SHIFTING GEAR

摘要

Last month, we covered troubleshooting on modern AMTs (automated manual transmissions), and how understanding power paths, shift mechanisms, etc, is crucial for matching fault symptoms to diagnosis and delivering the correct, most cost-effective and speedy repairs. Here we move on to gearbox construction, looking at the detail of transmission shafts and gears, their splitter, range and overdrive mechanisms, gear shifting, synchromesh and the automatic clutch assembly. We also provide an update on modern transmission fuel-saving shift strategies, and the role and purpose of advanced gear control modes. Taking it from the top, hopefully we all know that even 16-speed gearboxes rarely have more than three main drive gears - the numbers being made up with dual ranges (doubling to six) and splits (doubled again to 12, including overdrive), plus potentially crawler (low and high) and then reverse (low and high). If the gearbox does not have a splitter (for example, a standard four-over-four with range change), there may still only be three gears, with fourth (and hence also eighth) achieved by mating the input shaft directly to the main shaft for a 1:1 ratio.