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Cold Idle Gear Rattle in Manual Transmission Passenger Car - Temperature Based Phenomenon
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on September 15, 2020 by SAE International in United States
Gear rattle is due to impact noise of unloaded gears in transmission having freedom to move in backlash region. The problem is induced by engine order vibrations in the presence of backlash in meshing pairs. It is a system behaviour wherein flywheel end torsional vibrations, the pre-damper characteristics and transmission drag plays a vital role in cold condition. This is a severe issue in idle speed which is highly noticeable in cold/ morning condition. Rattling observed in idle condition is idle rattle or neutral gear rattle, specifically in cold condition is a “Cold idle rattle” and this is the critical noise parameter for entire vehicle NVH. Damper mechanism in clutch, is used to serve better isolation (by reducing input excitation to transmission parts) of vibrations between engine and transmission their by reduces gear rattle intensity. Clutch parameters like pre-damper stiffness, hysteresis and windup angle affects more to cold idle rattle phenomenon. Irrespective to that rattling phenomenon is also depend on vehicle operating temperatures. Temperature variation affect the frictional drag of transmission which is most crucial parameter in clutch Pre-damper characteristics design to reduce rattle. Through experiments, effect of temperature variation on transmission drag and its effect on pre-damper which is sensitive for rattle phenomenon was noticed. Designer need to be understand the optimum values of clutch pre-damper parameters considering temperature effects to work with acceptable rattle. For this testing is carried out with different pre-damper characteristics on same powertrain. In short, it provides optimum clutch pre-damper properties which avoids cold idle rattle issue.