Wishing For A Smarter Cruise Control

[Smooth Operator]

Here are a couple of thoughts for improvements to the CC.

First, let the driver enter a minimum and maximum speed rather than a single speed. I think this would result in a more fuel efficient cruise control.

Currently the user enters a specific speed. Let's say 80 km per hour. If the speed drops to 79 km/h, power (likely the ICE) kicks in. If the speed picks up to 81 regen kicks in.

I rarely need to go at a precise speed. Somewhere between 78-83 km/h would probably be fine for me. Let the ICE kick in only when I drop down to 78 and not push me into regen until I get up to 83. And if I am between 78 and 83, the CC should let me deadband.

Second, shouldn't CC be smarter in terms of lowering my speed? My commute takes me from sea level to about 350 meters and back to sea level. It is pretty hilly. Cruise control is good about keeping my speed up on the uphills, but poor at keeping my speed down on the downhills.

Shouldn't it be easy for CC to kick in regen to slow my speed when I am going down hill?

It seems to me that both of these would be improvements to the cruise control and from my naive perspective would be only software fixes.

[tmorrowus]

I think those two features are implementable in software as you suggested, and would be useful to many people.

I'll play devil's advocate though... Toyota has to design a car that appeals to as many people as possible, and I'm sure that if they had a cruise control that drifted speed up and down they would get lots of people complaining or bringing their cars in for service, even if the customer themselves set the speed range. And there is a small but perhaps significant safety factor that comes from having the cruise control speed be completely predicable (e.g. constant). If the car started going faster when there was a tailwind and slower in a headwind that could potentially cause people who follow too close to get in accidents. Of course they shouldn't be in cruise control if they are following close but people do stupid things and it's nice when automation prevents stupid people from crashing into me.

Regen is the same thing... people just aren't used to cruise control doing braking for them, whether that braking is accomplished with regen or actual brake pads. It could lull some people into a false sense of security if their cruise control vehicles did regen braking on downhills, but when the downhill got steep enough that regen braking wasn't enough started speeding up.

I would like to see the "min/max" cruise feature myself.

[wrprice]

I don't think it would be that useful without some additional sensors and computing power.

We, as drivers, have the wonderful gift of being able to look down the road ahead and know whether we'll be going up or down a hill in the near future. That little bit of knowledge is very important and something we often take for granted. Let's say you set a minimum speed of 65 and a maximum speed of 75 in a 70mph zone thinking that you could slow down to 65 going up a hill and speed up to 75 when going down it.

This is easy to do as a driver, but the Prius needs more information. It could get it if it had a pair of range detectors that could tell if the road was slanting up or down at some distance X in front of the vehicle ... but that would also preclude having another vehicle in front of you to mess up the readings.

So, let's consider what the Prius could do with the information it has now... speed, torque/load on the wheels, etc.

It would know, after the fact, that it went down a hill when its speed increased without it applying additional power to the wheels -- so increasing to the maximum set speed is easy. If you were to come to a hill next, you'd slow down and the Prius would notice -- not wanting to apply more power until you were near the minimum speed. But what if there wasn't a hill after the initial descent? You'd continue across "level" ground at 75mph -- 5mph above the speed limit where, arguably, you might be ticketed.

Next, consider the opposite situation. You're climbing a hill and the Prius knows this because it has to apply more power to maintain the minimum speed of 65 mph. If you reach a downward slope, the Prius could regain 70 or 75mph. If you reached a plateau, however, the Prius would merely maintain 65mph as a minimum speed... and those SUVs you passed going up the hill will now find you as an annoying "slow" obstacle once they want to resume 70mph or more.

Furthermore, it's rare that you actually have a perfectly level stretch of road. That means the Prius would be speeding up or slowing down to one of the two endpoints of the set cruise range and then stay there for the majority of the time.

All in all, you'd spend very little time in the intermediate range and most of your time at one of the two values you programmed as the minimum and maximum. Sure, the Prius could try to get "smart" and guess when so little power is required to maintain speed that it aims for somewhere in the middle of the range...

... but when it comes down to it, you might as well have set a single speed target -- as we do now -- and not worry about the fluctuations up and down the hills. The cruise control we have now is easier for the user, a simpler system to design and implement, and it does what's optimal except in hilly areas.

Lastly... for the wish that it would limit your speed going down a hill... I imagine it's more efficient to pick up speed and let it bleed off at the bottom of the hill as the terrain levels or begins to rise than it is to inefficiently regenerate to hold a constant downhill speed and then use more energy quicker to maintain or increase speed at the same point that the road levels or rises again. In a way, it's *kinda* doing what you were talking about -- but consider the speed you set as the "minimum" with a top limit of 100mph that's only reached on a steep descent.

[tmorrowus]

wrprice, you raise a good point that the driver can maximize efficiency better because they know and/or see the upcoming topography. Those of us with the Nav system have always thought the hybrid system should take advantage of topo data that could be encoded on the DVD. I'm sure future models will do that.

But I do think the min/max cruise control would be better for efficiency in most situations. In flat nonwindy situations (easily detectable) it would revert to the average (middle) speed. When drag increases it could let the speed go down as much as to the min. When drag decreases it could let speed go up as much as to the max. This would go a long way towards smoothing out power usage, even though it can't do anticipatory throttling.

On the other hand, there seems to be some evidence that hybrids benefit from spiky power demands, where lots of power is requested for a short period and then less power is needed as the momentum is used to keept the car in motion. Many folks report better mileage in hills because of this effect: the engine is more efficient producing lots of power up the hills, and the momentum downhill is essentially a form of energy storage that is more efficient than the generator->battery->motor hybrid storage mechanism that loses much power due to heating.

So maybe it wouldn't even help at all.

[jfschultz]

First, let the driver enter a minimum and maximum speed rather than a single speed. I think this would result in a more fuel efficient cruise control.

This would probably be a problem to implement in a way that a driver can easily handle. Probably a better approach would be to use the MFD to set the amount that the speed can vary. This would allow the driver to set a speed just as is done now to be used as the middle of the speed variation range.

(One point of general improvement would be to make better use of the MFD to handle the various option settings rather that use "magic' button pushes.)

[Marlin]

It seems to me that all it would have to do is limit the acceleration it will use until the minimum speed is reached.

So lets say you enter a target speed, just like you do now, and the cruise control automatically sets the minimum speed to be 5 mph less.

As the speed begins to drop from the target speed, the car begins to accelerate. It could ramp the acceleration so that the further you get below the target speed, the more acceleration it provides. If the speed falls more than 5 mph below the target speed, then it behaves as it currently does.

It kind of does this now, but the ramp is too quick. If you drop just 1 mph below the target, the car is quite willing to floor the gas pedal to get back to the target speed.

[prius04]

A guy at work has a Lexus with a radar augmented CC. It really only works on the highway as the radar keeps his car a set distance from the car ahead. And if his CC is set higher than the car in front is going, then his car will go the slower speed until the car in front speeds up. Then his car will speed up at least to what he had the CC set at originally.

But looking down the road anticipating hills and stop signs would be a lot more complex. But rest assured, they are working on it. Eventually, there will be some very complex artificial intelligence going on.

But the point on having a "range" built in NOW seems to make sense and seems to be doable now, with no need for AI.

Some points for SO.

[DanMan32]

To answer the 2nd half of the original post,

I believe all CC is doing is emulating the accelerator pedal, as any conventional CC would do. Since letting completely go of the pedal would only induce simulated drag, that's all CC can get to slow down. Regen beyond simulated drag deceleration has to be commanded from the Skid ECU, even if it is the HV ECU that actually does the regen.

[Tyeise]

I'm not sure if this is the thread to as my question, or not. If not, please bear with me.

I've had Hondas the past few years, and the cruise control on their cars are fairly sensitive to the brake pedal. I can "turn off" the cruise just by touching the brake so lightly that the speed is not noticably changed. On the Prius, however, I have to really push on the brake pedal in order to disengage cruise (and even then it seems to be resisting the change in speed.) Which is normal? Is there any way to adjust the setting at which the brake disengages?

[Ron Dupuy]

I would really like to see a downhill limit. Both my F150 and AT Ram 2500 check the downhill speed. Once again today I found myself at 80 MPH when set at 65. I'm afraid I'll pick up a ticket accidentally.