Automotive Design


is said to offer a greatly improved driving experience through greater power, higher torque and better engine response. UniAir is a cam-actuated, electro-hydraulic valve train


system. For petrol engines, the UniAir systems enables throttle- free, continuously variable, software-based load control across the entire engine map. With diesel engines, regulation of the temperature of the combustion chamber is achieved via the precise control of exhaust gas recirculation rates. At the same time, the effective compression ratio in the cylinder can be varied and homogeneous combustion ensured. According to Schaeffler and Fiat, UniAir allows, for the


first time, not only variations in the valve stroke, but also in the opening and closing of valves several times during one cycle, at different points in time. Importantly, UniAir enables car engines to be downsized.


Low friction engine components


Schaeffler has also been working with Porsche in a project to reduce friction in engine components and throughout the powertrain. Visitors to the recent ATZ/MTZ Congress in Esslingen, Germany, saw the CO2


提供保护 ncept-10% concept vehicle,


which is based on the V8-engined Porsche Cayenne. In the joint development, Schaeffler was responsible for the design and testing of components, while Porsche managed system co- ordination and validation for the entire vehicle. In the CO2


ncept-10% concept vehicle the engine accounts


for 5.8 per cent of the optimised fuel consumption and associated CO2


emissions. Most of this (4.1 per cent) comes


from modification of the VarioCam Plus valve control system, by replacing hydraulic cam timers with electromechanical equivalents, as well as the use of optimised switching tappets on the intake side. An extra 1.7 per cent reduction is achieved through minimising frictional losses and by cross-system optimisation of the valve train, belt drive and chain drive components. Schaeffler’s double-row angular contact ball


bearings, which are installed in the front and rear axle differentials, account for a further 1.1 per cent in fuel savings (Fig. 1). Additional savings have been made via the chassis: by replacing the hydraulic roll stabiliser with an electromechanically controlled equivalent, and by using lower-friction wheel bearings to deliver a 3.2 per cent reduction in fuel consumption. As a further example of friction-


reduction technologies, NSK recently announced a low-torque bearing that offers a 50-60 per cent improvement in frictional losses compared to conventional bearings, thereby helping to improve fuel efficiency. It might have been assumed that it would be difficult to achieve further reductions in the torque loss of ball bearings beyond the current state of the art, yet NSK has achieved this by dramatically reducing the number of balls and by optimising the ball diameters, race dimensions and clearances. Losses have also been reduced by using specially shaped resin cages to agitate the lubricating oil during operation. This bearing technology will be adopted first


Fig. 2. CPT’s Variable Torque Enhancement System (VTES), which is a fast-acting electric supercharger.


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