[Mark]

MM,

RPM’s are determined by gear ratio in the drive axle and transmission.

Newer buses have followed a pattern to run at lower RPM’s for fuel economy by installing lower gear ratios.

Volvo has lowered the torque curve also in the motors to allow max pulling power at lower RPM.

We could go on for hours about this but that basically is how it works.

Later

bv

[Bernie]

Bernie, so, are you seeing about the same as me?

Thanks for the explanation as that is not my strong suit.

Mark

[Archived]

Yes MM, your fine at those numbers.

Later

bv

[Dick]

My older series 60 at 60 mph I would say right around 1300 rpm’s

[Archived]

My 2 Series 60 coaches were at 62 MPH at 1500 RPM.

The gearing of the differential is what determines RPM at a given speed.

The Volvo engine develops more torque at a lower RPM than the Series 60 that engine replaced, so Prevost took advantage of that to use less revs per MPH for fuel economy. The Series 60 torque curve peaked at a higher RPM, and unlike the Volvo which peaks and holds max torque over a wider RPM range the Series 60 RPM peaks later and then drops off.

I think if two coaches of identical weight were compared the Volvo engined coach would deliver 1/2 to 1 MPG better economy. For a commercial operator that is a big savings.

[Bernie]

Marks Volvo is a ES3 Platform motor and mine is a ES5 platform motor. The difference is Marks is the belt driven fan and mine has the electric fans to cool the engine. We argued on here a few years ago that power is power and wherever you get it from, belt driven or electric driven it would affect performance and economy.

I don’t find this to be true.

My bus was the 1st electric fan driven bus delivered to a converter. Therefore Quebec sent down Tommy and Johnny because I was complaining about power before my bus ever got here. I wanted the Volvo D16 and would of paid for it but to no avail.

Prevost wanted to be able to backup their power gain with the electric fans so after the bus came off the line at Marathon we took it to the dyno at Cat. We beat the hell out of it for an hour or so and found out some things.

There is no widened power curve, max HP was at 1450 RPM. 399 to the ground. So their motor in their minds was just fine, they allow 20% loss thru the torque converter.

I as other friends of mine were convinced Prevost was giving us the seated coach 435 HP tuning of the D13. Well after heatng my tires up to 200 degrees and numerous tests, I was on the gas, Tommy on a computer next to me and Johnny with a computer in the back they were happy with the test.

I pleaded for them to give me a little more power with the press of a computer key to no avail. What we did find is all the buses coming out of Quebec are setup for seated coach parameters for fuel economy.

We were able to change shift parameters on my trans for what I desired.

But the point of this post is fuel mileage. I do not calculate fuel like A1 does. At the end of the year what I spend is what I spend. My maintenance is spot on.

So the power of 1 alternator out of 4 supporting the electric fans is a great improvement over the belt drive. I am a mountain bus, 95% driving is west of the Continental Divide.

I have my normal fuel stops and my last Loves going North is Idaho Falls, ID. I normally pull in there on fumes. Now I go to Missoula, MT and arrive with a quarter tank left, that’s 300 miles further. That’s pulling a stacker.

I write this long post because years ago we didn’t know and everything discussed was theory.

Now I know.

Later

bv

[Archived]

Power is power is power Bernie. The difference you attribute to the electric fans can be directly attributable to both the number of fans and how they are controlled.

With engine driven fans the level of sophistication is they are on, on half way, or on all the way. Nothing about their operation rises to the level of sophistication your multiple fan coach has.

I do not know this and I am theorizing, but given their need to continue to improve mileage I would make serious bet control of those fans is highly regulated. I would probably wager as much as all of the dues money I collect next year that only the needed number of fans are brought on line on your coach on an as needed basis. I would surmise they have an algorithm that measures temperature, temperature trend up or down, ambient, power being used and probably the phase of the moon to only energize fans to the extent needed. The less fans the lower the engine load to make power from the alternators. That translates directly to less power and fuel consumed.

During a class at Prevost it was also explained Volvo has a lower fuel consuming emissions system so when all the subtle changes to engine efficiency are considered the engines are going to use less than their Series 60 counterparts.

[Archived]

So we agree power is power. Only 1 alternator controls the fans, it does not receive anything from the other 3.

All I’m saying is go back and read your posts with others on 11-15-19.

No one on here talks about new buses because there are so few of us and if a point is brought up you don’t like it’s dismissed.

Going back to my 11-15-19 post of a 2 mile per gallon gain over my DDECV is correct.

With your driving habits and electric fan drive you would be breaking mileage records A1

Later

bv

[Bernie]

If the following is wrong, it is because I am getting as senile as Tom. I think it is accurate however.

Your coach has a highly controlled charging system and if I remember correctly there are times when alternator output is turned off for the specific purpose of saving fuel. I am a little unclear on this but my foggy memory seems to recall one alternator will not be capable of replacing all radiator fan power consumed if all the fans were running all the time so when that occurs the fans are actually drawing down the batteries.

But since they only run as needed overall, that single alternator is more than enough.

BTW, they have to be more reliable than the shitty fan clutches we have been using.

[Mark]

I wish we had more members with newer buses, I’m at a complete loss with the Volvo’s other than what I read. Bernie is able to provide accurate information due to his hands on experience with the latest and greatest from Prevost and Marathon. What amazes me as things become more complex, the actual running cost seems to go down.

The way I see it, if you have a Prevost, the cost of fuel should be a non concern.

[Ed]

The fuel efficiency is likely driven by (1) the seated coach operators and (2) a concern (read “fear”) by Prevost that if the fuel economy of the coaches doesn’t improve over time, state/federal government regulators will be crawling around where they don’t belong.

The “shitty fan clutch” is only part of the problem with the cooling system. Many of you might recall I dropped a large stack of Benjamins in the Texas Hill County due to the shitty fan clutch apparently poking holes in our radiator when the fins on the clutch collided with the radiator brace, broke off, and were ballistically propelled into the radiator. As a result I’ve done lots of thinking about how that system could be improved.

The system from the crank shaft to the air bellows tensioner, to the right angle miter box on the hinged plate, to the shitty clutch, and to the fan was likely the high point of Rube Goldberg’s career. I can see him now … he was just giddy when Prevost asked him to take on the consulting engineering assignment of designing the system to spin the fan, pull air through the radiator, and cool the big Detroit Diesel.

Electric fans make the most sense. I suspect there are times when fans don’t need to turn at all or hardly at all. Like cold weather, going down a hill (longer the better). As Jon mentions there should be algorithms in the computer to manage the fans.

Obviously multiple fans for redundancy. Turn them on sequentially as they are needed. I can see the algorithms can take into account throttle position (are you going to need much cooling if at idle?), outside air temp (OAT), and the list goes on.

I’d think the fans would run off the chassis batteries. The algorithm could monitor chassis battery voltage and if the batteries have lots of juice and the demand on the fans is light, no need to pull juice from the alternator until the battery voltage drops into a recharge range. I could see the batteries being recharged going down a hill.

Would all these ideas save a material amount of fuel? Probably not, but this could and should be factored into the algorithm.

Another benefit of moving to electric fans would be weight. The current system is very heavy. I would think four to six electric fans, support structure, and shroud would be much, much lighter than what we have now.

Periodic maintenance would almost disappear.

Redundancy could be built into the algorithms that when a fan goes off-line, the remaining fans pick up the slack until a replacement can be FedEx’d to the coach. Replacement should be easy for most owner/operators. Jon and a few of the rest of use would carry a spare fan in the parts bay.

What would owner/operators of Prevosts like us be willing to pay for a system like this?

I’ve heard that the failure of the fan system in an H3 cost over $15,000 (I suspect the CAC was damaged along with the radiator). I think I spent $8,000 plus lost 12 days on a trip.

I’d probably spend $5,000 on an electric radiator fan system before I’m go to Li-Ion batteries … presuming its a one and done deal.

Would Detroit be willing to program support for a retrofit electric fan array in DDEC? Would Detroit be willing to engineer the system? Would Prevost be willing to put the package together? Or would a third party have to do it?

[steve]

Volvo electric fan upgrade must be Volvo 2010 or newer engine.

Rake rate about 30k depending on rear door DS configuration.

Later

bv

[Bernie]

Bernie, wow, $30K? I guess I’ll just change the belt. Ha ha.

I’m just about to turn 60,000 miles in the next day or two.

Are you in Indio this season? Liberty is going to have a show early 2021 and I thought I would stop by to check it out. My friend Jeanine use to be a bartender at the restaurant but everything changed. Sweetest girl west of the Mississippi!

Safe travels guys!

Mark

[Dick]

It’s a new process, they will figure it out and it will come down.

Actually I heard there’s a Liberty guy doing it to his 2017, 1st one.

Yes were home in La Quinta.

There shutting everything down again, nothing allowed inside. No place to eat but home.

Later

bv

[Chris]

On the dash display you can monitor the fan status. There is 2 parts to the display, one is the cooling fans and the second is the CAC fan status. The display the percent of fan cooling called for. I have not seen it go above 45% so far. The fans are basically electric fans like you would find on a car. If one fails it can be changed in about 30 minutes due to the design of the mounting.

The Volvo is getting about .7 to .8 better mileage than the Series 60 in my previous bus.

The previous bus did not have DEF, but DEF is available at almost all truck pumps now and its DEF consumption so far is about 5 gallons per 3,000 miles. I have been told when the engine gets more miles on it the consumption of DEF will go down. The exhaust out the roof sure keeps the toad cleaner.