hydraulic winch design question

[5middy]

Hi,

Im new to this forum and so far have found it very imteresting! I have a question that someone with a decent amount of hydraulic knowlwdge might be able to help with!

Im in the design stages of building a hydraulic winch to be run on a 4wd vehicle. i will be using a superwinch h8pn 8000lb unit which has a gearbox ratio of 6.5:1. It is fitted with a spring applied hydraulically released dry fail safe braking system. so basically when fluid power is applied to either side of the hydraulic motor ports the brake gets released. it takes between 300-350psi to release the brake however the manual supplied with the winch recommends between 1700-2000psi to maintain full braking pressure.

So what i am after is a reliable solution to enable me to automatically release the hydraulic braking system on the winch without the use of the hydraulic motor, without affecting the brakes operation efficiency. could this be achieved by means of valves? Pumps? Switches?



Thank you in advance and i look forward to your response!
fficiency

Could this be done by way of va.lves? Pumps? Switches

 

[Oldhydroman]

I'm not sure I understand exactly what it is you're trying to do.

You can consider the winch as a complete unit in itself - if you have a spring applied, hydrualically released brake then the hydraulic load control valve on the motor will be set up so that, when there is maximum hanging load on the winch, the pressure that you need to start to open the load holding valve (for "lowering" the load) will still be high enough to fully release the brake. Often the brake is arranged to be on a sprag clutch so that the brake doesn't have to be released when "lifting" the load - the brake does not prevent rotation of the drum in that direction so you don't ever have to worry about the [very low] pressure needed to pull in a slack rope being insufficient to release the brake. If you have no sprag clutch then there may be a second load holding valve to increase the minimum "lift" pressure to a value high enough to release the brake.

The 1700 psi requirement is a statement that your oil supply must be able to reach this pressure otherwise the full lifting capacity of your winch will not be available to you. In all liklihood, 2000 psi is the maximum pressure the winch hydraulic system can tolerate (so don't exceed this figure).

You have to let the brake release line get back to zero psi (completely depressurised) for the brake to fully apply - at which point it will be able to hold any load that the winch was able to lift (and probably a little more as well). You have to apply at least 300 psi to the brake release line to fully release the brake. When you apply a greater pressure to the brake release line it makes no difference because the brake will still be fully released (as long as the brake release system can tolerate the pressure you just applied to it).

If you could show the circuit diagram of your proposed set-up it would help us figure out what you're trying to do. Are you, for example looking for an arrangement where the hydraulic motor is not used at all and you want a manual (hydraulic) control of the brake? Or do you want to have an auxiliary means of releasing the brake (you will still have to let the motor free-wheel)?

DOL

 

[5middy]

Hi,

Thanks for your respomse oldhydroman!

With your reply you have given me a better understanding of how the brake system works, i will try and explain a bit better my objective.

Ok so im planning a build of a custom hydraulic winch. instead of having a hydraulic motor powering the winch head, im going to build a right angled drive with a gear reduction that will be attached to the winch head in lieu of the hraulic motor. the right angled drive will be powered through driveshafts off the transfer case mounted pto drive. so this is where my problem lies, now that there is no hydraulic motor mounted on the winch head, i need to find a solution to releasing the hydraulic brake. previously the brake was released when fluid power was put towards either motor port but now the hydraulic motor has been removed this is unable to happen. ok so do you follow me?

So how do i go about this effictively? Can it be done with a pump, valving, switchgear? or is it a case of finding another braking system all together?

Let me know what you think!

Thanks

 

[Oldhydroman]

Hi

I think you will find it very difficult to sequence the take-up of a suspended load with the release of the holding brake - it's the winching equivalent of performing a hill start in your car. You also have to accommodate a means of preventing the load from running away should there be a failure in your drive linkage or should the engine stall/cut-out. Then you will need to arrange a clutch mechanism of sorts and a means of reversing the drive.

On the whole I think you would be better sticking a hydraulic pump into your transmission power take off and stay with the hydraulic solution for the winch. It's not as if your proposed solution allows you to get rid of the hydraulics completely because you still have a hydraulic brake. A hydraulic solution will be: cheaper, lighter, more controllable, safer, easier to install/fix/replace parts, less maintenance intensive and less risky.

God forbid, but what if there were an accident and your suspended load ran away and smashed into a bus full of school children? Imagine how it would look in court if you had to explain to the judge and jury that you took a perfectly good [and proven] winch and changed its drive mechanism and braking arrangements to suit yourself. And then continue with the explanation that your degree of competance in doing this was so low that you had to ask an internet forum of professional engineers how it could be done. Wouldn't you rather be able to say "It's a standard Superwinch model H8PN, installed and used entirely in accordance with the manufacturer's instructions - I think the manufacturer should come to the courthouse now because I haven't done anything wrong"?

DOL

 

[hydtools]

5middy, what are you expecting to gain by using a PTO winch drive and having to add hydraulics instead of the as-manufactured winch and adding PTO hydraulics?

Ted

 

[kcj]

If you really want PTO drive, you might look for an older straight mechanical PTO driven winch. They have worm gearing in the drive that is self locking against backdriving, and a F N R gear selection for freespooling and direction change. The FNR gear change parts could be a bit finicky if worn.

My 47 Jeep pickup had a straight winich with no FNR gearing in the box. The worm gear was self locking, safer, but had no freespooling. It drove the PTO off the rear of the transmission. With transfer case in Neutral, PTO engaged, the 3 speeds and reverse of the transmission gave speed and direction, and the clutch was the soft start. That type probably isn't made any more. It was high tech and productive in 1947, but pretty slow and clunky by todays standards.

You could through-drive a very small hydr pump for the pressure signal, then use the through-drive for PTO transmission of the actual winching power, but the difficult part is the brake release signalling as noted above, not the actual source of hydraulic power.

If you have the complete winch, I'd stay with full hydraulic drive, from the PTO so it would rarely run. You could scrimp on tank size as it won't run long, so throttline and heat buildup are probably not an issue. I asssume it is for offroad intermittent use, not pulling a well or driving a continuous industrial load. The hydraulics gives you speed and direction control.