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Hybrid Vehicles Hybrid Vehicles - Archived Discussions How do Hybrids work? Newbie questions encouraged! 
139 messages, Last post on Aug 02, 2007 at 5:38 PM
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Replying to: zodiac2004 (Nov 04, 2005 9:25 am) 
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Replying to: falconone (Nov 04, 2005 1:26 pm) What were her other cars?
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Replying to: zodiac2004 (Nov 04, 2005 1:52 pm) |
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Hopefully this won't turn into a discussion about Einstein- so I'll keep my question as specific as possible. in reading a lot of these forums, there's a notion out there that the more you run on electric-only mode, the better your overall FE will be. (in the HH forum, seems like that has been discussed lately) So for the sake of this discussion, let's just talk about toyota systems. The way I understand hybrids to work (please correct me if I'm wrong) is that a gas engine is inneficient at low speeds. whereas an electric motor has an even torque band across the range of rpms. so hybrids use the electric motor to accelerate from a standstill and uses gas once the car is just cruising to maximize efficiency. So it would make sense to charge the battery while the car is "cruising" along when the ICE is running most efficiently. OK so here's my problem understanding why forcing the car to run at electic is good. why would you run the car at cruising speed in electric mode, when the gas engine is already at its most efficient "zone?" By depleting the battery, you are going to have to force the engine to charge it up at a later time perhaps when the engine is not runnig efficiently. as someone has already pointed out, transfering power from one source to another is not 100% efficient. (and let's ignore regen braking for the moment because the recomended fuel savings techniques tell you to anticipate stops and to minimize brake use.) wouldn't it make sense to selectively force the engine into running on electric-only. let's say you knew there was a down hill coming a mile after the red light so that you deplete the battery by running electric only, and you recharge it as you go down the big hill. But if you knew there was a big up hill coming, you might want to get that battery charging so that you could use the electric assist to climb up the hill. I know the computer in the car is programmed to seemlessly optimize when to charge and when to run on electric. But the computer cant sense the traffic ahead, the slope of the road, whether you're getting on/off the highway... etc. So ultimately is my thinking correct? Is the notion of arbitrarily trying to run in electric only mode a good one, or should we try to be more selective in when we try to force the car in electric mode?
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Replying to: otis1 (Jan 27, 2006 7:26 am) You wrote "Hopefully this won't turn into a discussion about Einstein" I second that !! Here's maybe what you are missing in your knowhow. Internal combustion engines typically have a maxx efficiency point around a 38% power loading. Lower power loadings are less efficient because fixed losses predominate. Higher loadings are less efficient because losses proportional to engine speed predominate. A 38% power loading is still too high for just plain cruising at any speed below 65mph. -- Others may wish to know what good this is well.... Prius hypermilers who want to travel efficiently below a steady 42mph can use a pulse and glide technique. They slowly come up to within 42mph in electric mode so the ICE won't have an excuse to start and gradually deplete the battery. This is the glide part of course. Then at around 20% state of charge (SOC) the engine will fire up automatically. The ICE now has two jobs, provide motive power and charge the battery. If the battery is warm it will have full capacity and charge in a few minutes to 90%. This double loading operates the ICE at its most optimum power for a short period which is known as the pulse. The driver monitors the display to know when 90% SOC is reached and will then momentarily slow to encourage the ICE to stop. Then 'feathers' the speed back up to within 42 mph under electric power only to begin the whole glide process over again. I hope this explanation answers some questions for you and helps a bunch more who are new to Prius. Visit john1701a.com for more Prius stuff. As another poster wrote " I can try explain it for you, but I cannot understand it for you". ! T2
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Replying to: toyolla2 (Feb 24, 2006 6:55 pm) What kind of driving can best charge the battery to 8 bars? Should I set the transmission to B instead of P? If I am at 6 bars, I cannot seem to get the battery to continue charging unless it is cold out or I am going down a long hill. Any help will be appreciated. AutocrossTom
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Replying to: autocrosstom (Mar 28, 2006 4:30 pm) Manual Charging With the Ready light on and the gear in P, press the accelerator padel. ICE will start and charge the HV battery Automatic Fast Charging 1. Start the car 2. Put it in Drive 3. Depress both the brake and gas pedal simultaneously to the floor. 4. The car will recognise that you want to charge the battery and move into a special "fast charging" mode. 5. This can take up to 5 minutes depending on the charge state of your battery (you can even get it up to 100% - FULL GREEN) 6. The car will NOT overrev and will adjust the engine speed back as the battery charges. Dennis |
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Replying to: midnightcowboy (Oct 27, 2005 7:47 am) Why? Because that's the basic principle of E-CVT. Yes, that's how HSD transmission works in a nutshell. The ICE make only 82 lbs-ft torque. It does not produce enough twisting power to properly accelerate the Prius. This situation prevents the ICE from making it's maximum power since it can't rev the RPM fast enough (already too hard to twist). So what does it do? The Power Split Device comes to the rescue. It spins the MG1 so fast that it generates electricity. This allows ICE to make maximum (or necessary) power while MG1 steals away that energy. MG1 generating electricity and supplying it to MG2 creates massive (295 lbs-ft) torque -- equivalent of 1st gear. Now, all the power of ICE is going out to the wheel. E-CVT stands for electrically controlled variable transmission. How does it control electrically? Well, it depends on the speed of MG1 -- how much electricity it generates. If you stop the MG1, you loose the control and it can't be variable anymore. You might as well call it E-NCST (Electrically Not Controlled Static Transmission). ---------------------------------------------------- "In my higher math, before calculus of several variables, I thought that 66 was greater than 51." You do not need Calculus for this, just Arithmetic and Common-sense. You are comparing 1.0 liter Insight ICE to 1.5 liter Prius ICE. Why don't you look at the Civic Hybrid 1.3 liter highway 47 mpg? Which is greater? 51 or 47? By looking at the results, Honda's IMA is less efficient because 1.3 liter engine is getting less mpg on the highway than Prius 1.5 liter engine. Prius is even bigger than Civic. ------------------------------------------------------- "Why is the highway mileage of the Prius less than the City mileage while the Insight is higher?" Because Insight simply sux in the City, even though there is less air drag in low speed city driving. Prius is equally good in both City and Highway. The reason Highway mpg is lower is due to air resistance at high speed. PS: I know I am replying to a very old post because no one actually addressed it. Dennis
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Replying to: usbseawolf2000 (Mar 28, 2006 6:54 pm) 
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Replying to: midnightcowboy (Mar 29, 2006 9:31 am) |
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