How come A/C compressors aren't driven by electric motors?

C13C13 Member Posts: 390
edited April 2014 in Mazda
Seems like you ought to be able to get enough power to drive the pump, and you wouldn't lose any power or drivability when the AC's on.

Would add alittle weight though.

Waddya think?


  • newcar31newcar31 Member Posts: 3,711
    You would still lose power with the AC if it was electronic motor driven, it would be working the alternator harder then. ANY power accessory is going to drain power via the alternator. How much power? Who knows?
  • andre1969andre1969 Member Posts: 24,876
    Considering how much air conditioner technology has improved over the years, I'm surprised that it's not feasible yet.

    My guess is that, for one, you'd need a larger alternator to generate the power, which is going to put more strain on the engine at all times, not just when the A/C is running. Or maybe you could get around it somehow by using a couple of deep cycle batteries that would take longer to deplete, but that would add weight.

    Or maybe A/C technology has improved enough that it's just not feasible to go with an electric one. I read somewhere awhile back that air conditioning adds about 150-175 lb to the weight of an average car, but maybe it's less nowadays.

    On another note, does anybody know how much the air conditioner belt and pulleys saps the power of a car when the A/C is turned off? After all, the A/C compressor's not running, but the belt and pulleys are. Maybe it'd be worthwhile to make a system that could totally disengage the belt from the crankshaft pulley, so it's not sapping any power at all. Y'know, kind of like the pulley that engages and disengages the blade deck on a riding lawn mower.

    I'd like to hear some thoughts on the more auto-educated out there!
  • 0patience0patience Oregon CoastMember Posts: 1,712
    The electric motor that would be required to run the AC efficiently would be farily large and have a draw in the neighborhood of at least 50 amps. That is pretty taxing on the charging system.
    Then they would have to figure out where to put it, since that size of motor would also create some pretty good heat, it would have to be somewhere that there is a fair amount of air flow.
    When the new higher voltage vehicles come out, we may see it yet.
  • swschradswschrad Member Posts: 2,171
    the figure I've seen around the years is that a/c takes 14-20 HP to run the compressor. you notice on a hot, humid, tropical day the engine chugs at idle under the compressor load? it's pushing against more resistance and loading the engine down more.

    the first law of thermodynamics is that there is no free lunch... every time you change energy forms, you lose some. the engine turns chemical energy into rotational force, and is maybe 10 percent efficient. the a/c compressor turns rotation into pressure, and loses energy.

    now, if the engine turned the alternator for 20 more HP, and you lose 90% of your input energy in generating electricity according to the steam power plant surveys quoted by the power companies, you are wasting 90 percent of 10 percent of applied energy. electric motors are supposedly 15-20% efficient once you get up into the big devils that power elevators and worse, and are much more inefficient in smaller sizes. a 20 HP electric motor is the size and weight of a big-block, all-iron car engine. you couple that to the a/c compressor, and how much power is left?

    plus you taxed the engine even more by adding half again the weight of your car for the electric motor, and have cut the airflow seriously by doubling-plus the engine compartment.

    we now have Yugo performance with a V-10 engine that gets 3 miles to the gallon when the a/c is on, and 3-1/2 mpg when it is off, and it takes two parking spaces.

    the physics condemns the idea.

    if you have a smaller passenger compartment, or a much more efficient refrigerant, or both, you can improve the odds slightly.

    rough numbers, but there's the facts... the more energy conversions you have, the worse off you are.

    oh, forgot something... starter motors for the diesels can run up to 40 amps. if you crank 'em for over a minute, they overheat and short out the coils. I'm talking about equipment built to last on your long drive to Gramma's house, not for short peak period use.
  • haspelbeinhaspelbein Member Posts: 227
    Swscrad is right on the spot, however one can put it in fewer words.

    Basically, right off the drive belt you get the kinetic energy to drive the compressor. No need to convert to electric energy and back, taking a loss at each conversion.
  • 0patience0patience Oregon CoastMember Posts: 1,712
    your hypothesis is incorrect.

    Well, those 20hp figures aren't very accurate.
    While there is no denying that it would require a healthy sized motor, especially being a DC motor, but if what your saying is true, then it would require at least 20 hp to run a household AC unit or an air compressor, yet in some instances, a 3 hp motor works just fine for them and at lengths of time.

    the engine turns chemical energy into rotational force, and is maybe 10 percent efficient.

    Uh, since when??
    If the engines were only 10% efficient, DEQ and EPA would have an absolute fit.
    Granted, they are much more than 40%, but that is quite a bit more than 10%.

    a 20 HP electric motor is the size and weight of a big-block, all-iron car engine.
    Sorry, but that isn't entirely true either.
    The 24 volt DC motors we run on trailor units for hydraulic units that are 10-20hp are a whole lot smaller than an engine.

    The last few years, the efficiencies of the AC units has jumped considerably (had to with the advent of R138).
    With alot of newer electric hybrid vehicles being made, using electrics to operate accesory drives, such as the AC are being looked at more and more.

    Now, these aren't any hard numbers or facts, just real world experience.
  • C13C13 Member Posts: 390
    Much appreciated.

    What do you think about harnessing wind power to cool the interior? That's the way they used to do it.

    Just kidding.
  • haspelbeinhaspelbein Member Posts: 227
    I have to admit that I hadn't thought about electric or hybrid vehicles. It would make sense there because you actually start with electric energy to begin with.
    No matter what the efficiency is for combustion engines, you'd end up with a loss going to electric energy first.
  • tboner1965tboner1965 Member Posts: 647
    ...I buy the fact that it is more efficient to drive the A/C compressor off the crankshaft as you have fewer types of energy conversions.

    Ok, then why do modern freight train engines use a diesel engine or gas turbine to drive a generator, then use electric motors to drive the wheels?


  • 0patience0patience Oregon CoastMember Posts: 1,712
    2 main reasons,
    1st is that the electric motors can provide more power.
    Now, someone can argue that, but we have large machines that lift log loads off of log trucks, they run a diesel engine for the electrics and everything is 480v electric. I talked to one of the engineers of the machines and he said they tried to rung a drivetrain on a few of them, but with a 40 ton load on them, they hardly move.

    2nd reason, you don't have to have a drivertrain from the engine to the drive.
    The electric motors can be placed in any position, as long as you can get the wiring to them.
  • haspelbeinhaspelbein Member Posts: 227
    0patience was too fast for me...but the lack of a drivetrain and the engine placement are key. You want to drive as many wheels as possible. With electric engines you can sometimes place them right in the wheel carriage or right above the wheel carriage.

    When saying that an electric engine provides more power (relative to its size), it is interesting to see pure electric train engines on electrified tracks. They are much smaller, but are far more powerful.

    Also, electric engines provide a relatively flat torque-curve and have torque at the very low end of their rpm range, which is key when actually trying to get a train into motion. The stress on a clutch for a diesel engine/drivetrain application would also be enormous.
  • hengheng Member Posts: 411
    But let me add:

    With the electric traction motors, you get torque with 0 rpm

    You can run the diesels at a nearly constant rpm (peak power mode) which means the size and weight of the diesels are minimized

    You don't need a transmission
  • 79377937 Member Posts: 390
    My 2c worth on electric motors for car aircons. You may be surprised to know that they are just around the corner! The aircon systems will be sealed units just like the ones in your home. The motors will be driven by alternating current as opposed to direct current motors.

    But first, the battery systems on automobiles will be a much higher voltage. Something in the region of 48 volts as opposed to 12 volts. All motors used on cars will be driven by alternating current obtained from an invertor which will convert the 48 volts direct current to a higher alternating voltage. This allows for motors of lower amperage and higher efficiency. Losses are lower because less current is drawn. That means voltage drop across the wiring is lower. The old 6 volt systems were very inefficient.

    Because the aircon will be driven by an electric motor it will be possible to mount the unit in a more convenient position. Also, being a sealed unit, the refrigerant should be less likely to leak out. Some domestic refrigerators run for 30 years without losing any refrigerant. The major source of leaks on car aircons at the moment is where the drive shaft passes into the compressor. The seals more often than not leak.
  • haspelbeinhaspelbein Member Posts: 227
    Interesting concept. I didn't realize that the refrigerant leakage was still such a problem. I never had to replace my refrigerant except on my old beaters.

    If I read your post correctly, you're saying that we'll start with a 48V battery, chop the DC to AC in the inverter and have 48V electric applications throughout the vehicle ?
  • 79377937 Member Posts: 390
    The invertor can boost the alternating voltage up to any voltage so that 120 volts for a motor is quite feasable in a motorcar. The higher the voltage the less current will be drawn for a given wattage. The whole system becomes more effecient. If we take the blower motor for example and use an alternating current motor with a thyristor speed control, we do away with power wasting dropping resistors for speed control as in a direct current motor. Even if future cars do away with the internal combustion engine and use fuel cells for example, the same alternating current methods will be used in order to conserve energy. The drive motors will also be alternating current types.
  • haspelbeinhaspelbein Member Posts: 227
    ...the methods you've described you be advantageous especially if you go away from the combustion engine.

    I do realize that an A/C electric motor is much simpler to build, more efficient and more reliable. I also realize that resistance (or impedance as we're talking A/C here) in wiring is reduced as we increase voltage.

    My concern would only be the complexity of having different voltage levels in the vehicle as most electronics do require DC.

    I'm also not 100% sold on the electric A/C compressor in combustion engines yet. But then, if we move to hybrid or fuel cell based vehicles soon, that might not be an issue at all.
  • 79377937 Member Posts: 390
    Well, if we look at a computer we realize that many voltages are used in them and they seem to work ok (sometimes). I don't think that is a big problem. Let's take a waterpump in a car now.. Drive it with an alternating current motor and mount it in a convenient place under the hood. Couple its electronic speed control to the cars computer. When the engine is cold, the pump does not run. As the engine heats up the motor starts to turn and pumps coolant. Depending on the engine temperature the pump will pump more or less coolant. No more troublesome thermostats needed. Also, if the car idles in traffic with a conventional pump the coolant flow is low and the engine heats up and can boil.. The electric driven water pump will start to pump when needed.

    Many systems in a car will will be more efficient. The lighting system can also be high voltage and run off the same voltage as the motors. Even if the starter motor is still left a direct current type, running it off 48 volts direct current from the battery will still be more effecient. Remember those old 6 volt starter motors?
  • haspelbeinhaspelbein Member Posts: 227
    ... to remember 6 volt starter motors. One friend of mine still had a car with a 6 volt system, but I never really checked it out back then. But I do take your word for it.

    Ironically, I drive a car with two waterpumps, one is electric and the other one is driven by a serpentine belt off the crankshaft. The car also uses a viscosity clutch for one radiator fan in addition to two smaller electric ones. The combination does indeed provide very good cooling during engine idle.

    The thermostat is actually still needed because you might want to divide the coolant flow differently depending on the operating conditions. (The heater circuit opens before the radiator circuit in cold weather.)

    I see your analogy with the computer, but most electric/electronic components (and the wiring in particular) are far less accessible. From my personal experience it is the electronics that often provide the greatest challenge to automotive mechanics.

    What I'm mostly afraid of is a push towards a proprietary standard. One might compare it to early fuel injected engines that were very proprietary. It took a while until a standard was developed.
  • 79377937 Member Posts: 390
    I'm sure a standard will be developed as to voltages used etc etc. We can't have everybody making their own voltage headlights for example. A simple way of making things easily repairable is to use plug-in electronic modules. Industrial electronic devices use modules because qualified people are not always available for complicated repairs. My take on the internal combustion engine is that it will be around for many more years. What will happen is that the 50 mile per gallon car will become the standard. To achieve that, drastic redesign of existing engines will have to be done.
  • swschradswschrad Member Posts: 2,171
    it seems a foregone conclusion that we will have "high voltage" DC systems in cars in a few years... and it is always easier to find space for the same power electric motor if it is run off a higher voltage, because that means current is lower, and the wire is smaller in diameter. all the tricks will have to be pulled out to get the 50-mpg car... high RPMs, aluminum alloys, unibody, maybe composite compounds instead of metals in frames and bodies... because you also have to cut the weight along with cutting the power in order to get acceptable performance. if they also put IR-blocking glass in the vehicle to reduce the greenhouse effect on the passengers, that will lower a/c load as well. I just wonder what kind of heaters these vehicles will have... up here in Minnesota, the heater is more important than the a/c, as you can always use the R265 system.. Roll down 2 and do 65 ;)
  • 0patience0patience Oregon CoastMember Posts: 1,712
    And are probably going to be seriously looked at in the next 5 years.
    Because of all of the electronics in vehicels to day, add to that, the power window, power seats, power this and that and it is seriously putting a strain on the electrical system.
  • spokanespokane Member Posts: 514
    This is a most interesting topic. The August 2000 issue of Popular Mechanics reported:

    "42-volt automotive electrical systems are soon to replace the existing 14-volt charging systems. Car makers can power electric steering, shifting, suspension and braking, etc. Electromagnetic valve actuators will replace the camshaft ... belt drives will disappear. The starter/alternator will be flywheel mounted. The water pump, PS, A/C compressor will be electrically powered and operated on demand only, saving power and fuel otherwise lost to belt drives. All car makers have agreed to 42 volts and the first systems will appear in next year in Europe."

    I am doubtful that the solenoid-actuated valves or all-electric brakes will be developed very soon but the electric power steering development is well under way by TRW. If inverters are used as you guys indicate, then sealed (and "submerged") induction motors can be used for the A/C compressor and water pump. This should allow the refrigeration circuitry of the A/C system to be optimized for greater efficiency but, at this point, don't you agree that it's doubtful the refrigeration improvements will offset the losses associated with the two energy conversions (mech/elec and then elec/mech) any voltage?

    Can you imagine an engine compartment with no drive belts ..each item driven by an electric motor located at the point of use?
  • 79377937 Member Posts: 390
    Invertors have become very effecient. The new type of switching transistors used in them have zero "contact resistence" when switched on. The mechanical losses of drive belts, bearing friction etc. are greater than present day electrical conversion systems. Electrical conversion systems promise to become even more effecient. You are right Opatience about the voltage being 42 volts. I was just giving a nominal voltage in my example.
  • haspelbeinhaspelbein Member Posts: 227
    I have no doubt that the inverter itself is very efficient. However, there is a loss associated with the power generation and at the electrical motor itself. (energy conversion)
    And I think that this is what most people on the board are talking about.
    Unfortunately, I don't have any good data on how much more efficient a more compact (electric) A/C unit would be, and if it would be enough to offset the initial energy loss in a combustion engine.

    I also don't think that we'll see a 100% electric braking system. I'm pretty sure we'll have an electronic brake linkage (like in the upcoming E-Class) in most vehicles in the near future, as it great simplifies ABS and electronic stability systems. But the hydraulic system still offers the great advantage of adding very little unsprung weight to the suspension.

    I'm further pretty sure that belt drives won't disappear completely. While they aren't the most reliable way of transferring mechanical energy, there is hardly anything more efficient.
    I'm pretty positive they're around to stay for applications as fan belts or alternator belts.
  • 79377937 Member Posts: 390
    Well. in the 1950's I had a German NSU scooter with a starter and it was combined with the generator and whole thing was mounted on the flywheel. When you started it, the generator would motorize and then start to generate electricity once the engine had started. It must have been pretty effecient for its time. The same thing could be done on a car only in this case you would use an alternator/motor mounted on the flywheel. The old German DKW cars used a similar system.

    And don't forget regenerative electrical braking. That is, if the car is electric motor powered the motor can be used to brake the car and feed energy back into the system as it becomes a generator. In fact, with computer control the motors can come to a standstill and lock. If each wheel is driven by its own motor, the computer can brake each wheel independantly and prevent skids and loss of control. I believe the time will come when a hybrid car with an internal combustion engine will do just that. That is, drive 4 lightweight flat motors built into the hubs of the wheels.

    These ideas are as old as motor vehicles. It's just that we now have the technology to put these ideas into practice.
  • haspelbeinhaspelbein Member Posts: 227
    Is actually used in many trains. I know that the German high speed trains feed their internal battery for their auxiliary systems through generators.

    The problem however is weight and complexity. To brake a car safely in such a fashion you'd need to either have generators mounted in each wheel hub or drive shafts to a more centrally located generator.
    The first approach would impact the handling of the vehicle (increase in unsprung weight), the second makes it more tricky to brake each wheel independently.

    Why look as far back as the DKU ? The Honda Insight has a starter motor that acts as a generator for its batteries. (I'm not sure if the main batteries also drives the 12V systems in that vehicle.)
  • 79377937 Member Posts: 390
    As I have said, lightweight flat motors can be made. If you look at a record player that played the old records just before CD's came in, you had a direct drive motor that was very flat in (or thin). The same method of construction is used in the motors I am talking about. They are about 1 inch thick and about 10 inches in diameter. They use extremely strong permanent magnets for the field. The rotor is made like a circular printed circuit board. Because of the diameter an extremely large torque can be had out of them. Now, if an opposing voltage is fed into them while they are turning, they become a brake. If sensors detect any movement while stopped at say a traffic light, a computer can feed correction voltages in and stop all movement. So here we are using the same motor for traction, for regenerative braking at speed and, finally, dead stop braking.

    I just mentioned the DKW car because they were using that type of starter back then already. Finally, If anybody had told me back in the 1950's when I was playing with gas powered model aeroplanes that an electric motor would be able to power a model plane one day, I would laughed at them. Electric motors have also come a long way and today you do get model planes that fly using batteries and electric motors.
  • spokanespokane Member Posts: 514
    Excellent points, haspelbein and 7937. I believe BMW is in the lead on the 42V system development. The fact that all major auto manufacturers have agreed to this new standard is an indication that some of these features are not too far in the future. As you say, 7937, these "thin" large-diameter motor-generators have surprisingly high power ratings. With the 42V system, this motor/generator will also serve as the starter; meaning that the separate starter motor, drive gear, overrunning clutch, and flywheel ring gear will be eliminated. Also, "cranking" the engine will be silent.

    I feel sure the overall vehicle energy efficiencies will ultimately improve as indicated in several above points. However, unless the inverter can be used to greatly increase refrigeration thermal efficiency by optimizing the compressor speed for the cooling load, I believe the overall A/C energy requirement will increase. Based on industrial drive data, power transmission efficiency of the existing belt drives is probably ~92%. For the electric drive (assuming 100% inverter efficiency to give the inverter benefit of any doubt) the mech-elec conversion efficiency of the generator will be ~88% and the subsequent elec-mech efficiency of the compressor motor will also be about 88%. The product of the two figures indicates efficiency in the range of 75% to 80% to the compressor. This is the power-conversion efficiency range that must be compared with the above ~92%. If anyone has more accurate 42V motor/generator efficiency data, I am certainly willing to "stand corrected".
  • 79377937 Member Posts: 390
    spokane, your figures seem right. However we never know what lies around the corner as far as developments go. Another source of energy that goes to waste in an internal combustion engine is the exhaust system heat. Now, what do we use for refrigeration in locations where there is no electrical power? Why, heat of course! We all know that refrigeration can be obtained by heating up a suitably arranged system of gas filled coiled up pipes.

    The only snag when using that in a car is the time lag involved in getting the system working from cold. However, if we use it as a back-up system for long trips, we only need to use a conventional system when staring up a cold engine. So, here we have a system of A/C that does not take any extra energy at all once it is up and running. No doubt that if the concept is followed through the A/C system can become a sort of hybrid system whereby elements of both systems are combined into one unit for economy of manufacture.
  • haspelbeinhaspelbein Member Posts: 227
    The A/C based on thermal gas expansion is possible, at least in theory. Refrigeration based on gas compression/expansion however is much more effective.

    Systems based on thermal gas expansion also need excellent ventilation to work, so you'd probably end up with another radiator system. Since it's based on differences in thermal energy, it would also work the least when the ambient temperature is the highest. I really don't think you wanna go there.
  • seaspyseaspy Member Posts: 6
    I have a 1995 maxima GLE ,103018 miles. recently I have had water leaking from the black box under glove compartment.It seems to occur when I sit at idle for extended period of time. I use this car for work I am in it 8 to 10 hrs a day and overall it has performed very well. no oil leaks or tranny problems. still has original timming belt. replaced the larger drive axle at 99k miles only because the boot was torn. Any one have a fix or a dianogistics for the A/C leak?
    thank you
  • 79377937 Member Posts: 390
    haspelbein, had you read my posting properly you would have seen that I did not say the one system must replace the other but rather, that they should compliment each other. I did after all talk about a hybrid system where the best of both would be combined. I can assure you - there are people working on such a concept........
  • haspelbeinhaspelbein Member Posts: 227
    please don't take me wrong, but wouldn't even take a hybrid system add quite some complexity for minimal savings ? Or to make the inverse statement: If I needed to add cost, weight and complexity to a vehicle in order to save fuel, such a hybrid A/C system wouldn't be on the top of my list.
  • 79377937 Member Posts: 390
    Such a system would certainly not be put onto the market if it were too complex and costly. So you have nothing to worry about there. The idea of such concepts, (energy conservation) is to squeeze as much gain out of them as possible and all avenues are always explored. A large amount of energy for refrigeration can be regained by simply wrapping a small pipe aroung the exhaust header and allowing it to heat up the refrigerant gas in the pipe. That would take load off the main compressor. Nothing complex or expensive about that! What might take more thought is how to combine the two systems of refrigeration into a hybrid system using only the main A/C components without adding more. My small camping refrigerator that use propane gas appears to be rather effecient as it certainly gets very cold with a small flame and the gas in the cylinder seems to last forever.
  • haspelbeinhaspelbein Member Posts: 227
    I would agree that the heater for such a system should be placed on the exhaust. However, the refrigerant would then have to be moved a much cooler spot (possibly a radiator) and a heat exchanger.
    I don't think you necessarily want to combine the two A/C systems. The conventional one works best when combined into a small unit to minimize heat losses.
    The thermal A/C needs to be stretched out to tap into different 'heat pools' to utilize the temperature gradient for refrigeration.

    This is also why a small camping refrigerator works well. It has a small (contained) heat source and a much cooler ambient temperature. The larger these units become the less efficient they get. (The problem is keeping the heat pools separated. This is mostly addressed through added ventilation, etc.)
  • 79377937 Member Posts: 390
    Well, the exhaust system is certainly much hotter than anywhere else (hundreds of degrees) and, also has a large surface area to tap into so that finding a big enough heat differential is not much of a problem. Anywhere else in the vehicle is much cooler than its exhaust system. The catalyctic convertor gets even hotter than the exhaust manifold. An enormous amount of energy gets wasted there.
  • haspelbeinhaspelbein Member Posts: 227
    Well, I think we can discuss to no end how well such a system would work. I think we both agree on how it would have to be implemented, but I'm not convinced that it would be awfully efficient.

    If you have your car retrofitted with this kind of A/C, I'll gladly pay you a visit in Belmont to find out for myself.
  • 79377937 Member Posts: 390
    We don't have to speak about effeciency in this case at all because we are using heat energy that is going to waste anyway. NOT to use it is a waste. Yeah well, I wont be using it in my present car.
  • mrdetailermrdetailer Member Posts: 1,118
    I just read in the paper this weekend that auto mileage could be significantly reduced if things like A/C and other accessories could be driven off of electric motors. Surprize.
  • spokanespokane Member Posts: 514
    The following is a 1999 speech given by William Powers, VP Research, Ford Motor Co. It includes an interesting perspective on the coming 42-Volt systems as well as some points on environmental issues that have been mentioned here.

  • hengheng Member Posts: 411
    Any engineering details of how they get around the conversion loss going from the rotating engine shaft through a generator and back to a rotating compressor?

    Please explain it.
  • spokanespokane Member Posts: 514
    Good question, heng. I have also watched for engineering numbers on the conversion loss comparison but haven't seen anything definitive. Do you suppose that optimization of the refrigeration system design for a constant-speed (inverter-driven) A/C system could provide some thermodynamic system improvement that would offset, or partly offset, the energy conversion losses associated with the new compressor drive?

    Although I have seen no such report, I would guess that one reason for considering the electric-drive compressor has to do with "packaging" in the engine compartment. If all belt-driven accessories can be electrically driven, less space is needed at that end of the engine. With transverse engines, lateral space is precious and the new flywheel-mounted generator/starter will need some room. I focus on the A/C system in this regard because it is surely the biggest challenge to convert to electric drive. Other thoughts?
  • 79377937 Member Posts: 390
    Not much extra space will be needed for the starter/alternator system because they will be of a "pancake" type. A thickness of one inch and thinner is quite feasable. The diameter will be the same as the present bell housings in which case a high amount of torque will be available.

    By having the A/C electric motor driven, the unit can be mounted quite remotely from the engine compartment. The engine compartment is the worst environment for the A/C system. If all belt driven accessories such as water pumps, power steering etc. are motor driven, design restraints as to engine layout are simplified. The pump for the power steering could be mounted on the steering rack for example. The water pump can also be moved to a more convenient position for engine designers. In fact, you could end up with more engine space.

    As to the efficiency of such an all electric system - the answer lies in the design of the motors. These will be of the alternating current type with variable frequency speed control. I myself have experimented with a standard 10 horsepower 3 phase electric motor using an off-the-shelf ac speed control unit that used variable frequency from zero Hz to 100Hz to control speed. I was impressed by the torque at all speed ranges. Start-up torque was impressive. Conversion losses by the speed control unit were minimal. This was about 25 years ago and my facts and figures for my experiments are not at hand at the moment. No doubt more effecient units are available today.
  • hengheng Member Posts: 411
    would offer some benefits in that it would be operating at peak efficiency. Maybe enough to offset the conversion loss.
  • 79377937 Member Posts: 390
    In talking about speed control I don't mean speed control of the A/C unit. That unit should always work at its optimum speed. I have tried to avoid as much as possible heavy technical jargon in my overview and that is all it is (the overview) in regards to this discussion.

    Briefly, what I imagine might happen in the future is this - the internal combustion engine will still be with us for many more years to come. But, the way energy is coupled to the drive wheels will undergo a radical change. Simply put, there will not be a mechanical transmission anymore. There are losses in a mechanical transmission. An electrical coupling has less. The internal combustion engine will drive an alternator. The output of the alternator will be rectified and converted to direct current. This will charge a 42 volt battery. The 42 volts in turn will be inverted to an alternating voltage which can then be any voltage the automaker chooses and will be much higher than 42 volts. It could be 120 volts ac for example. This is the voltage that can be used to drive all motors in the vehicle including the main drive motor or motors. Although the conversions seem many, just bear in mind what is happening in a conventional automatic transmission.

    In a conventional automatic we first have the torque convertor. A source of energy loss. In fact, if we follow through with all the energy wasting components in such a transmission we find out that a lot of the energy produced by the engine is lost in its journey to the drive wheels. The differential gears needed for turning corners can be eliminated by having a drive motor for each wheel. The computer can handle drive requirements as the vehicle turns.

    It is cheaper and easier to manufacture electric motors than what it is to produce automatic transmissions and differentials. Also, electric motors are easier to repair. This is a very brief overveiw.
  • jlflemmonsjlflemmons Member Posts: 2,242
    Industrial motors have used dynamic braking for years. A large resistance is dropped across the field windings, I believe, and the collapsing magnetic field slows the motor. Electric brakes are very common on large travel trailers. The friction pads are actuated by magnets which receive current from an electronic controller. While the brakes on a trailer can have either static or dynamic current feeds, it would be very simple to adapt the brake pedal of a car to the variable output of the controller. No more hydralics, power boosters, leaking wheel cylinders, etc. And you can determine if the brake on a wheel is getting the signal by placing a compass near the wheel and applying the brakes. The magnetic field will cause the compass to swing wildly.

  • spokanespokane Member Posts: 514
    You make an important point, 7937, that considerable engine space will be made available with the 42V system. There will be no starter motor as we know it, and the already-developed electric steering has the motor mounted on the steering rack. And, as you indicated, the A/C compressor probably will not be attached to the engine. Indeed, the additional space and component-location flexibility will be considerable .. perhaps enough to provide drivetrain engineers and even the body stylists considerable new latitude.

    I agree that inverter drives offer big benefits -- for example the A/C compressor speed could "ramp up" at starting over a period of 2-sec or so, thus making the start very smooth and quiet. However, I haven't seen any clear reporting from the industry that inverters are a part of the 42V plan. 7937, have you seen specifics on this?
  • tboner1965tboner1965 Member Posts: 647
    Most generators are AC. I believe even your alternator is AC, with an integral diode bridge (rectifier) that turns the AC into DC.

    So instead of an inverter, I believe a small portion of electricity will be converted to DC, while AC (naturally produced by a generator) could be used to drive the wheels, a/c compressor, etc.

    You would then have the engine run at a constant speed so the "Alternating" part of AC would be a consistent frequency.

    I wonder what sort of break in challenges that provides?

  • 79377937 Member Posts: 390
    The motors would be restricted to 42volt dc and would be direct current types if invertors were not used. By inverting the voltage to alternating current and increasing it, better control and efficiency is achieved. The higher the voltage, the lower the current for a given wattage. This allows motors to be wound with more turns with thinner wire for a given space. Also, the invertor will have a 3 phase output which makes motors even more efficient. The speed control for a 3 phase system is extremely good and full control of a motor can be achieved. Control can even be extended to braking the motor full stop and locking it.

    I myself am not involved in these developments but the company I work for supplies research equipment for laboratories which are involved in such research. I also meet researchers in the course of my duties and try and pry as much as my inquisitive self can out of these people. You must understand that a lot of the information is also (whisper) secret! I am deeply interested in power electronics and have always worked in such invironments.
  • 79377937 Member Posts: 390
    I saw your message after I posted mine. There is no need for the engine to run at a constant speed. That is what the 42volt battery is there for and that is why the invertor is driven by it. Even if the engine is switched off the battery will still power the invertor - until it runs down of course! During driving the engine speed is not determined by the driver but rather by the requirements of the battery. The accelerator pedal will be coupled to the motor speed control. Hope this answers your good question.
This discussion has been closed.