Mechatronic Shock Absorber

I don't know where you are, but my brother is in NC USA and he is an engineer for the Lord Corp. he specialises in variable damping for suspension systems and for truck seats etc...

He uses a ferromagnetic fluid instead of oil to pass and electric current through to adjust the vicosity of the fluid which changes the dampening of the suspension system.

look up ferrofluids on Google.

John.

There's also such stuff as electrorheologic fluids, the viscosity of which can be altered with electric field.

Same thing Bill, I remember my brother saying its NOT ferromanetic fluid because another company had grabbed that name as their trademark or something...

I've always wanted to play with some of that stuff though, ever since I designed an instrument which used a magnetic powder clutch.

John.

I thought you were referring to a magnetorheologic fluid.

http://www.kodama.hc.uec.ac.jp/spiral/

Cool video here:

http://www.youtube.com/watch?v=me5Zzm2TXh4

Ohhh heck! sorry Bill I may well do...

I've not had enough experience with these types of fluids to know or fully understand the differences between them.

Maybe I should just keep quiet!

John.

The current does not go through the fluid as it seams according to your formulation ( may be I misunderstood) but through a spool generating in a gap a more or less strong magnetic field. the magnetic particles in suspension in the fluid aggregates more or less according to the field strength modifying the resistance of the orifice.

The problem of all dampers is the fact that damping generates heat and this has to be dissipated if not due to the temperature increase the viscosity changes and with it the behaviour. A mechatronic device will compensate this negative aspect and could optimize the damping effect depending on several inputs as for instance accelerations. The more classical solution using a balanced spool and a proportional solenoid is under circumstances better since in case of maintenance need the components are more easily found and at a lower cost. The limits are the frequencies to be damped actively since active dampers are limited as long as they are based on magnetics. The fastest systems are using electrorheologic fluids and can reach several thousands Hz but they are as far as know not yet "industrial".

The Lord dampers are many times customized for the car industry.

If the damper is small even a flapper-nozzle pair can be used with good results. As for the cylinder a hydraulic cylinder in servo quality (with seals without stick-slip) and able to hold long time under short fast oscillations can do the job. Such cylinders are available every where.

If dynamics are not too high it is possible to use a motor+nut simple actuator for the spool positioning since a solenoid needs a permanent supply. With a self-locking actuator the supply is needed only when changes are to be done.

The problem with the self-locking device is the fail-safe position in case of supply loss.

With the solenoid it is possible to make a choice and have either the highest or the lowest damping in the fail-safe position which is not possible with the motor.

So that the solution choice depends on several factors which have to be defined very carefully from the start.

Google up old professor Moog - he's building this very thing.

Here at NASA we're using linear actuators driven by electric motors to provide the shock absorber function for a space craft docking system. You use load cells to sense the forces, then a closed loop feedback system to control the motorized actuators. To see it in action it looks exactly like traditional hydraulic shocks. I'm afraid the details are proprietary until the patent comes out, but it's a fairly straight forward control theory app.

You can build magnetic damper without oil. Or magnetic assisted with oil. For measurement, you're designing it so you decide what it gonna be.

Pineapple

Any flow control valve (splitting an input flow into two output flows) will do this by changing the amount of fluid going through the two exits and these exits connected to tubing with defined resitance.

!00% flow into line A (the higher resistance) will give the highest damping, 100% flow into B the lowest.

The other end of line A and line B to be connected together to a cylinder that supports the damping force with its piston the other port going to the input of the flow control valve.

Any major hydraulics supplier has these valves.

Operation is by an electrically driven linear motor that moves a piston with openings.

RHABE

Why splitting? It is sufficient to change the area of the orifice and let the fluid go forwards and backwards from one side to the other. Imagine a cylinder with a hydraulic shunt between the two active volumes and change the shunt value you have a damper. If the piston areas are different (as it is in many cases) it should be available an elastic volume to accumulate the difference when needed. To avoid cavitation which could occur if the pressure drop is too important it is recommendable to pressurize the whole. If damping should occur in one direction only then a check valve could be provided as a by-pass for the non active direction.

hello Rhabe: regarding your comment we have a question, how to control the fluid flow along those valves? I mean for example, how we can make 100 percent of the flow go into the valve A? thank you for your prompt answer and waiting for comments. Guest.....

Hello!

Thank you for your comment. For all the ideas I´ve got, yours is the most interesting for what I have to do.

I have some questions...

1. Which kind of valve would you recommend? name, manufacturer...

2. Do you know if it is small enough to fit in a car dashpot? I have to make the "virtual assembly" and I want to be sure it works.

Thank you for your time and comment.

ENGINEER BOILLOTA

Your suggestion reminds me of a nice story. It is said that Newton had 2 cats a grown up one and a kitten. He was disturbed because they asked many times a day either to live the room where he worked or to enter it. So that in order to avoid the interruptions he called a man and ordered to cut 2 ports a bigger one for the big cat and a smaller one for the kitten. The man said but Sir only one will be enough. Newton's answer came immediately: and through which port will pass the kitten?

The same with hydraulics. There are two possibilities:

- continuous change of damping according to different parameters

- change of damping with 2 possible situations : high damping and low damping.

In the 1st case a single orifice which can be controlled from a minimal value to a maximal one would be enough. As already mentioned a check valve can be used to by-pass the flow in one direction if damping is wished in one direction only.

In the 2nd case it is enough to have 2 restrictions in parallel and control only the low damping orifice with a 2/2 valve which will be for "high damping" closed and for "low damping" open. The decision to take is which position will be the "fail safe" one (valid as well for the single orifice solution). The same check valve will make damping unidirectional.

Both solutions are possible with available valves but the constrain introduced in the last message "use in automotive industry" makes usual industrial solutions available of the shelf less adapted.

On my modest opinion if the goal is to control the damping the solution with a single piloted orifice is the most adapted.

More than that the suppliers of such equipments develop the valves for a customer so that they do not have "standard" solutions as for industrial hydraulics.

If Mr. ENGINEER BOILLOTA is interested I could direct him/her to a supplier but it is not sure he/she will find the required valve for the damper they intend to use.