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FUEL LEVEL INDICATION CORRECTION AS A FUNCTION OF FUEL TANK PRESSURE, TEMPERATURE AND TIME

IP.com Disclosure Number: IPCOM000234612D
Publication Date: 2014-Jan-22
Document File: 4 page(s) / 252K

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The IP.com Prior Art Database

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FUEL LEVEL INDICATION CORRECTION AS A FUNCTION OF FUEL TANK PRESSURE, TEMPERATURE AND TIME

The majority of the fuel tanks used in automotive applications are manufactured out of high density polyethylene (HDPE) materials with a thicknesses designed to meet a range of functional requirements including cost, weight, permeation durability and safety performance (as examples). New uni-body platforms are driving fuel tanks with large surface areas. The larger the surface areas make the tank more prone to deflections from internal and external forces, as well as environmental conditions like temperature change. HDPE material is highly viscoelastic material that creeps or relaxes over time particularly at high temperature environment. Customers driving for long periods of time under hot ambient conditions can cause the fuel tank surfaces to deform due to its pressure and vacuum force in the tank (+5 to - 5 kPa). The deflection can be so severe to cause the fuel tank bottom to either ground the fuel level sensor or impede its travel, resulting in fuel level indication inaccuracies such as running out of fuel before the Distance to Empty message = 0 miles. The tank surface deflection can also lift up the fuel delivery module in the height direction that increases the amount of unusable fuel in tank.

One common solution to minimize tank deflection, thus reduce customer complaints of inaccurate fuel level indication, is to add rigidity to tanks, either through increasing the tank thickness or adding rib features. However, adding tank surface rigidity can lead to increased tank cost and weight or reduced volume.

A method is proposed to build tank top and bottom surface deflection curves as a function of tank pressure, temperature, and time into fuel level indication algorithm to compensate for the change of the fuel level sensor position change due to environment temperature change, length of driving periods, and internal pressure or vacuum level, thus to ensure more accurate fuel level indication. The tank deflection curves can be pre-determined either through physical testing or CAE modeling. The algorithm can be designed to represent the tank deflection as a transfer function with inputs of pressure, temperature, and time that can be measured or inferred during vehicle operation.

Method

As an example, consider that we have a new tank design. With the CAD data, the fuel tank and straps, fuel delivery module (FDM), and vehicle underbody geometry are discretized into finite element meshes (FEA model). HDPE material properties, including elastic, plastic, and viscoelastic parameters as a function of temperature, are applied. The tank model is installed as both straps move up to vehicle underbody, as on the vehicle assembly line. The tank model is compressed at the beginning, but will gradually relax due to HDPE material relaxation. Once it reaches its equilibrium, the tank bottom surface is defined as tank nominal initial plane (Fig.1).


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