Damper power dissipation

[Tim.Wright]

Has anyone out there calculated the power dissipated by their dampers? I'm doing some basic heat transfer calcs to size a damper and would like to check my input power number to see if its sort of ballpark.

I calculated approx 20Wrms per corner based on a lap around the Australian track.

I would imagine power dissipation would be less(?) around the US tracks as they are more open (less transients, less intensive on the dampers).

Anyone willing to share?

Regards

Tim Wright
Suspension & Vehicle Dynamics
Curtin Motorsport

[Tim.Wright]

Has anyone out there calculated the power dissipated by their dampers? I'm doing some basic heat transfer calcs to size a damper and would like to check my input power number to see if its sort of ballpark.

I calculated approx 20Wrms per corner based on a lap around the Australian track.

I would imagine power dissipation would be less(?) around the US tracks as they are more open (less transients, less intensive on the dampers).

Anyone willing to share?

Regards

Tim Wright
Suspension & Vehicle Dynamics
Curtin Motorsport

[HenningO]

I haven't done calculations of that kind but there's a thread at F1technical about shock absorbers and heat generation. Here is the link: http://www.f1technical.net/forum/viewtopic.php?t=4587&p...ostorder=asc&start=0 (http://www.f1technical.net/forum/viewtopic.php?t=4587&postdays=0&postorder=asc&start=0)

I'm also a bit curious why you use power dissipation as one dimensioning factors in your damper design. I would say there are a couple of factors of much greater importance, so I'd love to hear your take on it.

[Tim.Wright]

Your right, its only one of a number of factors I'm using to determine the stroke length and motion ratio.

I have pretty much settled on running the Cane Creek Double Barrell (mainly due to costs but with other reasons as well) These shocks are available in a number of different sizes and stroke lengths which is not typical of car shocks. So if the option (on stroke length) is there, then it should be optimised.

My thinking on stroke lengths are as follows:
"¢ Smallest shock for weight and packaging advantages
"¢ But not too small such that it will overheat - Hence the power calcs
"¢ Stroke length also affects the motion ratio which could in turn affects the shock speeds.

Any comments are welcome!

And thanks for the F1technical post

Tim Wright
Suspension & Vehicle Dynamics
Curtin Motorsport

[HenningO]

I don't think overheating is a problem with low short stroke lengths. I'd look into stuff like the increased hysteresis with shorter stroke length (with a low MR).

Depending on how much data you have, try to find at which damper velocities the dampers shifts to high speed (the knee in the damper curve). Using the DBs last year we never reached the hi speed region during normal driving.

[Christopher Catto]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by HenningO:
...try to find at which damper velocities the dampers shifts to high speed (the knee in the damper curve)... </div></BLOCKQUOTE>

Is your idea to run across the low/high speed range. Or just the high speed range??

The damper manufacturer should also be able to recommend some things in order to make the damper most efficient.

[Tim.Wright]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Using the DBs last year we never reached the hi speed region during normal driving. </div></BLOCKQUOTE>

Thanks for that info Henning, interesting. What motion ratios are you running (if you don't mind me asking).

Thanks for the heads up on the hysteresis too, something I hadn't put any though into as yet.

Ideally I would like to set things up so that
"¢ Low frequency [high amplitude] body roll and pitch due to cornering and braking is damped by the low speed region
"¢ High frequency [low amplitude] single wheel bump due to road surface is taken care of by the high speed region

This may mean modifiying/revalving the dampers.

Tim Wright
Suspension & Vehicle Dynamics
Curtin Motorsport

[HenningO]

The DBs were used in a monoshock setup so it differs a bit from a traditional setup.

The MR in heave (2 wheel bump,pitch) was around 1.4 (defined damper:wheel). We also ran the longest version of the DB as well, 75 mm stroke if memory serves me right.

I've heard about some teams modifying the DBs, by changing the oil. The DBs are not really designed to have changeable internals.

You are right with having the hi frequency excitations being taken care of by the hi speed region. However most tracks we compete at are fairly smooth, and I would imagine curbs or similar would be required to get into the the hi speed region.

[Tim.Wright]

Thanks for that.

I forgot you guys run on proving grounds over there which are nice and flat. Our track in the Australasian comp is a driver training (or similar) circuit complete with bumps and camber so I would expect to see a bit of high speed action.

Off the top of my head, our FOX shocks were at high speed about 70% of the time last year. I think Claude recomended a 50/50% split in between high and low speed which doesn't make much sense to me as it would be dependant on track surface.

Tim Wright
Suspension & Vehicle Dynamics
Curtin Motorsport

[flavorPacket]

don't get hung up on a specific ratio or some rule of thumb. look at the behavior of your sprung mass and 4 tires when subjected to various road inputs and how that effects vehicle performance. then make your curve and build your shock.

[HenningO]

I find Claude's statement a bit wierd. The knee (switch from high speed to low speed) is different on every damper.

flavourPacket's approach sounds like a good method. More specifically, look at the damping ratio at different speeds, then think about what you're seeing...