Engine auxilliary drive belt squeal

[tomaspin]

I am currently looking at a drive belt noise problem on a 4 cylinder diesel engine, and on some installations there is a problem with belt squeal on the fan pulley, especially when shutting the engine down.
The dive belt is a flat ribbed type, and the belt is tensioned on what would normally be the 'slack' side of the drive. The wrap angle on the belt is between 65-78 degrees

As the engine slows down, the inertia in the fan starts to 'drive' the belt, which causes the belt to lose tension and the fan pulley starts to slip and squeal.

The belt squeal corresponds to the last 5/6 compression strokes before the engine stops.

The problem usually starts to occur after about 500 hours use, as the drive belt becomes conditioned. New belts have been used without success.

Our client wants us to look at using a torsionally soft crank pulley to limit the belt shock loads, however I am inclined to recommend that a second belt tensioner is used to maintain tension and improve the wrap angle on fan pulley, as this adresses the root cause of the problem.

Is this type of belt squeal common, and are there any other solutions to it?

Thanks

Tom

 

[GregLocock]

Very common. A very funny solution is to spray it with water while it is squealing. I'm not sure what it proves, but it is a neat trick.


Have you any proof that increasing teh tension will help? Have you got a dynamic model of the FEAD - can you see if putting some damping into the tensioner, or taking some out, will help?

You may find that a material change on the pulley will help - if you fit an old belt to new pulleys does that help?

Sorry, I know this is all suck it and see. Most engine noise problems are.




Cheers

Greg Locock

 

[tomaspin]

Greg,

Thanks for the answer.

The logic behind the second tensioner is to cope with the shutdown situation where the fan inertia drives the belt. What is normally the 'tight' side of the belt under running conditions becomes the 'slack' side at shut down, so the existing tensioner is in the wrong place to do any good at shutdown.

The other difficulty is that the belt doesn't squeal all the time, and wouldn't do it at all when I was there! This makes assessing the impact of any changes quite difficult.

I don't have a dynamic model of the drive system, as this application is a new area for me - I normally deal with rubber a/v mounts.

I will certainly look at the drive belt material in more detail. Maybe something slightly softer with better heat ageing properties might help. I will also look at the pulley material and surface finish.

I'm due a second meeting with the customer this week, so I'll see what happens then.

Regards,

Tom