Patent ID: 9267493
Filing Date: 2016-02-23
CPC Classification: F03G

Claim Text:
1. A method of monitoring the operation of an on-vehicle device with a movable component capable of adopting at least two positions, the device being operated by direct current (DC) electricity provided by a vehicle battery, the device comprising: the movable component that is moved with respect to other components of the device by a linear shape memory alloy (SMA) actuator as a part of the device, the SMA actuator being in electrical communication with the vehicle battery for heating the SMA actuator, the heating of the actuator being selected to cause the SMA actuator to transform from a first metallurgical phase to a second metallurgical phase and to thereby shorten in length to move the moveable component from an initial position to a second position, the device further comprising a return spring arranged and adapted to stretch the SMA actuator when heating is discontinued and the SMA actuator cools and transforms from the second metallurgical phase to the first metallurgical phase, the extent of the stretching being limited by a stop, the stop being positioned so that the moveable component is moved from the second position and restored to the initial position to prepare the SMA actuator for repeated operation, the method of monitoring the on-vehicle device comprising: repeatedly operating the device in response to an actuating signal by applying, for at least a predetermined heating time, a predetermined direct current electrical potential across the full length of the linear SMA actuator to produce an electrical current through the length of the linear SMA actuator, the predetermined DC electrical potential and predetermined time period being selected to heat the linear actuator to a temperature sufficient to transform the linear SMA actuator to the second metallurgical phase in which the length of the linear actuator is shortened so as to reposition the movable component, and making, at time intervals during application of DC current to the SMA actuator, a series of simultaneous measurements of the instantaneous electrical potential and instantaneous electrical current, and using these measurements to compute a series of measures of the electrical resistance of the linear SMA actuator at like time intervals; then, stopping DC current flow and allowing the linear SMA actuator to cool to a temperature sufficient for the SMA actuator to transform to the first metallurgical phase in which the return spring strains the linear SMA actuator to its original length and returns the movable component to its original position to ready the device for subsequent operation; placing and retaining pre-specified data, or historical data, of acceptable heating current flow in the linear SMA actuator and variation in electrical resistance during the heating time of the linear SMA actuator in an on-vehicle computer system; and thereafter, during each use of the on-vehicle device, using the on-vehicle computer system, to compare values of current flow and electrical resistance experienced by the linear SMA actuator during application of DC electricity to monitor the present function and viability of the device, and to report a malfunction in the device to a vehicle operator or a device service location, where such comparing comprises the consideration of at least one of an initial current value and a sequence of current values over a time period, and also a sequence of electrical resistance values over a time period.