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Lexus RX 400h

2334 messages,  Last post on Oct 11, 2009 at 10:42 AM

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What is this discussion about? Lexus RX 400h, Hybrid Cars


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#2036 of 2334
Re: Strange/Weird... [wwest] by rx400hfan
Oct 13, 2005 (10:32 am)
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Replying to: wwest (Oct 13, 2005 9:09 am)

In all of the technical presentations of the HSD I have seen, MG1 is the Motor/Generator connected to the sun gear of the PSD and functions as a generator most of the time that the ICE is producing power. MG2 is the larger Motor/Generator connected to the ring gear of the PSD and through reductions gears to the front axle. Therefore MG2 in this example is the motor for which we are given the HP rating. Since the ICE is attached to the planetary gear carrier, anytime it is producing power a fixed percentage of torque will be provided to MG1 (Primarily a generator when the ICE is running) with the remaining percentage of torque applied to the front axle in parallel with MG2. I am not familiar with the gear ratios of the PSD used in the Lexus but the ratio was 28% to MG1 vs. 72% to MG2/Drivetrain on the Prius. Here is where it get rather complicated. Power is not a function of only torque but of torque & RPM so when we stomp the accelorator at low speed the engine power & rpm rise dramatically yet our road speed has not yet risen nearly as much. Therefore even though the axle is receiving 72% of the torque from the ICE it is receiving a much lower percentage of the power output of the engine. The only way the engine rpm & power can rise is for MG1 to spin up to a very high rpm and absorb all the remaing output power of the ICE by acting as a generator. So at low speed/high throttle a large portion of the power output of the ICE is in the form of electrical power from MG1, all this power is added to the power coming from the battary and fed into the large MG2 Traction motor.
#2037 of 2334
But.... by wwest
Oct 13, 2005 (12:27 pm)
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Lexus states that the TOTAL, net HP is 268.....
 
That's basically 208 from the ICE and 60 (45KW) from the "hybrid" aspect.
 
Is it possible that Lexus initially planned to have a ~140KW hybrid battery set and then things went awry for some reason before it entered production?
 
That would also account for the "400" in RX400h.
 
208HP ICE, 192HP (140KW) electrics.
 
And remember, keep in mind, the city/hwy MPG being reported by owners is completely out of whack, opposite, with the EPA estimates and what is being reported for the Prius.
 
Would a more robust battery pack had produced a more appropreate city MPG?
#2038 of 2334
Re: But.... [wwest] by rx400hfan
Oct 13, 2005 (1:23 pm)
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Replying to: wwest (Oct 13, 2005 12:27 pm)

No they didn't plan anything other than what it is. The 400 in RX400h stands for power equal to a 4.0 liter engine just like RX330 = 3.3 liter engine. You missed the whole point of the explanation above in that at low road speeds you need 192HP electrics to be able to use the 208HP of the ICE since most of the power takes the path of electric from MG1 to MG2 otherwise at low speed you would have to limit the power output of the ICE to a small fraction of what it has. This would be the equivalent of eliminating any lower gears on a regular vehicle.
#2039 of 2334
Okay.... by wwest
Oct 13, 2005 (2:09 pm)
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When I am WOT and the ICE is producing 208HP are you saying half of that drives the generator and then from the generator that half drives MG2...
 
CVT....
 
If I jack up the rear end of a RWD vehicle with just a simple open diff'l, put it gear with the engine running and hold one wheel stationary with just my little pinky...
 
If you think of the opposite wheel, now spinning rapidly, as MG1, that's the way I thought the CVT in the Prius, RXh and HH worked. Virtually no energy needed at MG1 to prevent the ICE from conveying energy to the roadbed via the opposite end of the diff'l if you want to remain stopped.
 
So how do I overcome the "traction" force of my pinky?? I stop allowing MG1 to "freewheel", in other words I supply it with enough energy to turn it AGAINST the motive force of the engine. Remember that MG1 has a serious mechanical advantage over the ICE via the planetary gearset, so it doesn't take much energy, relatively.
 
I assume the above moves the vehicle in reverse and if I apply AC power to MG1 to AID in supplying motive force the vehicle goes forward.
 
But yes, assuming I am not requiring WOT performance, the ICE torque can be used to to recharge the batteries.
#2040 of 2334
Re: But.... [rx400hfan] by wwest
Oct 13, 2005 (2:13 pm)
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Replying to: rx400hfan (Oct 13, 2005 1:23 pm)

Sorry.........
 
Are you confusing "low speed" with constant speed?
 
At a constant speed, even uphill or towing, very little of the ICE capability is required for forward motion, So clearly, it can then be used to recharge the batteries.
 
But if I am accelerating rapidly....
#2041 of 2334
Re: Okay.... [wwest] by rx400hfan
Oct 13, 2005 (6:06 pm)
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Replying to: wwest (Oct 13, 2005 2:09 pm)

The more accurate analogy is for your RWD car to have one side jacked up on a stand with castors and have it in gear and have someone step on the throttle. The car is not going to move but the jacked up wheel will spin madly. The only way to get the wheel still on the ground to move the car is for something to hold the spinning wheel back. I do know with absolute certainty that if you grab that wheel to slow it down to cause the other one to move the car, that it will take you apart before you can hold it back enough to get the car moving.
 
You are correct that MG1 will be freewheeling when the ICE is running and the Lexus is stationary, but when you push the accelerator MG1 does not hold back by taking power from the battery it holds back by being a generator and providing the generated power to MG2. Due to the laws of physics while the vehicle is still stationary 100% of the power output of the engine (less slight gear losses) will be through MG1 acting as a generator. This power is directed into MG2 in addition to the battery power. As the vehicle speed increases more and more of the ICE power goes directly to the wheels via the ring gear of the PSD. Since the ring gear of the PSD and MG2 are tied directly together and then to the drive axle their speed is directly tied to vehicle speed. At the point where ICE rpm = MG2 RPM 28% of the power from the ICE will be generating electric through MG1 and 72% will be applied to the drive train.
#2043 of 2334
RX 400h overpriced? by justg0
Oct 27, 2005 (11:30 pm)
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So I am looking to buy a SUV and have narrowed my choices to BMW X5 4.4i and Lexus RX 400h. Both these are quite similarly priced (X5 a little higher).
 
The factors that are important to me are (in no particular order): luxury, performance, reliability and depreciation. Based on my test drive and research that I have done, here's what I have concluded (very simply put):
 
1. Luxury: Both are good
2. Performance: X5 4.4i has an edge
3. Reliability: Rx 400h wins (based on Lexus's reputation)
4. Depreciation: Not sure here about RX 400h?
 
Lexus RX 330 retains it value quite well, so one can say that so should 400h. But my concern is that Lexus is overpricing 400h because of very limited supply and more demand (simple economics). I will also have to pay MSRP (I am in the Seattle area), though if I wait till next year I may be able to get some tax credit. I am not trying to do the fuel math and I don't care much about that (and you typically lose that anyway), but I believe that RX 400h should be priced higher than a similarly equipped RX 300 just because it has more power (similar to why V8 is priced more than V6). But consider the situation 5 years from now when there is no shortage of hybrid vehicles and there are lot more hybrid models from Lexus & other manufactures. Will the value of 2005 Lexus 400h drop considerably? Why does Edmunds (based on their TMV) think the Lexus will depreciate approx $10,000 in the first year (considerably higher than other SUVs like X5, RX 330)?
 
Did anyone conduct such analysis before deciding to purchase (or not) Rx400h and what did you conclude?
#2044 of 2334
choices by katzjamr
Oct 27, 2005 (11:49 pm)
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Its hard to understand where they get that 10K figure im sure its a guess. Dealers are selling used 400h (admittedly low miles) for about 3K below msrp. I think there will be high demand for the hybrids on the west coast for a long time. I have a 400h with 4300 miles and its been great. I agree it is alot of money for a car, i can justify it for business use. My salesman asked me to consider leasing, as it offers tax advantages, and in three years when you turn yours in it should coincide with the next model RX hybrid. I did purchase mine as i usually keep them for 5 or 6 years. Yes you will have a tax credit next year that is over 2K. The bmw is a great car and better offroad, as the 400h is not reccommended for this type of use. At the same time the Hybrid Synergy Drive in the toyotas has been very reliable as reported by owners online and consumer reports finding it much more reliable than average. To get the best mileage you will have to adopt a hybrid driving style but its makes driving interesting, and you wont feel stressed in traffic jams. The smooth linear power across the whole power band is incredible in the 400h and it is a great combination of safety, options, comfort speed and as you mentioned reliability. Gas is only going to go up and the 400h affords you a no compromises way to deal with that. The real unanswered question for me is the cost of repairs to the HSD if you keep one that is out of warranty. There is no doubt that the parts and labor are going to be expensive. Yes that is 7 years or 100K down the road but it will probably cause me to trade my 400h in earlier, than the longer period i would normally own the car. sorry for the stream of consciousness post but those are my thots.
#2045 of 2334
Re: RX 400h overpriced? [justg0] by falconone
Oct 28, 2005 (3:59 am)
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Replying to: justg0 (Oct 27, 2005 11:30 pm)

Whatever you do, DON'T buy the X5. My friend had one on lease and it has lots of problems. Even CR shows poor reliability. Test drive the RX330 NON hybrid fully loaded and see if you like that. It's less than the X5 and MUCH more reliable.

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