Understanding Coach/RV Performance by CAT

[blueblood]

Here is an excellent paper written by CAT that has good info applicable to any motorhome with a diesel engine and gas as well.

https://ohe.cat.com/cda/files/287140/7/LEGT5364.pdf

 

[Jeff]

Blueblood:

Good info!

 

[WTD]

Blueblood,
Excellent article!!
I not only learned what the "economy" Button is for and how it works, but was reminded to keep a light foot on the accelerator.

IMHO this article would be outstanding required reading for all of us who are driving these lovely monsters down the road. ;D

I have saved a copy and plan to re-read it often!

WTD

 

[Gary RV_Wizard]

Great article - it legitimizes and quantifies what some of us have "known" for some time. Hope it is based on real data!

 

[Smoky]

Thanks Leo, you always provide us with such neat info.

In addition to a good explanation on economy mode button, it also gives the "I always leave my engine break on" folk some food for thought.

 

[Jim Godward]

Smnoky,

I noticed a small increase in fuel mileage since we installed the BrakeSwitch on the MH.? Check www.brakeswitch.com for details.? It allows for esy coasting while still in cruise with the Ehaust Brake "on".  I understand that the trans can be programed to do the samething but did not verify with Allison as the programming would cost much more than the BrakeSwitch!  VBG

 

[Smoky]

Jim:

Our coach came with the switch already installed.  I only use it when I need braking power, such as descending a mountain or coasting to a stop and sometimes when cresting a smaller hill.  I was pleased that my self teaching turned out to exactly match all the recommendations of the article.  But the article gave me a much better understanding of the physics behind the techniques.

 

[Jim Godward]

Smoky,

Wrong switch.  Yours turns the Exhaust Brake on and off while with the BrakeSwitch, that switch is left on almost all the time and the exhaust brake is controlled by the brake pedal and the accellerator.  Different strokes for different folks,

 

[Smoky]

Jim:

I am not sure what you mean by wrong switch.  Our switch has nothing to do with the foot brake.  When I turn it on I experience immediate braking with the Allison pre-programmed to begin downshifting until the pre-select gear is reached, which in our case is second gear.  I can feel it kick in as soon as I throw the switch... no foot brake at all.  It works exactly as described in Blueblood's article.  The article recommends leaving it off unless conditions warrant it... such as descending steep grades. or bringing the coach to a stop.  If you are to believe the article, leaving it turned on all the time would degrade mileage efficiency. 

Maybe I misunderstood what you are explaining.

 

[Jeff]

Smoky:

The OEM switch insetalled in our coaches ARMS the brake which is activated when we allow the accelerator go to the idle position. The BrakeSwich prevents the activation UNTIL you tap the brake pedal which means you do more coasting at the idle position. It goes back to the arm position when you apply power with the accelerator.

For me that means I  do not have to turn the exhaust brake off to prevent its activation with the cruise control on because if it is armed the cruise activates it every time the engines goes to idle going down a slight grade.

 

[Jim Godward]

Smoky,

I think Jeff explained it very well.  I thought you would go to the URL and check it out.  Sorry I did not include a more detailed explanation.  :-((

 

[Smoky]

What can I say?  Mine DEFINITELY activates as soon as I switch it on.  You can "feel" it.  No foot tap needed.  If I accelerate, I do not change the braking action.  I have to turn off the switch if I am going to get out of the mode and move to a mode where I do not feel the braking action.

The article that Blueblood gave us at the top also instructs when to turn on the switch, so while not directly expressed, the implication is that the normal running position is off.  It also refers to the mileage implications.

These points of confusion have come up in other threads.  I believe there are several kinds of braking systemsbeing discussed.  Likely everyone here is correct, but from the viewpoint of different coaches and configurations.  When I get to the factory I will find out more about this subject.

 

[Jeff]

What can I say?  Mine DEFINITELY activates as soon as I switch it on.  You can "feel" it.  No foot tap needed.  If I accelerate, I do not change the braking action.  I have to turn off the switch if I am going to get out of the mode and move to a mode where I do not feel the braking action.
So does mine, that is what the BrakeSwitch prevents by requiring a tap of the brakes to activate the exhaust brake.

The article that Blueblood gave us at the top also instructs when to turn on the switch, so while not directly expressed, the implication is that the normal running position is off.  What the BrakeSwitrch does (amoung other things) is to avoid reaching for that switch when you need exhaust braking, just tap the brake.

It also refers to the mileage implications. You will improve your mileage because the coach will coast more until you touch the brake.
These points of confusion have come up in other threads.  I believe there are several kinds of braking systemsbeing discussed.  Likely everyone here is correct, but from the viewpoint of different coaches and configurations.  When I get to the factory I will find out more about this subject.

 

[Smoky]

Ah, thanks for eliminating the confusion Jeff.  I misread your "BrakeSwitch" description as applying to my coach.  And I may have confused Jim earlier because I refer to my existing switch as a Brake Switch, which appears to be a product name LOL.

At any rate I am very certain I increase mileage by not turning on MY brake switch unless I need it.

 

[Chet18013]

Definately a good read! My standard cruse control setting is 60 mph. We have about 38,000+ pounds going down the road when fully loaded and always run the generator when underway. At this speed we consistantly average 8.5 mpg. When setting at 65 mpg, the fuel economy drops to 7.6 mpg. It's right in line with what this article says.

Chet18013

 

[Gasser]

Definately a good read! My standard cruse control setting is 60 mph. We have about 38,000+ pounds going down the road when fully loaded and always run the generator when underway. At this speed we consistantly average 8.5 mpg. When setting at 65 mpg, the fuel economy drops to 7.6 mpg. It's right in line with what this article says.

Chet18013

Why do you run the gen. while under way?  Is it to run the roof air?  Do most people run their gen while driving down the road?  My coach gets a little warm in the back while driving down the road.  Not a problem for me and the wife if we are by ourselves but if our kids are with us they get a little warm out back.

 

[Smoky]

Gasser:

My experience is the same as yours.? We have been in 100 plus degree weather and never had to turn on the roof air.? The dash air keeps us plenty cool.? Like you it gets a little warm in the back, but we are only back there to relieve ourselves or fix a cold drink.? I think it is a waste of mileage to run the roof air.? I admit this might vary with older coaches and some folk might need to run there roof air.?

We have the same year KS as you, by the way.? Ours is like yours, the KS 3910 DP.  Color here is Nimbus Grey. Great coaches aren't they?

 

[BernieD]

  Like you it gets a little warm in the back, but we are only back there to relieve ourselves or fix a cold drink. 

Smoky

Do you leave the cruise control on when you go back there ??? ;D ??? ;D ???

By the way, when you run the generator for the roof air, the dash air should be turned off. That would increase your fuel mileage by a greater amount than the fuel used to run the generator.

 

[Gasser]

Gasser:

My experience is the same as yours.? We have been in 100 plus degree weather and never had to turn on the roof air.? The dash air keeps us plenty cool.? Like you it gets a little warm in the back, but we are only back there to relieve ourselves or fix a cold drink.? I think it is a waste of mileage to run the roof air.? I admit this might vary with older coaches and some folk might need to run there roof air.?

We have the same year KS as you, by the way.? Ours is like yours, the KS 3910 DP.? Color here is Nimbus Grey. Great coaches aren't they?

I don't live in mine as much as you do but I agree, it is awesome for the money.? I think a real BANG for the buck.? Sure an Essex would have been nice but all that extra fancy stuff would have been waisted on me. ;D? ?I agree, the front A/C in our coach is top notch.? Even in 100 deg. heat, I stay very cool up front.? The back is not bad but I like it cold.? I guess if I ever need to take a nap while someone else is driving (doubtfull) then I can fire up the ole getset.

Jeff

I was not sure if people run the gen but I guess its not that big of a deal.? You just give up some of your milage to cool air.

 

[Gasser]

Smoky

Do you leave the cruise control on when you go back there ??? ;D ??? ;D ???

By the way, when you run the generator for the roof air, the dash air should be turned off. That would increase your fuel mileage by a greater amount than the fuel used to run the generator.

Has this been studied?? Does this hold true for all coaches and generators?? How about wear and tear on the generator?? If I can cool the entire coach and get better milage to boot then this may be a good option.? My front air works VERY well but so does my roof air.? I don't know if my generator 8.0 KW will run both roof airs.? I assume it will.????

I never thought about the trade off between the engine run compressor and the generator compressor.? Conservation of energy tells me that just cooling the front vrs the whole coach will use less fuel unless the roof air is SOOO much more efficient than the front A/C.? You can't get something from nothing.? No free lunch so to speak.? Converting Diesel to cold air either by the gen and roof air or the engine and compressor is the same end result baring the efficiency differences between the compressors.

Any real world data?

Jeff