Quote:
Originally Posted by Kirk
So Jake... if we guess this super secret factor will you confirm if it is correct or not? I have seen Charles Navarro of LN state that he would take this secret to his grave!
I am going to throw out my guess and I am going to bet that I am spot on.
The issue is that in the design of the intermediate shaft the ball bearing application is compromised (not optimal) and the magic number (or constant) that it is compromised by is 20%. We state load numbers for the 6204 bearing based on manufacturer's numbers, but those numbers assume that the inner race of the bearing is turning. In most applications the inner race is fitted to a shaft through an interference fit, the shaft rotates, the inner race rotates, and the outer race is held in place in a fixed housing. Bearing load numbers are based on this scenario.
This is not what happens on the intermediate shaft though. That scenario is exactly the opposite. The inner race is fixed and it is the outer race that is pressed INSIDE the intermediate shaft that rotates.
So who cares if it's the outer race that rotates rather than the inner race? Engineers care because this one little difference has a significant impact on how much load the bearing can take. The general rule that is used in bearing calculations is that the impact is a 20% decrease in load. Decreased load effects calculated bearing life and failure rates.
Is this significant then? 20%? Damn straight that is significant. So how to address this? LN went to a stronger ceramic bearing with a much higher load rating than OEM. But eventually LN went to a plain bearing with significantly different load characteristics altogether.
So what do you say Jake? Do I get the gold star??? :dance:
Kirk Bristol
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This is just another piece of the very complicated puzzle. When we first started looking at this problem, the use of the bearing in outer race rotation was one of the first problems I knew exactly how to tackle. That's the reason for a ceramic hybrid bearing with sintered silicon nitride balls to be specific.
Jake and I have been using sintered silicon nitride for various components including lifters in pushrod Porsche engines primarily for their wear performance, but the added weight savings is huge.
Now consider the reduced mass of the ceramic balls and how that relates to the loads exerted on the races during the constantly varying acceleration and deceleration of the IMS bearing. This is even more important considering the load on the IMS bearing isn't even across the whole circumference of the races. Since the sintered silicon nitride balls are only 40% of the weight of equivalent steel balls, centrifugal force is lower - the lower weight of silicon nitride balls enables rapid accelerations and decelerations with reduced wear.
At any given time a very small surface area of the bearing is carrying all the load. To simplify what's happening, the balls are slung round 3/4 of the circumference of the bearing and they go from unloaded to fully loaded with only 1 to 2 balls carrying all the load. This is why we see flat spotting of the balls and skidding in the races leading to pitting and eventually complete bearing failure.
Integrated Reliability Solutions
Considering the bearing is in outer race rotation and already prone to skidding, this is just one of the reasons we chose against roller bearings from the very beginning and focused on ceramic hybrid bearings.
However, I will clarify that just going to a ceramic hybrid doesn't give you a higher load capacity than an equivalent conventional bearing but their benefits certainly outweigh the cost.
Hybrid Ceramic Bearings | Applied.com
PS. George is my dad. He used to work in the aerospace field in sales and he came to LN a few years ago to help my wife and I.