In gear for automation
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The design of the synchromesh gearbox has not fundamentally changed in more than 60 years, and most recent developments have been concerned with gearshift control systems rather than the gearbox itself. Has the manual gearbox had its day?
by Toby Clark
• ZF has been working on improving synchromesh gearbox design for more than 60 years—and it shows.
An early Ecosplit 16-speed box from 1979 had a torque rating of 1,300Nm and weighed 380kg. Some 20 years later, torque ratings are up to 2,700Nm but the latest box weighs just 310kg. Now, according to Dr Manfred Schwab, who is in charge of truck driveline technology at ZF's Friedrichshafen headquarters: "We are waiting for the 3,000Nm engine."
At the moment ZF is putting most of its effort into ASTronic; the electronically-synchronised 16-speed range could last for the next 20 years. The box was designed to allow fully automatic operation: "Even a very good driver has deviations from his best perfor
mance—we can narrow this range," says Schwab. But it has been initially adopted by Iveco as the EuroTronic (see road test, page 28) in semi-automatic form. "We think that was a very wise decision," says Schwab. "You need to gain the acceptance of the driver and going straight to a full auto could have been too big a step."
Bandwagon
Iveco's exclusive European rights to the box are over now, but apart from Isuzu in Japan no other truck builders have jumped onto the AS-Tronic bandwagon. The initial cost is a little frightening—at the moment, around twice as much as an Ecosplit—and this is a problem. "Costs are a major driving factor for development— we are still in a phase where unit costs dominate. But we try to bring in lifetime cost," says Schwab. For example, ZF has released a CD-Rom which allows users to estimate the likely running cost benefits of its Intarder—and the firm now claims to be the largest retarder manufacturer in the world.
The AS-Tronic should reduce costs, because it includes a very sophisticated clutch control system. In fact, in the German market Iveco is giving EuroTronics a clutch-life warranty of 800,000km. More than 5,000 boxes are in service, with no real problems, and a fully automatic variant is being tested.
Manufacturers
Perhaps ZF's second-generation AS-Tronic will persuade other truck manufacturers. The 16AS2301 will be launched at the Hanover Show in September. It will feature helical gears to reduce noise; the Ivecoonly 16AS2200 has straight-cut gears but a fully encapsulated position. It also has a betterintegrated electronic control module cooled in the gearbox oil flow—and a higher torque rating of 2.300Nm (1,6961bft).
A similar 10-speed, the 10AS2301, will be announced for PCV applications.
Another launch at Hanover will be Ecomat 2, the latest version of ZF's torque-converter/ epicyclic automatic gearbox, which will be EDC and CAN bus-compatible, with electrohydraulic control, mechanical refinements and electronic retarder control (see
Technology Update, CM 28 July).
What about smaller gearboxes? There is a marketing problem; the initial on-cost of automation is similar to that for larger boxes. How ever, "There will be a similar development as for hea vy trucks—an automated manual box makes even more sense for distribution than for haulage," says Schwab. "But within five years we will see a lightweight ZF six-speed box in the 900-1,200Nm range, with an automated clutch and perhaps a fore-and-aft gearlever. The driver will select the gear rather than engaging it."
So why hasn't ZF made any impact on the US truck market? According to spokesman Bert Ettwein: "We are waiting for Eaton and Dana Spicer to educate the market regarding synchromesh gearboxes." So there are no Ecosplits or Ecomids in North America.
But Ford's 17-Series pickup—the best-selling range of vehicles in the world—now uses the Ecolite S5-42 gearbox, to the tune of 80,000-100,000 units per year. And, according to the marketing department's Michael Stork: "Our major competitor is not Eaton-it's the vertically integrated manufacturers."
Volvo, Scania, Renault, and of course Mercedes, still make some or all of their own gearboxes. "These gays think that transmissions are much more important than axles," says Stork They are a major element in product differentiation, but can this state of affairs last?
Transmission
Maybe not—ZF has agreed to take over RVI's Boutheon transmission plant, and is making the Ecomid there.
Within two to three years RVI will cease production of the B9/B18 range of heavy synchromesh gearboxes, to be replaced by the Ecosplit. And the heavy development costs of components may force other manufacturers to switch away from their own transmissions. If vehicle manufacturers have to develop new automated transmissions, like AS-Tronic, then we may have a chance," says Stork.
And the truck builders may not lose their individual identities; after all, if you adopt an electronically controlled gearbox, giving it a unique control interface is relatively simple.
• ZF recognises that the conventional synchromesh gearbox has many years of life yet, but says there is still room For improvement.
"Our goal is to come as r close as possible to a pas\ senger car in terms of shift force," says Dr Manfred Schwab, in
charge of truck driveline technology at ZF's Friedrichshafen headquarters. Alternative materials and designs can help, but a high-torque synchromesh gearbox will always require a certain amount of force to shift.
This is where the Servoshift system comes in: the shift lever is connected by a standard rod linkage—rod, cable or hydraulic—to the gear selector shaft, but it is supplemented by a pneumatic servo-actuator. This senses the force being applied and adds enough to accomplish the shift. The truck manufacturer can arrange the geometry of the linkage to reduce the manual force required, or the gear lever throw, or both. A typical setup reduces shift force by 60% and lever throw from 125mm to 80mm—and reduces in-cab vibration due to the gearbox.
Servoshift needs only one air connection, no modification to the engine or wiring loom is required, and it still allows normal shifting if the system fails. It is now built into the 16-speed Ecosplit gearbox itself; an earlier shift-assist system—as fitted to current Ecosplit-equipped Nino chassis—was a separate unit. CM drove an MAN 19.463 tractive unit fitted with the latest system around a route of stop-start urban roads and twisty hills. The MAN is so powerful that not too many shifts were necessary, although it was laden to 40 tonnes. But the difference in shift forces was remarkable. As a bonus, shifts Felt more certain than before. The Servoshift system was turned on or off for comparison and after a few minutes with shift assistance switched on you wouldn't want it any other way. • The system will debut on the latest MAN F2000s at the Hanover Show.