Drive belt tensioner

[NoSpark]

Sorry if this has been mentioned before but all the talk of belt chirping and light flickering makes me wonder if the generators on these slow speed diesels would benefit from a "decoupler" or clutch pulley. Years ago I started seeing pulleys on automotive alternators that behaved like a sprag clutch on a starter drive allowing the alternator to freewheel when its speed or momentum was greater than the belt speed. I originally assumed that because it was on a diesel engine that it was only used to keep the alternator and/or belt from being damaged or chirping from the sudden engine stops. I have since seen them on gas powered engines also, notably on Chryslers where they start to make noise for a few seconds after shutdown. The link explains how they cut down on belt slippage.

http://www.tendeco.com/website/decouplers/decouplers_func.html


Notice in the beginning and end that the mass(behind the driven pulley with arrow on it) freewheels when the drive pulley slows or stops.
http://www.youtube.com/watch?v=PHXWvVwmthM 

[Diesel Head]

I’m just about finished with my 2/12 genset project. I’m using an eight grove 100in serpentine belt with a home made belt tension devise. It’s made from a 2x2x15in long square tubing pivoting on two pillow block bearings at one end and a 8in dia idler wheel in the other end. The belt tension comes from the mass of the arm and idler and from the load of a simple tension spring mounted around a standard auto shock absorber. Picture an automotive strut that works in extension instead of compression. The shock absorber helps reduce the “bounce” that comes from the power stoke and from abrupt changes in generator load. It also seems to make the drive uniform and smoother than I saw with other drives I tried. If there is any interest in this I can try to post some pictures of the setup.

Soren

[mobile_bob]

please do go ahead and post it!

your idea has merit, and has been kicked around some in the past
although i don't remember anyone getting one up and running posting results

the idea of a spring loaded shock being able to absorb the power pulse and then return
the stored energy on the compression stroke would be pretty cool, but maybe tough
to tune in,, especially under a wide variety of loading.

maybe an air shock? that would provide variable rate
then one could work out his favorite automation technique to apply the appropriate amount
of air based on generator loading.

that might be quite an interesting project in my opinion,, might even take away or mitigate the flicker problem
if done right.

yes please do post your pics, we need some new topics around here

bob g

[oliver90owner]

Mobile_bob,

Sounds similar to the flat belt tensioner on the early engine-driven balers.  We had a Massey Harris 701.  It had a large belt tension pulley as a drive 'clutch'.  That was a proper belt. Not dissimilar to the present drives but was a heavy duty set-up and not, I would think, that loss free!

4 inch flat, endless belt on a 6 inch diameter (or probably less) flat pulley driving about a 2 foot 6 inch to 3 foot flywheel .  Power was about 20HP max and engine speed was less than 2000rpm (Wisconsin VE4).  I would have to look in the garage, as I have the original pulley in there somewhere, to find the actual dimensions.  I would think the drive take-up pulley was probably 9 or 10 inches in diameter (from memory).  That belt did not slip.  It may have screeched a bit, when pulling the handle to start the baler ram drive, but would easily stall out the engine if the baler was overloaded.  They also fitted an Armstrong Siddely twin cylinder diesel to that baler model, as well (as an option).

I still have the engine that was on the baler but it has been seized for several years now.  It has a Rockwell clutch on it that may be used on some other project one day......

Regards, RAB

[mobile_bob]

hot tip for you if the engine is rust siezed

forget using penetrating oils and other patent stuff to unsieze it

take the heads off, tip one side up level and fill the cylinder with fresh clean water
water makes an excellent rust solvent, it will soften the rust so the pistons can be made to
break free without damaging the pistons or ringlands.

i learned that from an old junk yard man, and have used his method exclusively every since.

it works amazingly well.

bob g

[Diesel Head]

Thanks for the encouragement Bob G.

If this is inappropriate for the forum, please ignore this post.

I have done a little writeup of the project, and I have tried to include six pictures with the text.
For some reason I'm not able to get the pictures into the post, can someone give me a clue about how to do that please?

Thanks, Soren

[Diesel Head]

Thanks for the encouragement Bob G. Tanks for the picture tutorial Jens.

Here is a follow up on my post from yesterday.

One of the reasons I went through the work of constructing the tensioning mechanism was to stay reasonably close in construction to an antique setup that I saw in Europe many years ago. The base for the engine and generator is constructed from 6x6 in lumber. It’s held together with four lap joints and the bolts that secure the engine and generator extend through the center of the joints. No glue or other fasteners are used in the structure. The mounting surfaces for the engine and generator are reinforced with 3x3x0.25 in angel iron to avoid gauging the wood.

I may have gone a little over board by applying five layers of clear polyurethane to the base. It ended up looking better than some of the furniture in our living room.

The whole assembly is supported on six dampers. Between the natural dampening characteristics of the wood base and the dampening provided by the six supports there are virtually no vibrations or motions transmitted to the floor. I chose six support pads to help with both the lateral forces from the pistons and valve as well as the torsional (rocking) forces due to the constant acceleration and de-acceleration of the fly wheels and crank. The support dampers are not all the same since they serve different functions.

The casters in picture 5 are only used to facilitate moving the whole assembly around during construction and maintenance. During operation the frame is lowered to the floor and is supported on the dampers.

Cooling is accomplished with a small automobile radiator (a severe break with the antique setup). The radiator is mounted to allow natural thermal siphoning. I use a pair of 120 mm fans that turn on when the coolant reaches 90 deg. Celsius.

If there is interest in more details about the project or the ideas I’ve tried to implement, feel free to comment and question my reasons and maybe my sanity for doing what I have done.

Soren



Pic. 1. Shows the 3x3x15 in arm with two 1 in dia bearing blocks to pivot the arm. The pivot shaft is bolted to the face of the generator. The idler wheel is a 6.75 in dia x 1.75 in thick steel wheel running on two ball bearings. On the left you can see part of the shock absorber and the loading spring. The top part of the shock is mounted to the end of the pivot arm and the bottom of the shock is mounted to movable lever that is used to “tune” the belt tension and also make it easy to unload the belt. The C-clamp on the right is a temporary adjustment point for the tensioning lever.

Without the damping provided by the shock absorber and the force delivered by the spring, it was difficult to get the belt to track reliably.



Pic. 2. Shows the tensioning lever pivot point near the lower left corner of the generator face. The right side of the lever is resting on the temporary C-clamp putting tension on the spring and loading the belt.


Pic. 3. Shows the tensioning lever in the “down” position unloading the belt.


Pic. 4. Full view of shock absorber and belt tension spring.


Pic. 5.


Pic. 6.

[Diesel Head]

Sorry about the small size of the pictures. It's my first attempt at posting pictures so I still need to figure out how to size them.

Soren

[needenginerunnin]

afternoon all

forgive me if it has already been said, but.
if you engineer out the belt noises isnt it just going to make the flicker worse as it all stems from the same cause 'power stroke'.
from what i have read on here folks dislike the flicker as much as belt noises.
nature of the beast, live with it
KISS counts for a lot in my book.
shame you couldnt use the rear wheel design off a drag car, problem solved?

cheers needenginerunnin