I have to agree with several of the posts here.

What is the point in having an electric motor, batteries and regen braking if you don't use them?

Taking off from lights you may as well use the available electric power that is stored because you will ultimately recoup the loss at the next set of lights.

If you take off very gently without assist, yes this is very efficient use of the ICE, but why have the electrics at all?

I think that although I have been using very little assist on take off up until now, I will now try a more agressive approach.

 

But that has more to do with marketing and consumer choice than technology. In Europe you can buy cars with 1 litre petrol engines and have been able to for years. Even a twenty year old Mini will get you in excess of 40mpg(US) if well maintained. If you want performance you can go with a Turbo Diesel. The performance of a 2 litre petrol car with fuel consumption of not far off 40mpg(US).

My '02 Civic has a 1.6litre engine. 0-60 of 10 seconds. I don't habitually burn rubber but I don't dawdle around either. I get 34mpg (US) from it. The 1.4litre version will still be a capable little car and will probably be getting over 40mpg(US). Get rid of the turbo and get a smaller engine and you have a perfectly respectable vehicle getting well over 50mpg (US).

Don't get me wrong:I do like the IMA. I think the HCHII is fantastic. OTOH I see it very much as a compromise and I'm buying it more for the CVT than the economy. The regen is a neat idea but not really why I'm buying it.

 

In a very limited situation, I've gotten IMA Assist without using a lot of gas, but it's a very specific situation, and not that practical. Before I describe it, some of you might be familiar with Mike Dabroski's MIMA hack on the Insight (see http://www.99mpg.com/). It overrides Honda's conservative use of the Assist. I have simulated it....

Recently, I have drafted closely with 18-wheelers. On Honda's, if you punch the accelerator, the Assist bar will max out, with only a small drop in the instant mpg bar. I've managed to increase my trip mpg doing this, so I can conclude the electric motor reacts faster than the ICE.

"Punching the accelerator" is from a half to maybe a full second. What makes this impractical is you want to return the throttle to whereever is was before punching it. The acceleration is limited as well.

The thumbnail is it's possible to trick IMA to do short bursts of Assist without corresponding consumption of gas, but it's not easy and in limited situations.

 

I don’t use the light foot when accelerating from a stop unless it’s stop and go traffic, but when I’m up to speed the ‘light foot’ comes in handy, along with a vigilant monitoring of the road. My last tank of gas lasted 513.1 miles at file up netting me 52.8mpg.



I find the design of the IMA system along with the technically advanced combustion engine (i-VTEC) in the 06-Civic pretty cool since it nets me high mpg.



Ref.: Honda’s video about the functionality of their IMA system.

http://world.honda.com/HDTV/news/2005-4050705b/

 

Aussie,

Think of it this way, the car does not break the laws of physics. It will perform the most efficiently when it is operating in its normal power band. When I feel the car struglling, I pulse the speed back up using the assist and then go back into an overdrive siutation on the CVT, which it normally at 1500rpms or below. You don't really even need to look at the mpg meter, as I can guarantee it is probably up over 60 mpg if there is no forced regen and you get into this overdrive situation with low load. Managing SOC and using the assit when needed are the ways to get high mileage on this vehicle. Think about time in a low mileage vs. high mileage scenario as the most important factor, which simply makes sense since the mpg meter is only an instantaneous meter and more time spent above 50 vs. below will generally yield mileage over 50 mpg.

 

Dave.


I just posted a reply to one of your other threads on this matter.

I will now try gently using only the ICE up to about 10kph then using full assist up to desired speed to minimise the time I'm using the ICE...then peg back the FE.

Anyway...it's in the other post. Thanks.

 

Aussie,

The 10 mph figure was just an estimate. The point being to make sure you get the car rolling a bit without nailing the assist as a DC motor will pull infinite amps at a stuck rotor position and will pull the maximum allowed by the IMA system during initial acceleration from a stop. I just find that slowly getting it rolling with the ICE first seems to minimize the impact on the SOC. My SOC takes a big hit if I continuously nail the accelerator from a dead stop. Hope to hear back from you on your experience after testing it for a day or two. Just reset one of your trip meters and give it a try.

 

What you have suggested in your accelerations is typically what I will do, from a rolling start, I will "surge" the accelerator pedal. The CVT downshifting "lags" slightly, so the IMA will kick in a lot of its torque while the transmisssion is momentarily in a higher ratio with a high throttle position. Then, I gradually decrease pedal pressure in order to hold a steady RPM as I gain speed (rather than letting the engine wind way out, which is extremely inefficient). This should be the most efficient way to accelerate, as it has the advantage of reduced engine aspriation losses (moderately high throttle position), without the friction losses and less efficient loading of high RPMs.

This is also the fundamental idea behind pulse and glide, which really has nothing to do (inherenetly) with hybrid drivetrains. The idea is to run the engine in briefl high-output, high-efficiency pulses, store up extra momentum, and coast, rather than maintain speed with a steady, partial throttle position (which causes aspriation losses) that whole time.

Accelerating a lot from a dead stop is what kills my state of charge most -- my battery will get depleted from rolling around in parking lots with lots of stops and speed bumps where my engine never really gets to contribute much.

 

Well...guess what...it works.


Up until now I've been struggling to get better than 5L/100klm (47mpg), for this tank I'm now sitting somewhere between 4.7 and 4.8 (50mpg)!!!!

This really has made a noticeable difference - all members should take note.

You can achieve reasonably good FE with a very light foot, but you can get better using this techique.

On take off allow the ICE to get you rolling then about 1/2 to 2/3 throttle with maybe 5-7 assist bars, getting up to speedly quickly. Not flooring it, just using the assist as it was designed to be used.

It really does make a difference!

Naturally you have to keep an eye on the SOC, and regen where appropriate - which is not hard to do.

It's far more like driving a normal car now, and I get the added bonus of better FE...WOW!

It sort of feels contrary to what you feel you should be doing, but it works.

Thanks all....

 

Thanks Double Trinity for the details, at least that shows I am not crazy. This is my first hybrid, but I am a mechanical engineer and just figuring it out. It drove me a bit crazy at the beginning as I was always getting high mileage with my wife getting terrible mileage. I finally traced it down how she was accelerating from lights while bogging the car down at low rpms. The best part about the solution is to drive the car more normally, which people behind you will appreciate. I also let off the brake a few seconds early to allow the ICE to restart to be ready to accelerate with everyone else.