Elastic bearing couplings quieten transmission
A
Saint-Gobain Performance Plastics product story
Edited by the Engineeringtalk editorial team
May 27, 2009
Using elastic bearing couplings in the CVT chain adjuster has been shown to significantly reduce transmission noise.
This affirms the research findings, announced by Saint-Gobain Performance Plastics Rencol, that the de-coupling effects of tolerance rings help reduce the vibration within the bearing and the amount of vibration energy being transferred to noise.
Marked improvements in transmission noise have been observed when using elastic bearing couplings in the CVT chain adjuster.
Continuously variable transmissions, or CVTs, are a type of automatic transmission that can be found in cars from Audi, Ford, Honda, Nissan and other car manufacturers.
The driver's controls for a CVT are the same as an automatic; but while an automatic transmission has a set-number of gear ratios, or speeds, the CVT constantly changes the relationship of engine speed to car speed.
Though there are several types of CVTs, most cars use a pair of variable-diameter pulleys with a metal belt or chain running between them.
One pulley is connected to the engine (input shaft), the other to the drive wheels (output shaft).
Adjusting the diameter of the pulleys varies the transmission's ratio: making the input pulley smaller and the output pulley larger gives a low ratio for better low-speed acceleration.
As the car accelerates, the pulleys continuously vary their diameter; this lowers engine speed/RPM.
The advantages of this type of transmission for car manufacturers and the driver is that the CVT provides more useable power, better fuel economy and a smoother driving experience than a traditional automatic.
However, one of the major drawbacks associated with CVTs is chain noise.
This noise is caused by the impact of the chain links on the pulley sets and significant acoustic improvements in the chain have already been achieved.
But the interruption of the noise transmission paths within the chain adjuster promises further improvements.
Luk is already improving acoustics in the chain adjuster.
Acoustic tests identified that the impulse between the chain and the pulleys is carried as structure-borne noise via the pulley-set bearings into the transmission housing and continues from there as airborne noise.
By utilising the de-coupling effects of tolerance rings, the structure-borne noise at the bearings is suppressed significantly.
This concurs with Rencol's finding that, as the stiffness of a joint using a tolerance ring is lower than that of a more traditional press fit or glue bearing mount, the transmitted force through the bearing into the housing is reduced.
In addition, with a tolerance ring mount, the damping ratio is increased, effectively absorbing more of the vibration energy.
Hence, with less vibration, less noise is produced during running.
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