Variable Valve Timing
Joined: Mar 2004
Posts: 10,652
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From: Market Harborough, Leics.
Originally Posted by Saxo Boy,Feb 26 2007, 01:29 PM
VTEC et al is a solution to an engineering compromise. Designers are always working to compromise one set of goals to achieve another. Power vs smooth, fast vs efficient, etc, etc. Vtec allow the use of a low-lift profile to achieve a smooth running engine with reasonable economy at low-rpm and a high-lift profile for high rpm power production. I see little point of fannying around lowering the point of change-over since in both cases the driver should be selecting the optimal gear for his situation. In other words if you want to go fast; change down and drop her into vtec. At a guess Honda did their sums when they picked 6000rpm as an appropriate switching point.
I'm amazed that nobody has made a production engine with valves controlled electronically by some sort of soleniod. This would allow continous adjustment of the lift and duration of not only the inlet and exhaust valves but each valve individually (if there was ever an application for such detailed level of control). Where currently we have machined cam profiles you'd be able to get your profile remapped in the way we can set boost targets, ignition advance and so on when mapping turbo cars currently. You'd also do away with a cam-belt/chain which can cause the death of many an engine. I'd like to know what the limitation is that has prevented this from being done - I can only assume its one of reliability. (i.e. if the ecu or any solenoid ####s up even once for a split second it'll screw the engine!).
With the traditional belt and camshaft system once its set up its locked into the cycle of the engine so that the only way it can fail is if something physically snaps/sheers.
I'm amazed that nobody has made a production engine with valves controlled electronically by some sort of soleniod. This would allow continous adjustment of the lift and duration of not only the inlet and exhaust valves but each valve individually (if there was ever an application for such detailed level of control). Where currently we have machined cam profiles you'd be able to get your profile remapped in the way we can set boost targets, ignition advance and so on when mapping turbo cars currently. You'd also do away with a cam-belt/chain which can cause the death of many an engine. I'd like to know what the limitation is that has prevented this from being done - I can only assume its one of reliability. (i.e. if the ecu or any solenoid ####s up even once for a split second it'll screw the engine!).
With the traditional belt and camshaft system once its set up its locked into the cycle of the engine so that the only way it can fail is if something physically snaps/sheers.
They've got them working with 48volt electrics, but that causes other problems elsewhere with other components.
Joined: Mar 2001
Posts: 31,181
Likes: 58
From: Hertford
What you want is infinitely varying lift & duration, to cover all loads & rev bands. Then you can lose that inefficient butterfly throttle entirely.
VTEC was the first step. A-VTEC is (like valvetronic) the holy grail.
I posted about its virtues some weeks back, but it was generally perceived as pearls before swine, sadly.
VTEC was the first step. A-VTEC is (like valvetronic) the holy grail.
I posted about its virtues some weeks back, but it was generally perceived as pearls before swine, sadly.
Registered User
Joined: Jun 2001
Posts: 5,704
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From: South Staffordshire
weren't renault the first to go with pneumatics replacing the springs on the valves.. more than 20years ago when 13,000rpm was a lot.. I think it was Senna's Gerard Ducarouge designed lotus..
however the amount of complexity and horsepower loss from the compressor doesn't make sense unless you are going for max revs/power.
however the amount of complexity and horsepower loss from the compressor doesn't make sense unless you are going for max revs/power.
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Joined: Jan 2004
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From: The Middle of Nowhere
I had a weird idea about this once.
If you make the lift point on the cam shaft like a very large drill bit and the push it forwards or backwards with some hydraulic presure, you would have a variable system on a single cam
Difficult to explain see picture in my head....
If you make the lift point on the cam shaft like a very large drill bit and the push it forwards or backwards with some hydraulic presure, you would have a variable system on a single cam
Difficult to explain see picture in my head....
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From: The Middle of Nowhere
Ok imagine the wee green bits (the valve lifters) were knurled like this
Pushing the camshaft forwards and backwards would vary the lift point within a range but very smoothly.
Joined: Mar 2001
Posts: 31,181
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From: Hertford
Originally Posted by C7BLE,Feb 26 2007, 02:44 PM
I had a weird idea about this once.
If you make the lift point on the cam shaft like a very large drill bit and the push it forwards or backwards with some hydraulic presure, you would have a variable system on a single cam
Difficult to explain see picture in my head....
If you make the lift point on the cam shaft like a very large drill bit and the push it forwards or backwards with some hydraulic presure, you would have a variable system on a single cam
Difficult to explain see picture in my head....
You slid the camshaft along, to reach the higher lift range.
The wear killed it.
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Joined: Jan 2004
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From: The Middle of Nowhere
Originally Posted by Nick Graves,Feb 26 2007, 02:54 PM
FIAT were looking into that; each cam was big at one end and smaller at the other.
You slid the camshaft along, to reach the higher lift range.
The wear killed it.
You slid the camshaft along, to reach the higher lift range.
The wear killed it.
Ah well back to computers
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