I think I've just figured out why I get better gas mileage with the cruise control: everything here points to the TCH cruise control being programmed for a robo-pulse-and-glide: hit a hill, slow down(glide), then get the car to over your average speed (pulse) and then glide again. Interesting. I'll have to watch the speed tolarance of the TCH CC. It would seem having an 'Eco' like mode on the CC could alleviate this problem: user selects 'spot-on' mode, or 'eco' mode. Hmmm...

 

Sure sounds to me like 2 different cruise control modes. How do I get my "Precision Speed" CC mode switched to "High FE" CC mode? I think it would be great to be able to switch between the two. I suspect this is why so many have claimed to get better FE with CC than without, while I have little problem doing better with my foot.

-- Alan

 

Or it could be that the TCH just doesn't have enough 'get up and go' to make it up a hill without losing speed. I'm just not sure Toyota would intentionally build an 'Eco' mode into the CC, IMO.

 

On the steepest section of I-17 from Phoenix to Flagstaff, where the freeway speed limit drops from 75 to 65 MPH and an extra right slow vehicle lane is added, I checked my TCH abilities. From 65 MPH I punched it and got to 85 in very short order before I backed off. My Lexus GS had little additional punch (but a much higher top end!!!!) over this slightly heavier TCH. I've never seen the TCH loose speed with the CC due to the incline, and I do plenty of mountain driving, often with the cruise on.

I'm guessing there are two modes on the CC and I'm hoping the switch is easily user accessible! I would love to be able to put the CC in high-FE mode!

-- Alan

 

I don't doubt the TCH's ability to accelerate uphill. I was able to test that merging onto the freeway going uphill. It's good to know you aren't having the CC problem on an incline. As previously mentioned that was a concern of mine. Hopefully my TCH won't have that problem.

I still don't think there are two CC modes. I've glanced through the user manual (PDF format) and I don't recall any mention of two different CC modes. That would be a cool feature though...

 

As I posted in the thread "Cruise control vs. my foot" (Posts #6 & 8), I believe that the TCH cruise control is working as designed. For your information, my TCH VIN is 9487 made in Japan, but I'd guess that we all have the same cruise control firmware version. The controller algorithm seems to me improperly designed. The slow speed pickup is, I believe, intentional in order to achieve better FE. But, the ECU waits far too long before starting to apply power to maintain speed on the icline portion of rolling hills. This is why the car falls so far below the set speed when the incline starts. The small speed variations per se don't worry me — what concerns me is the fact that the car has to apply full power in order to catch up after it realizes (too late) that its speed has dropped too far. This significant time delay (seconds) inside a feedback control loop is a potential cause of instability. I don't understand the reason for this long delay. Granted, the TCH has to coordinate power delivery from two sources, the ICE and the MGs/battery, but this delay is just too long. That's why I said that I hoped Toyota would bring out revised firmware for the cruise control. I did report this to my dealer many months ago, but didn't register a formal complaint.

A story may be in order. Shortly after I bought my previous 1993 Camry LE V6, I hit an invisible patch of "black ice" at speed (~120 km/h) on the highway at night, with the cruise control on. The front wheels started slipping, the cruise control removed all power from the ICE, the front wheels gripped again, the cruise control applied full ICE power, and the cycle repeated. The car was lurching violently forwards and backwards as the accelerator went from full "up" to full "down" repeatedly. This was alarming to say the least. Fortunately, I quickly realized what was going on and switched off the cruise control. It didn't disable itself, even though a full-scale oscillation was occurring. A good controller design should have detected the start of the instability and disabled the cruise control itself. A driver who didn't realize the cause of the car's behavior could easily have had a serious accident. What the TCH's cruise control does on rolling hills is close to instability, and I think that the cause is the time delay inside the control loop.

I'll have a few more comments shortly, but I have to run now!

Stan

 

Big-Foot — The Hybrid Vehicle Control ECU performs the cruise control function. The stop light switch is a double switch for safety — one normally-open contact closes while another normally-closed contact opens when the brake pedal is depressed. These two signals go to the ECU, which then cancels the cruise control, and can detect whether there's a problem with either switch, and if so record a trouble code. The normally-open switch contact illuminates the stop lights. Perhaps the sequencing of your two switches is wrong, or the stop light switch's position relative to the brake pedal needs adjusting. See the attached pages CC-27to29, BR-18to20, and BR-74to75 from the Repair Manual for more information.

tnsig — The Continuously Variable Transmission (CVT) can vary its effective "gear ratio" continuously, through the agency of MG1. Hence it can and does indeed "downshift" to maintain speed on an incline. As you say charlesc, the TCH uses multiple power sources (gas and electric) together with the CVT to maximize FE when negotiating hills and dales. mikieboyblue, the problem is in the controller algorithm design, I believe. No, you can't change the cruise control's settings.

Stan

 

Toyota....write a new algorithm...!!

Boy it would be fun to hack your ECU....lol

 

Well I took my TCH for an extented test drive today before purchasing and I had no problems with the CC. At most I lost 1MPH. This weekend I will probably take it on a longer drive that has steeper inclines to see how it does