Combining Alternator and Starter Motor?
Discussion
I have been thinking about why don't car manufacturers not combine the 2, as they as essentially the same item(from my basic understanding of physics).
Power from battery turns it to start the engine, and the it taken over as alternator duty (disconnecting when the battery doesn't need topping up of course).
I'm sure someone more clued up in auto engineering can fill me in, but it seems there is a bit of cost saving/weight to be had there...
Power from battery turns it to start the engine, and the it taken over as alternator duty (disconnecting when the battery doesn't need topping up of course).
I'm sure someone more clued up in auto engineering can fill me in, but it seems there is a bit of cost saving/weight to be had there...
Alternator is totally different to a starter motor. A dynamo is more like a starter, but they're pretty s
te.
An alternator gives out 80A+, a good dynamo can output maybe 20A on high revs.
The brushes on a starter running backwards would wear out in a week, if it was being asked to run at up to 7000rpm+ backwards.
Straight cut gearing between the flywheel and the starter would whine like a stuck pig.
There's only a few reasons why it's a silly idea.
te.An alternator gives out 80A+, a good dynamo can output maybe 20A on high revs.
The brushes on a starter running backwards would wear out in a week, if it was being asked to run at up to 7000rpm+ backwards.
Straight cut gearing between the flywheel and the starter would whine like a stuck pig.
There's only a few reasons why it's a silly idea.
This is exactly how most mild hybrids work.
http://en.wikipedia.org/wiki/Start-stop_system
Citroen use it, and I think Audi do too.
http://en.wikipedia.org/wiki/Start-stop_system
Citroen use it, and I think Audi do too.
*Al* said:
Nice thought but i'm sure car developers would have looked at this a long time ago.
They have for a while, CO2 banding is now making it relevant, most systems are above 12V though so need expensive DcDc converters and thing likrle supercapacitors for the current demand. 12v system are currentky developing well though.It's a simple issue of torque.
The starter motor needs to provide something like 200Nm at the crank to spin the engine over. It does that by having a high ratio gear train (both the "big" gear of the flywheel ring gear and the small motor drive pinion, but also with an internal epicyclic gear train). The problem is that because of this large reduction ratio it can only get the engine to approx 150-200rpm before the electric motor reaches it's max rpm.
The alternator is fundamentally a high speed, low torque machine, that uses the belt to provide a gear ratio of approx 3:1. A typical alternator has a peak speed of approx 18krpm.
An electrical machine mounted directly onto the crank would have to produce a huge torque without the benefit of a gear system (and large torque = large current = large losses)
Several Tier1's have demonstated "belt ISG" (Integrated Starter Generators), like Speedstart ( http://www.cpowert.com/products/speedstart.htm ) and StARSv ( http://www.valeo.com/en/press-releases/details.htm... )
The serious issue is how to transfer the required torque via a belt system, which unlike the gears used by a starter motor (that only engage during starting at less that 200rpm) has to also operate at high rpm, and of course, get wet, damp, cold, frozen etc.
To date, the only applications for belt ISG's has been on small engined cars.
There are solutions to the issue of belt load, that can also deliver other benefits:
http://www.integralp.com/technologies/hybrid_techn...
The starter motor needs to provide something like 200Nm at the crank to spin the engine over. It does that by having a high ratio gear train (both the "big" gear of the flywheel ring gear and the small motor drive pinion, but also with an internal epicyclic gear train). The problem is that because of this large reduction ratio it can only get the engine to approx 150-200rpm before the electric motor reaches it's max rpm.
The alternator is fundamentally a high speed, low torque machine, that uses the belt to provide a gear ratio of approx 3:1. A typical alternator has a peak speed of approx 18krpm.
An electrical machine mounted directly onto the crank would have to produce a huge torque without the benefit of a gear system (and large torque = large current = large losses)
Several Tier1's have demonstated "belt ISG" (Integrated Starter Generators), like Speedstart ( http://www.cpowert.com/products/speedstart.htm ) and StARSv ( http://www.valeo.com/en/press-releases/details.htm... )
The serious issue is how to transfer the required torque via a belt system, which unlike the gears used by a starter motor (that only engage during starting at less that 200rpm) has to also operate at high rpm, and of course, get wet, damp, cold, frozen etc.
To date, the only applications for belt ISG's has been on small engined cars.
There are solutions to the issue of belt load, that can also deliver other benefits:
http://www.integralp.com/technologies/hybrid_techn...
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