Case Study: Transmission Planetary Assembly

Processes: Conventional powder metallurgy & powder forging
Density: 7.83 g/cm³
Tensile Strength: 1, 310 MPa (190,000 psi) core
1,932 MPa (280,200 psi) carburized

Yield Strength: 1,070 MPa (155,200 psi) core
1,725 MPa (250,200 psi) carburized

Hardness: 38 HRC core
60 HRC carburized

End Use and Function

The 32-part planetary assembly connects to the input shaft from the engine and supports the planetary pinion gears. This carrier assembly is used in the HF 35 Hybrid Transmission, which is assemble into the hybrid cars—Lincoln MKZ, C-MAX, and Fusion Hybrid vehicles. The carrier assembly must be extra quiet in operation as poor geometry creates a noisy gear which can easily be heard in a hybrid transmission.

Fabrication

The helical pinion gears are sinter forged to full density using tools that must also rotate and exactly match the gears’ 24.5° angle; it is the first time such a gear has been used in an automotive transmission application.

Results

It is estimated that the customer realized cost savings on the order of 25% by going this route. In over two years of production of this carrier with about a quarter of a million assemblies shipped, there have been no field returns.