SANYO may develop Mercedes-Benz hybrid batteries

A 28 module NiMH battery with 6 Ah, 200 Volts and 1.2 kWh was used. It weighs 99.3 lbs, was supplied by Varta and could supply 20 kW for 30 seconds.

A driver can constantly follow the driving modes on a small monitor next to the steering wheel. The display shows the interaction between the combustion engine and the electric motor, and between the energy storage devices and the electronic control units.

Stuttgart. December 1, 2003. The English word "hybrid" derives from the Latin "hybrida", which means "half-breed". In the automotive industry, engineers use the term hybrid vehicle to designate an automobile that has two energy converters - combustion engine and an electric motor, let's say. Because it has two power sources, such a vehicle also requires two energy stores - a fuel tank and a high-voltage battery. But if you took a peek under the hood of one of the latest hybrid vehicles developed by DaimlerChrysler Research — the M-Class HYPER — you would hardly believe that this sport-utility vehicle is a hybrid. Although the standard 2.7-liter CDI diesel engine would be impossible to overlook, you would notice that the M-Class HYPER doesn’t appear to be equipped with a conventional electric motor and the associated battery.

Head of Advanced Propulsion Systems, Prof. Karl E. Noreikat, holds the key to this mystery. “We have already achieved a high degree of integration of the two drive units,” he explains. “The electric motor is being ever-more tightly integrated into the powertrain and now takes up almost no additional space. It is positioned directly on the clutch shaft, between the clutch and the transmission, with which it forms a connected unit.”

From the cylinder to the disc

This integration was realized thanks to a new design for the electric motor. The motor doesn’t have the elongated, cylinder-shaped rotor found in conventional electric motors, such as those in drills, for example. Instead, the new type of electric motor features a very narrow, ring-shaped rotor with a comparatively large diameter. Noreikat and his team refer to the contrasting designs as the “sausage” and the “disc” motors.

With an output of 61 hp (45 kW), the high-torque disc motor has the advantage that it can be easily incorporated into existing drive trains. And its sophisticated electronic control system and state-of-the-art clutch offer even more benefits:

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  The disc motor serves as both a starter and a generator, eliminating the need for these components. In addition to reducing vehicle weight, this also simplifies the entire powertrain and the wiring.
  
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  There also is no need for the second electric motor found in the majority of hybrid vehicles already on the market. Such second motors increase the weight and costs of a vehicle, and they also take up a lot of space.
  
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  And in contrast to hybrid concepts realized to date, the regenerative power — the electrical energy recovered from the vehicle’s kinetic energy per time unit — is twice as much as achieved by previous hybrid concepts. One result of this is that the M-Class HYPER consumes up to 20 percent less fuel than the comparable Mercedes-Benz ML 270 CDI production vehicle, according to the New European Driving Cycle.
  

Lower fuel consumption, fewer emissions, superior driving dynamics and easy integration into the powertrain — the advantages of the M-Class HYPER are the results of the work carried out by Noreikat’s team in their search for a simple and compact solution. “Our aim was to develop effective new combinations of proven parts that would allow us to come up with reliable, cost-effective solutions,” explains Noreikat.

The engineers succeeded in making optimal use of the advantages of hybrid technology. Using a simple “parallel hybrid concept,” they retained all of the comfort-enhancing and performance features of a conventional drive train — and even improved them. “One advantage here was that we didn’t have to modify the transfer case of the permanent four-wheel drive in order to assemble the hybrid system,” reports Christof Bunz, a member of Noreikat’s team. Bunz and his colleagues made a considerable investment of time and effort in the development of the electronically controlled clutch unit, which controls the constantly changing interaction between the combustion engine, the electric motor and the automated 6-speed manual transmission. The clutch is remarkable because it can balance the different speeds and torques of the motor, the engine and the transmission so gently that the vehicle is guaranteed to run smoothly. And drivers will barely be aware of gear shifts during acceleration. A closer look at the different driving modes gives a clearer understanding of just how clever the clutch really is:

When starting up, driving at low speeds in city traffic or when stuck in a traffic jam, the diesel engine is switched off altogether; only the electric motor propels the vehicle. Depending on driving conditions, the clutch ensures that the combustion engine is push-started once the vehicle reaches approximately 25 km/h. In normal driving mode, the combustion engine powers the car. “Here, the electric motor is only used to synchronize the transmission during gear shifts,” says Bunz. During the acceleration process — while overtaking, for example — the electric motor is automatically activated, so that the torques of the motor and the engine are combined. This is what engineers call the “booster function.” During extended application of the vehicle’s brakes, the diesel engine switches off and the electric motor is used for regeneration. The motor is powered by the wheels via the transmission and functions as a generator, converting kinetic energy into electrical energy. This energy is then fed into the car’s battery. The battery is also charged when the vehicle is being driven at a constant highway cruising speed, and the combustion engine is not required to operate at its maximum output. In this mode it is the engine, not the transmission, that turns the motor so that it functions as a generator and charges the battery.

Water-cooled battery

The battery used in the hybrid vehicle is a water-cooled, nickel metal-hydride battery with an output of 50 kW. It is installed together with the electronic battery control in the spare wheel well at the rear of the vehicle. And in addition to being a space-saver, this arrangement also solves the mystery of that missing second energy-storage device. You remember. The one that was nowhere to be found under the hood.

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