We previously talked about how important it is to insist on flexible couplings when you purchase heavy equipment. Continuous vibration and intermittent shocks can cause numerous difficulties – from gear tooth fatigue to broken driveshafts—and flexible couplings can prevent these problems by reducing the vibrations transmitted to downstream components.
But what do you do if your equipment already features elastomeric couplings and you have a higher driveline vibration than you would like? How do you reduce the driveline vibration?
One of our customers had this situation and turned to us to help resolve the question.
The agricultural equipment manufacturer was experiencing vibration isolation issues with a track tractor. Amplification issues (aka vibrations) were evident at the idle speed. The manufacturer was using a continually variable transmission (CVT) and the vibration would appear as it transitioned into idle.
LORD’s flexible, elastomeric couplings are made to connect engine components (like the transmission, pump or compressor); they can also be used to connect starters, alternators, fans and other mechanisms. These flexible couplings reduce the magnitude of transmitted forces, mitigate shock events, decrease vibrations, and accommodate small misalignments between components. Couplings are generally available in a variety of flexibility levels (based on the type of heavy equipment and location within the drive train) and are rated across a range of horsepower.
Elastomeric couplings offer a comparatively low up-front cost (included during manufacturing) and require no end-user maintenance. Additionally, the performance of flexible couplings is not adversely affected by dirt or other contaminants—an important consideration for vehicles operating off-road or over soft ground, not to mention the constant exposure to dirt and debris during loading and operation.
Resolving the Issue
After comprehensive testing and analysis, LORD engineers recommended using a softer elastomeric compound with the same coupling—using the existing mold but replacing the stiffer elastomer previously used with a softer one that would significantly improve vibration isolation at their idle speed.
Please note that there are drawbacks and benefits to choosing either type of coupling, it’s not the proper choice for every situation. For instance, using a more flexible compound would result in better vibration isolation but a potential reduction in part life. The specific coupling chosen here has a predicted life of over 10,000 engine or “run” hours. In this instance, the softer coupling was the correct choice.
While we can’t share the specific details, increasing the flexibility (or reducing the stiffness) resulted in better isolation for our customer. Accelerometer tests showed a 3x reduction in transmissibility between the flywheel and transmission input shaft.
The Proof Is in the Numbers
Accelerometers were positioned on the flywheel and transmission input shaft to measure the vibration being transmitted through the system.
As shown in the chart here, vibration in the transmission input shaft measured with the stiffer coupling peaked at the engine’s idle speed of 1,000 revolutions per minute (RPM). After switching out the elastomer for a softer compound, vibrations peaked at only 460 RPM, which is well below the operating range of the engine.
By reducing the vibration transmitted to downstream components, the manufacturer has helped to prevent future difficulties in the equipment. This is a low-cost choice that requires no maintenance from the end-user and is not affected by the constant exposure to dirt and debris during operation—and a beneficial decision for both manufacturer and end-user.