Friction Clutches...help!?

[jenni-leigh]

Hey u guys!

Im new, and I need help, if anyone can offer! I have a project to do where I need to design a clutch for a Leisure Kart. This is the background I was given:

'It has been recognised that the direct drive between the engine and rear axle of a leisure kart has engendered a certain amount of sales resistance. It was proposed that the implications of incorporating a friction clutch in the drive line between the engine and rear axle should be investigated. The outcome of these investigations indicated that the standard gearing was inadequate and that a change speed gearbox is required. The proposed gearbox is a three speed epicyclic device mounted co-axially with the rear axle. The rear axle sprocket is bolted to the gearbox input flange.'

I have to design a friction clutch for this which is both mechanically and thermally suitable for the duty. I have been given technical data such as engine characteristics, the sprockets, the change speed box, the tyres, and inertias.

I am looking for a bit of help from someone, who may know what my first step should be in designing this, and what sort of design I should do. Any help would be a great help, and in case anyone uses MSN, my email is [e-mail]

I look forward to hearing from someone soon!

Jen

[gdr]

You could cheat and just give them one of these belt drive torque convertors as often used on leisure karts. www.gokartsupply.com/comet.htm But sounds like you need to replace variable pitch belt drive with epicyclic gears and design the clutch. Long time since I did mech eng degree but I guess start by working out how much torque clutch needs to handle, size the plate (need friction co-eff of clutch plate material) and then try and package it.

>> Edited by gdr on Tuesday 5th October 07:48

[jenni-leigh]

Thankyou!

[grahambell]

Agree with gdr that you'd be better off with one of those CVT (constantly variable transmission) belt drives as it effectively give you clutch and gears in one.

Been involved with development of off-road buggy this year and we ditched original centrifugal clutch and differential in favour of one of these.

Used a lot on quad bikes, snowmobiles and scooters.

Be aware though that you will need to accomodate an extra shaft or axle as you run the belt drive from the engine to an intermediate shaft/axle and then a chain drive from that to your final axle.

Edited to add that you might not need an extra shaft/axle and chain drive.

We used it as do quads because we needed some final reduction gearing to suit the tyres, but if using small diameter kart tyres you might get away without.



>> Edited by grahambell on Thursday 7th October 19:49

[GavinPearson]

jenni-leigh said:

Hey u guys! Im new, and I need help, if anyone can offer! I have a project to do where I need to design a clutch for a Leisure Kart. This is the background I was given: 'It has been recognised that the direct drive between the engine and rear axle of a leisure kart has engendered a certain amount of sales resistance. It was proposed that the implications of incorporating a friction clutch in the drive line between the engine and rear axle should be investigated. The outcome of these investigations indicated that the standard gearing was inadequate and that a change speed gearbox is required. The proposed gearbox is a three speed epicyclic device mounted co-axially with the rear axle. The rear axle sprocket is bolted to the gearbox input flange.' I have to design a friction clutch for this which is both mechanically and thermally suitable for the duty. I have been given technical data such as engine characteristics, the sprockets, the change speed box, the tyres, and inertias. I am looking for a bit of help from someone, who may know what my first step should be in designing this, and what sort of design I should do. Any help would be a great help, and in case anyone uses MSN, my email is [e-mail] I look forward to hearing from someone soon! Jen

If you know how fat the drivers of the karts will be (assume 120Kg) + kart weight (assume 120 Kg) you know what mass you are accelerating. You know wheel details and weight so you know wheel inertia. You know a kart axle is solid steel 30 mm in diameter and 1 metre long. A brake disc on a kart is about 8 mm wide and 9" diameter. So now you can sum the inertias.

If you know the first gear ratio you can work out how much energy is required to go into the clutch to get the vehicle moving to the point where the clutch shouldn't slip. The torque curve of the engine will show a sensible point to have lockup or not. I suggest 80% of peak torque. If you know the energy, and the heat capacity of the lining you know what size to make them. If you know the speed target you know the strength of the springs to use. The torque transfer requirement and minimising inertia are key factors in sizing the clutch.

As the clutch has to engage into something I suggest thinking about a brake drum. Only yours will be much smaller. So you want it to be ferrous, and consider the rotational speed, plus the force on it from the clutch to judge strength requirement. Select either a steel or cast iron and use the BS number to specify it. Also consider that you need a sprocket attached to the side.

There's a fair amount of work involved in this but that is what the lecturer is looking for you to work out.

What will be more impressive is if you can make it of something commercially available and ideally cheap. If it can be machined of EN8 then that is good, if you have to buy the world's stock of unobtanium then that's probably bad.

[350zwelgje]

Added to the information given already:
In cars (I don't know carts) the clutch is also designed to slip again when more torque is applied during braking that could kill the engine.
Think why: the engine can produce torque, but if you brake in gear is is very easy to apply a lot of torque back to the engine - and thus engine parts can break due to this.


Rob

[GavinPearson]

350zwelgje said:

Added to the information given already: In cars (I don't know carts) the clutch is also designed to slip again when more torque is applied during braking that could kill the engine. Think why: the engine can produce torque, but if you brake in gear is is very easy to apply a lot of torque back to the engine - and thus engine parts can break due to this. Rob

I think you have misinterpreted the facts slightly - you don't get any designed in slip, but what you do have is the feature of the linings bursting if oversped. So for example, you're in fith, need fourt, accidently select second, and the clutch disc is doing 9000 rpm. The linings burts ,and the engine is saved from overrrevving. Fuel cut off won't fix an incorrect gear selection, but linings bursting will.

[jenni-leigh]

Thanks everyone for your help!
I have included most of the info you all gave me in my report, and handed it in yesterday, so I shall let you all know what mark I got! I did try pasting some pics of my fianl design on here, but it doesnt seem to work!!!


I now have a new project if anyone is interested...its on designing a gearbox for a microlight...but I will post that in a new thread, if anyone wants a read!

Thanks again!

Jenni

[matt_t16]

jenni-leigh said:

Thanks everyone for your help! I have included most of the info you all gave me in my report, and handed it in yesterday, so I shall let you all know what mark I got! I did try pasting some pics of my fianl design on here, but it doesnt seem to work!!! I now have a new project if anyone is interested...its on designing a gearbox for a microlight...but I will post that in a new thread, if anyone wants a read! Thanks again! Jenni

That Microlight box isn't for use with a variable pitch propellor is it? Just had a mate of my cousin phone up for advice on that

Matt

[jenni-leigh]

We havent been told what sort of propeller it is...all thats known is its mass and speed at 6200rpm engine speed.