PTO Soft Start

[Vigo]

Too large of an implement to not have a slip clutch, maybe.. but if everyone had to stay 100% within the 'recommended limits' of a tractor to not break it, damn near everyone's first tractor would end up a smoking heap and some people would break every tractor they touched for the rest of their lives! If cars were built that way (they were in the beginning..) half of everyone driving today would not be able to drive. You can't 'stupid proof' tractor use in general but you can stupid proof a clutch application in the design phase and it's not hard. There are way more clutches out there WITH that than without it nowadays.. tractors are the exception to the rule.

I'm not 100% against the idea that the 20' mower is oversize for the machine, but i also don't like the idea of 'don't ask for a better design, ask for a bigger one!' Stupid-proofing by just adding metal is a race to the bottom. Fine sometimes but not if it's your go-to thing as a designer. That's why i said the practice is 'lazy'. But at the end of the day, if you can't DIY 'the fix' on your tractor/implement combo, you either have to live with the problem or pay for whatever solution is available, whether you like that solution or not.

 

[troverman]

At some point, you get to the limit of what a machine was designed to do. If we took your philosophy literally, you could pull a 20' batwing mower with a BX machine. While I love seeing well-engineered and overbuilt designs, sometimes you just need a bigger machine. Putting an 8' steel snowplow on a half-ton pickup might be OK for gently plowing a personal driveway, but used commercially...there are a lot of things that will break. Get the 3/4 ton for that type of work.

 

[cthomas]

OK, instead of feathering the PTO engagement, how about a slow assist to the PTO shaft?
Thinking a one-way pulley welded to the shaft with a belt to a 12 starter motor. Or maybe a hydraulic motor off of the rear hydraulics. Maybe a 12 volt motor with a rubber tire on it that only touches when the implement is raised? If I remember right some of the bigger airplanes spin the tires up before they land to lessen the "shock load". I know this sounds a little extreme but take a case of beer to the techs that are replacing the main shafts and see what they can come up with. This is what they use on fire trucks. The technology used within Muncie Start®, the latest solution to reducing startup torque and allowing for a gradual engagement of the PTO's clutch mechanism, consists of a custom, pulse width modulation (PWM) electric module and a proportional solenoid valve. Key to this technology is the custom electric module that proportionally shifts the valve that controls the clutch pack engagement. I am not sure how your tractor engages the PTO.

 

[cthomas]

OR I did find this
TORQUE CONVERTER ELIMINATES DAMAGING SHOCK FROM PTO ENGAGEMENT
JUNE 24, 2014
by Paul


Torque Converter
Problem: On a day-to-day basis, it is becoming more and more difficult to find drivers that are able to operate standard transmissions versus automatic transmissions. In addition, it is also not ideal to switch to hydraulic drive systems due to the expense. When engaging the PTO with an automatic transmission, damage can occur to the gearbox and coupler because of the harsh start-up. Not only does this create expense for replacement parts, it also adds to the expense because of downtime.

Solution: A torque converter was developed that is installed on the input of the right angle gearbox drive. This converter acts as a clutch and eliminates the shock load between the gearbox and the coupler while still allowing you to operate an automatic transmission. It softly starts the blower versus a more harsh, abrupt method. Pik Rite has packages available for both Robuschi and NVE blowers.

Results: By using the torque converter, the potential of damage to your transmission, gearbox, couplers or blower system is greatly reduced which in turn reduces the amount of downtime. The safer start allows you to continue to use automatic transmissions which means more drivers can operate your equipment with ease. There is no need to switch transmissions, when you can add the converter and function safely and efficiently.

For more information, contact one of our professionals at 1-800-326-9763 or sales@pikrite.com.

I would see if they had any ideas as this would act as the fuse in the driveline system if some was to fail.

 

[jyoutz]

I agree that engaging at too high a RPM would probably cause premature damage, but so would the banging engagement that comes from engaging at too low an RPM. There is a happy medium, and I believe that I found it for my machine. I have to believe that the clutch pack is designed to take some slippage while engaging.

I’m not understanding this discussion about too low of RPMs for engaging the pto. I have an electric over hydraulic switch and I always throttle down when engaging the pto, then come back up to 540 pto RPMs. This method makes the smoothest engagement on my machine.

 

[cthomas]

Its like when I pulled a 1 ton dually with my VW jetta. Letting the clutch out at idle would just kill the engine, but revving to 2K and slowly letting the clutch out I could pull it(Yes there was a clutch smell, but VW was buying it back). That small diesel could do it but it was not quick(or happy).

 

[armylifer]

I’m not understanding this discussion about too low of RPMs for engaging the pto. I have an electric over hydraulic switch and I always throttle down when engaging the pto, then come back up to 540 pto RPMs. This method makes the smoothest engagement on my machine.

Some members were experiencing a bang along with a screeching noise when the PTO clutch engaged. That typically happens on BX and some other models when engaging the PTO at less than 1200 RPM or so, depending on the machine. In my case, I engage the mid PTO for my mower at 1600 to 1700 RPM and I don't get the bang on engagement at those RPM.

 

[jyoutz]

Some members were experiencing a bang along with a screeching noise when the PTO clutch engaged. That typically happens on BX and some other models when engaging the PTO at less than 1200 RPM or so, depending on the machine. In my case, I engage the mid PTO for my mower at 1600 to 1700 RPM and I don't get the bang on engagement at those RPM.

Ok. I don’t experience that at lower RPMs on my MX. it seems to engage smoothly at lower RPMs, then I raise the throttle.

 

[hoobie]

Would it help to depress the clutch pedal, engage the PTO, then release the clutch?

That is what I do on my mx5100. Depress clutch, engage pto switch, and feather the clutch out slowly to gently engage the bush hog mower. No problem.

 

[Vigo]

So smooth for the operator and nice for the clutch are not necessarily the same thing. I can operate a stick and gears clutch pedal to make a manual transmission behave as if it were a CVT, but id be killing it. Not saying engaging at a higher rpm is ‘killing’ those people’s pto clutch, but if it engages ‘smoother’ at high rpm it is only because the clutch immediately slips rather than immediately gripping. Friction surfaces are wearing more during this than they wouldif the clutch grabbed immediately.

However, the OP’s original symptom was broken shafts, not a broken pto clutch, and a slipping clutch is easier on the shafts than a gripping clutch, so it would address the shaft problem even if it was technically just moving the weakest link to something potentially more expensive and harder to access.

I have done some (not much..) drag racing with a manual transmission on slicks and studied a lot of more serious racers and car builds and noticed some of the same patterns that would apply here. For example, some cars can run 10 second 1/4 miles on stock cv axles while other people will break them with only a fraction of the power, or even on a completely stock (and slow, not fast!) car. It really comes down to ‘lash’ or slack in the driveline. Kinetic energy goes up with the square of speed (i think) which means any time one part can get a ‘running start’ before impacting another part, it transfers MUCH more energy on initial ‘impact’. For me in the car, the main ‘trick’ to not breaking axle shafts was to very slowly release clutch until i felt the first little bit of movement of the vehicle, which meant the clutch had gently ‘taken up all the slack’ in the driveline, and from that point i could pretty much ‘dump’ the clutch as hard as i wanted. BUT, if i just revved it up and jumped off the clutch without feeling out the initial engagement point, id be a lot more likely to break something right there on the start line.

So the idea of ‘basically anything’ spinning up the implement before clutching to it is on to something, but it’s even less than that really. You wouldnt even need to SPIN the implement, you would just need to preload it with a little force to take all the slack out of the many joints before engaging to it. Now is that practical to implement? Not particularly. But it WOULD address the problem!