Hybrid Cars No Better than 'Intelligent' Cars

eldavojohn writes "There's no doubt been a lot of analysis done recently on energy consumption, especially on the road. Now, a study released today reveals that cars with traffic flow sensors built into them can perform just as efficiently as hybrids. The concept of an 'intelligent' car that communicates with the highway or other cars is an old idea, but the idea of them using sensors to anticipate braking could vastly reduce fossil fuel consumption. From the article, 'Under the US and European cycles, hybrid-matching fuel economy was reached with a look-ahead predictability of less than 60 seconds. If the predictability was boosted to 180 seconds, the newly-intelligent car was 33 percent more fuel-efficient than when it was unconverted.' Now, the real question will be whether or not you can convince consumers that the three minutes of coasting up to a red light or halted traffic is worth the 33 percent less gas and replacing your brake pads/cylinders less often."

Re:Why not both?

[Mr. Underbridge]

From the tone of the post, it seems like they're making an argument against hybrid cars by showing that they're no more efficient than regular cars with this new tech... but why not just stop comparing the two and combine them? Shouldn't the title read "Hybrid Car Efficiency Improves Even More with new Technology?"

Yup, they lose the debate through the old "Not mutually exclusive" argument. Not only that, but those "intelligent" driving techniques aren't always practicable, like in bumper to bumper traffic. That sort of thing is where Hybrids really shine - where speeds are averaging less than 20 mph and people spend time sitting. If I'm in a hybrid, my engine cuts off and I run off the battery for the start-n-stop traffic, and it charges back later. A regular car will typically get well under 10 mph in such situations; a hybrid will get around 60.

In other words, hybrids totally kick ass in the city - small, nimble, typically a short turning radius, and great mileage in city driving.

Re:You can do it without sensors, too.

[stevedcc]

Perhaps when gas costs more, people will choose to drive more efficiently.

In the UK, "gas" as you call it ("petrol" as we call it") costs £0.95 to £1.00 a litre - which is over $7 a US gallon. Despite this, people still don't drive intelligently

how about intelligent city design?

[nominanuda]

I have a honda insight, and since I've moved to Providence, RI, I've seen my fuel efficiency drop from an average of 70 miles per gallon per tank of gas (in Connecticut driving mostly on back roads at moderate speeds) to 60ish (mostly city driving) in Ann Arbor, to barely 45 mpg here in Rhode Island. I am convinced that it is mostly the fault of poor traffic planning here. I've never seen a city with worse timing for the lights. You will often get a green light only to be forced to stop 30-40 feet away at another light that turned red the very instant your light turned green (Benefit and Waterman/Angell anyone?)

with that said, i always did wonder how much of my great mileage in Connecticut was due to the fact that I could watch and keep track of my mpg. ie. would I see a similar increase in mileage in a non-hybrid car just by being able to monitor my driving efficiency?

The cars themselves would be a lot cheaper

[Anonymous Coward]

Hybrid cars are sufficiently expensive that they can't be justified on the basis of fuel savings. Computing power, on the other hand, is dirt cheap. The 'intelligent' bits might add less than $1000 to the price of a car. That would be economic.

I saw an article recently that accounted for all the energy that went into making, driving and scrapping a hybrid car. The hybrid was actually worse in environmental terms than most other cars on the road, once you took everything into account.

Re:VAR (Vehicular Area Network)?

[name_already_taken]

How do you stop someone from fixing their car to constantly broadcast "DANGER: MOOSE AHEAD" or "EMERGENCY VEHICLE APPROACHING" so they can use it to get through traffic faster?

Ummmm... make it illegal to transmit false traffic data? Just like it's illegal in many jurisdictions to use those devices that signal to traffic lights that your car is an emergency vehicle so that the lights give you priority (unless your car is actually an emergency vehicle).

Seems kinda obvious.

Re:can't you just do this now?

[Brickwall]

That's not a new technology; I had a Ford T-Bird back in the 80's (when it was the big boat) that flashed a red "Economy" light on the dash when you floored it. And you are correct - unless I was trying to pass a truck on a two-lane highway, when the light flashed, I would usually lift my foot off the gas.

Re:can't you just do this now?

[bhtooefr]

Try a ScanGauge [scangauge.com]. I don't have one, because my car's too old, but a Yaris (actually, most 1996 and newer cars) will almost certainly work with it.

Re:Hmmm.

[AaronW]

Actually, the Prius can run the gasoline motor at a constant RPM in the way it is designed. The actual speed of the output is controlled exclusively by two motors/generators. One motor is optimized for generating electricity and the other is optimized for providing torque to the wheels. By varying the amount of power shunted from the generator to the motor the output speed can be controlled since more power from the generator causes it to draw higher torque from the engine which in turn causes the power sent to the wheels from the engine to decrease, but increases the speed. A diagram is shown here [howstuffworks.com].

In practice, the engine runs at a variety of speeds, but it seems to prefer running the engine at the most efficient speed and torque when it can.

Stick-shift Economy Lamp

[Latent Heat]

The professional drivers who run the EPA test cycles on the rollers upshift pretty aggressively to save gas on the test. The EPA said, "No way anyone drives that way" so I think that applied yet another deduction to the test numbers of EPA mileage for stick-shift cars to account for the opposite extreme of the lamer who allow the engine to fully rev before each shift. I didn't think they told the test drivers what the shift points should be but instead applied a deduction to account for non-geek drivers who don't know about engine maps.

The loophole around that deduction was if you had an E-light (economy) or U-light (for upshift), you could get a waiver from the mandatory deduction and hence report higher gas mileage for your model of car.

If you drive the E-light, it does feel like you are lugging the engine and putting more stress on the bearings, but the object of the gas mileage test was to shift in such a way as to optimize gas mileage, not engine life. I have driven with an E-light, and it is annoying because even if you know what you are doing, it keeps nagging you with flashes, but keep in mind that it has to do with government regs and is not a serious driving aid, although it can tell you how much upshifting the engineers had in mind.

Re:can't you just do this now?

[Brickwall]

Oh, sure. It happens because cruise control is not based on constant RPM, but constant speed. If you're travelling through hilly country (we go through the New Hampshire White Mountains to visit a pal in Maine), the engine will speed up, and often downshift to a lower gear, to keep the speed constant on the uphill slogs. When in the mountains, I turn the cruise off, and let the speed slack off a bit on a steep climb. You get much better mileage this way.

Re:can't you just do this now?

[davmoo]

Sorry, but there is more to it than "keep the engine RPM low". There is a "too low" point also.

I drive a Chrysler Sebring, and as one of the OPs talked about on his relative's car, it has a digital display of "at that second" MPG as well as an averaged MPG (and a bunch of other things). And between that and watching my gasoline receipts, I know for a fact that my car gets its best mileage at approximately 2000 RPM. It sucks gas like a big dog above 3000 RPM...but it also starts getting bad as it goes below 1500 RPM, and gets worse the further down it goes.

Prius owner chiming in, braking not the big winner

[Weaselmancer]

I own a 2007 Prius. IMHO, you're correct about the regenerative braking not being the big money maker in the vehicle. It's the hybrid train switching off the engine when you're on the freeway on slight declines.

It's got a screen that shows your energy consumption, including the net gains from the regenerative braking, and I watch it fairly closely as I drive. If you're on a slight decline, the car gets around 75mpg with the gas engine providing minimal torque. The scale maxes at 100 when the engine shuts off, and that'll happen on the freeway sometimes too. Occasionally I can drive the thing on a non-flat road under 35mph it'll switch to all electric as well. On slight incline, it's about 20-25mpg, depending on if I'm trying to accelerate. A round trip averages out to around 50mpg, and that's what I'm seeing. My average is 52mpg.

As for the regenerative braking, the display will show you how much energy you net in a five minute period by a collection of little green "leaves". For every 50 watt-hours, you get a green leaf. Usually I net a half of one in a five minute period. That's not much at all. Best I've done is 4 I think, and I was coasting downhill a lot on that 5 minute segment.

So a really good five minute drive will net you three leaves, or about 150w/h. If we do the math on that, here's how that breaks down. (no pun intended)

A gasoline engine is about 20% efficient. [wikipedia.org] A gallon of gas holds 115,000 BTUs [ornl.gov], which is 33.69Kwh. A car will make use of about 20% of that, so a gallon of gasoline will provide you with 6.738Kwh, or 6378wh. Those three leaves add up to 2.35% of a gallon of gas. With gas at $3/gallon, those three leaves save you $3 * 2.35% = 7 cents.

Nope, not much money there. The big savings is when the thing coasts or nearly coasts on the freeway. That's why the smart-car idea that makes you coast a lot produces similar savings. No surprises there.

Re:can't you just do this now?

[iksbob]

Coasting in neutral to a stop may actually consume more gas than coasting in gear. Modern fuel injected cars cut off the fuel supply to the engine when the throttle is closed, and the engine above idle speed. That means if you coast to a stop in gear (compression braking), you're not using any fuel. If you shift to neutral while coasting, the engine speed will drop and it will start using fuel to maintain idle.

Re:NO, you can't just do this now.

[mykdavies]

The longer you take to move up, the more traffic backs up at the back, and the more people who obstructed who are trying to get on/off the road. But at least you save 5 cents on your petrol bill...

Come on, think about the engineering here; which is more efficient: turbulent or laminar flow?

The standard reference for this take on the topic is here: http://amasci.com/amateur/traffic/trafexp.html [amasci.com]

Re:can't you just do this now?

[zacronos]

I'd be surprised to see any modern car above the absolute lowest class without some kind of device that would keep track of fuel consumption.

That was GP's point -- you don't get that in modern cars unless you buy some outrageous upgrade. I'm not vouching for the truth of that statement, I'm just pointing out that GP is saying that most modern cars don't have a MPG meter.

Just because older cars don't have the MPG meter doesn't mean it has spread to almost all modern cars. Imagine this scenario: car manufacturers start including MPG meters in their cars. Drivers start to notice that 98% of the time, their car doesn't get the MPG the manufacturer advertised, and in fact sometimes gets a good bit less. Drivers start complaining. Someone has the bright idea that if they don't include these MPG meters as standard features they can eliminate the dissatisfaction. Hence, newer cars don't typically include a MPG meter, and only provide one as part of an expensive upgrade bundle (since that profit from the upgrade will probably help more than the dissatisfaction will hurt). If, in addition, it could be shown that the presence of an easily readable MPG meter on the dashboard would lead to significantly lower gasoline consumption (and thus correspondingly less pollution), would this not be an appropriate situation for regulation? The interests of the car manufacturer are hurt by including a MPG meter, so they won't readily do so in a free market, however the interests of the public are advanced by including it. Thus the government steps in and regulates in the public interest. That's how things are supposed to work, and I don't think it's that much of a stretch to think things might have gone as I described.

I'm not saying that's the best use of our lawmakers' working time, but I am saying it's not as ridiculous an idea as you make out. Have you ever lived in a metropolitan area that has ozone alerts [nih.gov] in warmer weather resulting partly from the large amounts of car exhaust? It's not fun.

Re:Misinformation about manifold vacuum

[cecil_turtle]

Your post is well titled, as it does in fact contain misinformation about manifold vacuum :) . I also never stated that watching vacuum was a good way of maximizing fuel efficiency, I was merely explaining the theory to my parent. Later in my post I explained what actually determines maximum MPG efficiency.

you want the engine to be in an efficient power band, which is actually at low manifold vacuum and lower engine revs.

Efficiency <> low manifold vacuum <> lower engine revs (necessarily). Greater vacuum is caused by the difference between the current throttle position and current engine speed / power output. Once the engine has "caught up" to the throttle position the vacuum diminishes. For an exaggerated example look at how turbo cars build boost - floor it from idle = maximum vacuum, then it approaches atmospheric pressure as the engine speeds up, then the turbo spools up and you build toward positive pressure and maximum boost - somewhere in the positive pressure side is where you achieve maximum fuel efficiency (vs. engine power). Also, your statement that I quoted above seems to be at odds with your later statement:

there is an island of maximum fuel efficiency in the mid RPM range somewhat below but not much below wide open throttle.

So are you saying fuel efficiency is achieved at "low manifold vacuum and lower engine revs" or "not much below wide open throttle"?

Let me clarify something: fuel efficiency <> MPG efficiency. They can be related, but fuel efficiency is with regard to fuel consumption vs. engine power, MPG is fuel consumption vs. distance traveled. Achieving MPG efficiency involves many more variables external to the engine, most of which grossly outweigh operating the engine at its peak efficiency. There should definitely be a correlation in vehicles that are designed for good MPG, but again see my original post for more explanation of the dynamics involved.

so that a little bit of manifold vacuum is required to prevent spark knock, and at wide open throttle, you retard the spark and operate a little bit less efficiently

I'm not really sure what you're driving at here. I assume the "knock" you're speaking of is pre-ignition and not detonation. At WFO you retard the spark not to operate less efficiently, but to be timed with the down stroke and not pound the top of the piston prematurely. If the compression were too high for the fuel, pre-ignition would occur on compression and delaying the spark would have no effect. As such, delaying the spark is to increase efficiency.

accelerate so slowly that the gauge never comes out of the "green." That kind of driving is just plain sillyness.

Agreed. Driving at +15psi boost is much more fun.

Re:can't you just do this now?

[Technician]

Also, energy capture during regenerative braking is imperfect both because it is easy to exceed the maximum charging rate of the batteries, and also because the charge/discharge cycle is not all that efficient (about 70% both ways, if memory serves.)

I have a hybrid and you are entirely correct in your assessment. Stop and go driving is hard on gas in both a conventional car and a hybrid. Mine shows the KW regenerated. Best economy is when I have little to no regeneration. Slowing gently instead of rush to a light and slam on the brakes saves gas by shutting down burning gas early. In creep and stop traffic a hybrid gets poor economy, but not near as bad as a conventional car simply becasue it shuts down. To get good MPG you have to travel the miles. Real slow and stopped do not acheive miles very fast. A hybrid makes great sense for stop and go driving such as UPS deliveries, City Buses, and Taxi Cabs.

Remember Katrina and the people running out of gas between 30 and 60 miles from New Orleans? In the same situation, in a hybrid, you may drop from about 50 MPG to 35 MPG, but you are not going to drain the tank of 16 gallons in 60 miles like many cars did. I'll take 25-30 MPG in a hybrid in creep and crawl traffic instead of 2-5 MPG some cars got. Just remember to shut off the AC and roll down the windows. Running the engine to run the AC when not moving burns a lot of gas.

A big advantage of regenerative braking is the majority of braking is regenerative at higher speeds. This greatly reduces wear. At 80 K miles, I bought new tires and had the brakes checked. I have 80% of the pads left. There is no alternator, power steering pump, fan, water pump, and other belt driven high failure items. My only belt is for the AC. On newer models they eliminated that belt and went to sealed electric AC. This change eliminating several other high wear high failure parts. (belts, AC clutch, flaxible hoses, shaft seal) As a benifit, the engine can run much less to provide AC in creep and go driving saving fuel. There is further saving by running the compresser at a speed independant of the enging speed. You get good cooling at a stop sign and you are not wasting fuel on the freeway by running the compressor at higher speed than needed. The savings is greater than the effeciency loss of the electric drive instead of the belt drive. Reliability by removal of high wear item is built in. I wish I had this feature on my car.

A smart car assumes an ocassional traffic slowdown. In a creep and stop situation, a smart car will not perform better than a hybrid which shuts the engine off before reaching a stop.

FYI, my average for last month is 45.6 MPG. It includes typical rush hour traffic with some creep and stop driving and a long trip of 180 miles each way over the mountains. I drive an 02 Prius. How you drive makes big changes in your results.

Re:Why not combine the technologies?

[bhtooefr]

Here's the latest:

http://www.channel4.com/4car/feature/feature.jsp?i d=740 [channel4.com]

And, VW's been doing this for ages - I've found evidence of their "single-shaft" diesel-electric hybrid prototype dating back to 1987. I don't know about the function of the Golf ECO.Power, which is VW's latest version, but they claimed an AVERAGE of 3.8 L/100km with that one. (That's 62 US MPG.) Not too shabby.