California Partners for Advanced Transportation Technology

Automated vehicles require sufficiently accurate system models in order to achieve a desired level of closed-loop performance in, for example, automated highways systems or smart cruise control systems. Parameters of the models are one of the important factors that determine the accuracy of system modeling and, eventually, the overall performance of the closed-loop system. Current GPS sensing technology enables estimation of road grade and, consequently, simple treatment of parameter estimation from a static force balance. This work has demonstrated that road grade can be reliably estimated using synchronized two antennae GPS system or the vertical to horizontal velocity ratio from GPS speed measurements. While both methods provide similar performance in road grade estimation with comparable errors, the velocity-ratio based, single-antenna system is a better choice since it is more economical to implement than two-antenna system. Accurate estimation of road grade enables the estimations of other important vehicle parameters. With reliable and accurate road grade estimates and the assumption of low frequency dynamics, the vehicle mass estimates have been shown to converge quickly within 2% and 5% of the measured values for a passenger car and a heavy truck, respectively. This work also presented a new method for maintaining and improving string stability by preventing actuator saturation in automated vehicles on highways. Instead of relying on feedback controllers to deal with the issue of actuator saturation after the fact, reference commands are fed through an FIR filter called an input shaper so that harmful components in the reference commands are reduced or removed. Input shaping is a command modification technique in which a reference command to a system is modified or shaped through convolution with an FIR filter. Original (unmodified) reference signals are passed through the input shaper and the shaped (modified) signals are then fed to the system. The purpose of this modification is to remove frequency content from the reference command that can produce oscillations in the closed-loop system due to lightly damped, flexible modes. With properly chosen impulses, the effect can be very significant.