Bender
NAXJA Forum User
- Location
- Cambridge, Ontario
GroversXJ,
I think you're getting your equations confused. i.e. you're using the torstional stress equations but instead of using the radius of gyration for the u-joint you are using the cross section moment of inertia of the trunnion..totally different things.
BrianHo12 has the right idea though.
If you put 100 in-lb through two different u-joints and you want to figure out the force being applied to the bearing cap you divide 100 in-lb by the distance from the u-joint centre to the bearing cap. So BrianHo12's example is correct. A u-joint that has twice the centre to cap distance will experience half the force at the cap itself. This will increase the lifespan of the u-joint as there will be less stress in the needle bearings due to the lower forces going through them. (Again this is assuming both bearings are the same)
It is in this situation where the Stress = Moment*radius/moment of inertia applies where the moment of inertia is calculated using the cross section of the trunnion. As long as both trunnions are the same diameter and have the same size grease hole (if one is present) they will both have the same moment of interia. Using this you could calculate the stress at any point along the trunnion and you can see the stress at the bottom of the trunnion would be the same for both joints assuming they have the same sized bodies but one has longer trunnions. This is where I think the 1330 must have a larger body to get the 3/4 ton rating. It makes sense the needle bearings would last longer since they will be experiencing less load however if both bodies are the same size they will both be experiencing almost identical stresses.
In GroversXJ's example the same sort of equation applies however it is calculating the stress in the u-joint in a different plane. In this case you are using the radius of gyration of the u-joint using a plane perpendicular to the axis of the driveshaft. i.e. a cross section of the entire joint as opposed to just a trunnion. In this situation a larger joint would indeed have a larger radius of gyration which makes his simlifications false. However, you would come up with the same conclusions as shown in the method above if you were to take the time to actually calculate the radius of gyration of two different size joints.
Just to note I'm simplifying the above stuff quite a bit. There would be other factors like fatigue and energy absorbing capabilities that would come into play to change the lifespan and strength of the two joints.
Then again...I could be completely wrong so feel free to point out my mistakes. It's been a few years since I've had to use this sort of stuff
I think you're getting your equations confused. i.e. you're using the torstional stress equations but instead of using the radius of gyration for the u-joint you are using the cross section moment of inertia of the trunnion..totally different things.
BrianHo12 has the right idea though.
If you put 100 in-lb through two different u-joints and you want to figure out the force being applied to the bearing cap you divide 100 in-lb by the distance from the u-joint centre to the bearing cap. So BrianHo12's example is correct. A u-joint that has twice the centre to cap distance will experience half the force at the cap itself. This will increase the lifespan of the u-joint as there will be less stress in the needle bearings due to the lower forces going through them. (Again this is assuming both bearings are the same)
It is in this situation where the Stress = Moment*radius/moment of inertia applies where the moment of inertia is calculated using the cross section of the trunnion. As long as both trunnions are the same diameter and have the same size grease hole (if one is present) they will both have the same moment of interia. Using this you could calculate the stress at any point along the trunnion and you can see the stress at the bottom of the trunnion would be the same for both joints assuming they have the same sized bodies but one has longer trunnions. This is where I think the 1330 must have a larger body to get the 3/4 ton rating. It makes sense the needle bearings would last longer since they will be experiencing less load however if both bodies are the same size they will both be experiencing almost identical stresses.
In GroversXJ's example the same sort of equation applies however it is calculating the stress in the u-joint in a different plane. In this case you are using the radius of gyration of the u-joint using a plane perpendicular to the axis of the driveshaft. i.e. a cross section of the entire joint as opposed to just a trunnion. In this situation a larger joint would indeed have a larger radius of gyration which makes his simlifications false. However, you would come up with the same conclusions as shown in the method above if you were to take the time to actually calculate the radius of gyration of two different size joints.
Just to note I'm simplifying the above stuff quite a bit. There would be other factors like fatigue and energy absorbing capabilities that would come into play to change the lifespan and strength of the two joints.
Then again...I could be completely wrong so feel free to point out my mistakes. It's been a few years since I've had to use this sort of stuff
