Comparing a CVT to a Four-speed Automatic Transmission on Stress to the ATF

This study focused on two areas of interest to CVT fluid developers. The primary set of experiments investigated whether continuously variable transmissions (CVTs) and their conventional step-type automatic transmission counterparts stress their fluids differently. The investigation compared the push-belt CVT (PB-CVT) in a '98 Nissan Bluebird to the General Motors (GM) Hydra-Matic 4L60 (four-speed) automatic transmission. Chemical, physical and performance comparisons of fresh and used fluids revealed the fluid stresses from the Nissan Bluebird CVT were similar to those from the 4L60 transmission. A second set of tests probed the question of how well results from two standard steel-on-steel friction bench tests correlate to CVT dynamometer (belt box) findings. The bench test models captured about half of the critical trends in the belt box data, as evidenced by prediction R² values in the 0.5 to 0.7 range.