Evaporative emission control canister system for reducing breakthrough emissions

• US 6,279,548 B1
• Filed: 12/13/1999
• Issued: 08/28/2001
• Est. Priority Date: 12/13/1999
• Status: Expired due to Fees

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Reddy, Sam Raghuma
• Primary Examiner(s): Moulis, Thomas N.
• Application Number:
  US09/459,101
• Time in Patent Office: 624 Days
• Field of Search: 123/516, 123/518, 123/519, 123/520, 123/549, 123/557
• US Class Current: 123/520
• CPC Class Codes: B01D 2253/102 Carbon
• CPC Class Codes: B01D 2257/7022 Aliphatic hydrocarbons
• CPC Class Codes: B01D 2259/4516 for fuel vapour recovery systems
• CPC Class Codes: B01D 53/02 by adsorption, e.g. preparative gas chromatography solid sorbent compositions B01J20/00, preparation of inorganic compounds or elements C01
• CPC Class Codes: B01D 53/0407 Constructional details of adsorbing systems
• CPC Class Codes: B60K 15/03504 adapted to avoid loss of fuel or fuel vapour, e.g. with vapour recovery systems
• CPC Class Codes: B60K 2015/03514 with vapor recovery means
• CPC Class Codes: F02M 25/0854 Details of the absorption canister
• CPC Class Codes: F02M 25/089 Layout of the fuel vapour installation

Abstract

The effectiveness against vapor breakthrough of an adsorbent material (e.g., activated carbon granules) containing canister in an evaporative fuel emission control system is greatly increased by employing a relatively small secondary volume of adsorbent downstream of the vapor vent of the primary adsorbent volume and heating the secondary volume just prior to commencing the flow of purge air back through the two adsorbent volumes to remove adsorbed fuel and carry the purged fuel to the induction system of an associated engine. The secondary volume is heated to a temperature enabling complete purging of hydrocarbons from it and, thus, to greatly increase the capacity of that volume to prevent fuel vapor breakthrough during the subsequent engine-off fuel vapor storage cycle. The secondary volume may be contained in a common canister with the primary volume or in a secondary canister.

Claims

1. An evaporative emissions control system for a vehicle, said system comprising, in combination, a fuel tank for storing a volatile fuel, an engine having an air induction system and adapted to consume said fuel, a canister containing a first volume of fuel vapor adsorbent material for temporarily adsorbing and storing fuel vapor from said tank, a conduit for conducting fuel vapor from said tank to a canister vapor inlet, a fuel vapor purge conduit from a canister purge outlet to said induction system of said engine, and a vent/air inlet for venting said canister and for admission of air to said canister during operation of said engine induction system;

said canister defining an air flow path through said first volume of adsorbent between a first region of said canister at said vent/air inlet and a second region at said purge outlet, and a vapor flow path from said vapor inlet toward said vent/air inlet, such that fuel vapor formed in said tank flows through said vapor inlet into said first volume of adsorbent where it is adsorbed and, during operation of said engine induction system, ambient air flows in a path to and through said vent/air inlet and along said air flow path in said canister through said first volume and said purge outlet to the induction system of said engine, said flow of air removing a portion of said adsorbed fuel vapor but leaving a residue of fuel in said first volume;

said emissions control system further comprising a second volume of adsorbent, smaller than said first volume, said second volume being located either inside of said canister within said first region or outside of said canister but in the flow path of said ambient air to said vent/air inlet and said first region, and heating means within said second volume adapted and controllable to heat said second volume of adsorbent prior to said flow of air to a temperature at which said air flowing through said second volume removes substantially all adsorbed fuel.

2. An evaporative emissions control system as recited in claim 1 in which said second volume of adsorbent is located within said first region of said canister.

3. An evaporative emissions system as recited in claim 1 in which said second volume of adsorbent is contained outside of said canister in the flow path of ambient air to said vent/air inlet.

4. An evaporative emissions system as recited in claim 1 in which said second volume is about one to ten percent of said first volume.

5. An evaporative emissions system as recited in claim 1 in which said second is about one to five percent of said first volume.

6. An evaporative emissions control system as recited in any one of claims 1-5 in which said fuel vapor adsorbent material consists essentially of activated carbon granules.

7. A second stage adsorbent filled canister for use in an emissions control system for a vehicle, said system comprising, in combination, a fuel tank for storing a volatile fuel, an engine having an air induction system and adapted to consume said fuel, a first stage canister containing a first volume of fuel vapor adsorbent material for temporarily adsorbing and storing fuel vapor from said tank, a conduit for conducting fuel vapor from said tank to a first stage canister vapor inlet, a fuel vapor purge conduit from a first stage canister purge outlet to said induction system of said engine, and a vent/air inlet for venting said first stage canister and for admission of air to said first stage canister during operation of said engine induction system;

said second stage canister comprising a second volume of fuel vapor adsorbent material for temporarily adsorbing and storing fuel vapor overflowing said first stage canister, a vapor inlet/purge outlet for receiving said vapor from said first stage canister, a vent/air inlet, a fuel vapor flow path from said vapor inlet/purge outlet through said second volume to said vent/air inlet, a flow path through said second volume for ambient air induced to flow during said engine operation from said vent/air inlet to said vapor inlet/purge outlet and heating means within said second volume adapted to heat said second volume of adsorbent to a temperature at which said air flowing through said second volume removes substantially all adsorbed fuel.

8. A second stage canister as recited in claim 7 in which said second volume is in the range of about one to ten percent of said first volume.

9. A second stage canister as recited in claim 7 in which said second volume is in the range of about one to five percent of said first volume.

11. A method as recited in claim 8 in which said absorbent material consists essentially of carbon granules.

12. A method as recited in claim 8 in which said second volume of adsorbent material is contiguous with said first volume of adsorbent material in a common canister.

13. A method as recited in claim 8 in which said second volume of adsorbent material is contained in a second canister and said first adsorbent volume is contained in a first canister.

14. A method as recited in claim 8 comprising heating said second volume of adsorbent material prior to and during a portion of each period of air flow.

10. In the method of operating an evaporative fuel emissions control system in combination with an engine adapted to consume said fuel, said method comprising

directing, during, a period when said engine is not running, the flow of fuel vapor emanating from a fuel tank into a first volume of fuel adsorbent material, said first volume having a vapor inlet and a vent, said vapor flowing in a first direction from said inlet toward said vent, to temporarily adsorb said vapor and, thereafter, during a following period of engine operation,

promoting a flow of ambient air in an opposing path, through said vent and said first volume of adsorbent material to a air purge outlet, by the action of an engine air induction system, said flow of air removing some, but not all, of the adsorbed fuel from said first volume of adsorbent material and carrying it to said engine in which it is consumed, and in which method said adsorbing and removing of vapor is cyclically repeated, and wherein the capacity of said first volume of adsorbent is sometimes exceeded and fuel vapor escapes the first volume of adsorbent to the atmosphere, the improvement comprising;

placing a second volume of adsorbent material in a location downstream of said vapor flow vent of said first volume of fuel adsorbent and upstream of said vent, with respect to the direction of said vapor removing air flow, and in the flow path of said airflow, said second volume being no greater than about ten percent of said first volume, and

prior to each cycle of promoting said air flow, heating said second volume of adsorbent to a temperature enabling the subsequent airflow to remove substantially all adsorbed fuel from said second volume of adsorbent and thereby reduce the escape of fuel vapor from said control system during the subsequent vapor adsorption cycle.