HRH gear / Hypoid gear

HRH gear

The history of gear technology is said to span more than 3,000 years, and its evolution continues even today.
After developing proprietary gear cutting machines, our company became in 1987 the first in Japan
to successfully develop and mass-produce the high reduction ratio hypoid (HRH) Gear.
The key feature of the HRH Gear is its ability to achieve a high reduction ratio of up to 1/360 with a single pair of gears, contributing significantly to the compactness of the overall mechanism.
At present, reduction ratios of up to 1/120 have been adopted in commercial products.
Furthermore, through increases in pinion diameter and improvements in the contact ratio, further enhancements in strength, quiet operation, and durability are expected. As a result, the HRH Gear is highly regarded across a wide range of applications and industries.

Comparison of Spiral Bevel Gears, Hypoid Gears, and HRH Gears

	Spiral Bevel Gear	Hypoid gear	HRH gear (High Ratio Hypoid gear)
Reduction ratio	1/1 to 1/10	1/3 to 1/15	1/10 to 1/360
Tooth surface finish	Gear cutting, CBN gear tooth grinding, gear tooth grinding with wheel	Gear cutting, CBN gear tooth grinding, gear tooth grinding with wheel	Gear cutting, CBN gear tooth grinding
Efficiency	More than 99%	Less than 96%	Less than 90%
Offset value	No	Gear outer diameter less than 20%	Gear outer diameter less than 30%
Pinion	From 5 teeth	From 5 teeth	From 1 to 4 teeth
Gear tooth profile	Gleason gear profile	Gleason gear profile	Complex surface
Self-locking	No	No	Yes (1/30 and above)

Feature 1: Compactness

The HRH gear achieves an exceptionally high reduction ratio with just a single gear pair, dramatically reducing the number of internal
components such as gears and bearings. This streamlined design enables lightweight, compact gear units while helping reduce manufacturing costs and improve serviceability.

e.g.) Combination example of reduction ratio 1/60

Case study	Spiral Bevel Gear	Hypoid gear	HRH gear (High Ratio Hypoid gear)
	Bevel 1/2 + Spur 1/5 + Spur 1/6 3-stage reducer	Hypoid 1/5 + Spur 1/12 2-stage reducer	HRH gear 1/60 1-stage reducer

Feature 2: Durability

By offsetting the pinion shaft, both the pinion outside diameter and the contact ratio are increased, which enlarges the tooth root
cross‑sectional area and improves strength.
Furthermore, the higher contact ratio enhances the tooth surface durability, improving resistance to pitting and torque capacity; this in turn
contributes to improved durability of the gear unit.

	Spiral Bevel Gear	Hypoid gear
Module	2
Gear tooth ratio	５×75
Pinion outer diameter	-	30％UP
Pinion layout position

Feature 3: Quiet operation

By offsetting the pinion shaft, a higher contact ratio is achieved, which suppresses vibration during gear rotation and mitigates shock loads,
resulting in improved quiet operation.
This effectively reduces the “tooth surface impact noise” commonly associated with bevel gears, contributing to a quieter gear unit overall.

Offset Position	A.C.（Above Center）	B.C.（Below Center）
Helix direction	Gear - Left Pinion - Right	Gear - Right Pinion - Left
Pinion layout position

Application Examples

Fully integrated into our gear reducers, and widely adopted across diverse industries.

General Industrial Equipment

Reducers/Gearmotors
AGV

Robot

Vertically articulated robot
SCARA robot

Machine tools

Machining center
- └Indexing Table
- └ATC (Auto Tool Changer)