This invention relates to a motor vehicle inflatable restraint system including a seat belt tension sensor for characterizing the occupant of a vehicle seat to determine whether to allow or suppress deployment of restraints for the occupant, and more particularly to a system arrangement for processing and communicating information provided by the seat belt tension sensor.
Various occupant-responsive sensing devices can be employed to characterize the occupant of a vehicle seat for purposes of determining whether deployment of air bags and other restraints should be allowed or suppressed. For example, it is generally desired to allow normal deployment for an adult, to reduce deployment force for a child, and to suppress deployment entirely for an infant seat secured to the vehicle seat with a seat belt. A particularly effective and yet inexpensive way of achieving this functionality is to sense both the seat belt tension and the occupant weight applied to the bottom cushion of the seat. In general, the measured occupant weight may be reduced in proportion to the measured seat belt tension to be more reflective of the actual occupant weight applied to the seat, and seat belt tension in excess of a calibrated value is indicative of a cinched down infant seat.
The present invention is directed to an improved and cost effective mechanization of a vehicle restraint system including a seat belt tension sensor and an occupant detection module for characterizing the occupant of a vehicle seat to determine whether to allow or suppress deployment of supplemental inflatable restraints for the occupant. According to the invention, the belt tension sensor includes on-board signal processing circuitry and is coupled to occupant detection module via a two wire interface that both powers the sensor and its signal processing circuitry and supports communication of belt tension data to the occupant detection module. The sensor produces an electrical signal responsive to seat belt tension, and the processing circuitry generates one of a specified number of messages pertaining to the range of the measured tension, and then modulates a loop current in the two wire interface to communicate the generated message to the occupant detection module.