Lexus RX 400h and 450h

wwest

rolled on the I90 exit in Issaquah WA back in Nov of 91. The driver slipped upwards out of his seatbelt, head through the moonroof as it did the second roll.

Nuff said.

Some things are hard to forget.

falconone

.....then there's the story of the guy driving with his sunroof open and a bird craps on his head.

fizban

Hehe... did the story mention that's a risk of simply being outdoors? :shades:

dylan hixon

This is not correct.

I went back and did a more careful battery calculation. 6.5 Ah and 288V is a capacity of 1.87kWh. Assume 90% of that gets to the wheels because of various losses, so 1.68kWh.That is 0.2kWh per bar of charge, or 1.3kWh for the useable capacity of 6 bars (I have seen both full 8 bars and 2 bars). . (It is important to note that the state of charge (SOC) guage is not linear from what I read on the Prius sites, but I dont know to what degree.)

Gasoline contains 33.7kWh per gallon of energy, but only about a third of it gets to the wheels, 11.1kWh.So your batteries hold the useful equivalent of 0.12 gal of gas, or 0.02 gal per bar.

Net battery use can be corrected out of a test. Take the 40mpg for 27.5 miles. That is 0.69 gals consumed. If the net change in battery power (it makes no difference whether the batteries are charged by the brakes or motor, the car is a closed system) is 4 bars consumed, that is like using 0.076 extra gallons. 27.5 miles/(0.69+0.076)gal=36mpg

Still damn good, and I doubt if 4 bars were consumed.

Light traffic city driving is the best (other than a test track at a steady 20 mph). I saw a news story that the Hyrid Escape was drive around New York during the car show for a whole tank, 38.5 mpg. That is above the EPA city rating of 36, and being driven by a variety of people, including celebrities, on NY city streets where traffic is never really light.

http://www.findarticles.com/p/articles/mi_m3102/is_7_123/ai_n6137981

dylan hixon

"Absent this bit of knowledge, battery charge source, ICE% vs regeneration%, It is impossible for any of us to compute average MPG except over several tanks of gas, maybe even 10."

All that matters, and all that the the computer looks at, is fuel delivered and miles driven. You can calculate out the effect of net battery usage as I did above, but it seems negligable. If the battery charge is about the same when you start and when you end, then all that matters is the fuel consumption, because you did not use any net electric energy out of the battery. It doesn't matter what happens in between, obviousIy the battery is constantly charging and discharging at various rates.

I don't know what you mean about 10 tanks and different charging sources. Just think of the battery as a 0.12 gal (one pint) auxilliary fuel tank which is constantly filled and emptied, but hovers around half.

Yes, you can fool the system by using battery only for a short time. That is how you peg the mpg history display at 60+mpg for a bar or two, you certainly are not getting 70mpg, but you have to pay the piper soon and recharge, by braking or engine. If you drove electric only at an energy consumption rate equal to 40mpg, full battery to 2 bars would only get you 4.8 miles, so you can't fool the system for long since you are running off of your one pint aux tank.

"That's why the city MPG rating is always better than highway, highway cruise ofters very little opportunity to recover inertial energy via regenerative braking or simulation of engine compression braking."

No. City mpg is higher because you are going slower, and the speed of the car determines the minimum fuel that can be consumed over a given distance. The faster the speed, or average speed, the more energy required to travel that given distance. Any stops increase the fuel consumption over that minimum (hybrids only lessen that increase somewhat), otherwise you have a perpetual motion machine again.

otis1

Gasoline contains 33.7kWh per gallon of energy, but only about a third of it gets to the wheels

wow, that much? I always thought it was much less. regardless what it is (20% or 33%), your point is still valid.

joed2

I am using the Motorola v710 with Verizon service. I looked at the compatibility matrix offered by Verizon and there is an issue with the sync between the phone book on the phone and the phone book in the car. It will not down load the phone book into the car phone book. Its a problem because its hard to dial from the phone (not supposed to do that anyway) and not take advantage of this feature on the car console.
Anybody have any additional info on this?

mirex

I finally figured out how to get phone numbers from my Nextel i605 (Motorola) phone into my RX400h navigation system. It was complicated and I sometimes had to try transferring a number more than once. I could only transfer 1 number at a time, but that was ok since I only want a few of my phone book numbers transferred.

I followed the directions on my 400h until the screen told me to transfer a number from my phone. From my i605 I went to contacts, then highlighted an individual name, clicked the far left button that normally activates Java apps. I then scrolled down to transfer and clicked ok, then Bluetooth, and finally the name I had given my phone.

Once contact was made the transfer began and completed in a few seconds. Following the directions in the navigation manual I set the desired contact up as 1-button which allows me to dial while the vehicle is moving.

One strange quirk--if you have a home phone number and a cell phone number for the same contact, only the home number would transfer. I got around this by creating a 2nd contact for the same person and only put the cell number in.

While driving I extend the antenna on the i605 and place it upright in the forward right box in the console located between the front seats.

There may be an easier way to do this, but I haven't found one. My brother has not figured out how to transfer contacts from his Nextel Blackberry to his Lexus GX. Unfortunately there does not seem to be any standardization from one phone to the next.

joed2

I ordered the interior wood trim option on my 400h. I was surprised to find upon delivery that the wood trim option did not include a wood steering wheel. When I was at the dealer showroom I was directed to cars with the wood trim option to cars with wood trim and a wood steering wheel and I unfortunately assumed that the wood trim included the wood steering wheel. Has anyone had a similiar experience with this. Other than that the car is a real beauty but the wood steering wheel would really finish off the interior.

PF_Flyer

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News & Views, Wagons, & Hybrid Vehicles

maxamigo

Thanks so much for all feedbacks regarding Bluetooth for phones!!

I think I will stick with Nextel for free-incoming plans... seems their Bluetooth performance is good enough.

maxamigo

I haven't look at it from the 10 tanks point of view.

I would argue that if you take a trip at elevation X and complete a round trip back to the same elevation, then you gas mileage reading is quite valid, assuming there is no difference between inbound and outbound amount of trafic. Or do two of the same round trips, one on heavy inbound and one on heavy outbound trafic. That should be close enough.

In any case, there are two large determining factors affecting gas mileage:
1. change in elevation
2. difference in trafic pattern/amount.

If you can overcome those variables adequately, then you gas mileage reading should be quite correct for YOUR case.

wwest

this way.

Instead of the battery storing extra energy think of it as an extra gas tank of say, 3 gallons, that on some random basis cannot be refilled at the pump regardless of its fill level.

Then the only way to know your actual MPG would be to average your fill-ups over 10 or more tanks.

shackman

Joed2,
I am very interested in your experience since I have the same Verizon model that I bought specifically for my RX 400h. That was the only Bluetooth model available. Please tell me exactly what it can do. I have already been told that I will not be able to use the phone book.

otis1

I agree that you need to make multiple measurements to get an idea of what your MPG is. I think 10 is a little excessive- maybe 3-4 is ok. But this has nothing to do with the battery capacity. I think the "gas equivalent" of a charged battery is closer to 0.25 gallon of gas, not 3 gallons- making a MPG difference of about 0.5 for a tank of gas- amd this is assuming you go from compleately charged to discharged.

Lets say you take 100 measurements (of "typical conditions") and find that 28 is the average, and 95% of the measurements fall between 25 and 31. if you were to rely on only 1 measurement, it's not unlikely that you might calculate 30 mpg and think, "wow, that's great." Or maybe you calculate 26 and think it's not too impressive. this is why an average of multiple calculations is necessary. the MAX potential contribution of the battery of 0.5 MPG gets washed among other factors.

mirex

See my post #1575.

I would assume that a Motorola i605 would use the same steps for transferring phone contacts Nextel and Verizon although assuming anything about cell phones can be dangerous.

If you go to http://lexus.letstalk.com and put your zip code in for the RX 2005 you will see the phone models that Lexus has tested. Neither Nextel of Verizon are listed for my area code.

My son works for Verizon and says that Verizon is planning to come out with several new models that are Bluetooth capable, but no dates are available. Nextel has the same story.

cyclone4

Dylan,

I am back from my weekend trip to Chicago. It was a lot of fun going to Wrigley for the first time ever. However, the results of the 2 games so far were not what I was looking for. I hope the Sox take the final game this evening.

Did I answer some of the questions (post #1571) you had for me concerning the test drive I conducted last week?

headless

Games sound like fun...and I'm sure suffering in the LS430 wasn't all that bad! Laser cruise...interesting...don't know if I'd trust it...too many factors that affect lasers...

Anyway, I've spoken with several people who have our RX400...they're all in the same boat....mid 20s for mileage overall...I think you are the ONLY one with the really high numbers...

I am driving with efforts to coast a lot, but will not surrender the performance of the vehicle if I need to move quickly for a moment or two. The car does move quickly if you want it to...I am finding that highway speeds of 75 mph with AC on will get you around 25 mpg...and that's okay as 75 is a good speed...

The highlander hybrids are out...I know a couple of people who have gotten them...(yeah, already!)...they are just getting used to driving them but so far, 3 out of 3 say low 20s...just like where we were...

I think the numbers for the RX will settle around 25 mpg as an average...and this is below the 27/31 by a good amount...this is with 'normal' driving...meaning, driving like you're not always looking at a MPG gauge... Cyclone, I read you're doing better...but you're the only one I've heard of who's doing this well...your driving environment must be very, very different from most others who own the vehicle...in addition, I doubt you're utilizing the excellent performance ability of the vehicle...

Headless

headless

Wow...what a talk about moonroofs....

I love mine..esp. the one touch open and close...

If you live in a temperate climate, the feature is grea...I guess if you're in southern florida where it's at least 85 degrees everyday...and humid...you're not going to get many moonroof days...

Headless

rocky7

Who is your dealer? I was not aware you could any kind of wood trim on the 400h. If this is after market I would like to call them to find out details.

wwest

Please, only traditional naysayers need respond.

I am on the verge, cusp, of commiting to buying an RX400h.

My idea is to have custom ground intake cams made and installed to convert the engine to the atkinson cycle. I don't need V8 performance and as I see it the loss of about 20% would put me back into an RX330 equivalent insofar as HP/torque is concerned but also with an equivalent 20% GAIN in fuel economy.

For the rest of you, sorry, but my wife says I don't need encouragement in this possible venture. Also, I am finding that all the dealers I have visited, WA & OR, seem to have surplus RX400h inventory.

gagrice

My idea is to have custom ground intake cams made and installed to convert the engine to the atkinson cycle.

Tell them you will pay Invoice and they will not be bothered with warranty work. Your plan is to transform the vehicle into a true high mileage SUV and the warranty may be in question when you are finished. Go for it, you have wanted one since before anyone even started talking about them.

wwest

My primary Lexus dealer already knows that once the vehicle leaves their lot they NEVER get to touch it again.

But then NONE have needed more than routine maintainance.

gagrice

Do you think it would gain you much in mileage? I take it this would then match the Prius design closer?

wwest

The atkinson cycle leaves the intake valve open for a portion of the compression cycle, typically up to 30%. A portion of the intake mixture is forced out of the cyclinder and back into the intake plenum. The effect is that you get a "longer" power stroke, more of the mixture's explosive energy is used in the power stroke.

Turbocharging an Atkinson cycle engine doesn't work because unlike the otto cycle there is not enough energy left at the exhaust outlet to run a turbocharger.

I think the fuel economy gain that Mazda quotes for the Millenia S is 23%. In their case they also use a supercharger so the engine performance doesn't suffer and they still get ~20% mpg GAINS.

I've been trying to figure out why Toyota doesn't use the Atkinson cycle in the RX400h since they use it in the Prius. I finally came to realize that it likely has something to do with keeping the catalytic converter "lit-off", fully heated. That may very well be why the RX400h runs the ICE so often, it must keep the catalyst up to operating temperature.

Atkinson cycle = less/no wasted energy out the exhaust = no HEAT for the catalyst.

anthonyp

Man go for it...I also think we will be getting one...It surely would be nice to hear your reports from time to time, and also your encouragement or lack of....Tony

fizban

Go for it!
Interesting theory on the catalytic converter. Hadn't thought about that.

dylan hixon

Yes you answered my questions. I still have not had time to make an ultra high mpg run, but I want to try to break your record for 25 miles!

I think 25mpg is about all the car will do with normal driving: reasonably fast speeds, decent accelerations, and AC. I suggest that all posters put their lifetime mpg (not average, total miles over total fuel) at the end of posts.

25 is about right as a real world mpg. This whole hybrid overstatement of mpg is a little like the Audi 5000 "unintended" acceleration, it actually happens with all cars. Take a look at this AAA test of real world mpg for various cars from the Honda Insight to the Lexus LX 470. The average of the cars on the list get only 80% of their combines mpg ratings. At 25mpg, the 400h is getting 86% of its combined rating, and, coincidentally, at 48mpg (which is what I hear for an average) the prius also gets 86%. Perhaps this test was more stringent, and the 400h and Prius (neither were tested) would do worse, but they seem to be in the same range of mpg underperformance.

Remember to keep in perspective how good even 25 mpg is for a V8 (equivalent), 4WD SUV. The 2005 Mercedes ML500, similar weight, performance, and price, is RATED at 15mpg combined on 91 octane premium! 29mpg EPA combined is the same rating as the Toyota Camry 4 cylinder!

lifetime mpg 25.51 1374 miles

dylan hixon

"think of it as an extra gas tank of say, 3 gallons"

Where do you get 3 gallons? On a straight energy basis, the battery capacity is 0.056 gallons, if you correct for the higher coversion ratio of the battery energy versus the gasoline, it is more like 0.12 gals.

"that on some random basis cannot be refilled at the pump regardless of its fill level."

Yes but it has its own gauge so you can see roughly how much of it you used, and calculate the effect for a tank, although you will find the increase of decrease of mpg diminimus. The difference in the auto stop on two gas pumps will have more effect on mpg than a few bars of net battery consumption.

dylan hixon

First of all let me congratulate you on a ballsy plan. Hacking is the great american way, and all of this damn computerized technology has stiffled home grown automotive innovation. If I get the nerve, I will look at doing some plug in hybrid mods to my car, though both my wife and the leasing company may have something to say about it.

A few considerations for your plan.

There is plenty of energy left in the exhaust of an Atkinson engine, the catalyst on the Prius and Escape work fine for SULEV.

The Atkinson cycle uses a high expansion ratio geometry with an expansion stroke longer than the compression stroke to extract more energy out of the charge. The Prius has a 9.5:1 compression ratio, and a 13:1 expansion ratio. The two things you need for the engine to function well in Atkinson are enough compression for good combustion, and enough expansion ratio to get a benefit. If you drop the effective compression ratio with a late intake valve closure cam, then you won't get good combustion. If you raise the intake pressure with forced induction (Mazda's Miller cycle uses a supercharger, but to help low end torque not compression) then you get good combustion, but you lose the expansion ratio because the engine geometry only provides 10.8:1. I think you will need high compression pistons, 13 or 14:1, then drop the effective compression ratio with the cam.

Stuff like this can be done, I have a friend who turbocharged his Insight. He actually intended not to increase his MPG, but to get the current high at higher speeds. He is still testing.

I think the 400h does not use Atkinson for performance, and engine development cost reasons. It is a shame because the Atkinson cycle is a great fit for a hybrid. They have bad low end torque, but the electric motors more than make up for it.

peralta

The RX400H engine is (and I say this clear) ATKINSON CYCLE.
You are correct about atkinson intake cam setting. It is very efficient but less powerful especially at low RPM.

However, the same cam setting at higher engine speed has supercharging effect, the rush and momentum (or inertia) of intake air continues to fill the cylinder far after the bottom dead center. You will see that the torque curve is very peaky.

With atkinson cycle, it can produce low level of horsepower extremely effeiciently. Most of the time while the vehicle is at steady speed you only need 30-40 horsepower. Regular V6 is not efficient in producing 10-15% of power capacity.

The hybrid RX is also more fuel efficient on the highway not just in the city.

wwest

How does removing some of the charge via late intake timing differ from a low charge due to partial throttle?

Except at/near WOT which is where I expect the electrics to bring me back into the realm of V6 performance.

cyclone4

The discussions you are having are fascinating but I would venture to guess that most of us on this board have no clue what you are talking about. I am interested in your discussions, but is it possible to explain in "layman's" language? Are you trying to say that in order to get the best gas mileage, you have to somehow cut down on performance and vise-versa?

mirex

The first hybrids were slugs (good mileage, but no power or performance). In developing the 400h, Lexis chose performance over gas mileage. What you get with the 400h over the RX330 is better performance and better mpg. They could have gotten even better mpg, but at the sacrifice of performance.

I have just under 500 miles on my 400h and like the balance between mpg and performance. Both are much better than my 2003 RX300. I am presently getting 30.2 mpg after my last fill up (90% highway and 10 % city with the air conditioner off and driving at posted speed limits). I will be better able to evaluate my 400h after a couple more thousand miles.

stevedebi

Because the car pollution controls are computer controlled; if you modify the engine, it will not pass the smog tests required for vehicle registration. You only have to get the car smogged every few years, but it would most likely fail when tested.

Unless you can also modify the computer codes to somehow compensate? But then that would require testing apparatus to determine when the vehicle was back in smog specs...

cyclone4

Thank you mirex! I sort of knew that was the case, but I do not understand all the engineering talk. So how inferior is the Prius in performance than the 400h? Does it rocket its way on highway passing like the 400h does? I sometimes envy the people getting 45-55 mpg on the Prius. But then again, it is probably a "slow poke" compared to the 400h.

I am very happy to hear that you are getting great gas mileage with the 400h to this point. That is impressive considering that it is mostly highway driving. As I have posted on several occasions now, wind speed and direction is critical on gas mileage when driving on the interstates. A 15 mph tail wind as opposed to a head wind will probably result in at least 5-6 mpg difference. A cross wind is probably about as detrimental for gas mileage as a head wind. By the way, where do you live to allow you to drive with no air conditioning this time of year? Is it in the Seattle area by any chance?

wwest

Some of us, me and seemingly others, are quite satisfied with the RX300 and/or the RX330's level of performance...engine HP/torque.

Assuming some way can be found to keep the catalytic converter heated there would be no way for the emissions inspection system, nor the on board ECUs, to detect the difference between a vehicle retrofitted with a new cam to implement the atkinson cycle and one with the throttle slightly more closed to generate the same level of HP/Torque.

The engine ECU would still control, continuously adjust, the fuel/air mixture to satisfy the downstream oxygen sensor regardless of throttle position. The only exception would be the same as the OEM system, at idle the ECU would have to "learn" the correct fuel injector duty cycle to use to obtain the factory designated engine RPM rate.

An analog of the atkinson cycle:

In a normal otto cycle engine operating at a given RPM, say 1400, under load with the throttle 1/3 open, pick a number for each cylinder to "intake" on each intake stroke, for example let's just arbitrarily pick 1 quart of air (sea level, standard day) with the correct fuel mixture. Now the mixture will be fully compressed on the next cycle then the ignition will fire the plug and the piston will begin the power stroke.

As the fuel/air mixture explosive front propagates throughout the fuel/air mixture volume the piston will be forced downward until it reaches BDC, bottom dead center. At that point it will begin its upward travel, the exhaust cycle, forcing the HOT exhaust gasses out of the cylinder and into the exhaust manifold.

Now we all know, I should think, that a not an insignificant portion of the mixture's explosive energy, mostly in the form of heat and pressure, travels down the exhaust system, some of that heat being used to keep the catalyst "lit-off", at an elevated operating temperature.

Some engineers content that operation of a turbocharger, downstream of the exhaust manifold, is a form of "free" energy. While free is not exactly correct it is very true that in the standard otto cycle engine there is wasted energy, lots of it, exhausted out the tailpipe. Absent being used to "reheat" the catalyst and/or spin a turbocharger that is.

The atkinson cycle is simply a method whereby more of the explosive energy of the mixture is used to force the piston downward during the power stroke. With a little research here on the internet you can find examples of a mechanical device whereby the piston's intake cycle travel, actual physical distance, during the intake stroke is less than the piston travel distance on the compression and power strokes.

In short it is a way to use less fuel to make more (useable) energy.

Leaving the intake valve open for a portion of the compression stroke allows us to move 1/3 of that "quart" back into the intake manifold. Now we have reduced the level of fuel used for each cycle of the engine by 1/3. That would ordinarily mean a loss of 1/3 of the engine's capability. But now on the power cycle we effectively have a longer "burn" period, more of the explosive energy is used to move the piston downward resulting a a much lower level of energy wasted out the exhaust.

So, first we removed 1/3 of the fuel intake, and now we gain a rather significant level of that POWER capability back using, effectively, a longer power stroke than the intake stroke.

The net effect being that the loss in power output is more than made up for by the increase in fuel economy.

Sounds, even to me, like a bit of black magic, hocus/pocus, but that is the way it works at least as I understand it.

Does anyone know how the RX400h ECU engine control system "knows" when to restart the ICE in order to keep the catalytic converter "lit-off", heated to optimum operating temperature.

Does it by any chance have a thermocouple within the catalyst itself?

Karen_S

Join other RX 400h enthusiasts in Edmunds.com Lexus RX 400h Owners Club!

dylan hixon

"How does removing some of the charge via late intake timing differ from a low charge due to partial throttle?"

The difference is that by eliminating 30% of the compression stroke, you get less compression heating of the charge. The cooler charge burns slower and more poorly.

Also, although it sounds obvious, you must increase the expansion ratio to get a high expansion ratio engine. Otherwise, you wont extract any more energy than the regular 10.8:1CR 400h.

What you are talking about doing is called "load control by LIVC" (late intake valve closure). By closing the intake valve later, within reason, you can open the throttle wider for a given load and reduce pumping losses, specifically throttleing losses. That will increase efficiency, since throttleing losses reduce efficiency by something like 20%. It is one of the reasons why unthrottled engines like diesels are so efficient.

joed2

Lexus of Smithtown, Long Island NewYork is the dealership where I purchased the car.. There is 21 piece wood trim after market option that improves the interior look quite a bit.

joed2

The car system (interfaced to cell phone) will only be able to receive and make calls. It cannot store a local phone book ...yet. I will be going back to the dealer within a couple of weeks to find out what software flash is available will allow for the download of the phone book in the phone to the car. I tried the Verizon route with no luck via a phone call to their technical support. The dealer was telling me there is a "lock" on this procedure from the software on the phone. I will not give up easily......

peralta

Sorry for the long post but read on, I think this is valuable information for everyone.

"The net effect being that the loss in power output is more than made up for by the increase in fuel economy. "

It is not just the cam phasing that counts in Toyota's Atkinson. The moving parts can be made lighter since it has less "peak load" and less peak RPM, to a weight reduction of maybe 20%. This results to less mechanical parasitic loss coming from reciprocating parts.

It also has a "crankshaft offset", center a little bit off to one side to minimize cylinder "side slap friction" on power stroke.

Intake butterfly can add resistance to flow of intake air, which I think is also eliminated in toyota's engine.

The toyota's atkinson is a marvel of innovations when it comes to fuel saving measures. I am sure there are lots of other measures that toyota doesn't want to reveal.

It is not just the engine that contribute to toyota's excellent fuel economy, The CVT is very efficient. The split drive routes 72% of torque directly to the wheel which has a mechanical efficiency of almost 100% (no other transmission can beat that) the other 28% is routed to generator and then to motor and/or battery. That route is about 50-60% efficient at most. But when you combine them, the result speaks for itself.

The transmission/engine combination is always close to its peak efficiency no matter how you drive the car. That is in contrast to conventional drivetrains where the engine and transmission have their “highs and lows” efficiency all throughout the operating range.

The biggest hurdle was to integrate the CVT split routes into a smooth unobtrusive operation. This took Toyota the bulk of their R&D money and brains.

In crawling stop and go traffic, the battery takes care of it so no fuel is wasted on unnecessary engine idling.

Plus of course the regenerative braking which recaptures the energy spent on previous accelerations explains the phenomenal city mileage.

"Does anyone know how the RX400h ECU engine control system "knows" when to restart the ICE in order to keep the catalytic converter "lit-off", heated to optimum operating temperature”.

I guess once the catalytic converter is hot, it takes hours before it cools down, so stop and go traffic would not require engine to restart just to reheat the cat, and if you ever need to reheat the cat, not much energy is lost since you are charging the battery at the same time.

The Toyota’s synergy drive is a whole different animal and is certainly here to stay. Other car companies are scrambling to catch up.

I would say Honda is close behind in hybrid technology and would soon make cars capable of battery power alone by putting the IMA to the transmission side instead of the current location which is at the engine side (that’s my prediction).

It would be very interesting how the future toyota and Honda hybrid compare especially that their approaches are radically very very different.

peralta

One article from an interview with ford engineer about the Ford Escape hybrid said (I don't have the link anymore) that they have exhausted all variety of settings to the Escape hybrid and "any further adjustments to the current setting will only hurt the fuel economy".

This is from a ford hybrid engineer who headed the R&D. So folks, it is very likely that other hybrids have been also optimized for fuel economy and any alteration would only adversely afect it.

One exception is maybe put a low rolling resistance tires to RX400H, while sacrificng traction and ride comfort.

wwest

I'm sure I have read somewhere that the RX400h DOES NOT use the atkinson cycle as does the Prius.

Wrong?

wwest

Assuming you are correct how is it then possible for the Millenia S to couple the atkinson cycle with the burden of driving a Supercharger (now becomes "Miller" cycle) and yet still yield a ~20% improvement in fuel economy?

Due to the SC compression we are now back to putting the full "quart" of mixture into the cylinder during the intake cycle, all the pumping losses remain equal. Now the only difference is a shorter compression cycle.

mirex

Correct....the RX400h does not use the atkinson concept.

gagrice

Dave Hermance, executive engineer of environmental engineering at Toyota’s Technical Center, said performance, not fuel economy, was the goal with the RX400h system. Consequently, the V-6 engine uses the regular Otto combustion cycle and not the Atkinson cycle used in the Prius.

http://www.familycar.com/RoadTests/LexusRX400h/

peralta

I stand corrected, the RX400H is not atkinson but is tuned to produce minimal horsepower very efficiently needed for steady speed.

The vvti setting is similar to atkinson at low RPM, having low torque, but this is taken cared off by the electric motor.

At higher RPM the vvti setting is closer to otto cycle with emphasis more on fuel economy.

gagrice

Get a hold of the engineers at Lexus and tell them you want your RX400h built using the Atkinson cycle. That you are going after the world record mileage in an SUV. You got stroke there at Lexus with all the cars you have bought. They must have tried several configurations. They opted for the 0-60 over the 45 MPG.

larsb

quote gagrice-"They opted for the 0-60 over the 45 MPG."-end quote

No, they did not "opt" for that.....that nature of building a hybrid SUV of that size was the deciding factor.

To get 45 MPG out of a 4500 pound SUV would have meant about a 25 second 0-60 time and about a 60 HP engine - something we all know would never have sold....

Hybrid does not necessarily mean "high MPG vehicle." If you can improve MPG over a comparable sized non-hybrid model (which is what they did in this case and in the HH) then you are doing good work.