Cruise Control

[Brechin Slate]

My wife did a 140 mile round trip (essential journey). On the way there she drove the car like a hybrid, small increments of throttle and brake, coasting etc and got good mpg.  On the return journey, cruise control was not as fuel efficient as lower limb input.  I guess this is a uniquely hybrid thing but would like to understand the science if anyone has ideas?

[Mincey]

Many moons ago, Clarkson did a London to Glasgow/Edinburgh (can't remember which) in an Audi A8 on a full tank of fuel. My lasting memory is him saying that cruise control wasn't a patch on a human brain for getting good economy. Your good lady's experience would tend to confirm that. I've found the same thing too.

With your foot you can anticipate hills, idiot drivers etc. Cruise control cannot, even when radar guided. Excuse me while i nip to Ladbrookes to put some money on someone coming along to contradict that :-)

[Brechin Slate]

22 minutes ago, Mincey said:

Many moons ago, Clarkson did a London to Glasgow/Edinburgh

I remember that, he had everything including the radio turned off as he came back into London, the car was running on vapours.  I thought it was  a Jag though, time dulls the memory!

[Linas.P]

I would say that best consumption is achieved when you keep speed and RPM as consistent as possible - it does not matter if you achieve it with cruise control or by your foot. For that to happen a lot of perdition and anticipation is needed in realistic traffic scenario. So cruise control may be go if road is very quiet and very even, but in real life there will be cases where you will have to brake and cancel cruise control of simply letting the accelerator pedal off in anticipation for slowdown.

Other thing I noticed, if you put car in "Eco mode" it tends to "up-shift" (obviously it is CVT) too far and keep too low RPM, then when you come to incline engine does not have enough power and has to "down-shift" to keep the speed and does it less smoothly than one could do with their foot. As such the best MPG I was able to achieve whilst using cruise control with both 300h and 200t were on at least "normal" or even "sport mode" (not sport+). Although, it tends to "down-shift" earlier and "up-shift" later car was overall more consistent and smooth, and had better MPG. "Eco mode" just "up-shift" too early and aggressively and result in less consistent and smooth driving, and as result I suspect worse economy.  

1 minute ago, Brechin Slate said:

I remember that, he had everything including the radio turned off as he came back into London, the car was running on vapours.  I thought it was  a Jag though, time dulls the memory!

I think he did Jag West cost to East cost, to catch sunrise. 

[Mincey]

4 minutes ago, Brechin Slate said:

I remember that, he had everything including the radio turned off as he came back into London, the car was running on vapours.  I thought it was  a Jag though, time dulls the memory!

You've got me thinking now - I was convinced it was an Audi. I'm prepared to be corrected though!

[Linas.P]

Yes he did 800 miles in A8,

They did diesel Xj from Switzerland to Blackpool... and Jag XJ R (supercharged) west to east cost.

[royoftherovers]

44 minutes ago, Mincey said:

You've got me thinking now - I was convinced it was an Audi. I'm prepared to be corrected though!

You have need for correction James. It was an A8.

[BigChange]

Have to agree with Linas.  My mpg is marginally better in Normal on a long run and in Eco I am also conscious of the engine having to work harder.  On balance I prefer Normal because it is also more responsive when overtaking. 

[ColinBarber]

7 hours ago, Mincey said:

With your foot you can anticipate hills, idiot drivers etc. Cruise control cannot, even when radar guided

I agree, and many drivers will allow the vehicle to slow slightly going up a hill rather than waste a bit more fuel trying to maintain a very specific speed, which the CC will do. I also find that if you are slowed down by another vehicle, to get back up to cruising speed again the CC will accelerate harder than a normal driver will do - again using more fuel.

[Linas.P]

1 hour ago, ColinBarber said:

I agree, and many drivers will allow the vehicle to slow slightly going up a hill rather than waste a bit more fuel trying to maintain a very specific speed, which the CC will do. I also find that if you are slowed down by another vehicle, to get back up to cruising speed again the CC will accelerate harder than a normal driver will do - again using more fuel.

Same here, CC accelerates much harder than I would do, then blows past limit by 3 miles and slows down. At least that was the case for older cars like IS mk2, mk3 and RC.

I must say that CC is much improved in LC, NX and even UX. Allows for very quick and specific adjustment (1 mile or 5 mile increments), works smoother and actually stays on target speed rather well. Obviously they are still limited to the same issues when it comes to predicting future and anticipating changes in the circumstances ahead.

I would conclude that CC is comfort feature like AC, rather than a tool which helps to make the car more fuel efficient. If you really want to hypermile using your foot is still the best.

[m4rkw]

1 hour ago, ColinBarber said:

I agree, and many drivers will allow the vehicle to slow slightly going up a hill rather than waste a bit more fuel trying to maintain a very specific speed, which the CC will do. I also find that if you are slowed down by another vehicle, to get back up to cruising speed again the CC will accelerate harder than a normal driver will do - again using more fuel.

Haha not my janky aftermarket cruise control. It slowly loses speed up steep hills until it passes some threshold and disengages XD

[Ala Larj]

7 hours ago, BigChange said:

Have to agree with Linas.  My mpg is marginally better in Normal on a long run and in Eco I am also conscious of the engine having to work harder.  On balance I prefer Normal because it is also more responsive when overtaking. 

My handbook says to use normal mode for normal driving but eco mode in stop/start traffic. Which makes sense as it uses the Battery more improving fuel consumption in town traffic. 

[Thackeray]

19 hours ago, ColinBarber said:

to get back up to cruising speed again the CC will accelerate harder than a normal driver will do

Interesting to read this. The experience I've had with my car is different.

On previous cars, re-engaging cruise control after slowing down used to bring aggressive acceleration back up to the cruising speed - much more aggressive than my usual driving style. I sometimes felt like apologising to passengers, saying "It's not me accelerating like this -  it's the car."

So I was surprised and pleased when I first discovered the behaviour of my IS300h. I was driving along a 70mph dual carriageway interrupted by roundabouts every half mile or so. So I slowed down for the roundabout and then re-engaged cruise control at about 30mph as I left the roundabout. And instead of the aggressive acceleration I was used to from previous cars, it gently gathered speed, intelligently increasing the rate of acceleration until it reached cruising speed again. It behaved pretty much the same as I would have done if I was doing the acceleration. I was quite impressed.

I wondered if it made any difference if you were in ECO or normal or Sport. But I didn't notice any difference. It's surprising that others have had a different experience.

On 2/25/2021 at 11:31 AM, Brechin Slate said:

I guess this is a uniquely hybrid thing but would like to understand the science if anyone has ideas?

As for the fuel consumption I don't think it has anything to do with it being a hybrid. For pretty well all cars, the faster you go the less mpg you will get.

Cruise control is designed to keep you going fast in circumstances when you as a driver might choose to go slower. Like going up hills, as Colin mentions. Going up a long steep hill with cruise control is often an experience of overtaking car after car, as other drivers instinctively (or perhaps unconsciously) slow down for the hill. And the faster you go, the worse mpg you will get. So cruise control isn't really an economy feature and it's no surprise that it can use more fuel in hilly terrain.

[NemesisUK]

36 minutes ago, Thackeray said:

As for the fuel consumption I don't think it has anything to do with it being a hybrid. For pretty well all cars, the faster you go the less mpg you will get.

But the difference is more marked in hybrids because at higher speeds the ICE will be engaged all/most of the time. Hybrid economy comes mainly in low speed urban driving when the Battery power can be used effectively. 

[Brechin Slate]

2 hours ago, Thackeray said:

re-engaging cruise control after slowing down used to bring aggressive acceleration back up to the cruising speed

This is my experience with my 300h but it was much more gentle on the IS250.  Also on the IS250 I could increase the speed fairly gently in 1 mph increments using the stalk but on the 300h it's like planting your foot if you do anything but nudge the stalk for a fraction of a second.  Not a complaint, just an observation, we learn to adjust ourselves to what we have.

[Alex34]

I've only had my IS300h for almost three weeks now but have done about 800 miles in it so far. 

CC is a lot less polished than I expected from this car and unless you are on flat clear roads I can't see any mpg gains from it. Some one with a well trained foot can easily do better for smoothness and mpg. I only use it early mornings when the motorway is clear.

I'm getting 52.8 mpg average (based or car's computer) and I spend most time in Standard mode. I do a mixture of motorway, A roads and B roads. Mostly 30 to 40 mile journeys to work. I don't drive during rush hours so roads are mostly clear for my journeys. I find that ECO mode is an absolute waste if driving normally and I would only use it in traffic jam scenarios. Standard is alright but still quiet a bit of lag at the bottom end. Sport mode is how the car should drive in my opinion and I don't think there will be much loss in MPG when compared to Standard... unless you are always giving it the beans. I will continue my driving style until I have to fill up again then try the next 1K miles in Sport mode.

[200h]

21 hours ago, Linas.P said:

I must say that CC is much improved in LC, NX and even UX. Allows for very quick and specific adjustment (1 mile or 5 mile increments),

when i had my 63 plate 300h without radar the cruise control worked in the same manner 1mph or 5mph increments

tap it 1 mph change press and hold 5mph change

[Linas.P]

In my experience they "drifted" and were not consistent e.g. you set it to 70 and after 20 miles it goes like 69 or 72 consistently. Or you click it once nothing, happens, click it twice nothing happens, click it third time and it goes 2 miles-up. It felt really analog somehow.. like on my old IS250

In comparison to cars I mentioned it feels very digital 1click=1mile-up.

[paulrnx]

2 hours ago, Alex34 said:

I've only had my IS300h for almost three weeks now but have done about 800 miles in it so far. 

CC is a lot less polished than I expected from this car and unless you are on flat clear roads I can't see any mpg gains from it. Some one with a well trained foot can easily do better for smoothness and mpg. I only use it early mornings when the motorway is clear.

I'm getting 52.8 mpg average (based or car's computer) and I spend most time in Standard mode. I do a mixture of motorway, A roads and B roads. Mostly 30 to 40 mile journeys to work. I don't drive during rush hours so roads are mostly clear for my journeys. I find that ECO mode is an absolute waste if driving normally and I would only use it in traffic jam scenarios. Standard is alright but still quiet a bit of lag at the bottom end. Sport mode is how the car should drive in my opinion and I don't think there will be much loss in MPG when compared to Standard... unless you are always giving it the beans. I will continue my driving style until I have to fill up again then try the next 1K miles in Sport mode.

I completely agree with what you say. I always felt that Sport should be normal and then Sport should be a maximum combination of ICE and motor with a much more aggressive ICE map too. 194bhp from a 2.5 litre is poor. On longer motorway journeys I’ve always found that Sport mode gives better economy because I don’t have to mash the accelerator to the carpet to make some progress. On my 4th 300h hybrid now. In urban conditions the cars are superb though.

[200h]

if you didnt have the mode dial then Sport would be the normal

everyday power configuration that would be used ,having the dial

makes all other modes down tuned versions to improve economy .

[200h]

9 minutes ago, paulrnx said:

194bhp from a 2.5 litre is poor.

due to the Atkinson cycle the engine use and not the otto cycle

the valves stay open for longer this results in lower compression

and BHP

[paulrnx]

Pulling out into the outside lane of a motorway in Normal mode is a foot to the floor revs through the roof kind of operation. It’s not as frantic in Sport mode.

[paulrnx]

1 minute ago, 200h said:

due to the Atkinson cycle the engine use and not the otto cycle

the valves stay open for longer this results in lower compression

and BHP

Yeah I know the reasons why. I think an IS would be a fantastic car with a better ICE.

[Linas.P]

18 minutes ago, paulrnx said:

Yeah I know the reasons why. I think an IS would be a fantastic car with a better ICE.

I have argued previously that instead of wasting money on developing the engine Lexus could have used 4GR-FSE with little updates - like adding secondary port injection, adding Atkinson cycle (like in newer 2UR) and then pugging hybrid on top... like a baby 450h. I think that would have actually made decent car - fast and economical. And then they could have further save money by not developing 200t either.

As well agree re sport mode. It really something similar to normal mode on older cars and I think it save fuel for exact reason you mentioned. In eco or normal mode - when you press acceleration nothing happens, making you push it more than you actually intended and then car just jumps forward. Whereas in sport you can accelerate more evenly. 

[ColinBarber]

2 hours ago, Linas.P said:

Lexus could have used 4GR-FSE with little updates - like adding secondary port injection, adding Atkinson cycle (like in newer 2UR) and then pugging hybrid on top.

The smaller hybrids are about economy and emissions. Why you would use an engine that is inherently heavier and less economical, and doesn't actual produce any more power.