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Discussion Starter #1
Hi

Isn't this efficient to continue having the engine on while you are gliding/cruising downhill like 0-15MPH? Prius turns itself off only when you need to gain more power. But for Insight, the engine just stays ON. Not sure if anybody has any idea if I miss any technological benefit out of this?

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If I'm not mistaken the engine shuts off at coast and just freewheels. You have to keep your foot on the accelerator slightly to balance right between regen and ignition. I do this every day on even slight downhills and my instant MPG pegs at 150 until I reengage throttle at the bottom. I read somewhere on this forum where someone switched their display from MPG to LPK to verify that there was zero fuel used.
 

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ah i c. I guess I need to practice more.
Finally got your drift by reading the subject line in addition to the text;)

Yes it is inefficient. You can avoid that inefficiency by getting the engine to autostop. Push the clutch in and shift to neutral. The engine will stop if you are below approx. 18 MPH. Keep your foot off the brake and the accelerator and it will stay stopped until you shift into gear again. Engine needs to be warm before autostop will work.
 

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Discussion Starter #5 (Edited)
Hmm? Does 2013 Insight have a clutch? As far as I know the ONLY clear way to shut down the engine is to press on the break paddle, shifting to N does not stop the engine. Also what Captain_Insight said should stop the engine too. Did I miss something? tx
 

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The 2013 Insight does have a clutch but it's automated. When the car's warmed up it will run on the motor only with fuel cut off and light gas pedal pressure at low speeds. Autostop works with your foot on the brake as the car drops under 8mph in D but and will stay shut off if you shift to N.

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Oh, I'm sorry. I'm an old Gen 1 guy and I just have to assume everything is about Gen 1;)

A dangerous assumption since we seem to be getting more Gen2 folks - a good thing. For those young enough to remember Roseanne Rosana Dana on SNL, never mind!
 

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Discussion Starter #9
Uriel. thanks for the reply. and what I dislike the most is to "maintain" my foot on the break pedal. I want to take the advantage of shutting off engine while moving really slow (5 MPH) like in some traffic jam. With this design, its almost impossible, the engine has to be on at all time.
 

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I have the same irritation. I prefer the stop start implementation in some manual non-hybrids I've driven. They stop the engine when you shift to neutral and take your feet off the brake and clutch. When the car is stopped, I like to give my foot a rest.

Having driven both, I think that's the only area where a Prius really outshines an I2 - crawling traffic. Once you're on the move I prefer the Insight.

The best you can do in crawling traffic with the I2 is turn off the climate control (this makes autostop engaging much more likely), leave a slight gap when he car in front moves, then accelerate to 8mph and just touch the brake slightly. With very light pressure, you can keep the car rolling with the engine off for some distance on the flat or a slight downhill

In slightly faster traffic, once you're over about 11mph you should be able to keep the car in EV mode with a very steady right foot over some fair distances too. Don't abuse it though. You only need to use the battery enough to generate capacity for regenerative braking. If you use the motor too much, the car will go into forced regen and that's bad for fuel economy.
 

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Discussion Starter #11
Yap totally agree with you. I love my Prius in that sense. The more traffic jam, the better MPG I get because the engine is OFF. Well, the drawback in Prius is it doesn't give you the power like Insight.

However, I do see both cars give me similar MPG though, the only thing left bothering me is my tiring right leg :D
 

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All vehicles for years have completely shut off fuel delivery when you take your foot off the gas. The Insight, like most hybrids
Also recharge the Battery pack if you also use the brakes. You can read some old threads about how best to use regenerative braking.


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Actually it is not a good idea to set the car to Neutral when coasting downhill. In some places its even illegal. When driving downhill the motor should do most of the braking. Many Drivers which are not used to drive in the Mountains will disengage the gear and use the brakes only. But the car brakes are not made for prolonged operation. Thus they heat up and the brake fades. I only step on the brake before sharp turns.
The Honda Insight will cut the fuel even the engine itself is turning. You can see this in the info display. Its even possible to use some electrical assist while the fuel injection is still off. AFAIK the valves of the engine close minimizing pumping losses. Of course the Prius system is a bit better. But still there is no fuel burnt when running downhill in an Insight.
 

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Matt, while I agree with everything you said if it is done by key-off, and I'll add that brake boost is lost after a couple of applications, NOTHING makes the fuel economy sail upward quicker than turning off the engine at speed. We hypermilers call it FAS(forced auto stop), the term having been invented by Wayne Gerdes over on CleanMPG.com.

The practice is made much safer by using a well designed FAS circuit, such as the one that Mike Dabrowski invented. That circuit causes the FAS operation to function just like an ordinary autostop. The car will restart automatically if brake boost is lost, or a gear in again engaged. Very slick ;)

All this applies to the MT Gen1 of course, so maybe I'm a bit off subject.

I won't defend the practice, but it is fairly widely used by hypermilers, another Gerdes invented term, here in U.S.
 

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Well, having the ima motor in parallel to the gas motor causes both to spin rather they are in use or not. The prius has an arrangement of sun, planet and ring gears with the gas and several electric motors in a unique configuration to get you down the road. Whats neat is that as you speed up one of the electric motors starts to stop, then spins in the opposite direction while you continue down the road. :cool:
 

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Cobb, I think you might mean "series" rather than "parallel" in the case of the Honda IMA setup. The IMA motor/generator is bolted directly to the back of the ICE crankshaft.

The Prius system is indeed much more flexible in the way that the electric motor compliments, or replaces, the ICE. The Synergy Drive is, as you point out, a very interesting system with a lot more flexibility.
 

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Right, the ima rotor is in parallel to the engine?

Now its a series style hybrid vs a parallel style hybrid, no?

Now which is better? The IMA for highway, HDS for city.
 

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I wasnot talking about hypermiling but about driving downhill. As long no fuel is injected it would be nice if the battery is charged. after the battery is full the potential energy is also wasted Hence i can use maximum AC on the downhill without increasing full consumption. The aerodynamics and rolling resistance are quite low so even with charging the insight is accelerating downhill. So i need to apply the brake a bit to force maximum charging.
My priority to optimise would be following.

1. Better battery control. If the battery is full on the top of the hill more energy must be wasted.
2 Larger battery.
3 Heat/Cold Storage for HVAC use
4 Brake resistors. Energy is still wasted but the disk brakes have much less wear.
 

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I like option 4 having "dump" resistors. :)

1/2 I wish the ima rotor was independed from the drivetrain and could be spun up to several thousand rpms in addition to charging the ima pack like the flywheel in a kurbs system.

3, Peter has experimented with a thermos for storing heated coolant, but I do not believe it helped much. The Prius no longer uses that either, but instead route coolant through the exhaust system to aid in heating.

Not sure about storing coolant or freon. I had the idea you could add a sump to the ac unit so it can build up some liquidized freon from the condenser to go into the evaporator and let the ac compressor cycle more if not tie that into auto stop at stops. Of course a larger compressor to build up excess coolant for such a need may use more power or may cause more problems with it cycling off and on more vs running continuous.

I know in homes they have moved to variable compressors that change as needed vs being off and on.
 

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after the battery is full the potential energy is also wasted Hence i can use maximum AC on the downhill without increasing full consumption. The aerodynamics and rolling resistance are quite low so even with charging the insight is accelerating downhill
True. Actually I should resist the urge to comment in this thread, since you guys are talking CVG Gen 2. It is entirely different from MT Gen 1;)
 
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