ZF’s nine-speed geared for front-transverse engines

  • 04-Mar-2013 01:33 EST

The housing of ZF's 9HP consists of two essential parts: a converter housing and a main housing with an aluminum cover. By default, the 9HP is connected to the vehicle radiator via pipes, and a transmission cooler can optionally be attached directly to the housing.

After debuting as a concept study at IAA in 2009, ZF’s nine-speed automatic transmission (9HP) is hitting the road for real in 2013. Production starts this year at the company’s Greenville, SC, plant with an expected annual production volume of 400,000. The unit will be highlighted at the SAE 2013 World Congress in Detroit April 16-18 in ZF's booth (#525).

The 9HP has been designed for vehicles with transverse engines and front- or four-wheel drive and thus, says ZF, can be installed in 75% of all cars produced worldwide. While there are currently seven- and eight-gear transmissions with high transmission-ratio spreads on the market for longitudinally installed drivelines, that had not been the case for vehicles with a transverse-mounted front engine.

ZF achieved the high number of speeds via four individual gear sets nested within the transmission, and six shifting elements with nine gears sets. The 9HP also features what ZF says is the first-ever use of interlocking dog clutches for power shifting and is supplemented by using hydraulically operated constant-mesh elements that reduce its impact on the overall transmission length and optimizes efficiency.

Its high total gear spread of 9.81 enables the 9HP to reduce 0-60 times by 2 s and achieve a 10 to 16% fuel consumption savings compared to standard six-speed automatic transmissions.

Additionally, extremely small gear ratios are achieved, which positively affect driving comfort and enable the engine to continually run in the consumption-optimal speed range. At engine speeds of 75 mph (121 km/h), rpms are lowered by approximately 700 with the 9HP, resulting in less noise.

A torque converter is used as the 9HP’s standard starting element, which provides smooth starting and improved maneuvering quality. A multilevel torsion damper system minimizes hydraulic losses while facilitating the quick closing of the torque converter lock-up clutch. This system is beneficial not only for fuel consumption but also improves driving dynamics. 

ZF engineers did not use a fully integrated mechatronics module for the sensors, actuators, and the electronic control unit (ECU) in the 9HP. Instead, the ECU is installed separately from the now “significantly smaller” hydraulic control unit on the upper side of the transmission housing. The sensors can be found inside the transmission; vehicle-side signals are connected directly to the male plug of the ECU.

In a first for the company, ZF developed internally the complete ECU. A powerful embedded flash controller can realize complex control algorithms, with a calculation performance comparable to the controller used in the eight-speed automatic transmission that can be increased by about 30% on demand for even more comprehensive software functionality. The layout of the ECU printed circuit board has been designed so that the different OEM hardware requirements of OEMs can be met.

The 9HP is built on a construction kit principle that creates the flexibility for the basic transmission to be supplemented with special requirements by OEMs and to accommodate different starting elements (i.e., start-stop, hybrid) and all-wheel-drive applications. This setup allows for easy adaptability across applications and can be implemented cost-effectively given the restricted installation space conditions. It will be available in two model ranges that will cover a torque range between 150 and 355 lb·ft (200-480 N·m).

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