ei8htohms
8555
it's a little complicated
Hi Choup,
This is a fairly technical subject and to properly answer would require quite a bit of text and pictures and, frankly, the more I say about it, the more likely I am to say something stupid. In the interest of brevity (for my sake and yours) as well as protecting my fragile ego, here's a very short overview of the most common systems employed by integrated mechanical chronographs.
The most traditional chronograph arrangment is the transfer wheel. It generally involves an auxiliary wheel mounted on top of the fourth wheel. The auxiliary wheel (sometimes called a drive wheel) gears directly with an intermediate chronograph wheel (sometimes called a transfer wheel) mounted on the chronograph lever. When activated, the chronograph lever moves laterally and engages the intermediate chronograph wheel with the chronograph wheel in the center of the movement. The chronograph wheel has a long arbor that passes through the center of the movement and carries the chronograph seconds hand.
This is the oldest (to my knowledge) and therefor most "classic" type of chronograph coupling and is used in a variety of Lemania chronographs including the Omega Speedmaster movements (manual wind versions and a few of the weird mid-period automatics), the Lemania 2310 (used by Patek, Vacheron and Breguet), the Lange Datograph and Dato-split and countless other historic and current movements, high-grade and otherwise.
The second most common chronograph engagement currently (the seconds as in, the second one I'm discussing, I don't really know how to rank them in terms of actual "commoness") is the vertical clutch coupling. It involves a complex, compound chronograph wheel with a friction coupling built into it. The fourth wheel is free floating on the chronograph wheel when the chronogaph is off, then when the chronograph is engaged, the (vertical) clutch is released and the chronograph wheel begins to turn with the fourth wheel.
This is a very reliable, robust mechanism and, although the chrono wheel itself is pretty complicated, the rest of the chronograph mechanism is relatively simple and requires fewer adjustments to work well than traditional chronographs do. This system was invented by Pierce (with only moderate success from what I understand) but refined and made reliable and mass producable by Citizen and Seiko in the 60's. The Piguet 1185 uses such a system and has been around since 1988, used extensively by Blancpain, but also a host of other high-end brands including Audemars, Vacheron, Franck Muller, etc. Rolex's new Daytona movement (dating from 1999) uses a similar mechanism as do a couple of Lemanias (like the famous if crude 5100). The latest JLC movement of course is also a vertical clutch design.
Another very popular chronograph coupling mechanism is the tilting (rocker) pinion approach. It involves a pinion permanently engaged with a wheel (usually the fourth wheel) on one side, that leans to the side when disengaged. When the chrongraph is activated, the pinion is made to stand up straight where it engages with the chronograph wheel.
This is a also a very reliable and robust system and generally cheaper than a traditional transfer wheel to produce if not quite as functionally elegant as a vertical clutch. It's reliability (and inexpensiveness) is evidenced by the fact that this is the system employed by the ubiquitous ETA 7750, undoubtedly the most popular mechanical chronograph movement the world has ever seen. A similar system is employed in the recent high-end offerings from Seiko (and Credor) as well as the mono-pusher chronographs from Ulysse Nardin and Cartier (among others).
As I said, those are the three most common mechanisms for integrated chronographs. Modular chronographs are becoming more and more common as well, but I don't really have the faintest idea how they work.
_john
General question on the different types of chronograph
