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Written by Dan Carney
After the sales success of the compact, front-drive-basedCLA-Class sedan, Mercedes-Benz has migrated that car"s platform into thehotter-selling compact crossover market with the GLA-Class, the GLA250 and the GLA45AMG. These crossovers largely mirror their sedan counterparts, but the CLA45reflects unique changes due to the different dynamic of the taller body style and lessons already learned from the CLA45 and applied to theGLA45. CLA45 has so far represented 5 to 6% of CLA-Classsales in the U.S., according to AMG Product Manager William Vetter. GLA"s salesmix will likely be similar, he added. As in the CLA45, the GLA45 has a 355-hp (265-kW), 332-lb ft (245-N m),turbocharged, 2.0-L four-cylinder engine driving all four wheels through aseven-speed dual-clutch transmission (DCT) front transaxle with a power take-off sending a maximumof 50% of the torque to the rear wheels through a two-piece driveshaft. The engine"s block is sand cast aluminum with Mercedes" Nanoslidecylinder-liner technology, and the crankshaft and pistons are forged fordurability. The BorgWarner dual-scroll turbocharger ducts two distinctexhaust streams from separate pairs of cylinders to the impeller with the aimof spooling up the turbo early to its 26.1-psi (1.8-bar) maximum boost. Exhaust exitsthrough a larger 3-in (76-mm) diameter pipe that maintains that size all the way tothe tip. As with all AMG engines, the GLA45"s four-cylinder is built by asingle technician whose signature is on a plaque atop the engine. However,unlike previous AMG engines, this one is assembled at the company"s HungarianKecskemet factory rather than at AMG"s Affalterbach headquarters outsideStuttgart. The engine"s basic architecture represents one bank of thecompany"s new AMG GT sports coupe unit, Vetter pointed out, indicating that engine"spower potential. "You can imagine what we can do with the V8 if we wantto," he said. The GLA45 uses an active vane in the muffler to meter flow basedon throttle position, engine speed, and load condition. This is a technologythat will migrate to the S-Class and then proliferate through Mercedes" productfamilies, said Vetter. The variability permits free flow of the exhaust gas andallows for an exciting sound, without punishing occupants while cruising on thehighway at a steady speed, he said. "You can cruise in this without itbeing annoying." The GLA45"s electronic stability system features three drivingmodes to allow drivers more fun than the single mode of the GLA250"s system.The modes are On, Sport Handling, and Off.Torque vectoring uses braking applied to the inside rear wheel to send more powerto the outside rear wheel during aggressive cornering. On is the regular mode, while the sport setting permits driversmore leeway in enthusiastic driving before intervening. Off actuallymeans off, unlike some other systems that are only mostly off in that mode. TheGLA45"s Off mode, however does revert to On when thebrakes are applied because in that case the driver isn"t trying to add powerand may be in a sticky situation that needs addressing. The transaxle sends power rearward continuously. It is appliedto the rear differential by a hydraulically controlled clutch pack. In regulardriving, the clutch is disengaged, leaving the GLA in fuel-saving front-drivemode. When wheel slip is detected at the front, the clutch pack engagesto send as much as half the engine"s power to the rear wheels. Like the stability control system, the transmission also hasthree driving modes: M for manual, S for sport, and C for controlled efficiency. In M and Smodes, the engine management system coordinates with the transmission to retardignition timing and suppress fuel injection under full load for faster shifts.Along with the open muffler vane, the intent is to provide a sporty sound onthe upshift as we"ve heard with the raucous Jaguar F-Type"s V8 engine. Driversmay debate among themselves the success of that sound when produced by aturbocharged four-cylinder engine. The transmission features a race start function for maximumacceleration from a standing start, which contributes to the car"s speedy4.8-s 0-60 mph (0-97 km/h) acceleration time. In tepid starts during regular driving,the transmission can feel slow to engage at throttle tip-in, but Vetter saysthis is because of the very conservative baseline of the car"s adaptive shiftprogramming. It will engage the clutches more aggressively over time if that iswhat it learns the driver wants, he said. The company"s aim was to avoid the jerky, abrupt engagement thatcan turn off first-time DCT drivers who are accustomed to the creamy smoothnessof a torque-converter automatic transmission, Vetter explained. The CLA45 has unique chassis details too. The GLA"s engine sitsnearly 2 in (50 mm) higher than that in the CLA-Class, providing for additionalground clearance. That clearance is 8 in (203 mm) in the GLA250, but only 4.8 in (122 mm)in the GLA45 as a result of its 2-in (50-mm) lower ride height than the GLA250 andbecause of its front air dam and other aerodynamic parts. The GLA45 can even be equipped with front dive planes like thosecommonly seen on endurance racing sports cars and a rear spoiler atop its hatchthat appears aimed at attracting buyers graduating from the Subaru WRX. The GLA45 has stiffer spring and shock rates than the GLA250, butthey aren"t as stiff as those on the CLA45 because that car"s buyers reportedthat its suspension may be too stiff for their liking, according to Vetter."This car is more enjoyable to drive because it isn"t so stiff," hesaid. However, the available Performance Pack is 20% stiffer than theregular CLA45 setup. The GLA45"s brakes are four-piston fixed calipers from Brembo inthe front, squeezing larger 13.8-in (351-mm) rotors, compared to 12.6-in (320-mm) rotors onthe GLA250. At the rear, the GLA45 uses floating single-piston TRW caliperswith 13-in (330-mm) rotors in place of the 11.6-in (295-mm) units on the GLA250. With the AMG Driver"s package, these calipers are splashed withthe ever-popular red paint and are more visible thanks to the larger openings inthe 20-in wheels that replace the standard 19-in wheels. The GLA45"s top speed is electronically limited to 155 mph (250 km/h), butthanks in part to a slightly taller 4.13:1 final drive (compared to 4.60:1 forthe GLA250), it is only 2 mpg thirstier in the EPA"s combined rating, with anexpected city score of 23 mpg and highway rating of 29 mpg.
Date: 10-Oct-2014 01:00 EDT
More of this article on the SAE International website
ID: 1027
After the sales success of the compact, front-drive-basedCLA-Class sedan, Mercedes-Benz has migrated that car"s platform into thehotter-selling compact crossover market with the GLA-Class, the GLA250 and the GLA45AMG. These crossovers largely mirror their sedan counterparts, but the CLA45reflects unique changes due to the different dynamic of the taller body style and lessons already learned from the CLA45 and applied to theGLA45. CLA45 has so far represented 5 to 6% of CLA-Classsales in the U.S., according to AMG Product Manager William Vetter. GLA"s salesmix will likely be similar, he added. As in the CLA45, the GLA45 has a 355-hp (265-kW), 332-lb ft (245-N m),turbocharged, 2.0-L four-cylinder engine driving all four wheels through aseven-speed dual-clutch transmission (DCT) front transaxle with a power take-off sending a maximumof 50% of the torque to the rear wheels through a two-piece driveshaft. The engine"s block is sand cast aluminum with Mercedes" Nanoslidecylinder-liner technology, and the crankshaft and pistons are forged fordurability. The BorgWarner dual-scroll turbocharger ducts two distinctexhaust streams from separate pairs of cylinders to the impeller with the aimof spooling up the turbo early to its 26.1-psi (1.8-bar) maximum boost. Exhaust exitsthrough a larger 3-in (76-mm) diameter pipe that maintains that size all the way tothe tip. As with all AMG engines, the GLA45"s four-cylinder is built by asingle technician whose signature is on a plaque atop the engine. However,unlike previous AMG engines, this one is assembled at the company"s HungarianKecskemet factory rather than at AMG"s Affalterbach headquarters outsideStuttgart. The engine"s basic architecture represents one bank of thecompany"s new AMG GT sports coupe unit, Vetter pointed out, indicating that engine"spower potential. "You can imagine what we can do with the V8 if we wantto," he said. The GLA45 uses an active vane in the muffler to meter flow basedon throttle position, engine speed, and load condition. This is a technologythat will migrate to the S-Class and then proliferate through Mercedes" productfamilies, said Vetter. The variability permits free flow of the exhaust gas andallows for an exciting sound, without punishing occupants while cruising on thehighway at a steady speed, he said. "You can cruise in this without itbeing annoying." The GLA45"s electronic stability system features three drivingmodes to allow drivers more fun than the single mode of the GLA250"s system.The modes are On, Sport Handling, and Off.Torque vectoring uses braking applied to the inside rear wheel to send more powerto the outside rear wheel during aggressive cornering. On is the regular mode, while the sport setting permits driversmore leeway in enthusiastic driving before intervening. Off actuallymeans off, unlike some other systems that are only mostly off in that mode. TheGLA45"s Off mode, however does revert to On when thebrakes are applied because in that case the driver isn"t trying to add powerand may be in a sticky situation that needs addressing. The transaxle sends power rearward continuously. It is appliedto the rear differential by a hydraulically controlled clutch pack. In regulardriving, the clutch is disengaged, leaving the GLA in fuel-saving front-drivemode. When wheel slip is detected at the front, the clutch pack engagesto send as much as half the engine"s power to the rear wheels. Like the stability control system, the transmission also hasthree driving modes: M for manual, S for sport, and C for controlled efficiency. In M and Smodes, the engine management system coordinates with the transmission to retardignition timing and suppress fuel injection under full load for faster shifts.Along with the open muffler vane, the intent is to provide a sporty sound onthe upshift as we"ve heard with the raucous Jaguar F-Type"s V8 engine. Driversmay debate among themselves the success of that sound when produced by aturbocharged four-cylinder engine. The transmission features a race start function for maximumacceleration from a standing start, which contributes to the car"s speedy4.8-s 0-60 mph (0-97 km/h) acceleration time. In tepid starts during regular driving,the transmission can feel slow to engage at throttle tip-in, but Vetter saysthis is because of the very conservative baseline of the car"s adaptive shiftprogramming. It will engage the clutches more aggressively over time if that iswhat it learns the driver wants, he said. The company"s aim was to avoid the jerky, abrupt engagement thatcan turn off first-time DCT drivers who are accustomed to the creamy smoothnessof a torque-converter automatic transmission, Vetter explained. The CLA45 has unique chassis details too. The GLA"s engine sitsnearly 2 in (50 mm) higher than that in the CLA-Class, providing for additionalground clearance. That clearance is 8 in (203 mm) in the GLA250, but only 4.8 in (122 mm)in the GLA45 as a result of its 2-in (50-mm) lower ride height than the GLA250 andbecause of its front air dam and other aerodynamic parts. The GLA45 can even be equipped with front dive planes like thosecommonly seen on endurance racing sports cars and a rear spoiler atop its hatchthat appears aimed at attracting buyers graduating from the Subaru WRX. The GLA45 has stiffer spring and shock rates than the GLA250, butthey aren"t as stiff as those on the CLA45 because that car"s buyers reportedthat its suspension may be too stiff for their liking, according to Vetter."This car is more enjoyable to drive because it isn"t so stiff," hesaid. However, the available Performance Pack is 20% stiffer than theregular CLA45 setup. The GLA45"s brakes are four-piston fixed calipers from Brembo inthe front, squeezing larger 13.8-in (351-mm) rotors, compared to 12.6-in (320-mm) rotors onthe GLA250. At the rear, the GLA45 uses floating single-piston TRW caliperswith 13-in (330-mm) rotors in place of the 11.6-in (295-mm) units on the GLA250. With the AMG Driver"s package, these calipers are splashed withthe ever-popular red paint and are more visible thanks to the larger openings inthe 20-in wheels that replace the standard 19-in wheels. The GLA45"s top speed is electronically limited to 155 mph (250 km/h), butthanks in part to a slightly taller 4.13:1 final drive (compared to 4.60:1 forthe GLA250), it is only 2 mpg thirstier in the EPA"s combined rating, with anexpected city score of 23 mpg and highway rating of 29 mpg.
Date: 10-Oct-2014 01:00 EDT
More of this article on the SAE International website
ID: 1027
