Gravity works

[davidbrady]

Anyone ever heard of droop? Okay, stop looking in the mirror - not that kind of droop!

Ever wonder why truckers drive the way they do? One minute they're on your tail next minute your passing them like they're standing still.

Well, it turns out this is by design. See, a good trucker or more correctly a trucker who can't pass fuel surcharges off to an unsuspecting public knows how to conserve fuel. He also knows how to get a million miles out of his engine.

A good trucker plays a perpetual motion game. This kinda game works well on the right side of this country (east of the Mississippi).

What a good trucker does is let gravity work for him. The hills are rolling so he's not afraid of running out of brake before the next up hill. He lets his speed build on the downhill and he aids it if necessary with added boost. As he progresses thru the depths of the valley his speeds may reach 70 mph and his turbo is freewheeling. He's building his momentum.

As Sir Isaac Newton taught us, momentum is conserved. The momentum built coming down the hill is given back when climbing the hill. Well, not completely given back or we'd have a perpetual motion machine and God would never allow that or we may become Gods ourselves!

So we have this head of steam coming down the hill. As the next hill approaches he lets this gift of nature propel him up. Now he feathers the boost to get the most out of his gift. He lets his speed drop slowly as he dials in more boost, but he's careful to maximize his gift. He doesn't want to peg the boost and loose all his advantage, and why waste fuel fighting air, so he lets his speed diminish to 65, then 60, then 55 where rolling resistance exceeds air resistance, then he feathers on the boost. As the crest approaches he completely backs off letting his momentum propel him over.

He dances a delicate dance. Time and again he trades off a thirsty steady speed for a frugal undulating one. Like a pendulum he swings from peak to peak letting gravity return to him a portion of the fuel he burned to make the next peak.

So, how is this related to droop? Well, turns out our cruise controls are fuel burners. If you want to save a half mile per gallon then you need to get off the cruise and drive the bus. The problem with our cruise control is that it wants to always maintain a constant speed. If you also have the jake on then it's a double whammy. That gift of nature is wasted and is being turned into global warming.

See, our cruise controls are too good. They dial in full boost at the slightest decrease in speed. If we know that we're close to cresting the hill, and we know that momentum will provide us a free ride, then we don't need full boost.

Droop is a DDEC parameter. It's the number of rpm's that the DDEC will allow the engine to fall before full boost is applied. It's programmable and your local Detroit Diesel Allison Service Center can change it for you. This modification will allow you to use cruise control to drive the hills like a good trucker without the attentiveness required. But, if you really want to do it right and gain half a mile per gallon, turn off the cruise

[al perna]

David , the chinese must have been taking some lessons from our truckers here in the U.S . Twice a year I have the opportunity, LOL to go to China . Our day trips take us many miles out side the city of Shanghie .

My driver will build his speed to 100 mph or so , then place shift into neutral OUGH !! he will then coast down to around 60 mph and repeat this proscess over and over for 2 or so hours .

as you can imagine beside being a bit nervous at his speed , Iam also a bit sea sick also . When I asked my interpreter , WHY he drove in this manor I was told he was saving fuel .

Well I now pay for fuel !!

[Itchintogo]

David,

Shhhh! Your letting all my secrets out. One thing you never do is take your rig out of gear folks in case anyone is thinking of trying that. Very dangerous. But David has got it right.

David next you will be telling them how to synchronize lights and drive through urban areas with as few stops as possible.

Now I am about to board a ferry this morning and go to the Island. It is kind of choppy today can you send a educative note to the Captain?

[Ms. Bee]

(04-05-2013 23:37)davidmbrady Wrote:  Anyone ever heard of droop? Okay, stop looking in the mirror - not that kind of droop!

Ever wonder why truckers drive the way they do? One minute they're on your tail next minute your passing them like they're standing still.

Well, it turns out this is by design. See, a good trucker or more correctly a trucker who can't pass fuel surcharges off to an unsuspecting public knows how to conserve fuel. He also knows how to get a million miles out of his engine.

A good trucker plays a perpetual motion game. This kinda game works well on the right side of this country (east of the Mississippi).

What a good trucker does is let gravity work for him. The hills are rolling so he's not afraid of running out of brake before the next up hill. He lets his speed build on the downhill and he aids it if necessary with added boost. As he progresses thru the depths of the valley his speeds may reach 70 mph and his turbo is freewheeling. He's building his momentum.

As Sir Isaac Newton taught us, momentum is conserved. The momentum built coming down the hill is given back when climbing the hill. Well, not completely given back or we'd have a perpetual motion machine and God would never allow that or we may become Gods ourselves!

So we have this head of steam coming down the hill. As the next hill approaches he lets this gift of nature propel him up. Now he feathers the boost to get the most out of his gift. He lets his speed drop slowly as he dials in more boost, but he's careful to maximize his gift. He doesn't want to peg the boost and loose all his advantage, and why waste fuel fighting air, so he lets his speed diminish to 65, then 60, then 55 where rolling resistance exceeds air resistance, then he feathers on the boost. As the crest approaches he completely backs off letting his momentum propel him over.

He dances a delicate dance. Time and again he trades off a thirsty steady speed for a frugal undulating one. Like a pendulum he swings from peak to peak letting gravity return to him a portion of the fuel he burned to make the next peak.

So, how is this related to droop? Well, turns out our cruise controls are fuel burners. If you want to save a half mile per gallon then you need to get off the cruise and drive the bus. The problem with our cruise control is that it wants to always maintain a constant speed. If you also have the jake on then it's a double whammy. That gift of nature is wasted and is being turned into global warming.

See, our cruise controls are too good. They dial in full boost at the slightest decrease in speed. If we know that we're close to cresting the hill, and we know that momentum will provide us a free ride, then we don't need full boost.

Droop is a DDEC parameter. It's the number of rpm's that the DDEC will allow the engine to fall before full boost is applied. It's programmable and your local Detroit Diesel Allison Service Center can change it for you. This modification will allow you to use cruise control to drive the hills like a good trucker without the attentiveness required. But, if you really want to do it right and gain half a mile per gallon, turn off the cruise

For the layman, David could one liken this to not wanting to apply one's brakes going downhill on a bicycle in order to have more momentum going back up the next hill?

[davidbrady]

(04-06-2013 10:57)Ms. Bee Wrote:  For the layman, David could one liken this to not wanting to apply one's brakes going downhill on a bicycle in order to have more momentum going back up the next hill?

Hi Ms. Bee,

Yes, that's a perfect analogy. When you're fuel limited like on a bicycle you find ways to improve your efficiency. It comes very naturally when bicycling.

Since I got the channel I'd like to propose something else. For those of us with Detroit Diesel ProDrivers here's something you can do: Shave off a down arrow!

On the ProDriver there's five up arrows and five down arrows. No arrows means your achieving your long term average fuel mileage, one or more up arrows means you're doing better, and one or more down arrows means your doing worse.

When the cruise control engages you'll see that it'll often result in five down arrows, meaning your instantaneous mileage is way worse than average. So for a big fuel savings, try not to let it do that; that is, shave off a down arrow or put another way, drive so that you see at most four down arrows.

You'll find to do this you'll have to drive the turbo boost gauge. If you let the boost max out at 29 psi you'll see 5 down arrows, if you limit boost to 20 psi, you'll only see four down arrows.

At 1500 rpm with 20 psi of boost and four down arrows my S60 is a 350hp engine. At 1500 rpm with 29 psi of boost its a 500hp engine. All things being equal, boost cost fuel. More boost, more fuel.

So Shave off a Down Arrow, and watch your average mileage skyrocket!