New transmission for North America: New Jersey transit is first U.S. fleet to use ZF's AS Tronic automated manual transmission - Powertrain

Diesel Progress North American Edition, Feb, 2002 by Mike Brezonick

One of the advantages of being a global manufacturer is the ability to develop and prove a product in one region, then hit the ground running with it in another. The latest example of this capability comes courtesy of ZF, which recently introduced its AS Tronic automated manual transmission to the North American coach market.

The AS Tronic transmission was originally introduced in 1997 and has logged millions of miles in heavy-truck and bus service in Europe. Its first U.S. application is in a 2001 Motor Coach Industries (MCI) model D4000 owned and operated by New Jersey Transit (NJT) in suburban route service.

"The plan to bring this product to the U.S. market became a dream of ours about two years ago," said Wolfgang Schilha, vice president, Bus Driveline Technology & Customer Service at ZF-Friedrichshafen. "At the same time New Jersey Transit was looking at replacing a large number of OTR buses and coaches for their suburban service.

"When we told them about it, our friends at New Jersey Transit became very excited about a new approach to using fully automated transmissions in high-performance, high-powered vehicles."

It was no accident that NJT was the first fleet operator to incorporate the ZF transmission, as the two organizations have a long history together. Currently, some 1250 NJT buses utilize ZF transmissions and steering components.

"In 1994 when I first joined the company here in New Jersey, and did our first bus purchase under the leadership that now exists, our product of choice for that transit application was ZF," said Maureen Milan, vice president and general manger of Bus & Light Rail operations at NJT. "When we were looking toward a fleet of over-the-road coaches for the 21st century, one of the first plane trips we took was to Friedrichshafen to again explore the product offerings that ZF had."

That exploration led NJT to the AS Tronic transmission, which is designed to offer the flexibility of semi- and fully automated gearshifts, with electronic synchronization taking the place of conventional mechanical synchromesh systems. In its NJT iteration, the AS Tronic provides 10 forward speeds and can accommodate input torques as high as 1750 lb.ft.

The transmission is modular in design, incorporating a gearbox, shift module, clutch module and optional retarder with heat exchanger. The twin countershaft gearbox houses an integrated splitter group and planetary range change group. Power is split into the two countershaffs via constant gears and the power split is returned to the mainshaft via the appropriate gear in the three-speed section. High-performance helical cut gearing is used to reduce noise and increase efficiency.

The shift module contains four 24 V pneumatic cylinders. Both the splitter and range change group have one shift cylinder each for shifting. The third shift cylinder is used for range selection within the main gearbox section, while the fourth cylinder is used to engage the selected range.

The shift module is installed on the upper section of the transmission for easy access. It handles gearshifts pneumatically and features integrated electronic controls that communicate through a CAN bus. The transmission electronics control all procedures in the transmission and communicate continuously with the connected vehicle systems. The requisite valves, cylinders, sensors and outer connections are integrated in the shift module, resulting in a clean, streamlined design.

"Because of the high-speed communications, the transmission takes a lot of the strain off the driveline," said Rick Manna, sales manager, AS Tronic. "With every gear shift, the engine is controlled by the transmission, which relieves strain on the driveline and extends life."

The transmission housing is a three-section, aluminum case that also integrates the clutch bell housing. As there are no clutch pedals or hydraulics, the standard dry clutch is actuated by the clutch module. Clutch adjustment is automatic and the system alerts the driver through a display when the clutch is overloaded or needs changing.

"One thing you may notice is that there is no cooling," said Manna. "There is no torque converter and no cooler required. The heat that's created by the AS Tronic is from the turning of gears inside the transmission.

"As EPA tightens its engine emissions, the engines are going to run hotter and hotter and so this is a significant feature."

The AS Tronic transmission allows drivers to select between automatic and manual modes using a touch-pad shifter, eliminating the need for a manual clutch. In automatic mode, the transmission shifts automatically, allowing the operator to keep both hands on the steering wheel. The electronic control system selects the shift points and can recognize driver characteristics. If necessary, gear corrections can be made by the driver using the touch pad.

In manual mode the transmission shifts in response to the driver's request, with automatic clutch engagement or disengagement as required. The transmission automatically selects a starting gear, which the driver can accept or change through use of the touch pad.