Is it better to use cruise control or not for better mpg?

I prefer cruise control but do not have adaptive cruise control. Using cruise control is the core of efficient driving and leads to reproducible results.

When I bought our first used 2003 Prius and new 2010 Prius, on the drive from the dealer, I ran a series of benchmarks using cruise control on flat roads to plot:

This gives an mph vs MPG chart to plan trip fuel consumption. By factoring in weather and altitude changes, I can make informed choices between trip duration and expected fuel consumption.

There is a cold-soak, warm-up cost of 30 MPG for the first 2-3 miles or 5 minutes. Short of having a plug-in Prius, there are a few, marginally effective techniques to mitigate the warm-up cost.

Efficient driving is pretty lazy, no special accelerator technique. Accelerate modestly with traffic and set the cruise control. Thereafter, feet on the floor and follow, not tailgate, the slowest traffic available. Tailgating takes too many speed changes and is inefficient compared to using the cruise control stalk to maintain following distance.

There are other driving techniques but an engineer and private pilot, I prefer efficient driving and predictable methods.

Bob Wilson

 

I have not measued it from tank to tank but according to board computer I can do better than the CC if not on flat usind DWL technique. I basically let the car speed up during downhill and then let it slow down on the uphill.

for flat roads CC is definately better.

andrej

 

I like cruise control. I like DRCC best. I use cruise control whenever I can. When on the interstate in EV mode, I find it almost impossible to stay at 62 MPH to keep the ICE from starting. Cruise control solves that problem.

 

You might consider 'doing the experiment' but I am curious, what is "board computer?"

The cruise control stalk still allows tuning the speed. A pat down reduces the speed 1 mph. A pat up increases speed 1 mph. I do this all the time to maintain safe following distances in traffic. Unlike the accelerator, the car makes these changes smoothly . . . no fretting.

Since I generally follow slower traffic, I can shift into "N" as needed on downgrades and convert potential energy into kinetic energy needed to sustain speed. Then back to "D" and resume to get back to speed and adjust speed with the stalk.

Bob Wilson

 

This may help you on PriusChat.
PriusChat Glossary | PriusChat

 

by board computer i ment what the trip shows me on average. I have an elm327 on the way so I will have a bit better data. I will maybe run an experiment to see what the real difference is wit toping the tank.

Details: Toyota - Prius - Prius - Spritmonitor.de

andrej

 

My apologies. I did not realize English might not be your native language. You might consider updating your profile to identify your location.

Bob Wilson

 

My problem with the cruise control is that it can use the regen to control speed downhill. So you arrive at the bottom of the hill at the set speed and then face the an uphill stretch which then becomes pedal to the metal. If the terrain is largely flat, then yes but in hilly terrain I don't use the cruise control and on downhill runs I back off to stop the ICE then apply enough throttle to let the car coast, if you need to control speed you can control how much regen to use. The Prius coasts better than other car and the way it feels I don't think there is any advantage putting it in N

 

No problem:

It turns out there are lots of ways to drive the car and as long as the speeds are moderate, the results are going to be pretty good. My preference is cruise control augmented by shifting between"N" and usually "B". But then I like to keep my feet on the floor.

I'm not a fan of regeneration except to moderate speed as a way to avoid heating the brake pads. The regenerative, round-trip efficiency, 81-90%, is lower than the kinetic-potential energy efficiency but much better than brake pad heating.

GOOD LUCK!
Bob Wilson

 

Hi M3, I see this is an old link, but a contemporary issue. Hypermiling with Saturns taught me to accelerate a bit before hills, and let up that speed gradually as you ascend, being down to cruise speed as you crest the hill. It was easy to beat CC mileage that way. The problem with cruise is all it sees is your speed, I want a cruise control that reads MAP, and looks ahead and considers upcoming GPS terrain info. I like to descend in neutral with the Prius, or keep a bit of throttle in, to prevent drag there. Now looking at ways to sautomatically shut off the AC under heavy manifold pressure, and electrically pre-heat coolant to get into closed loop faster. Good Luck! Robert

 

I drive in a similar fashion. I try to find an engine load that will take me to a speed at the start of the ascent such that the same throttle will get me to the crest at a speed just over the set-point for CC. The game takes experience and a certain type of mental calc that some people manage well.

If up = down, and down comes first then it is easy. Just keep the throttle about the same as level cruising.

 

There was a gizmo for that, called PassMaster. It came in 3 variants, one each for 4, 6 and 8 cylinder engines. It was a vacuum activated switch: with vacuum the switch was closed (current could flow), and when vacuum dropped it opened. In a nutshell it was a sort of oil can action, the vacuum sucked the metal diaphragm over to make contact.

You spliced it into the compressor power lead, and ran it's vacuum hose over to a source of intake manifold vacuum. It worked well: anytime you accelerated aggressively or encountered a steep hill, the air conditioning would cut out for the duration.

The only issue: it had 2 mounting holes. I made the mistake of screwing both down pretty securely, and with expension/contraction it ended up cracking. I got a replacement and didn't use any screws, just taped it to a conduit.

Doing a Google search right now, I didn't find anything promising, not sure if you could still get one.

 

I'd say manual will let you precisely control when and how much gas you use compared to CC, but I don't know how much of a savings it would confer.

I can't say how much CC impacts interstate miles compared to using manual throttle control. I do know it's easier than having to use your foot all the time, and I find my CC is fairly smooth in maintaining speed. Smooth usually equates to better fuel consumption.

 

Easily ten percent. As for comfort on long drives I use both.

 

Yes Mendel, something like that. I've been switching the ac off and on with terrain but I'm likely to wear out the switch! I'm looking for something with a variable pot that can take input from the MAP sensor and open the circuit upstream of the AC relay under lo manifold pressure. Then I need to make it keep the ac relay dogged in a little later under high pressure.

 

For a Gen 2 like yours, 42 MPH will always cause the engine to start. Below that you can be in an EV mode if you have enough State Of Charge on the big battery.

For the gen 2, here are the rules for the warm up stages:
http://drivesmartwi.com/uploads/DSW_Toyota_Prius_Initial_Stages_of_Warm-Up_Wayne_Revised_2_.pdf

 

Above 42 mph in the G2 Prius the ICE will spin but not necessarily burn fuel. E.g while going downhill.