I have been thinking about the fan clutch(side radiator)

[newmarokie]

I was cruising down the road and got to thinking about the fan clutch/gear box design. I wonder if Cummings engineering has been questioned about putting a clutch on the accessory drive pulley that powers the gear box/fan assembly? It seems that if a strong enough clutch assembly could be had, you could use a direct drive fan and the gear box would only be used when needed. Wouldn't this drastically reduce wear and tear on the gear box?

 

[JRS]

Actually it's not Cummins issue because it's the chassis manufacturer. On K2s Spartan uses hydraulic driven fans and on K3s mechanical driven. FLs use mechanical driven on both.
At the Hershey show in 2019 I asked a Spartan Tech why the K2 had the hydraulic driven but the K3 didn't and he couldn't answer....
Your clutch comment IDN

 

[newmarokie]

JRS,
I visited with my BIL last night. He is a hydraulic/electrical technician with a large equipment manufacturer. Specifically we talked about mechanical vs. hydraulic fan drives. He said they typically run mechanical drive fans if they can. You lose approximately 8-10% of available HP on a mechanical fan. A hydraulic fan robs 18-20% of HP. The mechanical is typically cheaper to buy and install as compared to hydraulic. So the determining factor is 1st space considerations. 2nd available HP. He thought the accessory drive replacement to a mag fan clutch would be doable. The conversion cost would be comparable existing fan replacement(Machined hub faces). Now the drawback would be you have to carry a replacement clutch in your spares bin. It would not be something you could get locally.

 

[Just George]

Wonder why the chassis folks have not adopted electric fans. Seems HP loss & maintenance items would go away. Technology seems to be proven with use on autos for years and I believe Newell and Prevost conversions also use electric. Perhaps there is a significant cost??

 

[newmarokie]

Me and BIL talked about that last night as well. The amount of air needed to be moved would take to large of an electric motor. Now why you can use an electric fan on pickups and cars and not this application I am not sure. You could be right on cost. Part of it would be the orientation of the radiator. I have driven many trucks with air clutches, but not electric

 

[Bigblockyeti]

When I was regularly servicing class 8 trucks, an air clutch was often employed for the cooling fan. Such a design would be easy to implement on a class A RV, someone just has to want to. Hydraulic fans are heavy, expensive, leak prone and add many more unnecessary failure points, plus they generate heat that mechanical systems do not. Electric fans are expensive for something kinda powerful and can't quite compete for air volume moved vs. a mechanical fan, plus they put considerable load on the alternator & batteries.

 

[Little Bitty Zitty]

JRS,
I visited with my BIL last night. He is a hydraulic/electrical technician with a large equipment manufacturer. Specifically we talked about mechanical vs. hydraulic fan drives. He said they typically run mechanical drive fans if they can. You lose approximately 8-10% of available HP on a mechanical fan. A hydraulic fan robs 18-20% of HP. The mechanical is typically cheaper to buy and install as compared to hydraulic. So the determining factor is 1st space considerations. 2nd available HP. He thought the accessory drive replacement to a mag fan clutch would be doable. The conversion cost would be comparable existing fan replacement(Machined hub faces). Now the drawback would be you have to carry a replacement clutch in your spares bin. It would not be something you could get locally.

First as am old racing guy and an ASE certified Master Mechanic since 1974 I would disput what you BL sa I d. Fans consume abou 5 HP. , not 10 to 20 %.

Your fan has a fan clutch which, when you are crushing at 60 mph is basically free wheeling consuming near 0 in hp.

When your engine begins to run hot the clutch will engage, now consuming hp.
An electric fan installed on front of the radiator assembly would help with that. Also an air dam under the radiator helps.

As fan as room, there is usually ample room for a electric fan inside the fan shroud if desired. The clutch fan and fan are removed with simple shorter mounting bolts install the hold the fully in place. However one must then install a thermal switch to turn the fan on when predetermined temp is reached. Now it becomes a balance act on hot enough to run engine at proper temp but cold enough to not have the fan run too much consuming electricity and over working the alternator.

 

[newmarokie]

Bitty,
He is working with 750 to 2000 hp Cummins, Cat, and Detroit diesel engines running at peak horsepower stationary for hours at a time. A car going down the road probably does not get robbed of horsepower like these engines. They have reams of data confirming those numbers. The more I have studied this problem, the more I think bigblock has the best idea with the air clutch. Once you figure out what works, you can probably get a replacement at most good truck shops.

 

[adamzdieselz]

Adding a clutch to the accessory drive pulley for the gear box and fan assembly could reduce wear and tear on the gear box and improve fuel efficiency by engaging the fan only when necessary. However, challenges include finding a durable clutch capable of handling heavy loads, increased system complexity, and potential delays in cooling response. While theoretically beneficial, these challenges may explain why this approach hasn’t been widely adopted in heavy-duty engine applications like Cummins.

 

[Kevin D Pem]

Adding a clutch to the accessory drive pulley for the gear box and fan assembly could reduce wear and tear on the gear box and improve fuel efficiency by engaging the fan only when necessary. However, challenges include finding a durable clutch capable of handling heavy loads, increased system complexity, and potential delays in cooling response. While theoretically beneficial, these challenges may explain why this approach hasn’t been widely adopted in heavy-duty engine applications like Cummins.

Story time!
Back in the day, many early conversion busses were old greyhounds. My brother inlaw did one! I must say a beautiful bus! Anyhow cars were his passion, so he did much of the things you're talking about.

But ultimately he found out pushers don't have enough air flow past the radiator to consider reducing fan efficiency. His attempts simply put him longside the road waiting for things to cool enough to continue his journey!

My guess is chassis manufacturers could specify any fan they choose for their products, and tested more than one. For them! Poor reliability hurts more than Poor milage!!!