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Title:
FUEL CUT-OFF SYSTEM FOR USE IN ROBOTIC VEHICLE REFUELING
Document Type and Number:
WIPO Patent Application WO/2001/044104
Kind Code:
A1
Abstract:
A system for automatically cutting off the flow of fuel from a robotic refueling nozzle assembly is disclosed. The fuel cut off system comprises first fuel cut off member having a sensor coupled to the robotic refueling operatively associated with the venturi vacuum sensor and a fuel shut off valve disposed upstream from the variable venturi vacuum generator, the fuel shut off valve controlled by the computer. The first fuel cut off member includes a primary high level cut off subsystem having a venturi vacuum normalization software and a software algorithm to compare pre-set optimal normalized venturi vacuum levels with sensed normalized venturi vacuum during refueling and to cut off fuel flow via the fuel shut off valve if a substantial negative pressure spike is detected. Also included is a fuel splash back stabilizing subsystem.

Inventors:
Boardman, Delton M. (2546 Briar Glen Acton, CA, 93510, US)
Application Number:
PCT/US2000/032950
Publication Date:
June 21, 2001
Filing Date:
December 05, 2000
Export Citation:
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Assignee:
SHELL OIL COMPANY (One Shell Plaza, 47th floor P.O. Box 2463 Houston, TX, 77252-2463, US)
Boardman, Delton M. (2546 Briar Glen Acton, CA, 93510, US)
International Classes:
B67D7/04; B67D7/46; (IPC1-7): B67D5/08; B67D5/372
Foreign References:
US5383500A1995-01-24
US4881581A1989-11-21
US5634503A1997-06-03
US5238034A1993-08-24
US4881581A1989-11-21
US5609190A1997-03-11
US5628351A1997-05-13
US5634503A1997-06-03
Attorney, Agent or Firm:
Christensen, Del S. (Shell Oil Company One Shell Plaza, 47th floor P.O. Box 2463 Houston, TX, 77252-2463, US)
Download PDF:
Claims:
What is Claimed is:
1. A system for automatically cutting off the flow of fuel from a robotic refueling nozzle assembly having a variable area venturi vacuum generator into a vehicle fuel tank when the vehicle fuel tank becomes full, comprising: first fuel cut off member having a sensor coupled to the robotic refueling nozzle assembly for sensing venturi vacuum during refueling, a computer operatively associated with said venturi vacuum sensor and a fuel shut off valve disposed upstream from the variable venturi vacuum generator, said fuel shut off valve controlled by said computer; second fuel cut off member having a sensor coupled to the robotic refueling nozzle assembly proximate to said venturi vacuum sensor for sensing fuel tank pressure during refueling, said fuel tank pressure sensor operatively associated with said computer; and third fuel cut off member having a sensor coupled to the robotic refueling nozzle for sensing fuel vapor pressure during refueling, said vapor pressure sensor operatively associated with said computer.
2. The system of Claim 1, wherein said venturi vacuum sensor includes a pressure transducer probing the vehicle fuel tank via a venturi vacuum sensor port.
3. The system of Claim 2, wherein said fuel tank pressure sensor includes a pressure transducer probing the vehicle fuel tank via a fuel tank pressure sensor port.
4. The system of Claim 3, wherein vapor pressure sensor includes a vapor pressure transducer probing the vapor recovery line via a vapor pressure sensor port.
5. The system of Claim 4, wherein said first fuel cut off member includes a primary high level cut off subsystem.
6. The system of Claim 5. wherein said primary high level cut off subsystem includes means for normalizing the venturi vacuum sensed by said venturi vacuum pressure transducer during refueling.
7. The system of Claim 6, wherein said normalizing means includes a venturi vacuum normalization software encoded on said computer.
8. The system of Claim 7, wherein said primary high level cut off subsystem further includes means for cutting off fuel flow when fuel covers said venturi vacuum sensor port.
9. The system of Claim 8, wherein said means for cutting off fuel flow when fuel covers said venturi vacuum sensor port is a software algorithm encoded on said computer. said algorithm continuously comparing preset optimal normalized venturi vacuum levels with sensed normalized venturi vacuum during refueling and cutting off fuel flow via said fuel shut off valve if a substantial venturi vacuum deviation is detected.
10. The system of Claim 9, wherein said first fuel cut off member further includes a fuel splash back stabilizing subsystem.
11. The system of Class 10, wherein said splash back stabilizing subsystem includes software algorithm encoded on said computer for slowing down fuel flow or varying the refueling position of the nozzle during refueling.
12. The system of Claim 11, wherein said second fuel cut off member includes a secondary high level cut off subsystem, said secondary high level cut off system serving as back up for said primary high level cut off subsystem.
13. The system of Claim 12, wherein said secondary high level cut off system includes means for monitoring fuel tank pressure within a plurality of preset fuel tank pressure limits during refueling.
14. The system of Claim 13, wherein said monitoring means includes sensing fuel tank pressure with said fuel tank pressure transducer.
15. The system of Claim 14, wherein said preset fuel tank pressure limits are 10 and +10 column inches water. said values encoded on said computer.
16. The system of Claim 15. further including means for cutting off fuel flow if said sensed fuel tank pressure falls outside of said10 and +10 column inches water pressure limits.
17. The system of Claim 16, wherein fuel flow is cut off via said fuel shut off valve.
18. The system of Claim 17, wherein said second fuel cut off member further includes a tertiary high level cut off subsystem for use in conjunction with said secondary high level cut off subsystem.
19. Claim.
20. The system of Claim 18, wherein said tertiary high level cut off subsystem includes means for monitoring sensed fuel tank pressure spikes.
21. Claim.
22. The system of Claim 19, wherein said fuel tank pressure spikes monitoring means includes a software algorithm encoded on said computer. said algorithm cutting off fuel flow via said fuel shut off valve if at least one substantial pressure spike is detected during refueling.
23. Claim.
24. The system of Claim 20. wherein said third fuel cut off member includes a quaternary high level cut off subsystem.
25. Claim.
26. The system of Claim 21, wherein said quaternary high level cut off subsystem includes means for monitoring vapor pressure sensed by said vapor pressure transducer during refueling.
27. Claim.
28. The system of Claim 22, wherein said vapor pressure monitoring means includes a software algorithm encoded on said computer, said algorithm comparing preset vapor line pressure levels with said sensed vapor pressure, said algorithm cutting off fuel flow via said fuel shut off valve if said sensed vapor pressure falls out of the range of the preset vapor line pressure.
Description:
FUEL CUT-OFF SYSTEM FOR USE IN ROBOTIC VEHICLE REFUELING BACKGROUND OF THE INVENTION Field of the Invention The present invention relates generally to vehicle refueling systems and more particularly to automatic fuel cut off systems for use in robotic refueling of vehicles.

Prior Art Automatic fuel cut off systems are increasingly in demand as they are needed for the most part in robotic refueling systems. A robotic refueling system may include an overhead gantry which supports a carriage upon which a robot is supported for appropriate movement relative to the vehicle to position the robot adjacent the fuel door on the vehicle. Alternatively, the robotic system may be supported on an island adjacent the vehicle and then moved to a position adjacent the fuel door. A system of this type is shown generally in U. S. Patent No. 5. 238. 034. An alternative robotic refueling system is shown in U. S. Patent No. 4, 881,581 which discloses a robotic system stowed underground and retrieved above ground after positioning the vehicle for refueling at a point adjacent the fuel door of the vehicle. Another form of robotic refueling apparatus is described in U. S. Patent Nos. 5, 609, 190; 5,628. 351 and 5. 634. 503 which are assigned to the assignee of the present application, the disclosures of which are incorporated herein by reference. As is therein generally shown, a refueling robot is stored on an overhead carriage which in turn is supported for movement upon a gantry so that the robot may be positioned on either side of the vehicle in accordance with the position of the vehicle fuel door. After the robot is appropriately positioned, the fuel door is automatically opened by the robot arm and the fuel hose which is equipped with a specialized nozzle is inserted into the vehicle fill pipe. After the vehicle fuel tank is filled, the fuel hose assembly is extracted from the fill pipe and retracted into the robot arm with the robotic assembly then safely stored overhead on the carriage and returned to a stowed position on the gantry.

The main purpose of installing robotic refueling systems is to increase the efficiency of the vehicle refueling operation which is expected to take not more than 2-3 minutes from start to finish. Therefore, having an efficient, reliable and adaptive automatic fuel cut off system is very important in robotic refueling.

Conventional robotic fuel dispenser systems, however, are equipped with a fuel cut off system having only primary and secondary high level fuel cut off systems. To increase the reliability and efficiency of such fuel cut off systems, multiple high level fuel cut off back up systems are needed during the refueling operation. In addition, a system of this type must also be adaptive so that it can be used in refueling of on-board refueling vapor recovery (ORVR)-equipped and non-ORVR equipped vehicles.

SUMMARY OF THE INVENTION The present invention is directed to a system for automatically cutting off the flow of fuel from a robotic refueling nozzle assembly having a variable area venturi vacuum generator into a vehicle fuel tank when the vehicle fuel tank becomes full, comprising first fuel cut off member having a sensor coupled to the robotic refueling nozzle assembly for sensing venturi vacuum during refueling, a computer operatively associated with the venturi vacuum sensor and a fuel shut off valve disposed upstream from the variable venturi vacuum generator, the fuel shut off valve controlled by the computer ; second fuel cut off member having a sensor coupled to the robotic refueling nozzle assembly proximate to the venturi vacuum sensor for sensing fuel tank pressure during refueling, the fuel tank pressure sensor operatively associated with the computer; and third fuel cut off member having a sensor coupled to the robotic refueling nozzle for sensing fuel vapor pressure during refueling, the vapor pressure sensor also operatively associated with the computer.

In accordance with one aspect of the present invention, the venturi vacuum sensor may include a pressure transducer probing the vehicle fuel tank via a venturi vacuum sensor port.

In accordance with another aspect of the present invention the fuel tank pressure sensor may include a pressure transducer probing the vehicle fuel tank via a fuel tank pressure sensor port.

In accordance with yet another aspect of the present invention, the vapor pressure sensor may include a vapor pressure transducer probing the vapor recovery line via a vapor pressure sensor port.

In accordance with a different aspect of the present invention, the first fuel cut off member may include a primary high level cut off subsystem. The primary high level cut off subsystem may comprise means for normalizing the venturi vacuum sensed by the venturi vacuum pressure transducer during refueling. The normalizing means could be a venturi vacuum normalization software encoded on the computer.

In accordance with a further aspect of the present invention, the first fuel cut off member may also include means for cutting off fuel flow when fuel covers the venturi vacuum sensor port which could be represented by a software algorithm encoded on the computer. the algorithm continuously comparing pre-set optimal normalized venturi vacuum levels with sensed normalized venturi vacuum during refueling and cutting off fuel flow via the fuel shut off valve if a substantial venturi vacuum deviation is detected. The first fuel cut off member may further include a fuel splash back stabilizing subsystem.

In accordance with a still further aspect of the present invention, the second fuel cut off member may comprise a secondary high level cut off subsystem, the secondary high level cut off system serving as back up for the primary high level cut off subsystem.

The secondary high level cut off system may include in turn means for monitoring fuel tank pressure within a plurality of pre-set fuel tank pressure limits during refueling and means for cutting off fuel flow if the sensed fuel tank pressure falls outside of the pre-set pressure limit via the fuel shut off valve.

In accordance with a still different aspect of the present invention, the second fuel cut off member may further include a tertiary high level cut off subsystem for use in conjunction with the secondary high level cut off subsystem. The tertiary high level cut off subsystem may include means for monitoring sensed fuel tank pressure spikes. The monitoring means may comprise a software algorithm encoded on the computer for cutting

off fuel flow via the fuel shut off valve if at least one substantial pressure spike is detected during refueling.

In accordance with a still another aspect of the present invention, the third fuel cut off member may include a quaternary high level cut off subsystem which may include in turn means for monitoring vapor pressure sensed by the vapor pressure transducer during refueling. The vapor pressure monitoring means may be represented by a software algorithm encoded on the computer for comparing pre-set vapor line pressure levels with the sensed vapor pressure and cutting off fuel flow via the fuel shut off valve if the sensed vapor pressure falls out of the range of the pre-set vapor line pressure.

These and other aspects of the present invention will become apparent from a review of the accompanying drawings and the following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a functional block diagram of a fuel cut off system for use in robotic vehicle refueling in accordance with the present invention; Figure 2 is a functional block diagram of one embodiment of the fuel cut off system of Figure 1; Figure 3 is a graph of measurements taken during robotic refueling testing of a vehicle in accordance with the present invention; Figure 4 is a graph of measurements taken during robotic refueling testing of another vehicle in accordance with the present invention; and Figure 5 is a graph of measurements taken during robotic refueling testing of yet another vehicle in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, some preferred embodiments of the present invention will be described in detail with reference to the related drawings of Figures 1-5. Additional

embodiments, features and/or advantages of the invention will become apparent from the ensuing description or may be learned by the practice of the invention.

The following description includes the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention.

Referring now more particularly to Figure 1, an automatic fuel cut off system generally referred to by reference numeral 2 is shown for use preferably in robotic refueling systems having a vacuum-assisted vapor recovery path such as shown in United States Patent Nos. 5,609,190; 5. 628. 351 and 5,634, 503, which are assigned to the assignee of the present application, the disclosures of which are incorporated herein by reference, in accordance with the principles of the present invention.

Fuel cut off system 2 receives fuel (regular, premium or blended) from underground storage tanks 8. Storage tanks 8 deliver regular fuel via fuel line 4a and premium fuel via line 4b to a standard multi-product fuel dispenser 10 which may be purchased from Gilbarco, Inc. of Greensboro, North Carolina or from other manufacturers.

Multi-product dispenser 10 mixes reguiar and premium fuel in pre-set proportions to produce blended fuel if desired by the user and outputs fuel to a mix manifold 12 via fuel lines 4c and 4d, respectively. Mix manifold 12 delivers the selected grade of fuel via line 4 to fuel cut off system 2. Fuel cut off system 2 delivers fuel vapor to multi-product dispenser 10 via vapor recovery line 6 which passes through a manipulator connector, a bridge connector and a gantry cable track (GCT) connector, all three connectors (not shown, only indicated in Fig. 1) being part of the type of robotic refueling system disclosed in the above-identified United States patents. Dispenser 10 sends in turn the vapor out to the underground storage tanks 8 for containment. Storage tanks 8 are equipped with a standard inward outward pressure relief valve 14 which is connected with storage tanks 8 via fluid line 16 and which circulates fresh air and vapor according to the needs of the system.

The inventive fuel cut off system overcomes the limitations of conventional fuel cut off systems by utilizing four separate high level fuel cut off (HLCO) subsystems (primary, secondary, tertiary and quaternary) for sensing when the vehicle fuel tank is full

and for cutting off fuel flow automatically. The four HLCO subsystems are also capable of avoiding premature fuel cut offs during refueling.

The primary HLCO subsystem includes a standard electronic pressure transducer 18 for sensing the level of venturi vacuum in the vehicle fuel tank filler neck.

The venturi vacuum is generated by a variable area venturi vacuum generator and check valve 20 which has a circular flow rate control orifice 22, preferably of about 0.035 inches diameter, disposed in the fuel/tube/fuel nozzle assembly, which is part of the robotic end effector assembly, disclosed in the above-identified United States patent and in co-pending patent applications entitled FUEL DISPENSER SHUT OFF APPARATUS AND METHOD UTILIZING VARIABLE VENTURI AND CHECK VALVE and QUICK RELEASE FUEL NOZZLE which are being filed concurrently with the present application and are assigned to the assignee of the present invention. the disclosures of which are incorporated herein by reference. As disclosed in the above-identified patent applications, transducer 18 is equipped with a pressure sensing tube 26 which runs through the fuel tube and ends with a nostril (opening) or sensor port 24 at the tip of the refueling nozzle. As further disclosed in the above-identified patent applications, orifice 22 serves to slow down the air/vapor/liquid fuel being drawn into variable area venturi generator 20 from sensor port 24 creating a sizable negative pressure drop which contributes to the reliability of the primary HLCO subsystem.

Transducer 18 continuously measures the level of venturi vacuum in the filler neck during refueling via sensor port 24, with the vacuum referenced against atmospheric pressure, and sends a corresponding electrical signal to a Device Net node 28.

Device Net node 28, which is located in the control compartment of the robotic fuel dispenser system disclosed in the above-identified United States patents, communicates constantly with a computer 30 during refueling, with the actual connection being through various interfaces such as a control compartment connector, a manipulator connector, a bridge connector, a GCT connector, a pillar junction and a power panel connector-all part of the robotic fuel dispenser system mentioned above. Computer 30 is programmed (via software) to normalize the measured venturi vacuum levels from the moment fuel flow starts until fuel flow is cut off with normalization being continuously subtracting the fuel tank

gauge pressure from the measured venturi vacuum values. Normalization is needed since the fuel tank pressure continuously varies (generally increases in the positive direction) during refueling. Fuel tank gauge pressure is measured by a separate transducer which will be described herein below.

In accordance with a preferred embodiment of the present invention, to avoid premature fuel cut-offs during refueling, a software look up table being actually a plot of optimal pre-determined HLCO normalized venturi vacuum (column inches of water) versus fuel flow rate (gpm) is installed on computer 30. The venturi vacuum values set in the plot are not dependent on vehicle type/model and are initially determined experimentally. It has been observed during vehicle refueling testing, however, that all vehicles cannot be refueled at the same optimal fuel flow rate which currently is about 10 gpm as set by CARB. Due to variations in filler neck and/or fuel tank configurations in the various vehicles tested, the optimal fuel flow rate in certain vehicles was determined to be lower than 10 gpm. For such cases, the software algorithm is capable of automatically adjusting its table values to reflect an expected lower optimal fuel flow rate (< 10 gpm) for a particular vehicle. The adjusting is done after the vehicle as positioned for refueling has been identified via the vehicle identification set up disclosed in the above-identified United States patents.

A specific maximum normalized HLCO venturi vacuum value is thus set in the software look up table for a specific fuel flow rate. During refueling, computer 30 constantly compares each measured normalized venturi vacuum value with the corresponding maximum HLCO normalized vacuum value set in the software table for the particular instant fuel flow rate and if the measured normalized venturi vacuum value happens to be under the maximum normalized HLCO vacuum table value, the refueling process is not interrupted. If, however, the measured normalized venturi vacuum value happens to be above the maximum normalized HLCO vacuum table value, the refueling process is interrupted via Device Net node 28. In such cases, Device Net node 28 sends an appropriate electrical signal to a standard three-way solenoid shut-off pilot valve 33 which outputs a corresponding pneumatic pilot line signal to a standard four-way spool and sleeve fuel shut-off valve 35 (both located in the control compartment of the robotic fuel dispenser shown in the above-identified United States patents) to shut off the fuel flow. Fuel

shut-off valve 35 is located on fuel line 4 relatively far downstream from mix manifold 12 to keep the fuel line pressurized behind it. Valve 35 opens and closes fuel line 4 on respective instructions from computer 30.

When the vehicle fuel tank is almost full, sensor port 24 is covered with liquid fuel which causes a considerable jump (spike) in normalized negative pressure which is sensed by pressure transducer 18. Such a spike is shown on curve 56 at about 75 seconds in the refueling process (plot of normalized venturi vacuum versus time) in Fig. 3, which will be described hereinbelow, and on curve 66 at about 77 seconds in the refueling process (plot of normalized venturi vacuum versus time) in Fig. 4 which also will be described hereinbelow. The reason for the considerable spike in normalized venturi vacuum pressure during fuel coverage of sensor port 24 is disclosed in the above-identified co-pending patent application entitled FUEL DISPENSER SHUT OFF APPARATUS AND METHOD UTILIZING VARIABLE VENTURI AND CHECK VALVE. Thereafter. transducer 18 sends a corresponding electrical signal to control compartment Device Net node 28 which notifies computer 30 of the same via the above-described interfaces. Since the received normalized negative pressure value is much higher than the corresponding optimal value set in the look up table, computer 30 instructs fuel shut-off valve 35 in the manner described above to shut off the flow of fuel. Furthermore, whenever fuel shut-off valve 35 is closed by computer 30, a conventional vapor shut-off valve 44 located on vapor recovery line 6 in the control compartment of the robotic fuel dispenser system (described in the above- identified United States patents) is also closed by computer 30. Computer 30 instructs valve 44 to close via Device Net node 28 which sends a corresponding electrical signal to a standard solenoid three-way vapor shut-off pilot valve 43 which outputs in turn a corresponding pneumatic signal to vapor shut-off valve 44.

It should be appreciated by a person skilled in that art, that the above- described primary HLCO subsystem may be used in refueling of ORVR-equipped and non- ORVR-quipped vehicles. No modifications are needed during ORVR-equipped vehicle refueling.

Turning to Fig. 2, the secondary HLCO subsystem comprises a vehicle fuel tank pressure sensor 40 coupled to a vehicle fuel tank 42 for sensing fuel tank gauge

pressure in the vehicle fuel tank filler neck during refueling. As further shown in Fig. 1, pressure sensor 40 includes a standard electronic pressure transducer 32 equipped with a pressure sensing tube 27 which runs through the fuel tube and ends with a nostril (opening) or sensor port 34 at the tip of the refueling nozzle proximate to HLCO sensor port 24.

Transducer 32 continuously measures via sensor port 34 fuel tank gauge pressure (fuel tank pressure being referenced against atmospheric pressure) in the fuel tank filler neck during refueling and sends a corresponding electrical signal to Device Net node 28. Transducer 32 is capable of sensing positive and negative fuel tank gauge pressures. Device Net node 28 communicates in turn constantly with computer 30 during the fueling operation.

In accordance with another preferred embodiment of the present invention, to avoid overfilling of the vehicle fuel tank in case the primary HLCO subsystem fails, computer 30 is programmed to continuously monitor the measured fuel tank gauge pressure (via Device Net node 28) so that it should fall within a pre-determined interval, namely-10 inches water to 10 inches water (Fig. 2), which is not dependent on vehicle type/model. If the measured (sensed by transducer 32) fuel tank gauge pressure is within the above interval during refueling, the refueling process is not interrupted. If, however. the measured fuel tank gauge pressure falls out of the pre-set interval at any time during refueling, computer 30 instructs fuel shut-off valve 35 via Device Net node 28 and shut-off pilot valve 33 (as described hereinabove) to shut off the fuel flow. With regards to the above interval, the-10 inches water value is in fact dictated by the National Conference on Weights And Measures.

CARB has adopted the same limit value in order to avoid fuel re-circulation in vacuum- assisted vapor recovery systems and to prevent possible damage to the vehicle fuel tank in view of the fact that a large negative pressure differential is not normaally recommended for any type of large surface area container as the walls may cave in under the pressure. The +10 inches water value, on the other hand, has been set as an absolute fuel overfill limit irrespective of vehicle fuel tank/model.

It should further be appreciated by a person skilled in that art, that the above- described secondary HLCO subsystem may be used in refueling of ORVR-equipped and non-ORVR-quipped vehicles. No modifications are again needed during ORVR-equipped vehicle refueling.

The tertiary HLCO subsystem comprises the same components as secondary HLCO subsystem with the exception of the encoded [-10.10 inches H20] software fuel tank gauge pressure interval and can be used in robotic refueling of ORVR-equipped and non- ORVR-equipped vehicles. This subsystem utilizes the functional relationship between sensed fuel tank gauge pressure and fuel flow. It is anticipated that this HLCO subsystem will be used in conjunction with the closed loop feedback vapor recovery control system disclosed in co-pending patent application VAPOR RECOVERY SYSTEM, which is filed concurrently with the present application and is assigned to the assignee of the present application, the disclosure of which is incorporated herein by reference. The closed loop feedback vapor recovery control system maintains the fuel tank gauge pressure relatively constant at 0 (or-1, or-2) inches of water during robotic refueling. Specifically, the tertiary HLCO subsystem contains a software algorithm stored in computer 30 which looks for prominent slope changes in the sensed fuel tank gauge pressure versus time curve. The slope change information is provided via sensor port 34, pressure transducer 32 and Device Net node 28 as described hereinabove. When a pronounced spike in the fuel tank gauge pressure is sensed by transducer 32 in the positive direction or in the negative direction followed by a spike in the positive direction, computer 30 instructs fuel shut-off valve 35 to shut off the fuel flow. This set up is intended to be used as a back up to the primary HLCO subsystem, but not as a back up to the secondary HLCO subsystem. Rather. it should be used in conjunction with the secondary HLCO subsystem.

Fig. 3 is a graph of actual measurements taken during robotic refueling testing on August 23, 1999 of a 1999 Saturn SL1 vehicle equipped with an ORVR system.

Specifically, middle curve 50 is a plot of measured fuel tank gauge pressure (inches water) versus time (seconds), lower curve 54 is a plot of vapor pump rpm versus time (second) and bottom curve 52 is a graph of fuel flow rate (gpm) versus time (seconds). Reviewing curves 50 and 52, it can be observed that as the relatively constant 10 gpm fuel flow rate approaches 74 seconds into the fueling process (fuel tank almost full), the fuel tank gauge pressure exhibits a pronounced spike in the positive direction. Such a spike is expected since at the point when the fuel tank is almost full, the fuel tank gauge pressure rises sharply in the positive direction. Furthermore, as seen from Fig. 3, the fuel tank gauge pressure is still

within the [-10, 10 inches water] interval (secondary HLCO subsystem). This HLCO subsystem may come into play if the primary HLCO subsystem has failed (which is not the case in Fig. 3). If the primary HLCO subsystem had failed prematurely, the algorithm in computer 30 would have closed fuel shut-off valve 35 cutting off the flow of fuel. With regards to curve 54, it is shown as a straight line which is expected since the vapor pump disclosed in the above-mentioned VAPOR RECOVERY SYSTEM patent application is turned off during refueling of ORVR-equipped vehicles.

The non-ORVR case is illustrated in Fig. 4 which is a graph of actual measurements taken during robotic refueling testing on August 23,1999 of a 1992 Nissan 240 SX vehicle not equipped with an ORVR system. Specifically, middle curve 60 is a plot of measured fuel tank gauge pressure (inches water) versus time (seconds), lower curve 62 is a graph of fuel flow rate (gpm) versus time (seconds) and bottom curve is a plot of vapor pump rpm versus time (seconds). Reviewing curves 60 and 62, it can be observed that curve 64 is no longer a straight line (as in the ORVR case) as the vapor pump is turned on and maintains fuel tank gauge pressure relatively constant around 0 inches water (curve 60). As the relatively constant 10 gpm fuel flow rate approaches 77 seconds into the fueling process (fuel tank almost full), curve 60 exhibits a relatively small pressure decrease in the negative direction followed by an increase (spike) in the positive direction (small bump). The small bump is caused by the relatively slow responding vapor pump control loop disclosed in the VAPOR RECOVERY SYSTEM patent application at this point, the fact that fuel is being driven into the fuel tank by momentum and because the vapor recovery line is being blocked by fuel in a nearly full vehicle fuel tank As can be seen from Fig. 4, the fuel tank gauge pressure is still within the [-10,10 inches water] interval (secondary HLCO subsystem). In this scenario, if the primary HLCO subsystem has failed (which is not the case in this Figure), the algorithm in computer 30 would close fuel shut-off valve 35 cutting off the flow of fuel.

Turning again to Fig. 1, the quaternary HLCO subsystem comprises a standard electronic pressure transducer 70 disposed on vapor recovery line 6 in the control compartment (of the robotic fuel dispenser system described in the above-identified United States patents) for sensing fuel vapor pressure during refueling. Transducer 70 is equipped

with a pressure sensing tube 74 which runs through the vapor recovery line 6 and ends with an opening or sensor port 72 which probes the interior of the fuel tank filler neck during refueling. Transducer 70 continuously measures vapor pressure in the vapor recovery line 6 during refueling via sensor port 72 and sends a corresponding electrical signal to Device Net node 28 which communicates constantly with computer 30. This HLCO subsystem is also intended for use with the vapor pump closed control loop disclosed in the above- mentioned VAPOR RECOVERY SYSTEM patent application.

In accordance with yet another preferred embodiment of the present invention, to establish an additional back up fuel cut-off system to the primary HLCO subsystem during refueling of non-ORVR-equipped vehicles, a software look up table representing a plot of pre-determined normal vapor pressure values (inches water) versus vapor pump rpm is installed on computer 30. Normally, the vapor recovery line will contain mostly fuel vapor, air and a relatively small percentage of liquid fuel droplets and the vapor pressure measured by transducer 70 will be negative pressure. If a pronounced vapor pressure spike in the negative direction is sensed by transducer 70 during refueling, computer 30 instructs fuel shut-off valve 35 and vapor shut-off valve 44 via Device Net node 28 to close cutting off fuel flow and the vapor path to the underground tanks 8. Such a negative spike may be due to liquid fuel entering the vapor line 6 at sensor port 72 (meaning that the fuel tank is full or about to overfill) which would block the return of vapor through vapor line 6 driving the vapor pressure in the vapor line very negative. This algorithm may not be used when refueling an ORVR-equipped vehicle as the vapor pump in that case is turned off. It has been observed in this regard that during ORVR refueling vapor line pressure generally tracks the sensed fuel tank gauge pressure and if the primary HLCO mechanism fails and the fuel tank gauge pressure starts rising, the vapor pressure will rise too.

In accordance with the best mode for practicing the invention, transducers 18,32 and 70 are calibrated (zeroed out) via software installed in computer 30 prior to refueling.

In accordance with yet another preferred embodiment of the present invention, a fuel splash back stabilizing mechanism is included for use in conjunction with

the primary HLCO subsystem. This splash back stabilizing mechanism comprises a software algorithm installed on computer 30 for tracking intermediate spikes in the normalized venturi vacuum versus time curve during ORVR and non-ORVR refueling.

Figure 5. which is a graph of actual measurements taken during robotic refueling testing on August 26, 1999 of a 1997 Ford F-150 pick up not equipped with an ORVR system. shows such a curve, namely curve 80 (plot of normalized venturi vacuum versus time) which exhibits a number of undesirable intermediate normalized venturi vacuum spikes which are due to splash backs during refueling. In such cases, computer 30 is programmed to either slow down the fuel flow rate or shift the position of the robotic end effector refueling nozzle inside the filler neck so as to reduce or eliminate the splash backs altogether thereby stabilizing the normalized venturi vacuum curve.

While the present invention has been described in detail with regards to the preferred embodiments, it should be appreciated that various modifications and variations may be made in the present invention without departing from the scope or spirit of the invention. Features illustrated or described as part of one embodiment can be used in another embodiment to provide yet another embodiment such that the features are not limited to the specific embodiments described above. Thus, it is intended that the present invention cover such modifications and variations as long as they come within the scope of the appended claims and their equivalents.