Patent ID: 9708959
Date: 2017-07-18
CPC Classifications: F01N,G01F,Y02A,Y02T

Claim:
1. A method, comprising: generating an ultrasonic signal in an exhaust fluid tank of a vehicle; in response to a strength of a received reflection of the ultrasonic signal being greater than a threshold, filtering the reflection based on a variance of the received reflection, and indicating a fluid level based on the filtered reflection; otherwise, not filtering the reflection, and maintaining a previous latest fluid level indication; and, limiting an output of an engine of the vehicle based on the level indication, wherein the fluid level is further based on a time shift of the reflected ultrasonic signal, and wherein the variance is a variance of instantaneous level measurements over the last N samples, where N is a number of samples, wherein the variance is a measure of a spread of the received reflection from a predetermined number of reflections received prior to the received reflection, the variance determined based on a probability density function assuming a random distribution of the received reflections.