Schaeffler demo vehicle hits 2020 CAFE targets without electrification; 15% cut in fuel consumption; 48V hybrid system for 2025
27 January 2014
|Schaeffler Efficient Future Mobility North America demo vehicle in Detroit. Click to enlarge.|
At the North American International Auto Show (NAIAS), Schaeffler highlighted its range of fuel-efficiency technologies and systems in the form of its current demonstration vehicle: Efficient Future Mobility North America. Based on the current version of a popular mid-size SUV, the demonstration vehicle achieves the limit values specified by the CAFE standard for 2020 with no additional electrification of the powertrain.
The use and optimization of a range of Schaeffler technologies allowed the vehicle’s fuel consumption to be reduced by 15%. These values were initially simulated using Schaeffler calculation programs and verified by Schaeffler’s experts in North America using measurements and test cycles, and then certified by an independent testing institute.
|Contributions to fuel efficiency improvement. Click to enlarge.||Schaeffler technology reduces camshaft friction torque. Click to enlarge.|
The concept vehicle employs Schaeffler systems such as a thermal management module and all-wheel drive (AWD) disconnect clutch. Other solutions that are on board include Schaeffler innovations for engine start-stop systems such as the “permanently engaged starter generator” with a wrap-spring one-way clutch and a latching valve that allows the vehicle to be driven for longer with the engine switched off without the need for energy-consuming pumps.
Contributions towards the results were also made by the detailed friction optimization work carried out on the belt drive, the valve train and the balancer shafts, as well as the optimization of the torque converter.
Products such as the new AWD disconnect clutch, which decouples the unused drive axle from the powertrain depending on the driving situation and thus makes a savings contribution of up to 6% on the highway demonstrate the significant potential for reducing CO2 emissions that is still offered by the powertrain.
However, it is in city traffic that the “permanently engaged starter generator” with a wrap-spring one-way clutch really demonstrates its capabilities. In addition to a considerable increase in comfort in so-called “change of mind” situations (in which the engine is already switched off but the driver then quickly decides to drive on), this engine start-stop component allows fuel consumption to be reduced by up to 6% in city traffic. Further, a latching valve stores hydraulic pressure and provides automatic vehicles with energy for a faster start-up after the engine has been stopped.
Fuel consumption can be lowered by an additional 1% through the integration of a thermal management module, which allows the optimum engine operating temperature to be reached in the shortest time possible and the temperature balance, which also includes other assemblies like the transmission and hybrid elements, to be precisely controlled.
Meticulously detailed work and new solutions for powertrains based on internal combustion engines still offer significant potential for reducing fuel consumption and emissions. And the electrification of the powertrain additionally helps to operate the internal combustion engine in its optimum range and to compensate for weak starting performance, so hybridization will continue to make rapid advances. Start-stop systems are becoming increasingly widespread and are set to develop from conventional starters into systems that can even provide features previously only available in hybrid vehicles. And energy recuperation will become more and more of an issue as the performance of on-board electric systems and equipment increases—after all, a reduction in the vehicle’s fuel consumption and CO2 emissions can also be achieved if this energy is used to drive the vehicle.—Prof. Peter Gutzmer, CTO at Schaeffler AG
48 Volt System. Schaeffler’s product range also includes solutions for the electrification of the powertrain, including engine start-stop functions, hybrid clutches, hybrid modules, and drives for hybrid and electric vehicles.
Schaeffler highlighted its concept of a high-performance low-voltage power system in a 48 V System exhibit. These ideas also demonstrate how the CAFE standards for 2025 can potentially be fulfilled in a cost-effective way.
The central element is a compact 48-volt electric drive module that includes a clutch and planetary transmission, and can be placed either on the front or rear axle. This drive module paves the way for economical hybridization. The low-voltage design of the solution reduces the costs and outlay compared to high-voltage solutions with their associated requirements.
Schaeffler says that this hybridization allows significant advances to be made in terms of drive efficiency, as the 48-volt electric system opens up operational possibilities that were previously the exclusive domain of vehicles with high-voltage hybrid components. Even with a 48-volt system, a significant level of energy recuperation can be achieved—i.e. a high proportion of the energy released when the vehicle decelerates can be recovered and fed back into the battery. This recovered energy can be used for the supplementary electric drive, which in turn directly reduces the vehicle’s fuel consumption.
In addition to energy recovery, the generator with an output of up to 12 kW can also be used to drive the vehicle. This provides options including “crawling”—electrically powered driving in dense inner-city traffic—as well as moving off, driving at low speeds, and parking using electric power. Electric “boosting” during starting and electric sailing—a driving mode in which the electric motor ensures constant speed while the internal combustion engine is switched off—make a positive contribution in terms of fuel consumption and emissions.
|Schaeffler 48V module. Click to enlarge.|
The electric drive, which has an output of up to 12 kW, acts as the hybrid vehicle’s sole source of power when crawling. The electrically generated propulsion of Schaeffler‘s 48-volt drive module is also sufficient for driving in residential areas, parking garages, and other low-speed driving situations. This is also true of sailing, in which the electric motor ensures virtually constant speed across a wide operating range while the internal combustion engine is switched off.
The electric drive assists the internal combustion engine by providing additional torque, e.g. when moving off from the traffic lights—i.e., boosting. The high performance of the 48-volt system also means that the drive element opens up new potential for energy recovery.
Due to the higher recovery capability, the kinetic energy released during deceleration is now no longer converted into heat that subsequently dissipates, but is instead fed back into the on-board electric system in the form of electrical energy. The choice of two gear stages for the Schaeffler drive also provides further benefits when it comes to regenerative braking.
|Click to enlarge.|
The compact design of the cylindrical drive module means that it can easily be integrated into the powertrain, so it can be integrated into the architecture of the vehicle without having to reduce the volume of the trunk or the fuel tank.
Automobile manufacturers who decide to install a second low-voltage on-board electric system (48 volts in addition to the standard 12-volt system) can also integrate other suitable innovations into the vehicle. These include high-performance, rapid-reaction actuators for the chassis that allow the ground clearance to be regulated according to the situation during driving, which has a positive affect on the vehicle’s aerodynamics and thus on its fuel consumption.
In addition to the high performance due to the higher voltage range, the second on-board electric system also offers the advantage of smaller cable cross-sections. This saves weight and facilitates the integration and installation of the wire harnesses in the vehicle.
A range of other functions that push today’s standard 12-volt systems to the limit of their performance can be practically integrated into the architecture of a 48-volt system. These range from mechanical tensioning elements for 48-volt belt-driven starter generators and a number of electromechanical adjusting elements for the clutch, steering, roll stabilization and self-leveling suspension through to hybrid modules, axle drive solutions, and electromechanical torque vectoring units.
The use of a 48-volt solution provides an ideal entry-level hybridization that makes it possible to reduce fuel consumption and CO2 emissions by up to a further 15 percent thanks to significant energy recuperation. This entry-level hybridization is thus an economically attractive option that offers the essential advantages of a hybrid vehicle.—Prof. Gutzmer
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