CountryByNet.com Forums :: Fuel Efficient 4WD Vehicle

Not to worry Dave. The rules committee met and voted to NOT recall your secret decoder ring and drum you out of the corps.

There are different "styles" of ICE-electric hybrids. I personally think the type in the Prius is the best for its application.

Toyota's Hybrid Synergy Drive as used in the Prius is essentially a computer controlled "drive by wire" system. It has a small ICE (gasoline but could just as well be a diesel and even better) and motor generators. It has a planetary gear set which acts like a CVT. The transmission has no reverse. reverse is accomplished totally by electric motor. The tranny does not have a set of ratios to shift through and is continuously variable under computer control.

The engine is designed to be stopped and started frequently with no deleterious effect. The engine has computer controlled valves.

Here is the engine start sceanario: the computer opens the valves, shuts down fueling and shuts off the spark. Then using a large motor not a little starter motor, spins up the engine to operating RPM and gets oil pressure up and circulating. Then the computer puts the valves in run position and turns on the fuel and spark and the engine is just running (no traditional cranking.)

This is a low stress and wear start and is hardly felt (you really have to pay attention) by passengers.

The ICE is likely to be started up by the computer when it is cold to get it warm. At startup the fuel/air induction system is preheated by a well insulated thermos bottle of hot water which was stored at the preceding shutdown. This helps with fuel vaporization and reduces waste and emissions.

Depending on various factors, some of which are: engine temp, demand, state of battery charge, and the like, the computer may propel the vehicle solely by ICE, solely by electric motor or any proportion of the two in concert. This is performed seamlessly by the computer and is not a driver concern. An alert and observant driver may, through their inputs, influence the computers decisions. An example is: Accelerate modestly from a stop and you may delay the ICE startup for a varying period of time depending on your demand, state of charge etc. You may cruise at 45 MPH for a while on electric only or the ICE may be started within the first few feet of a start from a stop (especially if you start off briskly which will probably use ICE and electric together. The Prius is no "slot car" but if you lead foot it you may be surprised by the rapidity with which it pulls away from a full stop and tops 100MPH. If you are on poor traction it will use computer traction control to prevent excess wheel spin and computer stability control to steer around a corner while accelerating or decelerating with poor traction (even ice or snow.) If you don't try to violate the laws of physics the car will let you steer around a corner on ice while accelerating or decelerating. You can even just stomp the brake and just steer and the computer will do all that is possible within the laws of physics to make the maneuver work.

You get a computer controlled seamlessly integrated proportioning of electric and ICE propulsion (excepting reverse) and although you and I, Dave, would be thinking about all this stuff a lot, it is not required for the driver to know it is a hybrid. Put gas in the tank, press the break pedal and touch the Start button (keyless ignition and security) and shift the dash control lever (electric switch) to R or D and go for it. There is a "B" position on the shifter. This is for engine braking and is reserved for steep downgrades. You have to love those computer controlled valves (holy jake brake batman) Ok, just kidding, maybe not full on Jake Brakes but effective engine braking.

As regular gas cars "back drag" (engine braking) when you take your foot off the accelerator, the Prius is programmed to bias a motor generator to extract as much kinetic energy as a normal car does with engine braking. So in traffic when the car ahead coasts and you take youir foot off the accelerator, you coast down at about the same rate and don't get the FREE WHEELING feel. This energy used up by spinning a motor generator is used to charge your battery. You may get to "recycle" this energy when you next accelerate.

The EPA estimates for the Prius MPG are larger for in town than on highway, the reverse of a "standard vehicle." In town driving you use your brakes a lot and travel mostly at moderate (low aerodynamic drag) speeds. If you use your brakes moderately and not always race to a stop and then slam on the brakes, the actual friction brakes (disk rotors and pads) aren't applied. The deceleration commanded by brake pedal force is generated by regenerative braking by spinning a motor-generator. You get to recycle that energy. With steady but not heavy braking the transition from regenerative braking to friction brakes is between 6-7 MPH and again you have to be super alert to feel it happen. In a panic stop you will get regenerative braking plus friction brakes controlled by an anti-lock system. Again, the driver really doesn't need to know or think about any of this.

Just consider any sufficiently advanced technology is magic and the driver can just think the car magically does what it has to do to git 'er done.

The short version: Yes a Prius is in many ways like a diesel electric submarine.

Dave with your interests and comprehension you would probably be fascinated with some info available on the web about the Prius. Everyone asks about THE BATTERY. There are two, one is a little 12 volt lead acid automotive type for all the 12 volt accessories and lights and the other is the BIGUN. The bigun is warranted for 100,000 miles (California gets significantly more warranty) and is built in clusters (modules) of cells which are independently replaceable (at the module level) should a cell fail. I personally know of no failures. Surely there must have been some at some time but I have never found an owner with that experience. In fact, out here the Prius is still rare enough that owners go out of their way to chat when they meet. I have yet to find anyone who was less than enthusiastic and happy with theirs.

At year 2 and year 3 I got offers from my dealer to buy back our Prius at a fairly attractive sum so they could sell it at a massive markup to someone with the bug to buy who couldn't get one fast enough through channels. Both times I reminded the sales manager that my wife and I had concealed carry and would defend our Prius possession.

The OEM LRR tires only lasted 30,000 miles. My friend with the '05 gets his tires replaced under warranty as a part of the "deal" he got when he bought. He is over 100,000 now in 3 years and "in love" with his Prius. We have had ours going on 4 years and just had the 35,000 mile service. We get free oil changes as long as we own it. I will keep it as long as it is safe, reliable, effective, and economical. When a trade could be prompted on economic grounds I will switch to whatever is the best deal at the time considering the extant factors and my surmise of the future trends. I guessed pretty good this time. I waited 8 months to get it and it arrived in July '04. It was a good deal then and given the gas prices currently and their trend, it is becoming a better deal all the time.

The hybrid SUV's will not come close to my mileage but for a SUV the hybrids are darned good and will just get better as gas prices continue to climb.

Pat

"I'm not from your planet, monkey boy!"

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Dave, I recall my dad telling me that some of the old cars, when first going with electric start, used the generator for a starter motor until cranking requirements grew with displacement and compression until a separate unit for each duty was a better idea. In the early days of carting, 12 volt generators were used as portable starting units.

My first few drives in a Prius had certain unsettling moments. Recall when you were a young driver and it was not that unusual for your cheap jalopy ride to die at a stop sign. Well the Prius usually switches the ICE off when you coast so at a stop the engine is dead and the vehicle is in eerie silence and with no vibration. Unsettling because you are trained to think the engine quitting is a bad thing. Of course as soon as you step on the "accelerator" (drive by wire acceleration demand input) you are telling the computer how much acceleration you want and it responds immediately with acceleration provided electrically and may start the ICE to assist or not depending on a few things the computer cares about.

Note the A/C is not parasite off the ICE but is driven by its own electric motor so it keeps its cool, and yours, when you are at a long light or watching a freight cross in front of you. If this depletes your energy reserve in the battery the ICE may kick in to spin the big MoGen and pump the batt back up. When I leave passengers in the car in summer to make a quick run into a shop, I leave the car "ON" and it runs the ICE a little every so often to keep the batt up and the A/C keeps everyone cool. Better than everyone having to trudge across a hot parking lot to get inside to stay cool. (I don't like to leave a "regular car" running parked for long.)

When tooling down the interstate on cruise control and you top a hill, going down the back side if coasting will maintain the set speed the engine is turned off. If coasting won't quite do it the ICE runs but the CVT effect is TALL GEARS.

There is a bar graph that shows near real time gas consumption (0-100MPG) and a bar graph showing the last 30 min of MPG in 6 each 5 min segments. As you top a hill and start down the other side you see the near real time MPG go way up even if the ICE is not switched off as it may not be contributing much. (Or it may be charging the battery and running harder than just enough to run the car downhill.) Then as you level out you see the MPG start to climb. On long downhill runs with the ICE off the battery gets charged pretty good as all the time the ICE is off and you are coasting the MG is biased on a bit to give the drag you would expect to feel in a standard gas vehicle.

Previously I said the Prius is listed with better EPA mileage in town than highway, the reverse of most cars. Most cars, in town, accelerate, drive a bit and then you hit the brakes to slow down or stop. All the energy consumed to get you going is now, less friction losses, converted into KE that is subsequently converted into heat in the brakes. With the Prius, the KE is converted to electricity to charge the battery unless you really get on the brakes hard. The brake pedal is an input to the computer to tell it how much you want to decelerate. IF that can be accomplished by biasing the MG to charge the batt then it does. If you ask for too much braking action then the computer adds in the friction brakes to help out as required. There are two immediate benefits: 1. if you don't brake hard a lot the friction brake wear parts last a long time and 2. yo get to recycle the energy of motion into electricity to use to get going again after you stop. This energy recycling is not 100% efficient as there are losses in the MG ==> batt and batt ==> MG but in a "regular car" there is ZERO recycling so the hybrid gets way ahead in the slow and go or stop and go of city driving.

At highway speeds the ICE has to provide the HP to overcome aerodynamic drag and various frictions. Then when you want a burst of acceleration to pass someone you make a withdrawal from your energy account stored in the battery. The ICE is a little 4 cyl thing. The Prius has a very low drag shape (Toyota spent lots of time in the wind tunnel.) The ICE can propel it well over 100MPH on a level road with no wind but at say 75-80 it doesn't have a huge reserve of torque and HP for passing going up a hill. Think of it like a standard flush toilet. It takes a while to fill the tank through that little tube but when you pull the handle there is a brief BLAST of water. The battery in the Prius will not support full acceleration for too long but will give you enough electric assist to be very safe merging onto the interstate, passing on a 2 lane, surprising the heck out of someone when the light turns green. If you are cruising along the battery is generally well charged and will give you a few minutes of hard acceleration, more than is ordinarily needed short of racing.

I refuse to drive a vehicle that is dangerously underpowered. I would not drive a Mercedes 240D (I say the D is for dog!) It just has not got sufficient acceleration to merge on the interstate or pass on a 2 lane. Our Mercedes 300TD (5 cylinder turbo diesel) met the minimums just fine. The Prius will totally smoke (euphemism only as the Prius is super low emissions and partial zero emissions rated) the 300TD off the line or at any normal cruise speed. My buddy with the '05 Prius drives from OKC to San Antonio to Seattle, to Pennsylvania in any order several times a year with his wife and sometimes grand daughter along and remains well satisfied. His previous car was a rather potent Mercury. He is a bit of a lead foot but still just loves the Prius. He gets about 40MPG and his wife gets 44-45 when she drives.

Hybrid SUV's will not do as good with MPG as the Prius but should still be way ahead of the regular ones.

Some Prius freaks have increased the battery capacity added plug in charging, and installed the electric only switch that prevents the ICE from starting up. (As is available on non USA Prius units) Short runs around the neighborhood can be accomplished with no engine running. I can not attest to the efficacy of these mods as the Prius was not designed to be an all electric vehicle but the guys that did it claim to be well served by the mods.

Oh, there is another down side to the Prius. In parking lots where speeds and acceleration is moderate the Prius often proceeds electrically only. This "STEALTH" mode requires you to be super vigilant as pedestrians do not hear you and just will abruptly step out in front of you as in these situations many folks detect close traffic by sound instead of looking. I have gently and briefly tapped my horn and had people nearly jump out of their skin in surprise as they had no idea as they walked along in the middle of the lane unaware a car was "dogging" them.

Oh, and one of the display modes on the dash mounted monitor is a cartoon of the car with colored arrows showing the flow of energy from the wheels to the batt or batt to wheels or engine through MG to batt or some combination of the above.

Pat

"I'm not from your planet, monkey boy!"

Edited by Pat (04/19/08 11:57 AM)

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