As gasoline or other fuel is pumped into an automobile or other motor vehicle from a

fuel delivery system, fuel vapour is released from the receiving tank. These vapours

must be collected to prevent their escape and pollution of the surrounding environment.

Vapour recovery systems are currently used to collect vapours released during a fuelling

operation. A current product of Gilbarco, Inc., assignee of the present invention, sold

under the name Vapor Vac ^R collects vapour released during a fuelling operation by using

a vapour pump to pump vapours into the vapour recovery system. The rate at which

vapour is collected is controlled by varying the speed of the vapour pump. For

maximum performance and efficiency of a vapour recovery system, the speed of the vapour pump must be controlled to collect vapour at a rate that corresponds to the instantaneous vapour volume released or generated during a fuelling operation while

drawing in little or no air.

As is pointed out in US Patent 5,040,577 to Pope, US Patent 5,156,199 to Hartsell et al

and co-pending US Application Serial No. 07/988,595 filed 29 October, 1992, the rate

at which the vapour must be recovered is determined by several variables including the

liquid fuel flow rate, the liquid fuel temperature, the ambient temperature and the amount

of fuel dispensed in the current fuelling operation.

To operate the vapour pump at an optimal speed, the vapour volume generated is

continuously determined by a processor during a fuelling operation. The processor computes the instantaneous vapour volume generated and produces corresponding

vapour pump control signals that are sent to the vapour pump. The control signals adjust

the speed of the vapour pump so that the rate of vapour recovery corresponds to the

computed vapour volume generated.

The processor generates the control signal to be sent to the vapour pump by solving a

control function. In known vapour recovery systems, the solution to the control function

is a value related to the ratio of the instantaneous volume of vapour generated divided

by the instantaneous volume of liquid fuel (V/L) dispensed during a fuelling operation.

The vapour recovery system uses the derived V/L ratio to generate the control signal for controlling the speed of the vapour pump such that the rate at which released fuel vapour is collected is as close as possible to the rate at which vapour is generated during a fuelling operation.

As mentioned, the control function used to generate the vapour pump control signal is dependent on a plurality of individual variables which each affect the instantaneous

volume of fuel vapour generated during a fuelling operation. The independent variables

of the control function include flow rate, volume dispensed, time, ambient temperature,

fuel temperature, and restrictions in the vapour path. The control function is solved by

measuring the independent variables and inputting the measured values into the control

function.

To precisely determine the optimal vapour pump speed, a complex control function that

models or approximates the thermodynamic, fluid, gas, and other physical laws which ultimately govern the V/L ratio must be solved. Such a complex control function takes

into account a plurality of independent variables and requires intensive numerical

operations. Implementation of a vapour recovery system that relies on a complex control

function to determine optimal vapour pump speed would require a moderate or high¬

speed processor. Examples of control functions of this sort are shown in the Hartsell et

al patent, supra and in US Patent 5,038,838 to Bergamini et al.

A moderate or high speed processor is required because the processor must be

sufficiently proficient to determine the solution to the control function in a time period that does not unduly degrade the accuracy of the system. If an extended period of time

is required, the phase margin of the system will be substantially degraded. That is, by the time the control function is computed by a slow processor, the computed value may

no longer be accurate.

Commercially available vapour recovery systems, such as the VaporVac* system sold by Gilbarco, Inc. of Greensboro, North Carolina, have a simplified control function to

determine optimal vapour pump speeds. The simplified control function includes two

simple sub-functions to approximate the V/L ratio. As another way to simplify the control function, US Patent 5,195,564 to Spalding uses a constant V/L ratio of 1.3: 1.

Because a simplified control function is used, a relatively simplified processor and

software can be used to solve the control function in a sufficiently short time period.

But, vapour recovery systems that rely on simplified control functions are less accurate

at recovering vapour. They may provide insufficient suction, letting the vapour escape to the atmosphere, or too much suction, unduly pressurizing underground pipes and

tanks.

A vapour recovery system is needed that is capable of accurately controlling the rate of

vapour recovery without the need of a moderate to high speed processor.

According to a first aspect of the present invention there is provided a fuel dispensing

system, comprising:

means for supplying fuel to a nozzle of a dispenser; vapour recovery means for recovering vapours released at the nozzle;

sensors for determining a number of independent variables affecting the quantity of vapour released at the nozzle; and processing means for generating a control signal for the vapour recovery means in dependence on the independent variable, characterised in that the processing means; generates the vapour recovery control signal by solving a vapour control function

having a dependent sub-function itself dependent on an independent variable;

the processing means comprises a look up table of values of subfunction

solutions; and

the processing means selects a sub-function solution corresponding to the value

of the independent variable by looking up a sub-function solution in the look up table

and processes the selected sub-function solution to produce the control signal for the

vapour recovery means.

By employing the present invention accurate real time control of the vapour recovery

rate is possible using more limited processing power than would otherwise be required,

the processing means, normally a microprocessors easily deriving the solution to a sub¬

function by looking up the appropriate pre computed solution from a look up table.

Preferably an independent variable is the volume dispersed from the nozzle and or fuel

flow and/or vapour flow and/or ambient temperature and/or fuel temperature as these

will all influence the quanitity of vapour released at the nozzle.

It may be desirable that the dependent sub-function be dependent on at least two

independent variables, for example fuel dispensed and ambient temperature.

In one embodiment the control signal can control the speed of a vapour recovery pump,

or alternatively it may control the setting of a proportional value. The former is preferred giving more precise control of the quantity of vapours recovered.

Advantageously the look up table is composed of solutions to the dependent sub¬

function for a predetermined range of values for the independent variable., and

preferably the look up table is composed between subsequent fueling operations.

According to a second aspect of the present invention there is provided a method of

controlling vapour recovery in a fuel delivery and vapour recovery system, the method

comprising the steps of:

a) pumping fuel from a fuel supply to a nozzle; b) recovering vapours released at the nozzle by vapour recovery means;

c) sensing a number of independent variables affecting the quantity of

vapour released at the nozzle and generating a control signal for the vapour recovery

means in dependence on the independent variables;

the method being characterised in further comprising the steps of:

d) generating the vapour recovery control signal by solving a vapour control

function having a dependent sub-function itself dependent on an independent variable;

e) selecting a sub-function solution corresponding to the value of the

independent variable by looking up a sub-function solution in a look-up table; and

f) processing the selected sub-function solution to produce the control signal for the vapour recovery means.

Two embodiments 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 illustration of a first embodiment of the vapour recovery system of the present invention;

Figure 2 is a schematic illustration of a look-up table of the vapour recovery system of

Figure 1;

Figure 3 is a schematic illustration of a second embodiment of the invention; and

Figure 4 is a flow chart of an alternate processing procedure used in either of the

embodiments of Figures 1 or 3.

The structures of fuel vapour recovery systems to which the present invention is

applicable are well known in the art, and therefore a detailed description of such is not

needed to provide those of ordinary skill in the art with knowledge of how to make and

use this invention. Such systems are to be found in US Patents 5,040,577, 5,156,199,

5,195,564, 5,038,838, 5,269,353, European Patent Application Publication Number

EP 0589615 and German Gebrauchsmuster G87-17378.6, the disclosures of which are

herein incorporated by way of reference.

With reference to Figure 1, vapour recovery system 10 comprises a vapour recovery

nozzle 12 which directs fuel pumped by fuel pump 15 through fuel delivery line 18 to a spout 20. The spout 20 is inserted into the filler neck of a receiving tank to pump the

fuel into the receiving tank (not shown). Nozzle 12 also includes a vapour inlet 22, which is communicatively connected to a vapour recovery line 24 that extends from

nozzle 12 to a reservoir or tank 26. Tank 26 is typically, but not necessarily, the ullage of the liquid fuel tank.

Connected in the vapour recovery line 24 is vapour pump 14. Vapour pump 14 is a

positive displacement pump driven by an electric motor 28 that is connected to the

vapour pump 14 by pump shaft 30. Electric motor 28 is controllable to vary the speed

(i.e. rotations per minute) at which the pump shaft 30 is driven. Therefore, the rate at

which vapour pump 14 pumps released vapour into the vapour recovery system 10 is

determined by the speed of the pump shaft 30.

Electric motor 28 rotates the pump shaft 30 at a selected speed in response to pump

control signals generated by digital processor 16. The pump control signals generated

by digital processor 16 are fed to a motor drive electronics unit 32 that is connected

between the processor 16 and electric motor 28. Motor drive electronics unit 32 converts

the pump control signals from processor 16 to control the voltage supplied to the electric

motor 28. In order to maximize the efficiency of vapour recovery system 10, processor

16 must operate vapour pump 14 to recover vapour at a rate that corresponds to the

instantaneous vapour volume generated during a fuelling operation.

Processor 16 determines the optimal speed of vapour pump 14 by solving a vapour pump

control function. A memory 17 is associated with the processor 16. The physical relationship of the look-up memory 17 and processor 16 can be any suitable arrangement of microprocessors and random access or read only or read- write memory devices.

These are well-known in digital processing and need no elaboration here. The solution to the control function represents the optimal speed at which vapour pump shaft 30 and vapour pump 14 should be operated. If desired, the function may also account for motor

speed feedback signals supplied on line 42. The control function is a function of

dependent sub-functions that are, in turn, dependent on one or more independent

variables which affect the volume of vapour generated during a fuelling operation. The

independent variables include fuel flow rate, fuel volume dispensed, time, ambient

temperature, fuel temperature, and restrictions in the vapour, flow path. The dependent

sub-functions of the control function can be modified to take into account additional

independent variables.

To determine at what speed vapour pump 14 should be operated, the values of the

independent variables must be measured and corresponding independent variable signals

inputted into processor 16. A plurality of sensors or transducers are connected to

processor 16 and are used to measure independent variables that affect the V/L ratio.

The transducers include a fuel flow transducer 34 *typically a pulser, well-known in the

fuel dispensing art), an ambient temperature transducer 36, a fuel temperature transducer

38, and a vapour path restriction transducer 40. Transducers 34-40 each generate an

independent variable signal which represents the value of the independent variable.

Other sources of signals representing independent variables affecting the V/L ratio may

also be used.

The fuel flow transducer 34 measures the rate of fuel flow to nozzle 12, the ambient temperature transducer 36 measures the ambient temperature which is representative of

the temperature of the vapour being recovered, the fuel temperature transducer 38 measures the temperature of the fuel being delivered to nozzle 12 and the vapour path restriction transducer 40 measures the restriction in vapour recovery line 24, and signals

representing each independent variable are transmitted to the processor 16.

The values of the independent variables are used to calculate the control function to

determine the optimal speed of vapour pump 14. The control function is repeatedly

solved and the optimal pump shaft velocity correspondingly adjusted as the independent

variables vary during a fuelling operation. In order for the control signals to accurately

represent the required pump shaft velocity, there must be minimal time delay between

the input of the values for the independent variables to processor 16 and the output of

the corresponding control signal. Accordingly, the solution of the control function must

be processed rapidly.

Vapour recovery system 10 provides for an efficient manner for solving the control

function by providing a look-up table. The look-up table contains pre-derived or

pre-computed solutions to the dependent sub-functions of the control function. The

dependent values contained in the look-up table are indexed by a selected range of

values for each of the independent variables. The dependent values are stored in a single

or multi-dimensional table depending on the number of independent variables on which the control function depends.

The look-up table is indexed by a selected range of values for each independent variable to allow dependent solutions to the dependent sub-function to be obtained via the look-up table. The range of values for each independent variable is selected to cover a

range of values that are likely to occur and be measured during a fuelling operation.

A single look-up table and its dependent values are stored in a non-volatile memory.

The dependent values of the look-up table are pre-computed once for the selected ranges

of values for the independent variables, and the processor 16 uses the same look-up table

for each successive fuelling operation. The values for the independent variables are

selected to cover the normal operating conditions for the vapour recovery system 10. If

a wide range of measured values for the independent variables can be expected during

the fuelling operations, then a relatively large look-up table will be required to contain

all the dependent values. The size of the memory required and the amount of time

required for processor 16 to access a dependent value in the look-up table must be

increased as the number of potential dependent values stored in the look-up table is

increased. The use of a single look-up table stored in memory is best suited where the

range of independent values does not vary widely during fuelling operations.

In an alternative embodiment of the present invention, the look-up table is stored in a

memory that can be changed, and the look-up tables are periodically updated, such as

between fuelling operations. The ability to generate updated look-up tables is useful

where the range of values of the independent variables may vary widely for different fuelling operations. This can permit smaller tables to be used. For example, for an

independent variable such as ambient temperature, a permanent look-up table of

expected values may have to range over one hundred or more degrees Fahrenheit. If the table need only be used for an hour or less, a ten degree range may be large enough. To

create the new look-up table, a new range of dependent values for one or more of the independent variables is selected and the dependent values corresponding to the new

ranges of independent variables are computed and stored in the table. Once the new

table has been created, the new look-up table replaces the former look-up table and is used for the next fuelling operation.

Processor 16 is programmed to generated an updated look-up table in anticipation of a

change in the range of expected independent values to be encountered in a fuelling

operation. When signalled to create a new look-up table, processor 16 begins to compute

dependent solutions for the selected ranges of values for the independent variables. The

former, completed look-up table is maintained in memory while the new look-up table

is being created. If a new fuelling operation begins during the creation of the new look-

up table, the partially-created, new look-up table is stored in memory and the completed,

former look-up table in existence is used for the fuelling operation. Creation of the new

look-up table is continued between other successive fuelling operations until the new

look-up table is completed and can replace the older look-up table. Scheduling the

creation of a new look-up table between fuelling operations limits the processing

demands placed on processor 16. The processor may be programmed to begin a new

table immediately upon completion of a table or to wait any desired period before

beginning a new table.

Use of a look-up table allows processor 16 to more efficiently solve the control function.

To rapidly solve the control function, processor 16 uses the look-up table to locate the dependent value of the dependent sub-function associated with the inputted independent

values. Relatively simple processing of the located dependent value is then performed to arrive at the solution to the control function. The additional processing is relatively

minor and does not place substantial time demands on the processor 16. In this regard, it is preferred to select the sub-functions for the look-up tables so that the resultant dependent sub-function values need only minor, quick computation to compute the

control function.

The solution to the control function is used to generate the control signal for controlling

the pump shaft velocity. To provide for more exact control of the pump shaft velocity,

electric motor 28 is connected to digital processor 16 by a tachometer feedback line 42.

Tachometer feedback line 42 is used to send tachometer feedback signals from electric

motor 28 to processor 16 as disclosed in European Patent Application Publication

Number 0,589,615. The tachometer feedback signals are used by processor 16 to

generate the vapour pump control signals so as to more precisely control the speed of

vapour pump 14.

As discussed previously, the control function used to generate the vapour pump control

signals includes a dependent sub-function that is dependent on several independent

variables known in the art. The precise function will be a characteristic of features of

the vapour recovery nozzle return line, pump and other components, so specific functions will not be discussed herein.

For explanation purposes, the operation of a vapour recovery system 10 including a control function having a sub-function dependent on two independent variables -

ambient temperature and dispensed volume - will be described. A vapour recovery system including a control function dependent on additional independent variables would operate in a manner analogous to the operation described below.

In operation, a control function for deterrnining optimal pump shaft velocity is stored in a memory 17 operatively associated with processor 16. The control function is the ratio

of a dependent sub-function dependent on a plurality of independent variables and a

computational factor which is proportional to the reciprocal of fuel flow rate. The

control function may be expressed as:

V rotations S(X,,...,X _B ) minute N counts/volume

where S is a dependent sub-function; x, , ..., x,. represent independent variables; and N

is a computational factor proportional to the reciprocal of fuel flow rate. Note that in this

example for clarity only two independent variables are used.

Also stored in the memory 17 operatively associated with processor 16 is a look-up table

44, as shown schematically in Figure 2. The look-up table 44 contains pre-computed

dependent values for the range of ambient temperature values (T,,...^ and the range of

fuel volume dispensed values (V,,...,V ₂ ). The temperature-dependent function may be as described in US Patent 5,156,199 to Hartsell et al or as described in US Patent 5,038,838 to Bergamini et al, or any other desired function. Alternatively, the ambient and fuel temperatures may be indices to a look-up table, with the desired vapour-to- liquid ratio as the output. This can be accessed using the temperature readings as data inputs to give the V/L ratio.

The volume dispensed-dependent function is preferably as described in US Patent

5,345,979. The dependent values are indexed by corresponding ambient temperature

values and fuel volume dispensed values.

When a fuelling operation begins, vapour recovery system 10 monitors the ambient

temperature and the amount of fuel volume dispensed. Ambient temperature is measured

directly by ambient temperature transducer 36.

Fuel volume is determined by measuring fluid flow with fuel flow transducer 34. As

fuel is dispensed, a fuel pulse is generated for a precise volume of fuel dispensed and is

directed to processor 16. Processor 16 accumulates the pulse count and, based on the

fuel pulse count and fuel volume per fuel pulse, processor 16 determines the fuel volume

dispensed.

Processor 16 uses the measured values for ambient temperature T and fuel volume

dispensed V to obtain the solution to the dependent sub-function which is associated

with the measured ambient temperature value and fuel volume dispensed value. The

look-up table shown in Figure 2 gives a solution, S, as a function of the T and V data

which can readily be read. Because the dependent values are indexed by the ambient

temperature values and fuel volume dispensed values, the solution to the dependent sub- functions for the measured values can be efficiently located by processor 16 in the look¬ up table 44. Those values then can be used simply by the processor 16 to determine the sub-function S. Alternatively, if desired, two one-dimensional tables could be used, giving output values requiring only simple further processing to arrive at S.

To solve the control function, processing of the obtained dependent value for the

dependent sub-function must be performed by processor 16. In particular, the dependent value obtained is divided by the parameter N, proportional to the reciprocal of fuel flow

rate.

The parameter N is determined by allowing a counter in processor 16 to increment at a

fixed rate, which is higher than the expected liquid flow pulse rate between two

successive flow rate pulses P, and P ₂ . If the counter is reset upon detection of each pulse, the count N, present after the second pulse P ₂ , will be proportional to the

reciprocal of the flow rate. As will be appreciated, the counter increments by counting

the number of pulses of a pulse source in the processor.

The actual fuel flow rate could be obtained by accumulating pulses over a fixed period

of time. However, the reciprocal of fuel flow is more advantageous in that only two

pulses from the fuel flow pulser must occur before flow rate is known for any flow rate,

whereas an extended duration of time must be allotted for accumulating pulses over time

to obtain a sufficiently usable accuracy, especially at low fuel flow rates.

The determination of N and the additional processing of the obtained dependent value

places little demand on processor 16. The control function can be computed by dividing S from the look-up table by N, a very quick operation. Accordingly, the determination of the solution for the control function is efficiently determined without excessive real- time processing demands.

Processor 16 also continuously receives tachometer signals from vapour pump electric

motor 28 for providing precise control of vapour pump speed. The tachometer vapour

pump signals are sent over the tachometer feedback line 42 and are used along with the

solution to the control function to generate a pump control signal that can compensate

for pump motor velocity slewing. Because the ambient temperature and fuel volume

dispensed vary during the fuelling operation, vapour pump control signals are

continuously generated and used to control vapour pump 14 as discussed above. (An

alternate embodiment involving an approximation of the temperature in these

calculations is described below n connection with Figure 4.) Controlling the vapour

pump 14 in this manner results in the vapour recovery rate of vapour recovery system

10 closely corresponding to the instantaneous rate of fuel vapour released at nozzle 12.

After the user ceases to pump fuel from nozzle 12, the fuelling operation ends, and

processor 16 is no longer required to monitor the rate of fuel vapour released at nozzle

12. No real-time processing demands are placed on processor 16 between fuelling

operations. As discussed previously, the processor 16 may be programmed so that an

updated look-up table is created between successive fuelling operations without placing

excessive demands on processor 16.

Referring now to Figure 3, an alternate embodiment of the invention is shown. This drawing depicts a modification of the apparatus of Figure 3 of German Gebrauchsmuster

G87-17378.6, the entire disclosure of which is herein incorporated by way of reference.

In this embodiment, the liquid gasoline is pumped out of the tank 126 through line 118 and past fluid flow transducer 134, ultimately being dispensed through vapour recovery

nozzle 122. The signals concerning the liquid flow rate are generated by the pulser 134 and communicated to a microprocessor in computer 116. Vapour recovered at the nozzle

122 is communicated along vapour recovery line 124 under the influence of vapour

pump 114, driven by motor 128. Motor 128 differs from motor 28 in being a constant

speed motor, so that pump 114 operates at a generally constant volumetric output rate

or constant rotational speed. The output of the pump 114 passes through a vapour valve

106 before being returned to the ullage of tank 126. The valve 106 is controlled by a motor 113 to vary the restriction in the vapour line 124. The valve 106 may be a

proportional valve. This has the effect of modulating the amount of vapour passed by

the pump 114. As noted above, the control of the amount of vapour is what is important,

whether it be by varying a pump speed as in the embodiment of Figure 1 or varying the

opening of the valve 106 as in the embodiment of Figure 3. Thus, the microprocessor

116 is provided with transducer inputs 136, 138, analogous to the transducer inputs 36

and 38 of the embodiment of Figure 1, along with liquid flow rate data from the pulser

134. The microprocessor 116 may use the transducer data to look up sub-function values

in a look-up table associated with the microprocessor 116 to compute the valve control function for output on line 127. The type of signal output of line 127 can be selected in

accordance with the design of the motor 113 to achieve the desired ends. In one embodiment, the motor 113 is a stepper motor, so that signals on line 127 can be pulse signals to stepper motor 113 to open or close the valve 106.

While the embodiment of Figure 3 is much less preferred than the embodiment of Figure 1 because it is believed that the embodiment of Figure 1 gives much more precise

control over the actual vapour flow rate, the invention is properly deemed to encompass

implementation of this technique to the apparatus in Figure 3.

If desired, the demands on the processor 116 can be reduced even further by not using

real-time values of the liquid and ambient temperatures from the transducers 136, 138:

Instead, recent values can be stored as a fixed constant under the assumption that the rate

of change of temperature will be slow enough that treating the temperatures as constants

will not introduce much error.

In this alternate embodiment, the microprocessor 116 takes a reading from the

transducers 136, 138 at the beginning of the day upon start-up of the equipment. This

data can be stored as raw data or used to re-compute a look-up table as described above.

The degree of sophistication of the electronics will be dictated by the degree of

sophistication of the control function being used. For example, if the control function

uses a simple ratio of the absolute value of the temperature of the vapour to the absolute

value of the temperature of the liquid, the ratio can be computed and stored itself.

Alternatively, if more complex functions like those shown at column 2, line 6, of US

Patent 5,156,199 of the Hartsell, Jr. et al patent or the equations shown in US Patent 5,038,838 to Bergamini et al are used, then more extensive calculations for storing the constant temperature values in look-up tables will be desired.

It will be appreciated that the control function to be used may very well be quite specifically designed for the equipment and its geometry, and the present invention is

deemed to cover all such control functions and their pre-computed or pre-stored microprocessor-usable sub-function values.

Also as can be seen in Figure 3, the microprocessor 116 includes a timer 120. If the time

between fuellings becomes excessively long, the pre-stored data from the transducers

136, 138 may become inaccurate thus, upon an expiration of a time measured by the

timer 120, fresh values can be obtained and stored as described above. An

implementation of this procedure is shown in the flow chart of Figure 4.

The present invention may, of course, be carried out in specific ways other than those

herein set forth without departing from the spirit and essential characteristics of the invention. For example, in an embodiment like the one shown in Figure 1, if a vapour pump other than a positive displacement pump is used, the computed control function may be adapted to control the vapour pumping rate according to the characteristics of the

chosen vapour pump, instead of focusing on the rotation speed of the driving motor.

The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.