pneumatic valves
Discussion
As greenv8 said, they simply(?!) replaced the steel springs. The system is filled with nitrogen becuase its more stable. however when it springs (no pun) a leak, the valves stay open and smash into the piston - hence the big blow-ups in F1
There is stuff on the net about it, becuase is was curios also!
There is stuff on the net about it, becuase is was curios also!
annodomini2 said:
Electrically actuated valves are in development, but nothing production scale yet. Some big diesel engines use compressed air valve actuation
As has been discussed on here previously, electro-hydralic valves are used on large diesal engines such as those used in ships (have links, which I think roospupret has seen, they are on other PC so can't post just now). However, curently these run at much lower speeds than car engines (~100 rpm or similar), the dificulty is getting them to operate at high speeds required for a high reving car engine.
As I understand it, the pneumatically actuated valves used in F1 and similar, as has been stated previously, use an air spring insted of a coil spring, as an air spring will return to its original size much faster than a coil spring hence allow the engine to run at higher speeds (although, as a cheaper way of obtaining this may be to use a titanium spring as these supposedly return faster-dont know about this though).
Pete
Another method is to use another cam to close the valve, Ducati do this, they caled it the desmo.... something 
. It allows for much higher RPM than springs can provide with definative closure of the valve with no bonce inheirent with springs, although I believe the 'pneuamtic' spring arrangement ala F1 is even higher reving AFAIK.
Harry
. It allows for much higher RPM than springs can provide with definative closure of the valve with no bonce inheirent with springs, although I believe the 'pneuamtic' spring arrangement ala F1 is even higher reving AFAIK. Harry
Desmodromic 
The Desmosedeci - current MotoGP bike - has been seen revving over 18000RPM if I remember right. I think either system could be developed to however much RPM the bottom end could take. Both systems get rid of the resonance in a steel coil spring which ultimately limits the rev capacity of such a system. Although I suppose the pneumatic system would have a resonance at several hundred thousand RPM . . . interestingly Mercedes also used a desmo system, way back in 1954, in the W196 racing car.
The Desmosedeci - current MotoGP bike - has been seen revving over 18000RPM if I remember right. I think either system could be developed to however much RPM the bottom end could take. Both systems get rid of the resonance in a steel coil spring which ultimately limits the rev capacity of such a system. Although I suppose the pneumatic system would have a resonance at several hundred thousand RPM . . . interestingly Mercedes also used a desmo system, way back in 1954, in the W196 racing car.
pistol pete said:
Electrically actuated valves are in development, but nothing production scale yet. Some big diesel engines use compressed air valve actuation
As has been discussed on here previously, electro-hydralic valves are used on large diesal engines
Pete
not electrohydraulic, electric (i.e. solenoid)actuated they can regulate timing and lift for each valve.
annodomini2 said:
not electrohydraulic, electric (i.e. solenoid)actuated they can regulate timing and lift for each valve.
You will find that what are often refered to as electric valves are electro hydraulic (I've seen car ones) -this is because there are a number of things which make solanoids difficult to use directly. Have you any idea how big a solanoid it would need to directly operate a valve? -Also, this would have a HUGE power consumption -if the magnetic field could operate reliably that near the HT leads and sparks. Also -the heat generated around the head is huge -drasticly reducing the lifespan of any electronics in the area.
Instead, what the manufacturers I am aware of have done is to develop an electro-hydraulic system -thus you can have a nice sealed metal box contaning 1 solanoid control (multiposition, not just on/off) valve per valve in the engine, the solanoid valves control the flow of hydralic fluid into a cylinder in the head - the piston in which is connected to the valve. This system can control the rate at which the valve opens, the amount that the valve opens (ie you can half open the valve, like changing the height of the cam while the engine runs as well as the timing of the opening/closing of the valve.
ps. I have just been dumped by a major sportscar manufacturer whom had previously planned to offer me a (graduate) job, so i'm now starting looking for something similar with someone else.
Cheers,
Pete
The company i work for has a working electric valve engine using solely electric valves but currently each valve requires a complex and expensive position sensor. They're working on a sensorless version, for when perfected, the division i work in will get the contract to build the ecu and develop the software for the control system.
The power consumption of the solenoid need not be large. Permanent magnets can hold it in the open or closed positions, so energy is only used to switch it; and most of that energy can be recycled by exploiting resonance. However, it would still be large and/or expensive and hard to manufacture compared with a hydraulic system. Also, it is a good idea to keep electrical devices well away from the heat and vibration of a cylinder head.
I have thought about this in the context of a supercharged two-stroke diesel, and hydraulic actuation is by far the most straightforward method. Also, the control inputs can be derived mechanically, and the engine thereby kept free of electrics (apart from the simple requirements for lighting and starting).
I have thought about this in the context of a supercharged two-stroke diesel, and hydraulic actuation is by far the most straightforward method. Also, the control inputs can be derived mechanically, and the engine thereby kept free of electrics (apart from the simple requirements for lighting and starting).
O/Tish:
Desmodromic systems don't use two cams. Instead a c or u shaped cam follower is held by the cam throughout its entire revolution, so the valve is pushed open and pulled closed, rather than relying on spring pressure to close it. Having said which, Ducatis do have a 'valve spring' but it's purely a helper spring to ease starting and give a smoother idle.
picture(video actually),words,thousand etc...
Desmodromic systems don't use two cams. Instead a c or u shaped cam follower is held by the cam throughout its entire revolution, so the valve is pushed open and pulled closed, rather than relying on spring pressure to close it. Having said which, Ducatis do have a 'valve spring' but it's purely a helper spring to ease starting and give a smoother idle.
picture(video actually),words,thousand etc...
Pigeon said:
The power consumption of the solenoid need not be large. Permanent magnets can hold it in the open or closed positions, so energy is only used to switch it;
Not a good Idea, you actually increase the amount of energy required to make a transition, not to mention response problems and control problems because you would lose the lift control, two solenoids open and close I believe is considered the most effective solution.
Pigeon said:
However, it would still be large and/or expensive and hard to manufacture compared with a hydraulic system.
Expensive maybe (but see further), large i doubt it, hard to manufacture no. It is certainly less complex in terms of engine components, some would argue the 'electronics' is overly complex, but the most expensive part of the system to develop is the software , but this is a one-off cost and can duplicated many times without cost. Plus if it was hydraulic if a problem was found with the control of the valves reworking of valves, cams, etc may be required, then you've got retooling and more, plus anything that has already reached the public would have to be replaced in part or at worst in total. With software you just upgrade the ecu. and you can do that with everyones. for a mere 5mins at a garage.
Pigeon said:
Also, it is a good idea to keep electrical devices well away from the heat and vibration of a cylinder head.
Yes this is a problem we deal with everyday and is just as much of a problem to a hydraulic system as it is to an electronic/electrical one.
sparkyjohn said:
O/Tish:
Desmodromic systems don't use two cams.
It dosen't use two camshafts, but that video clearly shows there is a separate openeing and closing lobe on the camshaft. If you think about it, there has to be as the C shaped arm could not be in contact with the top and bottom of the lobe all the time so the valve motion would not be controlled for a significant amount of the cams rotation.
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