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Mitsubishi Electric develops smallest, lightest motor controller unit for automotive power steering

Mitsubishi Electric Corporation has developed the smallest and lightest motor controller unit yet for electric power steering in automobiles. This next-generation motor controller unit is half in volume and 70% in weight compared to the company’s current products with equal output, contributing to the enhanced fuel efficiency of automobiles.

Mitsubishi Electric’s next generation motor controller unit. Click to enlarge.

Mitsubishi Electric has also upgraded steering assistance capabilities by improving the output performance of the motor by 30% through optimization of the electromagnetic design and the employment of the company’s original Poki-poki motor, which incorporates technologies that increase coil density. This prototype motor controller unit also features a unique control algorithm developed to provide enhanced steering sensation and stability. Mitsubishi Electric will provide the product to automobile and steering manufacturers in the near future.

Quick Specs
Controller part outside diameter
(excluding connectors)
φ93 mm
Motor part outside diameter φ80 mm
Total length 105~145 mm
Weight 1.7~3.1 kg
Rated torque 1.8~7.2 N·m

40% of new automobiles manufactured worldwide now incorporate electric power steering, which can reduce fuel cost by 3~5% compared to those using hydraulic steering. Automobile and steering manufacturers are increasingly calling for motors and controllers that are much smaller and lighter than current components to further improve fuel efficiency and facilitate installation of power steering systems. To fulfill these needs, Mitsubishi Electric has integrated the motor and controller into one unit, and aligned them on the same axis by improving the internal structure of the controller.

The Poki-poki motor uses a technology that can greatly improve lamination factor of winding and productivity, which helps to manufacture compact motors efficiently.

Click to enlarge.



The important % to 5% fuel consumption reduction claimed between hydraulic and electric power steering is almost unbelievable


Correction: should read .....3% to 5%


"can reduce fuel cost by 3~5%"

If I spend $1000 per year on fuel a 3% reduction is saving $30, that is not all that much.


Many people spend over $2K/year on fuel. At 5% this would represent $100+/year. However, what makes an electric power steering so fuel efficient?


Anything belt driven suffers frictional loses.

Nick Lyons


Expanding on SJC's comment: traditional power steering has a belt-driven hydraulic pump which is turning/pumping whenever the engine is running, so you have not only the frictional losses with the belt and pulley(s) but also within the pump itself. Electric power steering activates only when the steering wheel is turned. Some newer cars have electro-hydraulic power steering, whereby hydraulic pressure is generated by an electric pump, which only runs when needed.


You can look at electric power steering savings something like a start/stop system. It is only in use when you need it. Electric A/C is similar in that it is not belt driven. Even though belt drive A/Cs are clutched off when not in use there are still frictional loses as the A/C pulley is driven around by the belt at whatever speed the engine is running.


NL & SJC. Thank you for the pertinent info. From this, one could conclude that all (vehicle) accessories should be electrified with ON-OFF and variable speed e-units to better match the requirements and reduce wasted energy. Eventually, a low cost high efficiency roof top solar panel could produce all the energy used by e-accessories.

Recent very high efficiency Inverter type Heat Pumps have demonstrated that. Ours is working well, down to -17C. It is fully programmable and maintains very stable temperature to within 0.2C. Could it be adapted to (ICE-HEV-PHEV-BEV) vehicles?


We may see a lot more electric power steering. To date the reviews I have read on some cars with this is that it lacks "road feel". I would imagine that some clever programming might smooth all that out over time.

Henry Gibson

The fist step towards more efficient automobiles is to build an integrated starter generator into the flywheel. Then all belts are eliminated. ..HG..

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