Ford Ute, inertial/mass properties + suspension parameter info needed

[cavedweller]

Hi guys,

Searched over the net, through books, papers and i can't find the info i need. Sorry in advance for all the questions, im hoping some industry guys can help me out.

Im tyring to do some 1/2 car simulations of a ford courier / mazda bravo ute (i think they are the same) and without pulling the thing apart bit by bit and measuring it i have no idea of exact weights etc. Ford is no help with the info. Stock weight is 1760kg, wheelbase is 3m, static unloaded cog is approx 1.35 from the front

Information abounds for cars and the NHVSA data is good for inertial properties but lacks unsprung & suspension parameter details.

Does any body know, or have some good estimates of these things.

1. Front unsprung mass (tires, wheels, linkages)
2. Rear unsprung mass (tires, wheels, diff, leaf springs)
3. Pitch moment of inertia / dynamic index unloaded/loaded
4. Approximate equivalent linear front and rear spring stiffness and damping values unloaded/loaded

For cars the combined unsprung mass is around 10% of the total weight, i have read for commercial type vehicles with leaf springs and solid axle this can go up to 25%, so its obviously something that will effect simulations big time if its not right, especially in an unloaded state at the rear of the ute.

Also, the rear leaf springs are non-linear, but can anybody give me some rough spring k's for small and large amplitudes (seeing they are mass and amplitude dependant), again it is not possible for me to pull them off and do the test, we just don't have the facilities at our uni. I performed some static tests with weights and measured the deflection but im not sure how accurate they are seeing they are static. The small deflection k should be 3 times greater according to gillespie, but im not sure if ford put some special friction coatings on, and its dual rate as well complicating things further.

Finally, i am a bit confused as to whether i should include the lift forces and weight transfer effects from acceleration/deceleration.

I am not interested in any roll effects (it’s a half car model), and from my readings the effects of acceleration / deceleration are short transient effects and only effect front to rear weight transfer a few% under "normal" driving conditions. Im not talking about evasive manoeuvres here, just normal conservative driving like your grandma does. Can they be ignored without alot of error?

However, lift forces can contribute 5-10% unloading force according to the book im reading, this would effect the system natural frequencies a fair bit correct???? I understand its related to the square of the forward velocity, but at what speed would these forces really effect things?

Again, data for cars is around, would the lift coeffeceints of around 0.3 be valid for a ute?

I can handle short duration transients in my simulations (weight transfer/gear shifts etc) but a longterm 5-10% reduction will throw a spanner in the works. The purpose of the simulation is to get the time domain data for the bounce and pitch modes. I want to try and get it close to real, but not super complex.

Anything else that would effect bounce and pitch modes that i have completely over looked??

Thanks in advance, any links/books/papers appreciated

-Matt

 

[GregLocock]

1. Front unsprung mass (tires, wheels, linkages)

roughly 100 kg

2. Rear unsprung mass (tires, wheels, diff, leaf springs)

roughly 150 kg in bounce, less in tramp

3. Pitch moment of inertia / dynamic index unloaded/loaded

Use the values from the NHTSA website as a guide

4. Approximate equivalent linear front and rear spring stiffness and damping values unloaded/loaded

probably 50 N/mm front 70-200 rear as a ballpark


The only way to get this stuff is to measure it. I would have thought an hour with the car, a group of friends with known weights, and a tape measure would be rather helpful.

Shockers don't matter much, probably around 1000 N/m/s



Cheers

Greg Locock

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

 

[cavedweller]

Thanks for the quick reply Greg. Those figures you quote for unsprung are ball park to what i was using ( which was 70kg front, 150kg rear)

The static measurements i took for front and rear were approx 38,000N/m for the front pair excluding tire stiffness (which i assumed was 404,000N/m for the front /rear pairs), and the rear leaf spring pair 60,000 to 85,000N/m increasing in stiffness as the load increased (due to the dual rate leaf spring), except for the first loading condition which was 80,000N/m, this is low displacement high stiffness that is talked about i *think*, but its not 3 times higher as suggested by gillespie which made me question the validity of the static measurements, like i say, i don't have the facilities to perform a dynamic analysis of the leaf springs which is what i really need to construct the proper hysteris loop.

I am assuming that those figures you quoted are for individual front and rear sides, not pairs, and not including tire stiffness, otherwise my values are way off

Also, to do with Aerodynamic lift i performed some calcs last night. According to the results i got at 100km/hr you can have as much as 400kg of vertial lift, so approx 100kg per wheel, sounds very excessive, is this even ball park? I have little to no knowledge of aerodynamics of cars, and most aero books i have seen are for race cars trying to do the opposite thing

Thanks again

-Matt

 

[GregLocock]

Those unsprung masses are per axle.

The wheel rates are per side, but they are only guesses. Your results seem ridiculously low, I strongly urge you to go out to the car park.

Hysteresis is important, again as you see what happens when people jump on and off the back you'll get some ballpark figures.

I think your aero results are unlikely.



Cheers

Greg Locock

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

 

[cavedweller]

Yeh, i did some more reading on aerodynamic lift and the number the equation outputs is in newtowns, even though you input kg and meters, i really hate non SI equations. Don't i look silly.....

Hmmmm.... i thought my figures might at least be close. My understanding is the suspension stiffness is usually around 10% of the tire stiffness for a passenger car (which i assumed was 202000N/m or 404000N/m for a *pair* of tires), your values put the front at close to 25% and the rear 30-95% of the tire stiffness, is that right? Could explain a few issue i have been having.

Thanks for your time, details like this on semi commercial vehicles are hard to come by.