Next generation stop-start system

Controlled Power Technologies’ development of the world’s first bespoke belt-driven Integrated Starter Generator (B-ISG) to use a conventional 12-volt electrical system, and uniquely capable of starting a 2-litre diesel engine, will be demonstrated at the UK’s annual Low Carbon Vehicle Event being held at Millbrook Proving Ground this week (9-10 September 2009). The SpeedStart system has been designed from the outset for the purpose of stop-start and not simply engineered as a modification of existing technology.

CPT’s technical breakthrough has resulted in a unique 12-volt B-ISG with the high torque and power necessary to restart, quickly, smoothly and more frequently, most modern diesel and petrol engines. This means it can offer a more advanced solution to existing stop-start systems, which are all based on modifications to a conventional starter motor or conventional alternator. And it can do so without resorting to the high cost of developing a higher voltage system.

The production ready SpeedStart technology addresses three of the major challenges of existing stop-start systems; it is twice as fast as a conventional starter motor or alternator, the restart is exceptionally quiet and offers excellent refinement, and most importantly it is powerful enough to cope with a driver having a sudden change of mind when the stop-start system is already stopping the engine.

“One of the most challenging situations for a stop-start system occurs when a driver needs to move again at the same moment that a stop sequence has been initiated and the engine is already shutting down. This situation can arise many times at junctions, traffic lights and in crawling traffic. The stop-start system then has to re-crank the engine whilst at the same moment the driver is re-engaging the load of the vehicle mass through the clutch. This requires a high level of torque and power to be delivered almost instantly. To achieve this you need an electrical machine that can draw a high current into its windings. Existing stop-start systems simply cannot react fast enough,” comments Mike Dowsett senior manager for micro-hybrid systems at CPT.

“So long as stop-start technology can meet all the demands expected of it then we can confidently anticipate it becoming a standard fitment on all cars. The environmental feel good factor for motorists is very powerful when a car is stationery in traffic with the engine switched off and there are zero emissions. Yet, the market penetration of existing stop-start systems is only about 5 per cent and even with some forecasters saying this will reach 50 per cent these figures would seem to reflect the limitations of existing technology. The benefit-cost ratio of micro-hybrid stop-start technology is significantly higher than mild or full hybrid systems, so with the industry needing to drastically reduce its carbon emissions there really is every reason to anticipate a more widespread adoption of stop-start systems - providing the technology is up to scratch.”

Modern engine and transmission systems need little modification with the CPT SpeedStart system, which means that it can be introduced across a wide range of vehicle types. The additional benefit of SpeedStart’s high power generating capability means that the maximum advantage can be gained from intelligent regenerative charging during vehicle decelerations.

The SpeedStart system can deliver a 5 per cent reduction in fuel consumption and CO2 emissions over the New European Drive Cycle, but with the potential for even greater savings in real world urban driving situations when many more stop starts can typically be experienced. Unlike other systems whose control strategy will include inhibits that will avoid many potential stop-start events, SpeedStart can be activated more often thereby responding to many more fuel saving opportunities. And unlike existing systems SpeedStart can allow the vehicle to remain in gear when the engine cuts out, which is more natural for the driver and further facilitates a faster restart.

“Only by stopping the engine at every opportunity can the occasionally suggested 15-20 per cent fuel consumption saving in heavy urban traffic be realised,” says Dowsett.

The SpeedStart technology has been optimised for powertrains with gasoline engine displacements up to 3.0-litres and diesel engines up to 2.5-litres, thereby covering most vehicle segments. To demonstrate the technology CPT has installed its SpeedStart B-ISG system in a Volvo S40 equipped with a 2.0-litre common rail diesel engine, which it can restart in almost half the time required by a normal starter motor (0 to 750rpm in less than 0.4 seconds against typically 0.75 seconds).

CPT will also demonstrate in a Fiat Punto its VTES (variable torque enhancement system) electric supercharger, which boosts the performance of downsized engines and facilitates the trend to higher gearing. Downsizing or downspeeding is the most cost effective method for CO2 reduction but transient response at the lowest engine speeds may be disappointing and even turbocharged engines can be challenged to deliver the required performance. VTES eliminates any concerns about responsiveness and allows downsizing and downspeeding to be taken further, and the combination of these technologies can reduce fuel consumption by 20 per cent on a like for like performance basis.

“Small engines and higher gearing both reduce fuel consumption and carbon emissions, but drivers must feel confident that they can drive safely within the flow of traffic,” says Nick Pascoe chief executive officer CPT. “Our VTES supercharger can help deliver the required acceleration and driveability and it complements modern turbocharged diesel and gasoline engine technology. An electric supercharger can react instantly to high transient load conditions, delivering up to 25kW of additional power at the crankshaft in less than a second. That’s more than enough to compensate for any turbo lag and considerably more cost effective than adding a 25kW electric motor.”

It is the first time that CPT has taken part in a Cenex event and its CEO Nick Pascoe and engineering director Guy Morris will both be available to discuss the technology and other CO2 reducing initiatives being pursued by the company. Cenex (cenex.co.uk) is the UK's centre of excellence for low carbon and fuel cell technologies. It runs programmes and projects on behalf of the public sector designed to accelerate the introduction of low carbon vehicles.

Further information on Controlled Power Technologies is available at: cpowert.com.