I have read in several posts about light-footed driving to get the best FE, but that is also the best way to minimize the IMA usage -- which is what makes this car a hybrid, and therefore fuel efficient....

It's kind of a catch-22, isn't it?

 

Kinda, but not quite. Keeping a light foot on the throttle (which extends to more advanced technicues such as DWL and DWB) minimizes power demand on the car. This is a good thing even if it means less use of battery power via IMA. The reason: power for the battery is ultimately derived from gasoline through regen (forced or during braking) which involves conversion losses as you go from mechanical to battery and back to the wheels. In other words, you have to pay to re-fill that battery if you drain it!

The main purpose of IMA is to provide supplemental power to a smaller, highly efficient gasoline engine than the standard Civic. Think of it as something to use when you absolutely need it, but don't go out of your way to get into the assist. Not only will your mileage be excellent but you will save wear and tear on the battery with fewer and less severe discharge/recharge cycles.

 

I guess I am still getting used to the concept. It's weird trying to explain the system to a curious inquisitor when I don't have complete buy-in.

I have noticed IMA kicking in more in normal driving, so I am starting to feel it is worth something. Although tonight I noticed in cruise control at 70 mph rpms went up to 4k without IMA kicking in.

I am still learning... that is, the car is still teaching me how to drive.

 

What I have found however is that this does not really limit the IMA usage as much as it seems. Elecrtic assist and gasoline engine power appeared to increase jointly, so accelerating slower, while it engages IMA at a lower power level (only a few "bars"), the accelerating takes longer, so the total amount of battery power used to accelerate to a certain speed tends to be about the same. I climb a fairly steep hill every day to my house (up about 850' ft with stops, then back down 150') and I can climb fast and use lots of bars, or slowly and only a few assist bars, but either way the battery level always drops by the same amount.

If when accelerating you are at an RPM where the IMA is not engaging at all, that probably means you are running below the most efficient engine loading (typically low 2000s RPMs)-- The primary goal of the hybrid system is to allow the engine to run at its most efficient load most of the time, so if you are running below that, it won't offer any assist (doing so would make no sense), and though it may appear worse on the instant MPG, you'd probably be better off accelerating harder -- it will take the same amount of energy to accelerate a car to a given speed, so the goal is to accelerate with the engine in its most efficient RPM/load.

Allowing a car to perform well with a much smaller engine is a major contribution of the hybrid system. The engine's compression ratio and valve timing can also be tuned in such a way that it gains efficiency at the expense of low-end torque. This would comprimise driveability in a normal car, but works great when coupled with an elecrtic motor. Even if you only use that eletric power sparingly, its presence allows you to run a smaller, more efficient engine all the time, so it is still helping--even on flat highway runs. (This is the point critics miss when they claim hybrid systems don't help on the highway)

Another point of note is that the "charge" and "assist" bars are not to scale -- max charging is limited to 50amps, while max assist is 100amps -- judging by the scale it would seem charging far outweight assist but that's not really the case.

 

Thanks, that seems good advice. I recently bought a HCH 2006 (about 1000 miles clocked). I live in Singapore, where we don’t have big and long freeways as much as you do in the US, But even at around 50 mph speeds, I notice that I get a strong engine-brake like effect when I lift my foot off the gas pedal. The effect is much stronger than on conventional cars, e.g. my old 2002 Corolla. This effect tends to dampen the coasting speed, and pretty soon I have to apply foot on the pedal again to accelerate to highway speed, which tends to bring down the mpg, etc.

I understand that this effect is partly or wholly due to the recharging of the battery pack. If so- is the Honda IMA technology over-hyped? "What the Lord giveth the Lord taketh away" so similarly, what the IMA gives to boost acceleration, it takes away due to rapid deceleration (charging)?

Or am I doing something wrong? Please enlighten me. Thanks.

 

The purpose of the hybrid system is to increase gas mileage, which it does admirably, so no it is not overhyped. One thing we learn as we get experience in the HCH is to control the regen (battery charging) by light pressure on the accellerator. If you want to coast without charging the battery, and slowing down the car, it just takes a little light pressure on the gas pedal. When you do this, you will see the instantaneous gas mileage pegged on 100, and no bars of regen showing. It just take a little practice and it becomes second nature.

 

I actually get much better gas mileage using the IMA assist more aggresively but during the proper times in shorter bursts. For instance if I accelerate very slowly from light to light, you stay at low mpg situation, slowly losing charge the entire time. If I pulse aggresively up to say 20 or 30 mph and then pop into 50+ mpg and maintain or glide to the next stop, maximizing regen when it is inevitable that I will have to stop, I can keep a full SOC and average over 50 mpg for the trip, regardless of how many lights we hit. I guess what I am saying is that how long you use assist, or how long you stay below 50 mpg has a much bigger effect than how many bars you use. This also seems to be true for regen as well. Always try to enter regen as early and as agressively as possible when it is enevitable that you will need to stop. This ensures that you don't use the mechanical brakes and lose that energy. I always accelerate going down hill or on the flat for an upcoming hill, as the amperage used is much less with gravity helping you and then ride the momentum up the next hill. It is not uncommon for me to be able to go up most if not all the next hill at 50+ mpg. If I have to accelerate I do it aggresively for a short period and try to glide the rest of the way again. The bottom line is to manage the SOC properly and use the assist to the maximum advantage where it makes sense. All of my best trips end with the SOC at 7 bars or over. If you don't ,manage the SOC the computer will hit you with a big time forced regen penalty that makes it impossible to get anything over 50 unless going downhill while it is active.

 

This is probably my biggest gripe with Honda's design. Their engine actually has the least engine braking of any engine I know of -- the cyclinders completely seal so there is no compression braking, and there are very low friction piston rings as well. Making the charging kick in automatically I believe was done to simulate the feeling of a "normal" car as a marketing decision.

The 2006 model actually has a workaround for this though. Since the car is throttle-by-wire, tapping the gas pedal very lightly will not actually burn any fuel, it will cancel out the unwanted charging, but keep the engine sealed shut (minimal engine braking, no fuel consumption). Though I haven't driven a 2006 HCH, apparently the engine friction is so low, others have said it's like coasting in neutral on a standard vehicle.

There is no explicit indicator light, but the instant mileage gauge should be maxed out at any speed if the valves are shut off. There will still be RPMs showing though as the engine is still spinning, it's just sealed shut.

 

The key to this is understanding that the IMA system is a compromise. It is *not* designed to offer the most efficient use of petrol. It is designed to /improve efficiency without a serious loss of performance/.

If you want to optimise fuel economy you buy a car with the smallest engine possible and you accept that grannies pushing shopping trolley carts are going to be overtaking you.

The energy used by the motor comes from your fuel tank just as much as the energy used by the ICE. The 'only' (and note the quotation marks <g>) thing that the IMA system does which is green is reclaim some of the lost energy.

Worse still IMA cars are wasting energy by lugging a ruddy great battery around with them all the time.

Now don't get me wrong:I love the idea of IMA and if only Honda can get around to shipping some more to the UK I'll be ecstatic to own one. You just have to understand that IMA isn't the most fuel efficient motor vehicle you can buy.

 

In the US, actually, it is. The Honda Insight, an IMA vehicle, is the most fuel efficient car available in the US right now. It also allows the Civic to get almost exactly the same fuel economy as the Prius. Saying 'the only thing green about IMA is recovering lost energy' is kind of silly...of course it's the only thing, but it's HUGE. It takes a giant amount of kinetic energy that would be wasted in a traditional car, turns it into potential energy in the batteries and uses it to power the car back up....it's a fantastic way to decrease fuel consumption. It's an energy recycler, as all hybrids are. How do you think the Prius gets its energy for the batteries? Same thing...but carries more batteries. Though it does it very differently, and is better in stop and go traffic, overall, it gets the same fuel economy as the IMA system, so it's no better for the majority of drivers. Also, the newest IMA system can cut out all fuel consumption in low speed cruising or when going down hills at any speed. This reduces fuel consumption to zero during these stretches, and thus also has zero emissions. No matter how it does it, the IMA system significantly reduces both fuel consumption and emissions, and that's what it's supposed to do.