WO2002084231A1

WO2002084231A1 - Motor-vehicle-tank-sender-unit

Info

Publication number: WO2002084231A1
Application number: PCT/ZA2002/000063
Authority: WO
Inventors: Thomas Fanie Van Der Ness
Original assignee: Thomas Fanie Van Der Ness
Priority date: 2001-04-12
Filing date: 2002-04-11
Publication date: 2002-10-24

Abstract

A vehicle-tank-sender-unit that measures the volume of fuel or liquid in a geometrically complex shaped tank. A semiconducter pressure sensor is connected to the upper end of a capillary tube generating an output signal as a function of hydrostatic pressure being exerted on the surface of the fluid in which it is immersed. The fuel tank is decanted a litre at a time from full to empty and within an electronic circuit is contained a microprocessor containing RISC architecture that stores the input signals for each litre reading. The firmware therein, using mathematics, linearises the output signal as a total volume measurement of the fuel in the tank to within the nearest litre. The firmware also compensates for inaccurate fuel readings from input shifts caused by either varying inclines or fuel sloshing. The data for any specific vehicle make or model is stored externally and high-speed programming takes place in manufacture using the field programmable flash memory in the said apparatus.

Description

MOTOR-VEHICLE-TANK-SENDER-UNIT

FIELD OF INVENTION

This invention relates to a microprocessor-based sender-unit that uses programmable firmware and may be applied to determine the volume of the fuel in a vehicle tank and, more particularly, tanks of complex, irregular shapes.

BACKGROUND TO THE INVENTION

Although this invention will be described with particular reference to the measurement of the fuel in the fuel tank of a motor vehicle, it is to be clearly understood that the scope of the invention is not limited to this particular application.

It is known that to measure the level of fuel in the tank of a motor vehicle is by means of a float attached to a lever which wipes across a variable resistance and as the level of the float changes with the fuel volume, so does the output resistance.

This type of prior art sender-unit is expensive to produce because new tooling has to be manufactured for virtually every make and model of vehicle.

Such prior/art sender-units are inaccurate due to the effects of incline on the surface of the fuel in the tank and because the sloshing of the fuel in the tank is compensated for by introducing electronic hysteresis. A number of other methods for liquid containers exist that perform measurements with hydrostatic fill gauge's using hollow dipsticks. See US patents 5 802 910 and 5 060 512 ; German patents DE 3714956 A1 and DE 19638476 A1 ; French 86 04095 ; EP 1 006 319 A1 ; and PCT/2A00/00047.

In all instances of the above prior art which use hydrostatic pressure to measure volume or liquid level no account has been taken as to how to measure geometrically complex shaped tanks. OBJECT OF THE INVENTION

It is the object of this invention to provide a tank-sender-unit which will, at least partially, alleviate the above mentioned difficulties and disadvantages.

SUMMARY OF THE INVENTION

Like all hydrostatic measuring systems in accordance with this invention there is provided a semiconductor pressure transducer connected to the upper end of a capillary tube to generate an output signal as a function of hydrostatic pressure being exerted on the surface of the fluid in which it is immersed.

The pressure transducer output is amplified and this analogue voltage is converted into a digital signal by a microprocessor. The output is either supplied as a variable voltage or can be converted to a variable resistance.

The key feature of the invention is the methodology used to linearise the output for geometrically complex shaped fuel tanks using RISC (reduced instruction set computer) architecture with a serial peripheral interface for high-speed data transfer. The fuel tank is decanted a litre at a time from full to empty and each input signal is stored. The firmware is so designed that its versatility allows for the wildly diverse values of the signals from the transducer in a geometrically complex shaped tank, between when it is empty and full, to mathematically take this table of values and linearise the output.

Another feature of the invention is that the firmware is designed in such a way that, irrespective of the geometric complexity of any tank, the output reading will be accurate to within a litre. For each decanted volume reading stored by the firmware, the microprocessor mathematically, depending on whether the reading is higher or lower than 500 millilitres, either adds or subtracts the value of the nearest millilitre reading from the total. This value, to within the nearest litre reading, is used for the total volume output. Yet a further feature of the invention is its programmability. Because it is software based, it means that the invention can be used for all makes and models of vehicles without making any hardware design changes in perpetuity. The invention has field programmable flash memory so that, once a tank has been decanted a litre at a time and the values have been stored externally, this software data determines a given make or model of vehicle. The field programmable flash memory is to be used for high-speed programming in mass production.

Still further features of the invention are the rectification of incline readings and the inaccurate readings caused by the fuel sloshing around in a moving tank. A tank is placed on a variable incline table and the firmware stores these diverse values and mathematically adjusts the incline values to a level reading using the derivative of time over level. Exactly the same process is pursued to adjust for sloshing fuel.

BRIEF DESCRIPTION OF DRAWINGS

One embodiment of the invention is described below, by way of example only, and with reference to the accompanying drawings, in which:

FIG 1 is a graphic rendition of a typical geometrically complex tank.

FIG 2 is a graphic rendition of the principal of how the firmware works.

FIG 3 is a block diagram of the tank-sender-unit.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figures 1 to 3, in which features of the invention are indicated by like numerals. With reference to Figure 1 the semiconductor pressure transducer is mounted in an enclosure (1) having an axial. bore. The pressure transducer is mounted to a capillary tube in an airtight manner (2) such that the enclosure's (1) axial bore coincides with the capillary tube (2) diameter.

In use, the enclosure (1) is secured to the top of a fuel tank (3) of a motor vehicle and the capillary tube (2) being the same height as the tank (3) is immersed in the fuel contained therein. When retrofitted, the enclosure (1) is secured to the fuel tank (3) by drilling holes and screwing the enclosure (1) to the tank (3). It is common knowledge that most vehicle fuel tanks are now manufactured from plastic. With every new vehicle model it is necessary to manufacture new die's to blow-mould the plastic tank. In new models both the enclosure (1) and the capillary tube (2) will be made from plastic and incorporated into the fuel tank (3) blow-moulding process at time of manufacture.

It is understood that fuel will enter the capillary tube through the lower end and pressure will be exerted on the semiconductor pressure transducer by the air entrapped in the capillary tube. By amplification of the resultant output signal and using mathematical calculus, the output is proportional to the volume in the fuel tank (3).

With reference to Figure 2 and relative to prior art expedients, is an example of a comparative chart (4) showing the complex input curve (7) from the pressure transducer mounted to the geometrically complex tank (3) depicted in Figure 1 and the linear output (8) converted by the firmware. The X-a^ is (6) depicts the data input into the microprocessor from the pressure transducer and the linear output after it has been mathematically corrected. The Y-axis is calibrated in litres depicting both the input and output values. In the example used here it is to be clearly understood that the scope of the invention is not limited to this particular application. It will be appreciated that because most vehicles have numerous structural and functional parts within the fuel tank (3) mounting area, the fuel tanks (3) are consequently far more geometrically complex than the example shown in Figure 2. The resultant curve (7) from the pressure transducer hereshown will almost always be far less linear and more convoluted. Referring to Figuresl and 2, . the circuitry of Figure 3 is shown in more detail.

Referring to Figure 3, Block 1 indicates the semiconductor pressure transducer (1) that, depending on the complexity of the geometry of the fuel tank and the volume of fuel in it, will output a varying millivolt signal.

An amplifier to a signal level of between 0 and 5V DC amplifies the signal from the pressure transducer.

The signal from the amplifier is fed through an analogue to digital converter (3) within the microprocessor.

The RISC architecture (4) in the microprocessor contains the firmware to store the incoming data from the analogue to digital converter (3). The fuel tank is decanted a litre at a time from full to empty and each and every subsequent input signal is stored in the microprocessors' memory. Utilising the microprocessors' serial peripheral interface (5) for high-speed data conversion and mathematical calculus, the inputs are converted to adjust for any fuel tanks geometry. This is to ensure that the output is linear, irrespective of the non-linearity of the input signals from a complex shaped fuel tank. Also, when the readings of the volume of fuel in a tank are incorrect through a vehicle being on an incline, or the fuel sloshing about while a vehicle is in motion, the firmware (4) corrects the output accordingly.

Once the -software has been stored externally after the firmware has completed the mathematical calculations for any given fuel tank, the field programmable flash memory (6) in the microprocessor is utilised to programme the software peculiar to a specific make or model of vehicle fuel tank.

The output signal from the microprocessor is a digital pulse train that is converted to a variable DC voltage using a frequency to voltage converter (7). Because the prior art in present use is that of rheostat devices in vehicle fuel tanks, currant fuel-tank-sender-units all have variable resistance outputs. Using firmware, the charge on a capacitor is linearised using negative feedback if a resistance output is required.

Claims

I.The main feature of the invention is the use of a table that is representative of the exact volume in the tank by either filling or emptying it at a litre-at-a-time and both recording and linearising the output values.

2.The above decantation or incantion process needs to be carried out once only for any individual shaped tank because, using the same hardware, the mere programming of the stored table for each different make or model, determines its origin.

3.The fact that the same hardware is used, coupled to the high-speed programmability of the invention, determines that, not only is inventory kept to a minimum on any existing sender-unit manufacture, but consequently, new tooling and design is virtually non-existent for any new models.

4. When compared with existing prior art sender units, both the methodologies of manufacture and tank installation are cumbersome, whereas the fact that this invention is relatively tiny due to it being firmware-driven and not mechanical, obviates these problems. δ.The device has further firmware that can round the output reading up or dowh to within the nearest litre. β.Another important feature of the invention is that any inaccurate readings caused by fuel sloshing and incline are adjusted mathematically using the derivative of time over level.