Means and method for operating evaporative emission system leak detection pump

• US 5,499,614 A
• Filed: 11/03/1994
• Issued: 03/19/1996
• Est. Priority Date: 11/03/1994
• Status: Expired due to Term

• Current Assignee: Siemens Electric Limited
• Original Assignee: Siemens Electric Limited
• Inventors: Cook, John E., Perry, Paul D., Busato, Murray F.
• Primary Examiner(s): MILLER, CARL STUART
• Application Number:
  US08/333,824
• Time in Patent Office: 502 Days
• Field of Search: 123/520, 123/198 D, 123/518, 123/519, 123/516, 123/521
• US Class Current: 123/520
• CPC Class Codes: F02M 25/0809 Judging failure of purge control system

Abstract

An on-board diagnostic system for an evaporative emission control system of an internal combustion engine powered vehicle employs a positive displacement reciprocating pump to create in evaporative emission space a pressure that differs significantly from ambient atmospheric pressure. The pump is powered by using engine intake manifold vacuum to force an intake stroke during which both an internal spring is increasingly compressed and a charge of ambient atmospheric air is created in an air pumping chamber space. Vacuum is then removed, and the spring relaxes to force a compression stroke wherein a portion of the air charge is forced into the evaporative emission space. The pump operation is under the control of a computer that contains an algorithm for operating the pump in particular modes of operation to arrive at a decision concerning integrity of the evaporative emission space against leakage.

Claims

1. An automotive vehicle comprising an internal combustion engine and a fuel system for said engine which comprises a fuel tank for storing volatile liquid fuel for the engine and an evaporative emission control system which comprises a collection canister that in cooperative combination with headspace of said tank cooperatively defines an evaporative emission space wherein fuel vapors generated from the volatilization of fuel in said tank are temporarily confined and collected until periodically purged by means of a canister purge valve to an intake manifold of the engine for entrainment with induction flow of combustible mixture into combustion chamber space of the engine and ensuing combustion in said combustion chamber space, valve means via which said evaporative emission space is selectively communicated to atmosphere, said vehicle further comprising means, including pump means, for distinguishing between integrity and non-integrity of said evaporative emission control system, under conditions conducive to obtaining a reliable distinction between such integrity and non-integrity, against leakage of volatile fuel vapor from that portion thereof which includes said tank, said canister, said valve means, and said canister purge valve, said pump means comprising a positive displacement reciprocating pump having a mechanism that, while said valve means is closed to prevent communication of said evaporative emission space to atmosphere and while said canister purge valve is closed to prevent communication of said evaporative emission space to said intake manifold, executes reciprocating motion comprising an intake stroke and a compression stroke and that comprises means to intake air during each occurrence of an intake stroke for creating a measured charge volume of air at given pressure and means to compress a measured charge volume of air to pressure greater than such given pressure and force a portion thereof into said evaporative emission space during each occurrence of a compression stroke, said means to compress a measured charge volume of air to pressure greater than such given pressure and force a portion thereof into said evaporative emission space during each occurrence of a compression stroke comprises mechanical spring means to which energy in imparted during an intake stroke and which releases energy during a compression stroke, characterized in that;

operation of the pump is under control of a computer a) that causes the pump to operate initially in a first mode that accelerates initial pressurizing of said space by causing said movable wall to repeatedly execute less than a full compression stroke beginning at an initial position wherein maximum energy is stored in said spring means and ending before completing a full compression stroke, and b) that at the conclusion of said first mode causes the pump to operate in a second mode wherein said movable wall is caused to repeatedly execute full compression strokes.

2. An automotive vehicle as set forth in claim 1 characterized further in that during said second mode, said computer measures time required to execute a full compression stroke and ascertains if a predefined degree of stabilization of pressure in said space has been attained.

3. An automotive vehicle as set forth in claim 2 characterized further in that once the computer has ascertained attainment of such predefined degree of stabilization of pressure in said space, the computer further determines the extent of any leakage from said space.

4. An automotive vehicle as set forth in claim 3 characterized further in that the computer ascertains if such predefined degree of stabilization of pressure in said space has been attained by averaging the times of a number of previously completed full compression strokes and comparing the time of the most recent full compression stroke to such average.

5. An automotive vehicle as set forth in claim 4 characterized further in that the computer indicates the attainment of such predefined degree of stabilization of pressure in said space when the comparison indicates the attainment of a predetermined relationship between such average and the time of the most recent full compression stroke.

6. An automotive vehicle as set forth in claim 5 characterized further in that the computer obtains the difference between the time of the most recent full compression stroke and such average and determines that such predefined degree of stabilization has been attained when such difference is smaller than a certain amount.

7. An automotive vehicle as set forth in claim 6 characterized further in that said computer causes the pump operation to terminate if such predefined degree of stabilization of pressure is not attained within a certain amount of time.

8. An automotive vehicle as set forth in claim 2 characterized further in that said computer causes the pump operation to terminate if such predefined degree of stabilization of pressure is not attained within a certain amount of time.

9. An automotive vehicle comprising an internal combustion engine and a fuel system for said engine which comprises a fuel tank for storing volatile liquid fuel for the engine and an evaporative emission control system which comprises a collection canister that in cooperative combination with headspace of said tank cooperatively defines an evaporative emission space wherein fuel vapors generated from the volatilization of fuel in said tank are temporarily confined and collected until periodically purged by means of a canister purge valve to an intake manifold of the engine for entrainment with induction flow of combustible mixture into combustion chamber space of the engine and ensuing combustion in said combustion chamber space, valve means via which said evaporative emission space is selectively communicated to atmosphere, said vehicle further comprising means, including pump means, for distinguishing between integrity and non-integrity of said evaporative emission control system, under conditions conducive to obtaining a reliable distinction between such integrity and non-integrity, against leakage of volatile fuel vapor from that portion thereof which includes said tank, said canister, said valve means, and said canister purge valve, said pump means comprising a positive displacement reciprocating pump having a mechanism that, while said valve means is closed to prevent communication of said evaporative emission space to atmosphere and while said canister purge valve is closed to prevent communication of said evaporative emission space to said intake manifold, executes reciprocating motion comprising an intake stroke and a compression stroke and that comprises means to intake air during each occurrence of an intake stroke for creating a measured charge volume of air at given pressure and means to compress a measured charge volume of air to pressure greater than such given pressure and force a portion thereof into said evaporative emission space during each occurrence of a compression stroke, said means to compress a measured charge volume of air to pressure greater than such given pressure and force a portion thereof into said evaporative emission space during each occurrence of a compression stroke comprises mechanical spring means to which energy in imparted during an intake stroke and which releases energy during a compression stroke, characterized in that:

operation of the pump is under control of a computer that causes the pump to operate in a mode wherein said movable wall executes compression strokes of like stroke length, said computer measures time required to execute a compression stroke and ascertains if a predefined degree of stabilization of pressure in said space has been attained by averaging the times of a number of previously completed compression strokes and comparing the time of the most recent compression stroke to such average.

10. An automotive vehicle as set forth in claim 9 characterized further in that once the computer has ascertained attainment of such predefined degree of stabilization of pressure in said space, the computer further determines the extent of any leakage from said space.

11. An automotive vehicle as set forth in claim 10 characterized further in that the computer obtains the difference between the time of the most recent compression stroke and such average and determines that such predefined degree of stabilization has been attained when such difference is smaller than a certain amount.

12. An automotive vehicle as set forth in claim 11 characterized further in that said computer causes the pump operation to terminate if such predefined degree of stabilization of pressure is not attained within a certain amount of time.

13. An automotive vehicle as set forth in claim 9 characterized further in that said computer causes the pump operation to terminate if such predefined degree of stabilization of pressure is not attained within a certain amount of time.

14. A method for distinguishing between integrity and non-integrity of an evaporative emission control system of an internal combustion engine powered automotive vehicle having a fuel tank for storing volatile liquid fuel for the engine, said evaporative emission control system comprising a collection canister that in cooperative combination with headspace of said tank cooperatively defines an evaporative emission space wherein fuel vapors generated from the volatilization of fuel in said tank are temporarily confined and collected until periodically purged by means of a canister purge valve to an intake manifold of the engine for entrainment with induction flow of combustible mixture into combustion chamber space of the engine and ensuing combustion in said combustion chamber space, and valve means via which said evaporative emission space is selectively communicated to atmosphere, said method comprising closing both said valve means and said canister purge valve, and while they are closed, pressurizing said evaporative emission space to a pressure that is significantly different from atmospheric pressure by means of a reciprocating pump that contains a mechanical spring means from which energy is extracted during a compression stroke of the pump to pressurize said space, characterized in that:

a) the pump operates initially in a first mode that accelerates initial pressurizing of said space by causing said pump to repeatedly execute less than a full compression stroke beginning at an initial position wherein maximum energy is stored in said spring means and ending before completing a full compression stroke, and b) at the conclusion of said first mode, the pump operates in a second mode wherein the pump repeatedly executes full compression strokes.

15. A method as set forth in claim 14 characterized further in that during said second mode, time required to execute a full compression stroke is measured and such measurement is utilized to ascertain attainment of a predefined degree of stabilization of pressure in said space.

16. An automotive vehicle as set forth in claim 15 characterized further in that once attainment of such predefined degree of stabilization of pressure in said space has been ascertained, the extent of any leakage from said space is ascertained.

17. An automotive vehicle as set forth in claim 16 characterized further in that attainment of such predefined degree of stabilization of pressure in said space is ascertained by averaging the times of a number of previously completed full compression strokes and comparing the time of the most recent full compression stroke to such average.

18. A method for distinguishing between integrity and non-integrity of an evaporative emission control system of an internal combustion engine powered automotive vehicle having a fuel tank for storing volatile liquid fuel for the engine, said evaporative emission control system comprising a collection canister that in cooperative combination with headspace of said tank cooperatively defines an evaporative emission space wherein fuel vapors generated from the volatilization of fuel in said tank are temporarily confined and collected until periodically purged by means of a canister purge valve to an intake manifold of the engine for entrainment with induction flow of combustible mixture into combustion chamber space of the engine and ensuing combustion in said combustion chamber space, and valve means via which said evaporative emission space is selectively communicated to atmosphere, said method comprising closing both said valve means and said canister purge valve, and while they are closed, pressurizing said evaporative emission space to a pressure that is significantly different from atmospheric pressure by means of a reciprocating pump that contains a mechanical spring means from which energy is extracted during a compression stroke of the pump to pressurize said space, characterized in that:

the pump executes compression strokes of like stroke length, the time required to execute a compression stroke is measured, and a predefined degree of stabilization of pressure in said space is ascertained by averaging the times of a number of previously completed compression strokes and comparing the time of the most recent compression stroke to such average.

19. A method as set forth in claim 18 characterized further in that once such predefined degree of stabilization of pressure in said space has been ascertained, the extent of any leakage from said space is ascertained.

20. A method as set forth in claim 19 characterized further in that pump operation is terminated if such predefined degree of stabilization of pressure is not attained within a certain amount of time.