How many intermediate driving gears ?

[Stevdar]

I'am a little unsure on how many intermediate driving gears (idlers) there are in this valve train system and would like to know others thoughts?
the main driving is through a chain and then one cam drives the other with gears on the cams.

 

[BrianPetersen]

That is not hard to understand. What part of it don't you understand?

 

[Stevdar]

i know the large gear meshing with the crankshaft is an intermediate gear but not sure if the first cam is an intermediate for the second cam or if it is looked at differently ? i think not but it seems a bit grey to me

 

[ZDR1985]

The gear meshing with the crankshaft is the intermediate gear. But usually the 2 cams does not mesh with each other, they rotate the same direction through the chain. Or they can have intermediate gear in between.

 

[rb1957]

why do you need to mesh the two cam gears ? why not belt drive both of them ? I'd add one idler (to control belt tension), or not if it isn't critical.

another day in paradise, or is paradise one day closer ?

 

[JackAction]

I would consider this set up as 2 different gear sets (driver-driven) linked by a belt & timing gear set. No idler in there for me. Is a gear in a transmission considered an idler for the gears in the final drive?

That system was used on different Toyota engines like the 5S-FE and 4A-FE:

 

[Stevdar]

So the design has to comply with some rules

1. Valve timing system drive must be by one chain. An intermediate drive gear which rotates on only one axle or rotation centre is allowed in the system (refer to Diagram 7 in the Appendix for some examples of permitted systems).

I thought the proposed system would be good because the head is desmodromic and reducing the chain lengths will reduces the chance of timing misalignment from chain wear and reduce the need for chain replacement and reduce chain whip (I think this would be a good choice for a racing engine as long as i can get the intermediate gear light enough). the cam gears would look the same as this buell 1125r

 

[Stevdar]

Diagram 7

 

[Stevdar]

JackAction good point made on the transmission, that really makes it clear to me

 

[JackAction]

It may not be an idler gear, but it may be taken as «an intermediate drive gear», just like the one on the crankshaft side (so you have 2).

 

[BrianPetersen]

Why such a focus on what the gears are called?

I don't care about nomenclature as long as it works!

 

[desertfox]

Hi Stevdar

I don't see any idler gears in your diagram, to me an idler gear is defined as at this link

http://en.m.wikipedia.org/wiki/Idler-wheel

 

[Stevdar]

Because brianpetersen if i build it like that and its deemed to be in violation of the rules then all that work will be for nothing, so i need to be sure its within the rules.
I agree Desertfox, but it still seems like a bit on a grey area, thanks for your input.

 

[BrianPetersen]

Who is establishing the rules and why is this cast in stone?

Probably 99% of DOHC cam drives use a single belt or chain around the crank sprocket and the independent sprockets for each camshaft. No gears involved. There may be various idlers or other pulleys that drive other accessories or serve as tensioning rollers.

Some Toyota engines are as shown above, with belt/chain to one camshaft and then gears to the other one (which now must rotate in the opposite direction). It allows the camshafts to be closer together, e.g. to allow tighter valve angles (valves set closer to vertical).

Some motorcycle engines use an intermediate shaft with the camshafts driven in turn (by various means) from that. The mention of desmodromic valve operation suggests Ducati. Right/wrong?

 

[Tmoose]

I'm Not trying to be a wise guy, but ....
Do the rules specifically say gears, and only gears? The components that drive, and are driven by, chains and toothed belts are really sprockets.

 

[tbuelna]

If at least one chain drive is required in the system the best option in terms of efficiency, weight and complexity would be A in diagram 7. Fewer parts is usually better and don't make things more complicated than they need to be. The only reason for using additional gear stages is to alter the direction of rotation of the camshafts or to minimize the overall engine height by reducing the diameter of the driven sprockets on the camshafts. Single stage cam chain drives have long been used successfully on high rpm DOHC M/C engines. There should be no issue with chain wear/whip/stretch with a properly engineered system, even on a race engine.