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First time eDrive and xDrive tech has been combined in one vehicle

BMW has unveiled the Concept X5 eDrive, which will be showcased at the New York International Auto Show. Although the vehicle is labeled as a concept, it’s a dead ringer for the production plug-in hybrid version of BMW’s popular crossover that it plans to bring to market sometime within the next year or two.
 
The hybrid drive system gets its primary motivation from a 245hp turbocharged 4-cylinder engine. That gas engine is combined with a 95hp/184 lb-ft electric motor developed by the BMW Group. Power for the electric motor comes from a lithium-ion battery pack (which is mounted under the cargo area) that can charge from any wall outlet.
 
The Concept X5 eDrive can drive on electricity alone for up to 20 miles at speeds up to 75 mph. BMW says that the car will have an average fuel consumption of over 74.3 mpg in the EU testing cycle (which means we’ll likely see less than half of that quoted figure under EPA guidelines). BMW says that the X5 concept can reach 62mph in under 7-seconds.

 
The Concept X5 eDrive is the first from BMW that uses its xDrive all-wheel-drive system paired with eDrive hybrid technology.
 
The concept also has a ConnectedDrive system that helps plan routes and lists the location of charging stations on the GPS map. This allows the driver to find a charging station when they are around town in electric mode.

Source: BMW



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RE: Tesla!
By snhoj on 4/14/2014 11:08:09 PM , Rating: 2
quote:
REALLY? So the fact that electric motors' torque declines sharply as RPM increases is better than a gas engine, whose torque curve remains relatively flat as RPM increases, only to decrease gradually near the redline.

Actually no. During the current limiting phase of the electric motor acceleration (zero RPM to peak power) the electric motor will produce pretty much constant torque due to constant current. When the motor reaches peak power it goes into the voltage limited phase where the back EMF of the motor limits the current and available torque goes into gradual decline. Current limits and battery voltage are not set in stone but are chosen by design for reasons like extending battery life.

ICE's have zero torque available at zero RPM and therefore must idle. To get a car moving some slippage has to occur either by clutch or torque converter. An ICE's torque curve is far from flat anywhere in the RPM range.

From a design perspective constant torque is a nice thing to have. A constant torque at the driven wheels divided by the (constant) rolling radius of the wheels will produce a constant driving force pushing the car forward.


RE: Tesla!
By EricMartello on 4/15/2014 5:35:04 PM , Rating: 2
quote:
Actually no. During the current limiting phase of the electric motor acceleration (zero RPM to peak power) the electric motor will produce pretty much constant torque due to constant current. When the motor reaches peak power it goes into the voltage limited phase where the back EMF of the motor limits the current and available torque goes into gradual decline.


You say no, and then basically say what I just said followed by something you paraphrased from wikipedia in an attempt to seem smart but likely don't understand.

Back EMF does not limit current, it represents an increase in voltage that will rise until it matches the input voltage.

Voltage determines the speed of the engine; the current drawn will rise if a load is placed on the motor (which causes a drop in voltage). Current itself is limited by system wiring and the motor's windings, and exceeding this current would cause the motor and/or wiring to overheat.

Will be funny to see what happens if a tesla motor stalls while stuck at "full throttle". It will basically weld itself into a clump of molten metal in seconds.

quote:
Current limits and battery voltage are not set in stone but are chosen by design for reasons like extending battery life.


Current limits are more-less set in stone, as there is a limit to how much current can flow over a given gauge of wire before the wire heats up like a light bulb filament.

This limit also applies to the motor windings, and thus there is a practical limit as to how thick of a wire you can use for windings while still making the motor small enough and light enough for a certain application.

Increasing voltage may increase speed but the power of the motor will never exceed the maximum watts available from the batteries.

So it doesn't matter if you do 250 volts and 40 amps or 500 volts and 20 amps - in both instances the motor will never be able to produce more than 10 kW of power.

The Model S top version is rated at 416 HP (310 kW) and has 85 kW batteries that operate at 400V. To produce its peak rated power with 400 V, the batteries need to supply at least 775 amps to the inverter.

Since the motor is a 3-phase AC, they type often used in industrial applications like saws, pumps and large fans, it requires an inverter to change the direct current supplied by the batteries into 3-phase alternating current.

At full power, the batteries would last roughly 15 minutes before being fully depleted. There is a reason that peak numbers are played up, but the range of the vehicle is listed at (55 MPH), meaning that there will be substantial deviations from advertised miles based on driving conditions and style...and if you buy a car for its power, you'll want to use that power. With the Tesla, you could easily find yourself out of batteries after doing a few 0-60 sprints "for fun" at full throttle.

quote:
ICE's have zero torque available at zero RPM and therefore must idle. To get a car moving some slippage has to occur either by clutch or torque converter. An ICE's torque curve is far from flat anywhere in the RPM range.


Torque converter are viscous couplings and do not "slip". They do have a stall speed, which is the engine speed required before the torque converter spins the driveshaft. There is a lot of flexibility in what the manufacturer can select as the stall speed to optimize it for the particular engine.

Torque converters also have a property called "torque multiplication", which boosts the input torque by a certain amount when the converter is at its stall speed. If you have a fairly common 2:1 torque multiplication factor, an engine producing 200 ft-lbs of torque at the converter's stall speed (with the car not moving) will transmit 400 ft-lbs of force down the drive shaft. This phenomena lasts several seconds after the car starts moving.

ICE engines' produce a torque curve that rises with engine RPM does so fairly linearly.


RE: Tesla!
By Mint on 4/15/2014 7:29:53 PM , Rating: 2
quote:
Back EMF does not limit current, it represents an increase in voltage that will rise until it matches the input voltage.
I don't know if it was true that he was just quoting wikipedia, but back EMF does indirectly limit current. You are correct about the current limit due to wire heating, but that's at low RPM. At higher RPM, there's a power limit due to battery/electronics/cooling, so V*I*pf is roughly constant, and voltage goes up while current (and torque) goes down with RPM. At even higher RPM, you hit a voltage limit from wire insulation and/or IGBT limits. So now you can't keep V*I constant, and ever increasing back-EMF with RPM limits current even faster.

quote:
With the Tesla, you could easily find yourself out of batteries after doing a few 0-60 sprints "for fun" at full throttle.
If by "a few" you mean "hundreds", then sure.
https://www.youtube.com/watch?v=d82NP89O_ZQ

0-114mph sprint, and cruising back to zero. 1 mile travelled, 0.5kWh used. So even with a leadfoot, you can cover 150+ miles on a charge.

quote:
Torque converter are viscous couplings and do not "slip".
"Slip" is defined as the difference in rotation speed between input and output. Yes, viscous couplings have non-zero slip.


RE: Tesla!
By EricMartello on 4/15/2014 10:03:05 PM , Rating: 2
quote:
I don't know if it was true that he was just quoting wikipedia, but back EMF does indirectly limit current. You are correct about the current limit due to wire heating, but that's at low RPM. At higher RPM, there's a power limit due to battery/electronics/cooling, so V*I*pf is roughly constant, and voltage goes up while current (and torque) goes down with RPM. At even higher RPM, you hit a voltage limit from wire insulation and/or IGBT limits. So now you can't keep V*I constant, and ever increasing back-EMF with RPM limits current even faster.


Back EMF happens because all electric motors are also generators. If you turn an electric motor by hand and connect a voltmeter to the power terminals, you will see that you are generating a voltage.

When power is applied to turn the motor, it is applied at a certain voltage. The motor will accelerate and spin to the RPM at which the voltage generated from back EMF matches the input voltage. If you are driving the motor with 400V, then the maximum no-load RPM will be achieved when the motor is producing 400V of back EMF.

This has nothing to do with wire insulation; it's a property of all electric motors.

quote:
If by "a few" you mean "hundreds", then sure.

0-114mph sprint, and cruising back to zero. 1 mile travelled, 0.5kWh used. So even with a leadfoot, you can cover 150+ miles on a charge.


You find one youtube video that doesn't even show the car being driven and believe it. That's nice.

The fact of the matter is, that each time the batteries are discharged at such a high rate their effective capacity diminishes - yes, they hold less of a charge. Even with regenerative braking you'll be losing range and perhaps permanently damaging the batteries themselves.

BTW good luck recharging your batteries if you happen to drive beyond the range and do not have enough charge to get back home. Even with the "supercharger" stations (fastest) take 20-30 minutes for a partial charge. Meanwhile it takes like 2 minutes to fill a tank with gas, and then drive 400-500 miles.

quote:
"Slip" is defined as the difference in rotation speed between input and output. Yes, viscous couplings have non-zero slip.


Modern torque converters do not slip; they have a lock-up feature which causes the connection between the driveshaft and transmission to act as if it were mechanically coupled, similar to the clutch plates in a manual transmission. Sorry, but electric drivetrains have no advantage here.


RE: Tesla!
By snhoj on 4/15/2014 9:47:22 PM , Rating: 2
quote:
You say no, and then basically say what I just said followed by something you paraphrased from wikipedia in an attempt to seem smart but likely don't understand.


I'm not paraphrasing anybody!! Because your statement implieded that torque drops off (sharply) from zero RPM I stand by my disagreement with that.

quote:
Voltage determines the speed of the engine; the current drawn will rise if a load is placed on the motor (which causes a drop in voltage). Current itself is limited by system wiring and the motor's windings, and exceeding this current would cause the motor and/or wiring to overheat.
Will be funny to see what happens if a Tesla motor stalls while stuck at "full throttle". It will basically weld itself into a clump of molten metal in seconds.


You might know the electrical theory but you don’t know how EV’s work. The motor controller will limit the current available to the motor. At low motor RPM it will chop the voltage to ensure that the current doesn’t exceed its preset limit. This is what I call the current limited phase. As the current available is the preset limit it is constant as is available torque. It’s the motor controller that limits the current not the load. Of course that is semantics as the load will increase to match the current i.e. the car will accelerate there by loading up the motor. As the motor crosses peak power (maximum voltage, maximum current) the back EMF generated by the motor is sufficient to prevent the current from exceeding the preset limit of the controller.

If the Tesla was floored while resting against an immovable object the motor controller would limit the current flow and protect the motor just as it would even if the car wasn’t stalled.


RE: Tesla!
By EricMartello on 4/16/2014 4:34:10 PM , Rating: 2
quote:
I'm not paraphrasing anybody!! Because your statement implieded that torque drops off (sharply) from zero RPM I stand by my disagreement with that.


It does, and it must, as power is a derived value that's calculated from torque x RPM.

The point is that electric motors' having full torque from 0 RPM is not an advantage over the gas engine. Sure, it makes the car "feel" fast but the performance figures tell the full story, and they're not exactly shattering any records.

quote:
You might know the electrical theory but you don’t know how EV’s work. The motor controller will limit the current available to the motor. At low motor RPM it will chop the voltage to ensure that the current doesn’t exceed its preset limit. This is what I call the current limited phase. As the current available is the preset limit it is constant as is available torque. It’s the motor controller that limits the current not the load. Of course that is semantics as the load will increase to match the current i.e. the car will accelerate there by loading up the motor. As the motor crosses peak power (maximum voltage, maximum current) the back EMF generated by the motor is sufficient to prevent the current from exceeding the preset limit of the controller.


Current itself is not what drives the motor, it is VOLTAGE that makes things move. Voltage must be high enough to overcome the resistance of the system, and when a load is placed on the motor, resistance increases and voltage drops. To maintain a speed at a given voltage, more current is drawn by the motor.

The tesla uses an inverter to drive the motor. The inverter not only increases the battery voltage, but it generates 3 sine waves to provide 3-phase power to the motor. It controls the speed of the motor by varying the voltage and maintaining the flow of current required to sustain a given voltage level.

I do not know the specific operation current of tesla's drive unit, but I would estimate that it can sustain somewhere in the ballpark of 1,000 amps across its operating voltage range.


RE: Tesla!
By snhoj on 4/16/2014 9:09:14 PM , Rating: 2
quote:
The point is that electric motors' having full torque from 0 RPM is not an advantage over the gas engine. Sure, it makes the car "feel" fast but the performance figures tell the full story, and they're not exactly shattering any records.

The advantage is not having to have a clutch or some other device to engage the drive. It’s a mechanical simplification. In the case of Tesla the range of the motor is so broad that it also doesn’t need a gearbox and can make do with a single reduction ratio. A further mechanical simplification. This is of course a design compromise as motor redline limits top speed. A second ratio would allow a much higher top speed. I personally think 125 MPH is more than enough for a road car.
quote:
Current itself is not what drives the motor, it is VOLTAGE that makes things move. Voltage must be high enough to overcome the resistance of the system, and when a load is placed on the motor, resistance increases and voltage drops. To maintain a speed at a given voltage, more current is drawn by the motor.

In an EV we don't want to control the speed of the motor but the torque it puts out. If the accelerator position controlled speed the vehicle would be very difficult to drive. Hence the motor controller manipulates the current by manipulating the voltage but the voltage doesn't bear any direct relationship to the accelerator position. None of this is in disagreement with what you have said I’m just trying to add a different perspective. As for load when you encounter a hill the driver must adjust the accelerator pedal to maintain speed (as you currently do in your ICE powered car) increasing the current to maintain the voltage.


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