New Bosch system shuts off coasting cars' engines


January 8, 2014

Bosch's new system is intended to reduce fuel consumption and CO2 emissions

Bosch's new system is intended to reduce fuel consumption and CO2 emissions

Cars don't need to have their engines running when they're stopped at red lights. That's why a number of automakers have developed start-stop systems, which stop a car's engine when the vehicle comes to a halt, and start it again as soon as the gas pedal is pressed. Bosch, however, is taking things farther. Its new start-stop system shuts the engine off not only at stops, but also whenever the car is coasting.

Putting it simply, the "start-stop system with coasting mode" turns off the engine whenever the vehicle can maintain its present speed by rolling. In other words, if the driver's foot isn't on the gas or brake pedals, the engine is off. A simple touch of either pedal causes the engine to instantly start back up.

According to Bosch, tests carried out by the company indicate that most vehicles could coast for about one third of every trip. If the engine was shut off for those periods, it would result in fuel savings of about 10 percent. Additionally, Bosch claims that if every new car sold in Germany were equipped with the system, "the theoretical annual reduction in CO2 would amount to over 30,000 metric tons" (33,069 tons).

What's more, with the engine off, the decreased mechanical resistance should allow cars to coast for longer distances than would otherwise be possible.

The system can reportedly be added to almost any type of existing combustion engine (including hybrids), and requires the installation of relatively few additional parts. It can even be added to cars with manual transmissions, if Bosch's eClutch is also used – this disengages the clutch whenever the vehicle is in coasting mode.

There's no word on availability or pricing of the system, although it is described as "affordable."

Source: Bosch

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away. All articles by Ben Coxworth

I do not understand how this is different from Deceleration Fuel Cut-Off, which became standard on all cars in 1996, requiring the engine control unit to cut fuel after the accelerator is released. Some require certain RPMs or have other conditions, but it marginally improves fuel, while cutting emissions while at part throttle.

The engine continues turning without fuel, as long as the car is in-gear, the wheels turn the engine and alternator, so you still have power steering and brakes, electricity, everything, and the ECU starts sending fuel as soon as you touch the accelerator.

James Harold McNeil

Saving fuel is great, but if the engine is off while coasting, so is power steering. If you've tried to steer a vehicle when the power steering is inoperative, you know how difficult it can be. Also, imagine a string of start/stop cars at a red light. The light turns green and the accumulating delays between touching the gas and the engine resuming operation seems like it could cause a few lost tempers...


no more engine braking I guess then! Don't think I'd like that.


For those who haven't driven newer cars recently.

In many newer cars many of the ancillaries (including power steering) are electric. Therefore turning of the engine whilst driving doesn't affect these.

One thing which needs to be in place will be an electric brake booster (instead of vacuum powered boosters), though I assume (not familiar with the specifics) that in hybrid cars, and indeed other late model vehicles this already exists. (Or the brake circuit may be a high pressure, servo actuated system.)


I already have this feature on my car, it is called a clutch and a diesel. Diesels are astoeometric compression so use very little fuel under 0 load and the clutch provides engine / transmission disconnect for efficient coasting. And when I need power I just lift my foot off the clutch and I have instant power. I also maintain engine temperature on longer coasts (down mountain hills etc) so I don't have to waste more diesel warming the engine back up or worry about wearing out a starter, or freezing to death because my primary heat source is gone, or cooking while the ac compressor is off when it is hot.


In the UK, coasting (with the clutch in) is frowned upon during driving tests because it's considered 'potentially dangerous' for many of the reasons mentioned above:

Plus, as James said, ECUs have been using fuel-cut on overrun for years so this is redundant. It's just a gimmick to sell even more starter motors!

Alex Haws

There are many consequences of installing this technology, as the above comments indicate. However, I doubt that the engineers at Bosch will be surprised by any of them. Cars kill and any death that can be attributed to design error will result in criminal proceedings against all the engineers deemed to be responsible. Such a prospect tends to focus the attention somewhat. There will be no chance that any vehicle equipped with this system will have its braking and steering functions degraded as a result of its installation.

As for de-clutching on the overrun, free-wheel systems have been around for ages. They have never really caught on, but who knows, perhaps they are due for a re-think, especially if only fitted to the top one or two ratios so that engine braking was still available if the brakes failed. That, of course, assumes that the driver would be capable of letting go of the steering wheel with one of his white knuckled hands in order to change to a lower gear as the car rolled ever faster down the hill it was on!

Mel Tisdale

Sounds like a great idea but maybe the feeling of coasting without the engine running will seem a little weird at first. A small point re the calculated saving of 30,000 metric tonnes of CO2, surely this equates to approx. 29,500 tons not 33,000 as quoted.


As others have said, in Europe coasting will fail you on the driving test. You are expected to work down the gears, engine brake or use the brakes and only push the clutch in at the last moment where the engine begins to struggle before coming to a stop.

There are a number of reasons for this, where coasting is seen as a big no no. I also remember hearing topgear saying that you use no fuel at at all or next to nothing when you drive to a stop in gear, the cars wheels basically keeping the engine turning over as fuel is cut.

This technology would mean you could save fuel while coasting, but wouldn't save you any fuel compared to driving to a stop. Currently when you coast the engine has to keep itself ticking over instead of the wheels keeping it ticking over, so the engine could cut off.

But instead, just learn to drive properly, and drive to a stop, "coasting" in gear. Although it would be interesting to see how much people actually coast and how much could be saved.


Phew! What a bunch of negativity! I bought a Honda Insight in 2000. It has stop/start, obviously, and the only bad moment I had with it in 13+ years was during the initial test drive; we came to a stop light and I heard the engine "die" (or so I thought). The sales guy said "Oops, I forgot to tell you . . . " Regarding power steering, the engineers at Honda made sure that "stop" mode did not interfere with it. Real world performance over the past 130,000 miles: 53.4 mpg. If Bosch's 10 percent estimate is correct, that would have been 58.7 mpg--a home run, in any ballpark.

Mac McDougal

Round here in the Yorkshire Dales, our brakes have to work hard enough even when supplemented by engine braking.

Plus, having once put a car into the ditch because I didn't notice the engine had stalled going down a long hill and therefore there was no power steering when i came to the corner at the bottom, I don't fancy that at all.

Apart from the fact as observed above, that most/all modern ECUs cut the supply of fuel to the injectors while the engine RPM is above tickover and the vehicle is coasting.

All in all, fairly pointless IMO.


I challenge Bosch to beta test their stop/start kill on vehicles that have to travel daily the morass of Southern California's freeways, or should I say, parking lots. It will certainly give a whole new meaning to road rage.

Marco Corona

This method has been used for many years by a dedicated group of people who go under the term "Hypermilers" And while this method does indeed save gasoline, and by proxy,'s not worth the money you will lose when you get a ticket by the police department because turning off your engine while the vehicle is in motion is illegal in many places in the United States.


"I do not understand how this is different from Deceleration Fuel Cut-Off, which became standard on all cars in 1996, requiring the engine control unit to cut fuel after the accelerator is released."

I guess I'm not understanding what this is you are describing...

I own a 2002 VW Cabrio. It is an automatic. When I drive it and coast down a big, long hill close to my house, the engine stays running...If the engine is running, then that means that gasoline is being fed to the engine. Granted, not much, but my engine RPMs hold steady at 800 while coasting. If I drop the automatic into Neutral, the RPMs drop down to 600 while coasting. Unfortunately, if I don't put the vehicle back into gear at a particular speed, there is a noticeable CLUNK when putting the transmission from neutral to drive.

So how does this thing you're talking about work?


Ed, you almost answered your question with your description. The engine is rotating when coasting down hill because it is being driven by the potential energy of the car, transmitted via the wheels and the auto gearbox without any fuel being supplied to it. As soon as you move the pedal the ECU adds fuel. The 800rpm is probably to ensure that the ECU has time to take over when you select neutral; at 600 it might stall before the ecu takes over. I'm tempted to say the clunk is because you didn't buy a Lexus.....! but if the coasting car is not being robbed of energy to keep the engine turning it will increase speed until there is enough rpm mismatch to cause the clunk when you put it in gear.

alan c

Around here, when the light turns green, you'd better go. Waiting for the engine to start will cause road rage. I see this technology working on a hybrid, but not a pure gasoline car. I see this as a benefit to the environment but not to the driving experience.

Someone commented that in most newer cars the power steering is electric . . . I looked under the hood of my 2013 Highlander and there's still a power steering pump connected to the belt of my engine. I've not heard anything about power steering pumps being electric.


Is Bosch planning to test this in an hours long Los Angeles commute on a 100+ degree day?

The system had better have an override that kicks the engine in to charge the battery so the electric driven air conditioning doesn't drain the battery.

Up into the 1950's a popular manual transmission option was an overdrive gear with free-wheeling. Below about 30 MPH and in overdrive the overdrive would kick into free-wheeling, allowing the driveshaft to rotate with no connection to the transmission.

Dunno what the point of that was supposed to be but slowing down below freewheel speed was all on the non-power brakes unless the overdrive knob was pushed in to disengage it. Power brakes didn't come along until around 1954, same for power steering.

These overdrives also had an electric disengage system using a solenoid and a pushbutton switch under the gas pedal. Stomp it to the floor (most vehicles back then had floor hinged* gas pedals instead of suspended ones) and the overdrive would kick out for an instant no-clutch downshift to 1:1 ratio.

Watch many cartoons made in the 60's through the 90's and if there's an under dash shot of a vehicle it will most of the time anachronistically depict floor hinged pedals. Gregg Eshelman

SuperProgrammer I drive a 1979 Chevy pickup and habitually turn off the engine at stoplights and don't have any trouble responding in a timely manner to green lights.


Billysgrandad The Americans use a different ton to the rest of us. Their ton is only 2,000 lbs rather than the usual 2,240. They call this a short ton as opposed to the conventional long ton. To avoid confusion they often use thousands or tens of thousands of pounds rather that specifying how many tons are involved.

Cé hé sin
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