You naughty boy Steve, I can't believe that The Prince was that cavalier about testing and durability...or was he?
One of my last bits of work for a certain manufacturer was an investigation into battery warranty, with a view to how stop/start was going to affect the status quo.
Knowing nothing of the systems was a good place to start.
The existing warranty situation was, in my view, appalling. Partly down to long vehicle storage times off the end-of-line, but partly due to too much development work being done on the assumption of high state of charge batteries. I don't think a realistic enough analysis of customer usage cycles had been done. Ever.
My colleague and I also found that there was a disconnect in terms of the cranking capabilities of modern pre-engaged starters and the cut-off voltages of various OEM ECUs. A 1.6L gasoline system could carry on cranking at voltages so low that the ECU would either shut down or cease to be able to keep relays and driver stages functioning.
So, a customer could key-on and crank, and expect the engine speed to support a start, which would not happen.
Automatic manual transmissions are also a potential cause of problems. I saw one system where, once the battery voltage fell to a certain level, the control system for the gearbox started shuffling actuators about to re-register actuator positions and the consequent 40A(!!) current draw was pulling the battery even lover and, as above, still allowing the engine to crank but with no obvious ECU activity and no start.
I think that, if the vehicle has a belt drive 12v integrated starter/generator, or a flywheel starter generator, start-stop has better prospects than systems based on a beefed up pre-engaged starter system.
This still doesn't get away from the fact that vehicle OEMs want to spend less on stuff like batteries and save weight for emissions and economy, the result (for some OEMs) being a battery with about 18 months lifespan in stop/start+autobox systems.
Bill
