According to recent research studies, vehicles are at a standstill for one-third of the time while in urban areas. Stop-start systems could 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. The engine is switched back on very quickly when he/she releases the brake pedal.
Go deeper with GlobalData
A few years ago, the push for 42-volts appeared to be main reason for introducing integrated starter generators (ISG). But, for many reasons, the momentum for 42-volts power-net brigade has been reduced. These days, the issue of fuel economy has become a major promoter of ISG following the European carmakers’ association decision to self-regulate CO2 emissions down to a fleet average of just 140g/km by 2008.
There are 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, they offer more power, regenerative power from braking and even engine-assist ability under heavy load.
The main manufacturers of belt-driven and in-line units are Valeo, Continental, Bosch, Siemens VDO, ZF Sachs, Denso and Magneti Marelli. Visteon has also joined the ISG market.
Visteon’s SpeedStart12 is a belt-driven system that can be fitted to almost any vehicle engine, and as the name suggests, runs on 12-volts. The compact unit measures 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 the 400-millisecond 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.
How well do you really know your competitors?
Access the most comprehensive Company Profiles on the market, powered by GlobalData. Save hours of research. Gain competitive edge.
Thank you!
Your download email will arrive shortly
Not ready to buy yet? Download a free sample
We are confident about the unique quality of our Company Profiles. However, we want you to make the most beneficial decision for your business, so we offer a free sample that you can download by submitting the below form
By GlobalDataIn March 2005, Matthew Beecham talked with Mike Dowsett, senior product manager, advanced powertrain systems about how SpeedStart12 evolved.
Mike Dowsett: The history of SpeedStart12 goes back several years. Visteon has been very active in 42-volts, hybrid and now ISG vehicles. However, 42-volts has been pushed back. That is mainly to do with cost, not functionality. The 42-volts vehicle that Visteon developed had excellent stop-start capability, regenerative braking and launch assist. All of which are extremely desirable by the European manufacturers. In fact, we were among the leaders of that 42-volts push for advanced vehicles. So functionality was great but the cost was just too expensive.
So coming out of the 42-volts demonstrations that Visteon carried out in Europe, we were given a challenge by several carmakers to produce a 12-volt stop-start vehicle that offers the same kind of functionality – i.e. a vehicle that operated on a 12-volt architecture that started very quickly, as fast as the 42 volt vehicle that we were demonstrating.
If we look at standard start times of a typical starter motor, there is a region of 0.7 to 1.5 seconds from when you press the button or turn the key to the point when the vehicle reaches idle. But if you used that starter for stop-start systems, the driver would feel very disappointed. There would be a delay in responding, the vehicle would be slow to pull away and the driveability would be classed as very poor. So we needed to improve that start time. And from all of the work that we have done in the past with hybrid and 42 volt vehicles, we know that that start time needs to be 0.4 seconds or less. That was our clear design challenge.
just-auto.com: What was the starting point?
MD: In order to do that, we had to evaluate many technologies. There are basically four main ways of achieving 12-volt stop-start.
You can use a conventional starter motor but they are slow and too noisy.
You can use a powered alternator – take a conventional alternator, change the rotor, add some magnets, some control electronics and then you can start the engine through the belt system using a powered alternator. Visteon has evaluated this very closely but decided that it wasn’t quite fast enough. It was much faster than a conventional starter but it still didn’t get it down into the start times that would make it an imperceptible start especially on mid to large sized engines.
We also developed and evaluated an in-line or crankshaft ISG – the crankshaft ISG gives a superb starting event—very quiet and fast but unfortunately, it’s expensive. In order to come up with a crankshaft or an in-line ISG that is mounted between the engine and the transmission, it is effectively a 1:1 drive ratio. It has a large amount of electro-magnetics. You would typically have to put the power electronics that control it remotely and extend the length of the powertrain by 30 – 40 mm. Consequently, it poses a problem to package in a European vehicle where there really isn’t much space under the hood.
And the fourth way of achieving 12-volt stop-start is to design a custom ISG that has one thing in its mind – to achieve a very fast and quiet start cost effectively — and that is the Visteon SpeedStart12 system.
So we started with a clean sheet of paper. We designed a machine that would give the sub-0.4 second start that would also give some of the extra power that 42-volts systems were going to deliver. The generating efficiency of SpeedStart12 is greater than 80%, compared to around 60% for today’s alternators.
j-a.com: When will it enter production?
MD: Our current plans are for it to enter production towards the end of 2007. But that really depends on the vehicle manufacturers’ target plans and requirements.
j-a.com: What is the fuel economy benefit of SpeedStart12?
MD: At the moment, we would say that 5% on the new European drive cycle is very achievable on most applications. A conservative figure, maybe, but unfortunately that is the only thing that we are measured against.
j-a.com: What are the prospects for the SpeedStart12 to be applied to diesel engines?
MD: Our design concept from day one was that this technology would always be applied to diesel engines. The Visteon SpeedStart12 system is more than capable of cranking most European diesels in exactly the same way it would do it on gasoline engines.
Probably the most significant factor of the Visteon SpeedStart12 system is that we are the highest power belt-driven 12-volt ISG. We have the highest cranking torque and the highest cranking power. And that is why we are able to crank the diesel engine. The other key factor is that all of our electronics are mounted into the non-drive end of the machine. We don’t have a separate electronics module that would require additional packaging space next to the unit. From a manufacturer’s point of view, it is very easy to install on a vehicle. There are no extra modules to package or cables to run.
The other design criteria we wanted to meet was develop a system that fits cross-car line applications. The SpeedStart12 system by its nature and design means that one system will fit many different powertains, right across the board, from gasoline to diesel. Because the connection to the system is via a belt, it is very flexible. So each European or Asian OEM that adopts this technology will only have to make small bracketry changes in order to fit it to their different powertrains. That will help the introduction of this technology, make it very easy for the manufacturers to fit it across car lines and get overall CO2 reductions from their fleet of powertrains.
