An SUV crossover concept demonstrator developed by Schaeffler Group North America is undergoing a phase-two technology makeover, aimed at achieving a 35-mpg combined city/highway rating. The demonstrator is based on a 2013 Ford Escape, which in production trim carries a 24-mpg combined rating equipped with AWD, 2.0-L EcoBoost engine, and 6-speed automatic transaxle.
“In essence we’re taking all of the mechanical optimization efforts from the first part of the project and adding electrification to the vehicle powertrain to meet the 2025 CAFE (corporate average fuel economy) requirements,” said Philip George, Director of Advanced Development for Schaeffler Group North America, during the company's recent technology symposium in Detroit.
In the project’s first phase, the Escape underwent friction-reducing alterations to the valvetrain and balance shaft as well as the addition of a thermal management system. The demonstrator also was fitted with low-rolling resistance tires from Continental. Schaeffler’s AWD disconnect clutch, permanently engaged starter, and latching valve rounded out the phase one retrofit (see http://articles.sae.org/12740).
“We met 2020 CAFE targets with the mechanical optimization. That part of the project was really the lower-hanging fruit,” George told Automotive Engineering.
The package of phase one technology solutions on the so-called Efficient Future Mobility North America demonstrator vehicle are estimated to cost less than $40 per percent of fuel economy improvement, said Jeff Hemphill, Schaeffler North America's Chief Technology Officer.
Cleverly designed accessory drive
Phase two’s vehicle modification start point is a 48-volt parallel hybrid system. The demonstrator will retain phase one’s torque converter-equipped automatic transmission and the 2.0-L combustion engine. In explaining the phase-two technology strategy, George noted that “Electrification is a more expensive solution, but we feel it is necessary in order to meet the 2025 CAFE regulations.”
One of the notable phase-two changes is a new approach to the engine's front-end accessory drive. For proof-of-concept purposes, the accessory-drive components will remain in a conventional layout, with the power flow routed from the transmission to the belt drive, George explained. The belt drive uses a Schaeffler-designed pendulum tensioner.
“Because torque is either put into the motor-generator unit or it’s taken out of the motor-generator unit, the slack side of the belt changes depending on the vehicle’s operating mode," George noted. "This unique belt-tensioner system is a less complex way to manage the front-end accessory drive versus a typical production application that uses multiple tensioners.”
A novel Schaeffler clutching system will enable coupling or decoupling of the accessory chain from the transmission’s power-flow. In a disconnected mode that will allow the water pump, A/C compressor, and other accessories to be powered electrically. Because the system taps into the input shaft of the transmission, the engine can operate independent of the accessory chain.
“Because we now have electric power that can be used to drive the transmission pump, we will not need a separate pump to keep the transmission alive as you would with a normal hybrid system,” George said. A single pump will be used for engine-powered operation as well as electrical operation of the front-end accessory drive.
The motor-generator unit will be able to recover kinetic energy directly from the vehicle independent of engine operation. Excess energy will be stored in a 48-V, 1 kW·h lithium-ion battery and used as needed for either boosting or load-point shifting to improve overall powertrain efficiency.
The front-end accessories could be re-located in a production application. Schaeffler Group's proposed production layout arranges the components side-by-side along the width of the engine, George explained, rather than clustering them around the front-end. "The water pump, transmission pump, motor-generator unit, vacuum pump, engine oil pump, and air conditioning compressor components could be packaged in an axial arrangement,” he offered.
Such an atypical accessory component layout would more easily accommodate vehicle model variants, whether a dual-clutch, continuously-variable, planetary automatic, or manual transmission is used.
“Customers have asked, ‘Do I need two different types of engine dress now, one with accessories organized for the transmission driven arrangement and another one for a normal system?’ If you have a row of accessories that are connected on a common shaft, it’s possible to use a simple stretch belt from the crankshaft to the alternator if you’re not doing the hybrid part of it,” said George, adding, “You can then power the accessory chain in the conventional flow off the crankshaft nose.”.
Study results due in January
The electrification retrofit of the concept demonstrator is targeted to wrap in late 2014. Meantime, Schaeffler Group engineers are working on the control systems and software development.
"We have a lot more things to manage in the powertrain in order to integrate intelligently the systems that we had from phase one with the new things from phase two,” George noted.
Initial phase-two study results are scheduled for release during media days (January 12-13) at the 2015 North American International Auto Show. Said George, “We expect to be working on calibrations and various system refinements during the first and second quarters of 2015.”