An electric motor produces torque at the shaft that is proportional to the current. The inverter or motor controller is used to regulate the current according to the requested torque command.
The resulting speed that the motor turns is determined by the difference between the applied load and the generated torque--if the load exceeds the torque then the motor stalls, if the torque exceeds the load then the motor spins.
The resulting output power is calculated by multiplication of the generated torque and the resulting speed.
It is the design of the magnetics in the motor that determines the maximum possible torque that it can produce and not some peak hp rating.
You cannot calculate max torque of an electric motor from P and RPM. In motor used by Tesla 3 phase current is used to generate rotating magnetic field. This causes motor to turn, but there is a slip. Greater the slip is more torque motor produces.
Look at efficiency map from
http://www.acpropulsion.com/datasheet/ac150gen2.pdf
Since power is torque*RPM*unit conversion blue line in efficiency map is set by max torque. It can be calculated from the map.
I appreciate the comments and research you did on electric motors. I think that unhappy P85D owners and those that support their conclusions will benefit from understanding the technical side of the motor horsepower issues.
Unfortunately the discussions included in your posts do not take into account that electric motors in Tesla vehicles are fed by Power Electronic Modules (PEM, or inverter), and this is one of the reasons that they are inaccurate.
Tesla uses the newest and most sophisticated inverter scheme – Flux Vector PWM (pulse width modulation). I do not want to go into a lot of details on this, as this might be beyond the interest level of the majority of TMC members, but will summarize the essence as it applies to the discussion at hand. For those interested in technical details, I suggest the 4 part series “
Understanding Variable Speed Drives” published in EC&M magazine, as well as the motor control system section from Tesla Motors Patent: “
Voltage estimation feedback of overmodulated signal for an electric vehicle”
The just of it is that Tesla motor control includes a closed loop comprised of motor and inverter microprocessor. The close loop control is unique to the Flux Vector PWM inverters and is not used in any other type of inverters. This ultra-high speed close loop control system uses real time data from the motor to generate output voltage signal to precisely control motor torque and speed.
The power required to produce this output voltage is fed to the inverter from the battery and is not a motor control signal, rather just the byproduct of the Torque and speed which are the precisely controlled motor output parameters. The power required to produce the required motor torque and speed, of course, can be calculated using the formula that I as well as many others posted many times: Power = Torque x rpm / 5252.
The key result of the above (neglecting the transients) is that tesla drive unit output is a constant torque from rpm(0) to the rpm(maxP) at which power required to produce this torque is equal to the maximum hp rating of the motor calculated using the above formula. The corresponding portion of the power-speed curve is called constant torque portion and is represented by the straight line with angle between it and the speed axis proportional to the rated torque of the motor.
After the inflection point at the maximum rated motor hp, the power curve is a horizontal line representing the fact that motor reached its power limit. This portion of the curve is called constant power region. Based on the above formula, since the power has reached maximum allowable level, the torque is declining with the increase in speed.
The above is the reason that in Tesla drives motor horsepower rating uniquely identifies the motor rated torque and can be readily calculated using above formula (with the slight variations due to the transients).
Except that P85D is not a 463hp car (yes, you can't even get numbers straight). In order to have "463 hp car", you need to replace $691 motor hp drive units with 463 motor hp drive units. Once you do so, however, you will end up with the car performing similar to 85D. P85D is a car with 691 motor hp, battery limited to 463 hp. The higher motor hp is responsible for the performance boost that P85D has over 85D and your imaginary "463hp car".
Sure it is. Tesla even says so. And at highways speeds, it performs just like a sub 500 hp car does that weighs what it does.
Absolutely not. Tesla says that it is a car with motor hp rating and maximum motor shaft power limited by the battery. The result of what is explained above is a hybrid torque curve, with the initial portion defined by the combined motor rated horsepower (per ECE R85), and the second portion of it that is defined by the battery limited power.
The comparison between Model S and similar hp/weight ICE car is invalid, because the acceleration is defined by the difference of the car torque and the load (resistance) torque and inertia. The ICE car has different torque characteristic and is not an indication of the performance of an EV.
I understand your frustration that high speed performance of P85D did not meet your expectations. Tesla, however, never marketed the car using this metric. I am further sympathetic to the fact that you misinterpreted the data provided by Tesla to mean something that the company did not imply, but you expected.
For the record, as I’ve stated more than once before, I do not believe that Tesla handled presentation of the P85D specifications properly, but it clearly was not a conscientious attempt to defraud the customers. Having said this, however, I am not sure what would be the right way, short of posting a lot of technical stuff (which most definitely will be lost on absolute majority of consumers) and requiring prospective P85D owners take a 10-hour course on Tesla drivetrain. The enormous quantity of posts on the “691” threads, including mine, trying to explain the technical side of the issues, are proof that there is no easy solution here.
This is innovation problem, which became Tesla problem by association. I understand that Tesla is inseparable from the innovation it represents, and accept the whole package. You and other unhappy owners, I believe, want and crave the innovation, but want it without the side effects. This is not a realistic position.
A standard which the ECE says is preliminary and if we believe your interpretation, has nothing to do with vehicle horsepower.
The ECE R85 is not preliminary. Rev.1 of it was issued on August 2013 and is
available from the ECE Site. You are apparently looking at one of the preliminary copies of the Amendmends (there were 5 and all of them rolled in Rev.1)
Repeating “your interpretation” over and over in your posts is disingenuous. We had several substantive discussions on this topic and you simply ran out of arguments. Repeating “your interpretation” does not represent a convincing argument.
You apparently also ignoring that my interpretation is identical to Tesla’s interpretation and interpretation of the authorities that have jurisdiction over the Certificate of Conformity that is required for every vehicle registered in Europe.
The electric motor produces power that is proportional to the power fed it (voltage*current). The REST "power" log follows the power in this graph exactly, not the torque.
This is wrong. The motor in Tesla drivetrain produces torque and speed which it is *controlled* to produce. It draws power required to produce the controlled parameters – output torque and speed.
I am not convinced that it is OK to add the motor hp of both motors together to come to the 691 motor hp number.
It would be nice if Tesla could provide us with the graphical data to back up the claim that the theoretical combined motor hp of the 2 motors is in fact 691 (US metrics).
My EC certificate of conformity only states the motor hp of the individual motors, which is 193 kW front and 350 kW rear. Apparently the 691 motor hp figure is not according to ECE R85.
JB Straubel addressed this in his Blog:
The motor shaft horsepower, when operating alone, is a more consistent rating. In fact, it is only this (single or combined) motor shaft horsepower rating that is legally required to be posted in the European Union.
Neither does Tesla. They used to but then stopped back in May.
This is wrong. JB Straubel blog post is dated September 21. Excerpt is above.