Problems with cruise/speed control

[Prinsloo]

I went for a drive through Cat skills mountains today - very nice with few cars around. I noticed when I used the cruise control function and going down hill that the car continues to accellerate being unable to maintain the correct speed. Has anyone had the same experience? I had to discontinue using the function.

Note: it works fine on normal,horisontal gradients and slightly gradient slopes, but as soon as it is a little bit steep down hill, I am better off without it.

 

[EdVoylesHyundai]

I went for a drive through Cat skills mountains today - very nice with few cars around. I noticed when I used the cruise control function and going down hill that the car continues to accellerate being unable to maintain the correct speed. Has anyone had the same experience? I had to discontinue using the function.

Note: it works fine on normal,horisontal gradients and slightly gradient slopes, but as soon as it is a little bit steep down hill, I am better off without it.

The cruise control cannot apply the brakes. What you are experiencing is gravity pulling the car down the hill and it is accelerating as if it were in neutral. When the slope is very small, the wind/tire/drivetrain/engine braking all work together to maintain the speed without increasing it. When the hill is steeper, the car accelerates.

 

[Calvin]

Its my experience that the maximum deceleration a car can experience on cruise control is equivalent to when you take your foot off the gas and coast. The less efficient the car profile the better the deceleration, however the Genesis seems to be very efficient so the deceleration is probably limited.

 

[Sonata2009]

That, and the overdrive gear ratios . . .

 

[sandy]

That, and the overdrive gear ratios . . .

I notice the same thing compared to the five speed Saab I came from. I believe Sonata2009 has it right....brakes or engine compression will slow the car, and since Cruise Control won't apply brakes, it's engine compression and gear ratios that slow the car down...the more "shifts" or gear-ratios, the less efficient at slowing. So the Genesis with a 6-speed tranny will not slow as rapidly as a car with a four or five speed.

 

[CanukV6]

I don't know this as a fact and am just speculating, but is it possible that with the variable camshaft timing that Hyundai actually opens the exhaust valves on the overrun to reduce pumping losses (and therefore compression braking) in the engine? I know they shut off the fuel supply. The overdrive gear ratios certainly partly explain the lack of engine braking, but you would still be driving the engine fast enough to provide some braking.

 

[ctrcbob]

The next time I go down a nearby hill (yes, this is the Florida "Hill Country) I will pay attention to see what happens.

I've had other cars that when in Cruise Control, and going down a hill, the transmission would automaticlly either downshift, or somehow the engine holds the car back so as not to speed up. My Continental does this. I can watch the tach and feel the car being held back. (this is only with the cruise on)

Like I said, next time, I will pay attention when I get to that hill.

 

[Gold Z]

The cruise control in my Genesis varies as much as 3 miles per hour up or down from the set speed while driving on the gently raising hills of north Texas. I haven't owned a car in the last fifteen years that couldn't hold speed better than that.