Rant on terminology...

[jharrell]

A spring converts the shock into kinetic energy. The damper absorbs the kinetic energy. Plain and simple.

No a spring stores mechanical energy from the suspension and damper converts mechanical energy into heat energy, they both absorb mechanical energy from the suspension and do different things with it. They both work together to prevent the mechanical energy from being transferred to the main frame/body of the vehicle.

Since this is an electrical forum, Spring = capacitor, damper (shock) = resistor. Capacitors store electrical energy and resistors convert electrical energy into thermal energy, they both absorb electrical energy from the circuit.

https://en.wikipedia.org/wiki/Impedance_analogy

 

[RF_Burns]

I wish people would define their TLAs when they first use them in their post. Some of us can't remember their LFPs and SCC from their BMS.

Of course everyone knows a TLA is a Three Letter Acronym...right?

 

[Cal]

No a spring stores mechanical energy from the suspension and damper converts mechanical energy into heat energy, they both absorb mechanical energy from the suspension and do different things with it. They both work together to prevent the mechanical energy from being transferred to the main frame/body of the vehicle.

Since this is an electrical forum, Spring = capacitor, damper (shock) = resistor. Capacitors store electrical energy and resistors convert electrical energy into thermal energy, they both absorb electrical energy from the circuit.

https://en.wikipedia.org/wiki/Impedance_analogy

There are just two types of mechanical energy: kinetic and potential. We are dealing with kinetic energy when the spring gets energized. They do not BOTH absorb mechanical energy as you state. The damper absorbs virtually all the kinetic energy. The suspension does not prevent energy from being transferred to the vehicle chassis. The suspension minimizes the transferred effect, but does not prevent it. The effect is dependent on the damping ratio of the suspension. Typical vehicle damping ratio is about 0.2. That means if the vehicle hits a 6" bump, 3" will be transferred to the chassis (zeta = 0.2 has 50% overshoot).

 

[Cal]

I call them sway bars too knowing full well its not really the correct term, its just habit, but I wouldn't complain if someone corrected me, it would probably mean they actually know what they are talking about.

I fully agree with you. My rant is with those who insist calling them anti sway bars. Don't know how long the term sway bars has been used. Perhaps 75 years? The name has been well established. Why make a big fuss?

Yes, I have driven my motor home without the rear sway bar. Actually I've done quite a bit of suspension testing using an accelerometer datalogger. Sway bars work well only when the wheels are level to the road. If one wheel hits a pot hole or a bump then disaster strikes. The sway bar amplifies the impact.

Shown are two FFT (Fast Fourier Transfer) plots when traversing over a speed bump at an angle. After hitting the bump the vehicle rocks side to side. The accelerometer records x,y,z motions in the time domain. FFT is used to get a frequency spectrum. The dominate rocking frequency is 1 Hz. With sway bar maximum displacement is 140 units. Without sway bar displacement is only 40 units at 1 Hz.

 

[Supervstech]

I fully agree with you. My rant is with those who insist calling them anti sway bars. Don't know how long the term sway bars has been used. Perhaps 75 years? The name has been well established. Why make a big fuss?

Yes, I have driven my motor home without the rear sway bar. Actually I've done quite a bit of suspension testing using an accelerometer datalogger. Sway bars work well only when the wheels are level to the road. If one wheel hits a pot hole or a bump then disaster strikes. The sway bar amplifies the impact.

Shown are two FFT (Fast Fourier Transfer) plots when traversing over a speed bump at an angle. After hitting the bump the vehicle rocks side to side. The accelerometer records x,y,z motions in the time domain. FFT is used to get a frequency spectrum. The dominate rocking frequency is 1 Hz. With sway bar maximum displacement is 140 units. Without sway bar displacement is only 40 units at 1 Hz.

View attachment 74803

View attachment 74804

What a sway bar does on your particular vehicle has no bearing on what the bar is DESIGNED to handle.
They are not designed to do anything about a pothole...
They are designed to keep a vehicle level in a corner.
Thats it.
They are built to keep the vehicle chassis putting load on the lifted side of the suspension...
Antisquat, antisway what have you... all is fine.
They don't work perfectly... but it is what they are for.

 

[wattmatters]

There are just two types of mechanical energy: kinetic and potential. We are dealing with kinetic energy when the spring gets energized. They do not BOTH absorb mechanical energy as you state.

So you agree with me that only the spring (coil) is what converts kinetic energy into elastic potential energy. The spring is what stores that kinetic energy (briefly) and this is the shock absorption.

Absorb = store, even if only briefly.

But then you go and say this...

The damper absorbs virtually all the kinetic energy.

A damper does not store/absorb kinetic energy (i.e. the shock or impulse) as potential energy. If a damper stored kinetic energy as some form of potential energy, then it could also release that stored potential energy as kinetic energy. Dampers don't do that.

The damper does a different job, by providing a means of dissipating/transferring the kinetic energy, which is does via fluid flow / heat exchange. In this scenario, it is the air surrounding the damper which does the energy absorption. The kinetic energy it dissipates is either during the initial impulse or subsequent kinetic energy as the stored elastic potential energy in the coil is released.

If a damper did store/absorb energy, then you'd be able to quote me a potential energy constant for the damper (e.g. like a spring constant). You can't because it doesn't do that. As mentioned above, it is the surrounding air which absorbs the energy, and we can provide that energy storage constant - it's the specific heat index of the surrounding air.

The relevant mathematical / engineering characterisation for a damper is the damping constant in a Spring-Mass system with Viscous Damping. Here's a reasonable description of that type of system:

https://www.maplesoft.com/content/EngineeringFundamentals/6/MapleDocument_32/Free%20Response%20Part%202.pdf

Read part 1 if you want to go through the equations of motion for an undamped spring.

 

[Cal]

So you agree with me that only the spring (coil) is what converts kinetic energy into elastic potential energy. The spring is what stores that kinetic energy (briefly) and this is the shock absorption.

Absorb = store, even if only briefly.

But then you go and say this...

A damper does not store/absorb kinetic energy (i.e. the shock or impulse) as potential energy. If a damper stored kinetic energy as some form of potential energy, then it could also release that stored potential energy as kinetic energy. Dampers don't do that.

The damper does a different job, by providing a means of dissipating/transferring the kinetic energy, which is does via fluid flow / heat exchange. In this scenario, it is the air surrounding the damper which does the energy absorption. The kinetic energy it dissipates is either during the initial impulse or subsequent kinetic energy as the stored elastic potential energy in the coil is released.

If a damper did store/absorb energy, then you'd be able to quote me a potential energy constant for the damper (e.g. like a spring constant). You can't because it doesn't do that. As mentioned above, it is the surrounding air which absorbs the energy, and we can provide that energy storage constant - it's the specific heat index of the surrounding air.

The relevant mathematical / engineering characterisation for a damper is the damping constant in a Spring-Mass system with Viscous Damping. Here's a reasonable description of that type of system:

https://www.maplesoft.com/content/EngineeringFundamentals/6/MapleDocument_32/Free%20Response%20Part%202.pdf

Read part 1 if you want to go through the equations of motion for an undamped spring.

Again, we're talking semantics. The spring doesn't absorb energy as you proclaim. Due to a bump, the spring gets stretched or compressed by a specific distance (x). According to Hooks Law the spring acquires potential energy (E = 0.5 * k * x^2). As soon as the spring is released from the stretched or compressed position the spring begins to oscillate and now acquires kinetic energy. The damper absorbs the kinetic energy and turns it into heat. The damper responds exactly like a resistor. The resistor absorbs power (or energy over time) and turns it into heat. The damper like a resistor does not store energy. Energy is contained in the spring/mass.

Thank you, I'm familiar with those calculations. I notice their overlay graph of damped responses has an error. Zeta = 0.2 is not overdamped as written. It is underdamped. Likewise, zeta = 2 is not underdamped but overdamped.

 

[wattmatters]

The spring doesn't absorb energy as you proclaim. Due to a bump, the spring gets stretched or compressed by a specific distance (x). According to Hooks Law the spring acquires potential energy (E = 0.5 * k * x^2).

The spring acquires that potential energy by absorbing and storing the kinetic energy due to the rapid change in displacement caused by hitting the bump. The damper damps. The damper does no storing of energy.

 

[Cal]

You're talking in circles. We're done.

 

[740GLE]

No offense you guys were done 4 pages ago, but it was entertaining.

 

[jharrell]

I fully agree with you. My rant is with those who insist calling them anti sway bars. Don't know how long the term sway bars has been used. Perhaps 75 years? The name has been well established. Why make a big fuss?

I don't make a big fuss like saying "Anti roll bar is also a stupid description" no its not that is wrong, its actually more accurate but I am not going to make a big deal about it, I will simply conceded yeah that is more correct, I just say "sway bar" out of habit and its shorter.

I think we are on the same page, you seem to be one of the few who actually understands the down side of a sway bar vs the many who think is magic and you have actually done some measurements, I applaud that. If you have seen any of my post on IRV2 trying to convince people that a sway bar is not a magic bullet and can increase ride harshness due to increasing spring rate, well you would know. I just don't agree with your assessment of the terminology I think the grammar is clear, but language is only that which everyone agrees on, rules change over time and are still changing so whatever...which brings me to the next point, again pedantic:

Absorb: take in or soak up (energy or a liquid or other substance) by chemical or physical action.

Both a spring and shock absorb mechanical energy, a spring takes in mechanical energy and stores it, a shock takes in mechanical energy and converts it to thermal energy, absorb is the correct term for both based on my interpretation of the definition. I know what they both do and how they work, expressing with words can be tricky but still seems pretty clear. I guess I should have said they attempt to prevent transfer of mechanical energy to the frame by absorbing it, and that is their purpose but as with everything in the real world it is not perfect with a set of trade offs, black and white thinking is not the best approach and I assumed you would understand that.

 

[12VoltInstalls]

No offense you guys were done 4 pages ago, but it was entertaining.

It wasn’t entertaining to me at all. It actually took the point of the thread so ridiculously far to the inverse all the humor was lost in the antithesis.

 

[740GLE]

Ahhh it went so far to the crazy, it came back around to be ridiculous which is funny. People care so much about terminology when they are both saying the same thing, yet think they are arguing.

 

[wattmatters]

yet think they are arguing.

I'm not arguing. Who says I'm arguing?

 

[JoeHam]

FFT plots of driving over a speed bump at an angle ?

Makes me nappy.

Not sure if that’s nerd happy or just sleepy. ?

 

[FLD]

Not that I didn’t find the discussion about springs, bars and shocks interesting, the only spring I’m excited about is the spring season, which might be here in west Michigan in about five months.

 

[Roqm]

He had the perfect opportunity to call these things "Frog Amps" - current that jumps from one battery to the other.

Trademark and patent...

 

[Roqm]

Get rid of the Ford .... Ooooops .... probably just ticked of about 1/3 of you guys.

Behave!????

 

[Cal]

They are designed to keep a vehicle level in a corner.

They don't work perfectly... but it is what they are for.

The problem is that people don't understand them. They just see the good. They don't realize there's also the bad and the ugly inherent in the design. For the most part, stock torsion bars are correctly designed. A problem arises with motor homes. They have a huge side surface area. Many people can't handle when passing trucks or side winds push their vehicle around. They install a bigger torsion bar. Bigger is always better.

Here's the problem. Say the vehicle is going over a speed bump at an angle, or for that matter entering a driveway. One of the back wheels is higher in elevation than the other. The chassis is now sloping. The torsion bar is designed to keep the chassis level. The wheel that's on top of the bump has its spring compressed somewhat, but the chassis sitting on top of the spring is higher than the other side. The torsion bar forces the other spring to expand so that the chassis is more or less level again. Independent suspension is lost. Both springs are now energized, not just the spring sitting on top of the bump. Now you got one spring that is compressed and the other is forced to expanded. There's a lot more energy in this setup than without the bar. The larger the bar diameter the greater the springs potential energy.

So people install aftermarket sway bars. Knowing that bigger is always better, some install two monster bars, one behind the differential and a second in front of it. Since I do suspension evaluations, the guy with two bars wanted his motor home tested with my accelerometer logger. It's a simple test. Drive over a small (gentle) speed bump at an angle under 5 mph. I've never been so concerned of my safety. The vehicle rocked violently. Cabinet doors flew open. All contents went airborne. A can of corn crashed into my laptop and took out a key. All because of two huge sway bars in the rear.

Getting back on topic, someone stated they are now called stabilizers. Perhaps a better name is anti-stabilizers?

 

[jharrell]

Both springs are now energized, not just the spring sitting on top of the bump. Now you got one spring that is compressed and the other is forced to expanded. There's a lot more energy in this setup than without the bar. The larger the bar diameter the greater the springs potential energy.

Way over thinking this, the main springs and the anti-roll bar are in parallel, they are both springs, the mains are leafs (in a class A RV) and the bar is torsion, their spring rate is added together like any set of springs in parallel, they don't add energy to the main springs, they add spring rate like any helper spring.

Anti-roll bars are torsion springs that only engage when the axle is articulated, they have the same effect as adding stiffer springs except they have the advantage of not engaging if the axle moves up and down in unison, they are good simple compromise to add spring rate when needed in cornering and side wind and not when hitting bumps going across the road like expansion joints. However when you want your axle to articulate as when going over uneven bumps the anti-roll bars extra spring rate is not wanted.

RV's being mostly on-road highway vehicles with high center of gravities it is generally more pleasant to have stiffer sway bars, for the 2020 F53 chassis Ford upped the anti-roll bar diameter to 2" from 1.5" due to many handling complaints from customers where a common solution is to reduce leverage on the anti-roll bar by moving the link connection to the inner hole called the "Cheap Handling Fix" or adding after market thicker anti-roll bars or doubling up the bars. I have done the CHF myself and it is a large improvement in on-road handling while sacrificing some harshness over uneven bumps as you describe with hyperbole.

My Jeep has a electronic disconnect for the front bar which will not stay disconnected under 18 mph due to dangerous handling characteristics such as roll over at higher speed. The ride is much softer with the front bar disconnected and allows the front axle to articulate much better off-road but a quick maneuver can cause extreme body roll and potential roll over situation. Most cars main springs are too soft to function properly without a anti-roll bar, the spring rate is tuned assuming the presence of one for better ride with decent handling