. This directional continuity without extra components is the primary reason internal ring gears are used in every automotive automatic transmission stage worldwide.

Korea Ever-Power has decades of manufacturing experience and hundreds of inspectors with more than ten years of experience in automotive internal gears. Multi-material capability — 11 material options — covers the full spectrum of automotive internal gear requirements from POM window regulator ring gears to steel automatic transmission ring gears. ISO 9001:2008 / TS16949 certified. Sample 3–5 working days.

Automatic Transmission Planetary Stages

Alloy steel internal ring gears M1.0–M2.2 in the planetary stages of 6–10 speed automatic transmissions. Each shift in the automatic transmission is achieved by hydraulically holding or releasing a different ring gear or planet carrier combination — the ring gears are the functional elements that define which gear ratio is engaged. Accuracy grade AGMA 13 / DIN 5 required for the TCU's shift timing precision. TS16949 certification mandatory for AT OEM supply.

EV Motor Planetary Reduction

Alloy steel or aluminium internal ring gears M1.5–M2.2 in the single-speed or two-speed planetary reduction between the EV motor and the driven axle. The planetary stage's coaxial arrangement allows the EV drive unit to be compact and light — critical for EV packaging where every kilogram of drive unit weight reduces range. Aluminium ring gears at this module provide 78% weight reduction vs steel at adequate torque capacity for single-speed EV applications.

Electric Power Steering Planetary

Alloy or stainless steel internal ring gears M0.8–M1.5 in EPS column-assist or rack-assist planetary gear stages. EPS planetary ring gears must achieve AGMA 13 accuracy for low transmission error — any velocity fluctuation at the EPS output appears as steering feel irregularity detectable by the driver. Helical internal ring gears are used in premium EPS for lower noise.

Comfort System Actuators

POM or PPA internal ring gears M0.3–M1.0 in seat adjuster planetary drives, sunroof motor drives, convertible roof actuator planetary stages, and steering column adjustment mechanisms. Plastic ring gears provide the noise reduction, self-lubrication, and cost efficiency appropriate for comfort system actuators at the lower torque levels of these applications.

Braking System Actuators

Steel internal ring gears M1.0–M1.5 in electric parking brake (EPB) planetary caliper actuators and electro-hydraulic brake booster planetary drives. EPB ring gears must maintain dimensional accuracy across the full vehicle temperature range (−40°C to +150°C) and after 100,000+ actuation cycles — alloy steel with controlled heat treatment is the standard specification.

Fuel and Cooling System Drives

Brass or bronze internal ring gears M0.15–M0.5 in fuel pump gear drives and cooling pump planetary stages. Non-sparking brass suits fuel-adjacent applications; bronze's self-lubrication against steel suits the thin-film lubrication conditions of coolant pump drives. Both materials resist the chemical environment of automotive fuels and glycol coolants without a surface coating.

How long does it take to get an automotive internal gear sample?

Sample lead time for automotive internal gears is 3–5 working days from drawing confirmation. All samples are produced and tested to the same accuracy grade (AGMA 13 / DIN 5 standard) and TS16949 quality process as production parts — the sample is the quality verification part, not a rough prototype. DHL or UPS delivery; transit to South Korea 2–3 days. For automotive OEM programmes where the prototype timeline is critical, contact Korea Ever-Power with the required sample delivery date and we will confirm feasibility.

What materials can Korea Ever-Power cast or machine for automotive internal gears?

Korea Ever-Power can process stainless steel, duplex stainless steel, carbon steel, ductile cast iron, aluminium, copper, bronze, brass, and alloy metal. For plastic automotive internal gears, POM, PA, PPA, PBT, and PEEK are all available. The full material list — 11 metallic options and 5 plastic options — means a single TS16949 qualification at Korea Ever-Power covers every automotive internal gear material the programme may require as it evolves through development and into production.

Why does the automotive internal gear need to be checked for interference before specifying the tooth count combination?

Three types of interference can occur in an internal-external gear pair if the tooth count combination is incorrectly specified: involute interference (tooth tips foul the mating tooth flank at the start or end of contact), trochoid interference (the tip of the ring gear tooth fouls the fillet of the pinion during assembly), and trimming interference (the ring gear tooth tip fouls the pinion tooth tip during the gear cutting process). All three must be checked against the specific tooth count combination, module, pressure angle, and addendum coefficient. Korea Ever-Power's engineering team performs all three interference checks for every custom automotive internal gear design and will alert the customer if any condition is violated before production is started.

Does Korea Ever-Power provide ODM design service for new automotive internal gear programmes?

Yes — Korea Ever-Power provides ODM (Original Design Manufacturer) service for automotive internal gear programmes where the customer has the system requirement but not the finished gear design. The ODM service covers: module and tooth count selection for the required ratio, interference condition checking, material and heat treatment recommendation for the operating conditions, tooth profile optimisation for the accuracy and noise target, and production of the drawing for customer approval before production. Send the operating requirements — input torque, speed, ratio, OD envelope, temperature range, accuracy grade, and material preference — and Korea Ever-Power's design team will propose the ring gear specification. Contact our team to begin the ODM process.

"We supply EV motor planetary reduction stages to a Korean EV OEM. Korea Ever-Power's aluminium internal ring gears M2.0 DIN 6 achieved our weight target — 118 g vs 430 g for the equivalent alloy steel ring gear. TS16949 certification accepted at our OEM customer's supplier qualification audit. Sample in 4 working days. 3-day DHL delivery from Hangzhou to our Seoul engineering facility."

Kim Sang-hyeon  |  EV Drive System Engineer, Incheon EV Components Co.  ·  Q1 2026

"We design electric parking brake caliper actuators and used Korea Ever-Power's ODM service — we had the torque, ratio, and packaging space but no gear drawing. Their design team specified alloy steel M1.2 ring gear, checked the interference condition for our tooth count combination, and produced a DIN 5 drawing for our approval. Sample gears cycled 120,000 times at rated clamping force in our durability rig without tooth fatigue or dimensional change."

Lee Jae-hyeok  |  Brake Actuator Design Engineer, Gyeonggi Automotive Braking Systems Co.  ·  Q4 2025

"We manufacture automotive window regulator drives and specified POM automotive internal ring gears M0.8 AGMA 12 from Korea Ever-Power. The interference check confirmed our 15-tooth pinion / 60-tooth ring gear combination was outside the trochoid interference zone. AGMA 12 accuracy confirmed at our gear analyzer incoming check — all 20 sample gears within tolerance. TS16949 accepted at our passenger car OEM audit."

Park Jun-seok  |  Window Regulator Mechanism Engineer, Busan Automotive Actuators Co.  ·  Q2 2026

"We distribute automotive internal gears in 6 materials to Korean tier-1 and tier-2 suppliers. Korea Ever-Power's multi-material capability — 11 options, single TS16949 qualification — means one supplier approval covers POM comfort system gears through alloy steel AT gears in the same audit. Vacuum tray packaging ensures AGMA 13 accuracy is maintained during international express transit."

Choi Sung-jun  |  Automotive Parts Distribution Manager, Daejeon Automotive Components Co.  ·  Q3 2025

"We supply EPS column-assist planetary gear sets for the Korean market. Korea Ever-Power produces the stainless steel internal ring gear M1.0 DIN 5 for our EPS assembly with non-magnetic confirmation (Feritscope ≤ 1.5 FN). Transmission error measured on our gear test rig: within ±0.8 arc-minutes across 360° rotation — below our EPS feel specification of ±1.5 arc-minutes."

Yoon Jae-cheol  |  EPS System Engineer, Ulsan Automotive Steering Systems Co.  ·  Q1 2025