When I was first trying to understand how a pulley-based CVT (like the ones in our Hondas; unlike the ones in Toyota or Ford, which are planetary eCVTs) worked, the illustration on this page really made it click for me. You can see how a "gear" is really just a certain range of ratios of pulley cone diameters.

 

Nice link. If anything I can see how changing ratios could wear on the pulley but the ratios change constantly so there's no stopping that. But merely driving the engine at 4000 rpm instead of 2600 will do no damage. Hondas are not known for their fragility. And if it were an issue, there would be no S or L settings. The engine spins very fast in both settings regardless of one's speed.

 

My only question would be if keeping the transmission in "S" would keep the CVT from going into a higher range of gear ratio's like an normal transmission does when put into a lower gear?

 

I don't understand how what he is doing is a problem --he's doing exactly what the manual says the "S" mode is meant for -- allowing the engine to rev slightly higher for quicker acceleration. The '03 manual even reccomends it for saving the battery pack in stop-and-go traffic, to prevent an endless cycle of assist and regen. I don't believe the CVT shift-logic software would even allow the driver to damage the transmission by doing something like over-revving it, or putting too much torque on the belts. The different modes are entirely software based.

In my '03 I have used the "S" mode often down long declines to increase the engine braking effect (even regen is not enough to hold speed down in a few steeper sections of my regular drive). Another thing that is interesting is that even in "D", once the battery is full, and you're still coasting down a grade, the transmission will seamlessly "downshift" to mimic the effect of the regen braking, preventing you from suddenly lurching. It shifts gradually as the regen gradually cuts out. This is yet another one of the nice features of having the CVT transmission.

 

All S does as far as the ICE is concerned is it runs the ICE at a higher RPM than it otherwise would. Have you noticed how, in D, you can accelerate while keeping the engine at a steady 2000 rpm, or at 3000 rpm, or 4000, etc.? The engine maintains a constant rotation and the CVT ratio changes to allow the car to accelerate. Well S mode partly just runs the engine at a higher speed, like 4000 rpm all the time, but adjusting the ratio so you can still go any speed you want regardless of engine speed. But it has other effects as well, such as not using assist, and that's why I use it. It's not possible to accelerate well in D without using assist; pressing the gas pedal enough to accelerate automatically engages assist. S is a way around that.

xcel complained that he hadn't really heard of people accelerating onto the highway without assist, and it's because it's basically impossible without a downhill slope (or unless you consider 50 mph "highway speed"). S makes it easy.

 

Hi CGameProgrammer:

___Not a complaint about the HCH-II but a complaint about the way it is driven … There is a distinct difference between the two if there is in fact a way to bring her up without assist.

___The next logical question would be can you use S as an advantage in terms of increasing FE while accelerating to highway cruise? Can you achieve acceleration in the 1,200 - 1,500 RPM range while in S w/out assist would be a good question to have answered next? This sounds like something worth pursuing for those interested in the HCH-II in the not so distance future.

___Good Luck

___Wayne R. Gerdes

 

So let me get this straight. Accelerate in S to get up to highway speed to keep the assist from kicking in. The purpose of this is to keep the IMA systems battery at a "full" charge, instead of driving in D and using assist which causes battery drain. The battery drain will then be replensihed later by driving during regen, all while driving in D. The purpose of Assist is to help the engine and use less fuel. However, regen slows the car down when driving and cause less FE.?! Even so, driving in S without assist, shouldn't the engine use more fuel? Now we are back to square one? This sounds like a visious cycle. However, with more testing between FE when driving in D and driving in S would portary which method is more beneficial.

 

I think you have to find the right balance which depends on your individual driving conditions. If you're going to avoid assist and keep a full charge, only to run soon after into a situation where you're going downhill or having to stop without regen, because the pack is so full it can't take a charge, then you've hurt your FE.

Honda probably tried to find a compromise that optimizes for average driving conditions. It sounds like the individual driver has a way to improve on that optimization by using the S gear judiciously. My guess is that it's best to sustain something like a 90% SOC to leave room for some regen. If you see a 100% charge, it's probably okay to use D and use assist. But, as Wayne would say, I'm speculating.

 

The way the Hondas work, the assist only helps FE because it uses energy regained through decelerating, rather than wasting that energy. But when the regeneration happens while the car is driving, actually forcing the engine to generate that electricity, then yes, it reduces FE. Basically this only matters when doing long highway drives -- during short highway drives or driving anywhere else, it's best to stay in D. I just did a highway drive without using this trick and the battery was at four bars... I ended up getting 32 mpg. It was fairly uphill but I usually get 37-38 mpg at least... but this time I couldn't keep a light foot on the gas pedal since that made regeneration turn on and slow me down alot. The only way to maintain my speed (75 mph) was with a slightly heavier foot and I was doing exactly 32 mpg during this. That's bad.

 

This is good speculation. Usually when I start out in the morning, I have close to 90% SOC by the time i hit the highway onramp. At this time, it's fine to use D and assist to get up to highway speed, as long as I don't drop the SOC to the point where forced regen starts.

However, if the SOC is at midrange, at say, 4 bars, S sounds like a good idea because then I will not use assist that will put me in forced regen later on, hurting my FE. It also makes sense to use S up long hills as well, as many people will note when driving up long hills - when the battery charge depletes, and forced regen kicks in, you slow down greatly and have to rev higher. But if you use S to get uphill, and you drain less of the battery, you will not need to slow down later on because of regen. It can be a fine line. I have a couple long hills to test this on later this week (D or S up hill better mileage up and down)