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Schaeffler preparing 48V mild hybrid Audi TT for road testing

Schaeffler has been testing and demonstrating the performance capabilities of 48 volt hybridization in a range of concept vehicles including the“Gasoline Technology Car” (GTC), co-developed with Ford and Continental and the “Schaeffler Efficient Future Mobility North America” vehicle, as launched at the 2015 Detroit Motor Show (NAIAS) (earlier post). Schaeffler is now applying 48V hybridization to an Audi TT.

The drive for the “Schaeffler System 48 V” is based around an electrified rear axle which complements the front-wheel drive internal combustion engine. An additional belt-driven starter generator is connected to the engine which also operates at 48 V. The 48 V on-board electric subsystem uses a lithium-ion battery as its energy store. It is connected via a voltage transformer to the 12 V on-board electric system which powers all the different electrical components in the vehicle, from headlights to seat adjusters.


The Schaeffler PROtroniC prototype control unit controls and regulates the interaction between the components. The way in which the drive elements work together depends on which of two driving modes—“Eco” and “Sport”—the driver selects.

In Eco mode, which optimizes fuel consumption, the engine is switched off as often as possible. Driving at lower speeds, in stop/start traffic or when maneuvering into a parking space is all electric. When braking, the electric machines act as a generator and recharge the lithium-ion battery.

“Active sailing” is also possible with the electric rear axle: If, for example, when driving in town at a constant speed, very little driving power is required, the engine remains switched off and the electric machine takes over. If the engine has to be used, it is quickly and smoothly started by the belt-driven starter generator. Under acceleration, the engine and electric motor work together, increasing the power in the system. Also, when the engine is supported by the electric machine, it can run at operating points which improve fuel consumption.

Overall, Schaeffler is anticipating a noticeable reduction in fuel consumption—precise measurements will be made available once the concept vehicle has been fully completed. Selecting the right drive configuration also provides increased driving stability. The electric rear axle can provide all-wheel drive for short periods, for example, when setting off on snow or ice.

The characteristics of the whole drive train change if the driver selects Sport mode. In this mode, the engine is used all the time. It sends a permanent charge to the battery via the belt-driven starter generator so that sufficient energy is always available to extract maximum performance from the system. In Sport mode, the torque produced by the electric motor is distributed between the two rear wheels via an integral torque vectoring gear stage.



First I am not familiar with Schaeffler from this project it sounds like they are an engineering school.

It is nice to see an Audi involved in yet another "green" concept car while some of their diesels are less than "golden" right now.

It's hard to be positive on belt drive assisted systems. Is this ever likely to grab the attention of the average Audi TT buyer ? I think not.

It kind of shows the mindset of these legacy auto companies or whoever, hanging on for the sake of an obsolete technology particularly when there is some government handout somewhere along the road.

Meanwhile, in other news, the first Model X officially rolled off the production line yesterday evening from you-know-who. In a way this too is a concept car. But the concept here being that you can go online, assuming you have the wherewithal, and actually order this car today. Wow ! What a concept !

But to continue, the above article does not specify the battery capacity or motor therefore it is difficult to comment on perceived performance. For anyone doubting the facility of providing electric-only driving on city roads with only 48 Volts, well there was a time when I was involved with the design of a controller for a street legal EV which achieved 45mph pulling about 80 amps from a 36 volt Pb-acid 18Kwh pack electronically limited to 400amps. Of course, that was more than 30 years ago and we were doing it with our own money.

An electric rear transaxle will need to be similar to that fitted to the Lexus RX450h with two ratios and a clutching mechanism. It would be expected that a small motor geared initially for low speed driving must be able, later on, to avoid the major motor rpms that would otherwise be imposed on it when the gas engine pushes the vehicle above 100mph, which a TT might be expected to do.


EVs are so simple. Why all this complexity just to continue using gasoline? Wait and in two years, buy an EV and drive it for the next 30 years. ICEVs are obsolete and it's a matter of time before we all can afford an EV.

I watched the Tesla presentation and enjoyed it; but, nothing other than dreams will happen until Tesla can build a car we all can afford. Nissan and the other legacy companies have proven EVs are not their top priority else they would have made better progress by now in selling less limited EVs.

Nope, it's up to Tesla to drive the industry into EVs.

Dr. Strange Love

Lad. It is simple. The Present-Value Amortized Total Cost to Ownership of a Honda Civic, Toyota Corolla ... says it ALL for those who have Listen.

Besides, Gas is $1.90 at Costco and it refills in 5 minutes.

Engineering Economics 101


I will gladly own a Tesla as soon as someone gives me one, pays the insurance, and the taxes. I'll take care of the rest.

I don't even think 80 month loans make it affordable to me...even at 0% its almost half as much as what I make a month after taxes/insurance.

Just wait till big OEM get the mass market EV segment rolling... Tesla doesn't have their clout or supplier relationships. As soon as a viable battery technology comes to mass production, the big three will be on it. They don't do much niche work as its not profitable(most special editions, even though they are pricey, loose the companies millions and millions of dollars), even Tesla is hurting and it has NO competition.


I would love to see 48V or higher degrees of hybridisation becoming common.
Every morning I see lines of traffic stationary outside my house with the engines running, moving every minute or so, exhaling diesel and petrol (mostly diesel) fumes.
This would stop if they all had 48V systems and the urban air would be a lot cleaner.
Hopefully 48V system will be cheap enough for wide adoption (not like full hybrids which add too much cost to cars for wide adoption).
Q: Why did they stop at 48V, why not go to 60V ?

Dr. Strange Love

Mahonj. You said it. Idling is a top issue with transport vehicles - vehicles of any size, dimension and use. Every vehicle must be hybridized to fix this.


@ mahonj:

My Camry XLE Hybrid does that at no initial extra cost over the regular Camry XLE and a free extra 10 to 12 mpg. Ford-Lincoln offers the same deal.

A larger more efficient (Lithium) battery pack would help but Toyota is very slow to move.

The next step would be an affordable quick charge 500+ Km BEV (TESLA III-B+ or equivalent) for use exclusively with public quick charge stations.


"Why did they stop at 48V, why not go to 60V ?"
Actually nominal 48V is as close to 60V as they can get, taking into account safety margins never to exceed 60V in any case of overvoltage at any operating temperature.
When only lead-acid batteries were available, at the end of 1990s, the auto industry proposed 42V system. Those batteries had wider voltage fluctuations, so 42V was selected - See Wiki 42V system
It says: "The limiting factor for direct voltages is a shock-hazard protection limit of 60 V, which must not be exceeded even during voltage fluctuations caused by extreme conditions. This limit eliminates the option of an automotive electrical system with a nominal battery voltage of 48 V, because at low temperatures the charging voltage of the battery can attain 60 V. Also, the price, weight and volume of batteries are influenced by the number of cells, which must therefore be kept to a minimum."

Specification LV148 defines voltage levels for 48V system:
36V-52V - Standard Operation; Full components performance
52V-54V - Upper Limited Operation Range (Regen braking peak, Calibration)
54V-58.5V - Overvoltage Range; Overvoltage countermeasures to be activated
58.5V-60V - Safety Reserve

IMO it would make sense to have a PHEV 48V for cars that spent too much time in stop-n-go traffic, especially in areas where AC is used for many months of the year. Add the ability to precondition the car. Use 1kWh to 2 kWh battery. Single motor power is usually 5 kW continuous, and up to 12kW (or even 15kW) short peak power. But they can use 2 e-motors, with double power.
Such cars should be equipped w/ electric AC, and 48V electric powertrain should have at least two gears, so it can provide good performance moving cars in electric only mode up to 30 or 40kph. Lighter cars would benefit more from this system.
The main advantage of 48V system is said to be price - anything below 60V DC is considered Low Voltage, no safety measures needed.


@Alex, thanks, that is an excellent reply.
I agree, if we could electrify all traffic under 40 kph, we would have a lot less urban pollution for little cost.


I am happy to see that the 50 km/h usual limit for changing mode EV to HEV, slowly decreasing to 30-40 km/h for a better safety and costs. But not only, if you look behind the electric plug, and if you consider the complete energy cycles (regarding both efficiency and emissions). Even so, it is not the topic of the day.

My main remark is that it is a new parallel architecture which will be added to an already long list. Few innovations are trying to challenge series-parallel architectures (Prius type). This last has a huge innovative potential. For instance, in a 10KW power electric propulsion chain, you can increase the rotor inertia of the Genset in order to store kinetic energy (150 KJ which can have the same usage than the energy in a battery). During the rotor acceleration, the braking power of the Genset can be easily increased to 20 KW, even 30KW. In addition, there are plenty of other interesting developments. Design is a little more complex but equipment’s are not.


Vupilla wrote the braking power of the Genset can be easily increased to 20 KW, even 30KW.

Recently I was speaking to a Toyota mechanic who was understandably very familiar with Prius service issues.
I mentioned I had seen brake rotor discs that seemed like brand new despite tens of thousands of kilometers of use. He responded whether I had seen what the brake calipers look like ?

Normally the heat from the rotors is enough to dry out the calipers and prevent rusting. Everywhere, that is, except on the Prius where the recuperation of kinetic energy into electrical power interferes with that process causing brake systems to rust badly.

So having as little as the 10Kw braking allowed by Prius software already has quite an effect. I somehow doubt raising this to 20/30Kw will be any more propitious unless we can raise it significantly to a value that would allow removal of the front brakes entirely. I can see that if lobbying by those with EV interests can get to a point where side mirrors can be replaced by cameras (for aerodynamic reasons) then I can see elimination of some mechanical braking equipment being next on the agenda.

Finally we have to accept that except for the extreme cases - there will always be those living in underserved regions to whom gasoline vehicles make sense - the fact is the majority of the population will benefit from pure electrics supported by some form of reliable supercharger network.


Thanks for your comments,
Electrical braking in a Prius is made with the Motor working as a generator. A 54 kW Motor! Even if electronic limits the recovered power up to 10KW for protecting the battery. In fact the braking torque of the Genset is mainly used to control and to limit the Engine torque through a planetary gear. The fatal generated power is then recovered in the battery or in the Motor. I you want vehicle performances; you need a powerful electric propulsion chain for balancing the Engine torque through the planetary gear. The purpose of my example is to demonstrate that it can be achieved with less electrical power provide some innovative arrangements.
The wearing of the braking rotor is spectacular but it does not means that all braking power is recovered. A30 % limit for the energy recovering is usually admitted.
We have two problems with electricity:
-It should be produced and production is not clean yet. Having a small background in the field (35 years), I have the feeling that it will last.
As soon as you call for electrical power you multiply energy conversions: thermal - mechanical- electrical - chemical - electrical – mechanical without considering daily leaks and transport losses. Each conversion has its own cumulative inefficiency. At the end, global result is poor. In addition, energy losses are costly because they have been generated by top cost equipment’s.
For me, only the complete energy cycle should be considered regarding efficiency, emission and costs. What is genius in a Prius is that the electric power can be reduced as soon as the Engine has achieved its best working point.

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