A fuel dispenser

Abstract: A fuel dispenser comprises a fuel delivery line (32) and a pump (8) in the line to pump fuel there-along to a nozzle (10), a vapour return line (40) fom the nozzle, a vapour impulsion means (44) to induce vapour to flow through the vapour return line (40) at a vapour flow rate comparable to the liquid flow rate through the fuel delivery line during most of a fuelling operation, and a vapour impulsion booster to initially boost the vapour flow rate above the liquid flow rate at the start of a fuelling operation.

Description: The present invention relates to a fuel dispenser having an improved vapour recovery means and in particular, but not exclusively, to a fuel dispenser for fuelling motor vehicles. Vapour recovery fuel dispensers recover the vapour displaced from a vehicle fuel tank by the delivery of fuel thereto, and return the vapour to the fuel storage tank (normally underground), where the vapour condenses. The most widely used systems have operated on the "balance" principle in which an outer sheath is provided at the nozzle to fit around a filler pipe of a vehicle fuel tank. The sheath should make a tight fit around the filler cap so that vapour can pass only through the sheath (or, as it is commonly called, the "boot"), to a vapour return line connected with the service station's fuel storage tank. Thus, as the fuel is taken from the fuel tank and pumped into the vehicle, the liquid volume being reduced is supplanted with returning vapours. However, the balance systems, with their boots, are very cumbersome, and there are problems with reliably obtaining a good seal with the vehicle tank filler pipe, so that vapours are lost to the atmosphere. U.S. Patent 5,040,577 discloses a bootless system, with the vapours being returned under positive drive by a vapour pump located in the vapour return line. Various improvements on the Pope disclosure are made in co-pending European application 92306271. Both of these disclosures are hereby incorporated herein by reference. One of the advantages accruing from the use of a separately-provided vapour pump in the vapour return line is the ability to precisely control the vapour flow through the vapour return line, so that the vapour flow rate can be tailored to prescribed conditions ensuring that when dispensing substantially all the vapour is recovered without the requirement for a boot. However, the applicants have now found that a major vapour loss occurs with bootless systems at the start of the fuelling process, as the liquid fuel is first released from the nozzle into the fuel filler pipe. This "puff" of vapour is released quickly, as a transient event. The vapour recovery pump is effective in drawing virtually all of the vapour liberated, once the transient event has passed, and it is not desirable to raise the vapour pumping rate on a continuous basis, since air will be drawn in, which might lead to a dangerously lean vapour condition in the storage tanks. According to a first aspect of the present invention there is provided a fuel dispenser for dispensing liquid fuel comprising a fuel delivery system having a fuel delivery line and a pump in the line to pump fuel there-along to a nozzle, a vapour recovery subsystem including a vapour return line from the nozzle and a vapour impulsion means to induce vapour to flow through the vapour return line at an ordinary vapour flow rate derived from, and comparable to the liquid flow rate through the fuel delivery line during most of a fuelling operation, and a vapour impulsion booster to boost the vapour flow rate substantially above the ordinary vapour flow rate, and therefore above the fuel delivery rate, early in a fueling operation before returning to the ordinary flow rate. By employing the present invention the initial "puff" of vapour emerging from a tank at the beginning of a fuelling operation can be recovered without recovering excess air during the rest of the dispensing cycle. According to one aspect of the invention, the vapour impulsion means is a vapour pump, and the vapour impulsion booster includes a valve in the vapour return line upstream of the vapour pump and a delay means operable to prevent the opening of said valve and dispensing of fuel until after the vapour pump has been operating for a period such as to permit a reduced pressure to be generated in said vapour return line before fuel is dispensed, so that upon opening said valve vapour flows rapidly into said vapour return line. The vapour return line can include a reservoir portion to increase the amount of vapour recovered at the early stage of a fuelling operation. Alternatively, in another aspect the vapour impulsion means is a vapour pump and the vapour impulsion booster includes circuitry to operate the vapour pump at a speed to pump vapour at a rate greatly in excess of the liquid flow rate early in the fueling operation, normally at the start. Preferably, the excess may be characterized by a fast rise time to a maximum and a gradual decrease. In one embodiment the gradual decrease is a time-decaying exponential. But, the wave-form can be of any desired shape, including those selected from the group consisting of exponential, transcendental, ramp, step, pulse or a combination thereof. Also the gradual decrease may be modulated by sensing liquid passed in the fuelling operation or vapour recovered. Advantageously the vapour pump is an electrically driven pump and the vapour impulsion means includes circuitry to operate the vapour pump at a speed to pump vapour at a rate comparable to the liquid flow rate. Where the impulsion booster comprises a valve and delay means then once the initial reduced pressure in the vapour line has been depleted vapour will then be recovered at a rate substantially equivalent to the liquid flow rate. Where in the alternative embodiment the vapour pump speed is boosted, then after the initial boost the vapour pump will operate at a speed sufficient to withdraw vapour at substantially the same rate as fuel is delivered. The invention is particularly applicable in a dispenser where the nozzle is bootless. According to a further aspect of the invention, there is provided a method of dispensing volatile liquid fuel with recovery of fuel vapours including pumping fuel through a fuel delivery line at a liquid flow rate to a nozzle, returning vapours along a vapour return line from the nozzle at an ordinary vapour flow rate comparable to the liquid flow rate through the fuel delivery line during most of a fuelling operation, and boosting the vapour flow rate above the ordinary vapour flow rate early in a fuelling operation. Preferably, the boosting step includes pumping the vapour along the vapour return line while a valve in the vapour return line upstream of the vapour pump is closed and subsequently opening the valve and pumping the liquid, so that reduced pressure is generated in the vapour return line before liquid is pumped to provide a boost above the ordinary vapour flow rate at the start of the fuelling operation. In one embodiment, the excess may be characterized by a fast rise time to a maximum and a gradual, time-decaying exponential decrease. But, the wave-form can be of any desired shape, including those selected from the group consisting of exponential, transcendental, ramp, step, pulse or a combination thereof. And the gradual decrease may be modulated by the volume of liquid pumped or vapour recovered. One embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings of which: Figure 1 is a schematic block diagram of a fuel dispenser according to one embodiment of the invention; Figure 2 is a schematic diagram of a circuit used in the fuel dispenser embodiment of Figure 1; Figure 3 is a graph of two measurements of volatile hydrocarbon vapours escaping the fill neck of a vehicle fuel tank, comparing results obtained using the embodiment of Figure 2 and without; and Figure 4 is a schematic diagram of an alternate circuit for use in the fuel dispenser embodiment of Figure 1. A preferred embodiment of the invention is shown in schematic form in Figure 1. The fuel dispenser 10 is connected to a multiplicity of turbine pumps 8 in fuel storage tanks 12, 14, 16 through pipes 18, 20, 22, respectively. The pipes receive fuel from the tanks and the respective liquid flow rates are measured in meters 24, 26, 28. The fuel from the pipes is mixed in mixing manifold 30. The mixing manifold has downstream of it a pipe 32 which outlets to a hose 34, terminating in a controllable dispensing nozzle 38. The nozzle 38 is provided with a vapour return line which connects with a vapour return hose 36 in the hose 34, preferably concentrically within it. The vapour return hose 36 connects with a vapour line 40 extending to a vapour pump 44. An electrically operated solenoid valve 42 is provided in line 40 to close off the vapour line when not in use. Various other tank, liquid pump, vapour pump, and meter arrangements can also be used. In particular, the invention is useful for dispensers in which the output of each meter is passed to a separate hose, without any mixing. In such a case, the signals output on lines 56 will be exclusive; i.e. there will be a signal indicative of liquid flow only on one of the lines at a time. Dispensers of this type are sold by Gilbarco, Inc. under the MPD designation. A conventional handle 64 is mounted in the outside wall of the dispenser 10, on which the nozzle 38 can rest when not in use. As is conventional, the handle 64 is pivotally mounted, so it can be lifted after the nozzle is removed, to activate a switch, and the activation of the switch is signalled along line 62 to a transaction computer 66. Controller 50 is provided with electrical connections 56 with the meters 24, 26, 28, so that signals indicative of the liquid flow rate can be transmitted from the meters to the controller 50. Preferably the meters 24, 26, 28 are pulsers, such as are commonly used in fuel dispensers made by Gilbarco, Inc. The pulsers emit a pulse for every 1/1000th of a gallon of fuel passed by the meter. Thus, as the fuel is being pumped, a pulse train is delivered on the respective lines of the connections 56, with the pulse train frequencies corresponding to the liquid flow rate. The liquid pumps may, of course, be located in the dispenser 10, or elsewhere, and may have the metering devices integral with them. Controller 50 also has a connection 41 to the valve 42 to open or close that valve, as desired. Controller 50 also has connections 58, 60 to the transaction computer 66 which controls the overall operation of the dispenser 10, in conventional fashion. Line 58 transmits signals from the transaction computer 66 to the controller 50 indicating that pumping is desired, and line 60 transmits signals from the controller 50 to disable pumping, when the controller 50 has ascertained that pumping should be disabled, for example in the case of a malfunction. The vapour pump 44 is preferably a positive displacement pump, such as the Blackmer Model VRG3/4. It is driven by a motor 46, preferably a brushless three-phase DC motor. The brushless DC motor 46 includes three hall effect sensors, one for each phase of the three-phase motor. These are used in conventional motor drive electronics in the controller 50 to apply appropriately phased power to the three phase motor 46. The hall effect signals are a form of feedback and indicate the angular displacement of the motor. Rates of change of angular displacement signalled by the hall effect sensors by a pulse frequency are sent over lines 52 to the controller 50. That is, the lines 52 provide a tachometer reading of the rate of rotation of the motor 46. The motor drive electronics portion of the controller 50 outputs three-phase power over lines 54 to the motor to drive the motor as desired. Of course, if desired, the motor can be separately driven with a separately denominated motor drive which takes its instructions from the controller 50. The vapour of the vapour pump 44 is transmitted along line 48 back to a storage vessel such as tank 16. The returning vacuum can be transmitted via a manifold system to the plurality of tanks 12, 14, 16 or, as shown more simply in Figure 1, to one tank. The controller 50 plays a number of important roles which are fully described in Gilbarco's patent application serial number 07/946,741 filed September 16, 1992. However, to generalize, the flow rate of the liquid being pumped through the lines 18, 20, 22 as controlled by the transaction computer 66, via a connection not shown, is transmitted to the controller 50 over lines 56. The controller 50 evaluates the pulse trains 56 and output signals over lines 54 to the motor 46 to drive the vapour pump 44 at a rate comparable with the liquid pumping rate. Thus, generally the faster the liquid is pumped out, the faster the vapour is retrieved. The foregoing description is taken largely from US application serial no. 07/946,741 and describes in general the operation of a vapour recovery fuel dispenser in which a vapour pump is provided having its speed correlated with the speed of the liquid flow. However, in order to accommodate the retrieval of the "puff" generated at the start of the fuelling operation, an additional circuit shown in more detail in Figure 2 is desirable. The liquid flow rate data provided over electrical connections 56 are converted to an analog voltage and condensed into a single, analog FLOW_RATE_IN signal 156 indicative of the overall flow. The start of a train of pulses on lines 56 can also be used to derive a FLOW_DETECT_IN signal 158. The circuit shown in Figure 2 will act upon these two signals 156, 158 to generate modifications to the flow rate 156 at the inception of flow. The circuit will provide a COMPOSITE_OUT signal 154. Signal 154 is directly proportional to the speed of the vapour pump motor, from which the three-phase output signals 54 to the motor 46 are derived. At the inception of liquid flow as detected by signal 158, the COMPOSITE_OUT signal 154 will be used to drive the motor 46 at a high rate. Once the transient "puff" has passed, the COMPOSITE_OUT signal will be nearly congruent with the FLOW_RATE_IN signal 156. The burst compensation system of Figure 2 employs analog electronic techniques. However, those of ordinary skill in the art could likewise employ a variety of digital, software, or mechanical embodiments to achieve similar compensation effects. A time-decaying exponential is used as the boost term in this example. Any function which decreases or terminates with time, the volume of fuel dispensed, or the volume of vapours recovered, including but not limited to transcendentals, ramps, steps or pulses, or a combination thereof, could similarly be employed to remove an effective quantity of the vapour "puff". Also, in this example, the boost term is employed as an additive quantity to the flow rate term, although the effective vapour burst compensation may be similarly achieved by applying the boost term as a multiplicative term to the flow rate. Similarly, both additive or multiplicative techniques may be applied downstream to the final V/L (vapour to liquid proportion, which may well be other than 1:1, as disclosed in Gilbarco's U.S. Patent No. 5,156,199) term which is typically derived by multiplying the flow term by a scaling factor for the chosen V/L ratio, and which may also contain an offset term at this point. Finally, both additive and multiplicative operations may be applied simultaneously to the flow or V/L terms, using identical or differing boost function terms. Figure 2 depicts one such embodiment where at the detection of flow, inputted as the boolean term FLOW_DETECT_IN, the output of inverter U1 is driven low, causing transistor Q1, which is driven through current limiting resistor R1, to turn off. At the instance in time where transistor Q1 turns off, referenced as t = 0, capacitor C1 has very little accumulated charge, and therefore represents a small voltage drop. Consequently, the voltage potential appearing across potentiometer R5, V R5 is approximately represented by: V R5 = +V * R5 / (R2 + R3 + R4 + R5) At time greater than t = 0, capacitor C1 begins to accumulate a charge, which increases the voltage drop across capacitor C1. The time constant T, at which capacitor C1 accumulates charge, is given by: T = C1 * (R2 + R3 + R4 + R5) And the voltage across capacitor C1, V C1 , at any point in time, t, will be represented by the decaying exponential function: V C1 (t) = +V * (1 - e -t/T ) The time-variant voltage across potentiometer R5, V R5 may be represented by the function: V R5 (t) = (+V - V C1 (t)) * R5 / (R2 + R3 + R4 + R5) The desired level of boost is chosen by potentiometer R5, configured as a voltage divider. This voltage is then fed through isolation register R6, then into an operational amplified U2 configured as a voltage follower. Voltage follower U2 acts as an impedance converter, such that a high impedance is presented to the wiper of R5. For any given setting of R5, no appreciable loading or impedance change occurs in the network preceding and including R5. Additionally, the output of voltage follower U2 presents a low impedance, so the impedance into the next stage will be defined predominantly by resistor R7. The boost term, chosen as the level of V R5(t) selected at the rate of R5, is then added to the analogue term FLOW_RATE_IN, which is a voltage that is a direct function of fuel flow rate. The addition is performed by operational amplifier U3, configured as an inverting amplifier, whose respective gain is set as the ratio of feedback resistor R9 to input resistor R7 for the boost term, and resistor R8 for the flow term. The output of amplifier U3 is now a composite of both flow and boost terms, inverted in sign. This output is then input to operational amplifier U4, configured as an inverting amplifier, whose gain is set as the ratio of feedback resistor R11 to input resistor R18. The output of amplifier U4 is now corrected in sign, such that the sign of the output agrees with the original sign of FLOW_RATE_IN and the boost term provided by U2. This correlated output is labelled COMPOSITE_OUT, and represents a replacement term for the original FLOW_RATE_IN term in subsequent stages. COMPOSITE_OUT provides a time variant boost to the vapour recovery rate (increase in vapour pump RPM or vacuum) to draw in most of the vapour "puff". Expressed mathematically for this embodiment: COMPOSITE_OUT (t) = FLOW_RATE_IN + [k*(+V - V C (t)) * R5 / (R2 + R3 + R4 + R5)] Where k is a constant term representative of the chosen wiper position of potentiometer R5. The value of k will determine the amount of boost over the ordinary vapour flow rate and can be field-set or factory set to recover a maximum amount of the "puff" without drawing in excess air. Lastly, when the boolean term FLOW_DETECT_IN becomes false, the output of inverter U1 drives transistor Q1 into conduction through resistor R1. With Q1 now conducting, the capacitor is discharged through the path of transistor Q1, resistor R3, and diode CR1. After a period of time determined predominantly by the value of resistor R3, the circuit will again repeat the boost term generation task when FLOW_DETECT_IN becomes true. Figure 3 depicts two measurements of volatile hydrocarbon vapours escaping the fill neck of a vehicle fuel tank. The larger peak is the unmitigated vapour "puff" released at the onset of fuelling. The smaller peak is a repeated measurement of the vapour "puff" with the circuit of Figure 2 supplying the boost term as an additive quantity to the instantaneous flow rate. Figure 4 illustrates in block diagram form an alternate embodiment for circuitry for the controller 50 to deal with the transient "puff". In this case, a timer portion 250 of the block 50 is provided connected with the line 58 which transmits signals from the transaction computer 66. Similarly, lines 41, 60 are connected to the timer as are controls for lines 54 which pass power to the motor 46. The timer portion 250 is arrayed to have an input from the transaction computer 66 over line 58 indicating that fuelling is desired to begin. When this signal is received, a signal is passed on line 41 to close the valve 42 if it is not already closed, and a signal is passed over line 54 to drive the motor 46 to start pumping vapour through the line 40, this creating vacuum in line 40 between the valve 42 and pump 44. Also, a signal is passed to transaction computer 66 on line 60 to temporarily disable liquid pumping. Then, as the timer portion 250 expires after a delay period, signals are applied on lines 41 and 60 to open valve 42 and to permit liquid pumping. Thus, the built up vacuum in line 40 will provide a transient high suction to draw out the transient "puff", which would otherwise be released at the beginning of the liquid pumping. Another advantage of prestarting the motor is that delays which may otherwise be inherent in the motor achieving the desired rate are not encountered. Of course, if desired, the delay between initiation of vapour pumping and liquid pumping may be calculated otherwise, such as by sensing a desired low pressure in the line 40, or the like.

Claims: A fuel dispenser for dispensing liquid fuel comprising: a fuel delivery system including a fuel delivery line (32, 34) and a pump (8) in said line to pump fuel there-along to a nozzle (10), a vapour recovery subsystem including a vapour return line (36, 40, 48) from said nozzle and a vapour impulsion means (44, 46) to induce vapour to flow through said vapour return line at an ordinary vapour flow rate derived from, and comparable to the liquid flow rate through said fuel delivery line during most of a fueling operation, and a vapour impulsion booster to boost the vapour flow rate substantially above the ordinary vapour flow rate, and therefore above the fuel delivery rate, early in a fuelling operation before returning to the ordinary flow rate. A dispenser as claimed in claim 1 wherein said vapour impulsion means is a vapour pump (44, 46) and said vapour impulsion booster comprises a valve (42) in said vapour return line (40, 48) upstream of said vapour pump and delay means (250) operable to prevent the opening of said valve and dispensing of fuel until after the vapour pump has been operating for a period such as to permit a reduced pressure to be generated in said vapour return line before fuel is dispensed, so that upon opening said valve, vapour flows rapidly into said vapour return line. A dispenser as claimed in claim 1 wherein said vapour impulsion means is a vapour pump and said vapour impulsion booster comprises circuitry to operate said vapour pump at a speed to pump vapour at a rate greatly in excess of said liquid flow rate early in the fuelling operation. A dispenser as claimed in claim 3 wherein the excess is characterized by a fast rise time to a maximum and a gradual decrease. A dispenser as claimed in claim 3 wherein the gradual decrease is a time-decaying exponential. A dispenser as claimed in claim 4 wherein the gradual decrease is modulated by sensing the volume of liquid pumped. A dispenser as claimed in claim 4 or 6 wherein the gradual decrease is modulated by sensing the volume of vapour recovered. A dispenser as claimed in any preceding claim wherein said vapour impulsion means is an electrically driven pump and further comprising circuitry to operate said vapour pump at a speed to pump vapour at a rate comparable to said liquid flow rate as the ordinary vapour flow rate. A dispenser as claimed in any preceding claim wherein said nozzle is bootless. A method of dispensing volatile liquid fuel with recovery of fuel vapours comprising pumping fuel through a fuel delivery line at a liquid flow rate to a nozzle, returning vapours along a vapour return line from the nozzle at an ordinary vapour flow rate derived from, and comparable to the liquid flow rate through the fuel delivery line during most of a fuelling operation, and boosting the vapour flow rate above the ordinary vapour flow rate early in a fuelling operation. A method as claimed in claim 10 wherein said boosting step comprises pumping the vapour along the vapour return line while a valve in the vapour return line upstream of the vapour pump is closed and subsequently opening the valve and pumping the liquid, so that a reduced pressure is generated in the vapour return line before liquid is pumped to provide a boost to the vapour flow rate above the ordinary vapour flow rate early in the fuelling operation. A method as claimed in claim 10 wherein said vapour returning step comprises pumping the vapour with an electrically-driven vapour pump and said boosting step comprises supplying electrical signals to the vapour pump to operate the vapour pump at a speed to pump vapour at a rate greatly in excess of the liquid flow rate early in the fuelling operation. A method as claimed in claim 12 wherein the excess is characterized by a fast rise time to a maximum and a gradual decrease. A method as claimed in claim 13 wherein the gradual decrease is a time-decaying exponential. A method as claimed in claim 13 wherein the gradual decrease is modulated by sensing the volume of liquid pumped. A method as claimed in claim 13 wherein the gradual decrease is modulated by sensing the volume of vapour recovered. A method as claimed in any one of claims 10 to 16 wherein said fuel pumping step comprises pumping to a bootless nozzle. A method as claimed in any one of claims 10 to 17 wherein said vapour returning step comprises electrically driving a vapour pump at a speed to pump vapour at a rate comparable to the liquid flow rate as the ordinary vapour flow rate.

Inventors: MILLER PAUL D, PAYNE EDWARD A, TUCKER MARK B, MILLER, PAUL D., PAYNE, EDWARD A., TUCKER, MARK B.
Applicants: GILBARCO INC, GILBARCO INC.
Application year: 1993
Main classification: B67D5
IPC codes: B67D7