Temperature correction method and subsystem for automotive evaporative leak detection systems

• US 6,672,138 B2
• Filed: 12/21/2001
• Issued: 01/06/2004
• Est. Priority Date: 10/02/1997
• Status: Expired due to Term

• Current Assignee: Siemens Canada Limited (Siemens AG)
• Original Assignee: Siemens Canada Limited (Siemens AG)
• Inventors: Cook, John E., Perry, Paul D.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): Politzer, Jay L
• Application Number:
  US10/024,280
• Publication Number:
  US 20020078736A1
• Time in Patent Office: 746 Days
• Field of Search: 73/40, 73/405.R, 73/492, 73/454, 73/491, 73/493, 702/51
• US Class Current: 73/40.50R
• CPC Class Codes: F02M 25/0809 Judging failure of purge control system
• CPC Class Codes: F02M 25/0818 having means for pressurising the evaporative emission space

Abstract

A method and sensor or sensor subsystem permit improved evaporative leak detection in an automotive fuel system. The sensor or sensor subsystem computes temperature-compensated pressure values, thereby eliminating or reducing false positive or other adverse results triggered by temperature changes in the fuel tank. The temperature-compensated pressure measurement is then available for drawing an inference regarding the existence of a leak with reduced or eliminated false detection arising as a result of temperature fluctuations.

Claims

1. A method for making fast temperature-compensated pressure readings in an automotive evaporative leak detection system having a non-stabilized tank with a vapor pressure having a value P₁ at a first point in time, comprising the steps of:

a. measuring a first temperature T₁ of the vapor at substantially the first point in time;

b. measuring a second temperature T₂ of the vapor at a second point in time; and

c. computing a temperature-compensated pressure P_C=P₁(2−

T₂/T₁) wherein it is assumed that there are negligible changes in moles and volume of the tank.

2. In an automotive evaporative leak detection system, a temperature-compensated pressure sensor comprising:

a. a pressure sensing element;

b. a temperature sensing element;

b. a processor coupled to the pressure sensing element and to the temperature sensing element and receiving, respectively, pressure and temperature signals therefrom; and

c. logic implemented by the processor for computing a temperature-compensated pressure P_C=P₁(2−

T₂/T₁) wherein P₁ is a pressure measured at a first point in time, T₁ is a temperature measured at substantially the first point in time, and T₂ is a temperature measured at a second point in time, and wherein it is assumed that there are negligible changes in moles and volume of the system.

3. In an automotive evaporative leak detection system, a sensor subsystem for compensating for the effects on pressure measurement of changes in temperature of fuel tank vapor, the subsystem comprising:

a. a pressure sensor in fluid communication with the fuel tank vapor;

b. a temperature sensor in thermal contact with the fuel tank vapor;

c. a processor in electrical communication with the pressure sensor and with the temperature sensor; and

d. logic implemented by the processor for computing a temperature-compensated pressure P_c=P₁(2−

T₂/T₁) wherein P₁ is a pressure measured at a first point in time, T₁ is a temperature measured at substantially the first point in time, and T₂ is a temperature measured at a second point in time, and wherein it is assumed that there are negligible changes in moles and volume of the system.

4. The subsystem according to claim 3, wherein the logic also determines the presence or absence of a leak based upon the temperature-compensated pressure and the pressure measured at the second point in time.

5. The subsystem according to claim 3, wherein the logic also determines the presence or absence of a leak based upon the temperature-compensated pressure, P_C and the pressure measured at the second point in time, P₂.

6. The subsystem according to claim 5, wherein a leak is determined to exist if the pressure P₂ is less than the temperature-compensated pressure P_C.