The technology used within starter motors and alternators has become more advanced in response to the installation of an increasing number of electrical components in vehicles. Matthew Beecham reviews some recent innovations in the rotating electrics arena.
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Although the electric starter motor and alternator 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. 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.
“With the growing interest of preserving the environment, miniaturization is required to contribute to better fuel consumption,” said a spokesman for Denso Corp. “Therefore, we believe that the demand for smaller alternators and starters will increase. Along with technologies relating to reducing size and weight, we believe that demand will increase for higher quality, environment friendly technologies.”
Integrated starter-alternator systems aim to balance out irregularities in the running engine and drivetrain, providing more comfort for the driver. Clever electronics do the trick here. They help to control the starter-alternator operating state, depending on the load and battery charge status. Features such as the stop-start function are a major attraction for potential car buyers. According to recent research studies, vehicles are at a standstill for one-third of the time while in urban areas. Stop-start systems help make cities quieter, boost fuel efficiency and reduce exhaust pipe emissions. They operate by cutting the engine when the driver comes to a complete standstill.
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By GlobalDataThe engine is switched back on when he/she releases the brake pedal. Although sales of Citroën’s C2 and C3 Stop & Start cars have been slow, such systems are an easy way for carmakers to reduce emissions and meet CO2 reduction targets.
There are basically two main alternative design concepts:
- Belt-driven ISG device—shaped like an alternator, this electronically controlled machine replaces the starter motor and alternator, providing an instant stop-start function for fuel savings up to 5%. Various refinements of this belt-driven device can boost economy further – such as brake energy regeneration and mild engine boost.
- In-line units—mounted directly on the crankshaft between the engine and gearbox. Although the in-line systems are more expensive – requiring a complete under-bonnet re-think — they offer more power, regenerative power from braking and even engine-assist ability under heavy load.
On balance, belt-driven starter-alternators have a number of advantages over crankshaft-mounted integrated devices, in particular cost. “Other than cost, the belt versus crank decision is determined by both the size of engine being cranked and the level of hybridisation required,” said Stuart Bird, senior manager, power train electronics, Visteon Corp. “Visteon has increased the size of engines that can be seamlessly started using a 12 volt belt ISG system. This was achieved via greater control refinement and from the experience we have gained working on a range of vehicle installations.
A potential evolution of the 12 volt ISG, to crank larger engines or achieve higher levels of generation towards micro hybrid, is the offset mount ISG. This could displace some previously assumed crankshaft mounted solutions but not all. Crankshaft solutions are likely to remain on large engine mild hybrid vehicles or full hybrid vehicles where the capacity of a belt-mounted or offset ISG is not sufficient.”
A few years ago, the push for 42 volts appeared to be main reason for introducing integrated starter-alternators. But, for many reasons, the momentum for 42 volts has reduced. A spokesman for Denso Corp told us: “ISG technology was developed in response to emission regulations such as the CO2 emission regulations in Europe, and high costs for hybrid vehicle systems compared to other systems. However, the stagnant momentum for 42 volt systems has diminished most of the factors that push further development for ISG.”
“Emissions regulations are certainly one of the major drivers now,” added Uwe Möhrstädt, senior manager, sales, hybrid drives business centre, Continental Automotive Systems. “The other thing is the development of fuel prices. The general tendency and forecast says fuel prices will continue to increase. The third point is the added value by driving dynamic.”
“We think the main factor driving technical change affecting the integrated starter-alternator centres on fuel economy of the vehicle, especially in commercial vehicles,” added Dr Frank Speck, senior manager, advanced engineering for commercial vehicles, ZF. “Consequently, there is a strong focus on fuel economy. As we think that 42 volt power supply will not happen for some time, we are not interested in a system that is based on a 42 volt power level but instead we are working on systems with much higher voltage.”
For some time, ZF Sachs has been developing a crankshaft-mounted starter-alternator generator. During braking, the system can regenerate electrical current and feed it into the vehicle’s electrical system. When the driver puts his/her foot on the accelerator pedal, DynaStart operates as an engine booster. By means of the braking energy already stored, the crankshaft starter-generator – now working as an electric motor – helps the combustion engine to put out more torque. “The main benefits of DynaStart are the quick and smooth [engine] starting. The fuel consumption benefits will be about 10%,” said Michael Wetzel project and product manager, hybrid division, electric drives (light vehicles) ZF Sachs. “DynaStart is currently is series development phase so we are doing that together with a large [unnamed] car manufacturer. It will be most likely be possible to buy a luxury car with DynaStart at the end of 2008 or early 2009. Our intention is to launch [DynaStart] in the luxury class segment, then spread this system into the mid class and light commercial vehicles segments. It would be a system that would also benefit light commercial vehicles for fuel consumption because of high rates of start-stop. That could happen between 2009 and 2011.”
Meanwhile, Visteon has developed a belt-driven system that can be fitted to almost any vehicle engine. The so-called SpeedStart12 is a compact unit measuring roughly the same size as a medium frame alternator. By incorporating the motor and power electronics in the unit the SpeedStart12 is made especially compact and requires only an upgraded belt-drive system and a 12-volt VRLA battery designed for deep-cycle discharging and charging. Air cooling was originally considered for the unit, but given the typical 180°C under-bonnet temperatures of modern cars, water-cooling was adopted, and a simple T-insert allows it to run off the engine cooling system. Some vehicles may need a supplemental heat exchanger.
The most impressive aspect of the SpeedStart12 is its split-second re-start time, so that no matter how quickly the driver moves from brake to accelerator pedal, the engine always re-starts first. The engine also cuts out if the vehicle has not moved for 8 seconds, though as Visteon points out, each individual carmaker can tailor its own operating parameters for the system once fitted. Although based on 12-volt electrics, the SpeedStart12 can be re-designed to work with 42 volts. Bird added: “Speedstart has reached the point of being production ready. Visteon is working with the vehicle manufacturers to identify introduction timing for the technology.”
Although we have already seen some manufacturers introduce integrated starter-alternators, there are still a few obstacles to overcome before such systems become widespread fitment in cars. “Cost is still the main obstacle,” added Möhrstädt. “We have to consider two points. One is the system cost itself and the other is the integration cost that the car manufacturer has to cover. However we have to consider the differences of the various systems in the customer benefit. As we understand it, it is easier to integrate a belt-driven starter generator within existing powertrain. Most vehicle manufacturers are now reserving some space for integrated starter-alternator systems though there is an evolution to easier integrate the whole system into the drivetrain and covering with such system other customer benefit.”
While ISG technology represents a radical break from conventional rotating electric designs, its take-up will be gradual. “The market size for stop-start and micro-hybrid is a little more difficult to predict due to the slow down in the introduction of the technology,” said Martin Green, product marketing manager, Visteon Corp. “Our estimate of the market for stop start and micro-hybrids combined is 750,000 by 2010 and 1.5 million by 2015.”
Matthew Beecham
See also: Global market review of starter motors and alternators – forecasts to 2012 (download)
