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Hybrid Vehicles Toyota Prius What to expect from the next model year Prius
311 messages, Last post on Apr 26, 2009 at 5:43 AM
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Although Julian Edgar of Autospeed did find improvement with a turbocharger, his was an anaemic pre-Gen 1 model that was shipped from the Japanese market to Australia and not available in North America. The Gen I and Gen II that arrived on our shores in comparison are fully able to drive their MG1s to their full rating of 100 Amps. Increasing the power of their engines with some sort of forced induction scheme will not improve their performance. Here's why. First it should be noted that the magnetic field of MG1, which indirectly controls engine torque, is produced by neodymium magnets which are not adjustable. The effect of this field is that MG1 requires a torque value of 22lbs-ft from the sun gear when generating 100 amps of current. Since this generated current is electronically regulated not to exceed 100 Amps this simultaneously places a useable torque limitation on the engine. In other words it doesn't matter how much more torque capability you endow this engine with, it just cannot be allowed to push MG1 into generating more than 100 Amps or it will overload that machine. The intractable situation is that the more powerful you can make the engine, the more severe the throttling back by the Prius control system will be. Next regarding the gearbox ratio change, I'm assuming we're referring to the 4.113 transaxle ratio, which offers some possibilities. The Prius system develops its maximum contant power output of 104Hp from 51mph to 100mph so the gear ratio is ineffectual in this area as someone pointed out. On the other hand the point at which the constant power is reached can be lowered by using a higher ratio and that would have the effect of reducing the 0 to 50mph acceleration timing and improving hill climbing ability. Changing 4.113 to 5.00 will lower the entrance to the max constant power point to just 40mph. The result being the that the previously 68.6Hp being developed by the engine at this speed will be upped to the 76Hp maximum. A 10.8 % increase ? No, not quite, because the battery is supplying 28Hp so the actual System increase is only (104-68.6-28)/(68.6+28) X 100 = 7.7% . This is a surprising result since most of us would expect a 20% improvement in torque going from basically 4:1 to 5:1 in the final ratio. So at 40 mph only a 7.7% improvement is realized. The problem here is that you're fighting two constant power systems. MG2 constant power from 20mph to 50mph and then the engine itself from 51mph speeds and up. The 20% improvement should be present in the 0 to 20mph range, not that you would much notice, but then it becomes minimal in the all important 20 to 50mph range. I am going to leave this discussion by simply noting that it appears that in these connected constant power systems you cannot just improve one component i.e. the engine by itself. You will need to upgrade the MG1s and MG2s as well. The transaxle ratio (4.113) or the HSD planetary ratio (2.6) are merely the glue that holds the system together. I am sure that alteration to the HSD ratio to accommodate greater engine torque will lead to further circular reasoning that will oblige upgrades on the other electrical equipment to be necessary as well. As a side issue, the genius of the HSD becomes particularly apparent here. As MG2 fades above 51mph (the volts/herz issue) makeup power comes automatically from the direct mechanical link at 6.6Hp per 10mph. At 100mph 66Hp comes directly from the engine, while the now less capable MG2 will only be required to handle 38Hp (10Hp+28Hp). This would correlate well with electric motor theory were MG2 an induction motor, but with a brushless motor it's difficult to predict exactly how much power MG2 could deliver beyond the mandatory 10Hp as top speed is approached. Any takers ? T2
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Replying to: toyolla2 (Oct 23, 2007 8:39 pm) Not that such a thing is really in the realm of feasibility.... |
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Replying to: dramades (Jul 17, 2006 2:20 pm) I went to the trouble of flying to Virginia from Florida to buy my Silver car with package #6 a week ago. Very glad I did. Think of how much you would save in gas costs, insurance and repairs versus waiting for the 2009 Prius. I say buy now while they're available. Evro in Tampa. 
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wwest I understand you're suggesting we increase the HSD ratio to avoid having the more powerful ICE overwhelm MG1 ? The general HSD eqn of MG1 = ICE x 3.6 - MG2 x 2.6 ------- eqn #1 is to become, let's say, MG1 = ICE x 4.6 - MG2 x 3.6 ------- eqn #2 for the higher torque ICE. At the present ICE rpm and MG2 rpm are 3644rpm and 1200rpm respectively passing through 20mph while accelerating. If we wish to keep the ICE at 3644rpm, since lowering it would be defeatist, then substituting into Eqn #2 MG1 will have to move up from its current max of 10,000rpm to 12,442rpm. An almost 25% rise that we know from Hybrid Camry is possible. It will have the effect of raising MG1 electrical output from 42.2Hp to 52.5Hp. The copper loss at 100 amp would remain unchanged. There will however be an increase in the iron loss at the higher excitation frequency but this may have marginal effect since these revs are only maintained during full acceleration ramps that last a few seconds.The voltage on the system will also rise thus impacting the semiconductor specifications for the inverter. MG2 will be required to handle 52.5 +28 Hp or 80.5Hp instead of 67Hp and the machine loading above 51mph remains quite high because of the battery assist. It's a long answer. As you would expect the gear ratios must be chosen to keep the rotating components within reasonable spin rates. As a result any increases in power input would be more propitiously handled by increasing the torque capacity of all the components involved. 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. Secondly MG2 needs to be turning much faster at this speed. A 16,000rpm limit at 100mph would more than double the existing power density of MG2 if it was allowed its own 10:1 reducer at the wheel axle. T2
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Replying to: toyolla2 (Oct 28, 2007 7:31 am) And just who would object if the Prius' top speed were limited to ~80 MPH..?? Will the current model even do 100 mph except downhill?
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Replying to: wwest (Oct 30, 2007 11:56 am) Yessir........... By Gary Richards Mercury News Article Launched: 08/21/2007 01:39:13 AM PDT All right Al Gore III, you're still the tops when it comes to speeding in a Prius - but not by much. Steve Wozniak is right behind you. And when I say speeding, man o' man, do I mean speeding. You probably remember when the son of the former vice president was caught going 105 mph in Southern California last month. Well, a mention of that in a recent Roadshow column led a buddy of Wozniak's to check in, claiming that the co-founder of Apple Computer was ticketed for going 105 mph on Interstate 5 earlier this year. Whoa. Mr. Roadshow knows a good story when it plops into his lap. If true. "Not true," Wozniak replied: "104 mph." OK, squash that image of the Prius being wimpy, as Gov. Arnold Schwarzenegger had quipped this year. First, 105 mph, and then 104! "I pleaded guilty, with an explanation," Wozniak said in one of several e-mails exchanged the past few days. "I said that I was really scientific, and in the last year had been in Athens, Moscow, Berlin, Frankfurt, Munich (twice), Zurich, Canada (three times), Columbia, Singapore, Japan, London, etc., and had gotten used to kilometer speeds." The judge smiled. But he didn't buy it. The fine was about $700. Wozniak was headed to Las Vegas for a business trip with his pal Dan Sokol on March 28. Little head wind, light traffic, a straight road. His Prius was sailing along so smoothly that neither realized the speed Wozniak was reaching. Woz and Gore Jr. both clocked over 100 |
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Landspeed Prius Hits 130.794 mph at Bonneville On 23rd December 2004 a modified Toyota Prius reached 130.794 mph on the three-mile short course at the Bonneville Salt Flats. An engineering group from Toyota and Toyota Motorsports worked on the Prius for more than two months to prepare the vehicle. The Landspeed Prius ran a stock Hybrid Synergy Drive powertrain. The transmission final drive gear ratio for the gas engine was modified from the stock 4.113:1 to 3.2, while the inverter voltage was increased to 550 from 500 volts. The engine redline was also changed for optimum performance. A transmission cooling system was added to the front passenger area to decrease the temperature of the inverter and electric motors. Regular ice was constantly added to the system to prevent overheating. Ambient temperature on the salt flats was nearly 100 degrees with nearly 100 degrees humidity. Thanks to greencarscongress for the above, although this probably showed here on Edmunds News and Views at the time, it was likely archived somewhere. That aside, I have read that under ideal conditions Prius will cruise at 100mph with 49Hp so it would not be too severely taxed since the 1NZ-FXE engine produces 76Hp  5000rpm. As most know by now this engine has an almost flat torque curve with respect to speed, so this would correlate to an engine speed somewhere north of 3330 rpm. Bottom line At 100 mph Prius could cruise all day. On the otherhand, I would not object to an 80mph Prius, unfortunately the tradeoff of adding something to the bottom end would not be that great since we are dealing with the HSD which is mostly a constant power system. I should mention that here in the great white north they just added a new law. Go more than 30mph above posted limit and they impound the car, suspend your licence and impose fines between $2000-$10,000. The ink for this new law hardly dry but they've already caught (actually "surprised" would be a more accurate verb here !) over one thousand drivers. T2
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Replying to: toyolla2 (Oct 31, 2007 6:57 pm) The bottom end torque could be limited just as easily as top speed, not that TC wouldn't already, but only after the "fact". Perhaps a "snow" mode..?? |
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Replying to: toyolla2 (Oct 31, 2007 6:57 pm) I hope, like to think, they added some downforce "effects" and wider tread tires for that high speed run. |
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