The city bus automatic transmission ZF-EcoLife has hitherto been regarded as exceptionally fuel-efficient, powerful, and comfortable. Thanks to a special enhancement, these strengths are now even more pronounced, while also offering more practical functional benefits: A new electronic control unit developed in-house by the Friedrichshafen-based technology company ensures the advanced transmission system is guaranteed a long-term future.
An all-new transmission control unit lies at the heart of current and future innovations for the EcoLife with its six gears: “This now comes end to end from ZF – together with the software as well of course –, from development through to implementation,” explains Andreas Moser, Head of Axle & Transmission Systems for Buses & Coaches at ZF. The new control unit, which continues to be mounted directly on the exterior of the transmission, boasts twice as much computing power as the system used before.To provide greater connectivity, in other words networking options with other vehicle systems, it features an additional CAN bus. “This control unit allows us to implement customer-specific requirements and applications even more effectively and faster – while also creating a great deal of long-term leeway for EcoLife functional innovations,” stresses Moser.
ZF-EcoLife already stands out with one feature: ZF's ComfortStart system guarantees that buses on inclines and at stops, for example, do not inadvertently roll back. It maintains the bus firmly in position for seconds if required. ComfortStart notifies the driver whether and when they need to assume control again subsequently by gently decreasing the assistance. To this end, ZF has developed a special control strategy, which takes even highly dynamic situations in its stride – i.e. frequent changes between stop and go. The key aspect in this respect is that this convenience function is implemented purely by controlling an internal EcoLife clutch electronically. Consequently, ComfortStart works entirely without using the service brakes. “If the bus driver then presses the accelerator again, our electronics also intelligently coordinate all the other transmission clutches. Undesirable effects such as twisting in the driveline or moving off while braking are thus ruled out,” adds Dr.-Ing. Harry Nolzen, Head of Function Development Automatic Powershift Transmissions.
From the perspective of the ZF function developers, innovations such as ComfortStart illustrate another advantage: A unique advanced vehicle system, in this specific case the ZF-EcoLife automatic transmission together with a new high-performance control unit, is now sufficient to take over additional coordinating tasks when moving off. That in turn makes the applications themselves and their integration into the vehicle less complex – as well as speeding up the digital control process. The prerequisite for these and other improvements, however, still comes in the shape of a transmission mechanism like the one in the EcoLife, which can perfectly implement the increasingly sophisticated electronic commands.
Quiet, efficient gearshifts
The six speeds of the ZF-EcoLife allow for a close gear ratio spread and a high total spread of 12.6 – thus, the engine can be run in the low speed range in any operating condition. The standard control software TopoDyn Life shifts up as early as possible depending on the topography and the load. In practice, this reduces noise as the vehicle moves off at the bus stop – a process that tends to use a lot of power.
The reduction in engine speed significantly cuts fuel consumption and CO₂ emissions in particular: Compared with the last generation of the predecessor transmission Ecomat, the ZF-EcoLife including TopoDyn Life uses around five percent less fuel. Many other technical details help boost efficiency: A hydraulic pump, for instance, features on-demand control, which only provides the maximum output when driving with full power. In addition, the control software not only shifts into neutral when the vehicle is stationary at the bus stop, but also as the vehicle is rolling up to the stop at a speed below 12 km/h. As such, it is ensured very early on that the engine and brakes do not work against each other, thus impairing fuel consumption.
One graphic example illustrates the advances made by ZF with the electronics alone over the past few decades: Compared with the first electronic control unit for ZF bus transmissions made in 1978, the new unit is around 4.5 times smaller, measuring just 12 x 12 x 2 (L x W x H) centimeters – and still offers ample additional scope for new features despite the far greater range of tasks undertaken.