Application of Hybrid Pipes to Reduce the Noise Generated by a Pressure Transient in the Brake Fluid 2021-36-0412

The noise and vibration are directly related to the perceived quality of a vehicle and it is crucial that the manufacturers focus their efforts to reduce that. When an unusual noise appears, it is a great challenge to define an approach for understanding the phenomenon, identifying the cause and then defining a solution to reduce its effect. A “knocking noise” coming from the brake rigid pipes is perceived while driving the vehicle in a cobbled pavement at low speed and it coincides with the closure of brake system module inlet valves. When a valve closes quickly, there is a sudden change in the flow velocity, which generates a pressure transient in the brake fluid inducing vibrations in the rigid pipes. The pressure transient can be minimized by reducing the speed at which the pressure waves travel in the pipe. The bulk modulus, the density of the fluid, the velocity of valve closing, the Young’s modulus and the dimensions of the pipes, determine the wave speed. The objective of this work is, first to correlate the phenomenon with the theory regarding the transient flow by presenting the measurements of pressure change in the brake lines during the brake unit valves actuation. Afterwards, evaluate the experimental results of changing the variables that affect the wave speed, and its influence in the noise perception. At the end, show how the application of a hybrid pipe solution, which reduces the Young’s modulus of the brake line, can reduce the pressure transient as well as the “knocking noise”.