Cabin pressure control system and method that implements high-speed sampling and averaging techniques to compute cabin pressure rate of change

• US 7,549,916 B2
• Filed: 07/08/2005
• Issued: 06/23/2009
• Est. Priority Date: 07/08/2005
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: McCoy, Gerard L., Biss, Timothy C., Horner, Darrell W.
• Primary Examiner(s): McAllister; Steve
• Assistant Examiner(s): Kosanovic; Helena
• Application Number:
  US11/178,038
• Publication Number:
  US 20070010188A1
• Time in Patent Office: 1,446 Days
• Field of Search: 454/72, 341/116, 341/155
• US Class Current: 454/72
• CPC Class Codes: B64D 13/04 Automatic control of pressure
• CPC Class Codes: G01L 9/065 with temperature compensating means non electric temperature compensating means G01L19/04
• CPC Class Codes: G05D 16/2013 using throttling means as controlling means
• CPC Class Codes: Y02T 50/50 On board measures aiming to increase energy efficiency

Abstract

An aircraft cabin pressure control system and the method implement a technique that oversamples and filters a sensed cabin pressure signal, and then differentiates the oversampled and filtered pressure signal to generate cabin pressure rate-of-change. The oversampling and filtering technique removes circuit and sensor induced noise from the cabin pressure signal, and results in cabin pressure rate-of-change values with less noise than currently known systems and methods.

Claims

1. An aircraft cabin pressure control system, comprising:

a cabin pressure sensor configured to sense aircraft cabin pressure and supply a cabin pressure signal representative thereof;

an analog-to-digital converter (A/D) circuit coupled to receive the cabin pressure signal and operable, upon receipt thereof, to periodically sample the cabin pressure signal and supply digital cabin pressure values representative thereof;

a controller circuit configured to periodically read a predetermined number of the digital cabin pressure values supplied from the A/D circuit and to periodically compute (i) a single cabin pressure value from the predetermined number of digital cabin pressure values read thereby and (ii) aircraft cabin pressure rate of change based in part on the single aircraft cabin pressure value;

the controller circuit comprising;

two first order lag Tustin filters, each filter having a different time constant value; and

wherein the time constant values vary depending on a motor control law.

2. The system of claim 1, wherein:

the single cabin pressure value comprises an average cabin pressure value; and

the controller generates the average cabin pressure value by computing an average of the predetermined number of digital cabin pressure values.

3. The system of claim 1, further comprising:

a memory circuit coupled to receive and store the digital cabin pressure values supplied by the A/D circuit,

wherein the controller circuit reads the predetermined number of digital pressure values from the memory circuit.

4. The system of claim 1, wherein:

the A/D circuit samples the cabin pressure signal at a predetermined sampling frequency;

the controller circuit reads the predetermined number of values at a predetermined computation frequency; and

the predetermined sampling frequency is greater than the predetermined computation frequency.

5. The system of claim 4, wherein the predetermined sampling frequency and the predetermined read frequency are specified such that the A/D circuit oversamples the cabin pressure signal.

6. The system of claim 4, wherein the predetermined sampling frequency is 100 times greater than the predetermined read frequency.

7. The system of claim 1, wherein

at least one of the Tustin filters is implemented with a time constant of either 0.06667 or 0.267.

8. The system of claim 1, wherein the Tustin filters are coupled in series.

9. The system of claim 1, wherein the Tustin lag filters are coupled in parallel.

10. The system of claim 1, further comprising:

a cabin temperature sensor configured to sense aircraft cabin temperature and supply a cabin temperature signal representative thereof;

a second A/D circuit coupled to receive the cabin temperature signal and operable, upon receipt thereof, to periodically sample the cabin temperature signal and supply digital cabin temperature values representative thereof,

wherein the controller circuit is further configured to periodically (i) read the digital cabin temperature values supplied from the second A/D circuit (ii) temperature compensate the determined average aircraft cabin pressure and (iii) supply temperature compensated cabin pressure data.

11. The system of claim 1, wherein the controller circuit is further configured to supply outflow valve position commands representative of a desired outflow valve position, the outflow valve position command based at least in part on the determined aircraft cabin pressure rate of change.

12. The system of claim 11, further comprising:

a motor coupled to receive the outflow valve position commands and operable, upon receipt thereof, to supply a drive force; and

an outflow valve coupled to receive the drive force and operable, upon receipt thereof, to move to the desired outflow valve position.

13. A circuit for determining aircraft cabin pressure rate of change, comprising:

an analog-to-digital converter (A/D) circuit adapted to receive an analog cabin pressure signal and operable, upon receipt thereof, to periodically sample the analog cabin pressure signal and supply digital cabin pressure values representative thereof;

a controller circuit configured to periodically read a predetermined number of the digital cabin pressure values supplied from the A/D circuit and to periodically compute (i) a single cabin pressure value from the predetermined number of digital cabin pressure values read thereby and (ii) aircraft cabin pressure rate of change based in part on the single aircraft cabin pressure value;

the controller circuit comprising;

a first-order lag Tustin filter having a time constant value equal to 0.06667; and

a second first-order lag Tustin filter having a time constant value equal to 0.267.

14. The circuit of claim 13, wherein:

the single cabin pressure value is an average cabin pressure value; and

the controller generates the average cabin pressure value by computing an average of the predetermined number of digital cabin pressure values.

15. The circuit of claim 13, further comprising:

a memory circuit coupled receive and store the digital cabin pressure values supplied by the A/D circuit,

wherein the controller circuit reads the predetermined number of digital pressure values from the memory circuit.

16. The circuit of claim 13, wherein:

the A/D circuit samples the cabin pressure signal at a predetermined sampling frequency;

the controller circuit reads the predetermined number of values at a predetermined read frequency; and

the predetermined sampling frequency is greater than the predetermined read frequency.

17. The circuit of claim 16, wherein the predetermined sampling frequency and the predetermined read frequency are such that A/D circuit oversamples the cabin pressure signal.

18. The circuit of claim 16, wherein the predetermined sampling frequency is 100 times greater than the predetermined read frequency.

19. A method of periodically computing aircraft cabin pressure rate of change for modulating cabin pressure, the method comprising the steps of:

sampling, at a predetermined sampling frequency, an analog aircraft cabin pressure signal to thereby generate digital cabin pressure values;

computing, at a predetermined computation frequency, an average of a predetermined number of the digital cabin pressure values to thereby generate average cabin pressure values, the predetermined computation frequency less than the predetermined sampling frequency; and

computing, at the predetermined computation frequency, aircraft cabin pressure rate of change values based on the average aircraft cabin pressure values includes the steps of;

filtering the average aircraft cabin pressure values to derive the cabin pressure rate of change using a digital filter circuit implemented with a time constant value equal to 0.06667;

filtering the average aircraft cabin pressure values to derive the cabin pressure rate of change using the digital filter circuit implemented with a time constant value equal to 0.267;

supplying the cabin pressure rate-of-change to a control law to produce an outflow valve position command signal; and

controlling the position of an outflow valve in response to the outflow valve position command signal, to thereby modulate cabin pressure.

20. The method of claim 19, wherein the step of computing aircraft cabin pressure rate of change comprises:

computing an average cabin pressure difference value; and

dividing the average cabin pressure difference value by an elapsed time value,

wherein the average cabin pressure difference value is computed by subtracting a previous average pressure value from a current average pressure value, and the elapsed time value is an amount of time between when the current average pressure value is computed and the previous average pressure value was computed.

21. The method of claim 19, wherein the predetermined sampling frequency is 100 times greater than the predetermined computation frequency.

22. The method of claim 19, wherein the predetermined number of digital cabin pressure values that are averaged is 100.

23. The method of claim 19 wherein the step of filtering the average aircraft cabin pressure values to derive the cabin pressure rate of change using the digital filter circuit implemented with a time constant value equal to 0.267 is performed subsequent to the step of filtering the average aircraft cabin pressure values to derive the cabin pressure rate of change using the digital filter circuit implemented with a time constant value equal to 0.06667.

24. The method of claim 19 wherein the step of filtering the average aircraft cabin pressure values to derive the cabin pressure rate of change using the digital filter circuit implemented with a time constant value equal to 0.267 is performed in parallel with the step of filtering the average aircraft cabin pressure values to derive the cabin pressure rate of change using the digital filter circuit implemented with a time constant value equal to 0.06667.

25. The method of claim 24 further comprising the step of multiplying the output of the digital filter circuit by a unity gain term to yield the cabin pressure rate-of-change.