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Extra gear

Discussion in 'Roadster: Technical' started by WarpedOne, Oct 7, 2006.

  1. WarpedOne

    WarpedOne Supreme Premier

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    Here http://teslamotorsclub.com/forum/index.php/topic,90.new.html#new I found out that Tesla has enough power for some serius racing. It needs just another gear with 1,06:1 ratio. In this third gear maxumum engine power of 185kW would be achived at precise maximum speed of 160mph (262 km/h). Of course, at this speed not much driving would be possible, batteries would be drained in mere 17 minutes. This is probably why Tesla choose not to fit that gear. It would add little to general usfulness of the car.

    But this is certainly enough for a few laps at racing circuit. Roadster would probably need wider front tires that would increase aerodynamic drag and somewhat reduce the top speed but still you would have a serious racer. Mindblowing aceleration and speed.
     
  2. AGR

    AGR Member

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    The Roadster is limited with only a 2 speed transmission, most supercars have a 6 or 7 speed transmission not a 2 speed.

    First gear is good for about 65mph with the electric motor on the redline, Second gear will do about 130mph redlined.

    What do you do when you hit the apex of a turn at 60 mph? Do you downshift to First and immediately redline the motor, or do you leasurely power out of the apex in second gear at about 7,000 rpm?
     
  3. vfx

    vfx Well-Known Member

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    1st gear goes 0 to 70 with the best acceleration possible
    2nd gear can go from 0 to 130 with anyproblem at all

    So you would probably shift from 1st to 2nd gear at some point before you enter the turn.
     
  4. TEG

    TEG TMC Moderator

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    And I think the batteries would be rather unhappy if you tried to sustain much above 130mph.
    I think the 185kW may be a max power that it can make for short periods of time, but not continuous indefinitely.
     
  5. AGR

    AGR Member

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    You would slow down before the turn, hit the apex and then accelrate. Usually as you slow down you would be not only braking but also downshifting. (the popularity of paddle shifts and automated manual transmissions).

    Immediately past the apex you would be accelerating again, usually in a "lower gear" to gain speed as fast as possible.

    An electric motor will "torque" a car out of a turn probably better than an ICE motor, but how will an electric motor "power" a car beyond its torque curve. As ICE motors start generating power(which is what you need to go fast) at higher revolutions, electric motors do the opposite.

    You would have great "low end" flexibility with an electric motor, with compromised "high end" performance, which is the nature of electric motors. They have "linear" power and torque delivery and then fall off.
     
  6. vfx

    vfx Well-Known Member

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    We are getting into the specifics of your hypothetical track/turn. When you shift and what gear you use is certainly an infinately debatable subject. I'd be happy to go out on the track and spend an aftrenoon playing with your imaginary ICE race car to find the exact braking / shifting points and what gears would be optimal for maximum speed through the turn.

    Then with the 2 geared electric car I could do the same thing to find it's idea braking (which may be better with the regen lever set way high) and it's (one) shift point for that turn.

    The reason that multi geared ICE race cars shift up down and down up so much is because they have to! You are shifting your 5,6,and 7 gears all the time to keep within the motor's limited power-torque band. EVs not as much of a problem.

    I'm not saying the EV is better, perhaps the scenario with that track, on that turn, maybe the Electic car would be slower out of the gate. But maybe, just maybe, on all the other turns and straights, the non-shifting aspect of the EV would make it victorious.
     
  7. AGR

    AGR Member

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    At some point and time there will be comparisons on a track and we will see. In the meantime we can do a bit of "bench racing".

    Be it an ICE or Electric motor they both have a power band and torque band, and ideally you would want the motor to have the ability to operate within its "band". Is a 2 speed transmission adequate with an electric motor to perform in the same fashion as an ICE with a 6 speed transmission.

    Years ago Chaparral cars in the Cam Am series had a 2 speed automatic with a torque converter, it worked well in that specific application of light car / big motor, and the fact that the clutch pedal became the "wing pedal" to alter the angle of the rear wing.

    The trend in the automotive industry is to increase the "splits" where you now have 8 speed automatic transmissions. Does a CLK63 AMG or a M6 really need a 7 speed transmission?
     
  8. TEG

    TEG TMC Moderator

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    Tesla appears to be trying to keep everything as simple as they can.
    They seem to be meeting their performance targets without having to resort to more gears or a CVT.

    It also appears that racing performance isn't one of their design goals.
    This is a car meant to be drivien on the street, and offer street performance on par with just about anything else street legal one could buy for the USA.
     
  9. AGR

    AGR Member

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    Keeping it simple is the right way of doing it. The Roadster does not have a clutch, an electric motor does not idle, its on or off, must be that when the driver puts his foot on the brake it would go into "regen mode" and at lower speeds or almost a stopped power to the motor is interrupted.

    How do you shift from 1 to 2? The driver temporarily eases on the accelerator, to be in a position to shift?

    Or is it that if you want low speed acceleration you use 1st gear, and most of the time you would use 2nd gear, you would not actually shift from 1 to 2.
     
  10. WarpedOne

    WarpedOne Supreme Premier

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    Transmission is electro-hydraulicaly actuated meaning it really is "shift by wire". Accelerator is not directly connected with eMotor also but sends its position to computer. When you shift, the computer gets the request to shift gears. It checks if it can be safely done (shifting into reverse or into first gear at 100mph is obviously not safe) and then executes needed procedure for successful shift depending on many cirumstances: speed, rpm, current accelerator position, stability status, braking status etc.
     
  11. AGR

    AGR Member

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    Thank You!

    Its accelerates and shifts by wire. The motor will briefly "back off" to permit an upshift, would the motor "blip" to permit an downshift similar to an SMG transmission on a BMW?
     
  12. TEG

    TEG TMC Moderator

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    I would imagine so.

    What are you asking exactly?

    Tesla has demonstrated that 2nd gear alone is good enough for most driving duties.
    1st gear is really there only to "prove a point" when doing a 0-60 test, and for extra regen when going downhill.
     
  13. AGR

    AGR Member

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    TEG,

    My question was - do you shift 1 to 2 and 2 to 1 as one would use a manual transmission, which without a clutch can be challenging.

    From your statement, you leave it in second (high) and just use the accelerator without shifting, and first gear (low) would be used to prove a point as you say. Makes better sense, no clutch, no shifting under normal conditions.
     
  14. vfx

    vfx Well-Known Member

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    EP 2 (the red one) has had the gearbox locked in second for almost a year now. Think about all the shows, factory demos, test rides for buyers, potential buyers, Celebs, Diplomats, Press (Dan Neil even drove it) and lucky regular folks who have ridden in it with it's balls cut off. In second you can go 0 to 130. You never have to shift. First does 0 to 70. so for most street driving you never have to shift. In first gear though you are using more energy to get to top speed quicker and you get more stopping power from higher regen braking (and you get more charging to the batts) so you can choose to never shift in whatever mode suits you.

    Teslian drivers must inwardly smile when passengers are impressed by the more sedate 2nd gear accellaration demos they give.
     
  15. TEG

    TEG TMC Moderator

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    Thanks for that, vfx. I wasn't going to say anything about 2nd gear only from the ride I got (in EP2), but if it is well known then yeah - you are right.

    Off the line acceleration was certainly adequate but didn't get my heart pumping as much as I had anticipated.
    The 60-90mph push was pretty sweet. I had expected acceleration to get weak as we got near 90, but it felt like it would just keep on going, but traffic prevented any further demonstrations.

    By the way, how did you find out where the Santa Monica showroom is going to be? I doubt they intended that to be public knowledge this early on.
     
  16. vfx

    vfx Well-Known Member

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    The car shows a lot in So Cal. If you go to an Event (like CARB) the Tesla Marketing folks are generous with info about the car and the company. Sometimes they ask each other, "Hey!, Can we say if we are going to have a glovebox or not?" (Indeterminate, but see below).

    As for the 2nd gear thing it's been in much of the coverage. reviewers say "Our car was locked in second but...amazing..."
    I thought the time the Tesla broke down with Martin and a camera crew and they allowed the car to be filmed being fixed on was amazingly transparent. It is a prototype so they had no problem showing the warts of a car that was a year away.

    The picture is of under the passeger seat. A manual will fit there nicley. One of the Marketing guys did not even know about this one. :)
     
  17. AGR

    AGR Member

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    Would it be fair to conclude that the transmission is not made for shifting? The 0 to 60 times are "factory" times to be verified by the "potential customers" in actually going 0 to 60 in 4 seconds with their car.

    As anyone actually seen a Roadster do a few 0 to 60 passes in 4 seconds?
     
  18. TEG

    TEG TMC Moderator

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    In EP2 - at this point - yes.

    But in production I don't think they have any intention to discourage shifting.
    They just say you can be pretty happy staying in 2nd all the time, but 1st gear is there whenever you need it.

    The prototype transmission in those early test cars just needed a little work.
    Rest assured the production cars will let you shift!
     
  19. AGR

    AGR Member

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  20. TEG

    TEG TMC Moderator

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    Yes, that 599GTB is one sweet car... *but* it is front engined!
    Even if the car handles and performs as well as an Enzo, you are still sitting further back, and don't have the same "flying down the road" driving position. Plus I would want those sweet Ferrari engine noises behind me.
    But it is so "yesterday" now... Tesla or bust.

    Someday I hope Elon lets us know how close the Tesla Roadster comes to the "fun factor" he gets from his McLaren F1!
     

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