No-load knocking of gears is one of the important sources of vehicle knocking noise. No-load knocking usually occurs in two states:
The first occurs when an unselected driven gear oscillates within the backlash range on the tooth side of the active gear, resulting in an impact between the two gears.
Second, when the engine is idling, the mechanical power generated by fuel combustion at idle speed is used to friction and heat consumption of internal parts, where the transmission shifts without gears and the clutch is in a combined state.
The no-load knock noise of gears mainly consists of air-borne noise and structure-borne noise, in which air-borne noise is radiated directly by the teeth; structure-borne noise is mainly transmitted to the box by bearing vibration caused by dynamic load changes between gears for noise radiation.
The research shows that the air radiated sound pressure generated by no-load knocking of gears is proportional to the impact load.Therefore, the knocking characteristics under no-load conditions are studied by means of dynamic loads of gears.