That is likely part of the mechanism that pops up the back edge of the hood in a pedestrian impact situation to try to minimize the injuries. (We don't get that feature in the US.)
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Investor Engineering Discussions
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navguy12
Active Member
Anyone can help me explain what the axes of this graph shows:
Impact I assume means force. Impacts sounds more like number of impacts. But I thought the colors were numbers. What are the colors? If something is around say x,y=1,1 what does this mean? Is it a 45deg impact? Help me be less confused.
Impact I assume means force. Impacts sounds more like number of impacts. But I thought the colors were numbers. What are the colors? If something is around say x,y=1,1 what does this mean? Is it a 45deg impact? Help me be less confused.
I think:
Dot location is impact direction and velocity
Red/green are crash frequency
Black dots are industry standard tests
I think the graph is a physical space ---
- horizontal - Right -> left
- vertical - Rear to front...
The colors might be the frequency of force impacts?
Colors are more intense in the middle of the car perhaps because the forces from more crashes pass though that space.?
Or green indicate a more intense crash for and red indicates a lesser dampened force...
I assume red can only be higher for frequency, not intensity....?
Unless red indicates that only high intensity crashes impact that area?
I m not sure I have helped, but I did try...
jabloomf1230
Minister of Silly Walks
I saw that on X also. The comments seem to explain the scatter plot better than I could. The black points represent regulatory tests. The red is the highest frequency, then yellow, green and white(none). The axes give the scatter plot direction.
Direction of what? Is it of where on the car the impact happens? Of the velocity of the car? Is it for the car, of the environment or relative to the other car? Left hand impact on the right side, why?
Lets say we take a point at ~[5, -1] where there are 3 black dots nere each other. We have a lefthand frontal impact, mostly lefthand. Are we to assume that we are driving slowly forward and get hit by a car from the right going 5x faster than us? Faster than the forward collisions that are tested? Why are impacts from the side tested at higher velocities from the side than from the front? Don't people drive slower in intersections than at highways?
Could it be that direction is where the car is hit and the radius is abs(relative velocity)?
I assume the impacts from the side (black dots, regulatory tests) have more force transferred to the passenger compartment because there is less crumple zone distance to mitigate the crash. The front has a large crumple zone, so the force at the passenger compartment is less for any given crash speed. So the graph is showing the force transferred to the passenger compartment. A correlation is the green zone represents damage to the vehicle only, and red indicates potential injury.
Frontal impact is down so right and left look flipped, but it's all just rotated 180.
They may gave different X and Y scales. The side impacts represent getting T-boned (in an intersection or elsewhere)
I think this section is head on crashes along with small and medium overlap.
If it were a resulting force, then the black dots would be vehicle specific though?
Artful Dodger
"Neko no me"
Interesting.
The man has slightly different take on the reasoning behind skin depth than the one I've been using for decades; however, most of what I've been doing in that regard has to do with radiation shielding and high frequency (100's of MHz) signals and up. In fact, one year, after getting my Master's degree, I was sort of casually waiting around and doing job interviews while the SO finished up her degree. Three or so profs knew about that situation, cornered me in my office one day out of the blue, and said, "How'd you like to teach a course in Microwaves this summer, for those looking to pick up three credits? We'll even pay you!"
Next thing you know I'm up on a podium in front of 150 undergraduates, wearing this nifty tee shirt I had found in Alexandria, VA, that had a large Smith Chart printed on it. We all made it through in one piece. Albeit, that was some 36 years ago, but, fun.
Thing is: When one is playing with electricity, there's this duality: Current moving through a wire forces a magnetic field circling the wire and, if one has a magnetic field circling a wire, that magnetic field forces electrons to flow within the wire. Two faces of the same coin, actually.
If the magnetic field circling the wire is a constant, then there's a constant current in the wire. Interestingly, at DC, this current is everywhere through the conductor. Now, think about resistance: A piece of copper has a resistivity (so do all metals, there's charts). To get the DC resistance of a wire, one takes the cross-sectional area, divides it into the resistivity, then multiplies that by the length of said wire. (R = (resistivity/cross-sectional-area)*length) And that's the DC resistance, measurable with ye random ohmmeter.
With AC magnetic fields, things are different. As the energy flows down the wire, the electrons in the wire accelerate, moving towards the positive E field and away from the negative E field; as they do that, they create an electromagnetic field going the other way. (Think, and I am not joking here, about mirrors.) As a result, if one had perfectly flowing electrons, the electromagnetic field impinging upon the wire would be cancelled by the fields generated by these electrons (weird, but true) - and there'd be current at the surface of the conductor, and none inside, since the EMF (including the magnetic field) would be cancelled inside. No magnetic field: No electron movement
. Whee.However, those electrons aren't free-flowing: Yeah, it's kinda like a gas of electrons in there (that's a defining bit about metals, they have an electron gas), but as the electrons go flying along, they bump into atoms and get slowed down (Hi, resistance!), making the atoms jostle around (hi, heat!). Since the electrons didn't accelerate all the way up, the generated counter-EMF doesn't completely cancel the incident EMF.. and the EMF goes farther in, making the next bunch of electrons accelerate (but, again, not all the way up) doing some more cancelling of the incident EMF, and so on. The EMF as one goes into the conductor (with an AC EMF) exponentially decays as one goes in; when the EMF is down by 1/e, that's the skin depth. Go in, say, 5 skin depths, and the current in the conductor is effectively zero.
So, say one is playing with bus bars at 60 Hz. Over at the Power Company, the square bus bars tend to be hollow, since little current flows in the center. Just checking:
skin_depth = sqrt(2*resistivity/(2*pi*frequency*mu)) which, for copper at 60 Hz gives us
sqrt(2*1.68e-8/(2*3.14159*60*4*3.14159e-7*1.0)) = 16.84mm = 0.663".
Since were talking exponential decay, here, 5 times the skin depth results in a current of zero; that's about 3.3 inches. So, if one has a bus bar that's one foot square, then one is going to save a considerable amount of money on copper by making the bus bar hollow with the sides and tops 3.3" thick.
But, notice that in that stupid equation above (and, yeah, that's the simplified one) there's a "sqrt(1/frequency" in there; meaning that as one goes up in frequency, the thickness of copper that's actually carrying current is getting thinner and thinner. At, say, 10 MHz, that skin depth gets to be 20 um (that's micrometers). Remember what I said about resistance? It's the cross-sectional area of the conductor. The smaller that is, the bigger the resistance of an a wire; and, if all the current is restricted to the surface of a wire and 5 skin depths deep, that means that the resistance goes up, the wire gets hotter, and More Losses.
This is why, when one is looking at, say, ham radio transmitters running at 20 MHz or so, big inductors tend to be silver plated, because the current is in the surface of the conductor, silver's the best conductor, and that's a good way to minimize losses.
As one gets into the GHz, the losses on (say) coaxial cable get Really High on that center conductor, to the point where, say, MW-scale RADAR transmitters would loose all the power on the way from the transmitter to the antenna. Hence, waveguides, where we dispense with the center conductor and bounce electromagnetic waves down the interior of hollow, silver plated (yeah, we got currents there, too, but we spread 'em out) rectangular shaped bars of metal.
Now, back to motors. The point to be made here, and in the video, is that if one is running at, say, 200 kHz or so (I'm guessing that as the switching frequency of the electronics driving the motors), the majority of the current is traveling on the surface of the wires. Not in the wires. So, having more surface area reduces the overall resistance. So, with Teslas old-timey many many wires in each slot, that's a lot of wires: and the amount of surface area in all those wires is a heck of a lot more than, say, three wires in each slot or something, and that reduces the AC losses in the wire. As compared to the DC losses.
In fact, now that I think about it, he spent a little too much time talking about AC vs DC resistance; it's the AC vs DC losses that are the point. Losses tend to go as A*A*R; and if the value of R is less, there's less heating in the wires, less energy going to heating up the motor, and more available to move the car forward.
I'm not a motor guy (as if you all couldn't tell), but the story hangs together a bit. Fun.
GhostSkater
Member
I would say it's way lower than that, with small inverters I worked in the past the maximum I've seen was 35 kHz, with the usual being in the 20 to 25 kHz range
I can hear the switching frequency on the inverters on some video I've seen from Teslas, so at least one the harmonics are on the audible range, if not the fundamental, so likely in that range as well
One of the reason for the 25 kHz on the inverters I messed up with is that I bumped them from the default 20 kHz because I could rear it and was annoying as hell, 25 kHz makes it inaudible
Quick search shows it's from 2.5 to 20 kHz, makes sense with the low fundamental frequency of the motors, although 2.5 kHz seems way too low
What is the switching frequency of main EV/HEV e-powertrains? - Solutions for noise and vibration control of electrical systems
Description of main electric motors switching frequency choices for traction application in automotive industry.
e-nvh.eomys.com
Electric Drive Technology Trends, Challenges, and Opportunities for Future Electric Vehicles (Journal Article) | OSTI.GOV
The U.S. Department of Energy's Office of Scientific and Technical Information
www.osti.gov
Switching - E-Mobility Engineering
E-Mobility Engineering examines how new technologies are boosting the performance of inverters and onboard chargers
www.emobility-engineering.com
On the motor losses parts, looking at current alone is not representative, you have to look at current/turns or even better, motor constant (kM), which normalizes resistive losses per unit of torque
Depending on how you wound the motor, you can have the same torque for vastly different current, but the losses for unit of torque remains the same as long as the amount of copper is kept constant. Important note is that it will happen at different speeds
I would say it's way lower than that, with small inverters I worked in the past the maximum I've seen was 35 kHz, with the usual being in the 20 to 25 kHz range
I can hear the switching frequency on the inverters on some video I've seen from Teslas, so at least one the harmonics are on the audible range, if not the fundamental, so likely in that range as well
One of the reason for the 25 kHz on the inverters I messed up with is that I bumped them from the default 20 kHz because I could rear it and was annoying as hell, 25 kHz makes it inaudible
Quick search shows it's from 2.5 to 20 kHz, makes sense with the low fundamental frequency of the motors, although 2.5 kHz seems way too low
What is the switching frequency of main EV/HEV e-powertrains? - Solutions for noise and vibration control of electrical systems
Description of main electric motors switching frequency choices for traction application in automotive industry.
Electric Drive Technology Trends, Challenges, and Opportunities for Future Electric Vehicles (Journal Article) | OSTI.GOV
The U.S. Department of Energy's Office of Scientific and Technical Information
Switching - E-Mobility Engineering
E-Mobility Engineering examines how new technologies are boosting the performance of inverters and onboard chargers
On the motor losses parts, looking at current alone is not representative, you have to look at current/turns or even better, motor constant (kM), which normalizes resistive losses per unit of torque
Depending on how you wound the motor, you can have the same torque for vastly different current, but the losses for unit of torque remains the same as long as the amount of copper is kept constant. Important note is that it will happen at different speeds
err motors frequency != inverter AC "generation" frequency, motor windings will only see few hundreds Hz max.
GhostSkater
Member
True, the inductance will smooth it out, I mean mostly due to the NVH part
More than few hundred, for Model Y:
70 MPH * 720 rev/mile * 9:1 gearbox = 126 rev/sec
126 Hz * 6 commutation cycles per pole pair * 6 poles = 4.5 kHz commutation rate. However, coil waveform only cycles once per pole HHXLLX HHXLLX so coil frequency is:
126 * 6 = 756 Hz
(Unless I'm confusing poles and pole pairs)
Um. Being this pendant of sorts: Say the inverter is running at 25 kHz. Thing is, it's applying a squarish wave in voltage to the windings of the motor. Remember: The rule tends to be that the switching transistors are On, or they're OFF, and they spend as little time as possible in between, since that "in between" area is where the transistors dissipate power. (That is: with a dead short, power dissipation goes as I*I*R, and if R is down in the milli to sub-milliOhms Ohms, Pd goes to nada. And if the transistor is open, there's no current and no power dissipation.) This is how power converters can achieve 90+% efficiency.I would say it's way lower than that, with small inverters I worked in the past the maximum I've seen was 35 kHz, with the usual being in the 20 to 25 kHz range
I can hear the switching frequency on the inverters on some video I've seen from Teslas, so at least one the harmonics are on the audible range, if not the fundamental, so likely in that range as well
One of the reason for the 25 kHz on the inverters I messed up with is that I bumped them from the default 20 kHz because I could rear it and was annoying as hell, 25 kHz makes it inaudible
Quick search shows it's from 2.5 to 20 kHz, makes sense with the low fundamental frequency of the motors, although 2.5 kHz seems way too low
What is the switching frequency of main EV/HEV e-powertrains? - Solutions for noise and vibration control of electrical systems
Description of main electric motors switching frequency choices for traction application in automotive industry.
Electric Drive Technology Trends, Challenges, and Opportunities for Future Electric Vehicles (Journal Article) | OSTI.GOV
The U.S. Department of Energy's Office of Scientific and Technical Information
Switching - E-Mobility Engineering
E-Mobility Engineering examines how new technologies are boosting the performance of inverters and onboard chargers
On the motor losses parts, looking at current alone is not representative, you have to look at current/turns or even better, motor constant (kM), which normalizes resistive losses per unit of torque
Depending on how you wound the motor, you can have the same torque for vastly different current, but the losses for unit of torque remains the same as long as the amount of copper is kept constant. Important note is that it will happen at different speeds
Fine, so what? Well, yeah, apply a square wave of sorts in voltage to the windings of an inductor/motor, then the current goes something like
I = Io*(e^(t*R/L) -1)
That is, the current is doing little exponential rises and falls, where "R" in this case is both the resistance of wires, transistors, and such, but is also the resistance of physically spinning the motor in the presence of a load. One would like RL of the load to be >>> R(random lossy resistances).
So, stick with the R(random lossy resistances). Trick is, to those random resistances, we're apply a blinking square wave. Playing with good 'ol Fourier, to at least start with, a square wave isn't just one frequency, it's a base frequency (that 25 kHz of which you spoke) plus odd harmonics as high as one cares to go. Now, slow rise times tends to kill the higher-order harmonics (5, 7, 9, etc.), but the 3rd harmonic at 75 kHz is definitely going to be there. And the 5th is likely, too, at 125 kHz. So, we'd like the inductance of the motor to be an actual inductor at those frequencies; making the additional resistance because of skin effect at higher frequencies smaller is really important.
Like I said, I'm not really a motor guy, and it's been truly ages (back in my Navy days, in fact) where I got tutored up on how motors actually work, what with all those rotating magnetic fields and all. But one can see, as they say, where this is going.
The thing our video fellow mentioned was that at low vehicle speeds those "hairpin"-based motors weren't half bad. Note that the hairpin motors the ratio of the cross-sectional conducting area for the AC (i.e., skin effect) vs DC (all the way through) is less, which means that they're bad at high frequencies but not-so-bad at low frequencies. But this implies that there's higher current frequencies in the motor windings at high motor rpm than at lower rpm. Interesting.
And this brings to mind the BEV Porsche that came out a year or two ago, that actually shifted gears. That might have been because Porsche had a great, low-cost motor that was perfectly acceptable at low vehicle speeds, but got lossy and bad performing at high vehicle speeds; so they threw in a transmission that would lower the RPM of the motor at high vehicle speeds, so they could continue to get good power out of it.
But Tesla doesn't do that. I take a wild guess and state that Tesla's motor, what with a larger cross-sectional surface area to conductor area, doesn't have issues at high RPMs - and therefore doesn't need the extra expense, losses, and weight of a no-kidding gear shifting transmission.
Fun discussion. But there exist real, live power/motor engineers who would blow any and all of the above out of the water.
Isn't that only relevant at high resistance or high torque combined with low inductance?
For continuous conduction and say 20% ripple of a low resistance stator winding, the current is closer to a triangle wave than exponential with I*R being dwarfed by pack voltage - BEMF. (Or have I been oversimplifying it when making switching converters?)
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