Ahh ... thanks for the correction. That is a lot better.His dyno # was 588hp, not kW. And wheel power is measured the same regardless of the power plant; engine (ICE) or electric motor or steam engine. hp or kW are just units. Power is the same .
major
take a look at the graph I posted in #30Dual (or even triple) 'parallel' reduction is the way to go. Should make the gearheads happy.
That's the approach which I was suggesting....
In the chart, look at 55 mph. R_Tq for the L is 255 (whatever unit) and at 75 mph 163 and at 90 mph is 130.
55*255 = 14,025
75*163 = 12,225
90*130 = 11,700
Whatever the unit may be. You can see the power to the wheels decreasing, even though power input is almost constant. Between 55 mph and 90 mph, power input drops 3.4% while power output drops 16.6%...
I don't care much about marketing. Never have believed a car salesman.So power is not the same if marketing says so.
They can get more torque at the wheels below the current threshold speed - which they don't need - but not necessarily for less electrical power per unit of mechanical power.With a higher drive reduction ratio, they can get more torque for less power at the start...
I agree that a dual-clutch design is the obvious solution for automated shifting of a two-speed gearbox, and especially for multiple gearboxes (due to multiple motors). The Rimac Concept_One (more of a technology demonstrator than a production car, but a more-than-million-dollar extreme performance exotic) has this type of transmission for each rear drive motor (one per wheel)....
A dual clutch gearbox with only two gears can be designed by their engineers in their sleep. I fail to see the challenge in shifting gears with a dual dry clutch. They will kill two birds with one shot. I am certain electric supercars will all be multi-gear.
It could be that the cooling system is running, but that wouldn't take anything close to 40 kW and my guess - since the chart shows substantial torque output at zero speed - is that the motors are being driven and the car is being held by the mechanical brakes. This is the electric version of the classic run-up before launching, and should be expected of a current automated launch system (which would not be expected in a Leaf). Unlike other current production EVs and hybrids, Teslas have induction motors, so the stator field is rotating (at the slip speed) with the motors stalled - it seems to me that could take substantial power.It should be noted that according to the chart, the vehicle is drawing almost 40 kW at standstill. Compare this to a Leaf's 0.5 kW base load. I would guess that this may be the result of entering Ludicrous mode and the cooling system is feverishly pre-engaged to cool down the systems and the pack, prior to the sprint.
sure, just take a bulletproof existing design and throw in a couple clutches and gears that can handle the 1000 odd foot pounds and 16,000 rpm, for an imperceptible change in performance and efficiency, what could go wrong?The two-speed seems easy, but manufacturers are not consistently finding it worthwhile.
The Tesla gearbox is the most common layout for production EVs, which is a two-stage helical spur gear train. The final gear is the ring gear around the differential, just like a typical transverse front-wheel-drive transaxle, so yes... that quoted reduction ratio is the motor to wheel speed ratio.Wow - at this ratio, the motor RPM is about 21,000 at 95 mph assuming 245/45R19 tires. Does this reduction include the differential?
I haven't had a ride in a Tesla, so I have no idea what it sounds like, but I don't know why anyone would assume "at 21,000 RPM you are smoking a lot of things". Lots of machines run much faster than that, including gear trains and electric motors.At 21,000 RPM you are smoking a lot of things, and the noise is certainly not so pleasant (if you can hear that frequency!).
The gears are no problem, but yeah... with the clutches, the two-speed only seems easy. The design is actually straightforward, but dual-clutch transmissions in conventional cars have had varying success with durability of the clutches... although most work fine, even while shifting much more frequently than a 2-speed would require and slipping to get started (which the electric drive would not). It can certainly work, but most manufacturers think the risk or cost or weight or bulk or something is not worth the improvement in efficiency or available power.sure, just take a bulletproof existing design and throw in a couple clutches and gears that can handle the 1000 odd foot pounds and 16,000 rpm, for an imperceptible change in performance and efficiency, what could go wrong?
The standard rear tires for a smart are 185/60R15, which have a rolling circumference of 1.83 m. 1.1 m would be ridiculously small - 350 mm or 13.8" diameter, which is much smaller than the tires on 10" wheels of an original Austin Mini. It doesn't matter to the Telsa battery, but if you're working out examples, they won't produce realistic speeds with the wrong tire size.The first chart, running at 4000 rpm with 90 Nm of torque requires about 38 kW. Let's say this is an electric Smart car. With a tire circumference of 1.1 m...
Hi Sol,Does the inefficiency also reduce the torque, or just the output power?
What is causing this sudden drop in efficiency?
It goes to show that depending on the motor and load conditions, the motor can become so inefficient that if we just increase the power without accelerating, we will actually be using less power, per unit of work.
I reread the above statement and can't make any sense out of it. But I think it is academic anyway because nobody would operate a motor at such a condition.It goes to show that depending on the motor and load conditions, the motor can become so inefficient that if we just increase the power without accelerating, we will actually be using less power, per unit of work.
Well sure, but that limit is set to prevent exceeding or closely approaching breakdown torque in the case of the induction motor. Beyond BDT, more motor current doesn't produce more torque, less in fact.yep, flat top means you are at the limit of the controller.
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