Vehicle Fuel Level Sensor

The present invention relates to a vehicle fuel level sensor. In particular, the present invention relates to a sensor of the type comprising a hollow body, the bottom wall of which presents a hole through which the fuel flows into the said hollow body and acts on a float sliding along a vertical guide. The said vertical guide conveniently consists of a pipe supporting a resistive wire subjected to the action of a slide on the said float, so as to define a resistor varying as a function of the fuel level inside the tank.

In actual use, the pipe supporting the said resistive wire acts as an intake pipe for the fuel inside the tank, for the performance of which function the bottom end of the said pipe projects from the bottom wall of the said hollow body and communicates with the inside of the tank via a flat filter, usually fitted to the said bottom wall. A major drawback of sensors of the aforementioned type is that the filter, being located close to the bottom wall of the tank, is easily clogged by particles either in the fuel or settling at the bottom of the tank. On Diesel engine vehicles, for example, the paraffin in the Diesel fuel tends to solidify at low temperature and settle at the bottom of the tank, thus clogging the filter, impairing operation of the sensor, and cutting off fuel supply even when the tank is full.

The aim of the present invention is to provide a fuel level sensor designed to overcome the aforementioned drawbacks associated wtih the aforementioned known types of sensors.

With this aim in view, according to the present invention, there is provided a vehicle fuel level sensor comprising:

a hollow body designed to fit on to the top wall of the fuel tank and substantially presenting a side wall, and a bottom wall having a through hole through which, in use, the fuel flows into the said body;

a float designed to slide inside the said body by virtue of the hydrostatic thrust exerted by the said fuel; and

means for detecting the position of the said float; characterised by the fact that it comprises:

a filter mounted facing at least part of the outer surface of the said side wall of the said hollow body, close to the said bottom wall, and defining, with the said side wall, a first chamber; and

a body for supporting the said filter and facing the said bottom wall so as to define, with the said bottom wall, a second chamber communicating directly with the said first chamber and, via the said through hole, with the inside of the said hollow body.

A preferred non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which :

FIG. 1 shows a partial section of a sensor in accordance with the teachings of the present invention;

FIG. 1a shows an exploded cross-section of the circled portion of FIG. 1;

FIGS. 2 and 3 show larger-scale, partial plan views respectively of the filter and respective supporting body in FIG. 1;

FIGS. 4 and 5 show respective sections along lines IV-IV and V--V in FIGS. 2 and 3.

Number 1 in FIG. 1 indicates a sensor for detecting the fuel level inside a vehicle fuel tank (not shown). Sensor 1 comprises a hollow, substantially cylindrical body 2 housing a float 3 designed to slide along a tubular guide 4. The said body 2 presents a cylindrical side wall 5, and a bottom wall 6 to which the bottom end of guide 4 is secured in substantially known manner. The said bottom wall 6 presents a through hole 7 through which, in use, fuel flows into a chamber 8 in hollow body 2, so as to determine the position of float 3 as a function of the fuel level inside the said tank. The position of float 3 is detected in substantially known manner by means of a number of electrical contacts 11 on float 3, which contacts slide over the surface of tubular guide 4 which is wound with a resistive wire 12.

Next to the said side wall 5, hollow cylindrical body 2 presents a tubular portion 13 defining a fuel recirculating duct 14, which fuel is sucked in through the bottom end 15 of tubular guide 4. Both tubular portion 13 and guide 4 communicate with respective end portions 16, 17 on a flanged cover 18 designed to fit on to the top wall (not shown) of the said tank.

As shown, particularly in FIG. 1, according to the present invention, sensor 1 comprises a substantially tubular filter 20 mounted facing the bottom outer surface portion of side wall 5 on body 2, so as to define, with the said side wall 5, a substantially annular chamber 21. The said filter 20 is secured to hollow body 2 by means of a supporting body 22 substantially consisting of a plate 23 (FIGS. 3 and 5) mounted facing bottom wall 6 of body 2. In more detail, plate 23 is connected to an annular projection 24 extending from wall 6, by means of a number of appendixes 26 equally spaced along the edge of plate 23 itself. As shown, particularly in FIG. 1a, one end of each appendix 26 presents, on the outward side, a projection 27 defined by a spherical surface designed, in use, to engage an annular groove 28 on the inward side of annular projection 24, substantially next to bottom wall 6 of body 2. Body 22 supporting filter 20 is thus secured to cylindrical body 2 in such a manner as to define a chamber 30 together with opposite bottom wall 6 of body 2. The said chamber 30 communicates with chamber 21, defined by the opposite surfaces of filter 20 and side wall 5 of body 2, via cavities 31 (FIG. 5) defined by adjacent appendixes 26 on body 22.

Tubular filter 20 substantially consists of a coaxial pair of annular end portions 33, 34 connected longitudinally by a number of equally spaced longitudinal elements 35 between which are inserted a number of tight mesh filtering elements 36. Filter 20 is supported on body 22 by bottom annular end portion 34. In more detail, the said end portion 34 presents, inwards, an annular projection 37 having a rounded surface designed to engage an annular V-shaped groove 38 on the outside of plate 23 on supporting body 22 (FIGS. 4 and 5). As shown in FIG. 3, plate 23 also presents a through hole 39 through which fuel recirculating duct 14 (FIG. 1) communicates, in use, with the inside of the tank.

Operation of sensor 1 is as follows. Once sensor 1 is fitted to the tank through flanged cover 18, the fuel inside the tank flows into chamber 8 defined by body 2. In more detail, the fuel flows through filtering elements 36 of filter 20 into chamber 21 (FIG. 1a) and, from there, through cavities 31 into chamber 30 and, finally, into chamber 8 through hole 7, so as to settle at the same level as inside the tank. The hydrostatic thrust exerted by the fuel displaces float 3, the exact position of which inside sensor 1 is detected in known manner on the basis of the resistance of resistive wire 12 between its terminal and a contact portion over which slide the electrical contacts 11 on float 3. The fuel inside the tank in which sensor 1 is fitted is sucked up through end portion 15 of tubular guide 4, which sucks up the fuel inside the said chamber 30. In the case of Diesel fuel, this usually contains substances, such as paraffin, which solidify and settle on the bottom of the tank at low temperature, thus forming a layer which tends to clog filter 20 gradually upwards. By virtue of the said filter extending upwards, however, a fair percentage of filtering elements 36 (obviously the ones higher up) nevertheless still enable fuel to flow into chamber 21 and, from there, into chamber 30, thus enabling fuel intake to the engine and correct fuel level indication by float 3.

The advantages of sensor 1 according to the present invention will be clear from the foregoing description. Despite fuel continuing to be sucked up from the bottom of the tank, the present invention provides for substantially overcoming the problem of fuel intake being impaired by clogging of the filter of substances which, at low temperature, tend to solidify and settle on the bottom of the tank. Furthermore, such is achieved quite simply, while at the same time radically altering the position of the filter in relation to the sensor body.

To those skilled in the art it will be clear that changes may be made to sensor 1 as described and illustrated herein without, however, departing from the scope of the present invention. For example, instead of being tubular with filtering elements arranged as shown in FIG. 4, filter 20 may present a single filtering element conveniently spaced in relation to side wall 5 of body 2 so as to define a chamber (similar to chamber 21) for feeding fuel into the said chamber 20.