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DSD 12V e-machine with freewheel-in-transmission concept.

DSD’s low-cost 12V hybrid aims for small cars

As hybrid solutions for cars gain broader applications, reducing cost in technology-dense systems that demand 48V power is a constant challenge. It is particularly important for A-segment cars, superminis and microcars and equally vital for emerging markets such as India, which have traffic clogged major cities.

To this goal, driveline and transmission engineering specialist Drive System Design (DSD) recently revealed a mild hybrid concept that it claims offers up to 60% of the energy recovery typically achieved by more sophisticated (and costly) full hybrids. And it can be done using 12V electrical architecture as a major contributor to cost control.

According to DSD Technical Director Alex Tylee-Birdsall, the new concept "is especially suitable for small vehicles with manual or automated-manual transmissions.” He adds that significant CO2 vehicle emissions reductions can’t be achieved while the hybrid population of vehicles globally remains low. So small, high-volume hybrids would make a significant contribution.

DSD’s system connects a 12V electric machine via a freewheel device on the output (road wheel) side of a car’s transmission. It is compatible with manual gearboxes and facilitates engine-off mode while the e-machine provides creep and hill-hold functionality, Tylee-Birdsall claims. The system also provides a coast or sailing mode when the accelerator is released, so reducing torque-effect interruption during gear shift (invariably an AMT downside).

And when the engine is switched off, the system continues to provide electrical power. It will deliver what Tylee-Birdsall describes as “significant CO2 savings.”

The freewheel device facilitates engine and transmission decoupling from the road wheel, thus reducing drag. According to DSD engineers, mathematical modeling has demonstrated that a 12V machine on a small car could achieve over 60% of the energy recovery of a complex full hybrid system, obviating the need for an additional high-voltage battery pack, DC-DC converter and associated control systems.

As hybrids steadily gain market share, OEM and Tier 1 suppliers’ requirements are growing. To support its own and the industry’s testing needs, DSD has expanded its test facility capabilities, developing it to meet the particular challenges of determining driveline efficiency.

R&D work is concentrating on robust low-noise gear design for high volume production, in addition to efficiency improvements for axle and transmissions and lightweighting and e-drive solutions for both pure EV and hybrid architectures. In the recently expanded transmission and driveline test center, three new test cells were commissioned, bringing the total to ten. The company states that to maximize the value of the expanded facility, it has developed in-house techniques designed to solve the problem of determining driveline efficiency.

Rob Oliver, the company’s Chief Engineer, explains: “As torque capacity increases, the differences we are looking for become a smaller proportion of the maximum figure. To improve measurement accuracy, we have developed our own techniques for the calibration of torque transducers which help overcome this.”

The test facility also has the capability to enable hydraulics systems to be combined with their electronics before assembly in the transmission.

DSD’s largest test cell incorporates five electrical machines having output motors capable of 7000 N·m (5163 lb·ft) and 700 kW 939 hp), catering to 4WD and HEVs, plus drivelines of small cars to trucks and off-highway vehicles.

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