ZF’s EcoLife six-speed automatic transmission includes start/stop functionality for city bus applications.
Fuel savings of up to 10% are achieved by automatically shutting off the engine when the bus comes to a standstill.
A potential obstacle when applying start/stop to an automatic transmission is providing instantly available traction on engine restart.
Nigel Marson, OE Account Manager at ZF Services UK, explains: “The start/stop function requires the gear shift elements to be filled with oil as soon as the engine restarts, so the bus can pull away immediately. One possibility is to use a supplemental electric pump to provide transmission oil pressure while the engine is in the start-up phase.
“However, ZF instead adapted the EcoLife hydraulic system to use pressure stored in the primary retarder oil accumulator. This way, the system does not require an additional electric motor in the driveline.”
Unlimited stops and restarts are possible.
