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Permanently engaged starter generator with torque converter: makes starts seamless when quickly going from a decel to accel situation.
“We can achieve a 15% save at less than $40 per percentage of on-cost,” says Jeff Hemphill, vice president and chief technical officer of Schaeffler North America. He’s talking about a 15% fuel savings for OEMs that are trying to figure out the ways and means to achieve not only CAFE, but the European Union regulation that calls for carbon dioxide emissions of 95 g/km by 2020. He’s talking about an approach to modifying systems within an existing vehicle (they’re using a current-gen Ford Escape as their demonstrator) without wholesale powertrain replacement with massive electrification. Let’s face it: doing that would cost significantly more than $600 (i.e., $40 x 15).
What Hemphill and his colleagues have done is to take both a holistic look at powertrains as well as a detailed assessment of the ways and means improvements can be economically achieved.
For example, consider the balance shafts that are necessary for four-cylinder engines. “Normally,” Hemphill says, “they run in oil-lubricated bushings. We replaced them with rolling bearing elements.” He points out that because the shafts are spinning at twice the engine speed, there is a non-trivial amount of power that gets wasted in the bushings, so by making the switch to bearings, there can be performance improvements on the order of a 1% fuel savings.
Then there’s friction reduction technologies applied to direct-acting bucket tappets. Hemphill says that while there is still sliding friction involved, they reduce the amount by about 15% through the use of surface treatments. Again, 1%.
“A lot of things are system optimization,” he says. “You have to configure your system in a smart way.”
Smart like a thermal management system that replaces a conventional wax thermostat (on-off) with an active thermostat that, through connection via individual passages to the head, block, heater core, turbocharger, controls where hot and cold water flow. Again, 1%. (“Three percent,” Hemphill says, “in cars with less sophisticated thermal management.”)
Then there are start-stop systems. Hemphill says that they’re working on tech that is both economical and compact so that the systems can be proliferated across car lines, especially in the U.S. The geographic importance? Well, given that the majority of cars in the U.S. are fitted with automatic transmissions, which require continuous hydraulic pressure to operate, when the engine is shut off in a start-stop situation, the oil pressure is lost. So one solution is to use an electrically driven pump to maintain the pressure, a pump that is only used during the start-stop sequence. Schaeffler has developed a latching valve that is locked by a hydraulic pressure pulse before the engine stops; this means there is a small volume of pressurized oil stored, ready for the restart event.
On a larger scale (the latching valve is about an inch in diameter and an inch long), they’ve developed a permanently engaged starter. This is particularly useful in situations when the driver lifts from the accelerator, applies the brake, the engine shuts off, then the driver has a change of mind. “It takes about two seconds for an engine to go from running to zero speed, so if he lifts his foot from the brake and the engine is still coating down, you can’t push the starter gear into the ring gear.” So they’ve developed a system that is integrated into the housing of the torque converter that is based on a wrapped spring around the torque converter that acts as a one-way clutch. The starter pinion is always engaged with the ring gear. When the starter is activated, the clutch engages the torque converter so that the engine restarts. Once the engine is started, then the clutch is released. Hemphill points out that this is sufficiently compact for use in small front-drive vehicles. In the city driving cycle it provides about a 6% fuel economy improvement; adding in the highway cycle, the savings are on the order of 3 to 5%.
And speaking of connecting and disconnecting via a clutch, they’ve developed an all-wheel-drive (AWD) disconnect clutch that consists of a hydraulically operated synchronizer clutch that’s integrated on the input shaft on the power take-off unit (PTU) and electrically operated dog clutches on the rear axle. Hemphill says that this system allows reconnection to the AWD under more driving conditions than other systems on the market; fuel save is on the order of 5% combined and 8% on the highway cycle.
“We have a variety of hybrid and electric drive solutions,” Hemphill points out, lest it seem as though Schaeffler is only about modifying existing systems. Given the continued deployment of existing powertrains, the development that they’re making in terms of bearings, valves and clutches certainly can make a difference to both OEMs and their customers.—GSV