Ford gets a lift from plastic gears

1904

The Ford Motor Company’s Hi-Lex next-generation lift gate transmission has been developed with the involvement of Ticona in materials, design and R&D.

The Hi-Lex transmission was first seen on the 2005 Expedition SUV. (photo: Ford)

The reliability and quietness of Ford’s power lift gates have been ascribed to the Hi-Lex Controls transmission, which is driven by high-precision plastic shafts and gears developed by a team that included Ticona, the Engineering Polymers Business of Celanese Corporation.

The Hi-Lex transmission was first seen on the 2005 Expedition SUV and has subsequently appeared on all Ford power lift gates. The two-stage reduction transmission uses precision steel ball bearings mounted on plastic shafts and 2.5-inch diameter plastic gears, to achieve the required reduction between the electric motor and a flexible torsional cable. The first-stage gear and shaft, second-stage output plastic gear and second-stage output shaft are injection moulded from Celcon acetal copolymer (POM) and Celstran long fibre reinforced plastics (LFRT), both from Ticona.

Hi-Lex America uses high-performance thermoplastics from Ticona in gears and shafts to help maintain required mechanical properties and dimensional stability, even at high temperatures. (photo: SPE)

Less weight, lower cost and quieter

The Hi-Lex transmission with plastic gears cuts cost, weight and noise. The reduction in NVH (noise/vibration/harshness) was a specific target of a team led by Fred Eberle, a Gearing and Gear Drives Technical Specialist and Six-Sigma Master Black Belt with Hi-Lex in Rochester Hills, Michigan. The team defined, analysed and optimised the design to take advantage of a number of particular plastic gearing considerations, which can be more complex than those for standard metal gears. The decision was made to proceed with a two-stage reduction transmission, which relied on first- and second-stage plastic splined shafts attached to plastic gear wheels in a gearbox with a rated torque output capacity of about 12Nm (106lb (48kg)/inches).

Once the requirements were defined, the team identified materials for the gears and shafts that would maintain the required mechanical properties and dimensional stability, even at elevated temperatures. With the need to balance stiffness born very much in mind, the gear team selected Celcon M90, a general purpose, unreinforced POM, for the first-stage gear and shaft; and Celcon GC25T, a 25% glass-coupled POM for the second-stage output gear. Celstran PA66-GF50-02, a 50% long glass fibre PA66 that offers high strength and stiffness combined with high heat deflection was chosen for the second-stage output shaft. The team reported that the Hi-Lex gear train offers a lower-cost solution that meets extreme thermal constraints and achieves the NVH performance measurements defined by the customer.

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