Mitigation of Gear Whine Noise in Agricultural Tractor Application

In the realm of tractor gearbox applications, gear whine noise has long been a persistent challenge that significantly impacts the user experience and overall perceived performance of the vehicle. This paper delves into a comprehensive study that discusses the approach to tackling this issue through a combination of design optimizations, simulation techniques and physical validation processes.

The study begins by meticulously examining the load-dependent noise characteristics encountered during field operations, where distinct gear orders were observed prominently at given speed conditions in the noise order analysis. After conducting extensive drivetrain simulations, the research shifts its focus towards optimizing the gear tooth macro geometry, with specific emphasis on increasing the total contact ratio (helix angle and face width), while also incorporating refinements to the gear micro geometry within the confines of design and manufacturing constraints.

Moreover, the study delves into addressing gear manufacturing variations by transitioning from conventional shaving processes to tooth grinding methods, thereby effectively controlling the gear tooth profiles. To further validate the simulation model, a system-level bench test is conducted utilizing a gear contact pattern correlation approach.

Additionally, the research endeavors to develop prototype gears to facilitate physical experimentation, employing multiple parameter combinations to validate the proposed modifications. The culmination of these interventions results in a significant reduction in Operator Ear Noise Level (OENL), underscoring the efficacy of this comprehensive approach in analyzing and mitigating gear whine noise in real-world tractor applications.

This study underscores the critical importance of meticulous geometric modifications in effectively addressing and minimizing gear whine noise, ultimately contributing to an enhanced overall tractor performance and improved user experience.

Problem Statement

During the field testing of the new tractor transmission development project, gear noise was reported in a plowing application. Test data analysis was carried out to locate sources in the specific application, engine RPM range and gear engaged. Sound recordings reported by field test engineers revealed that this noise was tonal in character. The OENL was reviewed by the project team and was found to be unacceptable. A team was formed to work on the issue resolution. The objective was derived to reduce noise to an acceptable level. A multidisciplinary team was formed to address this issue which included team members from drivetrain design engineering, virtual verification, component bench testing, field testing, Noise, Vibration & Harshness (NVH) testing, prototyping, and manufacturing quality.

Literature Review

In a study by Liu et al. (Ref. 1), the impact of profile and face contact ratios on gear mesh stiffness and gear whine noise in helical gears was investigated. The research highlighted that while the total contact ratio should not be an integer, a face contact ratio close to an integer can help minimize noise. This study provided valuable insights into target contact ratios, moving away from the conventional “more is better” approach.

Munro and Houser (Ref. 2) outlined various gear noise excitations, including transmission error, mesh stiffness variations, axial shuttling, friction, and entrapment of oil or air. Post-test examinations ruled out flank friction and air entrapment as factors, and the absence of burnt oil traces eliminated oil entrapment as a parameter of interest. The study delves into the remaining factors later in this paper.

Lahoti, Patil, and Wagner (Ref. 3) emphasized the benefits of reducing transmission error and improving contact patterns to reduce gear whine noise. Their work demonstrated a strong correlation between reducing transmission error and minimizing noise, stressing the importance of analyzing these enhancements across the application load spectrum for consistent noise performance.

The work of Smith et al. (Refs. 5, 6) addressed the necessity and design considerations of tip reliefs, distinguishing between “short” and “long” tip reliefs and their respective applications.

This research integrates insights from these studies and applies them to a real-world gearbox noise issue. The paper also incorporates manufacturing trials to validate assumptions made in design and simulation, followed by testing and physical validation of the proposed solution.