I live in Albuquerque NM where the daytime temps reach into the mid-90s in mid-June and where the terrain features a constant and gradual slope from the Sandia Mountains and the valley (12 miles to the west). The altitude ranges from about 5,000 ft to 6,000 ft above sea level. The high altitude, high afternoon temps and steady sloping terrain conspires to kill the average MPG. I consider myself fortunate to achieve a year-round average 47.1 MPG.

During my daily commute, I cruise down the slope almost 14 miles to my workplace in the valley and my HCH II will average at least 75 MPG on that downhill leg of my commute. The morning temps average from 60 - 66 degrees farenheit, which is a nice operating temp for the IMA system. The return commute back home is the opposite in most regards. The drive involves a constant rise in altitude of about 900 feet between my workplace in the valley abd my home in the Sandia foothills. This constant though gradual climb results in a constant use of the IMA and the drain of the battery SOC. And the average afternoon temps reach up to the mid-90s, which accelerates the rate of drain of the battery. It is not unusual for the SOC meter to drop from full or near charge down to the zero bars by the end of the commute home.

Just recently I tried selecting the "S" mode on the CVT just for the drive home (uphill > 14 miles). In the S transmission mode the battery SOC does not drop much at all, leaving at least 4 - 5 bars on the SOC meter when I get home. Furthermore, the AC cools the interior better in the "S" tranny mode presumably due to the higher engine RPM as compared to the AC performance in the normal "D" mode and lower average engine RPM.

So I am wondering whether it is better for me to use "S" mode when driving uphill over a prolonged distance and when running the AC at higher outside ambient temps. Will following this practice prolong the battery life versus driving the car with the CVT in "D" mode and the daily full drain on the battery? I realize this practice results in higher fuel consumption, which I estimate to be about 5% or 2 - 3 MPG.

Please share you thoughts about this practice, and let me know how your driving environment compares with the driving environment I live with here in Albuquerque.

Thanks! Stu

 

Hi Stu;

Good thing you noticed the behavior and characteristics of the "S" mode. Many of us hypermiling the HCH-2 utilize the S mode in a variety of occasions all the while being aware of the FE penalty that it imposes.

For instance, when climbing a hill the "S" mode is the next trick after we bleed enough speed in our DWL. We do this carefully since we do not want to hit the pack.

We also put the transmission in S when accelerating from a stop at a faster rate of speed without hitting the pack either. Depending on the traffic conditions accelerating with no assist in D can be an unbearable challenge for the motorists behind us. So placing into in S until we reach 40km/h or 25 miles per hour is a good option. Why 25 miles per hour? Because the assist affinity is reduced by 50% beyond that speed marker and that makes it easier to build up speed with no assist in D.

Running the vehicle in S for extended periods of time may be a worthwhile compromise but only in very unique circumstances. I just don't know if doing it for the AC alone is worth it from an FE perspective. Instead, I would resort to a few well known strategies for managing SoC and then sustaining the AC in electric only mode for as long as possible.

The S mode is also very useful for the northern folks particularly when braking regen is hard to come by in very cold temperatures.

Cheers;

MSantos

 

That's an interesting technique. I find that my HCH likes to blow it's juice over the first set of foothills and then maintains SoC pretty well after that in the mountains--provided it has a chance to recharge. That doesn't do you much good though if you live on the foothills though...

I think arriving at home with a 5+ bar pack would be a very good thing because it would allow you to start your glide right away the next morning. That 2-3mpg that "S" costs you on the way home might be made up on the way to work tomorrow if you can glide the whole way--especially if you have some slow speed roads before you hit the highway.

Is your SoC full when you get to work? If not, maybe use regen braking a little more on the way down so you've got a little extra stored for the way home.

The other thing is: do you NEED AC? I used to use it all the time, but I don't touch it anymore on the HCH. We're lucky that we only have a few days in the mid 90s here, but since we're a dry climate, I can get by with just the windows even then.

Edit: How much do you glide on your way down? You have a 14 mile downhill and are getting in the neighborhood of 75mpg? I think you could be hitting a lot higher numbers on your way down.

 

If you aren't using the assist, you aren't pushing hard enough. I get perfectly acceptable (if not blistering) acceleration if I use enough throttle. I typically go for full assist for a few seconds and then back off a bit. The IMA helps the ICE spin up also.

If folks avoid using the IMA, what is the point of the system at all?

As for the OT, remember, you don't get something for nothing. More "S" means less mpg. It keeps the revs up, which gives more ICE power leading to less batter assist use.

 

The assist component is just one of the drains in the overall IMA architecture which for many seeking higher FE and lowest emissions also remains the most manageable. Whatever energy ends-up in the battery pack is the result of regenerative processes that are implicitly lossy even in a contemporary hybrid like the HCH or Prius.

Besides, even though today's high FE hybrids have advantages over regular cars when it comes to energy recovery during deceleration, the energy stored in the pack is used by more systems than the assist component... and along with the fact that only a small fraction of the stored energy is actually usable that makes this energy very expensive in the big scheme of things.

Now, that "energy" in the battery pack becomes even MORE expensive if you have to undergo a forced regen on a regular basis. As many of us have proven over the years, managing the pack through low assist in order to avoid a forced regen is mandatory if the goal is higher fuel economy.

Again, the best and easiest way to do so is to avoid assist as much as possible and leave that energy in the pack to feed the other systems that depend on it. This is the optimal use of the IMA architecture needed to unlock its true potential.

Sure.

Everyone is aware of the lower FE from accelerating in S and no assist compared to D with no assist. But what we are telling you is that using the S under these conditions is still more fuel efficient than keeping it in D with moderate levels of assist. Again, assist is very expensive and the energy it consumes is only a fraction of the energy that was originally sent to the pack.

To recap, the penalty for depleting the SoC is much, much higher than the cost of using the S mode in the conditions mentioned above.

Cheers;

MSantos

 

I guess that's a matter of taste. In my case, I consider the the potential to have the ability to drive normally and get decent performance without having to constantly manipulate something for an extra 5% FE/mpg. My biggest enjoyment from the hybrid idea, no matter its form, is capturing previously wasted energy.

I am no newbie to hybrids and driving for efficiency. I previously drove an Insight for a year, over 16K miles with an average of 72.3 mpg. Because I live in a hilly area, those numbers are even more impressive. It was a 5sp, so no "S" or "D" choice, and I used the IMA whenever needed.

 

Nope. Hardly a matter of taste for many of us at CleanMPG.

Minimizing assist for the pursuit of higher fuel economy is neither a fallacy nor is it a matter of getting just 5% improvements as you claim. You'd be closer to the truth if you had stated 25% improvement or more. And yes, many of our top scoring members have 5 speed Insights and their results are a testament to these principles.

I'll tell you what: Why don't you drop by CleanMPG and let's have a good conversation on this topic there?
I promise you that what you'll see and hear is a little more science and collective experience than the "taste" you refer to.

Cheers;

MSantos

 

Manuel, thank you for sharing and explaining the advantages of the "S" mode. I've been curious of how to take my FE driving to the next level and this may be it, for now.

When approaching a hill, though, is it okay to go from "D" to "S"? Or do you need to come to a complete stop and then go to "S"? The reason I ask is because I tried using the "S" to go up a rather steep incline, yesterday, and it still wanted to use 4-5 bars of assist, like the "D" mode wanted to.

Thanks

 

Jess, as you know there's no such thing as a free meal, particularly when tackling a steep incline. In such scenarios you will definitely give up some assist and more so if there's a minimum speed that you must adhere to.

With that said, small hills should be tackled with DWL... and especially when the speed is bleeding at a faster rate in "D" it makes sense to switch to "S" at some point to add some load to the engine. We do this with the intent of minimizing the assist on the last stretch of the hill - just enough to get you over the top. Again we do this strategically primarily to fit the circumstances.

The object of the "game" is to minimize assist and not necessarily to eliminate it because unlike the Toyota Prius, Honda hybrids which have only one MG, cannot Regen and Assist at the same time.

Yes, you can switch from "D" to "S" without stopping, but you should avoid that transition too early and at higher speeds since the RPM's will be higher and a higher rpm regime will always be thirstier.

If you have a Scangauge you can certainly tell when the optimal engine load in either "D" or "S" is doing its job. An LOD reading of 50 or higher is a pretty good indicator that the load is not only effective at lowest FE consumption rate possible but if you also see no assist you are actually placing a hidden charge into the battery.


Cheers;

MSantos

 

I think I can relate to holicow on this. Hybrids will save people fuel without the need for recruitment into obsessive behaviour, and for many this is enough. My fuel tracking shows that I'm aligned with the official EPA rating, and that is chiefly with city driving, normal climate control, and being conscientious about safety and motor traffic law. I don't want my drive to be off-putting to myself or my passengers, making them suffer indignities like a sweltering and harsh ride and a jerky power-and-glide cycle.

It isn't wrong that I should call it an obsession. The car has everything one needs for fuel economy already automated, but the "hypermiler" chooses to subvert all that in favour of controlling everything themselves. The more practised they are, the less it seems like an obsession. Then it becomes a mental illness, losing some perspective on things. It makes for good news copy (superficial validation), but personally CleanMPG is not something with which I want to be associated.