It's hard to tell, but it seems the TCH is better at managing ICE and HV under cruise control than using the accelerator pedal, even when light-footed. There are many variables that are difficult to control, so I could be mistaken, but even adjusting the cruise control speed by + or - seems to do the MPG better than I can.

Any other experiences or insight to this? Thanks.

 

I find the same thing with the Prius. Use cruise control all the time. The only time I can do better than CC is when I do pulse and glide. That will definitely get me better mpg than CC but it takes a lot of work.

 

I find the same to be true. One of the ways I can consistently achieve better than 40 mpg is by using cruise control. I even use it on city streets on occasion. The only time I don't is if the traffic is bumper to bumper or when going up hills.

 

The only downside to CC is that it sometimes kicks in the ICE for no apparent reason. I will be traveling at under 40, on a relatively level road, and the ICE kicks in. Here's a technique I've come up with that counters that problem: In one motion pull back on the cruise control lever (to cancel CC) followed by immediately pushing the CC lever down (to engage it). When you cancel the CC, the TCH foes into "neutral" and battery kicks in. When you re-engage the CC, the battery provides the acceleration to maintain speed.

 

I was never a fan of using cruise control in my previous car except for very long trips...but with my TCH, I find I do use it a lot more often and it does seem to improve FE...which really does make sense. I just wish my commute to/from work wasn't such bumper to bumper so I could use cruise control more often.

 

On relatively flat terrain, the cruise control maintains the car's speed pretty constant, without overshooting or undershooting the set speed. Under these circumstances, you are probably achieving optimal FE. Under manual accelerator control, the car's speed tends to drift up and down. Each time the car's speed changes [either up (accelerating) or down (decelerating)] there's energy flow taking place [either from the ICE/battery or to the battery] because the car's kinetic energy is being increased or decreased (but its potential energy is not changing since its altitude stays approximately constant). Since the ICE's FE drops when the car is accelerating, and since regenerative energy recovery is not 100% efficient, the best general strategy for maximizing FE is to keep the car's speed constant. I think that this may be why you're finding better FE when you use the cruise control.

Stan

 

I have tried the cruise control, and while keeping the speed constant on flat terrain is the most efficient, I have not found that to be the case for hilly terrain. In that terrain, I have found that loosing speed on the up side of the hill and gaining speed on the down hill side is best. Basicly keep the power constant and let the speed be determined by load.

 

ag4ever — I believe you! My comment was strictly about reletively flat terrain, where the cruise control behaves well, and maintains the desired speed well. On rolling hills, however, I find the cruise control's behavior really egregious. The car gains some speed above the set speed on the downhill sections (as expected, but this can be as much as 10 km/h over), but then the controller waits too long (a few seconds too long) when the uphill section begins. The speed drops significantly below the set speed (as much as 15 km/h under). Then it seems to "floor the accelerator" in order to catch up. The car then overshoots the set speed significantly, before finally settling down at the set speed. And this cycle repeats itself on each rolling hill! I've repeatedly found this in my travels. It seems to me that the feedback controller design is dreadfully suboptimal. Perhaps the long delay has to do with the signalling of the car's speed, etc., information to the cruise control ECU on the CAN bus. But the CAN is a speedy bus! Extra delay in the controller loop makes for potential instability, and this behavior verges on instability — the closed-loop system is very underdamped, and close to oscillating. I'm hoping that Toyota has a code update for this when the first firmware revision is released. Has anyone heard about such a release?

Stan

 

I have noticed the exact same thing. By the time I am nearing the top of the hill, I have overshot the set speed by 2-3 mph and on the other side by 5-8 MPH, then at the bottom I am under by 3-4 MPH. Flat land it is great, but that is not a real test of cruise control.

I had to leave work and head back into Houston for some personal business, but on my trip to work this moring I drove without cruise and got about 40 MPG indicated on my nav, on my second drive to work with cruise I got about 37 MPG. The temp in the morning was about 45 and the temp this afternoon was about 65, and all other conditions were fairly similar.

IMPO, the cruise should interact with the hybrid computer more. When the vehicle speed decreases, it must be from an incline, and thus the motors should assist more, and if the speed is increasing, it must be from a decline and the motors should regain some energy to keep the car at target speed. They could easily dampen the power needs of the ICE if they used this form of stratagey and get much better FE since the engine could be left in an efficient burn range and use the motors to adjust power output.

 

SPL I couldn't agree more. I just made a trip from Austin to Dallas over the weekend and was getting fed up with the CC in that it has these wide swings on the rolling hills. Drove me batty so I took it off CC while anywhere around these hills.

The problem is that the drivers behind me wonder what the heck I'm doing; taunting them with the speed fluctuations.

I called the dealer yesterday and the shop foreman hadn't heard of this problem. He said he'll open a problem report with Toyota support but suspected that the support team will need quite a few of these to investigate them and that if they do determine there is a problem, they'll need to reflash ECU to resolve. Looks like we'll be in a wait pattern for a while.