Are you shopping for a new vehicle and having trouble finding one, or have you been waiting a long time for a factory order? A reporter would like to speak with you; please reach out to [email protected] by Tues. 5/11 for more details.

Advanced Course in Hybrid Engineering

Kirstie_HKirstie_H EdmundsAdministrator Posts: 11,114
edited March 2014 in Toyota
Want to talk about the merits of various engine designs? Need to debate IMA vs. HSD? Have a penchant for performance statistics?

You've hit the right topic. Roll on!

Roving Host & Future Vehicles Host


Need help navigating? [email protected] - or send a private message by clicking on my name.

Share your vehicle reviews



  • toyolla2toyolla2 Member Posts: 158
    John 1701A observing that the two car companies active in the hybrid field have slightly different thrusts stated that :

     Toyota is for reduced emissions
     Honda is for increased efficiency

     But I would suggest a third thrust might be taken given that there is room for improvement in the efficacy of coupling the ICE to the road wheels.
     Consider the methods currently available:
      I am not saying that I don't enjoy driving stick in an Echo, it has great Torque/Mass ratio, equivalent to an Acura TSX , however efficient as it is; the Stick method is too tricky to lend itself to computer automation.
      So occasionally I drive the "relentless search for perfection" vehicle which comes with a transmission that is supposed to be computer friendly. And now I'll get the occasional tap in the rear while waiting at stoplights, the unexpected surge at low speed and finally when I egress the rolling backwards an inch or two. Sound familiar? So they can't get it right am I supposed to accept this as normal.
      Now for the hybrids, I invite you to observe the images provided by usbSEAWOLF2000 #193 on the Hybrid Honda Accord 2005 board. The first image is that of a Honda Civic Hybrid engine and the CVT as you can see is situated on the right hand side. That is one large and complicated piece of mechanical engineering I have to say.
       I find it incongruous with my experience in electronic drives that someone would come along and fit a mechanical variable speed device on shaft of this engine. This is probably the obvious
    solution for a company heavily biased in mechanical engineering. But in the new millennium I would have suggested alternative ideas. Such as increasing the stack length of that generator to up the capability
    to 80kw at 7000 rpm. Discard the CVT entirely. Select instead a 25hp (1800 rpm base speed )3-phase induction motor with rotor balanced for 12,000 rpm and a 30 second rating @ 75hp to be coupled into the trans axle with a 10:1 ratio.
    Additionally two inverters on the HV bus would be needed. The first would be the starter for the ICE and would subsequently degrade to become a 3-phase rectifier. The second would be the traction inverter. I would also place a couple of transistors in series across the HVbus as an UP/DOWN converter for the main battery pack. That's for those who want some "Stealth" capability and braking regen.
     I need to say something about the Prius. That planetary device with servo is way too complex IMHO for mechanics. Even on these boards there have been struggles to get a handle on the concept. Yeah a VCR/dvd player is complex but at least for $50 you can junk'em. But I gotta say I love that 200/500v bus idea. Constant v/f ratio would run out of headroom at 52mph otherwise.
    And because current costs but voltage is free it complements the fact that although we crave horsepower we drive torque (hybrid v Diesel Idletask #6) This means the system is able to maintain constant current (read torque) and optimal slip for the induction motor as the vehicle accelerates. As frequency increases it gets harder to force current into an induction motor so the torque would start dropping, not desirable obviously.Having extra voltage via an up converter (Prius) or increasing excitation to the alternator (series hybrid).
     I would carry over the technique to a series hybrid but go even further to as high as 800Vdc. Heck, European inverters hit 1000Vdc I'm told. If this doesn't sound too clear. Just trying to broach the idea of Power Envelopes. Hope this didn't appear preachy.

    Why series hybrid........
    The use of the traction inverter will insulate the driver from instantaneous power fluctuations from the ICE that the other systems are susceptible to. This was the original point I was trying to get over. But I got caught up in explaining how this would be done. After all you can talk the talk but how close is practicality is what I also wanted to demonstrate.

    I'm done.

    Hmm.. 5.00am it's really quiet on this board. Time for a Bark Off don't you think?
  • railroadjamesrailroadjames Member Posts: 560
    You really have delved deep and techno into this subject while I on the other hand have come to the Hybrid realm thru the world of railroading. Years ago in a galaxy far, far away there once was steam-powered locomotives but technology, as always, moved on and along came the diesel-powered engine that eventually became one of the first duel-powered vehicles of the 19th century when it was combined with traction-motors for the final power to the rails(kinda like the first hybrid).
    One thing for sure these hybrid cars sure can scare us with all the gadgetry and techno stuff. I've noticed quite abit of hesitation on the general public to grasp the transition to it all and take the plunge or as we say on the railroad,"Get On Board!". Toyota sure has made it more comfortable with the eight yr/100K coverage on the hybrid drivetrain. I must say that Motor Trend bestowing "CAR of the YEAR" award said volumes about the in the know thinking of an establishment long known for their love and bias to conventional combustion cars. One last tidbit, as to all your technical info shared with us novices,one question popped up several times...Where were you when American car manufactures piddled with turbine and the other like power sources? (they cudda used you)
                  Culliganman (retired hogger)
  • midnightcowboymidnightcowboy Member Posts: 1,978
    "...that Motor Trend bestowing "CAR of the YEAR" award ..."

    But you have to remember that Trend Micro has a very limited selection criteria, only brand new or substantially changed models

    and they have made some big fopahs in the past --Like when they named "Renault Alliance" car of the year.

    Me thinks the techno-gadgets and the current Hybrid-fad may have clouded their selection vision.


  • railroadjamesrailroadjames Member Posts: 560
    Well, you touched on a tender spot when you pointed out the Renault. I once had the "Encore". It was quite inovative with its extended wheelbase and frontwheel drive. Price was very friendly not to mention decent MPG's. I think its downfall was a lack of quality control back then. Since I knew this car I can speak with some knowledge. Your point is fair to say that M/T could have made a better choice (IN HIND SIGHT). As to comparing the PRIUS to the Renault well, the jury's still out but do remember that Toyota has been into this hybrid game for the better part of 10 yrs not to mention R&D with over 300 of their own patents per Hybrid Techno. If you really think that Hybrid Technology is a fad you might might want to re-think that since half a dozen models are out now and more than another half dozen are on the way.
    P.S. Maybe you think the HUMMER should have been "CAR OF THE YEAR" perhaps?
    Culliganman (toot toot)
  • toyolla2toyolla2 Member Posts: 158
    Hi Culliganman,
                          it is encouraging to get a positive response now and then. Your view that the public is slow to 'Get on board' with hybrids may be in part due to cost concerns regarding the repair of the hybrid powertrain. These costs can be the automotive equivalent of 'dropping it on the floor' if railroad parlance serves me right. Then there's the fact that there are some good non-hybrids available out there which have nearly the mileage but without the price premiums of the hybrid.
      This is my thinking:-
                  What we have in the market is the result of but two design teams and their solutions, IMA and THS. I would judge the Honda solution to be 95% mechanical, the Toyota about 50/50 mechanical/electrical. But there is no 95% electrical solution which I take to be the series hybrid.
       Reverse logic would imply that if the two methods presented so far were in fact la creme de la creme how is it that neither company dabbles in the other company's technology? Shouldn't competing technologies be about equal? Someone posted that Honda had limited resources to go further into the development of full hybrids. This I believed until the launch, recently, of their version of the Learjet. Or perhaps this was a different Honda :-)
       The Honda method is about reclaiming energy from braking and hill descents, I believe it does very little for performance. Considering the Honda IMA with Manual transmission if it were fitted with a tall gear in fifth (0.7). This would give it the superior mileage in longer hiway trips.
        The Toyota method has to emulate the tall gear which is comparitively lossy to do, so it cannot compete against the Honda on long hiway trips. However when fluctuations in speed are required the THS, which is always in the 'right' gear, delivers superior acceleration performance because the ICE rpm will not be sawtoothing up and down as in the Honda M/T as the driver rows through the gears. Maintaining a constant high speed from the ICE means that the THS is able to provide a higher average continuous power to the road. 30-50 MPH times bear this out.

          I ought to mention the Honda CVT (w/IMA)variant. Like the THS, not so good on long hiway trips compared to the Honda M/T(w/IMA). OTOH acceleration with the CVT should be very good as long as the system stays in top shape. The question is how long will they stand up to aggressive driving.
         As I understand it the CVT in the Honda is some form of hydraulic computer gear-changing gizmo, very mechanical and prone to go wrong with wear. CVTs had been used industrially quite a lot until DC thyristor drives became popular - about 35 years ago. They were followed later with a transistor invertor /induction motor combination.

        As Seinfeld would say, we know they've seen the fork, we've shown them the fork, so why are chopsticks still around. Do they think we haven't noticed?

        My opinion is that less mechanics means increased reliability.

        The series hybrid in my 95% electrical solution works on the acceptance that controlling mechanical power is difficult and gives lots of problems involving clutch /gearbox/CVTs/ICE stability over extended speed ranges.

         The solution as I see it is not to control mechanically but to control electrically. In this regard it is necessary to convert mechanical power as early as possible into electrical power. The ICE being directly coupled to the generator. Then finally an invertor feeding an induction motor which drives a differential with a 10:1 ratio would complete the system.
       The 100kw invertor/induction motor package would be similar to that used by GM's EV1. No risk there.
       The ICE would be a 'CLEAN' engine meaning there would be no power takeoffs, at 15,000 RPM they would not be too reliable. Two pistons on the same crank would allow the use of just two main bearings. Balanced firing 360 degrees apart to each cylinder. The generator rotor containing Neodymium magnets could be fitted to one end of the crankshaft or divided in two and placed at each end if overhang is a problem. Valves would be magnetically actuated.
         Comments please
  • electrictroyelectrictroy Member Posts: 564
    - As an engineer, one of the first things I consider is "What happens if a part fails?" I look at the Prius & I notice that if the electric motor #1 or motor #2 fails, the car will not move. The transmission will spin, but the car will go nowhere.

    - In contrast, the Honda Hybrids don't rely on the motor. Even if the motor is dead, the car can still move forward on engine power alone. And you can drive it as a conventional car until end-of-life.


    - Both the Prius & Civic Hybrid are approximately equal here (~50 mpg highway), but the Civic comes with a lean-burn engine. A careful Civic driver can watch the gauges, keep the engine in lean-burn, and routinely score 60 mpg highway.

  • gagricegagrice Pahrump, NevadaMember Posts: 31,450
    The 100kw invertor/induction motor package would be similar to that used by GM's EV1. No risk there.

    I appreciate what you said that I was able to understand. I lean toward the series hybrid with the more efficient diesel engine. I felt the EV-1 was buried before it had a chance to mature. Batteries being the big Achilles heel. I like the idea of plugging the car in at night with the option of a genset when out and about when no AC is available.
  • railroadjamesrailroadjames Member Posts: 560
    Sorry for the delay getting back to the details and you. I had some extenuating things come up. I too have had some miss-givings about the highly technical systems involved with the Prius and it's intricate electrical sys. but then I got to thinking...My wall switches and outlets at home (all 24 of them) are 52 yrs old and not one of them have gone bad. I have a ceiling fan thats 29 yrs old and again she's running like the first day up. Well, what I'm getting at is obvious. Toyota has put high quality electrics into the Prius starting with the main battery and continuing thru to the CVT transmittion. Let me add that we all put trust in our vehicles every day. When we turn the steering wheel, step on the brake, turn on the lights, wipers and even the electric starter. We've come to expect our cars to deliver unfailingly. Some do it better than others. Toyota (I think) is one of a select few. I now have nearly 12K on my PRIUS. I've had my hybrid over 110MPH and felt the car sure footed. I've driven her hard and I've babied her to extract as much as 56 MPG's. The Prius has delivered on all of my demands.
     People really fail to understand that to get a great car that delivers high mpg's (say over 45) and have roominess AND reasonable performance is almost unheard of until now. I'm convinced the PRIUS has filled the bill while others have only titillated the concept. Being an avid motorcyclist I have seen many a bike 2-4&;6 cylinders get a meager 34MPG's and even a few (Harley for one) get less while usually ridden hard. Bikes weigh in usually around 390 lbs while hybrids come in at around 2800 lbs There in lies the delimma. Alot of good milage is determined by one's own driving habits too. I simply find it satisfying that the hybrids have excelled at fuel efficiency and reduced pollutents to a very respectable and practacle low level.
    Culliganman (Green like Kermit)
  • explorerx4explorerx4 Central CTMember Posts: 15,688
    drove my sister's '05 prius today. it seems like a good real world vehicle. it drives normally and seems practicle for a family(4), plus attractively designed and well put together(interior). no faults with the exterior either. imo.
    to me the biggest problem is with peoples attitudes. when i told them my focus was rated pzev, they didn't know what that meant.
    2020 Ford Explorer XLT, 2019 Lincoln MKZ Reserve 1
  • stevedebistevedebi LAMember Posts: 4,098
    "My wall switches and outlets at home (all 24 of them) are 52 yrs old and not one of them have gone bad. I have a ceiling fan thats 29 yrs old and again she's running like the first day up. Well, what I'm getting at is obvious."

    The devices you mention are simple mechanical designs. Wall switches and outlets have no moving parts, and the fan is a very simple set of coils through which the electric current passes.

    The Prius is far more complex. It is not just the quality of the parts that makes for longevity, it is how many parts have to work together. The Prius is even more complex than other (already complex) modern cars. Complexity means more problems down the line.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    Do you guys see dealerships actually *repairing* these cars, or rather just swapping out large modules after a standardized diagnostic? If the latter, this could get very expensive for Toyota should they find say an 5-8% failure rate on some major componentry. I only have one anecdote about this so far--my friend's Prius died and they replaced (my friend says) a "controller and some other parts" and (my friend says) the warranty charge (which he peeked at) was something like $5,000.

    I dunno, just a yarn over a beer but it got me thinking.
  • larsblarsb Member Posts: 8,204
    whole battery system. The batteries are modular and can be replaced without replacing the whole system. I don't know the diags they would do to determine WHICH modules are problematic, but I'd bet they have a diag for that....
  • electrictroyelectrictroy Member Posts: 564
    A direct mechanical connection (stick-shift) provides the best efficiency.

    - You pointed out manual shifting is a pain, and automatic wastes energy, but VW has a solution called Direct Shift Gearing (DSG). It operates similar to an automatic, but has no torque converter, and provides 6 gears for optimum engine usage.

    - The Prius planetary gear is no more complex than an automatic planetary gear. In's simpler. No clutches. If a mechanic can fix an automatic, he can fix a prius transmission.


    "Select instead a 25hp (1800 rpm base speed )3-phase induction motor with rotor balanced for 12,000 rpm and a 30 second rating @ 75hp to be coupled into the trans axle with a 10:1 ratio."

    This concept sounds like a supreme waste of electricity/energy. I see no benefit to using such a contraption.
  • robertsmxrobertsmx Member Posts: 5,525
    Actually, Honda has been testing its own 6-speed "torque-converterless" automatic transmission. Let us hope the next HCH is the car that gets it. The transmission is configurable to have up to 8 speed. BTW, this would be an AAD transmission (Antonov).
  • alcanalcan Member Posts: 2,550
    Ford and GM are also currently developing a torque converterless 6 speed automatic trans as a joint venture.
  • toyolla2toyolla2 Member Posts: 158
    Electrictroy takes issue with a statement from my previous postings :

    "Select instead a 25hp (1800 rpm base speed )3-phase induction motor with rotor balanced for 12,000 rpm and a 30 second rating @ 75hp to be coupled into the trans axle with a 10:1 ratio."

    The statement of 1800 rpm base speed was included only to give readers a handle on the motor frame size I am referring to. I mentioned 1800rpm as it is a popular size in industrial machines. This gives a 256T frame weighing 200lbs. We can double the speed of this motor by rewinding the stator from 2 polepairs/phase to one polepair/phase. Since we now use all the copper and iron circuits twice as often it's allowable to say that we have also doubled the power of this motor to 50hp.
    But this is at nominal 60Hz. If we shift the frequency up to 100Hz the motor now has the capability of 83Hp at 6000 rpm corresponding to a road speed of something exceeding 40 mph. Increasing the frequency again to 200Hz will yield the 12,000rpm I wrote of earlier. This is a 2:1 constant power ratio which may be relevant or not depending on whose math you look at.

     Perhaps some people have misgivings about a 200lb motor, well the use of aluminum frames and end bells could knock this down by 60lbs. Remember these speculations have been applied to a motor which was expected to perform 24/7 working. No road vehicle has to meet that severe duty cycle. The motor being protected within the vehicle, cast iron durability is not required nor the weight penalty that comes with it.

    The industrial motor is also expected to provide continuous maximum power in an ambient temperature of 40 degrees C. Liquid cooling should handle the thermal management requirements but generally at 60mph the motor will be called upon to deliver less than 10Hp most of the time.
    This fact suggests that overcurrent during acceleration of 300 % may be admissible. If most acceleration ramps are less than 30 seconds the thermal time constant of the motor may be able to absorb the heating losses of these relatively occasional events. Why would we want this ? Well as it stands now we don't get 83Hp until 40 mph. Even a Toyota Echo will get 108Hp at this speed with its torque of 105lbs-ft. Our induction motor will only push out nominally 80lbs-ft at full load current, a lot less. But the application of 300% overcurrent could yield 200lbs-ft from zero to 12 mph and then gradually tail off to 80lbs-ft at 40mph since the 83Hp from the ICE would be the limiting factor. However the initial 200lbs-ft would fire the vehicle off the mark wouldn't you say ?

    It should be noted -
    Most vehicles at 40mph will have moved to 2nd gear
    including the Echo so its comparitive torque will be halved to 52.5lbs compared to 80lbs-ft of the induction motor which stays in its same fixed gear. You can see it's no contest.

    Hi Electrictroy,
     You wrote :

     "I see no benefit to using such a contraption."

    Have I changed your mind ?
  • electrictroyelectrictroy Member Posts: 564
    No. I still see that you're wasting electrical energy with your engine---motor---wheel coupling. IMHO it is more efficient to just use the standard engine---gear---wheel coupling.
  • toyolla2toyolla2 Member Posts: 158
    electrictroy - I originally thought you were critiquing just the induction motor/gearbox part of the SHEV but it now appears you have expanded the argument to include the the ICE/generator portion.
     So I am taking the statement "your engine---motor---wheel coupling"
    more accurately to mean "your engine---generator---motor---wheel coupling"

     Since it was you that made that block statement in the previous post, I think it is concomitant that you provide us with an approx breakdown of the losses you expect in the two systems ? All I'm asking is for your guesstimation of what %age losses in what components exist within the system paths of both systems. Show me where the extra losses are.
  • electrictroyelectrictroy Member Posts: 564
    First off, the burden of proof lies on the *inventor*. That would be you. Prove that your system is more efficient.


    Second, you want to create a system like this:

    to replace the standard automatic or manual transmission. You are losing ~10% in the generator to electricity to motor conversion due to resistance losses.


    The way cars are now:
    engine---auto/stick-shift transmission--wheels

    with the direct mechanical connection results in little energy loss.

  • toyolla2toyolla2 Member Posts: 158
             I agree with you that the two electrical conversions that define a SHEV will sustain total losses of around 10%. Even with the best design I doubt if any motor or generator will exceed 95% efficiency in its electrodynamic performance at the power levels being considered.

     Leaving that aside, you then make a qualitive statement to the effect that the direct mechanical connection (of a conventional M/T ) results in little energy loss.
     Hmm... I wonder what that little energy loss might be.
      I would be very interested to know what numerical value you would place on the %age loss through a M/T.

     In the meantime here is something to consider:-

    Spur gear to spur gear efficiency were both gears to have the same number of teeth is 95%. When the tooth ratio goes to 2:1 the transfer efficiency drops to 93%.

     This was an actual finding by the Eaton Corporation which built an EV with a two speed gearbox back in the early eighties as part of a DOE contract.

    Lets say that in a FWD M/T there are two of these gear interfaces including the final to the differential. A 5-speed M/T will also have losses of the other four meshed gears churning in the oil. Oil serving its secondary purpose of carrying away the heat generated by the sliding action of the gear teeth. Two gear interfaces means a total loss of 10%. But that's heaps better than a RWD.

    In a RWD M/T the second gear interface is a hypoid gear on the rear differential. Turning power through 90 degrees is very lossy. Hypoids are probably no more than 80% efficient. But the fact that manufacturers specify a special hypoid oil that won't overheat should give you a clue that it isn't business as usual back there.
    This efficiency issue is a good reason to avoid RWD platforms altogether.

    Leaving the RWD issue behind then the two systems are neck-a-neck at this point.

    However the SHEV does have one gear interface in the 10:1 step down. Which is another 5% loss the M/T doesn't have. Question is, does the SHEV have any mitigating conditions to counter this deficit, and I believe it does.

     It is the ability to use a two cylinder engine
    against a four or six cylinder.

    This should reduce friction budget quite a lot compared to a four or six cylinder engine, and now I am the one using a qualitive statement. I have no sources for stating this it just seems intuitive to me. There are just less moving parts to cause friction.

       Thus a two cylinder engine, that would be impractical to use with a M/T in a passenger vehicle otherwise, is able to become a viable candidate with electrodynamic conversion.

    That's my response ET.

    Have you noticed how .... ?
      ...people that favor a particular platform are always looking for the V6 availability (Cavalier and Corolla owners) Yeah, you know who you are.

      ...people who are V8 advocates out there describe a V6 engine as having a shortage of extra cylinders !

      ... Dennis Miller can bank on a cheap laugh when he states " The (PRIUS) would have to have a V8 to get me in one ".

     Remnants of 20th century thinking in a 21st century world.
      With the pure mechanical route we cling to now, of course cars become easier to drive the more cylinders the engine has. Now tell us something we don't know.

    As I have stated before an anachronism in automobiles is that while people have a penchant for horsepower in fact they drive torque. No one drives downtown @4000 rpm and only few drive more than 4000rpm on the hiway for that matter. Unless they are looking to find a police officer they didn't need.

     But most engines today need to hit 6300rpm or more, sometimes much more, to reach max horsepower. Most people change gear around 4000rpm so the horsepower envelope of the vehicles engine map is rarely tested. But the torque envelope is tested nearly every time we drive. Who hasn't put the pedal to the metal one or two times a week ?

    And that highlights one of the differences between the two systems. Maximum accelerator pedal depression in a M/T is a demand for instant max torque. In a SHEV (above base speed) maximum accelerator pedal depression is a demand for instant max power. For this reason an 80Hp ICE would rival a 160 Hp ICE in a M/T.
  • tigercat21tigercat21 Member Posts: 28
    Interesting post you wrote about efficiency of different gear setups.
    Do you happen to know how efficient chain connection to gears is (as in bicycles)? I remember an offhand remark by someone once that the old chain drives on cars was the most efficient method for transferring power...I was always curious whether that was true or not. TIA
  • electrictroyelectrictroy Member Posts: 564
    "Spur gear to spur gear efficiency were both gears to have the same number of teeth is 95%. When the tooth ratio goes to 2:1 the transfer efficiency drops to 93%."

    Interesting. That's almost as low as the 90% generator--->electric---> motor conversion.

    Perhaps your idea is "better" in terms of improving engine-to-wheel efficient? Do you know of any company that has tried the pure electric transmission?

  • 37453745 Member Posts: 152
    I'm also interested in the efficiency of chain drive because many transverse engines are coupled to the transmission by means of a chain. GM in particular uses it on all of its front drive vehicles.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    I can tell you from motorcycle experience that chain drive is more efficient that drive shafts for power transfer to the rear wheel, and more efficient than direct gearing for camshaft/crankshaft synchronization. But I don't know how this translates to automotive uses.
  • electrictroyelectrictroy Member Posts: 564
    Similar to a chain is the "belt drive" used in CVT cars. Any efficiency numbers on those?
  • 37453745 Member Posts: 152
    Thanks for that. Very interesting. Seems as if chain drive is pretty efficient compared to other methods.
  • toyolla2toyolla2 Member Posts: 158
    The constructive responses are appreciated, no one person can ever monopolize all the pieces necessary to put this jigsaw together.


      Following up on those links it became apparent that there were two major differences :


         Firstly the more favorable 1 : 1 ratios were under consideration.

      The induction motor on a SHEV needs a 10 : 1 ratio. This brings the implication that since the drive sprocket would need to have a 4" dia. to be efficient that would force the driven sprocket to be around 40" dia. !! (assuming a single stage step down) Clearly a spur gear system will scale down in size better since it doesn't have to accomodate the comparatively large chain rollers.


         Secondly the sprocket speeds of 200 revs/min under consideration are also quite removed from the 200 revs/sec encountered with the induction motor in the SHEV. In this environment the chain speed with a 12" circumference drive sprocket would be around 200'/sec.

    Of course as we know a motorcycle chain doesn't go anywhere near this velocity because primary gear reduction has already been accomplished inside its transmission.


    But applying this to the SHEV which is trying for the more efficient single stage reduction : -


    The ramification being that centrifugal forces proportional to the square of the chain velocity will end up at least 60 times 60 larger than those experienced in the bicycle application. This may promote a wear anomaly which may have not been significant before in that research carried out earlier at a mere 200 revs/min. Inertial losses in flexing the chain around the sprockets will go up 3600 times. That prediction could knock the 96.8% efficiency figure out of the ball park. Anyway the 40" driven sprocket is also a showstopper. Reducing the drive and driven sprockets is a research project in itself but who knows how far this could be done. GM decided in their wisdom to use a single reduction from the induction motor shaft to the differential shaft and I am pleased to leave it at that for now.


    But there is another solution which I did some work on in 1985 and which was similarly later proposed by Aeronvironment, the contractor used by GM, to produce the original "Show Car" the Impact. GM renamed it EV1. The solution in the original vehicle was to have individual induction motors for each of the front wheels, as some of you may recall. Well I do, still having a copy of the 1990 video they made about it. They were able to do this despite the limited distance between the front wheels by building the single stage planetary gear box of 10.75 ratio into the end bell of each motor.


     The internal tooth ring gear being rigidly fixed to the end bell as you would expect.

     One advantage of the planetary is that there is no side force on the bearings (load overhang) that you would get using a simple take off gear or a belt or chain drive. In fact you may be able to get away with just one bearing on the rotor. The other end of the rotor shaft would just have the sun gear on it. This gear would sit surrounded by three planet gears and be supported in place by them. It seems reasonable that once rotation begins that symmetrical gear tooth forces will ensure this gear will be forced to ride exactly in the centre. I don't know if they actually did this. At 12,000 rpm you want as few components involved as possible that can affect reliability.


    The third part of this system is the planetary carrier on which the bearings for the planet gears are mounted. A flange on the output shaft connects to the carrier and transfers the power outside the motor to the CV joints which is now plain vanilla engineering. Maybe GM was concerned for the longevity of these components plus they needed two motor/invertor sets which was why this idea was dropped.

     As a twin motor design of course it would have given automatic traction control and perhaps steering assist by shifting the torque ratio away from 1 : 1.


     And something the SHEV and HSD can do, but not the IMA, is electronic reverse. For mechanics who may not be familiar with the properties of the 3-phase ac motor, the following may be of interest. The ac induction motor can run with equal efficiency in either direction. The industrial motor is generally found to be reversed by using two switching contactors. One contactor connects for forward motion. The other contactor is hardwired such that two of the phases running to the motor are crossed over. When this contactor is pulled in we say that the phase rotation is now reversed, thus causing the motor to run backwards. But this is doing it the hard way.


     When you have the ac being generated by solid state equipment usually known as the 3-phase invertor, you have the three phases being each electronically synthesised to be equally spaced apart in a fixed order. But it requires only a change in the software to cause those signals to be issued in the reverse order. There are no contactors to be switched, the motor will just start running backwards.


      There has been some activity in the HAH board lately, surrounding the Dec 3rd release of this model. It bugs me that there are steep price premiums on these vehicles even before MSRP add-ons. Someone computed that use of an aluminum hood and run flat tires (no spare) (being some of the ameliorating measures taken to offset hybrid equipment) indicated actual weight of hybridism to be 300lbs. Don't these cretins learn anything ? Of course a 16Hp machine @ 840rpm is heavy. As a comparison, on the EV1 the whole 137Hp transaxle complete with induction motor weighed in at 68kg (150lb?) How come ? Well, its base speed was 6600rpm NOT 840rpm. I understand that they wish to retain the top road speed of 131 mph which would be compromised if the IMA was put anywhere else but on the crankshaft side of the gearbox.

  • xcelxcel Member Posts: 1,025
    Hi Toyolla2:


    ___Great post. Inside info on the EV-1 from almost 15 years ago! Did you have anything to do with any of the work on the “GM Precept” CI-DI-ICE/Hybrid as well? I would love to know the details of that one …




    ___Wayne R. Gerdes
  • tigercat21tigercat21 Member Posts: 28
    Thanks for the response, that was a lot of typing and its appreciated.


    "The second factor that affected efficiency was tension in the chain. The higher the chain tension, Spicer says, the higher the efficiency score. "This is actually not in the direction you'd expect, based simply on friction," he says. "It's not clear to us at this time why this occurs."

      This is a quote from one of the you have any theories on it? Also they downplay the importance of lubricants on the chain. They say its only important as a displacement of dirt. How can something with so many little parts not have its performance improved by being lubricated? It also seems a chain would wear out very quickly without lubricant, gears certainly do.

    Sorry for being off your topic, I know this isn't the intention of your discussion but you peaked my curiosity on this stuff. TIA
  • robertsmxrobertsmx Member Posts: 5,525
    And something the SHEV and HSD can do, but not the IMA, is electronic reverse.


    Are you trying to compare generator/motor characteristics of brushless DC motor versus 3-phase ac motor, or something else?


    Someone computed that use of an aluminum hood and run flat tires (no spare) (being some of the ameliorating measures taken to offset hybrid equipment) indicated actual weight of hybridism to be 300lbs


    IMO, that would be bad math. Hybridization itself isn’t adding more than 125 lb. to Accord’s curb weight (total weight differential between Accord Hybrid and Accord EXV6 is 116 lb). Use of aluminum hood would not shave off a whole lot of weight. In case of Civic Hybrid, the total weight gain is only 63 lb. over Civic EX.


    Mild hybrid systems (like IMA) do not add weight and cost as much as full hybrid systems do (Prius and Escape Hybrid).


    I understand that they wish to retain the top road speed of 131 mph which would be compromised if the IMA was put anywhere else but on the crankshaft side of the gearbox.


    I’m not sure what you’re trying to conclude out of this. 16 HP @ 840 rpm is the peak power. The brushless DC motor continues to add 15 HP at 6000 rpm to the 3.0/V6 output of 240 HP at 6000 rpm for a total of 255 HP. The output is channeled for both sources as a single output into the transmission.


    This could be different in other variations of IMA that we have not seen in production yet (like those in Honda Dual Note and Acura RDX prototypes).
  • stevewastevewa Member Posts: 203
    Mild hybrids add weight in different ways than full hybrids. Full hybrids have bigger battery packs and (in the case of current models on the market) a second motor. Mild hybrids have a larger ICE and a conventional gearbox.


    As to the maintenance factor, most mechanics don't repair modern auto trannies anymore, either...they slap in a rebuild and send the broken box to the factory.


    I think a serial hybrid is an intersting concept. However I'm not sure how well it's suited to automotive applications. Serial hybrid locomotives on the railroads are efficient because they run at nearly full output most of the time. That's not the way we use our cars, however. For peak output periods which are much briefer in autos, it makes sense to be able to couple both the prime mover (aka ICE) and the traction motors to the driveline. Furthermore, it's interesting to note how quickly the technology to control AC traction motors was adapted to work in cars when it took a very long time to become practical on the rails.
  • robertsmxrobertsmx Member Posts: 5,525
    Mild hybrids have a larger ICE and a conventional gearbox.


    Larger than full hybrids, but not necessarily larger there non-hybrid counterpart. For example, next Civic could offer 2.0-liter in non-hybrid form, but a 1.5-liter engine may be deemed enough for the hybrid. However, in the world of ICE, there isn’t likely to be a big weight/packaging size differential between a 1.5 and 2.0.


    The idea of must have conventional gearbox isn’t true either. What really differentiates full hybrid from mild hybrid is ability to run the vehicle without ICE for some distance/speed. A large enough energy storage could accomplish the same in a smaller electrical set up, with or without conventional gearbox.
  • vietviet Member Posts: 847
    Hi guys:


    The Accord Hybrid (HAH) keeps turning on and off the engine at stops lights or at speed lower than 10 MPH. When I drive the car into the garage, the speed is lower than 10 MPH so the engine shuts off while the car is not completely in the position I want that I can close the garage door without banging the garage door to the back of the car. Therefore, I have to release the brake and the engine turns on again so I can move the car further into the garage.


    My question is: The HAH's engine keeps turning off and on repeatedly. Is there any worn-out to the engine parts?
  • larsblarsb Member Posts: 8,204
    quote Viet-"My question is: The HAH's engine keeps turning off and on repeatedly. Is there any worn-out to the engine parts?"-end quote


    The only part being "taxed" repeatedly is the "Integrated Starter Generator" which starts the car under normal conditions.


    It is under warranty, and it probably covered as a part of the IMA system.


    I have never seen or heard on any instance of an ISG going bad on ANY hybrid, so I think you need not worry.
  • robertsmxrobertsmx Member Posts: 5,525
    Components in a well designed car are engineered with emphasis on the stress areas. For example, the 2.0-liter engine in S2000 was designed to redline at 8900 rpm. Not all engines can do that. Obviously there was engineering involved to ensure the engine is as reliable as another that does not rev as high.


    In case of hybrids, the emphasis will be in their own “stress areas”. If it is about auto-stop, then there it will be. There is no need to worry about it as long as it works as expected.
  • electrictroyelectrictroy Member Posts: 564
    "engine shuts off while the car is not completely in the position I want. Therefore, I have to release the brake and the engine turns on again so I can move the car further into the garage."




    Hmmmm.... in my manual-shift car I can over-ride the engine off, by keeping it in first gear. Is there some way to override the engine off in an automatic?


  • vietviet Member Posts: 847
    Thank you guys, especially Robertsmx. I still love your well-written message/ article in the other HAH's forum the other day. My friend said his S2000 can run fast at any gear.
  • vietviet Member Posts: 847
    Prius with top package 6:


    Package #6 -- includes driver and front passenger seat-mounted side and front and rear side curtain airbags [2]; anti-theft system and auto-dimming electrochromic rearview mirror with HomeLink® [3] universal transceiver; Smart Key System; High Intensity Discharge (HID) headlamps, integrated fog lamps and Vehicle Stability Control (VSC) [4]; JBL 3-in-1 AM/FM Cassette/6-disc in-dash CD changer, nine speakers in seven locations and FM diversity reception; and voice-activated DVD navigation system [5] with hands-free phone capability via Bluetooth TM [6] technology



    MSRP = $20,875 + 5,065 = $25,940 + TTL

    110 Net HP


    HAHA with Navi.: $32,505 + TTL

    255 Net HP.
  • lucaslucas Member Posts: 9
    If we could find someone in our auto industry with just a tiny bit of imagination, who knows what we could do?

    I've been trying to get someone to take a look at these ideas for some time. In one scale or another everyone of these systems have been proven.

    Like to produce a vehicle that can burn rubber on takeoff on all four wheels and get 90+ mpg?

    What I would like to see the automakers working on would have:

    A turbocharged, two cylinder opposed, 2-cycle, air-cooled diesel directly
    driving a generator. (It would not be running most of the time.) A 111 volt Lithium-Ion Polymer battery pack. Nothing but wires going from the
    controller to every wheel, except for the necessary additional friction
    brakes (of course). An added advantage of this would be the ability to recharge from the electrical grid while at home, saving even more on fuel.

    Each wheel, depending on the feedback to the controller from wheel speed sensors would drive with just the right power depending on the accelerator position. You would get recharging from deceleration just as you do in today's hybrids. You would also use this feedback to stop the wheel from skidding.

    Each wheel would have a stationary stator and a series of fixed magnets
    closely adjacent all around the inside of the wheel. In a sense it would
    operate each wheel in a very similar fashion that the mag-lev trains use,
    except the motion would be circular, of course. Something very different
    about this type of motor is that the stators are fixed to the axles and the
    magnets are driven around them. This gives a significant increase in
    mechanical advantage. That's like turning an ordinary electric motor inside out.

    There would be no need for ordinary electric motor brushes. In fact, many electric motors operating today are brushless.

    Such motors already exist in the model airplane field and their efficiently
    is amazing - approaching 90%. I've got a couple and doubt that I would ever buy any other type.

    It's possible to hang the model on the prop right out in front of you and
    accelerate straight up, like a rocket, with this type motor

    In the vehicle the motor/generator would not turn on to recharge the
    batteries until they needed it. There are already experimental Lithium-Ion
    driven cars that can get in excess of 200 miles before they have to be
    recharged by plugging them in.

    Lithium -Ion battery technology is so new that I doubt that very many
    automotive engineers have even heard of them, much less thought to use them in this manner. Their energy density exceeds that of any other form of rechargeable energy storage.

    The Lithium Ion battery is the most efficient battery available right now. So is the outer rotor electric motor the most efficient motor.

    Build an SUV right and it will weight less and have simpler, easier to repair/replace modules.

    Lets see what we can eliminate while improving performance and efficiency.

    Transmission - None

    Ignition system - None

    Liquid cooling - None

    Valves and valve train - None

    Use bio-oil/fuels for both fuel and lubrication.

    Feel free to pass this along to anyone you know in the Transportation business. I suffer from no delusion that any of them have the imagination to be able to see how something like this could jump them ahead of the competition.

    I bought a Honda Civic Hybrid last summer. I enjoy it more than any vehicle I've ever owned. I will Never buy another vehicle that isn't a Hybrid and doesn't get at least 50 mpg.

    As far as I can tell, Detroit isn't even thinking the same way I and the vast majority of it's potential customers are.
  • toyolla2toyolla2 Member Posts: 158
    Hi robertsmx,
    I will get back to you re the IMA later, but I noticed that you wrote in post #36 when generally discussing mild hybrids. There is a twist to your statement when considering SHEVs that is not well known or recognized and I read something recently in a Yamaha document that supports the idea I've been proposing for SHEV engines that they be high speed.

    "However, in the world of ICE, there isn’t likely to be a big weight/packaging size differential between a 1.5L and 2.0L."

    I kinda agree but...
    Let's see what I found from reading the maintenance manual for the Yamaha 'Waverunner'. This three-seater personal watercraft employs a 1046cc 4cyl engine which produces 170Hp @ 10,000rpm (it direct drives a water pump).
    Just TWO cylinders of this marine engine would be equal in power to the atkinsonised version of the Echo 1.5L that powers the Prius. I accept that the relation between engine mass and the size and number of cylinders is not linear there's lots of fixed mass that both engines must have. It does however highlight that for this particular type of load - an impeller in a hydraulic system - marine designers have found tradeoffs to increase engine powers to levels that appear distorted alongside conventional thinking regarding the weight/packaging size versus horsepower expected from automobile engines.

    Or as I am wont to put it, you can no more make an efficient Series Hybrid Electric Vehicle using a contemporary automobile engine than you can make a successful airplane out of cast iron.
  • toyolla2toyolla2 Member Posts: 158
    You mentioned direct drive wheel motors,here's my take.

    The only popular uses I know for direct drives are
    disk drives; to permit compactness and avoid the speed variation problems associated with rubber belts.
    And clothes driers to replace the two step-downs to the drum and the single phase motor; the one equipped with that fault prone centrifugal start-switch. But in this application whether the three phase direct drive pancake motor with inverter will provide the improvement of a more quiet and compact machine is open to question.

    However the problem with this technology in automobiles is two-fold.
    Firstly they add significant weight to the wheels and this unsprung mass, as it is called, out on the wheels will bring a large amount of vibration back into the vehicle unless you are driving on very smooth concrete which mostly of course you don't.

    Secondly the base RPM is low (600rpm on the wheel)so the horsepower will be low also. You only get to use the magnet and copper materials 10 times per second whereas at 12,000rpm you can use the same materials 200 times a second. It can mean the difference between 10Hp and 100Hp in this context. For simplicity I have been proposing a 10:1 planetary reducer built into the end bell as they did on the original EV1 back in 1990. Take a look at my post #31.

    It can be argued that an inverter grade induction motor is not significantly less efficient than a permanent magnet synchronous machine as you mentioned. But avoiding the expense of exotic neodymium magnets should also assist reducing its cost to Walmart proportions.
    I want a $500 motor not the $4000 say, that you will find on the PRIUS. When I was involved with electric vehicles, I used to have a saying of not "sacrificing yourself on the altar of high efficiency". You can always find a place elsewhere for the same money which will provide a better improvement overall.

    Having an inboard motor makes the sharing of coolant with the ICE more secure and further reduces the frame size you can get away with on this motor. My point is that liquid cooling will allow the specific power density of the motor to be increased.

    Regarding diesels - these are slow machines - even so called high speed diesels top out at 4000rpm. They have to. The first part of the stroke is constant pressure; the fuel continues burning while the piston moves down, you have to allow time for that process to occur; sure the elevated compression ratio they use brings the Air Standard Efficiency from 36 to 44%. If the diesel were required to work at full rated power, I would be with you on diesels unfortunately the nature of motoring is to need +100Hp while accelerating for 8 seconds or so followed by a considerably longer duration when the demand is 10Hp or less. The higher rpm of the conventional ICE is much more desirable in this application IMO. This probably explains why you won't be seeing F1 cars with diesel engines anytime soon.

    Turbos, well of course, in fact I think all vehicles should be fitted with turbos. Too bad the 3 cyl on Honda's INSIGHT didn't get one.
    After I read Hugh McInnis' book on Turbochargers I was a believer.

    Unfortunately these devices need some TLC, manufacturers have not installed the sensors and the microcontroller technology needed to prevent John Q. Public from abusing them, they've got a bad rap. In the hands of sports car aficionados and SAAB they continue to survive. But you don't see enough of these cars on the road to give me the confidence that service support would not be an issue.
    I'd be a lot more enthusiastic if Corollas and Civics started championing this technology.

    I would however have no trouble being a first time buyer of a SHEV with its induction motor and inverter drive because this type of technology is now meat and potatoes in the factory automation business. Motor generator sets are no big deal either even though the automobile version would be light years from the usual Honda standby set.
  • electrictroyelectrictroy Member Posts: 564
    "Yamaha 'Waverunner'. This three-seater personal watercraft employs a 1.0liter 4cyl engine which produces 170Hp @ 10,000rpm. Just TWO cylinders of this marine engine would be equal in power to the atkinsonised version of the Echo 1.5L that powers the Prius."

    The Waverunner engine is spinning at 10,000 rpm! If rev-limited to 5000 like the Prius, it would only generate ~85hp... about the same as the Prius engine.

    No miracle engineering there. They simply made the waverunner spin faster (and less fuel efficient).
  • toyolla2toyolla2 Member Posts: 158
    I was just pointing out that higher speed engines are already considered doable for the consumer market and not merely some near-term project that would need big R&D dollars. I wasn't intending to suggest that it was a replacement candidate for the Prius engine just that a two cylinder version of that engine could provide the same power.

    I agree, it may not be as fuel efficient as the Prius engine while running @ 10,000rpm but it could be as much as 100lbs lighter so there would be an automatic increase in mpg for that reason alone.

    Dare I say that some of the problem lies with your obsession for efficiency. Imagine if the Prius engine was an Atkinsonised V8 3.0L it could run half the speed and so be even more efficient (using your logic) than the current 1.5L. It goes without saying (but I'm going to anyway!) that the increase in vehicle mass with the V8 would cause the mpg to take a hit. You weren't expecting to lug all that extra weight around for free were you ?

  • robertsmxrobertsmx Member Posts: 5,525
    When discussing efficiency, you have to realize losses not just horsepower. An engine half the size of the Yamaha engine you quote could produce half the power (85 HP) at 10K rpm assuming similar efficiencies, and ultimately match 1.5-liter Atkinson Cycle motor as used in Prius in peak power output. But to relate power and fuel efficiency, we really need to look at BSFC.

    Efficiency of a hybrid drive train is going to be determined primarily by two factors. One, how much of the energy is recycled. And the efficiency of the non-electric motor involved. Parallel versus Series isn’t going to be an issue. It is all about efficiency.

    You may have seen a Honda example of a prototype hybrid vehicle earlier from me that involves an ICE mated to electric motor in Series as well as in Parallel mode. The active mode depends on demand. For normal cruising, the vehicle ran in series mode, with ICE charging battery pack running electric motor hence the vehicle. During start up and acceleration, ICE and electric motor run in parallel mode for greater power delivery due to increased load requirements.

    One of the best examples of a series hybrid is a diesel locomotive.

    I was just pointing out that higher speed engines are already considered doable for the consumer market

    High revving engines have been around in motorcycles for a long time. The problem isn’t with the output itself, but how you manage to put it down.

    It would be possible to replace a 3.0-liter, 150 HP motor with a 1.0-liter, 150 HP motor in a 3000 lb sedan. These are peak numbers of course, but assuming similar efficiencies, the 1.0-liter motor will need to spin at three times the rate of the 3.0-liter motor. Gearing will have to take care of this aspect, and spinning at 10K rpm versus 3000 rpm for same power output can be perceived or felt very differently in the same car. Not in terms of power, but in terms of NVH. And, high rpm isn’t the best way to increase fuel economy.

    As for weight, yes, if the 3.0-liter engine weighed 310 lb. as does Honda’s V6, and the 1.0-liter engine weighed 126 lb. as does Honda’s I-3 (in Insight), than you do gain 184 lb. in weight and the vehicle can be lighter. But, that’s probably going to, may be, compensate for added losses of higher revving design (in the engine, and the transmission itself).
  • toyolla2toyolla2 Member Posts: 158
    robertsmx, In your first paragraph you say that when

    ... discussing efficiency, you have to realize losses not just horsepower.
    ...But to relate power and fuel efficiency, we really need to look at BSFC.

    If we were discussing a stationary power plant I would agree entirely with those statements and the Specific Fuel Consumption (in lbs/Hp-hr)is king. But carrying excess weight on a mobile platform will require more horsepower and you will have more losses no matter how good your SFC is.

    As an extreme example even though we know jet engines are dreadfully inefficient we don't see WestJet or any other no frills airlines running around in Super Constellations no matter how more efficient their engines might be. So I am going to stick to my guns on this one that while SFC is important - in automobiles (and airplanes) Mass is too.

    Your last sentence of your post seems to infer a softening of your position

    ...vehicle can be lighter...that’s probably going to, may be, compensate for added losses of (a) higher revving design.

    I've always contended that such high revving will only occupy a small fraction of time over the full driving cycle anyways. The steeper gradients or the stoplight Grand Prix, that kind of stuff. I would anticipate that most of the time the ICE would be below 4000rpm @ 50mph so engine wear would not be an issue. As a reality check to what a typical car needs most of the time let me refer you to this piece that I just dug out, an old 1983 advertising copy from Ford. It says " Aerodynamically designed, LTD needs only 6.7Hp to push it through the air at 50mph".

    Oh and by the way, ...if saving 184lbs does compensate for the less efficient high revving...

    If we could be a little more optimistic here, supposing it does more than compensate... in which case, maybe, you just gained an increase in the torque/mass ratio of the vehicle.

    Then if you are not saying engine efficiency is paramount - no matter how much it weighs - where do you draw the line. I speculate Toyota went with the most advanced 1.5L engine block that was available at the time, they were taking enough risks.

    We know they certainly don't view high RPM as being a problem; they now have MG1 turning @10Krpm. In fact if they decided now on a liquid cooled motorcycle engine there is wiggle room on the PSD to have its ratio changed to suit.

    You make a point of the rpm being inversely proportional to the swept volume in the cylinders i.e. a 1.0L needing to run three times faster than a 3.0L. 2100rpm v 700rpm.
    The waverunner engine produces 16.5Hp per 1000rpm.
    Remember the LTD needing 6.7Hp @50mph, so while cruising in that car @1000rpm this engine would still have 10Hp in reserve via the throttle.
    A two cylinder version of the waverunner in this car (8.2Hp/1000rpm) would be quite highly loaded with only 1.5Hp in reserve. Increasing engine speed to 2000 rpm would restore a 10Hp reserve.

    If we go back to the real world, 2000rpm is just abit more than twice the minimum speed of the 3.0L VVTi 1MZ-FE engine, mine idles around 750 I can tell you.
    It has a capability of 36Hp/1000rpm assuming constant torque, giving 27Hp at idle.

    My conclusion is that most of the time this 0.5L engine need run only just over twice as fast as a conventional V6. Not 6 times faster as you would have proposed might be expected. Not forgetting that it is the sole ability of the PSD via MG1 to change its ratio so rapidly that makes this system usable.
    They have to make the Prius lighter and less expensive, I believe this is one of the ways open to accomplish that.
    Other than that let us agree to disagree.

    robertsmx, your postings certainly raise some points, too many to address in one go.
    By the way NVH = ? please

    The recycling of power is important but I see no system having advantage over any other where electronic regeneration back to the main pack is concerned.

    One more thing.
    The efficiency of the prime mover is not the be-all of the system as you infer. The transmission is also key - and it pivots on which of the SHEV or Prius PSD methods can do this function in the most efficient way.
    The SHEV is basically a system biased towards using larger power electronics.
    The PSD is a system biased towards mechanics.

    I did a post on separation of losses, some weeks back, because SHEVs get dismissed with what I call "lazy explanations".

    But if you want a supreme example of what can happen when a group of mechanical engineers try their hand at electrical engineering.....

    Next time it will be "Shark week for Honda"

    I will be discussing the IMA with figures gleaned from Honda's own website, in answer to previous posts.
  • vietviet Member Posts: 847
    Hi Robertsmx,

    I have enjoyed very much your well-written messages on automobile engineering. I do learn something from you. You must have lot of automobile engineering experience.
  • toyolla2toyolla2 Member Posts: 158
    Since this board has more to do with physics and electrical/engineering I hope no one who owns a hybrid will get upset with statements written here in good faith. It may be a truism that the effect of advertising is not merely to attract new buyers but to affirm to new owners that they made the right choice.
    To those I say, knowledge and experience are something you gain just after you needed them.
    To ruffle feathers is not my intent any more than writing here is part of a popularity contest.

    The Honda IMA is a motor affixed to the engine crankshaft. A 3-phase controller and a 144v NiMnH battery complete the system.

    Figures in bold are from Honda's website for the Honda Civic Hybrid.

    It's been written, ad nauseum, that the IMA's sole purpose is to reclaim kinetic energy normally lost by mechanical braking, the IMA becomes a generator and supplies current to the 144v battery, it therefore becomes a load on the shaft and slows the vehicle down. The slight brake pedal travel is detected as gentle braking so the system works on the IMA first , later more aggressive use of the brake pedal will engage the mechanical system.
    On acceleration the IMA becomes a motor and draws current from the 144v battery. This happens as long as the ICE revs are kept low. Aggressive acceleration keeps the revs high and the IMA may not be able "to motor". Honda's figures tell this story, they don't hide this fact, but no-one to my knowledge has ever interpreted this data in a forum anywhere. To most people this stuff is as unintelligible as a Mutual Fund prospectus anyway.

    The IMA is rated at 10kw and Honda further says their motor produces 361000RPM but this is only represents 5.1 KW when you do the math. Assuming the torque remains constant, by extrapolation we can probably expect the full 10kw @ 2000rpm.

    So torque 361000rpm
    increases to 36+87 lbs-ft @ 2000 rpm
    with the engine now pulling at full torque.

    We can expect that the IMA torque component, assuming constant 10kw Power, will decay inversely to speed. Right ? Sorry, Wrong. Torque roll-off is much more severe than that.

    See the figures from the Honda website, I noticed from their figures that at 3000rpm the IMA provided only 18lbs-ft of torque?
    But by the inverse law for constant horsepower shouldn't 36 lbs-ft @ 2000rpm
    become 24lbs-ft @3000rpm. What's with this?
    My calculator shows 18lbs-ft @3000rpm to be only 7.67kw. Where did the 10KW and 24lbs-ft, you would have expected, go to? And where will the torque be approaching 6000rpm? Try 3-4 lbs-ft.

    Well the problem is with the inverter being limited to 144v battery voltage. The first thing you have to be aware of is that the frequency of the applied voltage must always match the speed of the motor. This applied voltage produces a rotating magnetic field around the stator of the machine and must be in synchronism with the powerful magnets attached to the rotor. This is fairly easy to achieve with a crankshaft encoder feeding positional data to the electronic controller.

    But here are the problems. The stator winding producing this magnetic field has inductance. Inductance opposes changes in current. To make the motor rotate faster, higher frequencies have to be applied. The inductance produces even more opposition to this faster changing current. The net effect is that the controller finds increasing difficulty getting current into the motor. Torque drops.

    And there is another effect that is even more insidious. The magnets on the rotor produce a strong static magnetic field. When the rotor starts rotating this field similarly rotates with the rotor. The field passes through the stator winding and generates what's known as a back-emf.
    You want back-emf because that value multiplied by the current is a measure of motor power at that instant.
    This voltage increases with rotational speed until it reaches the battery voltage at which point it will be impossible to inject current into the motor. Torque will drop to zero.

    I predict this starts happening after the motor passes through 3000rpm at which point unless it it is disconnected the motor will behave as a generator and start charging the battery whether it needs to be charged or not.

    Of course the designers bank on you not being able to tell when this torque drop is happening. Neither do designers hang out in the advertising offices. So misleading sales information that adds the IMA power to the engine power sounds reasonable but is pure hype. Sales will need a greater MSRP for a hybrid, why not let the customers think they are getting a slightly more powerful system in the horsepower department.
    A case can be made that engine production spreads of +/- 5Hp at the top end are quite acceptable. This variation swamps the IMA power anyway so who cares.

    That doesn't change the fact that at the low end the extra 36lbs-ft helps extend the useful torque band down to 1000rpm so you may be able to hold 2nd gear from 10 to 50mph and achieve respectable acceleration.

    Of course for long road trips the IMA does nothing for mpg compared to what a tall gear in a non hybrid Civic could be doing.

    As I stated in a previous post for the HCH I think they should have set the IMA base speed for 1000rpm and picked up 72ft-lbs instead of the 36ft-lbs. I notice in the HAH they are using an 850 rpm 15Hp IMA. The Accord is not significantly heavier than the Civic so the reclaim energy is going to be roughly the same.
    The system components will therefore be similar too.
    I rest my case.

    Despite all this I can't help but say that winding electrical machines for low base speeds to improve the torque bandwidth of the gasoline engine is a misapplication of electrotechnology in automobiles. GM's EV1 had no problem regenerating to a stop with the same motor that would take it to 60 mph in a little over 8 seconds.
  • electrictroyelectrictroy Member Posts: 564
    "Of course the designers bank on you not being able to tell when this torque drop is happening. So misleading sales information that adds the IMA power to the engine power sounds reasonable but is pure hype."


    They didn't hide anything. The Insight brochures include this graph, which *clearly* shows the actual engine+motor horsepower & the fall-off in motor torque at 2000 rpm:

    (Please Note: The Prius' electric motor does the same torque falloff at 2400 rpm.)
  • xcelxcel Member Posts: 1,025
    Hi Toyolla2:

    Although I use IMA’s capabilities very sparingly, one item that you have not brought to light is that IMA acts as a quasi-balance shaft for the 3-cylinder ICE’s in all Insight’s.

    In terms of FE, IMA starts from a straight or forced Auto-stop is a force multiplier that a non-IMA equipped Honda lacks. There will always be traffic conditions not conducive to high FE that a non-IMA equipped Civic/Accord will not be able to take advantage of. The Honda hybrid’s on the other hand can achieve spectacular results even under the worst traffic conditions because of IMA. That is if the traffic conditions are handled properly with the IMA equipped Honda.

    Good Luck

    Wayne R. Gerdes
This discussion has been closed.