Systematic Study To Understand And Resolve Brake Pull In Commercial Vehicles Using Simulation And Proving Ground Tests

In traditional commercial vehicles with leaf spring suspension and Recirculating Ball Joint (RCBT) steering systems often experience undesirable pulling due to unsymmetrical steering mechanism during braking, especially when the suspension and steering hardpoints are not properly tuned. This study investigates the causes behind such pulling behavior, specifically focusing on brake steer and bump steer, which occur due to misalignments in the suspension and steering geometries. Brake steer happens when the braking forces generate a torque, causing the vehicle to pull towards one side. On the other hand, bump steer refers to the unwanted changes in the wheel alignment when the suspension undergoes travel, leading to instability or unintended steering input. These two phenomena, if not controlled, can result in undesirable vehicle handling, especially under heavy braking conditions. The study aims to understand and quantify these mechanisms, providing insights into how they can be mitigated through proper design and tuning of the suspension and steering hardpoints. To tackle these issues, a methodology has been developed for tuning the suspension and steering hardpoints, using Adams Car Multi-Body Dynamics (MBD) simulation to provide quick and reliable predictions of pull direction behavior. The key adjustments involve fine-tuning the front leaf spring pivot and Pitman arm draglink pivot to reduce bump steer, while optimizing the knuckle-to-draglink ball joint hardpoint to minimize brake steer. Simulation results show that the right-hand side pull, which was initially severe, was reduced to a mild left-hand side pull after the necessary adjustments to the hardpoints. While this study offers valuable insights into the tuning process and provides useful predictions regarding the direction of pull, it is important to note that exact numerical values for the magnitude of pull cannot be reliably predicted due to the inherent complexities of real-world vehicle dynamics. However, the study successfully establishes a method for predicting pull direction, which can serve as a strong foundation for further refining suspension and steering system designs in small commercial vehicles.