Hydraulic - Shaft Drive

[Wingnut]

This is totally free from Land Rover involvment (apart from the fact that the end product will be moved behind one - if it gets built) so Mods, if you deem it unsuitable, please delete.

I need to transmit drive from a hydraulic motor to a rotating shaft. To keep it neat and simple I want to drive the shaft directly from the motor, without belts or going through a gearbox.

The motor will have a shaft diamater of 25mm, keyed, and with a 1:8 taper. I need to drive a 'bright' steel bar of 40mm, which will also have a keyway cut into it. This is the best solution I have come across so far for some protection from shock loadings :-

http://www.bearingsrus.co.uk/l110-pilot-coupling-15mm-bore-3916-p.asp

The hydraulic motor is 22cc, rpm of 2,000 and is rated at about 10kw. The shaft will have a disc atached to it which will be subjected to some harsh shock loading. I am being intentionally vague at the moment as to what this will/may be, but it will be driven from a mini excavator.

Does anybody have any better ideas as far as a coupling is concerned, and is the one above up to the job? All ideas welcomed.

Peter.

[Retroanaconda]

Oooh, I wanna guess! Stump grinder? Peeler/pointer?

Anyway, some form of rubberised coupling is the way most things work I think. The peeler/pointer I use at work (Cundey De-Barker) has an engine driving a big metal flywheel with six blades on it that chop away at the post/rail/spile/whatever and so a method of absorbing shock loadings is needed. The solution is a big old rubber band that transmits the power and allows flex. Depending on the sort of scale your machine will be, that may be an option for you.

[ejparrott]

Thats the style of coupling I would suggest, although I can't size it for you. We use some at work on the winches we build, they are on a 40/42mm shaft, and IIRC the motor is 30Kw.

[simonr]

Torque? Length of shaft? Magnitude of shock loadings?

That's the sort of thing you need to tell accurately whether it's up to the job.

Si

[Wingnut]

This is all at the 'in my head stage' at the moment. A pair of V belts or a multi v belt would work as a shock absorbing system but I am trying to keep the unit compact and simple.

Torque etc. I have no idea of, I am a complete amateur and go with gut instinct most of the time - if it looks right it probably is. I will do more research into this as time allows.

Thanks for the replys,

Peter.

[RustyNissanPrairie]

The essex couplings are a pain when the rubber cush part starts to fail as you either have to remove one of the main components to split the coupling or knock half along the shaft (if there's room) and wiggle a new rubber in. They dont cope well with misalignment and you cant get the smaller sizes in taper lock fitments.

these are miles better;

http://www.eriks.co.uk/Power-transmission-solutions-from-Renold-Clutches-and-Couplings/3413

(pin and bush couplings) as you remove the drive members without needing to remove the hubs

[LandyManLuke]

Torque? Length of shaft? Magnitude of shock loadings?

That's the sort of thing you need to tell accurately whether it's up to the job.

Si

Also, what sort of angular, axial and radial play/misalignment do you need to accomodate? This information will be part of what dictates the type of coupling that is suitable.

10kW at 2000 rpm is 48Nm.

[Team Idris]

The other side is also very important if the shaft is going to change speed quickly. A cross line relief valve as close to the motor ports is a must, but even that takes time to react. So an accumulator could be a safe bet for a long product life. It'll take out any high speed pressure spikes from the incompressable oil.

[Wingnut]

I have looked at the Renold couplings - it all comes back to a balance of price and suitability in the end, hopefully I will be able to find time to see some couplings in the flesh next week. Eriks have opened a small depot in Swansea and this is relatively local to me (70 miles).

This type of coupling - http://www.eriks.co.uk/Fenaflex-Tyre-Couplings/450 - would solve any misalignment issues (with in reason), or I will have to fabricate the frame as accurately as possible, and then have the pump mounting bracket machined so that it sits square to the line of the shaft that it is driving in both planes.

LandyManLuke - thankyou for the calculation.

Team Idris - your point has been going around in my head aswell - there will probably be some sudden stops. I have thought about a cross line relief valve but I already have a rotating attachment (flail cutter head) that fits this machine and all it has is a pump-body drain that is independent of the pressure side of the system and returns directly to the hydraulic tank. So far it has worked well and no blown seals in the pump (as yet). I have finally been able to source a suitable hydraulic gear motor that should be up to the job, correct flow charecteristics, speed, pressure etc. so I have ordered it today.

One 'gentleman' suggested I use an 8cc pump because it was rated at the correct speed - when I asked him where the other 25 litres per minute of oil flow were going to go he was rather vague on the matter !

Regards,

Peter.

[Team Idris]

Ah, now I see where you are going. But there should be an overun valve, or you blow the seals out when you close the flail lever. Otherwise it would stop dead. It could be in the motor (likely) or spool valve. Cavitation is also an issue.

Cross line relief is like a self re-setting fuse for hydralics.

You may never use it, but when you do get a pressure build up it's not a problem