Is Cruise Control 'smart'?

[barrycoll]

Reading other posts, specifically about folks using c.c in M-way situations, and sometimes at quite press-on speeds, the resulting MPG's seem quite promising.

Does this mean that the cars diagnostics are optimizing the amount of throttle opening, and actively using

The Cruise feature? ?...or is it a bit more mindless than this?

my experiences are that the car uses too much throttle on gradients, but maybe I am wrong here???

[OldSkoO1]

I'm fairly new to the prius after only having mine 2 weeks but I've driven them and this extensively before owning one.

I believe the prius is highly configured and CC seems to be no exception.

I find it takes an awful lot of concentration to beat CC on a motorway journey.

It seems to optimise throttle opening a long with Battery regen and in most cases maintains a nice steady speed. I am amazed that I get better mpg going uphill than the other diesel rav4 in our family.

I'm writing this from 150 miles away after my first motorway stint in my own prius. 3 up and packed half full I arrived with a true cold start average of 64mpg. The cruise was set at 74mph and plenty of mixed conditions both ends.

Whilst I can't tell you definitively if the car optimises I can tell you the effort for me to hypermile using the hill technique far outweighs the small gains I might make over the computer controlled cruise!

I'm very impressed and I have a feeling the car is optimised to produce the best mileage at 33, 43, 54, 65 and 74.

It's very hard to accelerate before the hill and bleed off speed on the motorway and p&g is fairly meaningless at such fast speeds. It is temping on some hills to allow a small bleed off but I don't think it's worth it. Seasoned hypermilers will be much much better than me at this. I think you can get much better mpg being more observant and try to minimise speed changes on the motorway as bunching can affect it.

One thing I do find advantageous is knocking off CC in big downhills as it can !Removed! progress but using regenerative braking and the Battery is usually in the sweet spot on the motorway so I find it better to allow it to glide and gain speed than have it try to charge a nearly full Battery and keep the speed steady downhill. It means the glide can continue longer once you hit the flat and the speed comes down to the target again whilst using no battery I believe.

[barrycoll]

Very interesting osk, as I am off to Spain next weekend with a fully loaded car......

usually, I feel that I can do better than the CC (mpg wise), but maybe I am fooling myself?

[Joseph D]

Very interesting osk, as I am off to Spain next weekend with a fully loaded car......

usually, I feel that I can do better than the CC (mpg wise), but maybe I am fooling myself?

Take this with a grain of salt, as I drive a Gen II and the CC smarts maybe improved since then, but I'd say it depends on the terrain. I find that if the gradients are too steep, the CC tends to lag at the bottom of a hill and then overcompensate until it finds its balance again (i. e. it slows too much then overspeeds past the set speed, before settling back to the correct speed and all with a bit of disconcerting enthusiasm). The problem is if the hill is too short to do this, it gets into a very uncomfortable/annoying rhythm. I tend to help out (without disengaging the CC) by hitting the throttle earlier in anticipation of the up hill to keep the speed even and that seems to work ok OR not use CC until the undulating terrain was over. Also on the motorway if I'm on a gentle decline and can see an incline ahead, I'll give the accelerator a slight touch so that I'm accelerating (all the while never allowing the instantaneous MPG drop below my current MPG tank average, if possible). I could do this because normally I'd be travelling at somewhere between 68-74 mph (indicated), maybe less, and had head room to speed up to 88 mph (indicated, actual 80 mph) and therefore not be doing a ticketable speed. I found this technique worked quite well at preserving my average MPG's.

All of the above presumes the roads are clear enough so that you have room to do all this safely and considerately of others on the road. If the traffic is too dense, I find you cannot really use CC effectively.

All in all, I tend to use the CC a lot during long distance motorway driving as I find that although I may be able to do better at times, I find that with the constant concentration required I get mentally tired after a while and unless you can keep on your game you will start to do worse just because your focus wanders. Of course, each person will have different thresholds, therefore milage may vary.

[PeteB]

The main improvement on the Gen 3 is much stronger regen braking when using cc downhill. It rarely allows the speed to differ by more than one mph. However, its insistence on using as much power as needed to maintain speed up a hill seems wasteful - it would be nice if selecting ECO mode also dulled this persistence, in the same way that it slows down the a/c fan and reduces the use of the A/C compressor or ICE to cool or heat the car.

I used to cancel cc in my Gen 1 uphill to save a bit, but after more than ¼ million miles and 12 years in Hybrids, now I just leave it to it. I find it's at least as economical over a long journey as I would be, but less stressful than doing it myself. If only one could specify the radar cruise control on the T3!

[kithmo]

The main improvement on the Gen 3 is much stronger regen braking when using cc downhill. It rarely allows the speed to differ by more than one mph. However, its insistence on using as much power as needed to maintain speed up a hill seems wasteful - it would be nice if selecting ECO mode also dulled this persistence, in the same way that it slows down the a/c fan and reduces the use of the A/C compressor or ICE to cool or heat the car.

I used to cancel cc in my Gen 1 uphill to save a bit, but after more than ¼ million miles and 12 years in Hybrids, now I just leave it to it. I find it's at least as economical over a long journey as I would be, but less stressful than doing it myself. If only one could specify the radar cruise control on the T3!

Does CC still give it full beans up hill in ECO mode then ?

[PeteB]

...

Does CC still give it full beans up hill in ECO mode then ?

sure does!

[barrycoll]

yes, it does tend to go into the Power zone to maintain the set speed, whether in Eco or not

[GreenJuice]

My experience is the same as OldSko01 *and* JosephD!

I been playing around with hypermiling techniques for some years now. Whilst being able to make some worthwhile gains in the Gen2, I find c.c. really hard to beat in the Gen3.

The strategy I used was to allow some bleeding off of speed on inclines (therefore burning less by not attempting to maintain speed) and then regaining speed on the decline. I thought that over many cycles on a long journey any gains would be noticeable. Yes, for Gen2; not so for Gen3.

[Ten Ninety]

I don't think the CC is particularly 'smart' compared to any other CC system. The HSD system itself, however, is much better than most people (outside the hybrid community) seem to think at managing motorway speeds efficiently. When in CC the car will still do its usual tricks like kicking in to warp-stealth mode and using the Battery to add a gentle boost etc.

Like Joseph D, I tend to have CC on for long journeys but will also 'intervene' with the throttle; usually to stop CC from using re-gen to slow down on descents and occasionally to boost speed when passing slower vehicles, to avoid elephant-racing them HGV-style and causing a hold-up behind.

[barrycoll]

the consensus of opinion seems to come down very firmly on the side of a 'pretty smart' CC....not much dissent

my previous 'chipped' diesel Golf, would actually change down a gear on a Mway incline, totally refusing to use the shed load of torque that was available...

so seemingly the Gen 3 Prius is reliably set up to almost hypermile on a M-way run, which should make Sundays drive to Spain a bit easier on the right leg