[Delta Flyer]

It's been noted that in bumper-to-bumper traffic, the Prius is electric-only, helping to give it better city than highway mpg. When I'm stuck in that kind of traffic, the mpg read-out will be under 40 mpg, because the speed is under 5 mph.

A possible solution to engineer such low-speed operation to use just one-cylinder. The Accord drops from a V-6 to an inline 3. The Insight 2 is supposed to drop from 4 to 2 cylinders - why not just 1 cylinder in bumper-to-bumper traffic?

Technically this may be easier said than done, but with the IMA as a flywheel, it probably can be done.

 

[Foxpaw]

Hrmm. An easier solution might be to use just the IMA with the engine in fuel cut mode. This would drain the pack a bit and you wouldn't get much performance, but it should be enough if you insist on tailgating in gridlock instead of waiting for a fair sized space to develop ahead of you before moving up.

This would be much easier as it would only involve a chance to the ECM, and no mechanical reengineering. Plus I think if it dropped down to one cylinder it would be a fairly harsh acceleration which might make people think there is something wrong with the car and make people hesitant to purchase one.

 

[Delta Flyer]

It would be interesting to hear from the engineers at both Honda and Toyota.

The Prius was designed to be electric-only in slow, heavy traffic at short intervals. The Honda IMA was never designed to act alone to save weight and to keep things simple. My understanding (?) is even in very limited stop-and-go, the IMA batteries would be exhausted.

I admit that one-cylinder operation is not very attractive, but might be a way to cut the fuel losses in heavy traffic.

From the behaviorial standpoint, other drivers are not going to let you drive in a fuel-efficent manner in heavy bumper-to-bumper traffic. Anything that looks like a gap will be taken, encouraging tailgating. I generally try to commute early to avoid this situation.

 

[Guest]

Hi Delta Flyer:

___Autostop or forcing autostop will get you far higher then 40 mpg in stop and go traffic. Pulse driving as the Prius II owners like to call it but with a few twists … Leave a 3 or 4 car length distance between you and the guy in front. Wait until he moves and when a larger gap appears, take off very slowly in first, then second with no assist and before you need to stop again, you should have the ICE off via autostop or forced and coasting up to a similar distance behind him. On slight downhill’s, you can simply coast down the hill using a timing method although you are not timing lights, you are timing traffic patterns in the stop and go traffic jam with the ICE off of course. You should achieve fuel economy in the high 80’s to low 90’s using this method. While driving a std. ICE, you can use the forced autostop and coast down the slight declines as well. Crawling in the flats or uphill however is a bit tougher proposition as you can well imagine When you do start moving again no matter how slowly, you can actually make up some of your lost segment mpg’s. Just accelerate very very slowly while traffic is beginning to surge ahead and let the gaps expand and expand some more. There will be those that fill in that gap again and again from your left lanes but you will come up to their back bumpers in the next section of stop and go. You can slowly accelerate an Insight to 30 - 35 mph above 90 mpg in warmer temperatures when she is warmed up if you are very careful on the throttle. Just do not get frustrated and keep focused to what is going on in the traffic patterns for maybe ½ mile ahead is about all that needs to be added.

___Overall it is not a pretty proposition given our lightweight Insight’s could really us an all EV mode without ICE engagement but this forced pulse driving works. A Prius II running in EV mode will not achieve the fuel economy of an Insight in a stop and go traffic jam using the above technique because they pay in blood to bring that pack back to its 56% or so SoC or thereabouts afterwards. We just have to pay for the IMA start which isn’t really that bad given you might lose 2 or 3 bars after 20 minutes of this kind of behavior in a traffic nightmare. I usually sit in one of these SOB’s about 4 or 5 times a week when I am on day shift coming home

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email:1v1w2xor][email protected][/email:1v1w2xor]

 

[Chris]

Why didn't Honda make the Insight run on just the electric motor up to 40 mph or 20 or whatever mph it is that the Prius II does, then the Insight would get way better milage, I think.

 

[Delta Flyer]

Why didn't Honda make the Insight run on just the electric motor up to 40 mph or 20 or whatever mph it is that the Prius II does, then the Insight would get way better milage, I think.

It would add a considerable amount of weight to the car.

I do get autostop in stop-and-go-traffic, but when it's very crowded, there is not enough room to get the momementum to exceed 40 mpg very often. If I wait for it to clear, other drivers will fill in the space.

 

[kapps]

Why didn't Honda make the Insight run on just the electric motor up to 40 mph or 20 or whatever mph it is that the Prius II does, then the Insight would get way better milage, I think.

Not only do they have to add weight for the extra components but the battery pack also has to be larger and higher capacity. Honda made it simple and light by permanently mounting the IMA motor directly to the crank. The Prius has to use a 2nd differential to balance engine and IMA power.

 

[Tim Maddux]

I have used the technique Wayne describes to get 90+ mpg many many times in southern California stop-and-go highway traffic. The idea is to keep rolling at a steady speed that matches the average speed of the rest of traffic. While everyone else accelerates and brakes, I try to roll forward slowly, preferably in idle-stop. It works great if you can keep people from jumping in front.

I haven't found a similarly effective technique for city traffic.

 

[b1shmu63]

Comparing the IMA system to synergy drive in a city situation is not realistic. I have heard that the city mileage tests for a Prius were done with a fully charged hybrid battery that was depleated by the end of the test. If true, this eroneously skews the test in favor of the Prius. This is not the fault of the Prius but rather the fault of the test. (If I'm wrong on this then there should be at least a few Prius owners who use their cars in stop and go traffic almost exclusively and who have tank after tank ratings of 60 MPG or better, perhaps a taxi?)

A Prius running in electric only mode is actually running inneficiently, as the ICE engine must run to charge the batteries and then the bateries must be depleated to run the electric motor. There are energy losses at each stage: electric generation, battery storage, voltage up-conversion and switching, electric motor heat generation. As Wayne eluded to, you seem to be getting something for free but you have to pay the piper eventually.


The IMA system fails to opperate efficiently when the ICE engine must continue to run (moving pistons and valves and pumping air) when there is no forward motion of the car. The techniques that Wayne mentions can overcome this but are probably beyond the patience quotient of 95 percent of drivers.

Both hybrid systems are decades ahead of typical motors. Bottom line is what economy drivers are achieving in real life, and what car body style and driving style they are comfortable with.

 

[ElectricTroy]

As I pointed out in another thread:
engine--->motor--->battery--->motor---->wheels
...introduces a LOT of internal resistance losses. The pure electric mode is very energy inefficient.

 

[Delta Flyer]

...While everyone else accelerates and brakes, I try to roll forward slowly, preferably in idle-stop. It works great if you can keep people from jumping in front.

I haven't found a similarly effective technique for city traffic.

When traffic can crawl to at least 10 mph at a somewhat steady rate, mpg of over 50 is possible, otherwise it's going to be a lot worse. Yes, people will jump in front.

I think everyone will agree this situation is bad from a fuel economy standpoint because the engine's potential is way underutilized.

 

[ElectricTroy]

Two more practical solutions are:

- Honda's: a CVT drive that keeps the engine in optimum efficiency even at 5 mph (result: city mpg>highway mpg)

- Mine: idle slowly in 1st gear... I still get >50 mpg
- ...when stopped allow 5 cars lengths before moving forward again... don't waste energy on stop-n-go motion

Troy

 

[Delta Flyer]

I have to gently point out:

- Be it 5-speed or CVT, the Insight's engine is using way more gas than is necessary for zero-to-five-mph heavy traffic.

- Ideling slowly in 1st gear can be effective if traffic is moving a little faster, but the people in Dallas absolutely will not allow five car length to vacate


....if someone could find a practical way to put the pedals of a recursive bike in...

 

[Delta Flyer]

The last point tends for support Honda's simpler hybrid design of Toyota's.

It seems the Honda engineers concluded since all the energy is from the gas tank, make the gas engine as efficient as possible. Reserve the hybrid assist for driving from a stop, passing, climbing - i.e when extra power is needed. Regenerative braking does not recapture all the lost energy, batteries will lose their charge as well.

Honda seems to be building on this concept in the V-6 hybrid Accord. At cruising, the V-6 goes to an inline three. The hybrid assist is a flywheel to keep the inline three steady.

 

[b1shmu63]

There is something to be said for having 3.3 times the ICE power of the Prius if you need to pull something up hill, and having that power available even when the IMA batteries are drained. Toyota is responding with the powerful Lexus 400LH. Got to love a little competitiveness. :wink:

 

[ElectricTroy]

- Ideling slowly in 1st gear can be effective if traffic is moving a little faster, but the people in Dallas absolutely will not allow five car length to vacate

I'm sorry to hear that. People in the Baltimore area are a little more courteous. Yeah sometimes you get an ***hole who zig-zags through traffic and cuts you off, but for the most part people allow me to leave 4-5 car lengths worth of space.

As for idling, I forget the exact number, but when coasting at 55 down hills, I've checked the fuel gauge. It's only ~0.1 L/100km... ~2300 MPG... insignifigant.

In first gear at 5mph that translates to >50 mpg. Still impressive.

 

[Tim Maddux]

As for idling, I forget the exact number....

http://www.insightcentral.net/forum/viewtopic.php?t=447