Abstract
The brake noises have been broadly classified by using different words like judder, groan, moan, squeal, squeak, etc. For simplicity, based on their frequency ranges, they can be grouped into 3 categories: judder (around 10Hz), groan (50 – 150 Hz) and squeal (>1k Hz).Brake groan noise is generated when a brake pedal is slowly released especially in an automatic transmission car which was initially stationary. The main cause of this phenomenon is the stick-slip behaviour between the brake pads and the disc. Stick occurs when the pad and the disc move together with no relative movement between them, while Slip occurs when the brake force decreases and the wheel torque begins to catch up with the brake torque and eventually a wind up of the brake assembly causes a momentarily slip. Without further release of the brake pressure, the stick happens again and the cycle repeats. The noise and vibration due to this sustained stick-slip is called brake groan.
A sensitivity study was done on a Multibody quarter car model that was developed using a Multibody Simulations (MBS) software with data from Volvo Cars to simulate the Brake Groan phenomenon. The model contained a detailed brakes system and the quarter car front suspension system with all the suspension components modelled flexible (deformable). FE models were created for all the suspension components using an FE code. A modal reduction was carried out further to include them into the MBD model and connected appropriately. The required modes were considered for each suspension component to consider their flexibility.
Contacts between the pads and the discs were defined using the contact stiff-ness / damping and the parameters for friction. Dynamic friction law using a static (µstat ) and dynamic (µdyn ) coefficients of frictions was used, along with the corresponding Static (vstat) and Dynamic (vdyn) Velocities. The Brakes components on the other hand, eg. Brake pads, disc, callipers, piston etc. were modelled as rigid bodies. The aim of this work was to capture the stick-slip and understand the sound transfer paths as the brakes are slowly released and the vehicle is accelerated gradually. Additionally the aim was to carry out a sensitivity study by varying various model parameters to see the effect on Brake groan.
