Roll Center
Roll Center
(OP)
I wonder if someone can explain the attached suspension geometry to me. It's on my motorhome which is essentially a 3 axle bus. The attached drawings show the rear suspension which has a single hanger that supports both the drive and tag axles. The drive axle has 4 air springs, the tag axle 2. The drive axle has a panhard rod (item #34) that connects from the frame rail to the differential housing. I know that this is where the roll center is located for the drive axle. What I'm not sure of is the significance of the line of attack of the tag axle control arms. A line drawn thru the tag axles bushings 53 and 38 intersect the panhard bushing at 34. What was the engineer achieving by this arrangement?
RE: Roll Center
RE: Roll Center
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Roll Center
The manufacturer says this: "Single central hanger unitizes drive and tag suspensions allowing suspensions to operate in correct phase with drive line angles for maximum life of components". The part about "correct phase" prompted me to dig a little deeper. This is a diesel pusher bus suspension. I understand the desire to have the driveshaft move in a similar arc as the final drive, and the 4 leading link drive axle provides that. Is there more to the "correct phase" statement than that? Is there anything to do with body roll of the bus and the effects of axles moving in phase with one another? BTW, the tag axle suspension looks like your typical high roll resistance class 8 trailer suspension but it actually has significant one wheel bump independent motion. It's mounted to the hanger with 6 bushings, 3 on each side, and these bushings are capable of 6 deg of cardanic movement. FWIW.
RE: Roll Center
Cheers
dynatune, www.dynatune-xl.com
RE: Roll Center
RE: Roll Center
If you tried to corner hard, it would probably lift up the inside wheel of the tag axle, followed shortly thereafter by very alarming levels of body roll that hopefully scare the driver into slowing down before the bus rolls over. It might have antiroll bars built in somewhere; can't tell from the diagram. Air suspension, particularly with the air springs forced a good way in from the outside of the vehicle due to the significant width of the tires, is not good at resisting body roll.
RE: Roll Center
RE: Roll Center
If you cross the inlet and outlet lines on one side, you will create an air spring roll stabilize bar equivalent. If you put an orifice restriction in the crossover line, you will create roll damping as well.
RE: Roll Center