TYPE 01

MANUAL
TRANSMISSION

Helical gear specification: Module M2–M3.5, SCM420H or 20CrMnTi case carburized, AGMA 10–11, helix angle 20°–30°, case depth 0.4–0.7 mm, HRC 58–62. Manual transmission constant-mesh helical gears (all ratio gears are always in mesh; engagement is by synchroniser sleeve, not by sliding the gear in and out of mesh) must maintain low noise across all gears and all vehicle speeds. The gear whine frequency equals pitch line velocity divided by base pitch × 1,000 Hz/m — at 100 km/h in 4th gear (typically 1:1 ratio) on a vehicle with 65 mm pitch radius first gear: PLV ≈ 28 m/s, mesh frequency ≈ 1,800 Hz. Tip relief of 6–12 μm is applied to all constant-mesh helical gears to reduce the dynamic increment at this critical frequency.

TYPE 02

DUAL-CLUTCH
TRANSMISSION (DCT)

Helical gear specification: Module M1.75–M3, SCM420H or 18CrNiMo7, AGMA 11–12, helix angle 25°–30°. The DCT uses two independent clutches and two concentric input shafts — odd gears on one shaft, even gears on the other — allowing pre-selection of the next gear before the clutch change. The compact twin-shaft arrangement demands even smaller module than the equivalent manual transmission, with tighter centre distance tolerances (±0.015–0.025 mm) to ensure all helical gear pairs on both shafts share the correct backlash without interaction. DCT helical gears require AGMA 12 accuracy for the lowest transmission error and gear whine at the very high pitch line velocities (>30 m/s) of the high-ratio (overdrive) gear pairs.

TYPE 03

ELECTRIC VEHICLE
REDUCTION GEARBOX

Helical gear specification: Module M2–M4, 18CrNiMo7 or SCM420H, AGMA 11–12, helix angle 20°–30°, 1 or 2 stage reduction, ratio 7:1–15:1 total, PLV 25–40 m/s at maximum motor speed (12,000–20,000 RPM). EV reduction gearboxes impose the highest pitch line velocities of any automotive gear application. At 16,000 RPM motor speed and a 60 mm pitch radius pinion: PLV = 2π × 0.030 × 16,000/60 = 50.3 m/s. Gear noise at these speeds requires AGMA 12 quality, ultra-smooth ground tooth surface Ra < 0.4 μm, and precisely applied tip relief to avoid dynamic tooth separation at maximum speed. EV gearbox helical gears are typically ground on 5-axis CNC generating grinders with simultaneous profile and lead control to achieve the required NVH performance at all motor speeds.

TYPE 04

COMMERCIAL VEHICLE
GEARBOX

Helical gear specification: Module M3–M5, 18CrNiMo7-6 or 20CrMnTi, AGMA 10–11, helix angle 20°–25°, case depth 0.6–1.0 mm, ISO 6336 safety factors S_H ≥ 1.2 and S_F ≥ 1.3 at peak torque. Heavy truck and bus transmissions transmit peak input torques above 3,000 Nm through 9–16 forward gear ratios — the helical gear fatigue life requirement at these torques and duty cycles (truck gearboxes accumulate 1,000,000 km over 10–15-year service lives) drives module selection to the minimum that satisfies ISO 6336 fatigue criteria with the specified safety factors. Commercial vehicle transmission helical gears use wider face widths (b = 10–16 × module) than passenger car gears (b = 6–10 × module) to distribute the higher torque over more tooth face area.

Tip Relief (Involute Crowning)

Removal of 5–15 μm from the tooth tip involute form over the last 10–20% of active flank length. Eliminates the load-dependent dynamic tooth engagement impact as the incoming tooth tip contacts the flank of its mating tooth before the theoretical contact point — the primary source of gear whine at the gear mesh frequency harmonic. Optimised tip relief amplitude equals the tooth deflection under peak transmitted load.

Lead Crown (Lengthwise Crowning)

A slight barrel shape applied to the tooth face width — typically 4–8 μm convex relief from the crown to each end of the tooth. Lead crown concentrates the contact pattern in the centre one-third to one-half of the face width, preventing edge loading when shaft deflection under load shifts the contact toward the tooth end. Essential for automotive transmission helical gears where assembly tolerances and shaft deflection under peak torque would otherwise cause end contact.

Bias Correction (Twist)

A diagonal surface modification that compensates for the predictable contact pattern shift caused by gear shaft deflection under load (which moves the contact diagonally across the tooth face). Bias correction is applied as an additional helical deviation superimposed on the normal lead crown and tip relief — it is gear-pair and load-specific and requires finite element analysis of the gearbox shaft deflection under rated load to calculate the correct bias angle and amplitude.

What causes gear whine in automotive transmissions and how is it reduced at the gear level?

Gear whine (transmission whine) is tonal airborne noise generated at the gear mesh frequency and its harmonics — produced by the variation in the transmitted force as successive tooth pairs engage and disengage. This force variation is called transmission error (TE), defined as the deviation from perfectly uniform angular velocity ratio between the gear and pinion. Even gears manufactured to tight accuracy tolerances exhibit TE because elastic tooth deflection under load causes a predictable error that grows with transmitted torque. Reduction strategies at the gear level: (1) Tip relief — reduces the dynamic load spike as the incoming tooth engages by removing material from the tip zone proportional to the tooth deflection at rated load; (2) Higher accuracy class — moving from AGMA 10 to AGMA 12 reduces the tooth-to-tooth spacing error contribution to TE by approximately 50%; (3) Increased helix angle — higher helix increases the total contact ratio, which buffers tooth spacing errors and smooths the instantaneous torque transmission; (4) Lead crown — prevents end contact that introduces periodic high-force events at each tooth width end. Korea Ever-Power applies tip relief and lead crown to all automotive transmission helical gears as standard and can model the TE reduction from each modification on request.

Why do EV transmissions require higher quality class helical gears than conventional ICE transmissions?

EV reduction gearboxes impose two unique conditions that conventional ICE transmissions do not: (1) Much higher pitch line velocities — EV motors commonly reach 15,000–20,000 RPM maximum speed, producing gear pitch line velocities of 40–55 m/s at the gearbox high-speed stage, compared to 20–30 m/s for ICE manual transmissions. At these PLVs, the dynamic factor K_v in the ISO 6336 contact stress formula rises sharply unless gear accuracy is AGMA 12 or DIN 4. (2) No masking noise from the combustion engine — in an EV with no engine noise, the passenger compartment sound level in the 500–4,000 Hz gear mesh frequency band is typically 15–20 dB(A) lower than in an ICE vehicle at the same road speed. Any gear whine that was previously masked by engine noise becomes clearly audible, imposing much stricter NVH requirements on the EV gearbox helical gears than the equivalent manual transmission gear would need. These two factors together require EV reduction gearbox helical gears to be manufactured and inspected to AGMA 12 / DIN 4 quality class as a minimum — the tightest quality class in standard volume gear production.

Can Korea Ever-Power supply automotive transmission helical gears for aftermarket replacement and performance applications?

Yes — Korea Ever-Power manufactures automotive transmission helical gears for two distinct aftermarket segments: (1) OEM-equivalent replacement gears — same material grade, case depth, module, helix angle, and quality class as the original OEM gear, for high-kilometre transmission overhaul where the original gear has worn below serviceable limits. (2) Performance-upgraded replacement gears — same module and geometry as the OEM gear but manufactured in 18CrNiMo7 (vs SCM420H original) with AGMA 12 quality and refined tip relief, for motorsport, track-day, and high-performance street transmission applications where the standard gear durability under sustained high-speed, high-torque operation is insufficient. Korea Ever-Power produces both types from customer-supplied drawings or from measurements of the worn original gear. Lead time: 20–40 days for standard automotive transmission helical gear sets from drawing approval, depending on quality class and quantity.

What documentation does Korea Ever-Power provide for automotive-grade helical gear orders?

Korea Ever-Power provides a standard automotive documentation package with all automotive transmission helical gear orders: (1) Material certificate — mill certificate confirming steel grade with chemical composition and mechanical properties per heat number, traceable to the shipped gear lot; (2) Heat treatment report — carburization cycle, case depth cross-section photograph, surface hardness HRC at five tooth positions, core hardness HB; (3) Gear measurement report — tooth profile deviation, lead deviation, pitch spacing error, total profile form error, total lead form error, pitch diameter, runout, surface roughness Ra — all measured on a Klingelnberg or Zeiss gear measurement machine and reported per AGMA 915 or DIN 3960 format; (4) Flank modification confirmation — tip relief amplitude and roll angle range, lead crown amplitude, and any bias correction applied, confirmed by flank form measurement; (5) 100% dimensional inspection sheet for bore, OD, face width, and keyway dimensions; (6) ISO 9001:2015 conformance certificate. For OEM automotive production programmes, PPAP (Production Part Approval Process) documentation including Control Plan, PFMEA, and measurement system analysis (MSA) can be provided on request.

Spur Gears

M1–M20 · C45, 20CrMnTi, 316L

Helical Gears

Low noise · high contact ratio · AGMA 10–12

Engrenages coniques

Right-angle drives · differential · automotive

Worm Gears

High ratio · self-locking · valve, hoist

Ring Gears

Internal · planetary · automatic transmission

Planetary Gears

Compact · high torque density · EV, hybrid

Plastic Gears

POM · PA66 · PPS · self-lubricating