Apparatus for measuring quantities of liquid in gasoline pumps of motor vehicle filling stations

A flow meter includes a rotor housing having an inlet, an outlet, and a bore extending axially through the housing from the inlet to the outlet, and a screw spindle arrangement including at least two rotary helical worm bodies which are disposed in the bore and which engage in a form fit manner within one another. A pulse generator is mounted on one of the worm bodies and triggers electrical pulses in the mating measuring transducer which are dependent upon the rotational speed of the worm body. The measuring transducer has a pulse-adjusting and pulse-shaping stage which adjusts the magnitude and/or frequency of the pulses relative to a volumetric flow rate of fuel to the bore. An electric counting mechanism receives the electric pulses from the pulse-adjusting and pulse-shaping stage and typically transmits these pulses to a display unit for display.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to an apparatus, based on the principle of the 
displacer counter, for measuring quantities of liquid in gasoline pumps of 
motor vehicle filling stations during a fuelling process. 
2. Discussion of the Related Art 
For measuring quantities of liquid supplied to gasoline pumps of motor 
vehicle filling stations, it is generally known and common practice to use 
displacer counters, such as liquid measuring motors constructed in the 
manner of a piston slide valve. Such liquid measuring motors have the 
drawback that the liquid to be measured has to be supplied via a rotary 
slide valve to periodically and successively separated working chambers 
and connected, in a further control channel, to the outlet. During said 
process the liquid changes direction several times. There is also, in many 
cases, no linear correlation between revolution and throughflow volume. 
Finally, problems arise with adjustment of the delivery volume through 
piston stroke movement if high precision is an important factor and the 
counters, for billing measurements in the filling station business, have 
to be calibrated and regularly recalibrated under operating conditions. 
EP 0 016 928 B1 discloses a throughflow measuring device, which operates as 
a flow meter and has a cylindrical rotational solid having, on its outer 
periphery, helical turns which act as flow-past vanes and generate a 
torque at the rotational solid. 
In a throughflow measuring device according to EP 0 069 170 B1, likewise 
operating as a flow meter, a turbine wheel is used as an impeller wheel, 
its rotational speed and hence the throughflow of the liquid being 
measured using the light barrier principle. The electrical signals are 
supplied to an electronic measuring device and converted into an 
electrical measured variable. The throughflow measuring device is intended 
particularly for use as a fuel consumption meter for motor vehicles. 
In each of said known throughflow measuring devices, only a single 
rotational solid is provided in the flow channel. The measuring accuracy 
and appropriateness for verification of the throughflow measurement of 
liquid fuels in filling stations therefore depend exclusively on the 
cross-section of flow along said rotational solid as well as upon the 
shaping of the helical turns. 
A screw spindle arrangement having a plurality of rotary screws which 
engage one into the other is known from CH-PS 187 466. One of the rotary 
screws is connected to a counting mechanism for indirect measurement of 
the throughflow quantity of flowable media, such as liquids, and is 
provided at one end with a driving gear which, via a speed-transforming 
gear, drives the pointers of the counting mechanism. 
The drawback of said style of construction is that mechanical gear parts 
have to be used for transmission of the rotary motion with simultaneous 
speed reduction between the rotary screw and the counting mechanism 
pointers. A plurality of these mechanical gear parts have to be provided 
depending on the number of pointers to be set in rotation, and the gear 
parts have to be sealed off from the liquid to be measured and are also 
exposed to wear. 
From DE 39 42 857 C1 it is known, when using a quite conventional 
piston-type device for measuring the dispensed volume of fuel, to couple 
the piston-type measuring device to an optoelectronic pulse generator, 
whose pulses generated as a function of the measured volume of fuel are 
fed into a computer head. The drawbacks described initially in connection 
with fluid measuring motors constructed in the manner of a piston slide 
valve also apply to this known form of construction. 
An apparatus which is appropriate for verification and by means of which 
the throughflow may be measured and adjusted to a setpoint value is 
disclosed in U.S. Pat. No. 4,831,866. Measurement is effected by a 
volumetric displacement chamber. Adjustment is effected by electronic 
intervention into the pulse processing in such a way that a calibration 
factor for correcting the pulse number derived from the throughflow 
measuring device is automatically acquired during a fuelling process and 
is acquired after specific operating or dispensing intervals which each 
correspond to a specific volume of liquid. 
From DE 28 05 191 A1, a recording device for dispensing goods, in 
particular liquid motor vehicle fuel, in filling stations is known in 
which, to simplify billing, two pulse generators are associated with a 
throughflow measuring device and supply two counting pulse trains to a 
test circuit which produces a counting signal if they match and an error 
signal if they do not match. What is involved here, however, is merely a 
coincidence circuit by means of which double checking may be effected when 
billing for the dispensed quantity of fuel. 
OBJECTS AND SUMMARY OF THE INVENTION 
The object of the invention is, in an apparatus of the type described 
initially which operates on the principle of a displacer counter, to make 
the conveying route during volumetric detection of the fuel dispensed 
during a motor vehicle fuelling process more rectilinear than is the case 
with piston-type measuring motors and electronically to counteract 
distortions of the measuring signal which arise during measured value 
conversion in the low flow velocity range. 
Said object is achieved according to the invention by providing a flow 
meter comprising a rotor housing having an inlet, an outlet, and a bore 
extending axially through the housing from the inlet to the outlet, and a 
screw spindle arrangement including at least two rotary helical worm 
bodies which are disposed in the bore and which engage in a form fit 
manner within one another. A pulse generator is mounted on one of the worm 
bodies and triggers electrical pulses in the mating measuring transducer 
which are dependent upon the rotational speed of the worm body. The 
measuring transducer has a pulse-adjusting and pulse-shaping stage which 
adjusts the magnitude and/or frequency of the pulses relative to the 
volumetric flow rate of fuel to the bore. An electric counting mechanism 
receives the electric pulses from the pulse-adjusting bore. An electric 
counting mechanism receives the electric pulses from the pulse-adjusting 
and pulse-shaping stage and typically transmits these pulses to an 
arithmetic unit for display. 
Compared to liquid measuring motors constructed in the style of a piston 
slide valve, screw spindle counters offer the advantage of a more 
rectilinear throughflow of the liquid to be measured as well as a simpler 
style of construction which is less susceptible to faults and has 
correspondingly fewer structural parts. Screw spindle counters are 
advantageously made of metal materials. This results in better sliding 
properties for the throughflow liquid than in liquid measuring motors 
constructed in the style of a piston slide valve, which mostly have 
plastic structural parts, as well as in the structural parts being more 
resistant to aggressive constituents of the liquid to be measured. 
The correction circuit stage is provided for converting the generally 
sinusoidal signals supplied by the measuring transducer into pulse signals 
which may then be evaluated in the electric counting mechanism. Threshold 
criteria--mostly the zero crossing of the output signal supplied by the 
measuring transducer - are used as a rule for pulse generation. At low 
flow rates of the volume of liquid to be measured, in particular when the 
flow of dispensed fuel starts up and eases off at the beginning and end of 
the fuelling process, distorted or non-linear output signals of the 
measuring transducer arise and prevent an exact correlation between the 
counting pulses and the partial volumes of fuel for measurement associated 
with said pulses. The pulse correction circuit counteracts said behaviour 
in that its sensitivity to the output signals of the measuring transducer 
is artificially raised at lower flow rates, and hence at lower rotational 
speeds of the worm body connected to the pulse generator. 
Said sensitivity control is further utilized to allow the volumetric value 
of the pulses to be calibrated and recalibrated by pulse adjustment. By 
means of such an electronic correction, the measured volume values may be 
adjusted in adaptation to greater differences between operating 
temperature and design temperature and to the resultant differences in 
density. 
In an advantageous development of the invention, the pulse generating 
apparatus takes the form of a pulse disc which is connected to one of the 
worm bodies. In connection with the measuring transducer installed in a 
fixed manner in the rotor housing and advantageously with the pulse pulse 
correction circuit integrated therein, the revolutions of the worm body 
are converted into pulses, whose magnitude, number or repetition rate is 
directly proportional to the dispensed fuel quantity. 
In a further development of the invention, the pulses generated by rotation 
of the worm bodies are electronically adjustable in terms of their 
magnitude or repetition rate by externally acquired control or check-back 
pulses, which may be derived from the arithmetic unit of the electronic 
counting mechanism and are adjustable or readjustable as a function of 
operating or climatic parameters as well as being tunable to an 
arithmetical ratio relative to the throughflow quantity of dispensed fuel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
From an underground storage tank for fuel, e.g. gasoline, which is not 
shown in FIG. 1 of the drawing, an intake tube 2 leads through the base of 
a gasoline pump housing 1 to a fuel delivery pump 4, which is drivable by 
its own drive motor 3. The fuel conveyed upwards during a vehicle fuelling 
process passes via piping 5 to a screw spindle counter 6 acting as a 
liquid measuring motor in the bottom explosion-protected region of the 
gasoline pump housing 1 and continues via piping 9 to a gasoline pump hose 
10 having a dispensing valve 11 connected to its end. 
As FIG. 2 shows, two helical worm bodies 8 which engage in a form-fit 
manner one into the other are supported in control bore of rotor housing 7 
of the screw spindle counter 6 and are set in rotation by the liquid 
flowing axially through them during fuelling of a motor vehicle. One of 
said worm bodies 8 acts as an output shaft of the liquid measuring motor 
and carries on its end a pulse-generating apparatus 12 in the form of a 
pulse disc. With the aid of said lock washer, the revolutions of the worm 
body 8 connected to said disc are converted e.g., inductively, in a 
measuring transducer 13 which penetrates the rotor housing 7, into pulses 
whose magnitude, number or repetition rate is directly proportional to the 
dispensed fuel quantity. 
The pulse generator of the measuring transducer 13 is connected, outside of 
the rotor housing 7, to an electric line 14 leading to an electronic 
counting mechanism 15, which has an arithmetic unit and is connected to a 
display unit 16 in order to display the unit price, the dispensed fuel 
quantity and the price to pay in a window of the gasoline pump housing 1 
for the benefit of the filling station customer. The fuelling data 
acquired after conversion of the measuring data may be supplied to a 
monitor associated with each longitudinal side of a filling station island 
comprising a plurality of gasoline pumps and may be read by the filling 
station customer. 
The pulse generator integrated in the measuring transducer 13 comprises a 
correction circuit 17, by means of which the pulses generated by rotation 
of the worm bodies 8 may be electronically adjusted for calibration 
purposes before being supplied to the electronic counting mechanism 15 
with the electronic counter. During said process, the magnitude or 
repetition rate of the pulses is varied by externally acquired control or 
check-back pulses derived from the electronic counter of the electronic 
counting mechanism 15 in such a way that they are, for example, tuned to 
an arithmetical ratio relative to the throughflow quantity of the 
dispensed fuel. The pulse correction circuit 17 also converts the 
generally sinusoidal signals supplied by the measuring transducer 13 into 
pulse signals which may then be evaluated in the electronic counting 
mechanism 15 threshold criteria, mostly the zero crossing the output 
signal supplied by the measuring transducer 13, are used as a rule for 
pulse generation. At low liquid flow rates, in particular when the flow of 
dispensed fuel starts up and eases off at the beginning and end of a 
fueling process, distorted or non-linear output signals of the measuring 
transducer arise and prevent an exact correlation between the counting 
pulses and the partial volumes of fuel for measurement associated with 
these pulses. The pulse correction circuit counteracts this behavior in 
that its sensitivity to the output signals of the measuring transducer is 
artificially raised at lower flow rates by increasing the magnitude and/or 
frequency of the pulses measured by the measuring transducer 13 is 
artificially raised at lower flow rates, and hence at lower flow rates, 
and have lower rotational speeds of the worm body connected to the pulse 
generator. In the electronic counter of the electronic counting mechanism 
15, said control or check-back pulses are adjustable as a function of 
specific operating or climatic parameters or, if need be, are 
readjustable, say for calibration purposes, by staff designated for said 
task.