Help with steering system calculations

[OTCengi]

Ok, here's the question for all of you that I'm struggling to answer. The vehicle I'm currently working on is of a cab forward design, where the axles are all behind the cab. I'm trying to find equations which can be used to help me determine the phasing angles required in the system.

Right now, the steering wheel has a u-joint at the bottom connecting in to a 90* miter box. Another shaft leaves that box at a 30* angle (in 3-D space) passes through the cab floor, and then connects to another 90* box mounted behind and below the first (between the frame rails). There is then a 2nd shaft leaving the 2nd 90* box at a 10* horizontal angle (keeps the same height between the frame rails, but angles toward the center of the truck). From there it is supported by a bearing block and connected to a 3rd shaft which returns back to the steering gear with a 20* angle (again 3-D space) at the shaft 2/3 junction and a 15* angle entering the steering gear.

I'm having difficulty on calculating the phasing requirements due to the dual 90* boxes and would appreciate any assistance possible.

Thanks

 

[mloew]

This topic was covered in the Transmission and Driveline engineering Forum (forum78) in the thread Compound U-Joint Angles (thread78-53988) for drive-shafts, but the math is obviously the same.

A link to a resource I have found helpful in looking at U-Joint angles is here:

http://www1.mn.man.de/manted/aufbaurichtlinien/gb_f4.html#Anchor-21683

I recently had to solve a similar problem. I would recommend laying out the geometry in a CAD program (I use Pro/ENGINEER) and driving some geometric indicators from equations.

Good luck!

Best regards,

Matthew Ian Loew
"Luck is the residue of design."
Branch Rickey

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

 

[GregLocock]

I'd lay it out in ADAMS, as it is designed to solve exactly that sort of problem. You need a graph of steering ratio (steering wheel angle/steer angle of wheel) for each wheel, form lock to lock. Although this can be done analytically (obviously) I think you'd find it quicker to model it.

Cheers

Greg Locock

 

[mloew]

OTCengi,

Interested to hear how this worked out for you.

Best regards,

Matthew Ian Loew
"I don't grow up. In me is the small child of my early days" -- M.C. Escher

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

 

[OTCengi]

Well, the system is a bit complicated, but I'll have final results in a few weeks. Our components group had a spreadsheet that was modified for this project. What I came up with was a final system using 2 90-degree miter boxes and 3 shafts (2 are collapsible). The steering column feeds directly into the first 90-degree box at a 30-deg angle. Then the first collapsible shaft leaves the 90-degree box at a 35-deg composite angle going down and rearward. This shaft enters the second 90-degree box at the same 35-degree angle. Leaving the second miter box is a shaft at a 10-degree angle (horizontal toward the center of the vehicle only) which is connected by a u-joint to the final collabsible shaft at a 19-deg angle (composite) which returns the shafts to the LH frame rail and also down to the steering gear.

Complicated, but the calculations appear to support that this will work. The vehicle will be going for it's maiden drive on June 15th, so I'll let you know.

 

[mloew]

OTCengi,

How did the vehicle work out?



Best regards,

Matthew Ian Loew
"Organizations cannot make a genius out of an incompetent. On the other hand, disorganization can scarcely fail to result in efficiency." -- Dwight D. Eisenhower

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