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Toyota Prius, Hybrid Cars, Car Buying, Hatchback, Sedan
#132 of 311 1.8L Upgrade for 2009 ??
Feb 04, 2008 (12:19 pm)
First, if we are going to speculate let's look at some numbers. To start with, I've never fully understood why the current Prius engine runs only to 5000rpm, whereas the 2.4L in the Camry Hybrid runs at the same speed as the engine in the non-Hybrid Camry which is 6000rpm. With that in mind I would expect that before upgrading engine capacity to 1.8L, from Im2's Motor Trend reference, that Toyota would be addressing this rpm issue with the original engine first. Sure I'm not expecting them to get the full 108Hp from the Echo's 1NZ-FE engine but 20% increase from the 76Hp Atkinsonised engines, that were installed starting with the 2004 Prius, would be welcome. The following is a rehash of my #104 post of three months ago. It was in answer to wwest regarding the suggestions of more horsepower via forced induction. This unfortunate 1.8L idea being also a step in this direction. Even though I don't own one yet my test drive of the Prius told me the car is powerful enough. And incidently that's from the vantage point of someone who happens to drive a Lexus. Clearly fuel economy will suffer with a 1.8L and the last time I looked the Prius is under no threat in the horsepower race.
To continue with the simple expedient of merely increasing the engine rpm by 20% must needs the rest of the system to accomodate this. And inexpensively too I might add. The fact is you have to start with the MG2 system which will need upgrading 20% also, since at lower speeds the majority of the torque at the wheels comes from this machine - 259lbs-ft versus 59lbs-ft from the ICE. To do this the three stage reducer giving a 4.113 stepdown ratio needs to be stretched still further to 5.0. This will require MG2 to run at 7200rpm at 100mph and to do that will require the upconverter to supply a max of 650volts, up from the 500volts used previously. At the same time MG1 will need to reach 12000 rpm to generate this voltage also. All these things have been done with the Camry Hybrid by the way. The remaining gearing and motor currents will stay as before. Since voltage and rpm are 'free' only the minimal cost of the two gears being changed is the salient factor. Motor windings can remain the same since the engine torque is not being upgraded. The system continues to deal with the same torque as before but at a newer maximum rpm.
Let's determine the max power point using ICE = 6000rpm, MG1= 12000rpm.
Then 12000 - 3.6 x 6000 = - 2.6 x MG2,
so MG2 = 3692rpm and since 7200rpm = 100mph.....
The current Prius engine does not reach full power until 51.28mph, and the calculation shows this suggested new arrangement won't change things either. Of course MG2 would now be rated at 60kw with somewhat higher iron losses but these would be compensated by improved cooling. This is still the same vehicle so the rolling losses haven't changed, just the time the system can be run at full power at maximum acceleration has been reduced. It must be obvious to most that the more powerful you make the car the shorter the time you are going to have to use that power if top speed, as here, is clipped at 100mph. And this is what the designers are banking on. This also means that despite the expected performance uptick anyone who puts a towbar on this vehicle can still put the system at risk.
In #104 replying to wwest earlier I wrote one of the problems with HSD is the ring gear and the components connected to it. Rotating this assembly beyond 6000rpm raises a serious balance issue. It represents the output shaft of the whole system and this rpm at 100mph is fine for a planetary connected to a 4 cyl engine, later on however it may turn out to be too slow for the higher speed small engines in the pipeline It will be interesting to see whether this ring gear increase is the choice Toyota will make. Everything has risk but it's not like the greater population are regularly driving or should be driving this vehicle above 85mph anyway that would repeatedly test 7200rpm speeds on this component.
Finally I would like to see them copy the Camry design which has omitted the sprocket chain power takeoff - thereby possibly releasing a 6% gain in torque by my estimation. If you care to go to #470 on the Toyota Camry Hybrid board where USBSEAWOLF2000 has posted diagrams of the two systems you can see what I mean.
I am fairly sure they won't go so far as to copy that second planetary used to raise the specific power of MG2 that you will also see there. For that matter I think HSD design will stagnate until the Chevy Volt appears or Honda returns with a new hybrid but not with their mechanical CVT that can't seem to reach 100k miles nor with the IMA which becomes ineffective when the HV battery is exposed to extended sub zero temperatures.
#133 of 311 Re: 1.8L Upgrade for 2009 ?? [toyolla2]
Feb 04, 2008 (12:41 pm)
I suspect the RPM is limited due to the Atkinson cycle. That is, it's a longer stroke than the Echo engine, not exactly the -SAME- engine. Long stroke engines don't handle high RPM well. Note that the RPM was raised from the THS which ran up to 4500 RPM (current model is THS II). Toyota -may- change the engine, but from what I've heard, if they do it's because the current design is getting "long in the tooth". A newer design would give lower emissions, among other things, such as fully adjustable valve timing (intake -and- exhaust).
I don't know where these rumors begin, but I suspect it's magazines trying to sell copies, not real info. leaked from Toyota. Including the image showing a sleeker Prius. Do know that the "bean shaped" (my description, please don't read any of my feelings into that term) concept car first shown last year at the German Auto show has many design ideas that, according to Toyota, will be used in the next iteration.
I concur that the current car is powerful enough. And I'm comparing to a 2001 Nissan Pathfinder LE (240 HP 265 lb-ft of torque). My Prius passes better on 2 lane highways than the Pathfinder ever did! Probably a combination of lower weight, lower wind resistance, and electric motor torque assistance.
#134 of 311 Re: 1.8L Upgrade for 2009 ?? [pathstar1]
Feb 04, 2008 (1:30 pm)
I certainly don't have the technical expertise of you both but from a user's pov I too find that the current model has plenty of power. I liken it to a point guard being quick and nimble in traffic.
That being said a 'new' model has to offer something to make the next model attractive so as not to become stale. Increased fuel economy would be wonderful if it were to jump to to mid 50's under the new EPA standards; ( 1.8 gal / 100 mi driven or 4.28 l/100km ). With EV / ECON options it would be very appealing to certain groups of buyers.
As for a new engine it appears that Toyota is going to the 'R' structure across the board beginning with the 1GR in the current 4R. That's been followed by the 2GR, 3GR, 1UR, 3UR and most recently the 2ZR 1.8L in the new Corolla and Matrix. A new 2.7L I4 is forseen in the new Venza in the fall, 1AR? Would it not make sense to standardize everything to Atkinsonize the current 1ZR 1.6L for the next Prius?
#135 of 311 Seat upgrade?
Feb 04, 2008 (5:35 pm)
Just wondering if there is any info leaked out about if the new 2009 model will have better seats. If it had we would have bought one. Really needs a better drivers seat fro long trips even tho it's a city car. height adjustment as well as a more comfortable seat would be welcome.
#136 of 311 Re: 1.8L Upgrade for 2009 ?? [pathstar1]
Feb 05, 2008 (5:27 am)
I looked up the engine specs for bore and stroke for the 2007 Camry unchanged with the Atkinson variant. The 2.4L 2AZ-FXE engine has a longer stroke (96mm) than the Prius 1.5L (84.7mm). Furthermore the Camry's 6000rpm yields an astounding average piston speed of 19.2m/sec - that's close to racing engine territory.So your statement Long stroke engines don't handle high RPM well may be good theory but Toyota doesn't appear to be following it. In comparison the 1NZ-FXE engine in the Prius tops out at at a leisurely 13.55m/sec piston speed at 5000rpm.
I have to defer to your grasp of available engines. The 1.6L would work as an upgrade and in keeping with production conformity. I am not familiar with this engine. The HSD will of course just throttle back a more powerful engine to prevent torque overload on MG1. If this engine suited the 6000rpm mod that I outlined earlier - then fine. As a marketing ploy I am not sure this upgrade is a good idea.
My take is to go the other way with the adoption of a 1.0L 3 cyl similar to the Honda Insight engine. This would yield a big step in fuel economy for the careful driver. On the other hand aggressive driving would showcase the superiority of the HSD system particularly with smaller engines. If you remember, the original cars were fairly anaemic with the same 1NZ-FE engine. It was the 50 % upgrading of the power electronics for the 2004 model year that transformed this car and I am of the opinion that this fact alone will mask somewhat the adoption of a less powerful engine. Going to a tad lighter powertrain up front may affect positively the handling performance also.
#137 of 311 ICE RPM limit.
Feb 05, 2008 (9:33 am)
Might be a function of the torque/RPM limits of the AC synchronous motor on the opposite end of the CVT. If the ICE, at top RPM, produces 120 ft/lbs of torque then the AC motor must produce 40 ft/lbs at 3 times the ICE's RPM (assuming a 1:3 reduction ratio).
And my suggestion of a variable speed SC had to do with lowering the size of the ICE while producting the same level of torque and at the same time "evening out" the torque curve, raising the ICE torque at the low end.
There is also the additional issue with the SC boost available of not having to put the electrics to so much use for hwy use when it cannot be recharged except via the ICE.
#138 of 311 Re: ICE RPM limit. [wwest]
Feb 05, 2008 (6:03 pm)
I am going to respond as best I can.
I have to make a correction regarding your first paragraph. The torque of the ICE at 5000rpm is around 82lbs-ft not 120lbs-ft, that's if we are discussing the Prius that is. As you are no doubt aware the PSD is not accurately a Power Split Device as Toyota likes to describe it but actually a Torque Split Device. It's a trap I fell into a few years ago since those mathematical equations are a bore. To continue then, we have the PSD splitting the engine torque sending 1/3.6 times 82 or 22lbs-ft into MG1 and the remaining 2.6/3.6 times 82 or 59lbs-ft to the ring gear and ultimately the wheels which I am sure you know.Those figures are reached during maximum acceleration. However as I understand it, as a generator there is no limitation on MG1 except with the proviso that you don't let it generate more than 100 amps or exceed 10,000rpm else the ECU will cause the ICE to be throttled back On the Camry they've allowed a version of this machine to reach 14,000 rpm. So I am confident there is not an rpm issue with MG1 that correspondingly limits the ICE rpm. And MG1 is the critical machine in the HSD system.
Regarding your middle paragraph, I wasn't aware there was a bottom end torque deficiency but I'm taking your word for it. All I know is that those with scan tools said that Toyota likes to 'park' the engine at 1211 rpm when they need to keep it running when power demand is less than about 8 Hp. If torque was linear then at 1/4 speed as here we should expect 76/4 or 19Hp at this speed so that indeed corroborates what your stating. Naturally the longer you can keep the engine at these low revs the better the fuel economy -reduced engine frictional losses etc.
I don't get your last paragraph since the SC is not going to help during acceleration since the engine will move up its speed range quite quickly thanks to the partial decoupling of the engine from the wheels afforded by the HSD system.
Toyota may be addressing low speed torque deficiency with its double VVT-i engine at the next upgrade.
#139 of 311 '09 PRIUS = A Cross Between Tesla & Lexus?
Feb 18, 2008 (12:26 pm)
Alright, a slight exageration but still a very interesting thought. I can't help but feel the 2ND Generation Prius has ran its' unchanged body style to its' limits but I find it to be a valid testimony to what a great and functional style it has been. My '04 has kept up with the last 5 yrs of styles and weathered the trends well. Still. I would like to see a sleeker, somewhat sportier Prius with a sunroof. Could a hardtop convertable be asking too much? (probably too pricy)
As to some of the complaints of others about the seats. I've done several trips (2,000 miles plus) and found them to be more than comfortable. The car will never ride like a "Towncar" but reasonable people know this. A few things I'd like to see on the '09 Prius...SmartKey standard....Tiltwheel...Wider Tires... and (what I hope is coming) THE PLUG-IN Mode. Oh! By the way ...I hope Toyota improves the ease of replacing Hd Lt Bulbs. They're a %*#!!!!
Feb 21, 2008 (12:40 pm)
Is Toyota really going to have a 3rd gen Prius on the market that soon? If you mean model year 2009, that is only months away...If you mean calendar year 2009, then it's a 2010 model year most likely....I'd hate to buy a current Prius and then a new one comes out 12 months from now...!
#141 of 311 Re: 2009 [xhe518]
Feb 21, 2008 (5:26 pm)
Toyota is notoriously zipped-lipped about new offerings unless it suits their purposes to generate new interest.
The Prius has a very very loyal owner/fan base that's chomping at the bit to get some tidbit of real data on the next generation. All that Toyota has said is that they decided to delay implementation of the Li-Ion batteries until more validations could be done. I believe that they stated these would be at least 2 more years down the road. 2011 MY?
But they also denied that there was any delay in the production of the next Gen. Implying that it would be coming out 'on schedule' - whatever that is. The normal schedule for Toyotas is 5 years. That would put the next Gen coming here in mid-Oct of this year. Speculation but I'd feel confident of it.
My own speculation is that the body is somewhat redone but it's still a 5 door hatch which is one of the best features of the vehicle. I'd guess that it will use the 1.6L 1ZR engine that's already in use in Japan with improved electrics and gearing for somewhat more power and better fuel economy. The new HH has both an EV and an ECON mode. I can see the next Gen Prius having both as well.
Fuel economy? + 10-20% using the new EPA numbers.
There may also be a small Prius sedan with either really high fuel economy or one that has the same fuel economy as the 5 door hatch but a much lower price. There could also be a third version as well, pickup, small minivan, small utility vehicle? All speculation.
Interesting sidenote: When the first Prius' went on sale here in 2000 they were sold to a specific clientele . These buyers had to register with Toyota to be get on the list for one of the first ones to arrive here. These first buyers were called the Pioneers. When this current Gen was being brought to market in June/July of 2003 these Pioneers were given the opportunity to be the first ones to buy the new Gen. If you know one of these Pioneers you might keep an ear open to see if they receive an early offering from Toyota. I sold one of the first of the first back in July of 2000. This buyer also bought one of the first of the first of this current Gen.