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Design of the Daimler S400 Mild Hybrid System

Hybrid concept for the S 400 hybrid. Source: Daimler. Click to enlarge.

Daimler’s S400 BlueHYBRID, which goes on sale this month, is the first series production passenger car featuring a traction lithium-ion battery pack. (Earlier post.) At the Advanced Automotive Battery Conference 2009 in Long Beach, Dr. Uwe Wiedemann from Mercedes-Benz Cars/Development, Hybrid Systems & Components, presented an overview of the design of the system and components, with a particular emphasis on managing the small 0.8 kWh Li-ion pack.

The S400 Hybrid uses a parallel mild hybrid system with a small 15 kW e-motor connected to the crankshaft between the motor and transmission, along with a Lithium-ion battery pack for energy storage, power electronics and a complement of electrified auximilary systems. The system offers start/stop functions, regnerative braking and electrical drive support.

Although the motor seems small from a power output perspective, “for the given architecture it turned out that the maximum fuel reduction occurred at electrification of 15-16 kW. That’s why we chose a lower system,” Wiedemann said.

Combined torque curve for the S400 hybrid. Click to enlarge.

The high torque of the e-motor at low speeds offsets the reduction in low-end torque resulting from applying the Atkinson cycle to the combustion engine.

Moving to a more powerful e-motor increased the weight of the hybrid system and decreased the fuel consumption. Furthermore, at a higher electrical to combustion power ratio, the e-motor operates increasingly in less favorable areas of the performance map as maximum requirements increase. Although relatively low in power, the e-motor delivers rated torque of 160 N·m (118 lb-ft), contributing to a combined system torque of 385 N·m (284 lb-ft).

Power electronics. The power electronics—from Continental—comprise a control unit which acts as the master of the E-drive system and a power unit that converts the direct current generated by the battery. The power electronics can cope with continuous currents of 150A, and short-term as high as 310A. Power is supplied to the e-motor by a bus bar.

The power electronics are situated in the engine compartment in the location of the conventional starter motor and are cooled by a separate circuit.

The S400 hybrid battery pack. Click to enlarge.

Lithium-ion battery pack. The compact Li-ion pack, developed by Continental and JCS Saft, comprises 35 cells and provides 19 kW of power, with a capacity of 6.5 Ah. The battery is connected to the vehicle air conditioning circuit so it can be cooled independent from the engine.

Cut-off valves are integrated into the system that allows the customer to switchoff the air conditioning without interrupting battery cooling. When the engine is not running, the electric A/C compressor not only provides air conditioning but also guarantees that the battery’s operating temperature limits are not exceeded. Battery pack temperatures do not increased above 50 °C in any operating state to prevent serious damage.

Operating strategy. The operating strategy of the S400 hybrid is based around start/stop, regenerative braking, boost and load point shifting—i.e., moving the load point of the combustion engine to less consumption-intensive ranges while offsetting the torque deficit with the e-motor.

When providing support for load-point shifting, the operating strategy only allows shallow discharge cycle of the Li-ion battery to maintain the cycle strength. Fuller deployment of the electrical support is only provided based on the driver’s request, as indicated by accelerator pedal position and a large pedal value gradient.

The focus of state of charge (SOC) swings is in the range of 5%. Values of up to 10% occur less frequently, while SOC cycle of more than 10% are rarely observed. This contributes to the 10-year expected service life.



The best Li ion can do: "The focus of state of charge (SOC) swings is in the range of 5%. Values of up to 10% occur less frequently, while SOC cycle of more than 10% are rarely observed."

500 key technology patents, but Cobasys is broke? Sounds impossible, if not deliberately staged. No wonder Benz is sueing Chevron/Cobasys over withheld NiMH batteries. Maybe government can find a pair.. of batteries.


A strange article and comment.
When they say “Moving to a more powerful e-motor increased the weight of the hybrid system and decreased the fuel consumption.”
I guess they mean” increased” fuel consumption, and I have my doubts about that.
The article only mentions in passing that the this S400 has an Atkinson cycle engine.

What does ”The best Li ion can do: .. " mean?
Is the “500 key technology .. ..” meant for a different article?


Their battery is small compared to the Prius battery, in size, weight and capacity (0.8 kWh vs 1.3 kWh). That's a major benefit of LiIon.

Incidentally, the 80 bhp KERS unit in the current MacLaren Mercedes F1 car weighs just 25 kg, and that includes the battery, the motor AND the power electronics!


"The best Li ion can do: .." means the Lithium-ion battery in the article is only considered dependable using a ten(10) percent range of its capacity.

This Li-ion battery is a substitute for the NiMH battery the Chevron/Cobasys partnership was to provide. MB is sueing Cobasys because they failed to provide the batteries and claim near bankruptcy.

Chevron could finance Cobasys, but can own all of Cobasys/Stan Ovshinsky's NiMH battery and nearly 500 other key technology patent's(his life's work and his part of Cobasys) if Cobasys "default's in it's obligations".

Like deceit, it's a tangled web. Perhaps "Iraq, oil, and 'weapons of mass destruction'" provides a historic prospective to these sorts of business dealings.


I read that Stan did the deal with GM, because he wanted to see the EV1 produced. Then GM saw that the ZEV deal would not be supported by the EPA in the new administration after 2000, so in October of 2000 GM sold it to Texaco and 6 days later Chevron bought Texaco. I believe in coincidences, but then there are patterns that look like more than just random unrelated events.


"I read that Stan did the deal with GM, because he wanted to see the EV1 produced."

Yes, he wanted NiMH EV's everywhere and GM claimed they did also. But that is the last thing GM wanted. With a viable battery, anyone could manufacture EV's. EV's need no gas, have little pollution, and virtually no maintenance revenue or need for yearly 'new' models.

So, GM sabataged the 1996 EV1 with leaking Delco lead-acid batteries of 60 mile range. But Japan accepted CARB zero emissions as the law. The 1997 RAV4 and Honda EV's used NiMH batteries, had over 100 mile range, and leased for $100 less/month.

Thereafter, GM was exposed. They sold NiMH patents to an oil company for burial, spent most EV1 funds sueing CARB, lobbied Congress to effectively end mass EV's, and crushed the EV1 for spite.

They did similiar to mass transit earlier.

Watch "Taken for a Ride":

With hindsight, one doesn't need a business PHD, MBA, or Electrical Engineering degree to see what was done - and history repeats.


Maybe the typical U.S. mindset was, if you can't beat them sue them. Some talk about American know how and get it done attitude, but then the bean counters get involved and figure the "cost effective" route is to sue them out of existence. Let's hope we get back to honest productive methods.


If you try to watch "Taken for a Ride" on YouTube you'll have to hunt for all of it. I just watched all 55min of it without interuption on google videos. And this is something people SHOULD watch start to finish.


Here is a copy of Taken for a Ride.

There are times when corporate interests and national interests are at odds. What is good for GM is NOT necessarily good for America. Now that they have gotten their way for 100 years, they are bankrupt and we are left with crowded roads, smog and oil dependence.


ai vin, SJC - It's a consensus - thanks for the additional video sites. May the videos be viewed by many and often.


Well, it is at least an agreement of three :) It is not realistic to bring back the street cars, but if you notice light rail coming back, that could be a second life. I just want large format NiMH for plug in hybrids. I want a choice that we have been denied, so that we can decide on using NiMH or some form of lithium battery for the cost effective PHEVs that we need to reduce oil imports.


I have a question about NiMH's. A 30 kW-hr pack will get you decent range, enough to get around town no problem. Searching on Ebay, AA NiMH batteries start at about $0.25 a W-hr for the unknown brands, and Energizers are about 50 cents. So we'd need 30,000 * 0.33 cents = $10,000. For a large order like this you could probably get a discount.

Could you make adapter kits for AA's? All you'd need is the battery holders, the wiring, the CPU, the charger, and then all the regular stuff you use to convert over to electric. How much would all this cost? $15-20,000? You could add this to an old car that's cheap to begin with and for $30,000 have a decent electric car running off NiMH's.


Mark, that's not a new idea. The Tesla Roadster battery pack is comprised of about 6800 lithium-ion "18650 cells." This cell is called 'the 18650' because of its measurements of 18mm diameter by 65mm length (i.e., just a bit larger than a AA battery). The entire
pack has a mass of about 450kg.

What they did with lithium-ion you *could* do with NiMH but what would be the point? The engineers at Tesla Motors selected these cells for safety reasons. Due to its small size, the cell contains a limited amount of energy. If a failure event occurs with this cell, the effect will be much less than that expected from a cell many times larger. Billions of 18650 cells are made each year. Though the chance of a safety event in a
laptop is small, the number of safety incidents involving Li-ion batteries is rising each year because there are so many more devices using small and powerful power sources.

The question you should ask is whether the NiMH has the kind of safety issues that would need such precautions.



I've wondered if NiMH 'D' cells could be used with ~1/4 as many connections. Clearly, it would be many times easier and cheaper to use EV-95 batteries, like the 1997 through 2002 RAV4 EV, Honda EV, etc.

Of course, an energy company would know that if they sued the EV-95's out-of-existence, refused to license mass, viable, EV NiMH battery technology and hence forced and maintained near absolute oil dependancy on a climate warming/pollution threatened world.


I thought that it might be cheaper than Lithium ion and have a longer life. You cold get an electric car for $30,000 or less, which is cheaper than any option available.

The reason it took lithium batteries so long to come to market was because they had to overcome safety issues like laptops blowing up, which isn't acceptable for a car. You never hear about these problems with NiMH so I presume there isn't much of an issue. Just keep them cool and you should be OK. It would be like some third party developer would make the electronics and holders to hook up to 10,000 AA's and take care of the safety issues with electronic monitoring, and then you'd just buy your own batteries and install them yourself, thereby avoiding the large format NiMH patent.


@Mark, Tesla does hookup/control 6,400 Li-ion 'AA's for $109,000 - including car body, a bit expensive for most.


But most of those costs are sucked up by car development from scratch (eg, crash testing) and the large Li ion battery pack. If I was to instead take a 10 year old Toyota that's already been through all this shouldn't I be able to get the controls and electric motor for $10,000, and then another $10,000 for the AA's?


You can use 100s of 10 amp hour cells with tabs like these.

Many can handle 50 amp surges for 10 seconds. You could make a 24 khw pack. They cost $5 each in quantity so 2000 pieces would cost $10,000 plus labor and testing.


clett: You have it all wrong. Mercedes S400 was designed from scratch to use li-ion. When thinking of Cobasys, you are thinking of the Mercedes ML450. You should be ashamed of accusing Chevron for not wasting any more money on that monumental disaster, Cobasys - Chevron gave them hundreds of millions of dollars, and what did Cobasys deliver - leaking batteries that caused the total recall of the entire 2007 GM mild production! There is no "but" or "if" - Cobasys was a money-losing zombie company since the beginning - there is no value whatsover in Stan's technology patents (because all he patented were his high school experiments - he is simply the Charlatan Extraordinaire).

SJC: Did you think how much the pack would weight? You can do twice better with li-ion, and those things are 50c per Wh in volume.

Read here:

kelly: Yes, you should have heard of NiMH problems. If you haven't, read the above link as well. One of the market-share leaders recently recalled 41,000 AA NiMH batteries as they could "rapidly overheat, posing a burn hazard to the user."

Mark_BC: The link above will show you that Tesla's 56kwh li-ion pack costs $36,000 (easy to verify with pricing for quality 18650 cells in volume).


Sorry, my post above was addressed to kelly instead of clett and Mark_BC instead of SJC.


2000 NiMH cells would weight about 650 pounds versus maybe 450 pounds for lithium. I would rather go with something that runs 100,000 miles and 10 years than not know when the expensive lithium batteries will fail.


"...ashamed of accusing Chevron.."

Chevron shorted Cobasys so that they could claim non-performance by ECD and take the patents. Chevron never intended to make batteries, but keep them from being made.


@ECD Fan,

Please Google* chevron NiMH batteries *.

With over 28,000 links, Chevron's conduit and NiMH battery lawsuits seem well understood by expert and layman alike.

"there is no value whatsover in Stan's technology patents (because all he patented were his high school experiments - he is simply the Charlatan Extraordinaire"

Google Stan's name and see over 6000 links of praise, energy genius, scientific price winner etc: ...

With such an ECD fan, who needs enemies..


SJC: You forget that NiMH cells have about 1/2 the capacity of li-ion cells with the same weight. Moreover, li-ion is not much more expensive. I suggest you read (carefully!) the post in my blog and check the references there.

Also, please, stop spreading misinformation about Cobasys. Cobasys, formerly known as GM Ovonic, was created by GM and ECD, and after the EV1 disaster, Texaco (now part of Chevron) was the only one that was willing to give them hundreds of millions of dollars in equity and loans. In return, they got nothing. Chevron is not in the business of making batteries, but Cobasys was supposed to be. It turned out Cobasys' only business was making leaking batteries that ruined the entire 2007 GM hybrid production. Instead of blaming Chevron, study Cobasys financials a bit (they were disclosed in ECD's financials), and you will understand who is to blame.

kelly: Those 28,000 links are wrong, if that's what they say. Without Chevron, Cobasys would have been dead for years (would have closed doors immediately after GM dumped the EV1). The gullible Texaco actually wanted to help them to make something out of themselves.

Stan, of course is a Charlatan. Those 6000 links must be from people who are totally clueless. His lies are well documented and anybody who bothers to do a bit of due diligence will find out the truth. Here is a start for you:

Did that link come out in your google search?

Go to the library and check the references I have provided in that blog post. Then you will be the one who knows the truth.


"..stop spreading misinformation about Cobasys.."

I express my opinion and give links to support it, do NOT accuse me of it?

I will leave it up to the readers to make their own conclusions about the topics and their conclusions about you, whoever you really are. I do not think that you have much credibility here.

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