Peugeot reinvent the Dynastart !! (sort of boaty)

[Jcorstorphine]

Have just been trying to find out how my new 508 SW diesel engine “stop – start” system works. When you come to a standstill, the engine shuts down and when you take your foot off the brake it whispers back into life. However there is no noise from a starter motor such as a pre-engaged bendix flying in and out, just an engine starting up with no other noise.

Had a good look at it and came to the conclusion it must use the alternator as a starter motor which is actually what they have done. There is also a set of ultra capacitors which give the desired boost to get it up to speed.

As I said, its all been done before in a slightly different guise and was called the Dynastart as used by Volvo and RCA Dolphin etc.

Why is it sort of Boaty, well just filled the boot up with all my boat toolboxes etc.

 

[DaveS]

Are there any more details about this? While a DC generator (dynamo) will happily also run as a DC motor, and an alternator will also run as an AC motor, an automotive alternator with built in diodes to produce DC can't operate from DC as a motor. So presumably the diodes are external and an inverter is used to produce AC for driving the alternator as a motor?

 

[Jcorstorphine]

Are there any more details about this? While a DC generator (dynamo) will happily also run as a DC motor, and an alternator will also run as an AC motor, an automotive alternator with built in diodes to produce DC can't operate from DC as a motor. So presumably the diodes are external and an inverter is used to produce AC for driving the alternator as a motor?

This is an extract from the Peugeot blurb

The stop/start principle puts the engine into standby mode when the vehicle is stationary
and restarts it immediately and transparently when required.
Under deceleration or braking to stop the vehicle, the engine goes to standby mode before
stopping completely, and the ‘ECO’ light, located in the instrument cluster screen, comes
on. This occurs when the speed drops to less than 8 km/h and the brake pedal is being
applied.

The engine is held on standby if brake pressure is maintained or, in case of a long stop, by
engaging neutral and thus relieving the driver from pressing the brake. When the brake
pedal is released or a gear is engaged the engine restarts automatically. At all times the
driver may press the ‘ECO OFF’ button to reset the function and therefore restart.
The alternator was designed by VALEO, and is called the i-Stars. The alternator is
reversible as the energy conversion between the engine and the electrical equipment
works in both directions, unlike conventional alternators.

The alternator mode enables the reversible alternator to operate in the same way as a
conventional alternator; recharging the battery when the car engine is running and
powering electrical equipment. The starter motor mode enables the reversible alternator
to operate in the same way as a starter motor, to take electrical energy from the battery in
order to provide power to the engine in order to restart.

 

[halcyon]

Are there any more details about this? While a DC generator (dynamo) will happily also run as a DC motor, and an alternator will also run as an AC motor, an automotive alternator with built in diodes to produce DC can't operate from DC as a motor. So presumably the diodes are external and an inverter is used to produce AC for driving the alternator as a motor?

Does F1 and KERS come to mind.

Brian

 

[William_H]

Just speculating... Many small gas turbine engines use a starter generator for both starting and charging. These are however brush type starter electric motor and brush type generator. It is all a question of engine revs compared to the gear reduction needed for the motor to crank the engine but then to be able to cope with peak revs of the engine with resultant very high RPM for the generator. A gas turbine tends top have smaller rev range than a petrol engine.
Unfortunately the Peugeot blurb can be misleading. Any generator is in fact an alternator in producing AC. The old dynastart and generators used the commutator and brushes to switch the AC to DC while modern "alternators" use diodes. Yes it is conceivable that with modern high current transistors that DC could be converted to AC of a suitable frequency to operate an AC motor to start an engine. The rotor could be set up for charging alternator as well. Again it is a question of gear ratios for starting large ratio needed to charging when engine running at high speed when a low ratio is needed. At least diesels are not run to the high rpm of a petrol engine. But do need more torque to start.
All very interesting and hopefully someone will tell us the details. olewill

 

[Jabs]

Modern, very small gas turbines use a permanent magnet generator which uses a rare earth magnetic rotor to generate wild frequency AC which is converted into DC and 400hz AC for various functions in the vehicle.

Starting is effected by applying a rotating field to the generator which starts the rotor turning. The rotating frequency accelerates slightly faster than the engine thus providing starting torque.

The big difference, which fascinates me is that a small gas turbine requires very little torque to get it turning. A 2.0L diesel nneds a huge amount of torque so whatever they do is very clever.

Is the device belt driven?

Tony.

 

[Jcorstorphine]

Hi, the alternator just looks like a conventional unit but with perhaps a bit more ventilation. The alternator uses a ribbed type belt to start the engine and if you were looking at it, you would not know that it was any different from a standard setup.

The system uses a set of "ultra capacitors" to store additional energy to spin the engine. One difference you notice is that the starting background noise is very different from the usual start up with a motor engaged on the flywheel. The engine just starts like a machine driven by an AC motor and goes direct to tickover speed.

I am not sure yet but I think the Alternator is driven by DC rather than an invertor but still trying to find out the details. I have looked at the pully ratio between the alternator and the crankshaft pully and is about 1:4 so the mechanical advanate is not as good as the conventional flyweel starter motor.

HOWEVER, it does take a bit of getting used to the engine cutting out when you come to a standstill so I tend to switch it off the Start/Stop system while I get used to the rest of the cars functions like auto handbrake etc.

Some more info from Peugeot in Oz.

The e-HDI system uses Valeo’s second-generation Starter-Alternator Reversible System (StARS). (Earlier post.) StARS combines the alternator and starter functions. As a starter, it starts the engine instantly and silently using the alternator belt. This allows the machine to start the engine silently and without vibrations in less than 0.4 seconds, before immediately switching to alternator mode.

The StARS starter alternator is a synchronous machine using three-phase current. The rectification of the alternator current to battery current (AC/DC) is realized with field-effect transistors instead of diodes, which gives an excellent efficiency at >77% (VDA measurement), or 10 points higher than a traditional alternator and thus allows additional fuel savings, independently from the engine stop phases.

The starter-alternator is driven by the front-end accessory belt. A reversible tensioner allows power to be transmitted in both directions, depending on whether the StARS starter alternator is working as a starter or an alternator.

 

[MASH]

I drove a Honda civic with a similar system fitted recently. It was the most annoying car I've ever driven with the bloody engine stopping and starting every few seconds in traffic and a hesitation when pulling away because the engine had to start. In the true tradition of our politically (in)correct nanny state it couldn't be permanently disabled.

Why? What the $%@@ is it for? What is the point? I think I know. It must cost another £500 at the very least to design and fit such a piece of pointlessness, and that's another £500 that Peugeot/Honda etc make profit on.

The doubtless sell it on some spurious eco nonsense, but how much fuel does a car use at idle? practically none. And how much materiel, fuel etc is required to design and manufacture all those rare earth metals and electronics to make it happen? If you want fuel savings then ban those idiotic chelsea tractors that weigh 3.5 tons.

Is it a real saving or a psychological/political one?

I can guess. I don't want one thank you.

 

[Avocet]

It's a real (but small) saving. The level of the saving depends on how much town driving you do.

Again, it's hard to give figures that will be accurate across a broad range of vehicles, but there's a general rule of thumb, I believe, which suggests that a typical European petrol engine (under 2 litres), will use about the same amount of fuel idling for 2 minutes as it will when driving at a steady 30 for about a mile.

That's largely beside the point though. The thing is, all the European car manufacturers are bound by the "New Car CO2 Regulation" which (a) imposes a corporate average CO2 emissions limit and imposes fines PER VEHICLE if exceeded and (b) demands a rolling reduction in CO2 average emissions each year. They've had the "quick wins" like low rolling resistance tyres already. Now they're into stop-start. In a few years, we'll all be in hybrids. The other thing, of course, isn't what it actually save you in fuel, but if the savings just tip the car into the next road tax band below, you'll save a few quid each year.

My company car has stop-start, but its a 2 litre diesel, so it's a bit big to be started by its alternator. It just operates the starter in the usual way. I don't find a problem with it but I tend to disable the system when I'm in frequently-moving stop-start traffic. I'll let it work as intended at lights and other longer pauses though. I've not found it significantly impedes take-off though. As soon as the clutch pedal starts to be depressed, the starter operates. By the time it's in gear and the clutch is back on its way up again the engine's ready to go. I worry about what will happen when the car is 10 years old and not quite so willing to start though!