WO2001040103A1

WO2001040103A1 - Vapor recovery system

Info

Publication number: WO2001040103A1
Application number: PCT/US2000/032952
Authority: WO
Inventors: John W. Logan
Original assignee: Shell Oil Company
Priority date: 1999-12-06
Filing date: 2000-12-05
Publication date: 2001-06-07
Also published as: AU1945301A

Abstract

A vapor recovery system for controlling fuel tank pressure during robotic refueling of vehicles so as to sustain a unity vapor-to-fuel ratio is disclosed. The feedback is represented by a pressure sensor coupled to the vehicle fuel tank for sensing the tank pressure during refueling and producing a corresponding feedback signal. The feedback signal is passed through a feedback amplifier, differentiator and a feedback summer. The resultant feedback pressure signal is compared with a reference pressure signal to generate an error signal and passed on to a controller which is controlled by a computer. The controller regulates the speed of the vapor pump to maintain the vehicle fuel tank pressure substantially equal to the reference fuel tank pressure during refueling so as to ensure a unity vapor-to-fuel ratio as required by government environmental regulations. The vapor recovery system is capable of handling on-board refueling vapor recovery (ORVR)-equipped and non-ORVR-equipped vehicles.

Description

VAPOR RECOVERY SYSTEM

BACKGROUND OF THE INVENTION

Field of the Invention The present invention relates generally to vapor recovery systems used in vehicle refueling and more particularly to automatic vapor recovery control systems for maintaining a unity vapor-to-fuel ratio during robotic refueling of vehicles. Prior Art

When a vehicle is being refueled, fuel vapors from the vehicle fuel tank must be aspirated into an underground storage tank to avoid environmental pollution. Fuel dispensers are therefore required to have vapor recovery systems to remove fuel vapors expelled from the vehicle=s fuel filler neck during refueling. Conventional vapor recovery systems are either balance or vacuum-assist vapor recovery systems. The balance vapor recovery system utilizes fuel delivery nozzles with a bellows and face plate which is intended to tightly seal the vehicle fill pipe opening during refueling. The incoming fuel displaces the existing vapor space creating positive pressure inside the vehicle fuel tank. The higher pressure achieves equilibrium with the supply tank=s vapor pressure through the vapor return line balancing the system.

Vacuum-assist vapor recovery systems, on the other hand, may utilize more than one type of fuel delivery nozzles. One type of nozzle has a bellows and a face plate designed to make a Anon-intended≡ tight seal with the vehicle fill pipe opening. Another type of nozzle has no bellows, uses a coaxial metal fill spout with perforations in the outer tube to remove vapors and allows visual observation of the fuel pipe opening. Typically, these systems employ a mechanism to create vacuum which evacuates displaced fuel tank vapors by negative pressure in the vapor return line. The vapor return line includes a vapor vacuum pump in operation between the underground storage tank and the fuel dispenser.

The vapor pump is usually equipped with a pump controller which operates in an open loop

fashion with suction created based on the volume of fluid pumped. No sensors are conventionally available to provide feedback to the pump controller on whether suction

should be increased, decreased or maintained constant during refueling. Too little suction may result in overpressurizing the vehicle fuel tank which is undesirable. On the other hand, too much suction may result in overpressurizng the underground storage tank which is equipped with vent stacks to relieve overpressure. In either case, venting to the atmosphere via an overpressure relief valve is likely which results in polluting the environment with toxic hydrocarbons. Furthermore, conventional vapor pump controllers are incapable of compensating for changes in fueling conditions such as varying fuel flow rates, variable fuel tank filler neck configurations, temperature differentials between the fuel present in the vehicle before refueling starts and the fuel pumped in during refueling.

The California Air Resources Board (CARB), which is a branch of the United States Environmental Protection Agency (EPA), has outlined a variety of regulations aiming to limit the amount of hydrocarbon fuel vapor released into the atmosphere during refueling of a motor vehicle. One of the most important requirements in this regard is that the ratio of vapor volume recovered to liquid fuel volume dispensed into the vehicle tank

(V/L ratio) should be kept approximately equal to 1.00. Thus, there should be an exact balance (equilibrium) of incoming liquid versus outgoing vapor during refueling. No vapor

recovery system is certified by CARB as safe to use unless the system is capable of

maintaining a unity V/L ratio during operation. CARB uses special instrumentation to

-?. measure the V/L ratio during certification testing with the ratio being an important part of the vapor recovery system=s acceptance criteria.

Various approaches to maintaining the V/L ratio equal to 1.00 are known in the art, however none utilize monitoring the fuel tank gauge pressure during refueling via a closed loop feedback control system so as to keep the same substantially equal to a constant reference fuel tank pressure referenced to the atmospheric pressure.

Furthermore, conventional vacuum-assist vapor recovery systems are generally incapable of detecting vehicles equipped with on-board refueling vapor recovery (ORVR) systems. This results in a rapid increase in wear and tear of the ORVR system, ingestion of excessive air into the underground storage tank which leads to overpressurizing the storage tank due to the expanded volume of hydrocarbon-saturated air. Detecting and ORVR system and providing for an appropriate response from the vapor recovery system would avoid the redundancy inherent with trying to operate two vapor recovery systems at the same time.

On the other hand, automatic vacuum-assist vapor recovery systems are increasingly in demand as they are utilized 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 and reliable automatic vacuum-assist vapor recovery system in robotic refueling is extremely important. However, none of the prior art robotic systems implement such a vapor recovery system. Therefore, the need arises for an efficient and reliable automatic vacuum- assist vapor recovery system which can be used in conventional and/or robotic refueling and which can effectively control the speed of the vapor pump in a closed loop feedback fashion via the vapor pump controller to avoid overpressurizing either the vehicle fuel tank or the underground storage tank. Such a vapor recovery system should eliminate the leakage of fuel vapors to the environment during refueling and should be capable of handling all kinds of fueling conditions without a noticeable drop in performance. A vapor recovery system

of this type should preferably be capable of detecting an ORVR-equipped vehicle either before refueling or during refueling so as to avoid the redundant operation of two vapor recovery systems at the same time.

SUMMARY OF THE INVENTION

The present invention is directed to a vapor recovery system for controlling

fuel tank pressure during robotic refueling of vehicles so as to sustain a unity vapor-to-fuel ratio in accordance with government environmental regulations. The inventive vapor recovery system meets the above needs and comprises a vapor pump for aspirating fuel vapors from the vehicle fuel tank and for delivering the aspirated fuel vapors into a storage tank, feedback means associated with the vehicle fuel tank for producing a feedback fuel tank pressure signal, means for generating a reference fuel tank pressure signal, means for comparing the reference fuel tank pressure signal with the feedback fuel tank pressure signal and generating an error signal, means for amplifying the error signal, and a controller coupled to the vapor pump and associated with the amplifying means for receiving the amplified error signal and generating a vapor pump control signal. The vapor pump control signal controls the aspiration rate of the vapor pump to maintain the vehicle fuel tank pressure substantially equal to the reference fuel tank pressure during refueling so as to ensure a unity vapor-to-fuel ratio. A primary computer is coupled to the controller to control the same during vehicle refueling.

In accordance with one aspect of the present invention, the feedback means may include a fuel tank pressure sensor coupled to the vehicle fuel tank. The sensor may be utilized to sense vehicle fuel tank pressure during refueling and to produce a

corresponding feedback signal. The sensor could be represented by a pressure transducer probing the vehicle fuel tank via a tank pressure sensor port. In accordance with another aspect of the present invention, a secondary computer may be added with the secondary computer coupled between the primary computer and the pressure transducer for communication with the pressure transducer

during refueling. The secondary computer may be controlled by the primary computer.

In accordance with still another aspect of the present invention, the means for generating a reference fuel tank pressure signal may be a software program encoded on the primary computer. The software program will be capable of automatically generating the reference fuel tank pressure signal during refueling.

In accordance with a further aspect of the present invention, the comparing means may be a software comparator encoded on the primary computer with the comparator comparing the reference fuel tank pressure signal with the feedback fuel tank pressure signal and generating the error signal.

In accordance with a still further aspect of the present invention, the amplifying means may include a software-based forward path amplifier for amplifying the error signal, a software-based integrator for integrating the error signal, a software-based integrator amplifier for amplifying the integrated error signal and a software-based summer for summing the amplified error signal and the amplified integrated error signal and producing a corresponding output signal.

In accordance with yet another aspect of the present invention, the vapor

recovery system may include first means for sensing an on-board refueling vapor recovery (ORVR) system on a vehicle during refueling. The first ORVR sensing means may include

the fuel tank pressure sensor sensing the vehicle tank pressure as being substantially negative when refueling an ORVR-equipped vehicle which would automatically trigger a

vapor pump control signal from the controller to shut off the vapor pump. In accordance with a different aspect of the present invention, the vapor recovery system may include second means for sensing an ORVR system on a vehicle during refueling. The second ORVR sensing means may include a vehicle identification detector communicating with a software vehicle identification database stored on the primary computer. The database will have information on ORVR-equipped vehicles. The controller will automatically generate a control signal to the vapor pump not to turn on when the database identifies an ORVR-equipped vehicle positioned for refueling.

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 vapor recovery system in accordance with the present invention;

Figure 2 is a functional block diagram of one embodiment of the vapor recovery system of Figure 1 ; and Figure 3 is a graph of measurements taken of vehicle fuel tank gauge pressure, vapor pump speed and fuel flow during refueling of a 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 - 3. 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.

The present invention is directed to a vacuum-assist vapor recovery system which overcomes the limitations of conventional vacuum-assist vapor recovery systems by maintaining a substantially constant vehicle fuel tank pressure during robotic vehicle refueling to ensure a unity vapor-to-fuel ratio as required by current environmental government regulations. The inventive vapor recovery system includes a variable speed vacuum pump for aspirating fuel vapors from the vehicle fuel tank during refueling and for delivering the aspirated fuel vapors into an underground storage tank and is configured as a closed loop feedback control system with the controlled variable being measured fuel tank gauge pressure. The feedback portion of the loop is represented by a pressure sensor coupled to the vehicle fuel tank for sensing the fuel tank gauge pressure during refueling and producing a corresponding feedback signal. The feedback signal is passed through software- based feedback amplifier, differentiator and feedback summer. The resultant feedback fuel

tank pressure signal is compared with a reference fuel tank gauge pressure signal generated

in software to produce an error signal. The error signal is amplified, converted to an appropriate output signal and passed on to the vacuum pump controller which is controlled by a computer. The pump controller regulates the speed of the vapor pump to maintain the measured vehicle fuel tank gauge pressure substantially equal to the reference fuel tank gauge pressure during refueling so as to ensure the desired unity vapor-to-fuel ratio.

The novel vapor recovery system is closed to the outside world during refueling and can be utilized in refueling of ORVR-equipped and non-ORVR-equipped vehicles. Specifically, the closed loop vapor recovery control system is capable of sensing an ORVR-equipped vehicle during refueling. In this case, the fuel tank pressure sensor senses the vehicle tank pressure as being substantially negative which automatically triggers the pump controller to shut off the vapor pump. An alternative ORVR detection system is also implemented in the inventive vapor recovery system which includes a vehicle identification detector communicating with a software vehicle identification database stored on the computer. The database contains information on ORVR-equipped vehicles. When the database identifies an ORVR-equipped vehicle positioned for refueling, the controller is automatically triggered to turn off the vapor pump. With the vapor vacuum pump turned off, a vapor shut-off valve may be placed on the vapor recovery line between the vehicle fuel tank and the vapor pump to control the vapor path from the vehicle fuel tank to the underground storage tank. The vapor shut-off valve is computer-controlled and opened during ORVR refueling. Alternatively, a fresh air inlet valve may be provided between the vapor fuel shut off valve and the vehicle fuel tank to let fresh air flow into the vehicle fuel

tank during ORVR refueling. In this set up, the vapor shut-off valve is closed to prevent storage tank fumes from reaching the vehicle fuel tank while the fresh air inlet valve is

opened to the atmosphere. The fresh air inlet valve may be controlled with a pneumatic

AND gate eliminating the need for computer control of the valve. Referring now more particularly to Figure 1, a vapor recovery system generally referred to by reference numeral 10 is shown for use preferably in robotic refueling systems 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 and the disclosures of which are incorporated herein by reference, in accordance with the principles of the present invention. Vapor recovery system 10 comprises a vapor pump 12 which aspirates fuel vapors from a vehicle fuel tank 14 and delivers the aspirated fuel vapors into an underground (storage) fuel tank 16 during refueling of vehicles. Vapor pump 12 is a conventional variable speed vacuum pump with a brushless d.c. motor and preferably a maximum speed of 3600 rpm. Such vapor pumps are available commercially and may be purchased for example from Gilbarco, Inc. of Greensboro, North Carolina. Other vapor pumps may be used provided that they do not deviate from the intended purpose of the present invention. Vapor pumps of this type can be used in robotic and/or conventional fuel dispensing systems.

Vehicle fuel tank 14 is equipped with a conventional gas fill pipe (not shown) in which a fuel tube having a specialized nozzle (which is part of the robotic end effector described in the above-identified patents) is inserted during refueling with the inserted nozzle sealing the vehicle fuel tank from the outside world. Such a refueling nozzle is shown in co-pending patent application entitled QUICK RELEASE FUEL NOZZLE which is being 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, and

in co-pending patent application entitled FUEL DISPENSER SHUT OFF APPARATUS AND METHOD UTILIZING VARIABLE VENTURI AND CHECK VALVE which is also being filed concurrently with the present application and is also assigned to the assignee of the present application, the disclosure of which is incorporated herein by reference. This type of refueling nozzle has a plurality of pressure sensor ports (nostrils) at its tip which probe the interior of the vehicle fuel tank during refueling. A conventional electronic pressure transducer, which can be purchased for instance from Motorola, residing in the robotic end effector is equipped with a pressure sensing tube which runs through the fuel tube and ends with a nostril (opening). The transducer senses the fuel tank gauge pressure via its nostril and feeds continuously current fuel tank gauge pressure information back to a computer which controls the entire operation.

As shown in Fig. 1, a fuel tank pressure sensor 18 is coupled to vehicle tank 14 sensing the fuel tank gauge pressure (with the fuel tank pressure referenced to atmospheric pressure) during refueling in accordance with the principles of the present invention. Sensor 18 can sense positive and negative gauge pressures and includes a standard electronic pressure transducer (not shown) mounted in the end effector which probes the interior of fuel tank 14 via one of the above-mentioned pressure sensor ports and provides continuously electronic feedback on the gauge pressure level inside the fuel tank to a secondary computer 20 (Fig. 2). Secondary computer 20 is in constant electronic communication with the pressure transducer during refueling via appropriate wiring. A primary computer 22 (Fig. 2) continuously receives input via a serial data link from secondary computer 20 and controls the same accordingly throughout the refueling operation. Primary computer 22 performs all calculations needed to operate the inventive closed loop vapor recovery control system and is preferably a conventional Pentium II/III

personal computer that can be purchased from a variety of computer vendors such as

Gateway, Inc. of South Dakota. Secondary computer 20 is preferably a custom-made computer having a microprocessor which can be ordered from electronics manufacturers throughout the country. Secondary computer 20 communicates preferably via a Device Net bus with primary computer 22. Other types of computers may be used provided that they fall within the scope of the present invention. This set up is shown in detail in co-pending

patent application entitled FUEL CUT OFF SYSTEM FOR USE IN ROBOTIC REFUELING which is being 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 output from the electronic pressure transducer used by fuel tank pressure sensor 18 is a voltage feedback signal Vp proportional to the sensed fuel tank gauge pressure which is measured in inches H₂O. As illustrated in Fig. 1 , voltage feedback signal Vp is passed through a software-based feedback amplifier 24 which converts and amplifies the electrical signal at a certain gain in accordance with the purpose of the present invention with the units converted from volts to inches H₂O. The output is feedback pressure signal P_f (inches H₂O). The magnitude of the gain is fixed in the software code on primary computer 22 and is independent of the model of vehicle being refueled. A software-based differentiator 26 is then employed to differentiate the output P_f from feedback amplifier 24 to provide a degree of damping in the control system. Damping is needed to improve the dynamic characteristics of the closed loop feedback control system. Differentiator 26 therefore acts as a stabilizing element in the control system. The output (dP/dt) from differentiator 26 is then summed with the output P_f from feedback amplifier 24 by a software-based feedback summer 28 which outputs a relatively stable feedback fuel tank

pressure signal P_fs. In accordance with the principles of the present invention, software- based fuel tank pressure sensor 18, feedback amplifier 24, differentiator 26 and feedback summer 28 are all encoded on primary computer 22 (Fig. 2) and together comprise a feedback portion (element) 32 of the closed loop feedback vapor recovery system 10 (Fig.

1).

Thereafter, P_fs is compared via a software-based comparator 30 with a desired (reference) fuel tank gauge pressure command P_ref, which is preferably 0 inches H,O (referenced to the atmospheric pressure), to produce an error signal P_erτor (inches H₂O). In this regard, it should be noted that whenever the seal created at the vehicle fill pipe interface by the inserted robotic nozzle is not completely tight (which may be the case on certain vehicles), a slightly negative pressure, namely -1 to -2 inches H₂O reference fuel tank gauge pressure will be preferred to ensure a tight seal during refueling. Tight sealing is required by CARB to prevent fumes from escaping into the atmosphere. The reference pressure command is automatically executed in software encoded on primary computer 22 when refueling starts. It should be appreciated by a person skilled in the art that since the inventive vapor recovery control system is closed to the outside world (there are no vents to the atmosphere) during refueling, maintaining the measured fuel tank gauge pressure substantially equal to the zero inches H₂O reference fuel tank gauge pressure will ensure V/L ratio = 1.00 as currently required by CARB.

In furtherance of this goal, the error signal P_error (inches H₂O) is passed through an amplifying device 32 (Fig. 1). Amplifying device 32 preferably comprises a software-based forward path amplifier 34, a software-based integrator 36, a software-based integrator amplifier 38 and a software-based summer 40 which are encoded on primary

computer 22 in accordance with the present invention. Forward path amplifier 34 converts and amplifies the error signal (inches H₂O) at a certain gain in accordance with the purpose

of the present invention with the units converted from inches H₂O to pump rpm (rotations per minute). The magnitude of the gain is again fixed in the software code on primary computer 22 and is independent of the model of vehicle being refueled. The output signal

S from forward path amplifier 32 (pump φm) is thus proportional to P_eιror (inches H₂O).

Furthermore, error signal P_erτor (inches H₂O) is also passed through integrator 36 which integrates the same to provide a steady state error signal V_moτ__ss which would translate down the line into a steady state pump motor speed. The steady state error signal is then amplified via integrator amplifier 38 which converts and amplifies the signal at a certain gain in accordance with the puφose of the present invention with the units converted from inches H₂O to pump φm. The magnitude of the gain is also fixed in the software code on primary computer 22 and is independent of the model of vehicle being refueled. The output signal S,₃ from integrator amplifier 38 (pump φm) is proportional to steady state error signal P_^. _ss (inches H₂O). Output signals S_ιa and S^ are then summed by summer 40 providing an output φm signal S_2s which in turn is passed through appropriate electronic hardware interface (not shown) which converts the incoming φm signal into a proportional voltage signal. The electronic hardware interface may be purchased commercially from electronics manufacturers, or in this case it is being provided by applicant. The voltsΛpm signal is then fed into a vapor pump controller 42 which controls the variable speed (φm) of vapor pump 12 via its own conventional closed loop feedback system (not shown). Controller 42 may be purchased commercially from a specialized pump controller manufacturer such as for example, Gilbarco, Inc. of Greensboro, North Carolina. In response to the volts/φm signal, pump controller 42 outputs a corresponding control φm signal to vapor pump 12 to either

slow down or speed up according to the needs of the closed loop feedback control system with the primary goal of the system being, as mentioned above, to sustain the measured (sensed) fuel tank gauge pressure substantially equal to 0 inches H₂O reference fuel tank gauge pressure during the refueling operation.

It should also be appreciated by a person skilled in the art that the above- disclosed software-based control system components, namely, feedback amplifier 24, differentiator 26, feedback summer 28, comparator 30, forward path amplifier 34, integrator 36, integrator amplifier 38 and summer 40 may be alternatively configured in a functionally equivalent hardware (circuit board) form.

In accordance with the preferred embodiment of the present invention, the inventive software algorithm as encoded in primary computer 22 can to a large extent only command vapor pump 12 (via controller 42) to correct for sensed positive fuel tank gauge pressure increases. Therefore, if the sensed fuel tank gauge pressure becomes more positive during refueling, vapor pump 12 will speed up (increase in pump φm) which means more vapor suction from the vehicle fill pipe in order to keep the measured fuel tank gauge pressure at 0 inches H₂O. Alternatively, if the sensed fuel tank gauge pressure starts getting negative, pump 12 will at first slow down (decrease in pump φm) which means less vapor suction from the vehicle fill pipe, but if the sensed fuel tank gauge pressure continues to increase significantly in the negative direction (for whatever reason), vapor pump 12 can only react by stopping (zero φm) as no correction for substantial increases in negative fuel tank gauge pressure is provided in the algorithm.

In this regard, the functional relationship between sensed fuel tank gauge pressure, fuel flow and corresponding vapor pump φm versus time is clearly illustrated in Fig. 3 which is a graph of actual measurements taken during robotic refueling testing on

August 23, 1999 of a 1992 Nissan 240 SX four-door sedan. Specifically, bottom curve 44 represents a plot of vapor pump (φm/100) vs time (seconds), middle curve 46 represents a plot of fuel flow in gallons per minute (gpm) vs time (seconds) and top curve 48 represents measured (sensed) fuel tank gauge pressure (inches H₂O) vs time (seconds). Reviewing curves 44 and 48, it can be observed that as the gas starts flowing, the fuel tank gauge pressure is somewhat positive which causes the vapor pump to speed up. As the fuel tank gauge pressure crosses into the negative area, the vapor pump slows down. As the fuel tank gauge pressure picks up again (crosses into the positive area), the vapor pump speeds up accordingly. After about 20 seconds into the refueling operation, the resulting fuel tank gauge pressure curve is relatively steady at 0 inches H,O and in fact is almost linear in time which is precisely the desired result. At about 78 seconds into the refueling operation, curve 48 shows a somewhat significant spike in the positive direction (after an initial decrease in pressure - shown as a bump), while curve 44 shows a more pronounced spike in the opposite direction (vapor pump suddenly slowing down to 0 φm) which is the moment when the fuel flow was cut off by the robotic fuel dispensing system=s primary high level cut off mechanism which is described in detail in the above-mentioned co-pending patent application entitled FUEL CUT OFF SYSTEM FOR USE IN ROBOTIC REFUELING. The reason for the fuel cut off was that the fuel tank was at this moment full. The reason for the bump at the end of curve 48 is also explained in detail in the FUEL CUT OFF SYSTEM FOR USE IN ROBOTIC REFUELING patent application.

The above-disclosed vapor recovery system can be utilized not only in robotic refueling, but also in conventional non-robotic refueling systems provided that

appropriate modifications are made to the refueling nozzle and fuel tube used in standard vacuum-assist vapor recovery systems to accommodate the inventive fuel tank gauge

pressure sensor and the rest of the above-described closed loop feedback control system components. Vapor recovery control system 10 can be used to refuel ORVR-equipped and non-ORVR-equipped vehicles. Most importantly, the inventive closed loop vapor recovery control system is capable of detecting on its own an ORVR-equipped vehicle during refueling. In view of the inventive software control algorithm, whenever an ORVR- equipped vehicle is being refueled, fuel tank pressure sensor 18 will quickly sense the vehicle fuel tank gauge pressure as being substantially negative (more than -2 inches H₂O) which would automatically cause pump controller 42 to shut off vapor pump 12. The sensed fuel tank gauge pressure will be substantially negative due to the fact that the vehicle=s ORVR system is operative and continuously aspirating fumes from the interior of vehicle fuel tank 14 as the fuel flows in. In accordance with another preferred embodiment of the present invention, an alternative ORVR detection system is implemented in vapor recovery system 12. The alternative ORVR detection system comprises a vehicle identification detector (not shown) communicating with a software vehicle identification database stored on computer 22. Such a vehicle identification detector/database configuration is disclosed in U.S. Patent 5,644,1 19 assigned to the assignee of the present application, the disclosure of which is incoφorated herein by reference. The database contains information on ORVR-equipped vehicles with the information collected during vehicle refueling testing. When the database identifies an ORVR-equipped vehicle positioned for refueling, vapor pump controller 42 is automatically triggered by primary computer 22 to not turn on the vapor pump. Even though vapor vacuum pump 12 is off in both cases, vehicle refueling must nevertheless proceed. Therefore, a standard vapor shut-off valve (not shown) is

provided on the vapor recovery line preferably between vehicle fuel tank 14 and vapor pump 12 to control the vapor path between vehicle fuel tank 14 and underground storage tank 16 with the vapor pump passing vapor when not in operation. Such a configuration is disclosed in the above-mentioned co-pending patent application entitled FUEL CUT OFF SYSTEM FOR USE IN ROBOTIC REFUELING. The vapor shut-off valve is preferably controlled by secondary computer 20 which causes the vapor shut-off valve to open pneumatically during ORVR refueling so as to allow a vapor path back to underground storage tank 16. This, however, results in vehicle fuel tank 14 aspirating a relatively small percentage of fumes from storage tank 16 during refueling which in itself is acceptable by CARB standards as long as there is no leakage of vapors into the atmosphere from the vehicle fuel pipe/refueling nozzle interface which is readily handled by the inventive vapor control system as described hereinabove. To provide an alternative fuel tank breathing configuration, a fresh air inlet valve (not shown) may be provided on the vapor recovery line between the vapor shut-off valve and fuel tank 14 to allow fresh air flow into the vehicle fuel tank during ORVR refueling. During refueling, the vapor shut-off valve is closed by secondary computer 20 to prevent fumes (from storage tank 16) from reaching vehicle fuel tank 14 while the fresh air inlet valve is opened to the atmosphere. The opening of fresh air inlet valve may be controlled with a pneumatic AND gate, no computer control necessary. Alternatively, the vapor shut-off valve may be replaced by a three-way valve which would be computer controlled.

The above-disclosed novel vapor recovery system represents a major improvement in the field of automatic vapor recovery as it is capable of effectively

controlling the speed of the vapor pump in a closed loop feedback fashion completely avoiding oveφressurizing either the vehicle fuel tank or the underground storage tank during the refueling operation. The inventive vapor recovery system eliminates the leakage of fuel vapors to the environment during refueling and may be utilized in all kinds of fueling conditions and in conventional and/or robotic refueling systems. The ORVR detection capability of the present control system also avoids the redundant operation of two vapor recovery systems at the same time when an ORVR-vehicle is refueled.

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.

Claims

What is Claimed is:

1. A vapor recovery system for controlling fuel tank pressure during refueling of vehicles to sustain a unity vapor-to-fuel ratio, said vapor recovery system comprising: a vapor pump for aspirating fuel vapors from the vehicle fuel tank and for

delivering the aspirated fuel vapors into a storage tank; feedback means associated with the vehicle fuel tank for producing a feedback fuel tank pressure signal; means for generating a reference fuel tank pressure signal; means for comparing said reference fuel tank pressure signal with said feedback fuel tank pressure signal and generating an error signal; means for amplifying said error signal; and a controller coupled to said vapor pump and associated with said amplifying means for receiving said amplified error signal and generating a vapor pump control signal, said vapor pump control signal controlling the aspiration rate of said vapor pump to maintain the vehicle fuel tank pressure substantially equal to said reference fuel tank pressure during refueling so as to ensure a unity vapor-to-fuel ratio.

2. The vapor recovery system of Claim 1 , further comprising a primary computer coupled to said controller, said primary computer controlling said

controller during vehicle refueling.

3. The vapor recovery system of Claim 2, wherein said feedback means comprises a fuel tank pressure sensor coupled to the vehicle fuel tank, said sensor sensing vehicle fuel tank pressure during refueling and producing a corresponding feedback signal.

4. The vapor recovery system of Claim 3, wherein said fuel tank pressure sensor includes a pressure transducer probing the vehicle fuel tank via a tank pressure sensor port.

5. The vapor recovery system of Claim 4, further comprising a secondary computer coupled between said primary computer and said pressure transducer of said fuel tank pressure sensor for communicating with said pressure transducer during refueling, said secondary computer controlled by said primary computer.

6. The vapor recovery system of Claim 3, wherein said feedback means further comprises a feedback amplifier coupled to said fuel tank pressure sensor for receiving said feedback signal and generating an amplified feedback signal, said amplified feedback signal proportional to said sensed vehicle fuel tank pressure.

7. The vapor recovery system of Claim 6, wherein said feedback amplifier is a software feedback amplifier encoded on said primary computer.

8. The vapor recovery system of Claim 7, wherein said feedback means further comprises a differentiator coupled to said feedback amplifier for differentiating said amplified feedback signal.

9. The vapor recovery system of Claim 8, wherein said differentiator is a

software differentiator encoded on said primary computer.

10. The vapor recovery system of Claim 9, wherein said feedback means further comprises a feedback summer coupled to said feedback amplifier and said differentiator for summing said amplified feedback signal and said differentiated amplified feedback signal and producing said feedback fuel tank pressure signal.

11. The vapor recovery system of Claim 10, wherein said feedback summer is a software feedback summer encoded on said primary computer..

12. The vapor recovery system of Claim 11, wherein said means for generating a reference fuel tank pressure signal is a software program encoded on said primary computer, said software program automatically generating said reference fuel tank pressure signal during refueling.

13. The vapor recovery system of Claim 12, wherein said comparing means is a software comparator encoded on said primary computer, said comparator comparing said reference fuel tank pressure signal with said feedback fuel tank pressure signal and generating said error signal.

14. The vapor recovery system of Claim 13, wherein said amplifying means comprises a forward path amplifier for amplifying said error signal.

15. The vapor recovery system of Claim 14, wherein said forward path amplifier is a software forward path amplifier encoded on said primary computer.

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16. The vapor recovery system of Claim 15, wherein said amplifying means further comprises an integrator for integrating said error signal.

17. The vapor recovery system of Claim 16, wherein said integrator is a software integrator encoded on said primary computer.

18. The vapor recovery system of Claim 17, wherein said amplifying means further comprises an integrator amplifier for amplifying said integrated error signal, said integrator amplifier and said integrator connected in parallel with said forward path amplifier.

19. The vapor recovery system of Claim 18, wherein said integrator amplifier is a software integrator amplifier encoded on said primary computer.

20. The vapor recovery system of Claim 19, wherein said amplifying means further comprises a summer coupled to said integrator amplifier and said forward path amplifier for summing said amplified error signal and said amplified integrated error signal and producing a corresponding output signal, said summer coupled to said controller for feeding said output signal to said controller, said controller receiving said output signal from said summer and producing said vapor pump control signal whereby said vapor pump control signal controls the aspiration rate of said vapor pump by varying the speed of said

vapor pump so as to maintain the vehicle fuel tank pressure substantially equal to said reference fuel tank pressure during refueling.

21. The vapor recovery system of Claim 20, wherein said summer is a software summer encoded on said primary computer.

22. The vapor recovery system of Claim 21 , further comprising first means for sensing an on-board refueling vapor recovery (ORVR) system on a vehicle during refueling.

23. The vapor recovery system of Claim 22, wherein said first ORVR sensing means includes said fuel tank pressure sensor sensing the vehicle tank pressure being substantially negative when refueling an ORVR-equipped vehicle, said substantially negative vehicle tank pressure automatically generating a vapor pump control signal from said controller to shut off said vapor pump.

24. The vapor recovery system of Claim 23, further comprising second means for sensing an ORVR system on a vehicle during refueling.

25. The vapor recovery system of Claim 24, wherein said second ORVR sensing means comprises a vehicle identification detector communicating with a software vehicle identification database stored on said primary computer, said database having information on ORVR-equipped vehicles, said controller automatically generating a vapor pump control signal not to turn on said vapor pump when said database identifies an ORVR-equipped vehicle positioned for refueling.

26. The vapor recovery system of Claim 25, further comprising means for opening the vapor recovery path between the vehicle fuel tank and the storage tank when said vapor pump is off during ORVR refueling.

27. The vapor recovery system of Claims 5 and 26, wherein said means for opening the vapor recovery path between the vehicle fuel tank and the storage tank includes a vapor shut-off valve coupled between the vehicle fuel tank and said vapor pump, said vapor shut-off valve controlled by said secondary computer, said secondary computer causing said vapor shut-off valve to open during ORVR refueling.

28. The vapor recovery system of Claim 27, further comprising means for aspirating fresh air into the vehicle fuel tank when said vapor pump is off during ORVR refueling.

29. The vapor recovery system of Claim 28, wherein said fresh air aspirating means includes a fresh air inlet valve coupled between said vapor shut-off valve and the vehicle fuel tank, said fresh air inlet valve controlled with a pneumatic AND gate, said pneumatic AND gate causing said fresh air inlet valve to open to the atmosphere during

ORVR refueling, said secondary computer causing said vapor shut-off valve to close preventing aspiration of fumes into the vehicle fuel tank from the storage tank during ORVR refueling.