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Thread: Steer axles and cylinder force for trailers

  1. #1
    Associate Engineer
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    Sep 2018
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    Steer axles and cylinder force for trailers

    Please, I have a project I am working on with self-steer axles for trailers. I have been working on this project and I have not made any headway as of yet. Any Help to steer me in the right direction would be greatly appreciated.

    I have a self-steer axle I want to retrofit by mounting a linear actuator to help me steer the axle at low speed, this axle weighs 9000kg and would have a weight of max 9000kg on top of it when it steers.
    My main problem is selecting the right linear actuator and determining the location to mount it on. Af first when I was talking to an axle supplier he mentioned his force-steer axle has to generate at least 22000Lbf (this axle uses a hydraulic cylinder at 3 x 8 cylinder at 3000PSI) will generate enough force to steer the axle. I believe this would be too much and there has to be some moment somewhere that I did not take into account. I went back did some more research and came up with a research article from PARKER that asks to calculate the Kingpin torque (17000Lb/in) which I did and then I found the cylinder force (1400lb).

    1. I am confused as to if it takes 1400lb to steer the axle or it takes 22000lb because these values are very far apart.

    2. also from some of the pictures I have seen they mount the cylinders close to the pivot ends of the connecting rod but if the linear actuator is the actual one doing the pushing, would the force and the stresses generated from the application not break the end of the connecting pin. Please, How do I ensure that I am able to successfully carry out this application considering the factors involved?
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  2. #2
    Administrator Kelly Bramble's Avatar
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    Feb 2011
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    An analysis that considers worst case forces required to turn the axle is in order. A factor of safety (FOS) should be considered in the sizing of the hydraulic actuator.

    The senarios you have described are interesting however there is not correlation between the two presented.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Associate Engineer
    Join Date
    Sep 2018
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    Further inquiry

    Hello Kelly

    Sorry please, could you please explain further what you mean.

    In the picture here I have actuator connected to the end joint of the connecting rod, my idea is to use the push the rod at the point and get the wheels to turn as shown. How do I ensure that this works properly?

    I know it is easier to turn the wheels while in motion but if we are designing for a factor safety of 2 does that mean I would have to use an actuator of 3000Lbf. also, I am worried about the stress that would be generated on the steering arm that connects to the linkages, I want to make sure it can handle a load of 18000kgf.
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    Last edited by ighomuayeanthony; 12-05-2018 at 06:34 PM.

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