Engine racing when using dynamic cruise

[Corollanutter]

Due to the type of journeys I regularly do, I make very little use of the cruise control. However over the past couple of days on a long trip I have had occasion to switch it on - and noticed some strange behaviour. The engine seems to rev a lot higher to maintain speed on slight inclines (compared to when I'm driving without the cruise active) - and most disturbingly reved up to over 4000RPM when decending a longish hill at a set 60MPH (a situation where the engine would have normally turned off). On cancelling the cruise part way down the hill, the engine immediately shut down and "normal" behaviour was resumed. Is this normal with the dynamic cruise? It certainly didn't seem right to me. I tried switching it on again later on in the journey and experienced similar behiavours. 

[Chippy01]

It's difficult to imitate cruise control with manual input, so going up inclines manually vs cruise, the cruise will try to maintain the set speed immediately, while manual input could be more gentle in it's approach.

As for the going downhill bit, I would guess that the engine was trying to input some engine braking to keep your set speed, and to prevent a runaway situation.
When you cancelled the cruise going downhill, did you have to control the speed using the brakes, to prevent going too fast?

If you long press the cruise 'on' switch, the dynamic cruise becomes standard/normal cruise - minus the radar input. Try that as well, see if you get the same results.

 

[Cyker]

I find the cruise control tends to use higher revs than I do too; I find where a human would let the speed build to the target speed more gradually, the cruise control wants to try get to it faster before backing off so it tends to rev more initially, and will pathologically try to maintain that speed.

When a human gets to an incline, we'll have already increased throttle to compensate in advance, or we'd slight dip in speed as we start the ascent and just increase throttle slightly to bring it back up. The CC can only see speed and can't see impending inclines so the first it knows is when the speed starts drop, at which point it will be like "Oh no I just dropped 1mph below target speed and it's still dropping! POWAARRR!!!". You just get used to it after a while  But I do find I'm much better at driving for economy than the cruise control does.

With the braking, in cruise control the car won't normally brake unless it's an emergency or it's stopping and relies on regen most of the time to slow down. If the base regen isn't enough to slow it down enough, it will use the engine to slow itself down (a'la B-mode on the drive mode lever), which means dumping power into spinning the engine. I still find it a bit weird, being a former manual driver, but all the hybrids do it so I'm taking it to also be 'normal' behaviour  

I should note that when it does slow down or brake, the CC also tends to do it much later and sharper than a human would when cars are slowing in front, esp. if the vehicle in front is not driving very smoothly, so be aware that's a thing too!

 

[Corollanutter]

Thanks Phil and Cyker. Yes, it sure works differenty to a ICE cruise control system - and this is also my first auto. What you say now makes perfect sense - I guess it's just the sensation of the engine racing when the car is not accelerating being a bit disconcerting. I will try the standard cruise mode and see what that does. 

[TonyHSD]

Hi Chris, 

that’s pretty normal for Toyota hybrids. As explained already by others the car although auto and smart it is not as good as experienced driver and will wait until the very last moment before the beginning of the uphill and then will apply more throttle to overcome the incline where a pro driver will rise the speed a bit before the beginning of the climb and release the power slightly while just before the end of the climbing using less rpm and less fuel. If you about hyper milling best not to use cc in mountain regions. It is ok to loose or gain 5mph but remain in your sweet spot for efficiency. 
CC when going downhill is useful though as can do higher regenerative braking to maintain desired speed without using the brakes. 

[Cyker]

51 minutes ago, Corollanutter said:

Thanks Phil and Cyker. Yes, it sure works differenty to a ICE cruise control system - and this is also my first auto. What you say now makes perfect sense - I guess it's just the sensation of the engine racing when the car is not accelerating being a bit disconcerting. I will try the standard cruise mode and see what that does. 

Yeah this is a common complaint with CVT-type gearboxes, as unlike more normal gearboxes the engine speed is almost completely de-coupled from the road speed.

I know what you mean about it being disconcerting, as it definitely has that "oh no is my clutch slipping?" sensation if you're used to manuals, but just remember the hybrid drive doesn't have a clutch (Or really a gearbox for that matter  ) and let it do its thing. You get used to it after a while, and it even makes you tend to drive more efficiently as you'll tend to drive with less forceful accelerator inputs to keep the engine rpms at the lower end.

(Well, maybe... it hasn't worked so well for me as I have the opposite problem - I'm finding the instant torque at all speeds hard to resist... )

 

[TonyHSD]

15 minutes ago, Cyker said:

Yeah this is a common complaint with CVT-type gearboxes, as unlike more normal gearboxes the engine speed is almost completely de-coupled from the road speed.

I know what you mean about it being disconcerting, as it definitely has that "oh no is my clutch slipping?" sensation if you're used to manuals, but just remember the hybrid drive doesn't have a clutch (Or really a gearbox for that matter  ) and let it do its thing. You get used to it after a while, and it even makes you tend to drive more efficiently as you'll tend to drive with less forceful accelerator inputs to keep the engine rpms at the lower end.

(Well, maybe... it hasn't worked so well for me as I have the opposite problem - I'm finding the instant torque at all speeds hard to resist... )

 

Indeed, Toyota hybrids are great for driving, this instant response saved me and the car tho other day.
A large articulated lorry one of the M&S was driving slow on dual carriageway in the left lane I decided to overtake and while was in the middle of getting passed for no reason without any turn signal he decided to change the lane not looking into mirrors at all. Was a bit uncomfortable experience to me, luckily he didn’t swerve sharply so I had time to use the horn and to accelerate fast , just smashed the pedal and the car took off. 

[Bozz]

On 1/29/2023 at 5:53 PM, Cyker said:

With the braking, in cruise control the car won't normally brake unless it's an emergency or it's stopping and relies on regen most of the time to slow down. If the base regen isn't enough to slow it down enough, it will use the engine to slow itself down (a'la B-mode on the drive mode lever), which means dumping power into spinning the engine. I still find it a bit weird, being a former manual driver, but all the hybrids do it so I'm taking it to also be 'normal' behaviour  

I commented elsewhere on the forum that the engine 'braking' function is utilised significantly more often on the 1.8 than the 2.0 in fact I can't remember an instance when my 2.0f ever uses engine 'braking'.  I call it braking loosely.

[DC_Ms]

I don’t know about other drivers , but for me the CC is a welcome help only on boring straight dual carriageways and motorways , when the roads are cornering and uphill / downhill …. I like to drive 🤷‍♂️

[TonyHSD]

I like CC but almost never use it. The reason is simple, I drive at nights where cc will be very cool and easy working as not as much congestion however when it’s too easy it will become a risk for me to fell a sleep behind the wheel, something that I don’t want and any driver should think twice especially those driving at night after work.
Unless the cc can bring the car to a complete stop safely and wake you up I will refrain from using it, plus I do enjoy driving the car myself not been a passenger. 👍

[Ian.S]

On 2/1/2023 at 2:28 PM, Bozz said:

I commented elsewhere on the forum that the engine 'braking' function is utilised significantly more often on the 1.8 than the 2.0 in fact I can't remember an instance when my 2.0f ever uses engine 'braking'.  I call it braking loosely.

The 2lt doesn’t have ‘B’ function, you have to use the flappy paddles. 

[Cyker]

6 hours ago, TonyHSD said:

I like CC but almost never use it. The reason is simple, I drive at nights where cc will be very cool and easy working as not as much congestion however when it’s too easy it will become a risk for me to fell a sleep behind the wheel, something that I don’t want and any driver should think twice especially those driving at night after work.
Unless the cc can bring the car to a complete stop safely and wake you up I will refrain from using it, plus I do enjoy driving the car myself not been a passenger. 👍

If you ever get one of the new TNGA ones, you'll find the dynamic cruise control will actually help you stay awake!

It's true!

It lets the bit of your brain that controls the car have some down time... while increasing your adrenaline levels, as the car will randomly beep at you to hold the steering wheel, sometimes while you are already holding it, and it will also randomly turn itself off for a moment, and also try to follow a paint smear or non-existent line into the verge  

Where my 2am trapises down the M1 in the Mk1 and Mk2 sometimes were leading to that fizzy brain feeling you start to get when your brains telling you you really need to sleep, the Mk4's ACC has kept me so wired it's like if you were taking a nervous learner on a late night drive!  

[forkingabout]

I've had the steering warning without any cruise control switched on, was on a straight piece of dual carriageway so was seeing how true the tracking was by not moving the wheel ( its straight & fine ) & the alert to hold the steering wheel triggered after a few seconds.

 

[MarcusWatson]

I've used the ACC for thousands of miles. I use it and the separate speed limiter function every time I drive.

I use the limiter on anything less than a dual carriageway so that I can spend less time concentrating on speed.

On the motorway I use ACC but recently have started turning off lane keeping as it's just not good enough. I use it because I have largely given up trying to overtake on the M25 or other busy roads (where I spend most of my time). I just sit in lane 1 at whatever speed it's going and let the ACC do its job unless there's a clear and obvious need to overtake.

[AisinW]

I think it is very typical Toyota cruise control behaviour.  Always want to get to the set speed ASAP. Honda and Nissan are also the same.  VW does better job on reaching gradually to set speed.