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