Rev counter steady with cruise control on

josip

We've a 2015 2.0TDi Octavia and on the motorway I set it to just over 120 (on the clock) which works out at an even 2000rpm. But the rev counter stays locked on 2000rpm regardless of whether I'm going up or down steep inclines.
If I maintain a steady speed without cruise control the RPMs rise and fall.
Has anyone else in a VAG (TDi) noticed similar behaviour?

demanufactured

That's how cruise control works...it maintains engine speed and saves on fuel.

Jesus.

demanufactured wrote: »

That's how cruise control works...it maintains engine speed and saves on fuel.

I thought it was supposed to maintain your actual speed

coylemj

demanufactured wrote: »

That's how cruise control works...it maintains engine speed and saves on fuel.

Cruise control has nothing to do with saving fuel, it's purpose is to maintain a constant road speed which as the OP says, should involve more revs going uphill and less going downhill.

demanufactured

coylemj wrote: »

Cruise control has nothing to do with saving fuel, it's purpose is to maintain a constant road speed which as the OP says, should involve more revs going uphill and less going downhill.

If it maintains actual speed then how would the engine speed change....??

OP , Does your car maintain actual speed when using cruise control?

demanufactured

Jesus. wrote: »

I thought it was supposed to maintain your actual speed

It dies. ..which is why your engine speed won't change.
My 08 Mondeo sits at 2100 RPM at 120KPH...whether going uphill or downhill.

TheChizler

coylemj wrote: »

Cruise control has nothing to do with saving fuel, it's purpose is to maintain a constant road speed which as the OP says, should involve more revs going uphill and less going downhill.

How does your cruise control work?!?

Jesus.

demanufactured wrote: »

My 08 Mondeo sits at 2100 RPM at 120KPH...whether going uphill or downhill.

How does it manage that?

EDIT: Ah I think I get you now

mickdw

I think what the op is confusing here is how engine requires more or less fuel depending on climbing or down hill driving. This will also give a different engine note but with the car remaining in gear, the rpm will be constant at a given speed.
I guess it seems odd because when manually controlling speed you give it more fuel climbing hill to keep it at speed but with cruise the car does this automatically to good a constant speed and rpm.

TheChizler

Exactly, I'm guessing they mean more accelerator/fuel/power, not revs.

Jesus.

demanufactured wrote: »

That's how cruise control works...it maintains engine speed and saves on fuel.

CC actually uses more fuel

TheChizler

Jesus. wrote: »

CC actually uses more fuel

Not always. Depends on how aggressive the control loop is, whether it can use the brakes, if you're on the flat etc. Increasing the speed of a vehicle requires a lot of energy, cruise control minimizes that particular inefficiency.

Jesus.

You sure? It will only increase throttle on an incline when it actually hits the incline. The driver driving economically will know to increase his speed approaching an incline and then ride the throttle when he's on it, thus using his momentum to help him up the hill.

Senecio

Any car I've had with CC uses more fuel. CC is there for convenience not efficiency. As a previous poster pointed out. A driver that anticipates road changes will be more efficient than CC.

shietpilot

The CC system is able to calculate the exact amount of throttle needed and that's why it can stay at a fixed RPM Drivers are almost the polar opposite. You will notice with cruise control how other drivers vary their speeds on motorway, especially when going uphill or downhill.

I've started using CC on every trip now and it seems to save me fuel at least according to the dash :pac:

shietpilot

The CC system is able to calculate the exact amount of throttle needed and that's why it can stay at a fixed RPM Drivers are almost the polar opposite. You will notice with cruise control how other drivers vary their speeds on motorway, especially when going uphill or downhill.

I've started using CC on every trip now and it seems to save me fuel at least according to the dash :pac:

josip

Thanks for all the replies and the education
Yes, I was confusing throttle and revs.

SBPhoto

Jesus. wrote: »

CC actually uses more fuel

I dont agree, i get much better mileage MPG when i have the cruise control on

pippip

SBPhoto wrote: »

I dont agree, i get much better mileage MPG when i have the cruise control on

Well that just means your driving style isn't efficient. The mpg isn't based on cc versus non cc it's about cc versus your driving style. Everyone is different.

visual

Is your car manual or automatic ?
CC in automatics can and do change gear and revs will change also.
In manual it won't because once in gear the engine speed through gear box to wheel is a fixed ratio. X engine turns = Y wheel turns
Instant fuel usage will change more going up hill less going down

ianobrien

Cruise control being more efficient can depend on the vehicle. VAG cruise control keeps the speed generally to +/- 1kph of the set point. I can't keep the throttle to that setpoint (generally +/- 5kph) and I have found the VAG cruise control to be more economical than me driving. That's on two VAG cars at home.

The Fiat one, however, can be anything up to +/- 10kph and the control programming is too aggressive with the throttle. This makes it not more efficient than using your foot to get to +/- 5kph.

I find the cruise control safer to use on a journey as once I set the speed, I never have to look at the speedo, so there's more time spent observing traffic. If I want to be as economical as Cruise Control, and maintain my speed to within +/-1kph I spend too much time lookin at the speedo.

SBPhoto

pippip wrote: »

Well that just means your driving style isn't efficient. The mpg isn't based on cc versus non cc it's about cc versus your driving style. Everyone is different.

Not necessary, i have tried both ways, driving on the economy drive system and on cruise, get about 5mpg more on cruise each time. i drive a manual A3 Saloon TDI

9935452

josip wrote: »

We've a 2015 2.0TDi Octavia and on the motorway I set it to just over 120 (on the clock) which works out at an even 2000rpm. But the rev counter stays locked on 2000rpm regardless of whether I'm going up or down steep inclines.
If I maintain a steady speed without cruise control the RPMs rise and fall.
Has anyone else in a VAG (TDi) noticed similar behaviour?

Logically with a manually car assuming the clutch doesnt slip if the revs are kept constant the speed will remain constant. The revs cant increase or drop going up or downhill if the speed is constant

When you are driving the car the speed changes constantly by a few mph and thus the revs change and you are constantly adjusting the revs to adjust the speed. Using cruise control the car is constantly making small changes as the speed changes by tiny amounts so it looks like its remaining constant.

ezra_

shietpilot wrote: »

The CC system is able to calculate the exact amount of throttle needed and that's why it can stay at a fixed RPM Drivers are almost the polar opposite. You will notice with cruise control how other drivers vary their speeds on motorway, especially when going uphill or downhill.

This.

The wexford - waterford road (N25?) is a killer.
Nice open road, lots of space and few bends yet the cars on teh roads are constantly slowing / speeding / slowing / speeding

visual

I've been lucky enough to have CC in my last few cars and use CC on every long run

Get a bit strange when you overtake someone only for them to overtake you a few miles later and repeat this a few times. It doesn't seem to dawn on them that their speed is varying.

shietpilot

visual wrote: »

It doesn't seem to dawn on them that their speed is varying.

Maybe it's better that such drivers don't have access to cruise control or don't know how to use it