Marsilli advances ‘open poles’ motor winding for hybrids

Image: Marsilli open pole vs. traditional.jpg

Marsilli claims two main advantages gained with open-pole motor winding: higher power density allowing for a more powerful motor within the same size envelope; or, if the same power output is maintained, a possible reduction in size and weight.

According to Marsilli, a leading winding systems manufacturer based in Italy and an exhibitor at this year’s SAE World Congress in Detroit, brushless motor design is facing a “revolution phase” as traditional needle-wound or field-coil motors have reached their maximum efficiency, being limited mainly by the fill factor. Marsilli is advancing the open-poles motor winding concept to assist motor manufacturers in various markets, including automotive hybrids, actuators, and industrial automation, to increase motor performances by up to 20-25% and reduce material costs.

These performance improvements depend on the overall design of the motor and the specific motor application, according to S. Kumar Rajasekhara, President and CEO of Marsilli North America, based near Baltimore, MD. “It can be related to higher torque, better efficiency, and better material utilization. However, this performance result has been reported to us based on the increased fill factors that we can achieve through our innovative winding concepts…Our strength is our ability to participate in a co-design effort to redesign the customer’s motor in order to achieve more of their goals along the lines of smaller, lighter, and material cost savings.”

Open-poles winding makes it possible, within the same space, to apply more wire turns to obtain a higher motor torque, or to use a larger wire size, allowing a higher motor current. “The inner side of the lamination stack design in a traditional closed stator is conditioned by the air gap required to allow the needle passage between the pole-shoes,” the company explained. “Reducing the air gap between the pole-shoes, the magnetic field increases, reducing the cogging effect and making it possible to add more wire turns.”

Marsilli boasts two main advantages gained with this motor-winding process: higher power density allows for the manufacture of a more powerful motor within the same size envelope; or, if the same power output is maintained, it is possible to reduce size and weight—and, consequently, material costs as well.

Lower wire stress during winding can also result in material-cost reduction, according to Marsilli, by allowing use of a less-expensive type of wire (thinner and less sophisticated insulation enamel). In addition, wire-length optimization reduces the copper cost; “the magnetic field is proportional to the number of turns and not to their length, and considering that all wires out of the lamination are useless for creating the magnetic field,” the company noted.

A new motor winding product line, the MWM (Motor Winding by Marsilli), is structured on two different series. One series is designed for a single-pole motor winding concept, to enable winding single stator poles and then allow for assembling and connecting. The second series is designed to manage the chained phase concept—to wind an entire stator using the open chain pole and then closing the stator upon completion of winding.

For the single-pole MWM, known as the SX machine, the motor poles are wound singularly, then assembled on the lamination and electrically connected to create the stator. Suitable for complex winding designs (i.e., paired coils), the SX motor-winding machine features a wire-clamping gripper to keep the wire ends in position, a special programmable device to control the crossing of the wires, optional wire stripping, and allows easy product changeover.

With the CX motor-winding machine for the chain-poles concept, the motor poles (already integrating into the lamination) are aligned one on side of the other on a tool, then the motor phases are wound around the poles, without cutting the wire between the poles. The pole stack is then closed to create the stator. Some of its main features include an interpolation winding method using torque motors, three programmable axes shuttle for precise winding layering (Z axis) and loading/unloading operations, three programmable axes system for parking and cutting devices, wire parking clamps on the shuttle, movable holding fixtures to simplify loading/unloading operations, and an optional stator automatic closing unit.

“We have already applied these concepts in steering motor applications, starter-motor generators, torque motors in various automotive applications, stepper motors for gauges, etc.,” said Rajasekhara. “Although there is currently no hybrid application in production, there is frenetic activity ongoing in developing the hybrid motor applications. Due to confidentiality reasons, we cannot divulge too many details about this ongoing development and co-design efforts with our customers.”

Is the technology suitable for heavier-duty commercial vehicles as well? “In general, yes; however, it depends upon the sizes of motors to be considered,” Rajasekhara told SAE Magazines. “We continue to expand our product offerings to include larger wire sizes, motor sizes, etc., so it would not be appropriate to limit the applications that we would consider. We can also work with motorcycle and off-road vehicle applications.”

He added that Marsilli is “witnessing an explosion of the use of motors as energy-efficient replacements to power-hungry automotive solenoids, which typically perform simple on-off functions. We expect this trend to push us toward greater innovation within the automotive motor industry.”

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