Welcome to four questions with an engineer, a podcast about bearings and motion control. Each episode discusses one aspect of motion control and the bearings that make it happen. We are joined by Corey Helgeson, a mechanical engineer from CCTY Bearing’s US office.
On today’s episode we’re talking about bushings founding seats. Corey, can you tell us what purpose do bushings have and see the applications?
So in seat applications there’s generally two locations we work with. There’s a suspension, which basically just is a height adjustment for the seating, and then there’s a recliner bushing, which facilitates the reclining movement of the seats and it’s a bushing press fit into a gear bore. There’s PTFE on the inner surface that’s contacted by wedge blocks.
Now the the recliner bushing is very critical bushing. In the industry we always see the requirements getting harder and harder. Some of the main things it needs to be low friction but, more importantly, stable friction, which means throughout the life of the bushing, throughout all the durability, and you know all the up and down to the seat. It needs to maintain the same friction range to provide the same feel for users throughout the life.
Another important thing about this bushing is generally a bushing will have a shaft on the inside. It’s a wedge block. So the contact area on the bushing is a lot smaller than normal, so the stress in turn becomes a lot higher because of the small contact area.
Another unique thing about these bushings is a lot of times there’s welding going on very close to the bushing, which can create high temperature scenarios for a bushing and requires a bushing to be able to take the high tempts. And then, just because of the application being so tough, it needs a strong backing. And generally in PTFE bushings you’ll see low carbon steel, made carbon steel, as the backing, which we do use in many applications. But we have encountered some applications where we actually have to use high alloy steel as the backing because the strength actually needs to be that high.
I’d say there’s two main types of PTFE bushings. There’s PTFE bushings that are mechanically fastened by sintered bronze. So basically you have a steel backing and the PTFE formulation is poured and rolled into a centered bronzeand that’s how it’s mechanically fastened. Some bushings have PTFE tape. So you have a steel backing and then the PTFE is adhered to the steel backing.
How does welding impact the bushing choice?
Yeah, well, since the welding heat can transfer to the bushing and, you know, affect the liner, you need a bushing that can withstand very high temperatures in many applications. Our bushing is formulated to stand up to four hundred degrees Celsius. So it’s important in many applications.
How are seat bushing tested in the seat recliner application?
So generally OEMs will just test it in a few different ways, but the main durably tests will be like take the actual seat frame used in the vehicle and then attach a motor to it. The actual motor used the vehicle usually will overheat if they run it this much, so you have to use a better motor. But then you just run it continuously and we’ve seen the cycles go up and up on these tests, and that’s one part of the test. Another part is simple again, they’ll have weight blocks, usually a hundred to two hundred pounds, and attach it to the the upper part of the seat where you’re, you know, top your back would hit and then run the seat back and forth. And then another one of the important tests is a stall test, basically where the motor is running but the seat is not moving. And if you can imagine if you were trying to recline your seat up or down and there is something there. That is an actual situation that happens in real life. So it’s important that the bushing can withstand that.
At CCTY we have a seat frames we used to test bushings, but also what we know what’s really the best is a OEMs that we work with will just send us their seat frame and they’ll send us their recliner wedge block and everything and we will put our bushing in there and then we can just run four different seat frames continuously at our testing facility. That’s how we actually formulated our bushing materials so quickly, is because we have the ability to continuously test four different seats at all times. So testing different things and always improving our formulation.
And that’s all for today. Thanks for joining us for four questions with an engineer.