Post rigs

[DaveW]

How do you calculate Tyre heat rate?

The area enclosed by one cycle of a load-displacement trajectory is work done (heat) per cycle. Divide that by the time required to describe one cycle of the trajectory to obtain work done per unit of time. That is the principle, & it can be used to estimate work dissipated by the dampers & downforce actuators (if used). The total dissipated should be equal to the work input to the vehicle, which can be calculated independently. Discrepancies can be (should be) of interest....

[Jersey Tom]

I'm curious as to what method you're using for measuring tire temp on your rig.

[DaveW]

I'm curious as to what method you're using for measuring tire temp on your rig.

I don't (as a matter of course) attempt to measure tyre temperatures, JT. I try, as a principle, to extract as much information as I can with minimal changes to the vehicle (although tyre pressures do have to be adjusted slightly from start of day).

[Jersey Tom]

Ah ok, think I see what you're saying. You're literally looking at energy loss through your load cells, rather than measuring the temperature change of the tires directly. Gotcha.

[Belatti]

Now my question would be how does Dave distinguishes between dampers and tyre energy loss.

[DaveW]

Now my question would be how does Dave distinguishes between dampers and tyre energy loss.

Don't ask for trade secrets, my friend, & I won't be forced to tell untruths. I'm sure you will be able to work it out, however....

[ghost406]

How do you calculate Tyre heat rate?

The area enclosed by one cycle of a load-displacement trajectory is work done (heat) per cycle. Divide that by the time required to describe one cycle of the trajectory to obtain work done per unit of time. That is the principle, & it can be used to estimate work dissipated by the dampers & downforce actuators (if used). The total dissipated should be equal to the work input to the vehicle, which can be calculated independently. Discrepancies can be (should be) of interest....

Hi thank you for the answer,
you mean load cell and upright displacement to calculate the heat in the tyre.
the best thing is to do it for each cycle of the run and after you make a mean of the values?

[DaveW]

Hi thank you for the answer,
you mean load cell and upright displacement to calculate the heat in the tyre.
the best thing is to do it for each cycle of the run and after you make a mean of the values?

Actually, the calculation can be implemented in the frequency domain. It is then possible to present the results in several ways, depending on what is of interest.

Here is a useful (if distorted), presentation that contains response functions of work done for tyres, dampers & D/F actuators as a percentage of the overall energy input during a "heave" sweep. The legends contain numerical values extracted at a nominated frequency (5.273 Hz. in this case). The functions are distorted because energy input is not constant (it is small at both low & high frequencies).

The plot is useful because it showed (in this case) that the vehicle had a good structural integrity for frequencies below, say, 12 Hz. It was not so good at higher frequencies because the sprung mass was no longer a monolith (components such a radiators & driver ballast started to go their own ways). Interestingly, perhaps, strapping a real driver into the vehicle (not something I would recommend) demonstrated that, without realizing it, he "worked" with the vehicle to reduce the energy dissipated by the dampers - a mobile mass damper.

Actually, the structural integrity of the particular vehicle shown was very good. That is not always the case, however, and the plot referenced will highlight deficiencies very clearly. The plot also highlights deficiencies in the down force actuators - the rear actuator was in need of a service in this case...

[ghost406]

Hi thank you for the answer,
you mean load cell and upright displacement to calculate the heat in the tyre.
the best thing is to do it for each cycle of the run and after you make a mean of the values?

Actually, the calculation can be implemented in the frequency domain. It is then possible to present the results in several ways, depending on what is of interest.

Here is a useful (if distorted), presentation that contains response functions of work done for tyres, dampers & D/F actuators as a percentage of the overall energy input during a "heave" sweep. The legends contain numerical values extracted at a nominated frequency (5.273 Hz. in this case). The functions are distorted because energy input is not constant (it is small at both low & high frequencies).

The plot is useful because it showed (in this case) that the vehicle had a good structural integrity for frequencies below, say, 12 Hz. It was not so good at higher frequencies because the sprung mass was no longer a monolith (components such a radiators & driver ballast started to go their own ways). Interestingly, perhaps, strapping a real driver into the vehicle (not something I would recommend) demonstrated that, without realizing it, he "worked" with the vehicle to reduce the energy dissipated by the dampers - a mobile mass damper.

Actually, the structural integrity of the particular vehicle shown was very good. That is not always the case, however, and the plot referenced will highlight deficiencies very clearly. The plot also highlights deficiencies in the down force actuators - the rear actuator was in need of a service in this case...

Thxs

[Belatti]

Now my question would be how does Dave distinguishes between dampers and tyre energy loss.

Don't ask for trade secrets, my friend, & I won't be forced to tell untruths. I'm sure you will be able to work it out, however....

Sorry for being that naive

[Belatti]

Interestingly, perhaps, strapping a real driver into the vehicle (not something I would recommend) demonstrated that, without realizing it, he "worked" with the vehicle to reduce the energy dissipated by the dampers - a mobile mass damper.

This is very noticeable in karts! I have seen very good drivers working as mobile mass dampers!!

Have you ever rigtested a kart, Dave? I doubt a kart team would ask for your services because they may think: what for? we dont have dampers or unsprung mass!
But I think they could have a better understanding of their suspension: tyres, the very tuneable chasis stiffness and driver mobile mass damper.

[DaveW]

Sorry for being that naive

No need to apologise, Belatti. It was just my poor attempt at humour...., although I do try to stop short of telling the competition exactly how to do things.

I haven't tested a kart, although my colleagues in Canada have tested a snowmobile, I believe (but that does have a suspension).

[ghost406]

Now my question would be how does Dave distinguishes between dampers and tyre energy loss.

I would do like that:
- Dampers for the front: (Load Cell Front- 2*Mass Wheel Front*Accel Wheel Front- 2*Mass Actuator Front* Accel Actuator Front)*Damper Travel Front
-Tyre: (Mass Wheel Front*Accel Wheel Front)* Wheel Travel
And you do the same for the rear.

But I might be wrong???

What do you think?

[DaveW]

Just for interest, here is a frequency domain "work done" plot for a fairly high end production road vehicle extracted from a "heave" input run. No down force in this case (of course). The work done by dampers and tyres dropped to just over 50% of the input energy at 10 Hz., implying that almost 50% was dissipated by something else. Notice also the fairly dramatic increase in work done by the front tyres at frequencies above 10 Hz.

It turned out that the fundamental natural frequency of the power train on its simple rubber mounts occurred at a little over 10 Hz., and it was the (nominally undamped) mounts that were responsible for dissipating all that energy. Not, perhaps, the most intuitive result, even though the movement of the engine, etc. was truly impressive at that frequency (& out of phase with body motion).

Unsurprisingly, the vehicle had a persistent "shake" on the road, & it would be a reasonable guess that the life of the power train mounts might (would probably) be limited. The "fix" would be suitably tuned damped engine mounts. Something else that a four post rig can help with....

[ghost406]

Just for interest, here is a frequency domain "work done" plot for a fairly high end production road vehicle extracted from a "heave" input run. No down force in this case (of course). The work done by dampers and tyres dropped to just over 50% of the input energy at 10 Hz., implying that almost 50% was dissipated by something else. Notice also the fairly dramatic increase in work done by the front tyres at frequencies above 10 Hz.

It turned out that the fundamental natural frequency of the power train on its simple rubber mounts occurred at a little over 10 Hz., and it was the (nominally undamped) mounts that were responsible for dissipating all that energy. Not, perhaps, the most intuitive result, even though the movement of the engine, etc. was truly impressive at that frequency (& out of phase with body motion).

Unsurprisingly, the vehicle had a persistent "shake" on the road, & it would be a reasonable guess that the life of the power train mounts might (would probably) be limited. The "fix" would be suitably tuned damped engine mounts. Something else that a four post rig can help with....

If I calculate work done for tyre, dampers, aero actuators and if I had all this value it is not equals to the work input by the rig on my matlab model. I make a mistake but I do not know where...