The Idea to use solenoid valve coils is good, but I have already bought the magnets and am making the valve bodies to suit, but if I find the magnets do not work it will not be to difficult to modify the valve mechanism just by extending the steel rod to pass through the coil, I should have done more research before starting, but I just wanted to get going.
The matter of the encoder being incremental not absolute, I had not realized there are different types. If I use an an opto-switch or some other sensing device to determine TDC will I need one for each cylinder or can the other five be calculated from the one position, probably a stupid question but I have not much of a clue beyond simple electrics.

 

It would also work to trigger the electronic delay for each cylinder from the mechanical closing of the valve, perhaps a magnetic or optical sensor on each valve. Then you wouldn't need a TDC sensor.

 

There is not really any fixed mechanical closing, the exhaust valves are opened a couple of degrees before BDC by a cam built into the connecting rod, the tip of the exhaust valve bashes the inlet valve open just before the cam releases the exhaust valve just after TDC, the tip of the exhaust valve is blocking the inlet port until the piston starts to descend, the exhaust valve is kept shut by the pressure of air or steam, there is only 2mm off movement in the valve fully opening and closing . To pick up any movement in the inlet valve would be difficult as it is totally enclosed with the magnet sitting directly on the top.I don't think it will be too much of a problem to make some sort of sensing device for TDC, a disk and a proximity sensor would mean it could see all the TDC's if that is any help.
I have enclosed a photo of a piston with and without the exhaust valve fitted and a con rod showing the operating cam.

 

Most unusual steam engine your building, and that is meant in a good way. Most bash valve engine use piston porting for the exhaust.

One thing about your engine I can't figure out is, is it going to be reversible? The big advantage of steam engines is they don't need a transmission because of their reversibility.


I just went to the link you gave in the first post. I see that my idea for the solenoid coil is what Gelbart is using. The magnets you bought are like the ones in a magnetic chuck for a surface grinder. They could probably be modified. I was going to build a full size steam engine, at one time, and did a lot of research on it. But already have too many hobbies and projects going.

 

No I am afraid it is not reversible, the original Idea was to power the zero turn ride on mower I made, it is eventually to replace the Tecumsa engine that drives the hydraulic pumps, if it gets that far.

I was messing with the magnets this morning, tried them on a piece of steel, there is plenty of holding power but there was a problem with residual magnetism in the steel, so I tried a piece of the iron powder and resin I had kicking about, it did not hold as well as the steel but is released immediately. It is just a case of suck it and see, makes life interesting though.

 

A thin piece of non-magnetic material between the magnet pole and the steel will minimize the effect of the residual magnetism (of course it will also reduce the holding power somewhat when energized.)

 

If I use an an opto-switch or some other sensing device to determine TDC will I need one for each cylinder or can the other five be calculated from the one position

Calculation from one known shaft position should work. This is definitely a job for a microcontroller, if you want to avoid using a mountain of counter and logic ICs.

 

The encoder could be made with six optosensors and a wheel with one slot in it. As the slot goes through the sensor it would trigger a monostable for each cylinder. Six cylinders, six sensors, one slot, one retriggerable monostable, no micro controller.

 

The encoder could be made with six optosensors and a wheel with one slot in it. As the slot goes through the sensor it would trigger a monostable for each cylinder. Six cylinders, six sensors, one slot, one retriggerable monostable, no micro controller

Would this this method still allow me to vary the timing of the energizing of the magnets, if so it is possibly a more practical method for something like this but I have already purchased an encoder and would like to lean how to utilize it to do the job with a microprocessor, if I can get to understand a little bit about electronics who knows it could lead to a new hobby to "waste" my time on.

 

Would there be any overlap of adjacent valve timing? In other words, will the preceding value always be closed by the time the next valve opens? I suspect not. That determines whether you can share one timer delay or need six separate timer delays.

 

Would there be any overlap of adjacent valve timing? In other words, will the preceding value always be closed by the time the next valve opens? I suspect not. That determines whether you can share one timer delay or need six separate timer delays.

Yes there would be overlap,certainly when delivering any amount of power. I have an animation of it and it appears that there would only need to be two open (the one next to it, it inlets in order 123456) for idling it would probably only need one open at a time.

 

Yes there would be overlap,certainly when delivering any amount of power. I have an animation of it and it appears that there would only need to be two open (the one next to it, it inlets in order 123456) for idling it would probably only need one open at a time.

Then you would need at least two timers that are sequentially shared or 6 dedicated timers, one for each cylinder.

All in all such a circuit would likely require a fair amount of discrete logic devices (perhaps 15-20 or more). Certainly a microprocessor/controller would greatly reduce the number of parts, so you want to consider that. Arduino boards seem to be commonly used by hobbyists on this forum but I am not familiar with them. I believe they are programmed using a variant of the C language. I have used a Stamp board from Parallax Inc. with good success. They can be programmed in Basic, which is probably the simplest computer language to learn. Both plug into your computer for creating/debugging the program and downloading it to the micro.

Edit: A Picaxe is also a popular microprocessor that is programmed in Basic.

 

Alfacliff is correct...A major diesel engine manufacturer uses a Mosfet to energize a solenoid fuel valve, and then another Mosfet to reverse voltage the solenoid to allow it to drop out faster. You can test out this theory by energizing a DC electromagnet thru a DPDT switch; common terminals to the magnet coil, N.O. poles to the power supply and the opposite N.O. poles reverse polarity to the power supply. You can see how much quicker the magnet releases the load.
Sometimes, if the magnet has a close contact with the object it is lifting, you may find the load will not be released by cutting power; residual magnetism. Reversing the polarity (momentarily) will kill this residual magnetism.
Note: You should be able to buy a commercial valve timing control for an engine by searching the engine manufacturer's websites. Modern engines use microprocessors to control engine valve timing.

Cheers, DPW [Everything has limitations...and I hate limitations.]

Additionally, a crank angle sensing device (Proximity Sensor) counted the teeth of the flywheel to give the microprocessor direct control of where the crank shaft is in the cycle. I don't recall the number of teeth per revolution, but it may have been 360, or a multiple of that. With the microprocessor thus enabled, exact control of the valve timing is possible for any engine RPM or throttle position.

Cheers, DPW [ Everyone's knowledge is in-complete. EA]

 

Alfacliff is correct...

I did some quick tests the other day and there is a problem with residual magnetism, so I will definitely need to use a pulse of reverse power to help to speed up the release, so all ideas on how to do incorporate that into the circuitry would be welcome. What does N.O.poles mean when you say " N.O. poles to the power supply and the opposite N.O. poles", sorry I Googled it but found nothing.
Electronic control of valve timing is available from a few manufacturers these days but they all still retain a camshaft to open the valves, most alter the rotational relationship of the cam to the crankshaft to vary the timing. At the present time there is no cam-less engine commercially available but it is being developed, here is a link
http://www.launchpnt.com/portfolio/transportation/electromechanical-valve-actuator/

An off the shelf system would be to make it to easy (expensive really).

Short bus said
"The encoder could be made with six optosensors and a wheel with one slot in it. As the slot goes through the sensor it would trigger a monostable for each cylinder. Six cylinders, six sensors, one slot, one retriggerable monostable, no micro controller.

After doing some quick research the idea is starting to look very attractive, especially the monostable as a timer, it is the sort of level I nearly understand.
Anyway in the meantime it is all coming together slowly.

 

.........................
Short bus said
"The encoder could be made with six optosensors and a wheel with one slot in it. As the slot goes through the sensor it would trigger a monostable for each cylinder. Six cylinders, six sensors, one slot, one retriggerable monostable, no micro controller.
.....................

That won't work because of valve overlap that you said occurs. Overlap requires at least two separate delays since one delay will not be complete before the next delay starts. This will require some method of switching the two delay circuits alternately from one cylinder to the next.

And an analog monostable will give a fixed delay, independent of engine speed. I would think you would want the delay to be a fixed percentage of the crankshaft rotation (delay varies with speed). To achieve that you could use a counter for the resolver pulses.

 

I would think you would want the delay to be a fixed percentage of the crankshaft rotation (delay varies with speed).

Yes that is what I want, I will go with the encoder or a counter as you say. I have got a lot more to do before I reach that stage, so I will start to do some reading and hopefully learning.

 

The magnets your trying to use, like I said earlier, are like the ones used in a surface grinder magnetic chuck, or for that matter a scrap yard crane. Both of these use a reverse polarity pulse to release the material when shutting off.

This is what makes the solenoid coil, like the guy in the link is using, so much better. In a solenoid coil, the is no iron mass, other than the valve stem, to keep the valve open. This is why they use a solenoid coil in electric valves instead of the type of magnet your attempting to use.

 

New thought on this.

If you go to a solenoid coil, and put microswitches above them, when the bash valve opens it will trigger the microswitch. This will trigger the solenoid coil, then you just need a way to shut the coil off.

The shut off timing could be done with the 'shutter wheel'. With variable timing done by moving the ring holding the opto-sensors. The movement done mechanically, like a 'governor'.

 

Personally if it was me I would be looking at using the piezoelectric stack type actuators like modern drive by wire diesel engines use in their electronic injectors.

A little more complicated to initially set up but high speed plus precision timing operation is easy and reliable.

 

If you go to a solenoid coil, and put microswitches above them, when the bash valve opens it will trigger the microswitch. This will trigger the solenoid coil, then you just need a way to shut the coil off.

The shut off timing could be done with the 'shutter wheel'. With variable timing done by moving the ring holding the opto-sensors. The movement done mechanically, like a 'governor'.

I like idea of the movable sensor shutter. It would give a relatively simple solution electronically.

Here's a thought to also simplify the solenoid turn-on. Have the coil energized most of the time except when the opto-sensor detects the light from the "shutter wheel" delay. Thus when the valve is mechanically opened, it will stay open, (assuming the solenoid generates enough force to hold the valve open but not enough to open it when closed). The solenoid than momentarily releases long enough for the valve to close when the optical signal is detected. This eliminates the need for a separate sensor to turn the solenoid on.