GB2473073A

GB2473073A - Fuel level sensing device

Info

Publication number: GB2473073A
Application number: GB0916656A
Authority: GB
Inventors: Herman Vink; David Mcconochie
Original assignee: HILLRIVER Ltd
Current assignee: HILLRIVER Ltd
Priority date: 2009-09-01
Filing date: 2009-09-22
Publication date: 2011-03-02
Also published as: EP2289729B1; GB0915124D0; GB0916656D0; EP2289729A1

Abstract

A fuel level sensing device for mounting to a fuel tank and suitable for sensing a level of LPG in an LPG tank. The liquid level sensor is operable to make level measurements based on a first electrical property, preferably capacitance, inner and outer tubes 19 and 22 providing an elongate level probe 40. The device also includes a separate maximum fill sensor formed, for example, by the upper inner tube end plate 18 and adapter body 28, operable to sense that a predetermined maximum fill level has been reached, the position of each part of the liquid level sensor being independent of the liquid level in the tank. The device preferably includes a fill shut-off mechanism which switches off a pilot valve 38 when it is determined that the maximum fill level has been reached.

Description

FUEL LEVEL SENSING DEVICE

The present invention relates to a device for sensing the level of fuel in a tank.

Preferred embodiments are suitable for sensing the level of LPG (liquefied petroleum gas) in an LPG tank.

Existing tanks and sensing arrangements often rely on mechanical parts to provide level indication, for example by means of a floating element and a system of gears.

The floating element can jam giving either or both a false level reading and the inability to fill the tank. Furthermore, floats have been known to sink or fail off.

LPG tanks have a predetermined maximum fill level of 80% to prevent overfilling.

There are concerns regarding the safety of filling an LPG tank beyond this maximum.

However, using mechanical parts to provide level indication frequently leads to fillings of 90% or more, with subsequent safety issues.

Using a float also affects the ability to gauge low fuel levels. The size or volume of the float itself actually limits low level gauging. Sufficient volume of liquid is required to provide enough lift for the float to operate, and when the liquid falls below this level the float sinks on the bottom due to a lack of buoyancy and gives a false empty reading. A false empty reading is a particular problem in LPG tanks since it can cause a Bi Fuel vehicle to switch to a second fuel source unnecessarily.

Embodiments of an aspect of the present invention provide a fuel level sensing device for mounting to a fuel tank, including a liquid level sensor that is situated in the tank when in use and is operable to make level measurements based on a first electrical property, the device also including a separate maximum fill sensor operable to sense that a predetermined maximum fill level has been reached, in which the position of each part of the liquid level sensor is independent of the liquid level in the tank.

The first electrical property could be any suitable property such as inductance, resistance, or preferably, capacitance. The separate maximum fill sensor may be separate, for example, insofar as it does not sense the same property as the liquid level sensor between the same physical elements, or between the same extent of the same physical elements. Advantageously, sensing the liquid level based on a first electrical property using a sensor in which each part is positioned independently of the liquid level in the tank means that the problems associated with moving and floating parts can be avoided. A maximum fill sensor provided separately from the liquid level sensor improves reliability of the device, for example, by allowing the designer to optimise the design of each sensor independently.

Preferably, the maximum fill sensor comprises a liquid detecting part and associated control circuitry and each part of the maximum fill sensor is also independent of the liquid level in the tank. The liquid detecting part could be a capacitor, and it may be that the capacitor plates are not solely dedicated to maximum fill sensing, but that they are, for example, structural components of another part of the device, such as a face of a body or housing part of the device. The maximum fill sensor can be comprised exclusively of parts whose positions do not depend on the liquid level in the tank, so that reliability issues associated with moving and floating parts can be avoided.

Optionally, the liquid level sensor comprises an elongate level probe and associated control circuitry. An elongate level probe can extend into the tank so that accurate low-level sensing is achieved. Since no moving parts are required, the level probe can extend right to the bottom of the tank in order that accurate level sensing is achieved right down to very low levels. In some embodiments it may be necessary to provide a small amount of isolation between the tank and the elongate level probe.

In preferred embodiments, the elongate level probe comprises two elongate electrodes, preferably concentric conducting tubes, between which electrodes liquid penetrates as the tank is filled. If the electrical property upon which level measurements are based is capacitance, then the concentric conducting tubes form two electrodes of a capacitor.

The maximum fill sensor is operable to sense that a predetermined maximum fill level has been reached. The device preferably also includes a fill shut-off mechanism which switches off a pilot valve when it is determined that the maximum fill level has been reached. When the maximum fill sensor determines that the predetermined maximum fill level has been reached, a signal may be sent to the fill shut-off mechanism which switches off a pilot valve. A pilot valve could be any secondary valve that can be switched off by the fill shut-off mechanism. Advantageously, using a pilot valve can be more reliable than directly operating a main fill valve. In preferred embodiments, the fill shut-off mechanism also includes a main valve, and the pilot valve is switched on to fill the tank, moving in one direction to relieve back pressure and allow the main valve to open; and when the pilot valve is switched off it moves in the opposite direction to cause back pressure to shut the main valve. Using a pilot valve in this way to control back pressure on a main valve is a simple and reliable way of shutting off the flow of fuel into the tank when the predetermined maximum fill level is reached.

As well as the pilot valve and the main valve, there may also be an electrical switch and a non-return valve having a movable triggering portion, in which the triggering portion is operable, when an incoming flow of fuel against the non-return valve reaches a sufficient level, to move towards and trigger an electrical switch, and the electrical switch is operable, when triggered, to switch on the pilot valve. The electrical switch could be, for example, a reed switch. Advantageously, the triggering portion must be physically moved to switch on the pilot valve and allow the tank to fill. This has advantages in terms of reliability, insofar as the pilot valve will not be erroneously switched on. The non-return valve may be designed such that whilst there is a sufficient incoming flow of fuel, the triggering portion triggers and holds the electrical switch in a state which switches on the pilot valve and keeps the pilot valve switched on. When the incoming flow of fuel against the non-return valve drops from a sufficient level to a level below the sufficient level, the triggering portion moves away from the electrical switch, and the switch switches to a state in which the pilot valve is switched off. The pilot valve may be switched off as a result of the maximum fill sensor sensing that the predetermined maximum fill level has been reached, which would in turn cause the main valve to close and the non-return valve to close. Alternatively, the electrical switch may only briefly close in order to power up the electronics, at which point control passes to a microcontroller forming part of the control circuitry which also controls supply voltage.

Preferably, the maximum fill sensor is operable to sense that the maximum fill level has been reached based on measurements of a second electrical property, and at least one of the first electrical property and the second electrical property is capacitance.

The provision of two separate sensors, one or both of which are based on a measure of capacitance, provides a highly reliable fuel sensing device in which sensing is not reliant on movable parts.

According to embodiments of another aspect of the present invention, a fuel level sensing device for mounting to a fuel tank is provided including mounting means for mounting the device to the fuel tank, a liquid level sensor operable to make liquid level measurements, the liquid level sensor including a level probe extending into the tank, and support means for supporting the level probe within the tank; wherein the support means are operable to allow the level probe to be moved into a working position. The liquid level probe specifically comprises those elements of the liquid level sensor which extend into the tank and are used to detect or sense the liquid level. For example, in an en,bodirnent in which the liquid level sensor is a capacitor, the liquid level probe comprises two electrodes. Some fuel tanks, particularly LPG tanks, require equipment such as valves, fuel level sensing devices, or valves incorporating or including fuel level sensing devices, to be fitted to the tank in an angled mounting position. A probe extending perpendicularly away from the wall of the fuel tank onto which the device was mounted would thus extend into the fuel tank at an angle which may not be the optimum working angle for the probe. However, it is often necessary to insert the probe into the fuel tank with the probe extending perpendicularly away from the wall of the fuel tank onto which the sensing device is mounted, For example, some LPG tanks require a 52° mounting position, whereas a liquid level probe may have a preferred vertical working position. According to invention embodiments, once the level probe has been inserted into the fuel tank, it can be guided or agitated until it reaches the working position, at which point the support means would support the level probe in the working position. In some embodiments, the support means is an angled mounting bracket.

Preferably, the support means allow the level probe to be rotated. Advantageously, in many embodiments rotation will be a sufficient degree of movement to allow the level probe to be moved from the optical position for insertion into the tank, into the working position.

Preferably, the support means is operable to maintain the level probe in the working position. This may be a permanent fixture, or it may be that the support means maintain the level probe in the working position during normal operation of the fuel level sensing device, but can be released without being damaged should the fuel level sensing device need to be removed from the fuel tank. Supporting the level probe in the working position will ensure continuous effective operation of the fuel level sensing device.

Preferred embodiments also include a maximum fill sensor operable to sense that a predetermined maximum fill level has been reached, said maximum fill sensor including a maximum fill detector having an operating position. Advantageously, the maximum fill detector is fixedly attached to the upper end of the level probe in use so that when the level probe is in its working position, the maximum fill detector is in its operating position. Whilst the level probe will be used to take measurements to indicate the presence of fuel at a range of positions, the maximum sensor may have a detector, or detecting part, which only detects simply whether or not fuel is present at the location of the detector. In order to sense that a predetermined maximum fill level has been reached, the location of the detector should correspond to a position in the tank which, when there is fuel at that position, the predetermined maximum fill level has been reached. This location is the operating position of the maximum fill detector.

Preferably, the external faces of the maximum fill detector and level probe together form an integrated probe body. This integrated probe body therefore reduces the number of separate components required in the fuel level sensing device.

According to embodiments of another aspect of the invention, a fuel level sensing device for mounting to a fuel tank is provided including a liquid level sensor that is fixed in position in the tank when in use and includes a level probe that measures an electrical property, a maximum fill sensor operable to sense that a predetermined maximum fill level has been reached, and a memory operable to store a calibration reference value for the level probe. When the maximum fill sensor determines that the predetermined maximum fill level has been reached, the memory stores a value corresponding to a contemporaneous measurement of the electrical property from the level probe as a calibration reference value. Fuel may vary in its composition between suppliers, between batches from a given supplier, and with temperature. This is particularly true of LPG, in which the proportions of propane and butane used varies seasonally. If a liquid level sensor relies on measuring a property such as capacitance between two electrodes, the difference in composition of fuel means that a given capacitance may correspond to a range of possible liquid levels, depending on the particular composition of the fuel in the tank at that time. The maximum fill sensor can simply detect whether or not the fuel level has reached a certain position in the tank corresponding to the maximum fill level. Each time the maximum fill level is reached a measurement of the electrical property is made by the level probe. This measurement gives a calibration reference value which is a value of the electrical property at a known fill level. A value of the electrical property may be proportional to the liquid level at the time of the measurement, but a value of the electrical property at a known fill level is required to establish a proportionality relationship so that a more accurate liquid level reading can be obtained from a measurement of the electrical property.

Advantageously, storing a measurement of the electrical property being measured by the level probe at the time of the maximum fill level being reached will provide a calibration reference value to mitigate the inaccuracy in liquid level measurements caused by the variation in composition.

Preferably, embodiments also include control circuitry operable to generate a liquid level measurement corresponding to a value of the electrical property measured by the level probe and representing the liquid level in the tank, wherein the liquid level measurement is provided in dependence upon the value of the electrical property measured by the level probe and the calibration reference value. The calibration reference value can be used by control circuitry to calculate a liquid level measurement corresponding to the measured value of the electrical property. Preferably, embodiments also include signal output means operable to provide an output signal representing the liquid level measurement. Thus, the accurate liquid level measurement obtained by combining the measured value of the electrical property with the calibration reference value can be provided to external systems and to a user of equipment utilising the fuel level sensing device. In some embodiments, the output signal is provided while the ignition is on and is a resistive level signal varying between O-90fl. Alternative output signals include a voltage signai or a pulse width modulation signal.

Since most gauges work with mechanically operated resistive level sensors, it is desirable to provide an output signal which effectively mimics the signal that such mechanically operated sensors would provide. Therefore, in preferred embodiments the signal output means is a digital resistor, and the output signal is an electronic resistive output.

According to embodiments of another aspect of the invention, a fuel level sensing device for mounting to a fuel tank is provided including a liquid level sensor that makes level measurements based on an electrical property, the liquid level sensor having a level probe extending into the tank for measuring the electrical property, and associated control circuitry including reading circuitry for reading a value of the electrical property measured by the level probe, the control circuitry being disposed entirely within the volume of the tank. Providing control circuitry entirely within the volume of the tank provides a fuel level sensing device which is neat and is less likely to suffer from compatibility problems associated with fitting to differently shaped tanks.

When the control circuitry is provided on a PCB, a regular shape of PCB can be used, such as rectangle, without the expense of having to design a PCB that will fit around the external fittings on the tank. The reading circuitry is responsible for taking a reading of the electrical property, and may be connected directly to the level probe.

The control circuitry is responsible for functions of the fuel level sensing device such as processing the measurement obtained from the reading circuitry. The control circuitry may be a printed circuit board having a micro controller. The control circuitry is responsible for processing signals and generating instructions, but does not include the connections between the valves and switches of the device and the control circuitry.

Preferably, the control circuitry is not only disposed entirely within the volume of the tank, but is disposed such that as the tank fills with fuel, the control circuitry wilt be exposed to the fuel. This provides a simpler construction of fuel level sensing device, wherein there is no need to hermetically seat the control circuitry in a solid outer casting. The control circuitry is designed to function effectively when immersed in fuel in the tank.

Preferably, the electrical property is capacitance. When measuring capacitance it is advantageous for the reading circuitry to be as close as possible to the capacitor plates. This is because the internal capacitance of wires and other connective circuitry can affect the capacitance readings. Disposing the reading circuitry within the tank means that the reading circuitry can be close to or against the capacitor plates, and the accuracy of capacitance measurements can be improved.

In preferred embodiments the control circuitry is housed within the level probe. The level probe may be an inner and outer tube, with the control circuitry housed within the inner tube. For example, the inner and outer tube may be two plates of a capacitor of the liquid level sensor. In embodiments in which the control circuitry is exposed to the fuel, it is desirable to house the circuitry within a component of the device since it reduces the risk of damage occurring to the circuitry during operation, transit, or, where necessary, when fitting the device to a fuel tank.

LPG tanks come in a four hole configuration or a single hole configuration.

Components required are a fill valve with maximum fill shut off, a pressure relief (safety) valve, fuel level sensing, and a feed valve for supplying fuel to an engine. In a four hole configuration, it is common for each of these components to be provided separately, each utilising one of the four holes. When the invention embodiments are implemented in such a tank, only three holes are required, because the device incorporates both maximum fill and fuel level sensing functionality. Therefore one of the holes may be blocked off. According to invention embodiments there is provided a fuel tank including a fuel level sensing device according to any of the preceding aspects and embodiments, a pressure relief valve, and a feed valve.

in a single hole tank, a multivalve is used to provide the functionality of all four components in a single unit fitting to the tank using the single hole. According to embodiments of another aspect of the present invention, a fuel tank multivalve is provided comprising a fuel level sensing device according to any of the preceding aspects and embodiments, and also including at least one of a pressure relief valve and a feed valve operable to feed fuel out of the tank. Embodiments also extend to a fuel tank incorporating a fuel tank multivalve or a fuel level sensing device according to any of the preceding aspects or embodiments.

The skilled reader will appreciate that features of any or all of the above aspects may be combined, whether in part or in whole, since any or all of the features described may be present in a single device. Thus, for example, the fuel level sensing device may have control circuitry within the tank and also use the maximum fill sensor for calibration and/or have a design with no part moving in response to liquid level changes. Such a device may have a level probe which is rotatable into a working position'.

Preferred features of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:-Figure 1 is a cross-sectional diagram of a fuel level sensing device embodying the present invention; Figure 2 is a diagram of the exterior of a multivalve embodying the present invention; Figure 3 is a simplified circuit diagram illustrating operating principles of embodiments of the present invention; Figure 4 is a simplified hydraulic and electric diagram of devices embodying the present invention.

Figure 5 is a cross-sectional diagram of a section of an embodiment including a pilot valve and a main valve; Figure 6a is a diagram of the exterior of a fuel level sensing device embodying the present invention; Figure 6b is a diagram of a side view of the exterior of a fuel level sensing device embodying the present invention; Figure 7a is a perspective view of a device embodying the present invention fitted to a tank positioned for entry to the tank; Figure 7b is a perspective view of a device embodying the present invention fitted to a tank and in a working position; Figure 8 is a circuit diagram of a digital resistor of invention embodiments; Figure 9 is a cross sectional diagram of an integrated probe body with internal control circuitry and support means; Figure 10 is a diagram of a top view of a shoulder portion of an embodiment of the present invention; Figure 11 a is an external view of a toroidal shaped 4-hole tank with which invention embodiments may be used; Figure 11 b is a cross-sectional diagram of a toroidal shaped 4-hole tank illustrating a mounting angle; Figure 12a is an external view of a toroidal shaped single hole tank with a large manhole with which invention embodiments may be used; Figure 12b is a cross-sectional diagram of a toroidal shaped single hole tank with a large manhole; Figure 1 3a is an external view of a toroidal shaped single hole tank with a small manhole with which invention embodiments may be used; Figure 1 3b is a cross-sectional diagram of a toroidal shaped single hole tank with a small manhole.

Figure 1 is a diagram of a fuel level sensing device embodying the present invention.

A fill nipple 1 surrounds a non-return valve 2. An 0-ring seal 3 is provided behind the non-return valve 2. A spring 4 sits against the non-return valve 2, ensuring that the non-return valve is closed when there is no or insufficient incoming flow. In this embodiment the movable triggering portion is a magnet 5 attached to the non-return valve 2 so as to be movable. A reed switch 6, also referred to simply as an electrical switch, is provided behind the magnet 5. A sensor nut 7 surrounds the reed switch 6.

A further 0-ring seal 8 fits around the sensor nut 7. Another 0-ring seal 35 provides sealing around a channel downstream of the non-return valve 2. There are five electrical feedthroughs 9, each with associated bottom isolators 10, top isolators 12, and 0-ring seal 11, however only one set is depicted in Figure 1. A pilot valve 38 is provided below a main valve 32, the pilot valve 38 including a plunger 27, a coil 15, a coil housing 14, a coil housing end plate 26, and a spring 13. A further 0-ring seal 29 is provided at one end of the plunger 27. A socket screw 16 is provided on either side of the pilot valve 38. An inner tube 19 and outer tube 22 are provided as an elongate level probe 40 or liquid level probe 40 having concentric conducting tubes, or elongate electrodes. An inner tube cap 18 fits to each of the top and the bottom of the inner tube 19, and a top spacer/isolator 17 isolates the upper of the two inner tube caps 18 from the adapter body 28 and the rest of the device. A bottom spacer/isolator 20 isolates the lower of the inner tuber caps 18 from the outer tube cap 21, and also isolates the bottom outer tube cap 21 from the tank wall. The bottom outer tube cap 21 fits to the bottom of the outer tube 22. Fuel can penetrate into the space between the inner tube 19 and outer tube 22 and into the space inside the inner tube 19. The control circuitry is provided as a PCB 23 in the space within the inner tube 19, onto which the reading circuitry and control circuitry can be printed. Soldering pins 24 are provided connecting to the upper of the inner tube caps 18. An inner tube top 25 is provided between the inner tube 19 and the upper of the inner tube caps 18. The main valve 32 is provided downstream of the non-return valve 2 and upstream of the pilot valve 38, and includes a spring 31. Sealing about the main valve 32 is provided by an 0-ring 33 and a U-cup seal 30. The sensor nut 7, flange body 34, and adapter body 28 provide housing for the non-return valve 2, pilot valve 38, and main valve 32. In embodiments in which an integrated probe body including level probe and maximum fill level detecting part can be moved away from the rest of the device, components below the line i-i can be moved away, and an upper cap 37 of the outer tube 22 is provided.

When filling is commenced incoming fuel flows against the non-return valve 2, which is pushed inwards from its seat, moving the magnet 5 toward the electrical switch 6. The increased magnetic field closes or switches on the electrical switch 6, providing a fill signal to the connected control circuitry 23. If the electrical switch 6 is a reed switch, one end is connected to the sensor nut 7, so that the signal available to the other end of the reed switch 6 is a signal to ground. The connected control circuitry 23 includes the microcontroller 46 and supply voltage regulation 47. The main valve 32 is riot directly operated by the control circuitry 23. Instead, a pilot valve 38 operates the main valve 32. The control circuitry 23 operates the coil 15 of the pilot valve 38, causing the plunger 27 to be pulled inwards against the plunger spring 13, thereby relieving closing pressure underneath the main valve 32, allowing the main valve 32 to be pushed down against the spring 31. When filling is underway, that is, the main valve 32 is open, the maximum fill sensor constantly monitors whether or not the maximum fill level has been reached. The maximum fill level is usually 80% for LPG tank embodiments, and is an upper limit beyond which the tank should not be filled. During filling, the maximum fill level is detected by the control circuitry 23 constantly monitoring the capacitance of a capacitor formed by the upper inner tube end plate 18 and the adapter body 28, or by a capacitor formed by the upper inner tube end plate 18 and the upper cap 37 of the outer tube 22. The capacitance changes when liquid enters between the capacitor plates, and the maximum fill level sensor determines that the maximum fill level has been reached. The second capacitor plate is formed by an upper cap 37 of the outer tube 22 in embodiments (to be discussed later) in which a liquid detecting part of the maximum fill sensor is provided as part of an integrated probe body which moves into a working or operating position away from the adapter body 28. When it is determined that the maximum fill level is reached, the pilot valve 38 is switched off: the plunger 27 is released, closing a relief opening 62 and causing pressure underneath the main valve 32, which is sealed by a U-cup seal 30, to rapidly increase through a small hole in the main valve 32. The main valve 32 is pushed upwards, closing off the fill opening.

During normal operation, which in the case of embodiments used in a vehicle will be when the ignition is turned on, the level of LPG inside the tank is continuously monitored by the control circuitry 23. When the level probe of the liquid level sensor is in the working position, the liquid level within the level probe corresponds to the liquid level within the tank. The concentric inner tube 19 and outer tube 22 form two capacitor plates, and the capacitance is read by reading circuitry and converted into an output signal representing the liquid level in the tank by the control circuitry 23.

Each time the maximum fill level is reached, the reading circuitry takes a reading of the capacitance between the concentric inner tube 19 and outer tube 22 and stores this reading in memory as a calibration reference value. The capacitance between these two tubes is proportional to the liquid level, however a calibration is required to determine the proportionality relationship so that a capacitance value can be converted to a liquid level value. Since the calibration reference value corresponds to a maximum fill level, for example, 80%, other capacitance values can be converted to values corresponding to fill level by comparison with the calibration reference value. The effects of variations in fuel composition are eliminated. The output range of the output signal is rescaled between a minimum level value and the maximum level value.

Figure 2 is a diagram of the outside of a fuel tank multivalve embodying the present invention. Feed valve functionality for providing fuel to an engine is provided by a take-off solenoid 45 connected to a take-off tube 42. Pressure relief functionality is provided by a pressure relief valve 43. A manual relief valve 44 could also be provided; this is a legal requirement in some jurisdictions. The position at which an incoming flow of fuel enters the device can be seen at A. The electrical switch 6 is connected to control circuitry 23 housed within the integrated probe body 41. The integrated probe body 41 is made up of external plates of the maximum fill level detecting part 39 and the level probe 40. The electrical feedthroughs 9, 10, 11, 12 are provided for sending and receiving signals to and from external systems, such as the ignition.

Figure 3 is a simplified diagram illustrating some operating principles of embodiments of the invention. There are input voltages from the battery T30 VBAU and from the ignition Ti 5 VIGN. The supply voltage regulation 47 and microcontroller 46 compose the control circuitry 23. A system of switches is controlled by the control circuitry 23.

An electrical switch 6 is a pressure switch which closes when there is a sufficient incoming flow of fuel. The main valve 32 is controlled by a pilot valve 38, and the microcontroller 46 constantly monitors whether or not the maximum (80%) fill level has been reached using the maximum fill level detecting part 39 whenever the main valve 32 is open. The supply voltage regulation part 47 switches to accepting a supply voltage T30 VBAU from the battery when the electrical switch 6 closes to indicate filling.

As soon as the maximum (80%) flU level has been reached, the microcontroller 46 closes the main valve 32 and powers down the associated parts of the control circuitry 23. In the event filling is interrupted before the maximum fill level is reached, the valve is closed and the associated parts of the control circuitry are powered down after a timer has run out. The control circuitry 23 provides a resistive output signal representing liquid level measurement while the ignition is on, indicated by a signal T15 VIGN. The level probe 40 measures a value of an electrical property, and reading circuitry of the control circuitry reads the value. The microcontroller 46 converts the value to an output signal representing liquid level measurement via a digital resistor.

Figure 4 is a simplified schematic hydraulic/electric diagram. The inlet nipple 1 is shown as a spring-loaded non-return valve, immediately downstream is another spring-loaded non-return valve 2 with electrical switch 6. The electrical switch 6 connects to the control circuitry 23 inside the tank via a feedthrough 9. The main valve 32 is shown as a normally closed directional control valve, operated by a solenoid pilot valve 38.

The control circuitry 23 is connected to the pilot valve 38, the level probe 40, the maximum fill detecting part 39, the electrical switch 6, an external level indicator 58, and a supply voltage circuit is formed with the ignition switch 59 and battery. The control circuitry 23 also has an earthed connection. The take-off solenoid 45, excess flow limiter valve 60, and pressure relief valve 43 are only provided in multivalve embodiments. Take-off solenoid 45 feeds fuel out from the tank to an engine, a shut off is provided between the take-off solenoid 45 and the outward flow. An excess flow limiter valve 60 limits flow out of the tank.

An incoming flow opens the inlet nipple (fill connector) 1 and non-return valve 2, closing the electrical switch 6 which turns on the parts of the control circuitry 23 necessary for filling, including constantly monitoring whether or not the maximum fill level has been reached using the maximum fill level detecting part 39. Closing the electrical switch 6 causes the control circuitry 23 to switch the pilot valve 38 to the on position relieving back hydraulic pressure against the main valve 32 and allowing the main valve 32 to open, and fuel to flow into the tank. Whilst the ignition switch 59 is on, reading circuitry of the control circuitry 23 can measure a value using level probe 40, and convert the value to an indication of the fuel level in the tank to send to a level indicator 58. Level sensing may occur constantly, or it may occur at discrete time intervals.

Figure 5 is a diagram representing a mid-section of an embodiment of the fuel sensing device. This section of the device is mounted to the tank so that anything above the line u-u is outside of the tank, and anything below the line u-u is within the tank.

Individual components of the pilot valve 38 including the coil 15, coil housing end plate 26, spring 13, plunger 27 and sealing 0-ring 29 are illustrated, along with the channel 62 that the pilot valve 38 allows to open during filling of the tank to relieve back pressure on the main valve 32 and to allow fuel to flow into the tank.

Figures 6a and 6b are diagrams of the exterior of an embodiment having an integrated probe body 41 operable to be rotated into a working position once mounted to a tank.

The device is mounted to a tank by a screw through each corner of a shoulder portion 54. The five electrical feedthroughs 9 connect electronics such as control circuitry 23 inside the tank, to external components outside of the tank. An EMC (electromagnetic compatibility) board 68 is fixed in place with a fixing M2 screw 69. Arms 50 extend from a portion of the device which is not movable within the tank, to the integrated probe body 41 housing control circuitry 23 which can be rotated into the working position once inside the tank, then maintained in that position by the support means 55.

The support means 55 comprise a sleeve 50 surrounding the integrated probe body 41, two arms 51, a locking stop 52 attached to the sleeve 50, a pin 56 attached to each side of the sleeve 50, a screw 49 to attach each arm to a non-movable portion, a sprung locking finger 53 and a locking hand 57 at one end of each arm 51. Once the integrated probe body 41 is within the tank, it can be wiggled or pushed into the working position. The integrated probe body 41 and sleeve 50 are rotatable about the pin 56. When rotated correctly, the sprung locking finger 53 is pushed towards the arm 51 by the locking stop 52 until the end of the locking finger 53 passes the locking stop 52 and springs back, in which position the locking stop 52 is held between the locking finger 53 and the locking hand 57. The support means are sufficiently strong to maintain the integrated probe body 41 in the working position during normal operation of the device, but not to prevent a user from returning the body to the entry position as illustrated in Figures 6a and 6b.

Figure 7a is a perspective view diagram of an embodiment in entry position, which is preferable for initially fitting the device to the tank. Figure 7b is a perspective view diagram of an embodiment with an integrated probe body 41 in a working position. In the working position illustrated, the bottom of the integrated probe body 41 is close to the bottom of the tank without affecting capacitance measurements.

Figure 8 is a circuit diagram of a digital resistor 63 which is an example of signal output means, and may be included in control circuitry 23. The digital resistor 63 converts a signal representing a liquid level in the tank to a resistive output. The signal may be a binary signal, or it may be a signal whose amplitude corresponds to the liquid level in the tank. Each bit D0-Dn when low will cause the corresponding field effect transistor FETO-FETn to be closed, effectively shorting the connected resistor 2°R-2R. Each bit when high will cause the corresponding FET to be open, effectively putting the connected resistor in series with the connect gauge at i. The number of FETs open or closed is proportional to the liquid level in the tank.

Figure 9 is a cross sectional diagram of an integrated probe body 40 and other components of invention embodiments. The control circuitry 23 is realised as a printed circuit board within the inner tube 19. Wired connections between the control circuitry and connected components are enabled via a hole (not illustrated) in the inner tube 19 and outer tube 22. The proximity of the control circuitry 23 to the plates 7, 17 of the capacitor of the maximum fill level detecting part 39 can be appreciated. Similarly, Figure 10 illustrates that the control circuitry 23 is directly adjacent to the plates inner tube 19, outer tube 22) of the level probe 40. The sleeve 50 is fixed to the outside of the outer tube 22 and, supported by the arms, the integrated probe body 41 and the components within it can rotate about the pin 56. Holes 64 in the lower 21 and upper 37 caps of the outer tube 22 allow fuel to flow in and out of the space between the inner tube 19 and outer tube 22 so that the level of the fuel between the plates is the same as the level of fuel in the tank. There are also holes (not illustrated) in the inner tube, which prevent the air which is present until a number of fills has taken place from getting trapped inside the inner tube. The bottom spacer/isolator 20 may be shortened when the device is fitted to a tank to enable the bottom cap of the outer tube 22 to be as close as possible to the bottom of the tank.

Figure 10 is a diagram of the top of a shoulder portion 54 of an embodiment, the bottom of which shoulder portion fits against the outside of the tank. A hole in each corner of the shoulder accepts a screw for attaching the device to the tank.

Connections Cl to C5 correspond to electrical feedthroughs 9. In this embodiment, when properly fitted to a tank in a vehicle, Cl connects control circuitry 23 within the tank to a level indicator 58 outside of the tank. C2 connects control circuitry 23 within the tank to an electrical switch 6 outside of the tank. C3 connects control circuitry 23 within the tank to ground. C4 connects control circuitry 23 within the tank to ignition outside of the tank. C5 connects control circuitry 23 within the tank to a battery outside of the tank.

Figure ha illustrates the outside of a toroidal 4-hole tank 65. Figure llb is a cross sectional diagram of a toroidal 4-hole tank. 4 holes are provided for fitting one of each of a fill valve with a maximum fill level shut off, a pressure relief valve, a fuel level sensor with external level sending unit, and a feed valve. The 52° mounting position of a device is illustrated, hence embodiments of the present invention are provided with an angled locking mounting bracket as support means. A sleeve 50 surrounding and fixed to the integrated probe body 41 is aHowed to rotate through a 52° angle before locking into a working position in which the integrated probe body 41 is vertical. A fuel level sensing device embodying the present invention may be fitted to one hole of such a tank, in which case a blanking plate is used to cover another of the holes.

Figure 12a illustrates the outside of a toroidal single hole tank 66 with a large manhole 70. Manhole 70 in this document is taken to mean the access hole to the tank for valves and other connecting apparatus. Multivalve embodiments of the present invention which include a pressure relief valve 43 and take-off solenoid 45 can fit to a single hole tank, possibly using a fitting plate over the large manhole 70. A fuel level sensing device embodying the present invention can also fit to a toroidal single hole tank 66 with a large manhole, but with a three hole mounting plate fitted to accommodate separate feed and pressure relief valves. Figure 12b is a cross-sectional diagram of a toroidal single hole tank with large manhole 66. Embodiments of the present invention fitted to such a tank would not require an angled mounting bracket since the entry position of the device to the tank would correspond to the working position. The integrated probe body 41 would be substantially vertical on entry to the tank 66.

Figure 13a is a view of the exterior of a single hole tank 67 with a small manhole 71. A multivalve embodying the present invention can be fitted to such a tank. Figure 13b is a cross-sectional view which, similarly to the single hole tank 66 with large manhole 70, illustrates that a device fitting to the tank 67 would not require an angled mounting bracket.

Claims

CLAIMS: 1. A fuel level sensing device for mounting to a fuel tank, including a liquid level sensor that is situated in the tank when in use and is operable to make level measurements based on a first electrical property, the device also including a separate maximum fill sensor operable to sense that a predetermined maximum fill level has been reached, wherein the position of each part of the liquid level sensor is independent of the liquid level in the tank.
2. The fuel level sensing device according to claim 1, wherein the maximum fill sensor comprises a liquid detecting part and associated control circuitry and wherein position of each part of the maximum fill sensor is also independent of the liquid level in the tank.
3. The fuel level sensing device according to any of the preceding claims, wherein the liquid level sensor comprises an elongate level probe and associated control circuitry.
4. The fuel level sensing device according to claim 3, wherein the elongate level probe comprises two elongate electrodes, preferably concentric conducting tubes, between which electrodes liquid penetrates as the tank is filled.
5. The fuel level sensing device according to any of the preceding claims, wherein the device also includes a fill shut-off mechanism which switches off a pilot valve when it is determined that the maximum fill level has been reached.
6. The fuel level sensing device according to claim 5, wherein the fill shut-off mechanism also includes a main valve, in which the pilot valve is switched on to fill the tank, moving in one direction to relieve back pressure and allow the main valve to open; and in which when the pilot valve is switched off it moves in the opposite direction to cause back pressure to shut the main valve.
7. The fuel level sensing device according to claim 5 or 6, further comprising: an electrical switch, and a non-return valve having a movable triggering portion, wherein: the triggering portion is operable, when an incoming flow of fuel against the non-return valve reaches a sufficient level, to move towards and trigger an electrical switch; and the electrical switch is operable, when triggered, to switch on the pilot valve.
8. The fuel level sensing device according to any of the preceding claims, wherein the maximum fill sensor is operable to sense that the maximum fill level has been reached based on measurements of a second electrical property, and wherein at least one of the first electrical property and the second electrical property is capacitance.
9. A fuel level sensing device for mounting to a fuel tank including: mounting means for mounting the device to the fuel tank; a liquid level sensor operable to make liquid level measurements, the liquid level sensor including a level probe extending into the tank; and support means for supporting the level probe within the tank; wherein the support means are operable to allow the level probe to be moved into a working position.
10. The fuel level sensing device according to claim 9, wherein the support means allow the level probe to be rotated.
11. The fuel level sensing device according to claim 9 or 10, wherein the support means is operable to maintain the level probe in the working position.
12. The fuel level sensing device according to any of claims 9 to 11, also including a maximum fill sensor operable to sense that a predetermined maximum fill level has been reached, said maximum fill sensor including a maximum fill detector having an operating position, wherein the maximum fill detector is fixedly attached to the upper end of the level probe in use so that when the level probe is in its working position, the maximum fill detector is in its operating position.
13. The fuel level sensing device according to any of claims 9 to 12, wherein the external faces of the maximum fill detector and level probe together form an integrated probe body.
14. A fuel level sensing device for mounting to a fuel tank including: a liquid level sensor that is fixed in position in the tank when in use and includes a level probe that measures an electrical property; a maximum fill sensor operable to sense that a predetermined maximum fill level has been reached; and a memory operable to store a calibration reference value for the level probe; wherein when the maximum fill sensor determines that the predetermined maximum fill level has been reached, the memory stores a value corresponding to a contemporaneous measurement of the electrical property from the level probe as a calibration reference value.
15. The fuel level sensing device according to claim 14, also including: control circuitry operable to generate a liquid level measurement corresponding to a value of the electrical property measured by the level probe and representing the liquid level in the tank, wherein the liquid level measurement is provided in dependence upon the value of the electrical property measured by the level probe and the calibration reference value.
16. The fuel level sensing device according to claim 15, also including signal output means operable to provide an output signal representing the liquid level measurement.
17. The fuel level sensing device according to claim 16, wherein the signal output means is a digital resistor, and the output signal is an electronic resistive output.
18. A fuel level sensing device for mounting to a fuel tank including a liquid level sensor that makes level measurements based on an electrical property, the liquid level sensor having a level probe extending into the tank for measuring the electrical property, and associated control circuitry including reading circuitry for reading a value of the electrical property measured by the level probe; wherein the control circuitry is disposed entirely within the volume of the tank.
19. The fuel level sensing device according to claim 18, wherein the control circuitry is disposed such that as the tank fills with fuel, the control circuitry will be exposed to the fuel.
20. The fuel level sensing device according to claim 18 or 19, wherein the electrical property is capacitance.
21. The fuel level sensing device according to any of claims 18 to 20, wherein the control circuitry is housed within the level probe.
22. A fuel tank multivalve comprising a fuel level sensing device according to any of the preceding claims, and also including at least one of: a pressure relief valve; and a feed valve operable to feed fuel out of the tank.
23. A fuel tank incorporating a fuel tank multivalve according to claim 22, or a fuel level sensing device according to any of the preceding claims.