Concept realization of an 4x4 Vehicle's Transfer case - Thesis assignment

  • Oct. 24, 2014
  • Marcel Romijn

BRACE Automotive recently started a demonstrator project in cooperation with a thesis student of the Rotterdam University of Applied Sciences. Goal is to demonstrate the capabilities of BRACE in gears, bearings and housing design of a transmission. The demonstrator product will be a transfer case for a 4x4 vehicle that can work together with an automated transmission. The transfer case will handle the low- and high-gearing selection and the torque distribution function between front and rear axle. Also the differential will be equipped with a differential lock. Shifting between low and high gears and engaging the differential lock will be controlled by actuators.

This stage of the project mainly focuses on the mechanical aspect of the transfer case and should deliver a concept of the gear train as a result. This will include gear, shaft and bearing calculations so the complete gear train can be drawn in 3D CAD with the functionality of automatic shifting kept in mind. When the concept is finished, a 3D print of the transfer case gear train is planned to be produced which will provide a tangible result that can be used as a demonstrator for BRACE Automotive.

In order to design a concept the same steps as a development for a client were followed. A list of all requirements for the transfer case was set up. This list contains, for example, the functional requirements like the ability to shift between two gearing's, but also performance requirements like the amount of torque it should be able to distribute and limitations regarding the systems dimensions due to the packaging. The use in a 4x4 vehicle can complicate the strength analysis. These vehicles have a large array of use patterns. Some owners will use these vehicles for off-road driving, others will use them to pull heavy trailers and there will even be owners that have bought the vehicle just for the looks and have a more passenger car type of driving pattern.

When the requirements were defined, the first steps in the designing process were taken. The first design choice was made in order to cover the functional requirements and included a gear train consisting of helical gears with a synchromesh function on the input shaft, so shifting in difficult terrain conditions shall be easier for the actuator. To enable the system to distribute torque, the design choice was made to fit an internal differential to the output gear. A locking functionality was also added to enable a differential lock up, translating to an equal rotation of both output shafts. This last feature is a must for off-road driving where the characteristic of a differential would only send power to the wheel that has no traction. Because of the limited space available and the required center distance between the input and output shafts, it was not possible to place the shaft center distances in line.

A first 3D-CAD model, which illustrates the working principle of the transfer case and the design choices that were made was created. The thesis student's work was judged by BRACE engineers before the project was allowed to move on.

Following in this project is the analysis phase were the main purpose is to calculate the geometry of the gears and shafts in order to realize the gear ratio’s that were given by the client, without failing under the conditions that were set with the input load spectrum. Also the exact shape of the teeth on the gears will come from these calculations. The software that will be used for the calculations is KISSsoft/KISSsys.

Stay tuned for further blog posts!


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