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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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Replying to: stevedebi (Oct 17, 2007 1:02 pm) A slightly smaller, more efficient engine would be fine 95% of the time and on the rare occasions when I do need the boost, it would be there. I think my normal 45-48mpg would go up to over 50mpg except for 5% of the time when the "turbo" was on.
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Replying to: stevedebi (Oct 17, 2007 1:02 pm) If you could make the combustion process fully efficient the exhaust gasses would exit the cyclinder at the exact same temperature at which they initially entered the cyclinder. The Atkinson Cycle gets more efficiency from the fuel BURN by extracting more of the HEAT and converting it to mechanical motion. Less HEAT/(pressure) at BDC equals less pressure into the exhaust manifold once the exhaust valve opens. The SC technique I described allows for continuously variable boost pressure from zero to the maximum allowed by the mechanical limits of the engine and thereby NO LOAD on the ICE until boost is required/called for.
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Replying to: stevegold (Oct 17, 2007 1:45 pm) I was speaking of supercharging, not Turbocharging. |
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Replying to: wwest (Oct 17, 2007 2:23 pm) Don't try and put that statement to an automotive engineer, or a physics professor. I don't understand what kind of "technique" you are describing. Superchargers use the engine power to mechanically enhance the airflow into the engine - the same principle as the turbo charger, except the turbo is driven by exhaust gas, and therefore increases as the engine RPM increases, whereas a supercharger provides constant power - but the energy to power the supercharger has to come from somewhere, and the equipment adds weight to the engine.
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Replying to: stevedebi (Oct 17, 2007 4:45 pm) This is the electric turbo that I thought would work well in the 2004 Prius. It runs at high speed off the 12VDC battery but only when you floor the accelerator. |
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Replying to: stevegold (Oct 17, 2007 6:30 pm) Thanks for the link, interesting stuff. A couple of notes: 1. It is electrically driven, so it would impact the HSD, and the effect would be worse when the vehicle was accelerating - the traction battery would have to run the supercharger AND the electric drive motors. This would deplete the battery faster. 2. ONE PSI boost? 3. I'm not sure if adding boost to an Atkinson cycle engine would increase power. On an Otto cycle engine it works, but the Atkinson cycle is deliberately intended to work with less pressure. I don't know enough to have a definite opinion, just a question.
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Replying to: stevedebi (Mar 15, 2006 4:44 pm)  I smile because it wasn't mine. I didn't get the privilege of paying $4000 to repair it. And "they" dis the Prius because "they" think the battery would be expensive to replace! While some may feel more HP is necessary, many of us think the Prius does just fine, thank you. Mine will out accelerate my previous vehicle on the two lane secondary highways when passing 18 wheelers (it was a 240 HP 265 lb-ft torque 2001 Nissan Pathfinder, which, BTW, burned 2.5 times as much fuel for the same service). It will not keep up from a stop, mainly due to the "delay" of 1/2 to 1 sec. at startup. At any rate, this discussion is of the 2009 model, which, from all accounts, will not have a supercharger or turbocharger. In fact, it now appears it will be the last year of the current version car. Most now conclude the 2010 model will be the "changeup" year. Probably will have the same engine, a double sized battery, with plug in capability, and a cruising range on battery only of around 10 km. But this is all speculation, based on comments from Toyota spokespeople and their tests with the double battery pack Prius plug in test vehicle in Japan and California. They have also given some hints as to body design changes. Just have a look at the "bean shaped" (my description, not intended as criticism) concept car shown last winter in Germany. "Many things you will see on future hybrid cars from Toyota are on this concept car." Note he said "many", not all. Several posts ago, someone said a gearbox will raise the HP output. Sorry, a gearbox will change the torque and the RPM, but the HP stays the same (actually it drops a bit, due to losses in the gearbox). Energy MUST be conserved!
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Replying to: pathstar1 (Oct 18, 2007 11:48 am) Don't look at me, I didn't suggest it; I was responding to a different post... |
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Replying to: stevedebi (Mar 15, 2006 4:44 pm) The Prius is using delayed intake valve closing so that a portion of the A/F mixture is forced back out into the intake manifold (and into the "opposite" cylinder currently on an intake stroke) during the compression stroke. The result is effectively, logically, the same as with an actual Atkinson Cycle engine, a "lengthening" of the power stroke in comparison to the intake stroke. But in order to keep some of the "power" normally lost to the Atkinson Cycle the Prius' mechanical compression ratio is raised to 13:1 leaving an effective ratio still at 10:1. Basically that means using an SC would raise the "effective" CR above 10:1 which the engine may not be able to stand up to in the long term, even in short bursts of 30 seconds. Additionally I would be willing to bet that the e-charger's 1 PSI boost is only at low to mid engine RPM and actually goes negative, starving the engine, as it reaches the RPM in what would normally be PEAK HP. A toy, at best. |
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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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