Control Design for Differential Lock Synchronization in Heavy-Duty Trucks

Abstract

Heavy-duty trucks operating in low-traction environments rely on differential locks to maintain traction when a wheel spins out. These locks are commonly implemented with dog clutches, which require the connected shafts to be speed-matched before they can engage. Following a spin-out, achieving this match can force the driver to slow down or stop, wasting vehicle momentum and creating a safety risk on slopes. This thesis develops and compares active control strategies that synchronize the differential shafts after a wheel spin-out, enabling faster and safer dog clutch engagement. Individual wheel brakes and engine torque are used as actuators. A driveline model is derived for both the open and locked inter-axle differential configurations. A tire force estimator based on a Kalman filter provides feedforward disturbance cancellation, and a state transformation resolves an observability problem that arises when the inter-axle differential is locked. Three model-based controllers are designed and evaluated: a Linear-Quadratic Regulator (LQR), a Model Predictive Controller (MPC), and a Sliding Mode Controller (SMC). They are compared in simulation across split-friction and gravel road scenarios, using performance metrics for synchronization time, velocity loss, driver disturbance, and control effort, with tuning parameters swept to map the trade-offs between objectives. No significant trade-off is found between synchronization time and the remaining metrics: faster synchronization consistently coincides with lower velocity loss and does not worsen driver disturbance or control effort. A control strategy that follows the principles of the SMC is found to be best suited to the problem’s disturbance-heavy nature. Active engine torque control reduces velocity loss when traction allows, while on low-traction surfaces it must instead be limited to avoid excessive brake demand.