Please help me with a clutch question?

[frascati]

How does the EZ-GO clutch actually operate?

I'm building a vehicle that requires a mechanical (not electromagnetic) clutch between human (pedal) power and a 1.5hp stroke gasoline engine. The design requires some form of clutch as near to the pedal crank (ideally right at the pedal crank) as possible to reduce transmission drag losses when pedalling without the motor. The motor is intended to assist human input when required. A simple slip belt with tensioner would induce too much drag on the pedal crank when disengaged.

I've been searching the internet for weeks, calling clutch manufacturers, posting in ultralight aircraft, bicycle, motorcycle, engineering, ad infinitum forums and was consistently assured that there is no such thing as a compact, lightweight, mechanically actuated clutch in existence. All the ball/ramp clutches are specifically designed for wet type motorcycle use.

I don't know what I finally used in the search image query of Google, but on the first page was an exploded view of an EZ-GO aluminum bodied ramp actuated belt clutch.

Can anyone describe how these basically function? It appears to be mechanical, but I don't immediately see how it is actuated. Does Textron make these clutches or are they outsourced? What is the smallest version of any of them?

Thanks so much.


I went back and looked again at the diagram and it appears as if all of these clutches are the type that merely squeeze a vee belt between two pulley halves. I was hoping that some of them used interal friction plates for use with timing belts. Anyone aware of this type?

[Not so EZGO]

You'd have to pedal pretty fast to reach the 1200 RPM needed to activate the clutch centrifically. Not to mention the weight of the clutch (10-12 LBS or so).

[WILD-BILL]

I'm not sure if they will fit your application but they are pretty easy to under stand. I'm not really familiar with what's inside the clutch on my cart but there not much different in theoritcal application to what we use on Jr Dragsters.

Inside the driver clutch (on the engine PTO) is a set of springs, arms and weights. Depending on the tension of the spring, and weight of the arm will determine at what RPM the clutch will come in and start grabbing the belt.

The driven (one the rear or a jackshaft) has only a large spring and a helix. The tigher the spring pressure the longer it will stay in a lower gear ratio before the driven starts to open allowing the belt to drop and go 1 to 1.


Some of the smallest I beleive are chain drive clutches on minibikes but I have no real insight on how they work.

The smallest one I've seen or used on a Jr was the comet TAV2-30. Not a great clutch for the application but not exactly that expensive. You can get some parts to fine tune it but your options are limited.

Some other Jr dragster clutches you can fine tune every aspect of but are probably more than you want to know.

[frascati]

Correct. I cannot use a centrifugal clutch. Max rpm where I need to engage the drive is around 100rmp.

I was originally looking at the clutch described in this thread...
http://***********.com/forum/index.php?showtopic=1254
insert c a r t a h o l i c s

( i don't understand. why am I not allowed to reference another forum here?)

It has ramps, which (I'm guessing) are rotated against one plate to bring it closer to the other. I did not see weights in the dismantled clutch, so I assumed that this was somehow manually activated (by pedal and cable?) rather than centrifugally activated (by engine rpm). But I did not see any provision for a torque arm, cable arm, etc.

[WILD-BILL]

The part pictured in that other forum is the secondary or driven part of the clutch.

It does not open by rpm or have weights and arms like the primary or Driver. It is opened by shear force of the belt acting against the spring tension. It's the second part in a 2 part clutch.