Steering linkage loads, heavy trucks

[okeng]

I'm working on a steering linkage for a triple-steering-axle truck. I have the geometry all figured out and am trying to work out the loads for the pitman arms, which are nearly the only parts that aren't off-the-shelf components.

Can anyone advise me on what the design loads on this kind of system should be? I am headed in the direction of using the maximum torque that the steering box can develop at the load.

Any help would be greatly appreciated.

reference: thread60-54516

Thanks

 

[GregLocock]

Plus a factor for abuse eg whirling the steering wheel round stationary and the the tire hits a kerb.

The other thing to look at it is the force seen due to potholes and kerb strikes.

Since the steering is THE MOST CRITICAL safety system built into the vehicle, it is as well to overdesign it for strength.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[JStephen]

If you can work out allowable loads for some of the "off-the-shelf" items, you wouldn't necessarily need to exceed those loads.

Of course, seems like you have no way to know if any of the off-the-shelf items are adequate, either? Just because they make it for some other application doesn't mean it's good for yours...

 

[okeng]

Most of the other off-the shelf components are part of the axle assemblies that come from a supplier (two suppliers, actually). They've been through the usual rigorous application approval process. Part of the problem is that there are a number of suppliers involved, and while each is competent and thorough, it still falls on us to coordinate it all and take care of the connecting parts.

Thanks,

Jess Davis

 

[btrueblood]

I would agree with Greg, you want to look at a worst-case loading: downhill grade with truck fully loaded, brakes being applied, operator attempting to turn wheel as the wheel hits a large rock.

This happened to me, and the linkage snapped. Luckily, was creeping in compound low, and was able to counter-steer with the other wheel, and come to a stop with both wheels toed-out to their stops, before truck went over the 15-foot embankment (I was hauling the gravel for building the road at the time).

 

[Fabrico]

There are lots of steering arms for nearly every box out there. They are nice forged pieces, built for sefety and strength. Some have a large blanked area on the drag link end so a closer-in joint hole can be accomodated.

I would'nt get too creative, you could find yourself outside the design parameters of the steering box.