Vehicle Speed Estimation During Excessive Tyre Slip Conditions
Typ
Examensarbete för masterexamen
Program
Automotive engineering (MPAUT), MSc
Publicerad
2021
Författare
Storckenfeldt, Carl
Ganatra, Diler
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Vehicle speed is one of the most important states that needs to be estimated in a
vehicle. This quantity is safety critical as it drives a majority of the on-board safety
and driver-assistance systems. A normal modern car is equipped with wheel speed
sensors, Inertial Measurement Unit (IMU), steering angle sensor and powertrain
and brake torque sensors which makes the foundations for the speed estimate. The
wheel speed sensors provide a relatively good estimate of the vehicle speed in normal
conditions with limited wheel slip. However, in excessive wheel slip conditions
the wheels speeds significantly diverge from the true speed of the vehicle. In these
situations, no reliable direct measurement of the speed is available and the speed
estimate needs to be complemented with e.g. dead reckoning based on accelerometer
input. In this thesis, a kinematics based extended Kalman filter (EKF) for longitudinal
vehicle speed estimation in excessive all-wheel slip conditions is presented. The
filter uses combined vehicle orientation and speed estimation, only considering longitudinal
dynamics. The proposed filter utilizes a slip-detection system that detects
wheel slip and filters out wheel speed measurements from these slipping wheels. It
also has a separate logic for speed estimation in braking on slippery surfaces. Two
slip detection approaches are presented. One approach is to assume slip between
detection of certain events related to the powertrain torque, wheel acceleration and
braking. The other approach makes a decision about slip at every time step. The
filter and slip detection systems are tested on real-world driving data recorded from
two different all-wheel drive vehicles in excessive slip conditions. The results show
that the proposed method provides a better estimate than the reference brake supplier
estimate, keeping the estimate within ±4% of the ground truth speed for many
cases. Though, none of the slip-detection systems provide flawless slip detection
resulting in the filter to sometimes rely on non-representative wheel speed measurements
degrading the estimate. It becomes clear that the speed estimation is limited
both by the approach of detecting slip and by the limited sensor setup providing no
absolute measurement of the speed in excessive all-wheel slip.
Beskrivning
Ämne/nyckelord
vehicle speed estimation , excessive wheel slip , slip detection , dead reckoning , vehicle state estimation , extended Kalman filter