Honda Insight Forum banner

1 - 13 of 13 Posts

·
Premium Member
Joined
·
278 Posts
Discussion Starter #1
Taking your foot off the gas, what speed can you maintain on full assist alone? Eg can full assist maintain (if briefly) a 60mph cruise? Or even 70mph?

Trying to work out what proportion of highway driving could conceivably be provided within the 10kW electrical limit. I'm guessing quite a lot.... :wink:
 

·
Premium Member
Joined
·
4,389 Posts
Clett
What you are asking is not possible. If your foot is not on the gas, and you are going 60mph, the engine will slow you down, and although the electric drive can probably keep the speed and rpm up, it is working real hard to back drive the engine that wants to be running at idle.
If the car speed with the ICE idling, is the speed you are going.(second at ~20mph), then the joystick can control the speed both faster and slower, but becomes increasing less efficient the further you pull the ICE rpm away from the idle rpm.
We call this the prius stelth mode imulator . It is fun to do, but not that efficient as the load on the electric increases as you pull the rpm up with the IMA. Another case of you really have to try it out to get a feel for it.
 

·
Premium Member
Joined
·
2,897 Posts
MIMA

The Biggest problem aside from the fact that factory battery will be used up in probably a few seconds doing a full assist at those speeds .... putting that aside the biggest problem is that the engine itself will brake the car if you take your foot off the gas....

Even in 5th gear the engine will brake the car at just about anything above 40MPH ... and the faster you go the more braking action the engine will do.

10 KW of the motor on it's own would porobably be able to maintain the 60 to 70 MPH speeds for however breefly the ~500 Watts of usable power from the battery pack will last..... It is the braking action of the motor that will be the kicker and will probably not let you maintain those speeds....

But I do not have a MIMA yet ... so this would probably be best answered by sompeone with MIMA already who could try it.

But this would be very silly... and not the best use of MIMA.

My 2 bits
 

·
Premium Member
Joined
·
278 Posts
Discussion Starter #4
Hmm... was worried that might be the case. I suppose the other way of looking at it is how much does the instant mpg go up when under full assist compared to no assist at 60mph or 70mph? Does the display even tell you?

Thinking along these lines to try to estimate likely mpgs for a future plug-in charged electric-assist version of MIMA (sorry, I realise it's a long way down the line at the moment, but I can't resist thinking about it!)

I had been guessing that if the electric-motor could provide all of the motive power to push the vehicle at 60mph, then the gas use in that situation would only arise from keeping the revs up on the engine. If the gas use for that purpose was only 6-7% of pushing the car at 60mph, then 1,000 mpg highway should be possible under electric assist!

However, given what you're saying regarding the amount of engine braking experienced at these speeds, it's likely that most of the energy in the gas is going towards keeping the engine turning (ie a lot more than 6-7%!). This in mind, I think my first estimates may have been somewhat optimistic! :wink: But 200 mpg+ should still be entirely achievable.
 

·
Premium Member
Joined
·
278 Posts
Discussion Starter #6
Ah, with MIMA yes. I would agree that those figures (85-100mpg) are realistic, and that MIMA itself is a great step-forward over stock.

However I was talking about things to happen a good bit further in the future - using plug-in charging of additional batteries, with most of the energy coming from these and not from the gas (the whole electric-assist thing that was discussed briefly in the long thread?).

The logic behind the question was that I wanted to establish what the ceiling of possible mpg could be for a plug-in charged extra-capacity MIMA Insight, (not MIMA alone) given a notional limit of 10kW for propulsion. The only way of estimating that is to have direct control of assist, thereby determining the proportion between gas and electric use at different speeds. This is something that MIMA has only just made possible - hence my interest in the experiments.

Sorry if I'm jumping the gun again. I'm a big fan of the potential of plug-in hybrids and can't help my mind wandering to how good the Insight could be in this respect, especially given how rapid progress has been with MIMA and how close things now are to one of the first PHEVs....

Should let you get some rest before pestering you with ideas for new projects though! :roll:
 

·
Registered
Joined
·
1,819 Posts
Clett, I think you really should have bought a Prius :)

One consequence of Honda's basic design strategy is that you just aren't ever going to be able to run efficiently on electric alone, because the electric motor is bolted to the IC engine's crankshaft and is always turning the engine. If the engine isn't firing, the motor still has to do the work of overcoming the engine friction & compression.

It's a trade-off: on the upside, you avoid all the extra weight & cost of the Prius' planetary drive interconnect, plus you still get to have a manual transmission, so driving it can be fun :)
 

·
Premium Member
Joined
·
634 Posts
I think MIMA would be very efficient on both city and freeway driving, the efficiency would come from is, not having to take your foot off the gas, you could be in leanburn most of the time, every time you take your foot off the gas you lose momentum as well as the engine being used as a brake.

If you were driving up a midsize hill, and you were keeping the FCD at 125 mph, you would use assist to keep your speed, and keep the FCD at 125, you will use some of the battery charge, but on the way down you don't have to take your foot off the gas, you just keep it at 125 and the battery will charge real quick.
 

·
Premium Member
Joined
·
278 Posts
Discussion Starter #9
james said:
One consequence of Honda's basic design strategy is that you just aren't ever going to be able to run efficiently on electric alone, because the electric motor is bolted to the IC engine's crankshaft and is always turning the engine. If the engine isn't firing, the motor still has to do the work of overcoming the engine friction & compression.
Exactly! The current Honda set up can't be adapted to normal plug-in hybrid operation (ie with EV mode for the first 'x' miles, then gas use after) but it COULD be adapted to have electric assist of the gas engine (ie the gas engine is on and contributing at all times, but while there is charge in the pack, much, much less gas is used than normal - I reckon about a quarter normal gas consumption, or 4 times the normal mpg under this setup).

Why do I think it's still worth thinking about? Because currently the chances of Honda developing a plug-in hybrid are extremely slim. The problem is that there is zero chance of Honda ever signing a technology share agreement with their mortal enemy Toyota to use a power-split device allowing EV propulsion independently of the gas engine (the hatred between the two companies is unparalleled!). So, it appears that the PHEV route is difficult for Honda to take with the IMA system.

However, if we could demonstrate that electric-assist gives stellar mpg results by adapting one of the MIMA cars to plug-in charging, it could help nudge Honda in the direction of offering it as a factory-fit option to IMA buyers. And I for one would pay money for that!

But of course I realise that this is a project for the future, and we should be thankful that MIMA is on its way. So will keep my futuristic thoughts to myself for now! :)
 

·
Premium Member
Joined
·
2,332 Posts
CLet, on a long trip it is more efficient to use up the battery energy slowly, lets say over a period of a couple of hours or more. This is because the motor and the batteries loose less energy to resistive heating. There is really no advantage of using up the entire charge in the first half hour and then using pure gasoline power. A system like Prius only has an advantage on short runs around town where you can run mainly on electricity. If you are just doing short runs to work and back daily, then you are never going to pay back the 10,000 dollars worth of batteries that they put into a Prius at Tour de Sol. :wink:
 

·
Registered
Joined
·
224 Posts
My experience has been that the biggest benefit of the MIMA is the ability to keep the ICE at a lower fuel consumption rate (which may or may not actually be lean-burn in each respective case) while climbing the smaller / shorter hills. The sensation is a bit like having a helpful tailwind at exaclty the right place and time. As I've indicated before, I'm consistently realizing 10 - 20% improvement in fuel economy with selective use of the MIMA_L.

Perhaps differing here from Mike in my opinion, I'm not so much of a proponent of sustaining high levels of assist on the long and/or steep hills, as it's an inefficient use of the battery energy (heating losses) and the required recovery would either take a long time, or more rapid charging which is also inefficient and raises the temperature of the pack.
I'd also suggest that the heavy use of assist for starting from a stop on level terrain would have questionable ultimate benefits with the stock battery pack. It should be possible to calculate the comparitive efficiencies, but since I don't live in the flatlands, this has not been a priority.

With regard to expanded battery storage with grid charging, yesterday I had the opportunity to re-connect with a leading proponent of hybrid vehicle technology, who is a big fan of the "plug-in Prius" concept. When I commented that grid charging was not necessarily zero emissions, he reminded me that Quebec has a remarkable, mostly zero emissions hydro power generation system.
 

·
Premium Member
Joined
·
4,389 Posts
Since Brian has probably logged more commuter miles with his MIMA than I have (Im stuck inside working on all of your MIMAS.) I will not question his appraisal of how to use MIMA for efficient driving. As a lead fingered MIMA man, I have done many 50A power charges down long hills, and off ramps, and have not seen much change in battery temperature though, so while there must be some heating losses, my experience shows then to be small for regen.
I do see the temp rise when using the 100A assist for any length of time. In that case, I am using MIMA more as a turbo than a speed maintainer. I had one experience where I was passing a long line of cars going up a moderate hill, at ~85 MPH in 5th. I had the accelerator floored in normal IMA mode where the car was giving me ~45A of assist, and I was not able to accelerate. I switched to MIMA and lead fingered the joystick to full assist, and was soon accelerating up hill, and by the top of the hill was in the mid 90's. On the way down, left the accelerator at about 125MPG, and I used the full 50A forced charge to get back about 75% of what I used going up the hill, and by the bottom of the hill I was going about 70. Pretty extreem battery exercise, but As I said before, I would rather be the one that cooks my battery (excuse to do the Prius pack swap) than to have one of you do it. All endurance test need to test the limits, to know how much room you have to work in.
I have since then began to moderate my MIMA use up hills to speed maintenance and if no cars are behind me to a slight speed decrease.(still like to see the big MPG numbers)
I have blasted the pack enough to feel comfortable that most moderate MIMA use should not fall outside of what the pack can handle, and I have not even added the extra cooling fans.
The inefficiency in high rates of charging and discharging is real, but if every oppertunity to charge at the most aggressive rate possible is used, the pack can be maintained at over 50% SOC, and with MIMAs ability to control the charge, you never need to have the condition where you are at 60% SOC,no charging, going down a big hill, and you can not get any charge since the car feels it is not needed. (Corey's Max regen brake mod works just like full mima regen in this condition, but does not let you modulate the charging as MIMA does)
 

·
Registered
Joined
·
1,819 Posts
"...there is zero chance of Honda ever signing a technology share agreement with their mortal enemy Toyota to use a power-split device allowing EV propulsion independently of the gas engine..."

But why should they? As I said, Honda's system has a lot of advantages over the Toyota system, so why should Honda either want to use Toyota's technology, or develop their own, just for the sake of an around-town EV mode?

Even though there's no way to do a strict comparison (since Insight, Prius, and HCH are so different from each other), I believe that if you take into account average driving styles, cost of manufacture, &c, the Honda system would come out ahead on net energy savings, and way, way out in front on driveability. So what's the point?

I think it would make much better sense, once the cost of the necessary battery packs is low enough, for Honda to develop a pure-electric city/commute car, perhaps with an auxiliary generator for long trips.

Of course, this is just theorizing. Like Mike, I want MIMA primarily as an electric turbo :)
 
1 - 13 of 13 Posts
Top