A US motor manufacturer, Solomon Technologies, has filed a lawsuit alleging that the hybrid transmission drive that Toyota uses in its Prius and Highlander hybrid electric vehicles infringes several aspects of a US patent covering its own"Electric Wheel" technology. A version of this technology was used to propel NASA`s Sojourner rover on Mars.

The Florida company wants an injunction to bar further infringements of the patent and is seeking damages from Toyota for the unauthorised use of its patent.

Solomon launched its lawsuit following a detailed examination of a Prius transmission system. "While we are aware of the difficulties faced by a small company seeking to protect its patent rights against a large company like Toyota," says Solomon president, Peter DeVecchis, "we are determined to use every effort to realise for our shareholders the benefits from our patented technology."

Solomon`s Electric Wheel (shown above) combines two permanent magnet motors with an infinitely variable planetary-gear transmission. One rotor is fixed to the transmission`s outer ring gear, and the other to the inner sun gear. A three-pinion planetary gear set between the ring and sun gears turns the output shaft.

With the motors turning both gears, the transmission automatically and continuously shifts gear ratios as the output shaft gathers speed. When the shaft reaches operating speed, the motors, shaft and transmission turn together, eliminating frictional losses in the gears.

The high-torque, low-rpm motor is said to deliver full torque at any shaft speed, and to provide precise, instantaneous control. It can switch immediately from forward to reverse at any speed, without damage, and is inherently regenerative.

Apart from the Mars rover application, Solomon has focussed its efforts so far on marine propulsion applications. But the company believes that the Electric Wheel technology, which is scalable up to several megawatts, could have many other applications, including winch drives, conveyor belts, steel mills, HVAC systems - and hybrid vehicles.