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So BYD will be allowed to import 60 vehicles into the USA. This may have the guise of a pilot test but could this be the initial thrust of a marketing scheme ? I wonder how soon after this they are going to apply for dealerships - manufacturer owned of course. The recent low price of oil, and likely to remain low if EV penetration continues to be successful, is certainly making shipping costs from the Far East more attractive. Next question is : will the Trade Commission allow it ? Well look no further than a recent story here on GCC. It seems that in the case of Mitsubishi, which just announced the imminent closing of its US manufacturing facility in November 2015, the intention is to consolidate production at its home plant in Osaka from which an estimated 100,000/yr of their Outlander model can be exported into North America. The concern I have, as a TSLA stockholder, is that this car has a 61.4Kwh battery which brings it close to Tesla for range. The only serious competitor ATM being the Nissan Leaf whose battery has just 24Kwh in contrast. Not everyone wants, or is able to pay, the performance premium that ownership of a Tesla requires but here in the snow belt the range in winter temperatures needs the boost that a ~60Kwh battery will provide. In just over two years time we are to expect the Tesla Model E to enter this market with a battery of similar size. Speculation has been that it will use the 188Hp rear motor transaxle from the 70D. That said, I like that BYD is shipping this vehicle with only a 100Hp (75Kw) motor with a reasonable expectation to me of it having the performance equivalent of a 150Hp ICE. The selection of this size of motor is an assurance that the battery is unlikely to be abused nor have the motor performance susceptible to battery state of charge.
DaveM, I think you are mistaken. This article is based solely on ICE type hybrids unless I missed something. But even if fuel cell EV's are included in the mix, I am beginning to see that this will never be a race between two different types of automobile powertrains that both eschew the internal combustion engine. Rather it will be a race in infrastructure and with 400 superchargers already installed I feel that race has already been won by Tesla. The Number 2's of this world have always had a hard time against an established incumbent. Think Corel or Blackberry. First it is probably safe to say that the significant installation cost of a hydrogen dispensing station is unlikely to be comparable to that of a Tesla Supercharger facility. And when was the last time the attendant allowed you to refill a BBQ propane tank by yourself ? Hotels are already installing Level II chargers but the regulatory safety requirements surrounding hydrogen in populated areas are going to be prohibitive. Naturally this will rule out having them in the vicinity of hotels and shopping centers where they could be the most use.
It is interesting to observe the attempts by the automobile industry to ensure their customers remain aligned with the oil industry. Ignoring the fact that there already is an alternate distribution system in place for energy in the form of the national grid and the reality that a BEV will always leave home with a "full tank". At some point in the next decade Li-ion storage will be in the $200/Kwhr range permitting affordable vehicles with ranges of 150 miles per charge along with fast charging facilities on major highways able to add 120 miles in around 15 minutes. I have an idea that either Tesla or Nissan is going to be filling that performance niche within the next few years.
For the supply of automotive multiratio gearboxes this is undoubtedly a good fit for Magna. It should be noted that going forwards it is unlikely that EVs will ever be using these types of gearbox. The EV's ability to utilise both of a vehicles axles by fitting individual motor controllers which can be made to share the same torque demand signal being issued by the vehicle speed controller effectively gives the EV powertrain a 2:1 wheel torque advantage without the transfer case and the lossy 90 deg. gear boxes that ICE powertrains are obliged to use. While it is true that the Tesla roadster design did employ a Getrag box, the later Model S uses an inhouse design which accomplishes a 9.73 ratio with a two stage reducer.
I agree NP, this will not be an issue. Similar to Battery Swapping which required adequate compensation from the govt, when that evaporated so did Elon Musk's enthusiasm for it. No one is going to scrap an electric vehicle that still runs. Consider that a fifteen year old Leaf or even a Model S which can still drag itself 25 miles can yet have an afterlife as a viable grocery getter. For the elderly they can perform the role of a "four wheel overcoat". It's not something you may think much about and probably few are aware, but using the public transport system in the suburbs with a 30 minute schedule(sometimes hourly in evenings) particularly in winter can be arduous for old folk. It takes considerably more effort to perform a five minute walk to the nearest stop and stand at the bus stop for another five minutes than it is to drive a car. For that reason I perceive that limited range vehicles with low maintenance requirements will find a market.
800 to 1000 Km... that's what our future BEV or FCEV will have to do. Harvey if the aim is really to get mass adoption, as Elon Musk maintains, then larger batteries are not the answer. The EV has to be affordable and comments similar to yours will continually move the goal posts. Get used to it. What we have now works. I know it is difficult to relinquish the oil age but you will have to get used to the idea that for the most part HEVs are just a transitory technology phase. When it becomes necessary to tap into an energy source even the humble 110Vac socket will always be a lot more plentiful than the gas station and as for gas stations I expect them to become fewer as the EV population grows. I think you may have missed that part of the program wherein with an EV you always leave home with a FULL TANK. Allow your home charging to become the gas station that way the worry to make that special trip to seek one out just goes away..
As someone who lurks on TMC, I learned recently that Tesla has been working on liquid cooled cables to permit further 135Kw and beyond charging capability. The latest problem has been congestion at superchargers. These are now being located ever closer towards residential areas such that newbie owners intend never to charge at home but drive 3 miles or so to the "free charger". Tesla is also considering the use of valets during peak periods so that owners are less inclined to have a coffee and leave the car unattended and thus blocking further use of that station until they return.
Single-speed drives require the motors to have a high speed range in order to allow low-speed maneuvering as well as high-speed highway cruising. This requires the motors to run at high speeds. In order to make a motor run at high speed you need to overcome the resistance of the magnetic field by weakening the field. This field weakening requires additional power and larger inefficient power electronics, the company says. Or so the company says, eh. No one putting their name to this statement Huh ? Well the first two sentences are true but the weakening of the field bit is a no,no. Clearly the author is referring to a brushless AC servomotor where you are fighting not only the unrelenting back emf of a powerful permanent magnet system but also the machine's stator/rotor reflected inductance whose impedance increases with frequency. You can of course avoid the problem entirely by gearing the system to make base speed for the motor coincide with the maximum vehicle speed. No field weakening required there.The drawback to this is that then maximum power can only be reached at top speed. But supposing the marketing department specifies top speed to be 120mph and at the same time infers that the 0 to 60mph benchmark is also going to be an important sales feature ? Then clearly even if acceleration requires maximum current to be drawn, the motor itself will only be able to reach half its rated voltage at 60mph and therefore will be developing just half of its rated power. Just one thing, the frame size of the motor, which governs how much torque it can produce, will need to be sized so that it can produce the required power at just half its maximum rpm. However in this article what the mechanical engineers want to do is to take a motor, with a smaller frame size, and let it run to max revs at 60mph and then change the gear ratio by half in order to reach maximum revs again but this time it will occur at the vehicle's top speed. This is not so easy to do at high power and presents a severe challenge as Tesla engineers discovered in 2008, where even a split second counts. So continuing on with a larger frame size motor, achieving the required power at half maximum speed obviously requires twice the torque and this torque has to come from doubling the stator current which means choosing upgraded transistors with twice the original current ratings. Fortunately the power drawn from the battery will be exactly the same in both cases during the 0 to 60mph ramp even though the larger motor will be carrying twice the stator current of the smaller. What happens subsequently to achieving the 60mph ramp up is a different matter entirely as it will depend on the current limiting applied to the larger motor, since this motor will begin to draw more battery current as its stator voltage continues to rise even though it accelerates at constant stator current. Stator current limiting will probably be applied since this motor could pull up to twice its 60mph rating if acceleration is allowed to continue. Most battery inverters will have two types of current limit BTW. One circuit protects transistors from overcurrent while another limits the battery draw. Well, it would be nice if it were the case that the scenario thus described with the larger motor was actually used. Sadly, the reality is that cars which start off with an acceleration feeling like they were 10 sec cars (1/4mile) don't quite deliver on the promise. What's with that ? First I should say that performance vehicles aren't necessarily meant to be track cars. Nor should they be made to tow a caravan on an airstrip at 125mph until the engine blows as Top Gear has done. So if they are not delivering on the promise then compromises are being made but where ? Not with the motor where it is straightforward enough to arrange for all motor dimensions to be increased by 26% in order to double the torque output. However, regarding semiconductor upgrades, reasonable economics would suggest limiting transistor devices to 1000 amps. To accomodate such a shortfall in available stator current will require compensation elsewhere. It will be found in changing the stator winding such that the Volts/Hz coefficient of the motor will be increased. Consequently the full stator voltage will arrive earlier, somewhat below top speed, with a commensurate reduction required in the stator current excitation, although still able to deliver the original maximum torque. The question now becomes: how large should the Volts/Hz be allowed to be ? To answer that the limits must be explored. If the V/Hz is made sufficiently high enough the motor could develop maximum power at 60 mph with the use of relatively low current semiconductors. OTOH selecting a similar frame size motor possessing a low V/Hz that causes topping out at 120mph will require the semiconductor ratings to be doubled. So it appears, at first sight, that increasing the motor V/Hz, usually by changing the stator wiring paths, is a good thing as it allows the use of cheaper semiconductors without compromising performance to 60mph. It should be mentioned that going beyond 60 mph at max power will cause torque to decline with increasing speed. Eventually motor impedance, as speed progresses beyond 90mph, will have a greater effect and only half max power will be available at 120mph. You might compare that performance to the motor with the low V/Hz which likely will be developing twice maximum power at 120mph. In either case, providing aerodynamic losses do not exceed the motor power, acceleration will continue until the 120mph speed regulation kicks in. Here's where it gets risky with this V/Hz business. The question now becomes : how far below 60mph can maximum power be reached were we to make the V/Hz even larger. The expected result would a power peak with a flattish top as 60mph is approached. First up, let me say that I don't favor power peaks that occur in the 0-60 pass band. A power peak on the way to 60mph infers that for the next period a constant power path is experienced before entering a state of steady decline which we could call negative alpha territory. It should be needless to say that having power diminish during acceleration is something to be avoided but it is done. This is the point at which I reflect on design philosophy. System designers are often inclined to get too absorbed in that world of amps and volts associated with alternative stator wiring schemes along with their interactions with a specific topology of electronic devices and maybe lose sight. I find it more useful to focus on the electric motor, centering on the fact that there is a peak magnitude in the magnetic flux at optimum slip (or rotor skew for a BLDC) that can be preserved even as the motor continues to spin up thereby producing a steady maximum torque. There is no power peak from the motor's point of view. The faster it spins the more power it develops. It's simply rpm multiplied by torque - the way horsepower has always been. But if on independent testing a powertrain appears to have passed through a power peak, then clearly something has intervened and compromised that ideal. Let's imagine a motor that achieves rated power at 6600rpm but we would prefer that specific power to be attained at 4400rpm instead. We therefore require maximum voltage to be applied at the lower speed which means raising the V/Hz by 1.5 or 50%. The downside is that the new maximum current has to be 2/3 of the original to avoid saturating the stator iron since there will be 50% more turns around the poles. Since power = motor volts x motor amps then clipping the motor current to 2/3 also clips the available power by a similar amount. This is in line with my earlier statement -The faster it spins the more power it develops. So in this case maximum power can be reached at 4400rpm, but it won't compare with the maximum power it could have reached had the same stator been wired for the lower V/Hz and run to 6600rpm. Just to be quite clear on that. Gasoline engines do experience a power peak OTOH. The limitation on them is usually to maintain piston velocity somewhere approaching 20m/s (4032ft/min) therefore it is necessary to hold them within that boundary by substituting gear ratios that allow the engine to remain on its power peak until it experiences part load at which point an even lower ratio gear (overdrive) is selected to reduce needless mechanical sliding friction. An electric motor needs no such considerations. That is not to say that it couldn't benefit from a higher ratio when accelerating at lower speeds. It's just that when you factor in the mass and cost of the multi-ratio-with-clutch style gearbox against using a larger frame size motor then the larger frame size appears to be the more elegant and seamless solution. But so what if an overly high Volt/Hz characteristic is apt to promote negative alpha on the upper reaches of the power curve - who cares ? After all, if at any point the motor is developing more power than actual aerodynamic losses being experienced then acceleration of the vehicle is going to prevail anyway. Turns out it does matter when an EV is competing in the quarter mile alongside vehicles with turbo-charged I.C. engines. Leaving quarter mile performance aside for the moment, this is all well and good, but Toyolla2, you may say, despite all this a uniform acceleration ramp is not particularly efficacious since on an 8 second 60 mph ramp the vehicle reaching 30mph has had invested in it only one quarter of the kinetic energy needed to get to 60mph but has taken up exactly half the time. In other words during the next half of the ramp the vehicle powertrain will need to work three times as hard. Actually I am cognizant that a good launch is paramount to achieving a favorable elapsed time. But it is what it is. Only two solutions present themselves when torque is to be king. One way is to install a larger frame size motor. The other is to employ a larger gear ratio. The latter is preferable since it comes without the penalty of having to install a heavier motor. In either case the volt/Hz of the motor should allow for the 60mph ramp maximum power to be reached close to that speed but if the more stringent quarter mile is targeted then the maximum power point should extend to at least 90 mph. During the acceleration ramp towards maximum power the motor voltage would be seen to be rising proportionally with speed with the motor running in constant current which means the transistors are conducting with their maximum rated current. The only two variables are speed and voltage. So we can say that all other parameters are of minor importance providing the voltage/mph gradient is preserved. It turns out that this statement is profound in defining EV performance. For example, sometime in 2014 a Tesla Model S P85 was modified by a certain Mr Saleen by altering the gear ratio to improve torque at the expense of top speed. The intent was to tweak quarter mile performance. The results were less than spectacular since this changed the volts/mph ratio which in turn lowered the mph at which the powertrain traversed the point of maximum power, and it was low enough already I might add. Since raising the system voltage is not a low cost option, the motor should have been rewound for a lower volt/Hz rating to retain the original volts/mph ratio. That option will also require compensatory increase in transistor current to maintain the original motor torque. Even if that was possible there still remains the problem of the rewinding itself. Theoretical work I have done myself tells me that that is easier said than done since you are already dealing with one conductor per stator slot in order that a relatively low voltage supply will be able to force currents into the motor at frequencies of 480Hz or higher.
Prius and Li -ion batteries having been mentioned I might add that : Readied for release in the fall of 2008 the power battery for the 2009 Prius was intended to be of the more advanced Li-ion. However a year earlier there had been a series of fires associated with Sony laptops widely advertised as having Li-ion cells. Since the Prius had no serious competitors at the time ( and IMO still doesn't ) their marketing dept decided why take the risk with these new cells if their adoption was likely to impact sales of their hybrid marque, consequently the MY 2008 car was allowed to carry through September 2008 and become the MY2009. Meanwhile the intended car was partially reverse engineered to enable its use to continue with the existing NiMh battery. Because of the delay the new design car for 2009 MY was eventually released as a 2010 MY in March /April 2009 instead. That car was manufactured continuously from December 2008 all the way through to July 2010. And then for MY 2011 for those ordering leather seats, tan colored seating became an available option. AFAIK that was the only change noted in the MY 2011 brochure as Toyota sought to recover its losses regarding the battery anomaly. Or at least that is my speculation. Going back to the MY 2004 this was the first model year to use the 201Vdc battery with the newly introduced upconverter which allowed the MG1 and MG2 servomotors to run from 500Vdc and gave the Prius an acceptable driving characteristic. Both the earlier versions of previous years using the 273Vdc battery were known to be somewhat anaemic. Incidently both the 273Vdc and 201Vdc batteries were rated at 1.3 Kwh of storage. The conventional lead-acid installed within an ICE vehicle is around 0.9Kwh. The 21Kw upconverter supplied effectively 28Hp from the 201Vdc battery which along with 76Hp from the 1.5L 1NZ-FXE engine supplied a total of 104Hp from 51mph to 99 mph (electronically speed limited). During (regenerative) braking the power fed back into the battery was limited to just 10Kw for battery longevity reasons no doubt. Recently I remarked to a Toyota mechanic that I had seen photographs of Prius brake rotors which seemed lightly used even after 50K miles. He responded that from his end brake corrosion was an issue since there was not enough subsequent friction braking to dry out the rotors from driving in wet weather. For buyers wanting more than the 4 minutes of all-electric driving at speeds below 42mph, the Plug in Prius has been available but there have not been a large number of takers because of price sensitivity to this upgrade. For the same reason GM's Volt sales have not been all they could. Hopefully buyers will move away from this transitional technology and eventually go the full EV route now that public charging infrastructure is more prevalent. First however, manufacturers have to wise up and provide their snow belt customers with well insulated battery enclosures with good thermal management since costwise the battery is the car. My opinion on the future for the Toyota Prius is for the company to realize that the emissions crown is moving over to EVs. Prius is no longer exempt to congestion charges nor allowed HOV privileges in increasing locales. Toyota has to realise that fuel consumption is becoming more the name of the game for hybrids as cash strapped governments move to establish new gas taxes. Smaller engine displacements along with compensatory higher engine speeds will be needed in future for the Prius to attract buyers and this will appear as a more economical route than simply beefing up existing electrical systems. As regards battery chemistry the existing NiMh battery systems are proving good longevity and are unlikely to be swapped out any time soon. Neither do I see an AWD Prius be any more likely to attract buyers than AWD did for the Corolla back in the early nineties. This Hitachi battery may improve the Malibu hybrid but didn't they already take this model off the market once before ?
First just a coupla' nit picks. The phasing graph axis should end with 1440 deg not 1400. And surely the igniter firing order could just as easily be 123..123 etc as be 132..132 ? If you look carefully you can see the sequence 321..321.. which is just a 123 engine being made to run backwards ! Until this article I had never considered the possibility of rolling deactivation before. It seems like a good idea, and before a reader tells me how obvious this is, I might say that pretty much most good ideas are obvious, once someone has taken the time to point them out. So if you are cruising along with rolling de-activation engaged and suddenly need to accelerate then the firing circuits will return to the normal 3-cylinder sequence. In other words, the 480 deg firings revert back to a normal 240 deg sequence. But what is the main advantage here ? Does it allow the crankshaft to run slower in cruise with just three firings per four rotations thus allowing the cylinder loadings to be raised for max effcy ? I would like Ford to take this to a parallel twin model with a total cylinder area equal to that of the three cylinder they are now playing with. That would ensure the same power and by using the exact same stroke would subsequently ensure the same torque. Advantages would be that valve train friction losses would drop by 50%. And then there's the cost factor of the engine being proportional to the number of machined parts. I think it is fair to say that component size is not a cost driver as we are talking of parts made from iron and aluminum here.
Apparently air con units need over 3kw to run, and over 12kw to start them up. Then I would respectfully say that if your air con pulls a 12Kw surge at start up, then it's time to replace it with more modern equipment which doesn't rely on motor control technology from the 1950's.
Davemart, that is what I say too. My story concerns my older fridge that the local utility wanted me to replace. In their promotions, flyers with the bill and a feature in the local newspaper etc, I happened to notice that the model depicted was the exact same model that I had. Installed in May '96 and working perfectly ever since I should add. I was therefore motivated to phone the utility and see what their figures were for an 18cu-ft fridge consuming 683Kwh/yr - which I admit is not stellar performance in this class. Well, this otherwise know-it-all authority could not supply any financial proof of savings or ROI and said I should check with the metal recycler who's 1-800 number was in the promo as it is they who actually run the program. Spokesperson for the recycler said his responsibility was merely to get my address and pick up the fridge - which, incidently, must be in good working order??? Huh, the nerve. As for Mr Kettle back there. I use a 800W microwave to heat water for instant coffee, and a gas range for an actual kettle when I make tea. But that's just my english heritage. Regarding HVAC, I'm retired so it's safe to leave some windows open with bug screens in place most days. I will allow that there are days when humidity dictates employing the HVAC to dehumidify the house before things become unbearable. In California I think this may not be an option. A suggestion that Lead Acid batteries working out at $100/Kwh would be a cheaper solution met with disfavor by a friend who had served as a volunteer fireman. Apparently this type of backup solution has been known to have caused call-outs after someone was puttering about in the basement, while smoking and in the vicinity of cells which happened to be gassing at the time. TESLA's competence in thermal management of lithium ion energy storage enables safe in-home installations that will hopefully promote changes in the HVAC industry. Why not DC current compressor feeds ? Then there's the problem of 110vac LEDs, why not change to 24Vdc lighting circuits at the breaker/fuse box? Going forwards for the power receptacles, what really needs to be operating on 110Vac that now requires upwards of 50 receptacles in the average house ?
HG, spot price silver $16/oz spot price copper $2.76/lb says it all, assuming 40oz in an axial rotor. Even so it was interesting to find out silver has a conductivity / specific density product ratio which is not as favourable as copper due to the overwhelming greater density of silver. Regarding motor type, Musk has been adamant in favour of asynchronous working from the start. Both types require digital tach feedback for field oriented design but the synchronous motor requires stator sensors which must be accurately phased to the absolute rotor position. While it is true that asynchronous motor software is a little more difficult and there is the additional requirement for realtime modelling of the rotor temperature since a 100 deg C rise in temperature will increase the rotor resistance by about 30%, the robust nature of the 4-pole induction machine makes it a good choice for automotive powertrains.
Well if it can survive more than five years and hostile under the hood conditions without a thermal management system.... I was thinking that cold cranking of today's engines assisted by computer controlled ignition and fuel injection have already made winter starts significantly less problematic. That vulnerable first early morning start could be avoided, IMO, if all vehicles for use within the snow belt were equipped with block heaters. Even so subsequent starts with a warm engine and lower friction are less demanding on the battery anyway. Someone must tell me what I am missing since Li-ion is going to be priced well above $250 per Kwh. All the cars I have owned in the last 40 years have had the block heater supplied as a dealer fitted option. Here in SW Ontario we have come away with a record 48 days this winter where the temperature never rose above freezing.
The installation of 500 chargers through a government program seems to confirm what Mariana Mazzucota was saying on TVO's Agenda last week and in her book "The Entrepreneurial State" regarding the Private Sector Myth. I expect that once the government funded infrastructure is in place there will be some capitalist ready to grab the keys and drive away in order to privatise the profits having ensured that practically all the initial costs have been borne by the social sector. Mark my words. On a lighter note I see that California lawmakers have already set up laws to have landlords provide a proportion of outside electrical outlets so that apartment dwellers who have little political power don't get "left out in the cold" so to speak.
China has to recognize that they have a population problem as we equally are having in the West. Our aging population is being tasked with shouldering the cost of new public transportation infrastructure to be ready for future generations and avoid the gridlock we have today. Planners for the LRT project here have already predicted a 50% population increase in our area by 2032 which will no doubt necessitate further expenditure to be extracted from the existing population at that time for the 2055 predictions.... in a never ending circle. Perhaps it is time we revisited a different solution to this unbridled population problem. One rational approach could be to incentivise young couples to remain child free perhaps removing education levys on the property tax rolls for those without children comes to mind. There is likely to be a shortage of well paid jobs in the future and we are already seeing this in employment figures which show the number of new jobs being created is increasingly for low paid employees. The concentration of Telecommunication Companies is now being challenged by our government which yesterday made an order that in Canada, Cable companies must limit their charges for basic services to $25/month. That's what will become increasingly necessary if you support the idea of TV as being the opiate for the masses in lieu of inadequate disposable income.
It is the HEV version NOT the PHEV version that has the 10kw battery. Said system comes with a weight penalty of 20Kg. as DavidJ just pointed out and we would need to know what the kwh is to make any judgement here. The HEV battery, unlike that in the PHEV, will likely have electrodes formulated for POWER rather than ENERGY. It compares favorably in comparison with the Prius battery which is using twenty year old NiMH technology, weighing in at 100Kg though still able to supply 21Kw albeit with a capacity of merely 1.3Kwh. This salute to the oil industry may never make it to market with the diesel engine being discouraged for personal transport in Europe. In fact the growth of public charging infrastructure may make this bridge technology obsolete. Come to think of it have there been any successful mild hybrids out there ? At this late stage they seem to be more like compliance vehicles.
Alex , I ask that perhaps you could take some of these OT ideas to other places where they may find a more enthusiastic setting. Have you tried Endless Sphere ? Also DIY Electric. These will be my final comments here. I have tried to register in the discussion board. There is no register button in my browser so no go there. 5-Phase although of theoretical interest does require some inverter to motor topology changes since there are obvious ramifications to having legs separated by 72 deg. Also I have no idea what ZF's planetary twin ratio device is about. Assuming an automotive drive is under consideration, then unlike an ICE there never should be the need to have to spin down an IM in order to enter a coarser gear ratio when you want to go faster and thus avoid an RPM range that may exceed the motor's mechanical limits. Such a condition can only mean that the motor specified was seriously undertorque for the application. The max rpm of any machine should be just below the point at which the machine's rotor is likely to grenade. The reason is that motor power is proportional to rpm and since aerodynamic losses do not diminish with increasing vehicle speed it is preferable to gear the motor for its max rpm to coincide with the top road speed. That said, some electrical designs experience torque roll off at high speed. This is because the stator winding pattern has been deliberately arranged to present a high V/F (Volts per Herz) ratio to the inverter. Motor torque is proportional to the product of motor current and V/F ratio. Clearly a larger V/F means an equivalent torque can be still be produced but with a smaller current. It is a popular trick that is used to enable the current rating of the inverter transistors to be reduced. The drawback is that a large V/F ratio will have the motor present a high back EMF at relative low rpm such that a period of constant power is entered followed by another area where the torque begins to drop inversely as the square of the speed. To maintain some semblance of performance the ability to select a gear ratio that will slow the motor rpms relative to road speed will bring the motor out of voltage saturation and generally the restored motor torque will temporarily compensate for the coarser ratio of gear now employed. There is an elegant solution so that all this trouble can be avoided in the first place if the motor is wound for a low V/F and used along with an inverter with oversized transistors which is standard practice at Tesla. As a point of fact whereas a general purpose 480V 60Hz motor will have a V/F of 8.0, the corresponding frame size Tesla motor is estimated to have a V/F of 0.25, meaning that for equivalent torque the Tesla motor will have to draw as much as 32 times more current than the previous motor. A situation which is not problematic since the Tesla inverter is well equipped with no less than 850 amp transistor ratings.
@Alex _C interesting links BTW. On the electrical side I can answer some of your questions directly. Going forward maybe the GCC discussion pages should be used since topics that fall off the Home page have less accessability to the general user base as time goes by unless you have happened to have saved the exact URL of course. A discussion on AEVA (motor & controllers) entitled 14,000 rpm machines considers PM versus Induction. It was brought up in the first post with the expectation that PM would be summarily dismissed. As it turns out there was considerable interest perhaps as long as the Toyota Prius and Nissan Leaf continue to use them I suspect. For tow trucks and forklifts which are mostly used as mobile positioning systems they will always be a good choice. My experience is that 5-phase PM machines manufactured by VEXTA are mainly confined to applications known to be sensitive to normal torque ripple. The robust nature in both temperature and overcurrent points to the 4-pole per phase induction motor as optimal for automotive usage. The 6-pole per phase may produce better torque/mass ratio but needs research. Greater than 6-pole may be OK for the industrial market but has slotting issues which obviates its use with with smaller automotive frame sizes. For 4-pole motors, excitation frequency = RPM/30 Hz Copper loss is not a consideration in the stator. Electrical loss in the rotor -since that's where all the electrical power ends up after it crosses the annular gap- is key so copper rotors are mandatory but most industrial motors (premium effcy) are now using them today, see the Eurotherm catalog. Magnetic losses generated by hysterisis and eddy currents become less a consideration when manufacture includes the use of thinner laminations and the finest electrical steel that Accelor-Mittal can make. Simply put, the Tesla Model S with its latest $140k flagship P85D 5 seat sedan with insane 3.1 secs to 60mph exemplifies the induction motor as the go to solution for BEVs. Whether Tesla has found the optimal mechanical transmission layout where durability at high power will not be an issue remains to be seen. Tesla has seen problems because it is the only company pushing out sufficient quantities that even one in a hundred can no longer be considered as an inconsequential occurrence.
I have direct experience of comparing transverse electric motor mounts versus those using longitudinal coupling. Dyno results showed conclusively that turning power through 90 deg from a longitudinal motor, as is shown here, was proven to be the inferior choice. That aside, the architecture of using two motors, despite the incremental cost factor of the dual drive, looks to be an excellent idea. The ability to dispense with the differential components as done here, may avoid a problem that Tesla seems to be having with their two stage reduction box. Incidentally any visit to the Tesla website soon reveal it to be inhabited by moderators who are extremely sensitive to any fault details being released with regard to their gearbox, naturally speculation is inclined to be rampant. My take on the problem is that moving from motoring to regen braking is so fierce that the differential spider gears are being given a hard time. Fast changes in slew rate aren't problematic until you pass through the dead band and hear the clunk signature as pressure is suddenly exerted at the reverse face on the gear teeth that are already engaged. In fairness it should be pointed out that very few vehicles have exhibited this symptom straight out of the gate. So it could be exacerbated by driver style as much as anything. Many of the owners are A-types who don't appreciate they are confronting bleeding edge technology and while $140k of their money is on the line they resent even the slightest suggestion that perhaps they should not do pretty much as they damn well please. Avoidance of the gear lash within the differential requires consideration of the differential system being replaced by a dual drive system. It will become apparent that the amount of gear hobbing remains the same. The left/right wheel axles are terminated in gears which are standard helicals rather than bevels. If it is assumed that a two stage reducer layout is to be maintained then the final differential gear containing two, perhaps three spider gears is eliminated entirely with the placement of three new gears, one of which would be the motor pinion for the additional motor. The High RPM motor presents another interesting design avenue. Higher rpms effectively increase machine power density and permits the use of lighter motor frame sizes. Notice the stipulation on lighter rather than smaller frame sizes since it facilitates the options of either higher power or increased affordability. BTW Tesla has tested one of their induction motors for 24 hrs @ 24000 rpm. What is not known is the frame size and whether it was performing under load. Finally the "shared housing" may not be the best approach. Again Tesla uses this highly integrated approach and in my opinion it has been a disaster as far as maintenance costs go. Of course solid failures justify dropping out the transaxle but some complete transaxles were exchanged when just a shim needed replacement. Automotive training usually governs that area of how things are supposed to work, the experience to identify problems in these early years will take time to acquire by a dispersed group of people. In the meantime the ability to disassemble major components in situ is going to be a consideration if the cost of electric vehicle maintenance is not going to go through the roof.
Thanks for the responses. You are obviously more adept mechanically than I. Perhaps I ought to have stopped by my local transmission shop for their take before I posted. My life experience through aquaintances, who have kept older vehicles on the road, is that despite having immaculate interiors, no dings nor any signs of exterior rust at 150k kms will never be enough to prevent these vehicles from going to the crusher when their transmissions begin to fail. They just shrug and start searching for the next and newer CPO. CE88 , you countered mechanical reliabilty by introducing the question of EV battery longevity. I have to agree that this is a sensitive matter over on the Tesla Motors forum. There are a number of members on that website who are also owners of the Model S . Several of the latter group seem to be unaware that they are still in the early adopter phase for vehicles of that type, specifically the 300+Hp electric sedan. Regardless of that they persist in clocking up much more mileage than the average 1000 miles/month usually demanded from a typical gas car. One particular character increased his odometer reading by 17K miles in just four months ! Now we know that for the S85 (denotes the 85Kwh battery version) the complete powertrain warranty is eight years with unlimited mileage. The problem is trying to get a fix on exactly what this warranty supports in terms of battery failure. Leaving aside the obvious pack total failure, how the battery pack warranty intends to deal with a pack whose charge retention is beginning to deteriorate needs to be answered. On this Tesla is somewhat vague. There are of course a whole bunch who are quick to dive in and attest to their packs proficiency after 40K miles etc etc. Then there have been extreme cases that allow Tesla to extend some goodwill and do a full replacement. But there are now increasingly more cases where the company factors in the usage delivered and replaces the pack with one of similar wear. In some of these cases customers have turned around and demanded a pack which is capable of the original mileage at delivery on the grounds that so_and_so has reported that his battery is only a couple of miles down after a full year of use. That of course is the problem. Perhaps so_and_so has a commute where he doesn't exceed 45mph whereas the other profligate owner likes to bury the needle so to speak. Of course the console display is merely a computer prediction based on best practice modelling and headwinds and low ambient temperatures will also eat into the rated miles as displayed on that console. For the future maybe they should consider the pack's Kwh storage - let the supercharger decide - at ownership change and leave the car and the rest of the powertrain out of the equation. Finally mechanical transmisions are based on a mature technology with lots of history whereas battery packs are only on their second iteration. Time will tell.
CheeseEater, you reminded me that most, if not all transmissions (since 2000 at least) just get rebuilt at a remanufacturer, it cheaper to just swap for a rebuilt. I agree that back in the day, repair of three-speeds used by those 350 cubic inch engines was indeed practicable. However, following the advent of five speed or more sophisticated transmissions with their electronic interface to the ECU it is no longer so. At least not unless significant proprietry technical resources are made available. I would have to rebut that the more pricier rebuild may be the option for late model vehicles, but often or not, particularly outside of the warranty, it is increasingly becoming a deal breaker with older vehicles. ZF provides complex mechanical solutions in a world that is intent on moving the complexity part into the electronics where the reliability improvement is a thousand fold. In this world only the simplest mechanics will exist. On this note I predict that even Tesla will eventually eschew the differential final gear that is possibly giving them the occasional gear lash problem (from what I read) in favour of a slightly more robust twin motor drive. In manufacturing you strive for repeatability and reproduceability. That these goals are more easily reached with electronic systems is probably an understatement.
ZF has to keep current with its clients and those clients continue to specify and purchase something they understand. Another recent example of this is to see how successful auto dealerships have been at handling the sales of electric cars. Not. Of course it is one thing to have machines designed by those with Doctorates but out in the market the transmission repair shops don't have that luxury. For that reason it has been stated that the increasing sophistication of these devices has resulted in more than 50% of them being uneconomic to repair.
It is not a foregone conclusion that a self-driving vehicle would ever perform more safely than an experienced, middle-aged driver. Do I detect some ass covering here ? But OK, if that particular demographic is to represent the benchmark human driver then I, for one, would be quite satisfied if the autonomous vehicle could perform even as safely as an experienced, middle-aged driver. And by the same token it would follow that its ability should likely surpass the skill of all lesser drivers as well. You know, those drivers responsible for the road deaths of 34,600 people last year in NA. Would you agree ? As we like to say here - Good enough is not the enemy of perfect.
A rarely discussed problem concerns the fact that most of the superior chemistries are said to have unacceptable self-discharge rates when used in a 12 volt standalone application. There is also the cost factor of Li-ion batteries ~$240/Kwh whereas the average 0.9Kwh Pb-Acid goes for around $100.