Shrinking the Judder Test: A Sub-Scale Machine for Facing Sensitivity

Judder shows up as low-frequency, high-amplitude vibration when the clutch engages, and at sufficient intensity it makes a car unpleasant to drive. Assessing it has always been a vehicle activity. This work asks whether it has to be.

🔧 The problem

The judder test as practised is run in a car selected for being sensitive to judder. It takes a long time, and the reason is mechanical rather than procedural: each test requires assembling the complete clutch set — disc, clutch cover, flywheel. The measurement is quick; the preparation is not.

🎯 The approach

The aim of this work is to develop a methodology for classifying facing sensitivity to judder in a sub-scale bench test. The motivation is stated as two distinct objectives rather than one: reducing test time, and speeding up facing material development.

They are related but not identical — the second is about how many ideas can be tried, not just how fast one can be checked.

📊 What came out of it

The preliminary results are promising, with a good correlation observed between the sub-scale tests and the vehicle. At this stage the claim is deliberately modest: the correlation exists and justifies continuing, which is what a first result from a new test method should establish.

💡 Why it matters

This paper marks the point where judder classification starts moving from a vehicle-bound evaluation to a laboratory one. The work was subsequently extended and reported again with further correlation data, but the framing set out here — sub-scale first, vehicle for confirmation — is what the later work builds on.

📄 Full publication

Gregori, I. R. S.; Domingues, A. — Judder Based on Sub Scale Test Machine Concerning Facing. SAE Technical Papers, October 2012.

Read the full publication on ResearchGate

📚 Related Articles

• A Gold Standard for Torque: Separating Clutch Facings by Judder Behaviour - The follow-up: multivariate statistics on real bench torque signals separate facings by judder and set a reference behaviour.
• Predicting Clutch Judder from Torque Signals - A data-driven system that reads bench torque signals, tells six friction materials apart, and predicts vehicle judder.
• Building a Test Procedure for Friction Facing Durability - Another bench test built to contain the full range of vehicle conditions, so facings can be studied off-vehicle.