Automotive Design
by Toyota for its latest Prius, but NSK expects to see further sales to manufacturers of hybrid vehicles outside Japan. Improving the efficiency of a vehicle when it is moving is
clearly important but, when being driven in towns and cities, vehicles spend a considerable amount of time not moving. Start/stop technology has become available on standard production vehicles from a number of manufacturers, with typical start/stop systems delivering fuel consumption improvements in the range five to 10 per cent, depending on the driving conditions. . An innovation from Valeo is the StARS (Starter Alternator
Reversible System) micro-hybrid system that is said to offer emissions reductions of up 25 per cent in heavy urban traffic, with the benefit for automotive manufacturers of no radical changes being required to the engine architecture. In the latest development, SKF has supplied a new magnetic sensor bearing for StARS; this provides a powerful magnetic field that enables the bearing to function effectively under severe running conditions, including high temperatures and speeds. Furthermore, the accurate and repeatable magnetic field makes it possible to gather data on the speed and positioning of the shaft. Valeo’s StARS technology is used in a number of vehicles, including Citroen’s C2 and C3 Stop&Start models, the Smart Micro Hybrid Drive model, and the Mercedes-Benz A Class and B Class Blue Efficiency Models. Further stop/start innovations have recently been announced by Controlled Power Technologies (CPT). Following the launch of its earlier stop/start technology, the company has now developed a second-generation
engine, but restarts took around half the time taken by a conventional starter motor (0-750rpm in less than 0.4seconds against a typical time of 0.75seconds). Operating with up to 86 per cent efficiency, which is significantly better than state-of-the-art conventional alternators, the SpeedStart system employs switched reluctance motor technology, thereby offering the advantages of simple construction, accurate control and very high power density and efficiency. The breakthrough, according to CPT, results in a system with the torque and power necessary to restart quickly, smoothly and more frequently, whether the engine in question is diesel or petrol.
Fast-acting electric supercharger
SpeedStart also forms one element of CPT’s power regeneration and engine-boosting concept (RegEnBoost). This concept integrates a Variable Torque Enhancement System (VTES) - which is a fast-acting electric supercharger (Figs. 2 and 3) - and an advanced Turbo-generator Integrated Gas Energy Recovery System known as Tigers. The three technologies are integrated within a powertrain electrical power network (PEPN) that also includes a dc-to-dc converter and an enhanced lead-acid battery that is optimised for fast energy storage and release. The combination of electronics, advanced battery technology and charging techniques ensures the system can deliver the required rapid charge and discharge performance while maintaining a stable 12volts for the vehicle’s main electrical system. The overall concept ensures long-term energy storage for
delivering short bursts of power to the VTES supercharger during acceleration and to the SpeedStart stop-start device during engine restarts. Conversely, short bursts of power can be absorbed by the SpeedStart generator for recharging the battery during vehicle deceleration. Power for the battery and VTES electric supercharger is not only supplied by the SpeedStart integrated starter/generator (ISG) but also by the Tigers exhaust-driven turbo-generator. The electronic controls supervise the optimal switching between the SpeedStart and Tigers electrical generators according to the driving conditions and regenerative power availability. CPT says the RegEnBoost system enables a typical family- emissions of less than 100g/km
sized car to achieve CO2
Fig. 3. A Fiat Punto demonstrator equipped with CPT’s VTES electric supercharger.
system that it says is more efficient and usable than the first-generation systems. This latest evolution integrates all of the power and control electronics into a single electric motor assembly and, by maximising the number of stop/start
events, the system aims to reduce fuel consumption and CO2 emissions significantly. The fully developed system also meets manufacturers’ requirements for a service life of 10 years or 250 000km (160 000miles), which is in line with automotive industry standards for major powertrain components. To demonstrate the technology, CPT has installed its SpeedStart system in a Volvo S40 equipped with a 2.0-litre common rail diesel. Not only was the SpeedStart system more than capable of coping with this high-compression diesel
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with a 1-litre gasoline engine but, when required, the system can deliver the same performance and in-gear acceleration of a 2-litre naturally aspirated powertrain. This CO2
level is
comparable to that of equivalent-sized full hybrid vehicles, yet it avoids the need for high voltages and the significant impact that a hybrid’s large batteries and traction motors have on overall vehicle cost, mass and packaging.
Kinetic energy storage system
The cost and size implications of the battery pack is certainly one of the factors holding back hybridisation of vehicles, but a new technology developed by Ricardo could help. The company has devised Kinergy, a high-speed, hermetically- sealed flywheel kinetic energy storage system with an innovative and patented magnetic gearing and coupling mechanism. According to Ricardo, the high power density and long-life potential of its Kinergy technology combine both simplicity and effectiveness, avoiding the need for
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