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Bosch Start-Stop System to Move to Series Production; Standard Equipment on BMW 1-Series

A specially adapted starter is the central component of the Bosch Smart Electronic Start-Stop System.

Bosch has developed a Smart Electronic Start-Stop System that is moving into series production at BMW. First variants of the 1-Series will feature it as standard equipment from 1 March 2007.

The Bosch system switches the engine off when the vehicle is stationary, and starts it again automatically as soon as the driver indicates an intention to move off—by depressing the clutch pedal, for example.

The ECE15 measuring cycle, the urban component of the New European Driving Cycle (NEDC), calls for twelve 15 second stops over a distance of seven kilometers. During such a journey, the Bosch system reduces fuel consumption and CO2 emissions by as much as eight percent, depending on the vehicle. If the stops last longer, the actual saving of CO2 emissions and fuel can be significantly higher.

Bosch developers designed a specially adapted starter for the system, the Smart Starter Motor. The company already produces the battery sensor that is needed to detect the battery’s current state of charge and to communicate this information via the energy management system.

There is no need for any further adjustments to the drive train or the engine. This gives the system an excellent cost-benefit ratio, and makes it attractive compared with alternative systems.

The number of engine starts the starter has to make has been significantly increased for this application. In addition, the starter’s improved-performance electric motor, and a low-noise, stronger pinion-engaging mechanism ensure that the engine starts reliably, quickly, and quietly. Despite the increased number of functions, the starter is compact, and can be integrated into the vehicle just as easily and quickly as other starters.



Give me this system, a clutch micro switch and a starter adaptor plate mount...I'd buy it and spend the weekend installing it.

Of course I'd hate to see the markup a BMW dealership would tack on...more pedestrian dealerships already put a good 50-75% markup on parts sold to the average joe.


Boy! I don't know about this approach! It's cheap compared to the idea of an induction motor between the transmission and the engine; but, it seems to me the drive plates for most cars would need to be modified to take the extra duty cycles or you might start erasing teeth off the plate.


If people avoid trying to start an already running engine or starting an engine in gear their flywheel ring gear should last hundreds of thousands of miles through normal use.


You don't know about this approach? VW Polo Formel E in about, oh, 1986?


You don't know about this approach? VW Polo Formel E in about, oh, 1986?

Spokane Walt

There are tons of tricks that can be done like this to save fuel...

Didn't VOLVO have a system that threw the automatic transmission into neutral when you took your foot off the accelerator pedal - this was a number of years ago...

Hot Rodders have long since known to put a relay between the alternator and the rest of the car and kick it off under any sort of hard acceleration. They also typically will run the water pump off of an electric motor so if can run off the battery anytime full power is needed. Then when powering down into a turn or some other time when engine braking is desired, the alternator can be kicked on and recharge the battery. The trick is to watch the voltage gauge and make sure the battery doesn't run down. You can't tell me automotive engineers aren't smart enough to figure these things out?

I've got one that most people can do on their own. If your vehicle has daytime running lights, and there is a way to disable or bypass them, do so when travelling down a divided freeway during daylight hours on a clear day with very light traffic. They are to prevent head-on collisions, and really aren't needed when there are no oncoming traffic lanes nearby.

Here is another one - if it isn't foggy, raining heavy or snowing - turn off your FOG lights! Or, If you're travelling above 40MPH, they aren't doing anything accept giving you a false sense of better vision. Turn them off. If you choose to use your fog lights all the time - well then OPEC thanks you.


This technology is no breakthrough, neither is it new. It's already been used in the 3L VW Lupo in 1999. However I do appreciate its return to the mainstream market.


"standard equipment" is the key word here, lets only hope that others are paying attention.


Don't get me wrong. I like the idea even thought it's not a sophisticated solution. It is none the less an elegant answer because it is simple. And, I would be one of the first to retrofit my Volvo if it proves to be feasible and is made available for older cars. I just want it to be a reliable solution and I'm for anything that slows down the depletion of oil.


Spokane Walt wrote: I've got one that most people can do on their own. If your vehicle has daytime running lights, and there is a way to disable or bypass them, do so when travelling down a divided freeway during daylight hours on a clear day with very light traffic.

Walt, your other ideas were good, but I'd skip this one. The daytime running lights are lower wattage than regular headlights. It isn't worth the reduction in safety to save a few drops of fuel. People should take off unnecessary roof racks, get the junk out of the trunk, and inflate their tires instead.

Spokane Walt

Response to George:
Thanks for responding - I am glad someone reads these!

Depends on the vehicle - some are lower wattage, especially some newer ones. Some are not. I'd suggest people do thier own research on Daytime Running Lights and make thier own decision.

VW found that reducing the voltage as a method to reduce wattage shortens bulb life quite a bit. Murphy's Law dictates that almost all headlamp bulbs burn out at night when it is raining...

95% of the time, around town, in heavy traffic, etc - they are a good idea. Out in light traffic on a wide open freeway across some of the areas of the country with sparse population, light traffic on a limited access highway... Well, there might me some savings to turning them off, without sacrificing safety.

Even GM - one of the early proponents of Daytime running lights has backed all the way off to just running both turn signal lamps. Our 2000 Chevrolet Minivan has this feature, and I have never changed a single bulb anywhere on the vehicle. It has over 110K on it. Toyota is now on the bandwagon as well. My 2000 Jetta burns a set of headlamp bulb every 40K miles. (I am at 180K miles on that car)

There are some really bad downfalls to conventional headlamp based DRLs- If you haven't seen one of the drivers who forget to turn on thier lights at night, trust me you will. They have headlights (courtsey of the DRLs) so they don't turn on thier lights, and thus have no tail lights at night. To make this even worse, Toyota, on their Lexus RX300, turns on the Dash Illumination, so they get no clue that their taillights are not lit! I have seen this issue on this specific vehicle multiple times in the Seattle area, as well as on Interstate 90, once in very heavy fog - very scary!

IMHO - if the tail lights aren't on, the dash souldn't be illuminated!

In addition, some DRL setups are just downright irritating to other drivers on the roads - many of the older Saturns that use irritating high beams fall into this category. I am not completely Anti-DRL - I am just pro a proper installation of the technology.

For more information, check out these web sites:



hans wurst

The USA has DRL by law, right? So why not using durable and low consuming LED technique? Audi has now nice LED DRLs on its R8, A6 and A8 here in Germany. IMHO a very important safety feature. BMW and the other kraut-brands are a bit lazy though.
Sure, the start-stop system should be standard as well.

Rafael Seidl

Ruaraidh, Marius -

yes, idle-stop has been tried before. The reason it was not accepted by consumers back then is that the electrical system could not provide sufficient power to start the engine quickly. The ~5% savings in the NEDC were offset by worries that the engine would restart only slowly - or not at all - when the accelerator was depressed again.

These days, there are suitable electric motors that feature higher efficiency, plus the batteries are beefier and the grid management more sophisticated.

More importantly, Bosch has also figured out how to control the deceleration of the crankshaft such that the warm start is reliably powered by renewed combustion as early as the second revolution of the crankshaft, regardless of engine temperature. That means the energy drawn by the starter motor is reduced to a brief, controlled power spike. The engine reaches self-sustaining speed after ~0.3 seconds, less than half the time required for a conventional start.


A drawback seems not to be taken into account : which torque will drive the compression pump for the air conditionning system ?



I appreciate your comments but please compare apples with apples. The Bosch fast starting concept was originally based on the application of direct fuel injection with an absolute crank angle sensor to determine the position of the pistons at engine stop. A starter motor was used to bring the most appropriate piston to a position where combustion might occur after fuel injection. The assistance of that combustion event would get the crankshaft turning faster than with the starter motor alone. Direct injection was used because it was not dependent on inlet valve opening and it produced much better fuel atomisation when injected into a relatively cool and motionless air space.

If you include the prerequisite technologies for the fast start and the necessary electrically powered air conditioning compressor, the whole package is not looking that cheap or simple. Sure it might also work with port fuel injection but with how much success is open to speculation. If you have a published paper on the port injected version perhaps you can give us a link please.


Spokane Walt, yeah there are a few of us that read these things only because guys like you occasionally put in the effort to present informative, well thought out tid bits, thanks.
LED's are slowly pushing into the mainstream on tail lights. A very few are going into use as headlights on the very high end vehicles. I believe Audi is considering them on a few of theirs.

Rafael Seidl

daydreamer -

Bosch did indeed use direct injection for its direct start technology, which is fine for diesels and in increasing number of gasoline engine designs.

Bosch tried three different modes of direct start. In the first, they tried trapping fresh charge in one of the cylinders by stopping the engine at a suitable crank angle. This worked most of the time but very poorly once the engine was hot - there simply wasn't enough air mass to kick-start the engine using combustion alone.

The second option called for the first combustion event to rotate the crankshaft in reverse, compressing the gas in another cylinder. The expansion stroke in that second cylinder then forced the crank to rotate normally and spool up to self-sustaining RPM levels. This worked a little better but still not reliably enough when the engine was hot.

The third mode, which is what Bosch marketing refers to as "direct start", calls for the first full rotation of the crankshaft to be powered by the starter motor. Combustion assist starts with the second revolution, at which point the starter motor can be disengaged.

In theory, this third mode could be made to work with port injection as well, provided injection is cut early enough as the engine comes to a full stop and is resumed at just the right time. I haven't seen a publication implementing it yet, though. Perhaps the low velocity of the fresh charge in the initial injection events is a hurdle.


Since 95% of idle stop events take less than 40 seconds, the air conditioning issue can be addressed with a latent cold store. If you're stuck in a traffic jam on a hot day, there's usually no choice but to switch the engine on again after that, even if you're car cannot move.




So perhaps this application is not the Bosch direct-start at all but a much simpler concept. I am wondering how this works during normal driving with a manual gearbox. The concept requires the driver to put the transmission in neutral and release the clutch before the engine will stop. When the driver wants to move again they must engage the clutch, select a gear and accelerate. For short stops, which you describe as no problem for the A/C, it must be assumed that the driver always drops the transmission into neutral.

When the engine is cold I assume that this feature would not be operational. For example when I start the engine from cold and want to warm it up by idling. Likewise when it is hot and I want the A/C to operate as I sit in a parked car waiting. Or perhaps there is a switch in the cockpit to turn the start-stop function on and off when you need to.

By the way is there any production application of Bosch's direct start be it Diesel or gasoline?

DRD T-bone

The article doesn't seem to touch on whether or not a larger battery is required, but reading the source article it doesn't seem like this is the case. Neither this article nor the one above mention how they're going to apply brake-regen either. I guess I'm a fan of the GM BAS system (no starter, one simple motor/generator), but then again that may be my slight bias coming into play (Vue GL owner :) )

Rafael Seidl

DRD T-Bone -

I suspect the battery may have to be a heavy-duty model but otherwise still a regular 12V lead-acid type. The whole point of this is to achieve idle-stop with minimal additional hardware cost.

daydreamer -

many - not all - drivers of stick-shift cars anyhow shift into neutral and take their foot off the clutch, if only because it's less tiring on the foot. A light on the dashboard might be a good way to confirm that the engine has indeed stopped, because in modern cars you can hardly hear or feel the engine idle any more.

Afaik, the direct start system is not yet in production though I suspect BMW and others will introduce it in future generations of their products.


Leaving the clutch disengaged (your foot pressing down on the clutch pedal) for prolonged periods is a good way to wear out the thrust bearings and contribute to so-called "crank walk".

Spokane-Walt: Sounds like you are describing a system used by drag racers. I don't know of anyone who has ever bypassed their alternator for driving on a race track (whether it be SCCA, road races, rally, etc). I don't think that would be effective for the general populace who can't even remember to shut off their headlights, lock their doors, keep their keys with them (instead of leaving them inside the car), concentrate on driving (instead of talking on the phone, eating a big mac, reading a newspaper, or putting on makeup). Such a switch by a manufacturer just creates a HUGE liability and possible lawsuit that would drain millions of dollars from the company in question.

DRD T-bone

Do you know the plans to implement this to other models? The only beef I have with this particular application is that on the 1 series they're utilizing brake-regen as well as idle-stop using two separate systems as opposed to one combined system, but I suppose a team of BMW Engineers & Financial analysts see something that I don't :)



What limits start stop is he engine itself meeds some careful tweaks to prevent it from going to bits rapidly with it.

But as the replae more and more of the engines with newer models you will see it expand rapidly.


Hans, the US does not require DRLs, but I believe Canada does. As a result GM has made them standard in the US as well, presumably so as not to have to maintain two versions of all their North American models. So you see a lot of DRLs here, but they're not actually required by law.



You right about alternator, but simple relay switching off AC at full throttle is quite popular performance enhancing device.

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