Correct slip clutch

[rowbro]

Good day,

I am running a logging implement on my NH TT4.90, and the unit is rated for 3000 to 3500Nm of torque (at 540rpm), while the tractor engine torque produced by the tractor at 1400rpm is 340Nm. I assume there must be a material increase in torque at the PTO at 540rpm due to the gearing (also, for the PTO to be at 540rpm, the engine will be slightly higher on the power curve at 2198rpm).

1. Can anyone confirm the increase in torque at the PTO?
2. What slip clutch (in terms of Nm torque rating) should I be using between the implement and the tractor to avoid damaging the small tractor should the implement experience a shock?

Thanks,

 

[ericm979]

Torque at the pto at 540 pto rpm would be (2200/540) times the engine torque at 2200 engine rpm. Some engine power drives the pumps or is lost in gears but that'll be close.

Slip clutch torque rating is probably the maximum the slip clutch can handle, not the rpm it slips at. That is usually adjustable. You want a slip clutch that is rated for a higher torque than the tractor will deliver, then adjust it so it slips when there is too much stress on it.

 

[wirlybird]

I would start by looking at the HP ratings for PTO shaft by series.

Maybe this is a starting point.

POWER RATINGS AND DIMENSIONS - Aline Trading

AL01354 JOCKEY WHEEL. 455 KG Please refer to the data below for shaft sizes and capacities. When replacing an old shaft please check the diameter and width of the cross kit (dim A & B) to ensure you are selecting a shaft of equivalent rating. PRODUCT SPECS SERIES 540 – RPM 1000 – RPM MAX […]

alinetrading.com.au

 

[CobyRupert]

Seems to me that normally a slip clutch would be “set” (or provided in some cases) to protect the implement from a power source of unknown maximum. I don’t see why you have to know the tractor size. Seems the shaft rating would only have to be some safety / adjustment factor multiple of the clutch setting / implement rating. (I’d want to sacrifice the shaft before I sacrificed the implement.)

In the case of a smaller tractor, where slip clutch is set higher than tractor output, the implement is protected and it becomes a question of do you want the clutch to slip; or have an overload drop engine rpms or stall. Remember though, sometimes these are shock loads (when something jams) relying on engine to stall…depending on what type of implement and loads encountered. You don’t want to blow up tractors PTO and rear end.
…so slip clutch setting sometimes should be adjusted to tractor size.
…and shaft rating ends up being “oversized”. (I.e. bigger than anything it will see from that tractor).