Automobile Fuel Gaging by Pneumatic Methods

Problems in Implementation and New Strategies

Abstract

This paper describes how to implement volume measurement effectively using the pneumatic method for automobile fuel gaging.
The pneumatic method estimates the remaining fuel in a closed tank by subtracting the gas volume in the tank from the tank capacity. The gas volume is calculated by applying the ideal gas law to the relation between the gas volume and the pressure in the tank. The gas volume is inversely proportional to the amplitude of the pressure change due to a small change in tank capacity.
In implementing this method, we faced the following basic problems:
(1) Bias error due to the flexibility of the fuel tank.
(2) Noise due to tank wall vibration and liquid sloshing.
(3) The measurement system must be compact and simple.
Problem (1) and (2) are substantial causes of error and noise in using this method and problem (3) is a specified prerequisite for automobile equipment.
We investigate how the flexibility of the tank influence the bias error and show the strategy used to solve it. We present a new compact sensing system composed of a loud speaker and two microphones and investigate the robustness of the system for noise in the tank when driving. Experiments using a real 55 liter tank verified the validity of the gaging system. The maximum error when driving on a very rough road was found to be±1.5 liters.