EXHAUST SAMPLING SYSTEM AND METHOD FOR SYNCHRONIZING TIME ALIGNMENT AND DILATION

• US 20150177203A1
• Filed: 06/11/2013
• Published: 06/25/2015
• Est. Priority Date: 06/11/2012
• Status: Active Grant

• Current Assignee: AVL Test Systems, Inc.
• Original Assignee: AVL Test Systems, Inc.
• Inventors: Silvis, William Martin, Kingham, Sarah Montgomery
• Granted Patent: US 9,347,926 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: F01N 11/00 Monitoring or diagnostic devices for exhaust-gas treatment apparatus , e.g. for catalytic activity safety, indicating or supervising devices for internal combustion engines F02B77/08; testing of machines G01M13/00
• CPC Class Codes: F01N 2560/00 Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
• CPC Class Codes: F02D 2041/288 for performing a transformation into the frequency domain, e.g. Fourier transformation
• CPC Class Codes: F02D 2250/14 Timing of measurement, e.g. synchronisation of measurements to the engine cycle
• CPC Class Codes: F02D 41/1444 characterised by the characteristics of the combustion gases
• CPC Class Codes: F02D 41/1445 the characteristics being related to the exhaust flow
• CPC Class Codes: F02D 41/1466 the characteristics being a soot concentration or content
• CPC Class Codes: F02D 41/1467 with determination means using an estimation
• CPC Class Codes: F02D 41/28 Interface circuits
• CPC Class Codes: G01M 15/10 by monitoring exhaust gases or combustion flame
• CPC Class Codes: G01M 15/102 by monitoring exhaust gases
• CPC Class Codes: G01N 1/22 in the gaseous state specially adapted for biological material G01N33/497; measuring breath flow A61B5/087
• CPC Class Codes: G01N 1/2252 in a vehicle exhaust
• CPC Class Codes: G01N 33/0006 Calibrating gas analysers
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A system and method is provided for synchronizing a first and second signal of an exhaust sampling system. The first signal is generated by a first instrument and includes an exhaust flow rate component and a first instrument time stamp component. The second signal is generated by a second instrument and includes a pollutant concentration component and a second instrument time stamp component. The second instrument also generates a tertiary signal that has been influenced by the first signal and includes a second instrument time stamp component. A synchronization module determines a time relationship for synchronizing the first signal and the second signal by comparing the first flow rate component and the first instrument time stamp component of the first signal to the tertiary signal and the second instrument time stamp component of the tertiary signal. The synchronization provides accurate calculation of a pollutant mass flow rate.

Claims

1. A system for sampling exhaust produced by an engine comprising:

a first instrument measuring an exhaust flow rate of the exhaust leaving the engine and generating a first signal including an exhaust flow rate component indicating said exhaust flow rate and a first instrument time stamp component associated with sampling at a first time;

a second instrument measuring a pollutant concentration and generating a second signal including a pollutant concentration component indicating said pollutant concentration and a second instrument time stamp component associated with sampling at said first time and a tertiary signal that has been influenced by said first signal and said second instrument time stamp component; and

a synchronization module receiving and processing said first signal, said second signal, and said tertiary signal to determine a time relationship between said first signal and said second signal by comparing said exhaust flow rate component and said first instrument time stamp component of said first signal to said tertiary signal and said second instrument time stamp component of said tertiary signal.

2. The system of claim 1, wherein said synchronization module determines a time shift value that separates said first instrument time stamp of said first signal and said second instrument time stamp of said tertiary signal.

3. The system of claim 2, wherein said synchronization module equates said time relationship between said first signal and said second signal to said time shift value between said first signal and said tertiary signal.

4. The system of claim 3, wherein said synchronization module aligns said first signal with said second signal by subtracting said time shift value from said first instrument time stamp component of said first signal to generate a synchronized first signal having a synchronized exhaust flow rate component.

5. The system of claim 4, wherein said synchronization module calculates a pollutant mass flow rate by calculating the product of said synchronized exhaust flow rate component of said synchronized first signal and said pollutant concentration component of said second signal.

6. The system of claim 1, wherein said first instrument measures said exhaust flow rate at different times along a testing interval and generates a first array containing a plurality of data pairs spaced by a first time scale, each data pair of said first array indicating said exhaust flow rate and said first instrument time stamp.

7. The system of claim 6, wherein said second instrument measures said pollutant concentration at different times along said testing interval to generate a second array containing a plurality of data pairs spaced by a second time scale, each data pair of said second array indicating said pollutant concentration and said second instrument time stamp.

8. The system of claim 6, wherein said second instrument measures said tertiary signal at different times along said testing interval to generate a tertiary array containing a plurality of data pairs spaced by said second time scale, each data pair of said tertiary array indicating said influenced signal and said second instrument time stamp.

9. The system of claim 8, wherein said synchronization module determines a time relationship between said first array and said second array by comparing said first array and said second array, converts said first array to said second time scale based on said time relationship between said first array and said second array to generate a synchronized first array, and calculates a pollutant mass flow rate for said different times along said testing interval by calculating the product of said synchronized first array and said second array.

10. A system for sampling exhaust comprising:

a first instrument measuring a first flow rate of the exhaust passing by said first instrument and generating a first signal including a first flow rate component indicating said first flow rate and a first instrument time stamp component associated with sampling at a first time;

a second instrument measuring a pollutant concentration and generating a second signal including a pollutant concentration component indicating said pollutant concentration and a second instrument time stamp component associated with sampling at said first time and a tertiary signal that has been influenced by said first flow rate including said second instrument time stamp component; and

a synchronization module receiving and processing said first signal, said second signal, and said tertiary signal to determine a time relationship between said first signal and said second signal by comparing said first flow rate component and said first instrument time stamp component of said first signal to said tertiary signal and said second instrument time stamp component of said tertiary signal.

11. A method of synchronizing signals of an exhaust sampling system comprising:

detecting a first signal from a first instrument, the first signal including an exhaust flow rate component indicating an exhaust flow rate from an engine and a first instrument time stamp component associated with sampling at a first time;

detecting a second signal from a second instrument, the second signal including a pollutant concentration component indicating the pollutant concentration of exhaust within the second instrument and a second instrument time stamp component associated with sampling at the first time;

detecting a tertiary signal from the second instrument, the tertiary signal having been influenced by flow rate of exhaust within the first instrument and the second instrument time stamp component associated with the tertiary signal; and

determining a time relationship between the first signal and the second signal by comparing the exhaust flow rate component and the first instrument time stamp component of the first signal to the tertiary signal and the second instrument time stamp component of the tertiary signal.

12. The method of claim 11, further comprising determining a time shift value separating the first instrument time stamp of the first signal and the second instrument time stamp of the tertiary signal.

13. The method of claim 12, further comprising equating the time relationship between the first signal and the second signal to the time shift value between the first signal and the tertiary signal.

14. The method of claim 13, further comprising aligning the first signal with the second signal by subtracting the time shift value from the first instrument time stamp component of the first signal to generate a synchronized first signal having a synchronized exhaust flow rate component.

15. The method of claim 14, further comprising calculating a pollutant mass flow rate by calculating the product of the synchronized exhaust flow rate component of the synchronized first signal and the pollutant concentration component of the second signal.

16. The method of claim 15, further comprising identifying a time lag between the first signal and the tertiary signal by integrating a mathematical coincidence function relating the first signal and the tertiary signal, the mathematical coincidence function being f^og≡

∫

f(t)g(t−

τ

)dt;

converting the first signal and the tertiary signal from a time based domain to a frequency based domain by applying Fourier transformations to the first signal and the tertiary signal, the Fourier transformations being F(ω

)=[f(t)] and G(ω

)=[g(t)];

multiplying the complex conjugate first signal and the tertiary signal to generate a product of the signals in the frequency based domain;

converting the product of the signals from the frequency based domain to the time based domain to generate a lag function, the lag function being defined as Lag(t)=<sup>−

1</sup>(*(f_{low freq removed})(g)); and

identifying a peak of the lag function to determine the time shift value, the time shift value equaling τ

_shift={τ

;

Lag(τ

)=max}.

17. The method of claim 16, further comprising truncating portions of the first signal and the tertiary signal in the frequency based domain that are below a predetermined lower limit to eliminate low frequency variability resulting from variations in ambient air pressure.

18. The method of claim 15, further comprising:

repeating the steps of the method set forth in claim 15 at a second time that is spaced a predetermined number of time units from the first time to define a testing interval;

sampling the first signal at different times along the testing interval to generate a first array containing a plurality of data pairs spaced by a first time scale, each data pair indicating the exhaust flow rate from the engine and the corresponding first instrument time stamp;

sampling the second signal at different times along the testing interval to generate a second array containing a plurality of data pairs spaced by a second time scale, each data pair indicating the soot concentration of exhaust within the second instrument and the corresponding second instrument time stamp;

sampling the tertiary signal at different times along the testing interval to generate a tertiary array containing a plurality of data pairs spaced by the second time scale, each data pair indicating the filter flow rate of exhaust within the second instrument and the corresponding second instrument time stamp;

determining a time relationship between the first array and the second array by comparing the first array and the second array;

converting the first array to the second time scale based on the time relationship between the first array and the second array to generate a synchronized first array; and

calculating a pollutant mass flow rate for the different times along the testing interval by calculating the product of the synchronized first array and the second array.

19. The method of claim 18, further comprising:

aligning the first array with the tertiary array by defining the first array and the tertiary array as two continuous functions of time, the two continuous functions of time being and f_j=f(jΔ

t+t₀) j=1, . . . , n and f_k=f(kΔ

t′

+t₀′

) k=1, . . . , m; and

converting the first array to the second time scale by solving