Suggestions on improving solenoid response times

[MikeMM]

I'm building a new type of engine that uses a solenoid valve to control the spray of water into the engine. Having the valve open and close quickly is very important for timing. I am building the electronics to control this.

I was wondering why a solenoid needs time to energize and what techniques can be used to reduce reduce the open and close times? Also can high voltage solenoids produce quicker response times or doesn't it matter?

I have heard of people using a very brief high voltage pulse to energize the coil initially then letting it down to the normal voltage. I also have another idea I've been kicking around. If I were to send a low current signal to the solenoid a little bit before I want it to open that would be too low a current to open the valve would it help to energize the coil more quickly once the normall signal was sent?

Any suggestions would be helpfull.

thanks,

Mike

 

[SolderingGunslinger]

Hmmm...let me meditate on this a bit...Ohms...Ohms...Ohms.

What you are envisioning has already been invented, but for another fluid. It is called an Electronic Fuel Injector. A solinoid opens a valve and a fluid sprays into the intake or directly into the combustion chamber. This operation is done very quicky and with precision timing.

My motto has always been "Don't reinvent the wheel".

You don't mention how long the valve must remain open, nor do you state the volume of water which will be injected. You aren't looking at a water spray condensor for a steam engine...are you?

At any rate, I predict that you will be spending long days at the orifice (Bad pun intended :-D ) I remain,

The Old Soldering Gunslinger

 

[MikeMM]

My bad, I should have mentioned that I already looked into that and there are no injectors that would work.

Here's why:

1) Water and fuels like gasoline and diesel have very different properties and will not spray the same out of a fuel injector. I think this has something to do with surface tension but at least in the case of diesel if you get water in the fuel line you can actually blow part of the head off the injector.

2) Gasoline injector are too slow and use plastic o ring seals that are not designed to be exposed to the heat of combustion and would get scortched in my application.

3) Most diesel injectors are pressure not electronically actuated and are actually controlled by a complicated fuel pump which would not work for my application. Those that are electronically actuated are fast enough but still face problem 1, are designed for very high pressures I don't plan to use, and are extremely expensive.

I could try to design my own injector but I think the water injection system I am trying to create would give a better response time and be cheaper to build and could use a lot of off the shelf components like solenoid valves and water spray nozzles. Also there is no good purely mechanical solution for controlling the water injection.

Basically I am looking for the fastest response time I can get out of a solenoid valve. I would say 10 milliseconds to both open and close is the longest acceptable time but really the faster the better since ideally most though not all of the water should be sprayed as close to bottom dead center as possible.

This is not a steam engine but does have some things in common with it.

 

[Lakey]

Hi,

Have you looked at the Helenoid. I think it was patented by Lucas Industries Ltd in the UK.

I think there were a couple of articles floating about: -

[1] Vital Twist Overcomes Solenoid Inertia Problem, published by Eureka, July 1982

[2] A New Concept in Extremely Fast Acting Solenoids, by A.H. Seilly, SGRD Limited


A lot of small contactors/relays can operate within 10ms, but the speeds of operation will, basically, depend upon what you want to move and how far you want to move it.

Good luck & regards,

 

[Skogsgurra]

If we go back to the original question for a while...

Force from a solenoid is generally proportional to current squared. So, what you need is to get the current up very quickly - and down again.

Solenoids have some "inertia" towards fast current changes. It is expressed as the well-known e=-L*di/dt where L is the "inertia" aka inductance (henry) of the solenoid. We can forget about the minus sign. The rest of the relation says that you need a lot of e (volts) to get much change in "i" (amperes) for a certain amount of "t" (seconds). That is what the time derivative di/dt means.

So you should either have a quite low L or a high "e" to make things move fast. A low L usually means few turns in the solenoid - which means less force.

I would say that a solenoid designed for 20 - 30 percent of the available voltage and overdriven ON and having a MOV or zener taking care of the OFF voltage (if you do not have an H bridge arrangement) is optimal.

You have to make sure that the DC "plateau" in-between does not fry the solenoid. Simplest way of doing that is to use a series resistor. A current source would, of course, be more elegant. But needs more components, the power dissipation problems will be the same in both cases.

A series resistor with a parallel capacitor is yet another way of speeding the thing up. But that needs an H bridge.

Gunnar Englund

http://www.gke.org

 

[MJMurphy]

In fuel injector parlance, what you are looking for is called peak-and-hold. Even though your solenoids are not fuel injectors, you are using them in a similar fashion. Look at peak-and-hold fuel injector driver circuits for some ideas that may be applicable to your solenoid:

http://www.google.com/search?as_q=p...s_occt=any&as_dt=i&as_sitesearch=&safe=images

One way of providing high current for opening the solenoid (or fuel injector) is by charging a capacitor to 40 – 60 volts through a resistor. One device (BJT, MOSFET, IGBT, etc) supplies this to the load and another supplies a lower voltage sufficient to keep it open for the remaining time.

See thread71-124034

Some fuel injection web sites that may be helpful:

MegaSquirt EFI:

http://www.msefi.com/

DIY-EFI:

http://www.diy-efi.org/

Eric Fahlgren's web sit:

http://not2fast.wryday.com/

 

[sreid]

The way injector solenoids are electrically actuated is in a PWM H-Bridge with current feedback. A current request will cause the H-bridge to saturate at the supply voltage to ramp the current into the coil fast. When the current reaches the set point, the H-bridge PWM's to hold the current at the set point. The opposite happens to ramp the current down-the H-bridge can apply full reverse B+ voltage to the coil.

Take a look at Terfenol-D as an injector actuator material.

http://etrema-usa.com/

Using this magnetostrictive material, blazing fast actuators can be designed.

 

[OperaHouse]

You'll have fun, but I question the need for anything this sophisticated. The range of effective mixture is quite wide and the droplet size quite coarse. The real technical problem is the water. Good water is hard to find, there is the freezing problem, and you have to cary around as much water as gas. If short term drag application, I've seen these as simple as windshield washer pumps. An awsome old technology that electronics isn't going to help.