Valeoscope Commercial Vehicles Clutch 2020

Diagnosis Clutch slippage or lack of torque capacity

3.2 Clutch slippage or lack of torque capacity 3.2.1 External factors Vehicle behavior ●● Clutch slippage ●● Engagement point of clutch pedal is too high Reasons ●● Wrong adjustment of clutch linkage ●● No clearance between release bearing and diaphragm fingers (for system designed to have such clearance) Attention Ɂ Ɂ For linkage with clearance between diaphragm fingers and release bearing, wear adjustment must be done periodically depending on the wear rate of facings (mission profile). There is no standard rule.

Attention Ɂ Ɂ It is not necessary to have the gear fully engaged. As soon as the synchromesh is engaged, there is an overspeed of the clutch disc. This type of mistake is the reason for facings burst or destruction of the clutch disc. Advice   Inform the drivers of the mistakes' consequences on the clutch.. In robotised gearbox environment, synchronization between the engine and the gearbox speed is operated by electronics (Transmission Control Unit - TCU) thanks to the sensors. The TCU adjusts speed at the gearbox input to the engine speed through electronic management and presence of the primary shaft brake. Slipping energy is expressed in calories. When there is over slipping, it results in overheating. 3.1.5 Robotised Gearbox hard gear shifting

The touch point may change following the temperature of the clutch and of the energy spent during the slipping phases. It can provoke then judder during the re-clutch phase. 1. Diagnostic of "Jump" (sudden jerk) ●● Regular wear of the clutch components (progressive) leads to the evolution of touch point position; system learns regularly its optimal position of "touch point" according to sensors information. ●● Temporary overheating which modifies the shape of curb afterwards. In such case, vehicle must be returned in a workshop for reinitialisation of "touch point" position. The new curb during reinitialisation should be close to original manufacturer’s one. 2. Diagnostic of breakdown Following a deviation of the touch point curb, gearbox can point out a functional issue as: ●● no de-clutch ●● no gear shifting Alert is sent to driver. Switch-off the engine, wait for the clutch to cool down and restart after a few minutes to check if it is back to normal status (touch point). If not recovered from alert, it might be necessary to reinitialize with the diagnostic tool on site. 3. Diagnostic of judder (repeated oscillations felt in cabine) Effects of judder: ●● Discomfort for the driver: problem of comfort and difficulty of manoeuvrability ●● Judder is not always identified by system ●● Impact on engine good regulation Technical reasons: ●● Geometry issue (false parallelism of clutch cover, clutch disc sliding issue on gearbox input shaft) ●● Issue with friction material quality (non compliant product or thermal degradation of some materials) ●● Coupling stiffness is too short (non compliant product or mechanical degradation) Advice   Check that cover has been correctly bolted to avoid any issue of lack of parallelism of pressure plate.  Check that sliding of friction splines is smooth on shaft. (beware of burrs)

Example: Slave Cylinder ● ● Refuse lorry  weekly / monthly ● ● Long haul  every semester / yearly

Advice   Clutch linkage must be adjusted according to manufacturer’s instructions.

When overheating here are the possible consequences: Alert 1 (information on driver dashboard): system forces start-offs on a lower gear shift. Alert 2: temperature gets critical; system is no longer operational might be necessary to control in a workshop the status of the clutch and of the actuation. Concept of touch point for robotised gearbox Depending on vehicle generations and gearboxes, system may re-learn its clutch engagement point also called touch point. Gearbox understands where to find right "touch point" position according a theoretical curb designed by the vehicle manufacturer. This position is confirmed by automatic learning at first installation of the clutch.

Slave Cylinder

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