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Discussion Starter #1
Since I´m not a Prius owner yet, I have loads of different question about the technical constructions of the car that my local car dealers can´t answer. They just want to sell, cars or vacumcleaners doesn´t matter, they don´t care about the product anyway. So, I wonder how the cruise control works. Will it keep the wanted speed when going downhill by braking with the generator, or will the speed increase?
 

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I've not found this to be the case. It will happily exceed the set speed going downhill.

If I force it into B, it will slow down, but it kicks the cruise off when I shift (and it doesn't return when I shift back to D).

I wish it would hold speed downhill-- avoid tickets that way in a local downhill speed trap.
 

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I've driven it down a moderate hill set CC at 30MPH, and have seen regen take effect in energy screen. Guess it may depend on the hill. Perhaps it will only apply as much regen as you would get for coasting?
 

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Yes, I think youre right, Dan, it uses only the coast regen. The hills I see it speed up on are at higher speed and are steeper.

I don't see why it wouldn't use regen and ICE spinning to maintain the speed, though. The "cruise control" is really a "minimum speed limiter" and not a speed control.

In most cars, you'd have to add hardware to make it slow on downhills, but the Prius could ddo it in software.
 

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My recent experience agrees. On gentle hills the cruise will go as low as coast regen to maintain speed, but if you get onto a steep downhill you need to go into "B" manually to keep it from continuing to pick up speed... and the cruise won't go to the brake either!

I admit to being a cruise control weenie -- I am a control freak -- but I use it in the Prius because it maintains steady speed better than I do and I do get better mileage on a freemoving, not too crowded freeway. All cruise control only works the accelerator, right? It won't downshift into the equivalent of "B" on any car, will it?
 

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Discussion Starter #7
i just figured it would be a simple thing to just generate more power back to the battery by not letting the speed increase when going downhill. A car like the Prius really should be able to maintain the desired cruise controlled speed both uphill and downhill. It´s just a matter of programming, right?
 

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Well it does, up to the point you need to go into "B". "B" actually charges the battery LESS efficiently than normal cruise regen. I think it is doing the best it can, short of actually applying the brake, in terms of regen, and as well as it can at maintaining speed short of shifting into "B". You'll only pick up speed if the hill is quite steep.
 

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I don't know why it won't just go into B as necessary. If I set a speed, I WANT that speed, no faster, no slower. The legacy of cruise control" being just a throttle positioner, independent of any braking or downshifting, is no longer applicable to the HSD.
 

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It depends. Most of the time, it will try to hold the speed but if the hill's too steep, your speed will increase.
 

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I guess "steep" is relative. Steep in Illinois means something different than in California. ;-) Still begs the question, why not automatically use B mode to maintain speed downhill while cruising?
 

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To address the orignial question, the Prius is a throttle by wire vehicle, out of efficiency, but also out of necessity. So, when you are using the throttle, you are really just communicating a throttle position to the computers and they translate that into speed and acceleration, or decleration. Since the whole throttle system is really nothing more than a ground speed selector, the cruise control system works in the same manner. If you set your cruise at 60, the vehicle will command the hybrid system to maintain a highway speed of 60. And it does a very nice job of this on flat and up hills.

Downhills,coast regen does kick in, and can have the effect of maintaining your setpoint, but that is really a function of how steep the downhill grade you are driving on is. The Prius will pick up speed on steep downhill streches, and the use of brake or B mode is necessary. So, the cruise contorl is really just another function of the onboard computers.
 

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I took a trip over the Cascade Mt. Range to Eastern Washington. Wondered about the cruise control. The traffic on I-90 was pretty light, so I set the cruise on 70 mph to watch how it behaved over the pass and down the other side.

All the way over it kept to a steady 70, both up hill and down. It didn't vary the slightest. Best of all, with the CVT, it was smooth all the way. If was in the passenger seat and had my eyes closed, it would have felt like it was on the level the whole way.

A couple of months later, I took my F150 pu over. On the way up, it kept slowing at the grade then gave a wrenching shift to a lower gear. As the rpm increased it went from 55mph back to 70 then shifted back. This occurred every few minutes, so I finally took it off cruise and shifted off overdrive.

In July I am taking it to Colorado and will try out some bigger and steeper passes there.
 

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KTPhil said:
I don't know why it won't just go into B as necessary. If I set a speed, I WANT that speed, no faster, no slower. The legacy of cruise control" being just a throttle positioner, independent of any braking or downshifting, is no longer applicable to the HSD.
Interesting because I want just the opposite... When I set CC at 65, I want the car to see that as the goal, not an absolute... So when it hits an incline, it's ok to slow to 60 and it's ok to speed up to 70 on a decline.

Why, because I live in Florida, and the only 'hills' I see are overpasses. on CC, the car revs up the engine to climb one side, then goes into breaking mode on the way down the other side.... If it would just leave the throttle where it is, the car would eventually return to set speed.

What might be a good comprimise is a 'temporary throttle lock' button that I can hit at the start of the hill to let the car know it's not a mountain.
 

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I'm pretty certain the cruise control will apply a small amount of regen above the basic "coasting" you get with the accelerator pedal released.

I've disengaged cruise control while going downhill (without touching the accelerator) and felt the car surge forward, indicating that the CC was in fact retarding it slightly.
 

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KMO said:
I've disengaged cruise control while going downhill (without touching the accelerator) and felt the car surge forward, indicating that the CC was in fact retarding it slightly.

I had found the same to be true.
 

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Melgish, you're dreaming about the next generation... and by then, maybe it will also slow down when it senses cars in front of it slowing down, and will have feedback between the CC and mileage calculation to modify a bit here and there to maximize mileage and it will connect to the NAV system and we'll have autopilot.... :)
 

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When I set CC at 65, I want the car to see that as the goal, not an absolute
Concur. The CC is a bit of a compromise, probably because people's expectations are different. For me, I only use it in flat, boring roads where the CVT works against you in holding a steady speed. On my motorcycle I barely have to look at the speedo, I know by the noise what the engine revs are, and so I know what speed I'm doing. My Prius can make the same noise over an embarassingly large speed range.

The optimum for me would be a 3D geographic database linked to a GPS that KNOWS how high and what grade the hill is, and can set the optimum power setting to arrive at the top of the hill at a speed to best benefit from the regen braking on the other side!

This would not be acceptable to those who expect their machine to go plundering up a hill with the throttle wide open just to maintain an arbitrary speed limit (just horribly wasteful).
 
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