The concept vehicle is based on the current version of a mid-size SUV that is popular in North America and—as is the case with the majority of North American vehicles—features an automatic transmission with a torque converter. Schaeffler solutions such as a thermal management module and AWD separating clutch play a role as do Schaeffler’s engine start-stop technologies, such as the permanently engaged starter with a wrap spring one-way clutch.

The fuel savings improvements are the result of friction optimization work being carried out on belt drives and valve trains, as well as advancements to balancer shafts and wheel bearings—a mechanism for aerodynamically optimized closing of radiator grills—and the optimization of the torque converter.

AWD disconnect clutch. The new AWD disconnect clutch decouples the AWD drive train to minimize friction losses, and can provide a savings contribution of up to 6% (on the highway). The savings that can be achieved in city traffic are approximately 2%.

A conventional AWD system can increase the fuel consumption of a vehicle by up to ten percent if the friction losses in the drive train and the mass of the components are taken into consideration. Our AWD disconnect clutch reduces this additional friction by more than half by decoupling the secondary drive train and to improve its energy efficiency. Suppliers and the automotive industry have been working to uncover the smallest potential for optimization for many years. The AWD disconnect clutch makes a significant contribution to optimizing the drive train, which, in turn, helps automotive manufacturers meet the increasingly stringent fuel consumption standards.

—Prof. Peter Gutzmer, CTO of Schaeffler AG

Modern AWD vehicles typically have permanent all-wheel drive, in which the drive power for the rear axle is transferred to the wheels via the rear differential by means of a power transfer unit (PTU). In real driving conditions, one driven axle is sufficient to ensure safe and comfortable driving in most situations. During normal driving, the secondary axle is also engaged without transferring any force to the road via the rear wheels. However, a significant proportion of the energy is lost due to friction.

The Schaeffler AWD disconnect clutch decouples the drive train from the rear axle at the PTU. A second disconnection point is located in the rear axle to prevent torque from being transferred via the rotating rear wheels to the drive train, which is decoupled at the front of the vehicle. The AWD disconnect clutch comprises a hydraulically operated synchronizer clutch integrated in the input shaft on the PTU and electrically operated dog clutches on the rear axle.

The clutch located on the PTU has two functions: axial disk surfaces with a high friction coefficient are used to absorb synchronization energy; while a self- energizing, bi-directional wedge clutch supports high drive train torques. The disconnect clutch system includes continuous monitoring of driving conditions and the drive train environment to ensure lightning fast switches to AWD mode if required.

Stop-start system components. The concept employs two Schaeffler technologies to enable engine stop-start systems: a latching valve, which is controlled by pressure pulses; and a wrap spring one-way clutch for permanently connecting a starter to the housing of the torque converter.

Current ESS solutions are based on a two-stage multi-functional torque converter concept. In this concept, the engine and the transmission are decoupled when the engine is restarted. This allows the engine to be switched off when the engine is idling, which allows the vehicle to be driven for longer with the engine switched off to provide additional fuel savings. Electrically driven pumps and accumulators have thus far been commonly used to ensure a prompt engine restart even after the application pressure of the oil pump (driven by the internal combustion engine) has been lost—e.g. at a traffic light. However, when considering cost, benefits and design envelope, electric pumps and accumulator solutions are not ideal, Schaeffler suggests.

Instead, Schaeffler’s latching valve is activated by a hydraulic pressure pulse before the engine stops, which causes a small volume of pressurized oil to be stored in one of the transmission‘s switching elements for the subsequent start-up operation, thus allowing a more rapid closure and helping to ensure that the vehicle has the necessary acceleration capability. Since the signal is given hydraulically, there is also no need for plug connectors or wiring.

A further requirement placed on modern start-stop systems is a quick and comfortable engine restart. This applies not only to starting after an extended standstill period with the engine switched off, but also (and in particular) to so-called “change of mind” starts, i.e. when the driver quickly decides that she/he wants to accelerate again while switching off the engine.

Schaeffler’s wrap spring one-way clutch for permanently engaged starters is a solution developed by the company for integration into the housing of the torque converter. This allows fast and silent re-starting, and also supports additional functions, such as “sailing” or driving at high speeds with the drive train decoupled and the internal combustion engine off.

The permanently engaged starter generator encircles the torque converter by means of a wrap spring. This means that only a small amount of axial space is required. A spring-based, one-way clutch is used to engage the torque converter when the starter is activated. When the engine is running, it is decoupled from the torque converter (thus preventing wear) and the starter remains at a standstill despite being permanently connected to the drive train.

In addition to a considerable increase in comfort, due to the smooth engine start-stop function, and a significant improvement in “change of mind” situations (in which the engine is already switched off, but the driver quickly decides to drive on), this innovation helps to achieve fuel savings of up to 6% in city traffic.

Thermal management. Click to enlarge.

Thermal management. An additional 1% reduction in fuel consumption and an important emissions contribution can be achieved through the integration of a thermal management module.

The Schaeffler thermal management module is a temperature control unit for the entire drive train. It is integrated in a compact component manufactured from high-strength plastic and combines numerous functions. While engine temperature has traditionally been controlled in a rudimentary manner by a thermostat located close to the engine, this modern thermal management module controls the temperature conditions in the vehicle more precisely and enables operation in the optimal temperature window in the fastest possible time. This means that the cold running phase is significantly reduced by completely blocking off the cooling jacket.

Additionally, the individual components can be operated at higher temperatures than would be possible with a system controlled by a thermostat. The engine temperature can also be reduced under full load and the tendency for knocking and enrichment of the mixture under full load can be reduced.

The opportunities to increase efficiency by precisely controlling temperature range from the engine and heating system to the transmission and turbocharger. Controlling the temperature of alternators, hybrid modules and batteries is one of a range of possible tasks that can be performed by this sensor controlled component. They can also be efficiently cooled and heated according to requirements using the thermal management module from Schaeffler.

Precise control by means of a rotary slide valve enables the ideal temperature window for the engine and transmission to be reached rapidly. This has a positive effect on both the energy efficiency and life of components in the drive train. After cooling of the thermally stressed exhaust gas turbine can be individually controlled in the case of a turbocharger whose temperature is controlled by the thermal management module.

The individual components of the module are also optimized for reduced friction in accordance with Schaeffler’s energy efficiency requirements. This means that the thermal management module can be directly connected to the engine control unit without additional power stages due to its low power consumption.

The thermal management module also removes the design constraint of having to fit the component in close proximity to the engine block, as was traditionally the case with a thermostat located on the engine. Standardized, non-interchangeable hoses reduce assembly times and ensure a high level of seal integrity.