Braking distance

About: Braking distance is a research topic. Over the lifetime, 1843 publications have been published within this topic receiving 11296 citations. The topic is also known as: stopping distance.

Estimation of the Maximum Tire-Road Friction Coefficient

Abstract: We develop and test a "slip-based" method to estimate the maximum available tire-road friction during braking. The method is based on the hypothesis that the low-slip, low-μ parts of the slip curve used during normal driving can indicate the maximum tire-road friction coefficient, μ m a x . We find support for this hypothesis in the literature and through experiments. The friction estimation algorithm uses data from short braking maneuvers with peak accelerations of 3.9 m/s 2 to classify the road surface as either dry (μ m a x 1) or lubricated (μ m a x 0.6). Significant measurement noise makes it difficult to detect the subtle effect being measured, leading to a misclassification rate of 20%.

GPS-based real-time identification of tire-road friction coefficient

Abstract: Vehicle control systems such as collision avoidance, adaptive cruise control, and automated lane-keeping systems as well as ABS and stability control systems can benefit significantly from being made "road-adaptive." The estimation of tire-road friction coefficient at the wheels allows the control algorithm in such systems to adapt to external driving conditions. This paper develops a new tire-road friction coefficient estimation algorithm based on measurements related to the lateral dynamics of the vehicle. A lateral tire force model parameterized as a function of slip angle, friction coefficient, normal force and cornering stiffness is used. A real-time parameter identification algorithm that utilizes measurements from a differential global positioning system (DGPS) system and a gyroscope is used to identify the tire-road friction coefficient and cornering stiffness parameters of the tire. The advantage of the developed algorithm is that it does not require large longitudinal slip in order to provide reliable friction estimates. Simulation studies indicate that a parameter convergence rate of 1 s can be obtained. Experiments conducted on both dry and slippery road indicate that the algorithm can work very effectively in identifying a slippery road.

Friction estimation on highway vehicles using longitudinal measurements

Abstract: This paper develops a real-time tire-road friction coefficient measurement system that can reliably distinguish between different road surface friction levels and quickly detect abrupt changes in friction coefficient. The measurement system relies on the use of differential GPS and utilizes a nonlinear longitudinal tire force model. Compared to previously published results in literature, the advantage of the system developed in this paper is that it is applicable during both vehicle acceleration and braking and works reliably for a wide range of slip ratios, including high slip conditions. The system can be utilized on front/rear-wheel drive as well as all-wheel drive vehicles. Extensive results are presented from experimental results conducted on various surfaces with a winter maintenance vehicle called the SAFEPLOW. The experimental results show that the system performs reliably and quickly in estimating friction coefficient on different road surfaces during various vehicle maneuvers. The developed friction measurement system has many applications in vehicle safety systems such as ABS, skid control and collision avoidance systems and is also useful for winter maintenance vehicles in which knowledge of the friction coefficient can be used to determine the amount and type of deicing chemicals to be applied to a winter roadway.

Steering and brake controlling system

Abstract: Steering and braking are coordinated and controlled according to a sensed yaw rate error or lateral acceleration error to increase vehicle stability without increasing braking distance. A desired yaw rate or lateral acceleration rate is computed from the vehicle velocity and the steering wheel angle. If the yaw rate or the lateral acceleration is excessive, indicating instability, and the brakes are being operated, then both steering and braking are controlled to reduce the yaw rate or lateral acceleration rate. In all other cases, steering control alone is performed. The yaw rate or lateral acceleration rate is reduced under steering control by adjusting wheel positions in a direction opposite the direction of yaw or lateral acceleration. The control system of the present invention is applicable to both two-wheel and four-wheel steering and braking. The yaw rate or lateral acceleration is further reduced under braking control by decreasing brake pressure on a side of the vehicle corresponding to the direction of yaw or lateral acceleration and increasing brake pressure on the opposite side of the vehicle. In the case of anti-lock brakes, pressure is not increased beyond a slip rate threshold. Rather than controlling brake pressure, the slip rate threshold itself may be controlled in like manner to reduce the yaw rate or lateral acceleration.