Hybrid Spline Rattle 1

[IWPW]

Hello folks,

Hoping that any hybrid pros may have some insight into a spline rattling problem I'm working through. I'll try to keep this as succinct as possible:

I am working on a P2 (on axis) hybrid powertrain wherein a MGU is situated between an internal combustion engine and a torque converter automatic transmission. A shaft with external involute splines at each end couples the ICE with the MGU, a clutch allows the two to be de-coupled. The MGU has a continuous through shaft with internal splines at each end. At the back end of the MGU a bearing supported stub shaft engages the MGU and has a flange to accept a flexplate. All splines are designed / inspected per b92.1 and alignments of mating components are within .003"

The problem: When the ICE is at low speeds (<1500rpm) and the powertrain is under no load the stub shaft rattles loudly, as soon as a load is applied the noise subsides. If the ICE is de-coupled from the MGU (clutch open) there is no such noise.

Although both ends of the MGU share the same 14t spline the noise seems to appear only from the output side. I passed a recording of the rattling through an FFT and found the peak frequency corresponds to the second order of cylinder firing, which suggests that the torque spikes associated with the firing events are causing the splines to rattle back and forth from one contact face to the other.

As I understand it this is not an uncommon issue for P2 hybrid systems of this sort, however I cannot find much information on how to best address the issue - hoping that someone here can lend some advice.

Much appreciated.

 

[GregLocock]

Dual mass flywheel is the production solution as often as not. No idea how to fix it in service. Assuming it's an I4 most of the 2nd order comes from L/r ratio inertial forcing.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[TugboatEng]

Have you considered using a shear stable grease to dampen the rattle?

 

[IWPW]

Greg-
Fix (even 'band aid') in service and longer term are both front of mind. The ICE is V6 diesel so I expect that the majority of the effect is due to the firing impulses. Regardless a DMF might be the ticket for the next revision

Tugboat-
Currently using Lucas Red n Tacky - not Moly based as some suggest to be of importance but it has the right qualities otherwise.


The most recent idea for a quick fix is coating the splines with the nylon based material driveline manufacturers use on slip joint splines. I'm sure the service life would be poor, but it doesn't really need to live much longer than a couple thousand miles.

 

[TugboatEng]

Good to know. Red N Tacky is a lithium grease and is subject to shear in splined coupling applications. Couplings can't stir the oil and thickener back together so you need to look for shear staple greases. If you are a fan of the Lucas brand their X-Tra heavy duty brand is polyurea based and is shear stable so it won't separate in a spline coupling application.