CVT and coasting

[HCH2007]

Is there any detriment to the CVT by coasting to a stop or down a hill in neutral to gain MPG and reduce charging while braking, In the case of coasting in neutral down a hill and going back to drive when speed drops to the speed I was at before the coast can this hurt the transmission?

[msantos]

No significant functional harm worth noting if you do. However that approach is very far from optimal.

Ideally, you'll want to induce a soft-glide in that you control the accelerator pedal so that the ICE is OFF and you have no regen and no assist showing. The expert alternative to this is to induce a FAS but I suggest you master the first approach since it is built-in for exactly this purpose in and unlike a FAS it has no long term detriments. With practice it works very, very well.

If you coast the vehicle in N while not in a FAS pattern then you are actually burning fuel since that prevents the cylinder de-activation from taking place. I wholeheartedly recommend against doing so in a late gen IMA platform.

Cheers;

MSantos

[Kacey Green]

everything Manuel said there, if the key isn't off coast in gear using soft-glides

[HCH2007]

Originally Posted by msantos

No significant functional harm worth noting if you do. However that approach is very far from optimal.

Ideally, you'll want to induce a soft-glide in that you control the accelerator pedal so that the ICE is OFF and you have no regen and no assist showing. The expert alternative to this is to induce a FAS but I suggest you master the first approach since it is built-in for exactly this purpose in and unlike a FAS it has no long term detriments. With practice it works very, very well.

If you coast the vehicle in N while not in a FAS pattern then you are actually burning fuel since that prevents the cylinder de-activation from taking place. I wholeheartedly recommend against doing so in a late gen IMA platform.

Cheers;

MSantos

Not sure if I understand soft glide, I am totally new to hypermiling. I thought just gliding to a stop would burn more fuel than shifting to neutral and coasting to the stop and doesn't the transmission cause a braking effect on the vehicle? My vehicle does not FAS until I am almost at a complete stop, so I am not sure what I may be doing wrong or what it is I am not understanding. I really want to learn as much as I can as quickly as I can, fuel cost is ridiculous and the dependence on mid-eastern or any other oil for that matter is not a user friendly option. Is there a way to induce FAS without shutting of the ignition and losing all power assist? Any help or direction is very much appreciated, thank you.

[Right Lane Cruiser]

Welcome to the community, HCH2007! Have you read the article by Tarabell linked on the front page? Here's the link if you have not:

Adapting Basic Hypermiling Techniques to the HCH-II

In that document she calls "soft glide" simply "Glide" and you can find a description of both the mode and how to engage it in Section II. Essentially, if you back off the pedal enough to induce some regen the engine will go into deceleration fuel cut mode and use no fuel. If you apply enough pedal pressure to just cancel out the regen bars the engine will go into a special valve configuration to minimize pumping losses and will continue to burn zero fuel. In this mode the car will roll with very little drivetrain drag -- very much like a FAS with the transmission in neutral but without touching the key and instant power up with application of the accelerator.

This is also how you get to the limited EV mode of the HCH-II -- it will engage with gentle pressure on the accelerator and will continue as long as the battery state of charge and power demands allow... but we don't recommend that mode unless you have a big payoff (such as using it for a slight nudge over a hill to get to a nice long downhill where you can grab some regen to keep the battery state of charge up) because the battery pack is small and EV mode in the HCH-II is inefficient due to having to turn the engine as well as propel the vehicle. This mode can't be used to start the car rolling from a stop (though if you are on a downhill you could probably use it to accelerate after gravity gets the car rolling).

Once you learn to induce a soft glide you'll find that you'll know where to park your foot on the accelerator pedal to get it to engage with minimal regen. I found that there would always be a blip of regen but if I got the right spot I could hold steady through that regen and it would disappear... leaving me in a soft glide.

Good luck, happy browsing, and good fortune in your hypermiling efforts! You've got a fantastic vehicle to work with.

[msantos]

Hi HCH2007;

While I would not call this "soft-gliding" a hypermiling technique I would consider it to be a very good feature to use while hypermiling.
One of the main reasons while I suggest we master this feature first is because it always takes some practice to get it just right... and its perfectly applicable to a good number of other hybrid vehicles, including the Prius. In other words, learn it once and use it often type of thing.

Sure, many Prius owners still prefer to induce a glide by placing the "transmission" in N and provided that the ICE is already off (via similar footwork) then a glide pattern is easily produced.
I prefer doing the complete accelerator footwork instead because that is a very seamless thing to do and also leverages a valuable software feature already built into these cars (hence the "soft" in soft-glide).

Unlike the Prius and other hybrids however, you do not want place the car into N to glide unless under very rare situations since the ICE in a CVT equipped IMA will always idle away when in Neutral.

Sean's explanation and suggestions are spot on.

Cheers;


MSantos

[HCH2007]

Sean & MSantos, Thank you so much for the valuable infomation as we have seen I need all the help I can get.

[HCH2007]

I had one other thought and was reminded after reading parts of Tarabell's article. If one were to add a second or even a third battery pack in parallel with the existing pack, could we not utilize the EV mode even more especially in city driving thereby increasing our FE 2 to 3 times what it is now? If this would work and one were to keep a vehicle for an extended length of time it would pay for the additional battery pack(s), especially for someone who can build the pack for themselves and save even more money.

[pasadena_commut]

Originally Posted by HCH2007

If one were to add a second or even a third battery pack in parallel with the existing pack, could we not utilize the EV mode even more especially in city driving thereby increasing our FE 2 to 3 times what it is now?

I don't think so. The electric motor in the HCH is too small to use alone, so the extra battery capacity isn't going to let you go fully electric. Plus the extra weight. Plus there are losses in the electric system. My gut feeling is that it would be at best neutral for FE, especially since on my car at least the battery is never fully discharged and rarely at full charge.

A better question would be, what kind of FE does an HCH get if the big battery is disabled? Of course it will depend on driving patterns, but I'm betting the difference wouldn't be more than 25%. That is, most of the FE is from the tiny motor, and the Hybrid part mostly masks the poor acceleration that would result from the small motor alone.

[Right Lane Cruiser]

If the HCH-II is like the first gen Insight you might get a small bump by making the additional battery keep the SoC high in the stock battery -- the Insight doesn't like to have the SoC too high and will actually add some background assist you can't see on the dash gauge until the SoC drops down to where the computers prefer to see it.

Beyond that we are just talking about extra weight in the car unless you can manage to get the car to either see the entire capacity of the batteries (very difficult and would require hardware hacking) or you can manage to balance the drain rate of EV mode with charging rate from the additional batteries (still difficult but easier). The Prius can get away with additional capacity via an add-on kit like the second scenario (such as Enginer) but the system is finicky at best.

It is a fun idea but I don't believe it is practical without more control of the hybrid functionality... which I don't think you are going to be able to gain. This is quite aside from the lack of space for extra batteries, too.