This paper explains a method to estimate and reduce brake pulling of vehicles due to force difference between RH and LH brake during straight ahead braking. One of the cause of brake pulling during straight ahead braking is brake force difference between right and left brakes of front and rear axles. It is challenging to eliminate this unwanted pulling especially during panic braking in shorter wheelbase vehicles having high center of gravity (CG) and drum brake on all wheels.
A mathematical model is developed to estimate amount of brake pulling from known parameters like brake force, tire properties, steering geometry, suspension hard points, vehicle CG, scrub radius, castor angle etc.
Vehicle tests were conducted to measure amount of brake pulling and close correlation was observed between vehicle test results and derived model. Vehicle test results also revealed that brake force difference between LH and RH wheel can change considerably from start to end during a single braking event itself. In addition, brake force difference may vary significantly with change in brake temperature and pressure. Pulling while braking can also occur due to bump steer and brake steer because of suspension spring wind-off and backward movement of front axle. When pulling due of these factors is in the same direction as pulling due to brake force difference, extent of vehicle deviation increases considerably.
This model also identifies the most sensitive parameters causing brake pulling and helps in their optimization. The test vehicle was updated to have optimized parameters and was re-tested. Re-test results show substantial reduction in pulling as predicted by the mathematical model.