Novel clamping force control for electric parking brake systems

In this paper, we present a novel control method with clamping force estimation for an electric parking brake system. This simple control structure can be implemented at low cost as it does not require a clamping force sensor. The characteristic curve is conventionally used to estimate the clamping force through the angular displacement of the DC motor; however, this can result in error because of the dependence of the curve on the brake clearance between the brake pads and brake disk at release. We solve this problem by approximating the initial contact point using the angular velocity of the motor. We then propose a novel on-off control method to avoid excessive clamping forces by predicting the additional angular displacement after power-off caused by the inertia effect. Finally, we experimentally validate our proposed control method.