Driving with cruise control

Several folks have posted here saying they can get better economy without CC. I'm very skeptical! I believe CC can hold a steady throttle better than any human can and if the CC is instructed, by tap up and tap down as I described previously, it will give the best possible economy. If you insist you can get better fuel economy without CC PLEASE tell us, in detail, precisely what your technique is. What 'cues' do you use to adjust your right foot?

 

Well unfortunately for me? I learned this summer driving up the Oregon Coast that NOT driving 55 will get you a speeding ticket.

Two unfortunate and perhaps unfair tickets in the past year means I have to now drive very carefully. I use the CC now as a tool to help me "be careful".

But in the past I used it primarily as a tool of driving comfort. It's nice to be on open highway and be able to set at at whatever you feel comfortable with, and let it work.

And yes in those scenarios open, flat highway, I doubt the difference in MPG's between manual and CC would be all that noticeable.

 

Sorry you got thoses tickets, just today driving north on the Garden State Parkway I drove through a speed trap, trooper pointing radar gun right at me, going 65 in a 55 limit, in a pack of car going as fast or faster, trooper didn't even blink.

 

Most of the time, even driving 65 in the 55 sections, it feels like you're standing still.

 

I heard that Governor Christie's office told the state troopers to make sure only Democrats get speeding tickets.

 

If that were the case, there wouldn't be any debt in NJ.

 

Then they missed one!

 

in my short driving experience in the prius, much like most cars the basic CC is fairly "dumb". The idea is to maintain the programed speed with a +- factor of a couple MPH. if it get to high, Ie going down a hill it will begin to coast and when going up hill as the speed drops, it will floor it...

from the human aspect, we can increase the speed when going down a hill and maintain a larger "speed window" such that we can help keep the CC from "flooring it" when it hits the next incline.

On flat land I would think the CC would do a better job from a fuel econ standpoint...but on a hilly interstate the low torque of the engine means its going to have to rev pretty high to maintain speeds on the uphill climbs. I think some human intervention with the CC on hilly terrain would be the best of both worlds.

I wonder, if there any way to program a larger speed window into the prius CC. ie if you set it at 55, it would allow a wider range of speed before the computer decides to coast or floor it?

 

I just bought my third Prius, a plug-in. With all three I have always been able to get better fuel effeciency with my foot than relying on CC. This is especially true in areas where the interstate is particurarily hilly. I find that the cc wants to floor it on very hilly sections of interstate to try and maintain the set speed, and in very hilly areas like in Maryland simply tapping up and down doesn't work very well or as fast as my foot can whith the CC off. The 5,6 and 7% grades really cut into fuel effeciency if you let the CC run the car.

 

DWL is a name given to a method which many have already described here. It is essentially trying to keep a constant load on the engine regardless of inclines or declines. Put another way, it is slowing down going up hills and speeding up going down.

My modified DWL method using CC is one where you set a baseline speed that you don't want to go below using the CC. Then going downhills you modulate the throttle to be in a very efficient range (not doing regen or some other non efficient load) which essentially lets you speed up down these hills. Keep your foot there until you start going slow enough for the CC to kick in again. I've found I can get an additional 1-2 mpg without a ton of work.

 

the only thing cruise control 'knows' is the speed of the car, based on it's measurement point. when you hit a steep incline, even though it's faster on the draw than a human, that doesn't make up for applying the accellerator a little earlier when you see the incline coming. and the same goes for cresting a steep hill. 'eco' mode does nothing but modulate pedal travel, so it doesn't matter if your using cruise or not. hvac will be effected the same in each.

 

That's why it does more poorly than a skilled driver. It tries to maintain speed at all costs. CC doesn't see a hill coming and know that it's more efficient to gain some momentum before the hill and bleed off some speed up the hill (basically pulse and glide). What would be really great is a customizable CC where you could set the hysteresis and then have the car maintain constant engine load (fuel consumption) within that range rather than constant speed.

 

I wonder if there is an outside chance there is some legislation out there that says if you have cruise control on a vehicle it must stay in a certain small speed range when it's on.

 

Hummmmm don't know!

 

Never heard of any laws regarding CC. I think the auto manufacturers just program CC to what the average driver wants, to maintain the set speed.

 

"What would be really great is a customizable CC where you could set the hysteresis and then have the car maintain constant engine load (fuel consumption) within that range rather than constant speed."

Here is my custom use of CC for hilly southern Kentucky:
I am still perfecting this technique. I watch the HSI and the instant MPG and use tap up and tap down. Flat and level at 55 is about 1/4" right of center on the HSI and shows about 60 MPG. I maintain 1/4"right of center on the HSI on upgrades until my speed is as low as I care to go, say 45 if there is no traffic. On downgrades I tap up to keep the bar of the HSI right of center until I reach my mental max speed usually 62 for a 55 limit road. I used this technique today on a 120 mile round trip, all in HV mode, on which the computer shows 61 MPG and 47 MPH. BTW I removed the grill blocking as the outside temp was near 60f and I saw a coolant temp of 199f (reported by "Torque") on the outbound leg. Even with the grill unblocked I saw a coolant temp of 198 on the return leg and I actually used the AC.

 

I use the tap method you are talking about too, but it is not as smooth or effecient as my analog foot, which is contiunuously variable. This is especially true at least for me when driving in Maryland across the interstate from W Va to Baltimore for example where grades are long and steep.

 

every time you tapp the cc lever, you excite the system, which produces much sharper impulses than you do with your foot. those sharp reactions inevitably cost mpg's. how much are we talking about? aye, there's the rub.

 

"every time you tapp the cc lever, you excite the system, which produces much sharper impulses than you do with your foot. those sharp reactions inevitably cost mpg's."

That is an ASSumption! It may or, most likely, may not be true! The fact is the pedal position is converted to a digital value BEFORE the car's computers can act on it. It well may be that the minimum change in pedal position as seen by the computers is greater than the correction given by the CC. I suspect that the changes that CC induces into the powertrain following a tap up or tap down are in fact smoother than can be achieved with the foot, this suspicion is supported by watching the ICE power output, with Torque, under both driving techniques.

"how much are we talking about? aye, there's the rub."

I basically agree. It would be a very tedious test procedure to substantiate either method as superior and I'm very sure the difference would be VERY small. So I prefer to rest my legs and use my fingers.

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