So just what is so different about a diaphragm clutch

[dan williams]

OK so I got to thinking again. Dangerous I know but I'm bored with circuit theory at the moment so I figured I'd try to understand what the big whoop is with a diaphragm clutch since I haven't seen anyone explain the difference. This is my take on it. Feel free to shoot it full of holes and call me an idiot.

The diaphragm clutch.pdf

[kurtas]

Personally I have found that clutch drag was much worse with a diaphragm clutch than the basket clutch.

I think the main advantage of the diaphragm clutch for the general punter is that the nonlinear spring rate has the effect of lengthening the zone at the lever in which you can slip the clutch.
The basket clutch because of the linear rate reduces this length and makes the clutch feel more on/off.

The diaphragms clutches advantage for the manufacturer is its cheaper to produce, less plates, 1 Belleville washer spring instead of 5 or 6 coil springs and generally less complex machining required.
Another secondary advantage is the reduction in width that it affords.
I think the only real advantage the basket clutches have is that due to the extra plates and also the linear spring rate the effect of plate wear on the clutch action is much less significant than with the diaphragm design.

In saying all that I have no preference for either, it takes a small amount of time to adapt to each and only a minor amount of extra maintenance with the diaphragm.

[billyt]

Mmm Interesting

 😎

 

[dan williams]

I admit the graphs are exaggerated but I think this analysis gets to the core of the thing. I'll have to do more research and do some math on actual diaphragm springs and friction coefficients to see if I can refine the description. But like always, I could be barking mad and have no idea what I'm talking about. Certainly wouldn't be the first time. Probably won't be the last either.

But isn't it fun that life is full of mysteries to figure out. 😁

[TMofCumbria]

Bit surprised at the question but will answer it anyway. A traditional clutch uses coil springs (usually 6 on a trials bike). These provide relatively low force when the clutch is fully engaged and the pressure increases the further you pull the lever back towards the bars. The spring in a diaphragm clutch is a large "domed washer" a bit like a saucer with a hole in the middle. It exerts maximum pressure on the clutch plates when they are fully engaged. The pressure to compress the diaphragm gets less the further it is compressed by moving lever towards the bars. In theory a diaphragm clutch should be better because is minimises the likelihood of clutch slip whilst reducing lever pressure and increasing sensitivity at the bite point.

Diaphragm clutches have been used in industrial machinery for many years because when automated as in a cnc machine their energy consumption is lower than an equivalent coil spring clutch.

[kurtas]

This is the diagram from Schnoor on their Disc springs which illustrates the point about the non-linear spring rate of the belleville washer in the solid line.
The force to compress the spring continually gets larger but the extra force required to continue compressing the spring from where it was is reducing.

The coil spring would much more closely represent the linear line.

[feetupfun]

There is nothing new under the sun. Here is what a 1970s Maico MX clutch spring looks like. When stacked up top to top and bottom to bottom, these are used in Maico clutches in a similar way to the helical compression clutch springs of other brands. Maico were onto the unusual spring rate benefits of diaphragm springs for motorcycle clutches over 50 years ago

https://maicoatchippys.com.au/clutch-spring-cupped-belleville-washer-maico-all-to-81-and-82-gs/

[arnoux]

Villiers Starmaker 250, and probably others before that.

[dan williams]

I remember working on the clutch in my ‘77 AW400 and it was miserable. My buddy used to work on his by jacking up his truck, sliding the bike under, and lowering the truck using the frame to compress the clutch pack. 😁 There is a difference I think with the Maico disc springs vs the diaphragm. With the stacked discs the  spring rate is unaffected by the radial stress on the center of the hole in the disc. On the diaphragm spring compressing the spring should reduce the size of the center hole. Since there is a ring preventing that compression the compression in line with the fingers provides another torsion. I think that’s how the reduction in rate occurs as the diaphragm passes through flat. 
 

I never said the diaphragm clutch was new. Just that I never saw it explained in a way that made sense to me. I’m still learning. 

[billyt]

The above not withstanding.

Diaphragm Clutch: Radial energy being converted into Axial kinetic energy being converted into radial energy and being converted back into axial energy a BIG factor in this equation. 

All the above just within the clutch cases alone. 

There is a lengthy article I wrote on a trials clutch about 32 years ago on the original "Trials Action" Ian Johnstone site (the prior name to this site). Maybe I can find it and re-post it.  

Now where is my Tandy TR80 or my Commodore PC ? 

 

[dan williams]

19 hours ago, billyt said:

 

Now where is my Tandy TR80 or my Commodore PC ? 

 

Probably the same place as my Color Computer and Amiga.😃