Enhancing CVT Gearbox Reliability Through Optimized Oil Cooler Design: ANSYS Simulation and Vehicle Testing

Abstract

This study investigates the thermal performance of oil coolers for CVT gearboxes, aiming to mitigate fan motor burnout due to excessive oil temperatures. Using ANSYS Fluent, a computational fluid dynamics tool, the analysis evaluated U-shaped (10 passes), S-shaped (9 passes), and W-shaped (8 passes) oil cooler configurations, focusing on the influence of geometric variations on heat rejection. The models, constructed with aluminum fins and tubes, featured fin pitches of 300 FPM (3.33 mm), 700 FPM (1.428 mm), and 800 FPM (1.25 mm), reflecting diverse fin densities. Simulations were conducted under steady-state conditions with an oil inlet temperature of 113°C, ambient air temperatures ranging from 30°C to 55°C, an oil flow rate of 11 L/min, and air velocities between 7.2 and 162 km/h, simulating various vehicle speeds. A structured mesh with 1.2 million tetrahedral elements ensured accurate capture of temperature gradients, particularly around the fins. The U-shaped oil cooler (20 mm width, 300 FPM) exhibited a heat rejection capacity of 10.33 kW, resulting in an outlet temperature of 83.23°C, exceeding the 75°C threshold and causing prolonged fan operation. In contrast, the optimized U-shaped design (34 mm width, 700 FPM) achieved a capacity of 26.75 kW, reducing the outlet temperature to 35.89°C, while S-shaped and W-shaped designs yielded 22.17 kW and 20.45 kW, respectively. The enhanced performance stemmed from a 67% increase in heat transfer surface area and higher fin density (4250 fins), improving convective heat transfer coefficients. Vehicle tests validated these findings, showing the optimized design maintained oil temperatures below 70°C at 100 km/h, limiting fan operation to 3 minutes, compared to the original design’s 85°C peak and over 15 minutes of fan activity. Further analysis revealed that capacity increased with speed (e.g., U30I reached 27.56 kW at 162 km/h) but decreased with rising ambient temperature (e.g., U30I dropped from 20.62 to 13.06 kW as temperature rose from 25°C to 55°C). These insights underscore the importance of geometric optimization in enhancing thermal management, offering a practical solution for CVT reliability with potential for broader application.