Although the electric starter motor and alternator – commonly known as rotating electrics – has remained virtually unchanged since it was first invented over 80 years ago, the quest for weight and fuel reduction has triggered a raft of refinements. Magnetically geared starters continue to outweigh the non-geared, pre-engaged type because of pressure of size and output.
While a starter motor looks like a commodity product, appearances are deceptive. The motor has undergone major technical advances in an effort to improve longevity, offering more power as well as reducing both weight and costs compared to earlier generations. Significant advances in alternator specifications and performance are also under way, including new compact alternatives, and a new generation of starter motors is focusing on reduced dimensions. Over the last decade there has also been an increasing proliferation in the types of alternator available. Like starter motors, they are lightweight in construction with higher outputs and better reliability than ever before. In the 1970s, a starter motor weighed about 12kg; it now weighs in at around 5kg. For example, a major thrust of R&D at Denso is concentrated on ways in which to increase the magnetic flux density in starter motors to produce a smaller unit with high power output. Some of the technical advances by the major alternator manufacturers to date have also centered on addressing environmental, noise and high underbonnet temperature concerns.
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The increasing use of power-hungry options in modern passenger cars, such as heated seats, quick-defrost glass, electrically powered brakes, steering, water pumps, heated catalysts and advanced powertrains, is placing unprecedented demands on automotive charging systems. The traditional Lundell-type alternator is unable to handle loads of this scale, especially at idle speeds and looks set to be replaced by new machines that are 20% more efficient and significantly quieter.
New units currently under development by both major manufacturers and small independent R&D companies are capable of generating between 90% and 100% of their rated amperage at idle speeds. For some time, manufacturers have been focused on combining the starter motors and alternators. This was partly to provide the 4kW of electrical power that cars are forecast to demand over the next few years, and partly to optimise energy storage, engine starting and electricity generation into a single high-efficiency, lightweight and lower-cost package. Integrated starter-alternator systems aim to balance out irregularities in the running engine and in the drivetrain, providing more comfort. Clever electronics do the trick here. They help to control the starter-alternator operating state, depending on the load and battery charge status. A regenerative braking function allows low-consumption stop-start, as well as acceleration support when moving off from a standstill or under peak-load conditions. Features such as the stop-start function (which results in better fuel economy) will be a major attraction for potential car buyers.
There are two main alternative design concepts:
- belt-driven devices, which require little change to vehicle designs, can
generate up to around 5kW and can offer stop-start running; and - in-line units, mounted directly on the crankshaft between the engine
and gearbox.
Although the in-line systems are more expensive, theyoffer more power, regenerative power from braking and even engine-assist ability under heavy load. While belt-driven units are said to be cheaper, they produce less power and have the potential to save less fuel than in-line units. Given this scenario, some industry analysts predict a rosy future for the in-line system. They reckon that such crankshaft-mounted starter-alternators will become the preferred technology for 42-volt applications. In 2010, over 5% of starters and alternators are expected to be crankshaft-mounted, and this is expected to rise to 27% by 2015. We believe it is too early to say which technology will win out. While an in-line unit has its obvious advantages, it would mean major revisions to the vehicle platform and floor pan, whereas belt-driven units can be installed in the existing engine compartment without any major changes.
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By GlobalDataThe most promising market for the combined starter-alternator system is said to be in the C-segment market, though with the advent of 42-volt electrical systems, they are likely to become much more widely used.
Market trends
Given that small and compact cars are less prevalent in North America than they are elsewhere in the world, the stop-start system will be marketed mainly in Asia, Europe and South America. Another reason is the greater importance of fuel economy in those regions. Fuel prices in the US are less than half that in other countries. With a stop-start system, drivers can expect an approximate 5% improvement in fuel economy. The stop-start system also helps vehicles meet the stricter emission standards in force in Europe.
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According to a recent report in Automotive News Europe, PSA will begin introducing stop-and-go technology on its model range from late 2004. The vehicle maker calls the approach ‘mini hybrid’ and says it will help cut CO2 emissions 5% – 7% by stopping the engine when the car comes to a standstill.
PSA says it will also launch its DYNActive integrated starter-alternator between 2005 and 2007. This so-called mild-hybrid solution is expected to cut CO2 emissions by 8% – 15%.
Continental expects one million vehicles to be equipped with integrated starter-alternator units (all technologies) by 2006, rising to about ten million by 2010 worldwide.
All the major manufacturers of rotating electrics are developing starter-alternators for the 42-volt systems. Some newcomers have also entered this competitive arena, namely ZF Sachs, Continental and Siemens VDO. All three have opted for the novel in-line system. Continental-Teves is developing an Integrated Starter Alternator Damper (ISAD); Siemens VDO Integrated Starter Generator (ISG), whilst ZF Sachs is developing its Dynastart system.
Meanwhile, Valeo is developing its integrated starter alternator (ADI); Dana, a 12-volt starter-alternator known as RapidStart; and Visteon, an Integrated Starter Alternator (Visa). Ford has been developing its Explorer mild-hybrid vehicle featuring an Integrated Starter Alternator (ISA), an automatic transmission and electrohydraulic brakes. Volvo and Ricardo have also formed a partnership to develop a diesel mild-hybrid vehicle. Ricardo’s 42-volt ISA will boost the torque of the engine similar to that of a 2-litre diesel and is claimed to produce 6kW in the alternator mode.
