Electro servo valve


by wolram
Tags: electro, servo, valve
wolram
wolram is online now
#1
Sep15-06, 12:30 AM
PF Gold
wolram's Avatar
P: 3,671
A DOHC engine has the valves controled by two servo motors, an engine speed encoder controls the valves possitions via electronics, this is an obviuos solution to four stroke ice valve control, what are the reasons why it is not used?
Phys.Org News Partner Science news on Phys.org
Cougars' diverse diet helped them survive the Pleistocene mass extinction
Cyber risks can cause disruption on scale of 2008 crisis, study says
Mantis shrimp stronger than airplanes
Danger
Danger is offline
#2
Sep15-06, 11:52 AM
PF Gold
Danger's Avatar
P: 8,961
I don't quite understand the system that you're referring to. If the valves are controlled by servos, why does it have cams? Anyhow, if you mean servos instead of cams, I can't envision them being fast enough. Or do you mean that the servos control the cam profile?
OgreOwner
OgreOwner is offline
#3
Sep15-06, 10:34 PM
P: 5
Mechanical devices preceded electronic devices by quite a few years. Before electronics could keep up with the needs of an internal combustion engine, cams and pushrods had become such a mature technology that it is considerably cheaper to use them than to use an electronic solution. As the price of the electronics becomes lower, that may change. In one of the recent issues of Home Shop Machinist there was a serial article on building an engine with valves controlled by solenoids.

Karl Peterson

Danger
Danger is offline
#4
Sep16-06, 12:18 AM
PF Gold
Danger's Avatar
P: 8,961

Electro servo valve


Hey, Karl;
This is the first time that I've seen your name, even though you seem to have a few previous posts. Welcome aboard! Does that Home Shop Machinist article refer to helinoids or regular solenoids? I've never even heard of the publication before.
wolram
wolram is online now
#5
Sep16-06, 02:31 PM
PF Gold
wolram's Avatar
P: 3,671
The idea, (a first step) is to drive the cam shafts with servo motors, this would allow the cam shaft cycle to be maped, the profile of the cam would be less important, (it could be just an off center circle), the servo motor could ramp up or down at the required times to give maximum conrol of induction and exhuast phases.
turbo
turbo is offline
#6
Sep16-06, 03:17 PM
PF Gold
turbo's Avatar
P: 7,367
Interesting idea. This would allow the inlet and exhaust valves to be timed differently, and that could result in performance gains over DOHC arrangements in which the cams are in lock-step with the crankshaft and the ignition curve is varied to provide optimum power at various rpms and loads. If a desmodromic valve actuation system were incorporated, that would eliminate valve float and greatly eliminate cam/follower wear due to the friction caused by valve spring pressure.
wolram
wolram is online now
#7
Sep16-06, 03:57 PM
PF Gold
wolram's Avatar
P: 3,671
Turbo, the next step would be to do away with poppet vales, imagine a hollow tube sealed at one end with a port machined into it, the open end would either lead to carb or exhaust, this tube would run in the cylinder head casting and be driven at half engine speed via servo motor, the tube would be ceramic coated and close tolleranced, there may be some leakage while the engine is new but like the sleve valve engine would improve as carbon deposits are built up.
turbo
turbo is offline
#8
Sep16-06, 04:21 PM
PF Gold
turbo's Avatar
P: 7,367
Baby steps, Woolie! Multivalve heads are very well-devolped now, and can provide a very efficient distrubution of air-fuel mixtures. I think you've got a really good idea, though, since servo-driven camshafts in a DOHC application can allow the intake and exhaust valves to be timed differently. This would allow the engine to be tuned for maximum mileage, maximum performance, or a mix of these, with a flip of a switch. If you need extra valve opening overlap to acheive high exhaust scavanging rates at high rpms, you can make it happen. You could probably also make it possible to specify the RPM at which maximum torque is developed.
wolram
wolram is online now
#9
Sep16-06, 05:01 PM
PF Gold
wolram's Avatar
P: 3,671
Turbo, the problem i have is servo motor size and power requierments, i guess the electronics could be minimalized once the cam (proifiles) are found
to the best advantage, i just worry that electrical power saped from the engine would overcome any advantage.
turbo
turbo is offline
#10
Sep16-06, 05:30 PM
PF Gold
turbo's Avatar
P: 7,367
Quote Quote by wolram
Turbo, the problem i have is servo motor size and power requierments, i guess the electronics could be minimalized once the cam (proifiles) are found
to the best advantage, i just worry that electrical power saped from the engine would overcome any advantage.
With a desmodromic valve actuation system, there would be no drag imposed by the friction caused by the rocker arms/cam followers overcoming the force of the valve springs. The electrical drain on the system would likely be paid for by the losing the mechanical drag of a conventional valve train. You could also contemplate a mechanically-driven DOHC system with electronic advance/retardation.
wolram
wolram is online now
#11
Sep16-06, 06:05 PM
PF Gold
wolram's Avatar
P: 3,671
Turbo, to the best of my ability i will follow this idea, once i have found a suitable engie to modify, the problems of a tyro inventor will be many, so i hope i can ask questions and maybe share any advatages gained.
Danger
Danger is offline
#12
Sep16-06, 07:49 PM
PF Gold
Danger's Avatar
P: 8,961
Good luck with it, Woolie. Sounds interesting. I really don't think that the flow characteristics of a 'sleeve valve' system would be practical for an engine, but you should check with Clausius.
wolram
wolram is online now
#13
Sep18-06, 08:25 AM
PF Gold
wolram's Avatar
P: 3,671
Quote Quote by Danger
Good luck with it, Woolie. Sounds interesting. I really don't think that the flow characteristics of a 'sleeve valve' system would be practical for an engine, but you should check with Clausius.
What do you think of coupling the servo motor to an indexing gearbox to
provide cam dwell ?
Danger
Danger is offline
#14
Sep18-06, 12:31 PM
PF Gold
Danger's Avatar
P: 8,961
I'd pretty much need a much more elaborate description, or preferably a sketch, to form an opinion. I can't quite envision the mechanism.
brewnog
brewnog is offline
#15
Sep22-06, 12:11 PM
Sci Advisor
PF Gold
brewnog's Avatar
P: 2,793
Woolie, I think the reasons your original idea would not work are due to the speed at which such rotary servos can actuate. Obviously such a system would provide endless opportunities for variable timing and lift.

The favoured method of actuating this kind of system is to do away with the camshafts, but to have linear solenoids operating the valvegear. Currently, such actuators are horrendously expensive; those on the experimental engine I've seen cost something like £18,000 each.

Nice idea though, I'll keep a lookout for any advances (pardon the pun).
brewnog
brewnog is offline
#16
Sep22-06, 12:12 PM
Sci Advisor
PF Gold
brewnog's Avatar
P: 2,793
Quote Quote by turbo-1
You could also contemplate a mechanically-driven DOHC system with electronic advance/retardation.
Yes, and with variable lift I suppose too.

Have you seen anything like this? The only thing I'm aware of is the Ferrari-style arrangement whereby the camshaft moves along its axis through different lobe profiles.
denni89627
denni89627 is offline
#17
Sep22-06, 03:59 PM
P: 71
Quote Quote by brewnog
Yes, and with variable lift I suppose too.

Have you seen anything like this? The only thing I'm aware of is the Ferrari-style arrangement whereby the camshaft moves along its axis through different lobe profiles.

I've never heard of this but it sounds very interesting, and promising. It would be a good way to achieve max economy and max power for a given engine. I suppose when you "get on it" the computer would push the camshaft so the valves ride off a different part of each lobe. How is the cam driven? A chain with enough slop to allow for the movement along its axis? I guess it wouldn't have to move too far, quarter inch or so at a guess.
brewnog
brewnog is offline
#18
Sep22-06, 04:16 PM
Sci Advisor
PF Gold
brewnog's Avatar
P: 2,793
It'll be chain or belt driven, but probably uses a splined arrangement to allow the camshaft to slide relative to the cam gear; a chain with 'slop' would be misaligned and not capable of maintaining correct timing.

The lobe profiles vary from left to right, continuously, providing a mild profile at one end and an aggressive profile at the other. I would imagine the movement is 20mm or so.

Interestingly, googling the subject returned a physicsforums thread which several of us had posted in. Happy days.


Register to reply

Related Discussions
Electro hydraulic valve Mechanical Engineering 7
Urgent help required for F.B.D of servo system please Engineering, Comp Sci, & Technology Homework 0
servo motors Engineering Systems & Design 12
Servo drive controller Electrical Engineering 0
Servo controller Electrical Engineering 3