Capacitive Gauge for Fuel Tank

• US 20080276704A1
• Filed: 10/26/2006
• Published: 11/13/2008
• Est. Priority Date: 10/26/2005
• Status: Active Grant

• Current Assignee: Inergy Automotive Research Systems
• Original Assignee: Inergy Automotive Research Systems
• Inventors: Naydenov, Volodia
• Granted Patent: US 7,905,145 B2
• Time in Patent Office: Days
• US Class Current: 73/304.C
• CPC Class Codes: G01F 23/266 measuring circuits therefor

Abstract

Capacitive gauge for fuel tank comprising a measurement capacitor, a reference capacitor and at least one standard capacitive device, fed by and connected to an electronic interpretation circuit comprising switches for charging and discharging the capacitors and the capacitive device at a certain frequency; an integrator to which the charges of the measurement or reference capacitor can be transmitted and accumulated before being discharged into the standard capacitive device; a comparator for comparing an output value of the integrator with a threshold value; a counter; and a processor or computation unit for calculating the level of liquid in a fuel tank according to the equation:

h=[n_ref,empty/(n_ref−n_ref,empty)]·[(n_meas−n_meas,empty)/n_meas,empty],

where n are the values read by the counter respectively for the capacitance of the reference capacitor when empty (n_ref,empty), for the capacitance of the reference capacitor immersed in the fuel (n_ref), for the capacitance of the measurement capacitor when empty (n_meas,empty) and for the capacitance of the measurement capacitor in the liquid to be measured (n_meas); the standard capacitive device comprising at least two standard capacitors with electrical connections to the measurement capacitor.

Claims

1. A capacitive gauge for fuel tank comprising a measurement capacitor, a reference capacitor and at least one standard capacitive device, fed by and connected to an electronic interpretation circuit comprising switches for charging and discharging the capacitors and the capacitive device at a certain frequency;

an integrator to which the charges of the measurement or reference capacitor can be transmitted and accumulated before being discharged into the standard capacitive device;

a comparator for comparing an output value of the integrator with a threshold value;

a counter; and

a processor or computation unit for calculating the level of liquid in a fuel tank according to the equation;

h=[n_ref,empty/(n_ref−

n_ref,empty)]·

[(n_meas−

n_meas,empty)/n_mens,empty],

where n are the values read by the counter respectively for the capacitance of the reference capacitor when empty (n_ref,empty), for the capacitance of the reference capacitor immersed in the fuel (n_ref), for the capacitance of the measurement capacitor when empty (n_meas,empty) and for the capacitance of the measurement capacitor in the liquid to be measured (n_meas);

wherein the standard capacitive device comprises at least two standard capacitors with electrical connections to the measurement capacitor.

2. The gauge according to the preceding claim 1, wherein the standard capacitors cover a range from 500 to 25000 pF.

3. The gauge according to claim 1, wherein it comprises at least three standard capacitors with electrical connections only to the reference capacitor and at least three standard capacitors with electrical connections only to the measurement capacitor.

4. The gauge according to claim 1,

wherein it comprises at least four standard capacitors having electrical connections to both the measurement capacitor and to the reference capacitor.

5. The gauge according to claim 4, wherein the capacitive device comprises at least six standard capacitors having electrical connections to both the measurement capacitor and the reference capacitor.

6. The gauge according to claim 1, wherein it comprises or is linked to a connecting device enabling the electronic interpretation circuit to connect the measurement capacitor to the optimal standard capacitor.

7. The gauge according to claim 6, wherein the connecting device is actuated manually.

8. The gauge according to claim 6, wherein the connecting device is an electronic device incorporated in the electronic interpretation circuit,

9. The gauge according to claim 8, wherein the gauge is designed to operate as follows:

a) on starting a measurement, the electronic circuit provokes charging of the measurement capacitor with a given discrete charge and this by means of a correct positioning of the switches,

b) the position of the switches is modified so that the charge is transmitted to the integrator, which accumulates it,

c) the comparator compares an output value of the integrator (normally its voltage) with a threshold value (reference voltage),

d) the steps a to c are repeated cyclically at a certain frequency v₁ (charge frequency) until the output value of the integrator is greater than the threshold value,

e) at this moment, the counter is engaged and the integrator is discharged through the chosen standard capacitor,

f) the steps a to c are repeated cyclically at the frequency v₁ until the threshold value is reached for a second time, at which moment the counter is stopped,

g) the steps a to f are repeated with the reference capacitor and its own standard, if appropriate,

h) the computation unit determines the value of the corresponding liquid level (h),

10. The gauge according to claim 9, wherein it is designed to carry out, before the steps a to h, a measurement of the reference capacitor by choosing a predetermined standard capacitor, so as to roughly evaluate the dielectric constant of the fuel and choose the or each appropriate standard capacitor.