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Discussion Starter · #1 ·
I have read somewhere that at maximum speed, the motor is spinning at 15000 rpm or whatever revs it supposed to be spinning at?
Now I am just wondering if Tesla could engineer 2 speed box, so on long motorway runs, it reduces the motor rpm, therefore less energy consumption, right?

I am sure Tesla/Nissan/BMW would have thought of it, so why not? Or am I missing something here?? :confused:
 

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Top speed isn't until 155 mph. How fast do you go on your long motorway runs!?

Adding a gearbox adds un-needed weight and complexity to the drivetrain!
 

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The Tesla roadster was originally designed with a 2 speed box, but it was changed to single speed for quality reasons.

Reducing the speed, and thus upping the torque to achieve the same power, doesn't necessarily improve efficiency - indeed some motors are less efficient at low rpm.

Petrol and Diesel engines have limited torque at low rpm and thus require torque multiplication through a gearbox at low speed and a launch device such as a clutch, however electric motors typically have maximum torque at lower speed and thus their natural characteristic doesn't require a multi speed gearbox.
 

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Discussion Starter · #4 ·
Top speed isn't until 155 mph. How fast do you go on your long motorway runs!?

Adding a gearbox adds un-needed weight and complexity to the drivetrain!
I am not looking for higher top speed, as far as I am concern, 100mph is more than enough., i was looking for more range with a 2 sp box.
 

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Discussion Starter · #5 ·
.... however electric motors typically have maximum torque at lower speed and thus their natural characteristic doesn't require a multi speed gearbox.
Then surely a 2 sp box would make even more sense, lowering the revs down to its most efficient rev range.
 

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II am sure Tesla/Nissan/BMW would have thought of it, so why not? Or am I missing something here?? :confused:
The Gen 1 Tesla Roadster had a two speed gear box which kept exploding and Tesla moved to a Borg Warner single speed gearbox for production Roadsters.

Many of the worlds fastest EV's use two speed gearboxes and some out perform the Tesla Model S P85 today;

http://buildraceparty.com/ev-west-wins-refuel-2014/

As we move into a world of EV sports cars I believe some will use gearboxes.
 

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Then surely a 2 sp box would make even more sense, lowering the revs down to its most efficient rev range.
But lowering rpms and increasing torque proportionality doesn't necessarily improve efficiency.
The effect of the gearbox on an ICE car is to create a torque profile of highest wheel torque at lowest road speeds. Electric motors do this naturally do this without a gearbox, commonly having a high sustained constant torque at low speed transitioning to a constant power curve (and thus reducing torque) at higher speed.
 

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My understanding is that electric motors are at their most 'efficient' when they are running at full power. The problem is more related to weight and air (drag) at high speeds, so the balance is reached when you've got a motor that can provide enough torque to enable a car to travel at the maximum desired speed at the motors' maximum rpm. However, the larger the resistive forces (drag co-efficient & weight), the larger the motor is required, which requires more power (kW). The perfect electric motor for a particular car will have enough torque to enable said vehicle to reach the desired maximum speed at the motor's max rpm. (@Paul_Churchley @Kevin Sharpe is this correct?)
 

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It does help to improve efficiency if you can minimise back-emf from your main drive motor. The Volt/Ampera does this by using the planetary gearbox to reduce the revs of the main motor at higher speeds by using either the second motor/generator or the Ice as shared input. Ok so it still stops at 105 mph but the pull is good all the way up.
 

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My understanding is that electric motors are at their most 'efficient' when they are running at full power. The problem is more related to weight and air (drag) at high speeds, so the balance is reached when you've got a motor that can provide enough torque to enable a car to travel at the maximum desired speed at the motors' maximum rpm. However, the larger the resistive forces (drag co-efficient & weight), the larger the motor is required, which requires more power (kW). The perfect electric motor for a particular car will have enough torque to enable said vehicle to reach the desired maximum speed at the motor's max rpm. (@Paul_Churchley @Kevin Sharpe is this correct?)
If I look at a Lynch Type D motor for example it's >86% efficient from 30 to 300 Amps. It would seem that there's relatively little efficiency to be obtained by gearing in that region. However you'd need a full map of efficiency versus rpm and torque to model different operating patterns to make an informed decision. However to the best of my knowledge all production road-going EVs (not hybrids or PHEVs) are single speed.
 

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It does help to improve efficiency if you can minimise back-emf from your main drive motor. The Volt/Ampera does this by using the planetary gearbox to reduce the revs of the main motor at higher speeds by using either the second motor/generator or the Ice as shared input. Ok so it still stops at 105 mph but the pull is good all the way up.
However for much of the time the Volt / Ampera operates in single motor mode with the epicyclic transmission locked up. In this mode it's operating as a single speed transmission just like the pure EVs.
 

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Dual or tri motor setups will become common I think. The Ampera does it with a planetary gear and a couple of clutches, in an all EV design you can dump the clutches. model S D uses a motor on each axle with different gearing, vary power to each for different torque characteristics.

The problem with a mechanical fixed gear transmission is the amount of torque an EV can actually produce. I don't believe an automotive transmission exists that could cope with the Model S motor.
 

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Dual or tri motor setups will become common I think. The Ampera does it with a planetary gear and a couple of clutches, in an all EV design you can dump the clutches. model S D uses a motor on each axle with different gearing, vary power to each for different torque characteristics.

The problem with a mechanical fixed gear transmission is the amount of torque an EV can actually produce. I don't believe an automotive transmission exists that could cope with the Model S motor.
The Ampera / Volt arrangement is related to that in the Prius, Auris, Fusion and C-MAX - the common factor being they all have both ICEs and electric machines.
Depending on source the Ampera / Volt transmission has 2 or 3 clutches, a confusion which probably stems from whether you consider it to also have a transmission brake or not. The three devices are:
  1. Clutch between ICE and generator to allow dual motor operation without the ICE turning.
  2. Clutch between generator and transmission to mechanically isolate the generator set / range extender from the transmission to allow series hybrid / range extender operation.
  3. Clutch / brake on the transmission to stop the input shaft spinning freely when the clutch in item 2 is open. When this is locked the transmission becomes single speed with a fixed ratio between the traction motor and the wheels.
 

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Every time I read about the ampera/volt transmittion I have a feeling which is a combination of "wow" and "so many moving parts". I expect it could be the "high point" of sophistication and further developments will be around simplicity

I'm currently a leaf owner (lease in fact). That's up in 5 months but having moved, and with 2 kids now at uni I'm considering a little more *occasional* autonomy. The BMW i3 appears for it's relative simplicity and occasional built in plan-B backup with failing infrastructure but of course has nothing like the autonomy of the volt.
 

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Every time I read about the ampera/volt transmittion I have a feeling which is a combination of "wow" and "so many moving parts". I expect it could be the "high point" of sophistication and further developments will be around simplicity

I'm currently a leaf owner (lease in fact). That's up in 5 months but having moved, and with 2 kids now at uni I'm considering a little more *occasional* autonomy. The BMW i3 appears for it's relative simplicity and occasional built in plan-B backup with failing infrastructure but of course has nothing like the autonomy of the volt.
There is certainly a mystique about the Volt/Ampera transmission. I thinks it's such a surprise, because it came from the USA ;)
 

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There is certainly a mystique about the Volt/Ampera transmission. I thinks it's such a surprise, because it came from the USA ;)
The Ampera transmission is only a little bit more involved than that in a Prius for example (+ 2 clutches + transmission brake). The epicyclic transmission goes back many years - they were used in Model Ts.
 

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The Ampera transmission is only a little bit more involved than that in a Prius for example (+ 2 clutches + transmission brake). The epicyclic transmission goes back many years - they were used in Model Ts.
It's significantly harder to explain than a standard transmission though ;)
 
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