Dexter axle shock absorber

[Dextersp1]

Originally Posted by Darral T.

I'm lost. I see very little difference between the two charts- one with the shocks and one without.

Yes, no difference between the big and small shocks? On the smaller 2 of the 3 parts don't show a difference. The 3rd one does but that just could be a difference in test procedure.

If you look at the chart for the first bump the information looks almost identical with and without shocks - strange.

[Fallon]

Jump on the bumper of your car/truck & jump off. It will bounce once. Try the same on an old beater with toasted shocks. It will bounce up and down like a basketball for a while. Shocks can only dampen the initial impact slightly & you don't want them to stop it. If they did stop the axle from moving why even have a suspension? They prevent the suspension from continuing to bounce around once its absorbed the impact. It prevents or drastically minimizes aftershocks.

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[dleverton]

Shocks dampen the oscillations of a mass on a spring and in this case the mass is the wheel. On cars this is necessary because if the wheel continues to oscillate after a bump, then the tire spends some time off the ground so not providing steering force or acceleration or braking force. The cost of using shocks is that shock of bumps is transmitted from the road to the car through the shock absorber and the ride is rougher (talk about misnaming a device). Trailer tires are less dependant on braking and not at all dependant on acceleration and do not need the bump forces transmitted from the road. I would not put shocks on a trailer. Just my opinion.


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Doug L

[WizWid]

Originally Posted by dleverton

.... The cost of using shocks is that shock of bumps is transmitted from the road to the car through the shock absorber and the ride is rougher (talk about misnaming a device). .....
Doug L

With respect - I completely disagree with this notion -and the proof lies in that chart a few posts up. The shock is absolutely NOT transmitted to the trailer. It IS absorbed by the shock absorber and turned into heat. Please look at the waveforms again.

--Jim.

[redbarron55]

Actually the proper term for shock absorber and as used by the Brits is DAMPER and its purpose is to damp the oscillations on a spring supported system.
The rubber suspension tends to damp the oscillations (turning the excess movement into heat), but the damping is not complete. Ideally the shocks would be smart enough to have variable damping to change their effect for sharp jolts, high displacement regular frequency etc. as necessary and the new, better valved shocks and electronic controlled for cars do this so you get a smooth ride on smooth roads and higher damping for rough roads.
Shocks are valved to have a greater effect on jounce and rebound, since the initial movement needs to be undamped (to some extent) and the rebound is damped. This means that the first part of the bump moves the wheel and the rebound is slowed. The shock valving does this. Shocks are rated as to 50-50, 20-80 etc depending on what the chassis tuner is looking for.
What we are looking for the the carryover oscillations to be damped so that the trailer is not bouncing all over and shaking the contents more than necessary.
AL-KO in the US contends and the other torsion axle manufacturers say that the damping of the rubber is enough for a trailer.. AL-KO Europe adds shocks and the Euro axle is setup to add the shocks to the axle and their trailer frames. Viewing their video shows the usefulness clearly. The benefit is in smoother ride and damping the tendency to sway from side to side.
The enemy of towing a trailer is the tendency of the combiner tow vehicle and trailer to enter into undamped oscillations and the amplitude of such increase instead of being damped and decreasing. Not only do the shock absorbers create a smoother damped ride, but also damp the side to side oscillation from the CG of the trailer being higher than the roll center.
All in all a Win - Win for shock absorbers. Perhaps the fitment of an anti roll bar would complement the suspension of trailers as well for the same reason?
This damping of the oscillations is the reason I think that my VW Sportwagen tows so well. The IRS and the fairly stiff shocks damp the oscillations better than a softly sprung SUV. The result is what is called Dead beat damping where displacement is quickly damped out and swaying is minimized. Shocks on the trailer could only help!
The addition of an anti sway bar to the trailer to TV combination adds the friction damping to help this sway and all it does is change the energy to heat like any other damping system. in the European AL-KO setup the actual coupling has friction pads that are clamped to the ball with a lever to do the same thing and the Hitch balls do not mount with a threaded shaft and nut that would be loosened for this reason.


Since Al-KO basically invented the rubber sprung torsion axle they probably have a fairly good idea as to the best way to operate one as well.

[Dextersp1]

Originally Posted by widgetwizard

With respect - I completely disagree with this notion -and the proof lies in that chart a few posts up. The shock is absolutely NOT transmitted to the trailer. It IS absorbed by the shock absorber and turned into heat. Please look at the waveforms again.

--Jim.

The charts are showing that the readings are the same for the largests shocks - they all read between 9.5 to 10 with or without shocks.

In between the largest shocks there the first set does not show much of a difference with or without shocks.

For the last two bumps we don't have a point of reference. We don't know for example if we were riding in the trailer, would we notice if there were shocks or not being used.

With all due respect I think dleverton has some good points.

[WizWid]

Originally Posted by Dextersp1

....For the last two bumps we don't have a point of reference. ..

Dex,

We absolutely have a point of reference.
No anecdotes here - just data.
This is a "g" meter mounted on the fiberglass of a Casita.
It is showing how much energy the trailer is "seeing"

Jim

[tractors1]

Looks like an accelerometer using a serial cable to feed Megunolink software. Curious why the Y axis units are called "Bounce" - which is a bit confusing as that indicates to me a distance rather than a force (g-force.)

[WizWid]

Originally Posted by tractors1

Looks like an accelerometer using a serial cable to feed Megunolink software. Curious why the Y axis units are called "Bounce" - which is a bit confusing as that indicates to me a distance rather than a force (g-force.)

Charlie,

Because in my original "discussions" with Dex I was trying to make the point (using real data) that it is the excessive "bounce" that we are trying to eliminate.
8.2 on the Y axis = 1G

Jim

[Dextersp1]

Originally Posted by widgetwizard

Dex,

We absolutely have a point of reference.
No anecdotes here - just data.
This is a "g" meter mounted on the fiberglass of a Casita.
It is showing how much energy the trailer is "seeing"

Jim

Jim,
You didn't quote the whole statement I made. It isn't if the 'g' meter measured something. It is if that measurement has any realistic meaning.

The 'g' meter measured the 3 largest shocks and from that the charts are showing they all read between 9.5 to 10 with or without shocks. That tells us that the shocks do not have a benefit for those circumstances.

After the large bump only 2 of 3 measurements show a noticeable difference.

Originally Posted by Dextersp1

For the last two bumps we don't have a point of reference. We don't know for example if we were riding in the trailer, would we notice if there were shocks or not being used.

[WizWid]

Originally Posted by Dextersp1

Jim,
You didn't quote the whole statement I made. It isn't if the 'g' meter measured something. It is if that measurement has any realistic meaning.

The 'g' meter measured the 3 largest shocks and from that the charts are showing they all read between 9.5 to 10 with or without shocks. That tells us that the shocks do not have a benefit for those circumstances.

After the large bump only 2 of 3 measurements show a noticeable difference.

Do we really have to go through this over and over?
The initial "bang" will be the same with or without shocks.
That is the suspension doing its work.
After that, on the "down" part mostly - the shocks do their thing and dampen out the later oscillations.

Jim

[Dextersp1]

Originally Posted by widgetwizard

Do we really have to go through this over and over?
The initial "bang" will be the same with or without shocks.
That is the suspension doing its work.
After that, on the "down" part mostly - the shocks do their thing and dampen out the later oscillations.

Jim

Jim,

OK, so we agree there is no difference on the initial bump with or without shocks. So no benefit to adding shocks in that aspect.

The graphs only show dampening in 2 of the 3 after bumps - 66% of the time. What we don't know is if that dampening has any value.

If, for example, a person riding in the trailer would not notice a reading of 5 there is no value in shocks that lowers the reading to lower than 5. Another way of saying it is: If there is no problem with secondary bumps of 5 then there is no value in shocks that lower that number.

[WizWid]

Originally Posted by Dextersp1

Jim,

OK, so we agree there is no difference on the initial bump with or without shocks. So no benefit to adding shocks in that aspect.

The graphs only show dampening in 2 of the 3 after bumps - 66%. What we don't know is if that dampening has any value.

If, for example, a person riding in the trailer would not notice a reading of 5 there is no value in shocks that lowers the reading to lower than 5. Another way of saying it is: If there is no problem with secondary bumps of 5 then there is no value in shocks that lower that number.

Yes we agree on your first sentence.
The rest is back to the anecdotal problem.
We have plenty of anecdotal evidence that they make a significant improvement.
This is just data to try to get away from that.

I think we can agree that I know they work and you know they dont and just leave it at that before this thread gets shut down.

Cheers,

Jim

[WaltP]

Thanks Jim!!!!!!

[redbarron55]

Jim,

How about investigating an anti-roll bar for trailers?
The side to side tipping moment could be improved. There has been very little work done on trailers since no one rides in them to complain!
However the oscillation side to side as it coincides with the frequency of the sway is a problem.
The added roll stiffness without increasing the spring rate overall would be a plus. Especially on a lifted Casita.
The key is to move the natural frequency of the system lower than the excitation to damp out unwanted oscillations. This way the damping and spring rate from the one side would be added to the other via the anti-roll bar.
Of course each bar would have to be made for the distance between trailing arms.
This would counteract some of the IRS effect of the rubber torsion axle, but only to a minor degree.
To some degree the weight distributing hitch accomplishes the same thing, but only on the tongue. This along with the added friction is a part of the effect of this type of hitch.
Here is a picture of a similar rear torsion beam car axle with anti-roll bar:

[dleverton]

Originally Posted by widgetwizard

With respect - I completely disagree with this notion -and the proof lies in that chart a few posts up. The shock is absolutely NOT transmitted to the trailer. It IS absorbed by the shock absorber and turned into heat. Please look at the waveforms again.



--Jim.

Hey Jim no problem, it is a complex thing.
The shock is a device that can be compressed or expanded easily at slow speed but the faster the rate the larger the force required. It is analogous to a capacitor. So for an impact it behaves like it is a solid object and as such any fast impact on one end is transferred to the other end. The curves above are classic. The unshocked curve shows the oscillations carrying on much longer than the shocked curve. It is the energy of those oscillations that is transferred to the shock and presents as heat and so reduce the oscillations more quickly. You are correct that the initial bump also imparts energy to the shock, but that bump is conducted better to the frame than if there were no shock. You can get adjustable shocks that allow bump and rebound to be independently adjusted and competitive racing teams use a machine to decide the adjustments that minimize oscillations without too much direct impact to the frame on bump. To further muddy the waters, most shocks now come pressurized with nitrogen. The purpose of the nitrogen is to keep the damping fluid from developing air bubbles and causing cavitation which erodes the fluid orifice, but with the nitrogen pressure the shock also acts as a spring in parallel with the shock. Springs act in an different manner, that is the more you compress them, the higher the force required. Springs are primarily not rate dependant like shocks and so do a better job of not transferring high rate bump to the chassis (although there are secondary transfer mechanisms that do). I spent more than a decade driving the national rally championship and suspension dynamics are only second to tire dynamics in terms of building a competitive rally car. So it became a bit of a passion / obsession for me and I can blather on and bore people to death given any excuse...please excuse.
What a wonderful discussion.


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Doug L

[WizWid]

Originally Posted by dleverton

Hey Jim no problem, it is a complex thing.
The shock is a device that can be compressed or expanded easily at slow speed but the faster the rate the larger the force required. It is analogous to a capacitor. So for an impact it behaves like it is a solid object and as such any fast impact on one end is transferred to the other end. The curves above are classic. The unshocked curve shows the oscillations carrying on much longer than the shocked curve. It is the energy of those oscillations that is transferred to the shock and presents as heat and so reduce the oscillations more quickly. You are correct that the initial bump also imparts energy to the shock, but that bump is conducted better to the frame than if there were no shock. You can get adjustable shocks that allow bump and rebound to be independently adjusted and competitive racing teams use a machine to decide the adjustments that minimize oscillations without too much direct impact to the frame on bump. To further muddy the waters, most shocks now come pressurized with nitrogen. The purpose of the nitrogen is to keep the damping fluid from developing air bubbles and causing cavitation which erodes the fluid orifice, but with the nitrogen pressure the shock also acts as a spring in parallel with the shock. Springs act in an different manner, that is the more you compress them, the higher the force required. Springs are primarily not rate dependant like shocks and so do a better job of not transferring high rate bump to the chassis (although there are secondary transfer mechanisms that do). I spent more than a decade driving the national rally championship and suspension dynamics are only second to tire dynamics in terms of building a competitive rally car. So it became a bit of a passion / obsession for me and I can blather on and bore people to death given any excuse...please excuse.



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Doug L

Thanks Doug - nicely explained.
And we are using nitrogen charged shocks here. Monroe 555003

Cheers,

Jim

[dleverton]

Originally Posted by redbarron55

Jim,

How about investigating an anti-roll bar for trailers?
The side to side tipping moment could be improved. There has been very little work done on trailers since no one rides in them to complain!
However the oscillation side to side as it coincides with the frequency of the sway is a problem.
The added roll stiffness without increasing the spring rate overall would be a plus. Especially on a lifted Casita.
The key is to move the natural frequency of the system lower than the excitation to damp out unwanted oscillations. This way the damping and spring rate from the one side would be added to the other via the anti-roll bar.
Of course each bar would have to be made for the distance between trailing arms.
This would counteract some of the IRS effect of the rubber torsion axle, but only to a minor degree.
To some degree the weight distributing hitch accomplishes the same thing, but only on the tongue. This along with the added friction is a part of the effect of this type of hitch.
Here is a picture of a similar rear torsion beam car axle with anti-roll bar:

Hey RedBarron
That is a really good idea.
There is no cost with respect to ride harshness and trailers often have a lot of roll.


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Doug L

[Andrew Gibbens]

An anti-roll bar is not going to have much effect on a trailer, since 100% of its roll stiffness is at the axle and making it stiffer won't do anything but reduce roll (and transfer some shock loads to the other wheel over bumps). Reducing roll alone won't improve handling and won't change the side-to-side weight transfer

Anti-roll bars on four-wheeled vehicles transfer roll stiffness from front to back or vice versa in order to increase/reduce oversteer or understeer, which is a whole different barrel of apples.

[redbarron55]

Anti-roll bars on four-wheeled vehicles transfer roll stiffness from front to back or vice versa in order to increase/reduce oversteer or understeer, which is a whole different barrel of apples.
As far as this statementgoes it is correct, however the addition of the roll to the sway or snaking add to the amplitude of the swing.
The effect would be like adding air to tires that are underinflated.
No suspension at all would be more stable than a very soft trailer suspension. The added rate from the anti-roll bar would shift the resonant frequency in a more favorable direction.
Soft springs and no damping woule be similar to having a water tank 1/2 full across the trailer with the water sloshing back and forth. Even more like a unsecured water tank sliding across the floor in a sway event.
The anti-roll bar wold be like that tank moving to the other side against the shifting force.
The tipping from side to side or roll aggravates the swaying action making it worse.
Very little work has been done in this country on trailer dynamics and handling.