How to Select a One Way Clutch Bearing Based on Torque and Speed: How-To Guide

Select a one way clutch bearing on torque and speed by first calculating the torque the drive transmits with a safety factor for shock, then comparing it with the clutch's rated TKN, and finally checking the overrunning speed against the inner-race (nimax) and outer-race (namax) limits. Higher torque usually means a larger, wider clutch with lower allowable speed, so torque and speed must be balanced rather than maximised. Get the balance right and the clutch locks firmly and runs cool.

Why This Selection Goes Wrong

In a sprag clutch, larger torque capacity comes from more or bigger sprags and a wider race, which increases centrifugal effects during overrunning. That is exactly why a high-torque model allows lower freewheel speed. A clutch chosen for torque alone can overheat at speed, while one chosen for speed alone can slip under load. Both numbers must be satisfied at once.

How a Sprag One Way Clutch Works

Inside a sprag clutch, a cage holds many sprags between an inner and outer race. In one direction the sprags tilt into the gap and lock, so torque passes through; reversing the direction lets them relax and freewheel. SUMA DC series units use GCr15 bearing steel hardened to HRC 60–62 on the surface and HRC 35–45 at the core, and are supplied as cages only, which means the shaft and housing must provide hardened races.

Key Parameters and Why They Matter

Real SUMA Selection Data

As torque rises, allowable overrunning speed falls — match both to the drive, never one alone.

Selection Advice: Overrunning, Indexing or Backstopping

Each duty loads the clutch differently. Use overrunning where a drive must engage one way and release the other, as in dual or auxiliary drives, and watch the overrunning speed limit. Use indexing where rotation must translate into precise, repeatable steps, so torque and accuracy rule. Use backstopping where reverse rotation must be blocked, as on inclined conveyors, so holding torque and reliable lock-up are decisive.

How to Select, Step by Step

• Calculate steady drive torque and add a shock factor.
• Select a model whose TKN exceeds the result (peak ≈ 2 × TKN).
• Identify the overrunning race and take the smaller speed limit.
• Keep operating speed clearly below that limit.
• Confirm bore, fit and lubrication for the final choice.

Typical Applications

• Gearboxes & reducers — moderate torque at higher speed.
• Mining equipment — high torque at low speed.
• Cement equipment — continuous high torque.

Installation and Maintenance Notes

• Machine races to HRC 60–62 surface hardness (core HRC 35–45).
• Avoid recesses on the race so sprags seat along the full contact width.
• Follow the version's lubrication and sealing recommendation.
• Verify mounting direction so the clutch locks in the required sense.

FAQ

Q1: Which comes first, torque or speed?
A: Size for torque, then verify the overrunning speed limit.

Q2: What is peak torque?
A: About 2 × TKN, so allow margin for shock loads.

Q3: Can a bigger clutch handle more speed?
A: No, larger high-torque clutches allow lower overrunning speed.

Q4: Why not just pick the highest ratings?
A: Torque and speed trade off; the best model balances both for the drive.