Everything you wanted to know about the ZF 8-speed automatic

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Thread: Everything you wanted to know about the ZF 8-speed automatic

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    Thumbs up Everything you wanted to know about the ZF 8-speed automatic

    Read it all here

    Some of the details:

    • There are only five friction locking elements (three clutches, two brakes), and in any gear just two are open. Further, a low-viscosity lubricant is used (5.6 cSt vs. 7.5 cSt in the Chrysler 5-speed), which reduces spin losses. So total energy losses from drag through the transmission are under 2%.
    • Although there are four planetary gearsets, the total bill of material is less (467 parts vs. 471) than the ZF 6-speed with its three planetary sets. At about 91 kg (201 lb), weight of the 8HP is about 2-3 kg (4.4-6.6 lb) less than the ZF 6-speed, and the package size is the same. The 8-speed is just 3 kg (6.6 lb) heavier than Chrysler's 5-speed.
    • The oil pump is offset and chain-driven, so it is sized according to engineering requirements, rather than by dictates of a conventional location on a transmission main shaft. The pump itself is responsible for at least one percentage point of the fuel economy boost.
    • The torque converter includes an advanced damper adapted from the ZF 6-speed, which permits the converter clutch to lock up at lower speeds, even in top gear. The clutch can, however, partially unlock if necessary to reduce NVH in top gear.
    • The relatively tall first gear (4.71) reduces the amount of torque converter multiplication required. With the early lockup of its clutch, the converter is used almost exclusively for vehicle launch.
    • The transmission gearing (4.71, 3.14, 2.10, 1.67, 1.29, 1.00, 0.84, 0.67) means small ratio steps (1.50 or below) and a large overall ratio spread of 7.03 (4.71/0.67). The large spread contributes to fuel economy.


    The rear axle ratios selected —2.65 for the 300 RWD, 3.06 for the AWD model—locate shift points according to brake specific fuel consumption (BSFC) maps. And further, Chrysler has 40 control maps that modify the shift patterns for different operating conditions.

    ____________


    Additionally:

    Demand For 8-Speed Prompts Chrysler To Stop Pre-Orders On 2012 Charger, 300


    http://www.motorauthority.com/news/1...ger-300-report
    Last edited by Titanic; 08-02-2011 at 07:12 PM.

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    Re: Everything you wanted to know about the ZF 8-speed automatic

    I would prefer it to be a DCT but compared to what they have now it's a no brainer, win win as long as Chrysler nails the shift programming.

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    Re: Everything you wanted to know about the ZF 8-speed automatic

    I'd prefer they don't handicap it with a slow shifting program.
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    Re: Everything you wanted to know about the ZF 8-speed automatic

    Quote Originally Posted by PA Dweller View Post
    I'd prefer they don't handicap it with a slow shifting program.
    100% agree. The biggest problem I have had with my last 3 new cars is the trend to taking much longer to downshift when hitting the gas. It may be the single biggest thing in a modern automatic that makes a car less 'fun to drive.'

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    Re: Everything you wanted to know about the ZF 8-speed automatic

    Wow, kewl. That's a long tall Sally top gear, 1400 RPM @ 70 mph. That's 50 MPH/1000 RPM.

    Wonder when the Pentastar is getting DI.
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    Re: Everything you wanted to know about the ZF 8-speed automatic

    Quote Originally Posted by big swede View Post
    I would prefer it to be a DCT...
    The only real downside to it not being a DCT is that it needs to drive a pump...however, due to the TC essentially being locked in all but take-off/1st gear situations, it really is "the next best thing..." if not better.

    Quote Originally Posted by PA Dweller View Post
    I'd prefer they don't handicap it with a slow shifting program.
    Quote Originally Posted by mjd1001 View Post
    100% agree. The biggest problem I have had with my last 3 new cars is the trend to taking much longer to downshift when hitting the gas. It may be the single biggest thing in a modern automatic that makes a car less 'fun to drive.'
    It's hard to say what the downshifts will be like, but as far as the speeds of the shifts, it should happen relatively quickly. Being such small steps b/w gears allows them to ramp up the speed without increasing the harshness of the shifts themselves.

    I would imagine that downshifts would happen fairly quickly simply since there will be no dearth of appropriate gear selections that can be made without excessive engine revolutions being required, a reason for a manufacture to avoid having it in their shift maps.

    Quote Originally Posted by Neanderthal View Post
    Wonder when the Pentastar is getting DI.
    My guess is we won't see it unless it's in a turbo application and/or in a truck application...or until sufficient advancement is seen from toyota/honda with DI v6 engines that make the pentastar seem less competitive (which won't be for a while yet).

    I understand they're open to DI for use in truck applications not only for power benefits, but because the bit of harshness DI introduces is acceptable to most truck buyers (it'd still be smoother than most engines in trucks anyways).

    I will say that the Pentastar equipped Grand Cherokee I schlepped around Salt Lake a couple weeks ago was among the smoothest/quietest vehicles I've ever encountered. I could imagine the high pressure injectors making their presence known given how quiet/smooth the vehicle was overall.
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    Re: Everything you wanted to know about the ZF 8-speed automatic

    DCT transmissions are heavily overated. CVTs are even worse. As said above, they need to nail down the programming, and then they're doing real well with these new automatics.

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    Re: Everything you wanted to know about the ZF 8-speed automatic

    Quote Originally Posted by mjd1001 View Post
    100% agree. The biggest problem I have had with my last 3 new cars is the trend to taking much longer to downshift when hitting the gas. It may be the single biggest thing in a modern automatic that makes a car less 'fun to drive.'
    I agree, it seems the shifting gets better overtime but that lag really sucks.

    Quote Originally Posted by Prince Valiant View Post
    It's hard to say what the downshifts will be like, but as far as the speeds of the shifts, it should happen relatively quickly. Being such small steps b/w gears allows them to ramp up the speed without increasing the harshness of the shifts themselves.

    I would imagine that downshifts would happen fairly quickly simply since there will be no dearth of appropriate gear selections that can be made without excessive engine revolutions being required, a reason for a manufacture to avoid having it in their shift maps.
    I really hope so because most modern automatic transmissions have this issue and it doesn't need to be like this.
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