Study On Vehicle Terminal And Algorithms Of Automatic Crash Notification System

Automatic crash notification(ACN) system is a kind of post-accident safty technology. When crash happens, system identifies crash. Then crash data and geographical location information are sent to rescue center by wireless communication network. With ACN system, response rate and rescue efficiency can be increased. Currently, most of ACN systems share the trigger signal with air bag system and thus exist false trigger cases. And messages sent by systems cannot enable recuse center to predict injury of occupants. Consequently there will be a great significance to design vehicle terminal and research trigger algorithm and impact type identification algorithm of ACN system.Based on moving window integral algorithm, a trigger algorithm of ACN system is designed. By comparing the effect of different window width on the trigger algorithm, the window width of moving window integral algorithm is selected as 8 ms. After notification system is triggered, crash detecting module determines different notifying types according to the change of velocity in moving window.Old impact type identification algorithms identify frontal, left side, right side and rear-end impacts by principle direction of force(PDOF), but calculation result of PDOF is not precise enough. By enhanced PDOF calculation method, the accuracy of PDOF is increased. Then PDOF is used to identify four main impact types. If frontal impact was identified, three frontal impact types, full frontal impact, offset impact and oblique-angled impact should be identified. By significant differences in the change of y axis velocity and peak appearing time of |ΔVy|/|ΔVx|, three frontal impact types can be well distinguished. Comparing to old algorithms, new algorithm is more accurate and reliable, and more impact types can be identified.Vehicle terminal is composed of crash detecting module and crash notifying module. Hardware circuits of each module in vehicle terminal are designed, including accelemeter module, photo acquisition module, external storage module, wireless transmission module, LCD module, GPS module, GSM module, and system power module. Software designs of all functional modules are demonstrated in detail, including intiallization and working procedure.A sled impact simulation test is carried out according to GB14166-2003. Results show that crash detecting module collects impact acceleration signal precisely and calculates the change of velocity accurately. Notifying types can be determined by utilizing triggering algorithm and impact types can be identified by impact type identification algorithm. Crash notifying module displays impact information and GPS geographical location information, and then send a notifying message to presupposed cell phone successfully. Vehicle terminal has a good impact resistance and high reliability. A vehicle road test proves that automatic crash notification system had no false trigger cases in a situation where emergency brake or barricade is existed.