Wheel circumference meter

Abstract

The wheel circumference meter calculates the distance traveled by vehicles at every single turn of the wheel The measurement of the rolling radius of the wheel, which takes into account its crushing on the ground, is difficult to measure as the center of the wheel hub is almost always on an internal plane with respect to the tyre. The instrument, equipped with a laser pointer, allows the center of the wheel to be identified, measures its distance from the ground which is equivalent to the rolling radius of the tire and therefore calculates the distance traveled by the vehicle at every single turn of the wheel. A display will show the measurement reading. The invention can be used in the measurements to be carried out for the calibration of tachographs. 8 / 8

Description

[0001] WHEEL CIRCUMFERENCE METER DESCRIPTION

[0002] TECHNICAL FIELD

[0003] The wheel circumference meter is intended to be used to measure the route of a vehicle at each single revolution of the wheel that is to say the development of the tire on the ground which corresponds to its rolling circumference. The route does not coincide with the circumference of the tire due to its crushing on the ground (due to the weight of the vehicle) which reduces the rolling circumference of the wheel and therefore the route. Without a dedicated instrument it is very difficult to measure the rolling radius as the center of the wheel is almost always located on an internal plane with respect to the tyre.

[0004] The invention, the subject of the application, allows the development of the tire on the groundto be calculated by bringing the instrument closer to the wheel with its support. To carry out the measurement, point the center of the wheel hub with a laser beam by sliding the instrument on the support shaft perpendicular to the ground; the instrument display will show the measurement.

[0005] BACKGROUND ART

[0006] According to what emerged from the EPO research report, the state of the art closest to the invention covered by the application is that identified in the instrument FR 2974171 A1 discloses a wheel circumference meter for determining the circumference of a vehicle wheel comprising a support being fixed to the wheel rim and self-aligned with the wheel center, a sliding gauge being coupled to the support for determining the distance between the wheel center and the ground surface and a calculation unit for calculating and displaying the wheel circumference based on the detected distance. DISCLOSURE OF INVENTION

[0007] The wheel circumference meter differs from FR 2974171 A1 in that the measuring system comprises a freely rotating rod anchored by a hinge to an interconnection support and supporting a magnetic rotation sensor and a laser pointer hinged to the interconnection support for pointing the center of the wheel hub. The angle between the freely rotatable rod and the vertical direction is given by the sensor output signal. The multiplication of the cosine of this angle by the length of said rod enables the calculation unit to calculate and display the circumference of the wheel. In this way the circumference determination is achieved using a device having a simple mechanical structure and being easily centered with respect to the wheel using the laser pointer. In this way the determination of the wheel circumference is simplified. It is also equipped with a calculation unit with display designed to allow the sealing of metrologically relevant parts and the simple structure of the instrument makes it very economical and easy to create.

[0008] As shown schematically in Fig. 1 , the wheel circumference meter is essentially composed of: an interconnection support with slider (1 ) free to slide along the support shaft (perpendicular to the ground) which can be a pedestal support Fig. 2 or a magnetic support fixed to the wheel rim Fig. 3; by a laser pointer (2), anchored to the interconnection plate, which projects a beam, parallel to the ground, to be directed towards the center of the wheel hub, making the instrument rise or fall along the support shaft; by a rod (3), the end of which is fixed to the interconnection support in correspondence with the laser pointer (by means of a hinge), free to rotate along the plane perpendicular to that of the wheel circumference; by a magnetic band (4) positioned on a circular crown integral with the plate; by a sensor (5) integral with the rod, which when the latter rotates (raising or lowering the instrument) grazes the magnetic band; by a calculation unit with display (6) governed by a microprocessor.

[0009] If you use the wheel circumference meter with pedestal support, it must be positioned on the same support surface as the wheel (since it will have to calculate the distance of the center of the hub from the ground to calculate the rolling circumference of the tyre, i.e. the one that takes crushing into account of the tire to the ground) at a distance such that the horizontal line drawn by the laser pointer beam is clearly visible on the hub. By instead adopting the solution with a magnetic support, anchored to the wheel rim, the distance is already pre- established.

[0010] Once the instrument has been positioned, by sliding it on the shaft of the holder, ensure that the horizontal line of the laser pointer beam passes through the center of the wheel, identified by a recess on the hub. The movement of the instrument on the support shaft produces a rotation of the rod (which touches the ground), then the sensor, integral with the rod, slides on the magnetic strip and sends the information to the calculation unit which processes it making it available on the display the reading of the distance traveled by the vehicle at each turn of the wheel. In the rare cases in which the hub does not have any center reference, two measurements of the route will be carried out, taking as references first the top of the hub and then its lowest point, and then taking the average of the two measurements.

[0011] The positioning of the instrument outlines a right-angled triangle Fig. 4 which has as vertices the center of the hinge hinge, its projection to the ground and the point of contact of the rod with the ground. To carry out the measurement, the calculation unit measures the angle (a). This is possible because the magnetic strip is positioned on a circular crown so it is possible to convert the pulses coming from the sensor from linear to radial measurement. Once the angle a has been measured, the value of the cosine corresponding to it can be calculated. By multiplying the cosine of a by the measurement of the hypotenuse (B) (which is a known datum being a peculiarity of the instrument - the data was inserted into the microprocessor memory in the programming phase) we obtain the measurement of the cathetus (A) which does not is nothing more than the projection of the rolling radius (Rr). In summary, the calculation unit reads the pulses coming from the sensor that grazes the magnetic strip, measures the angle (a), calculates the cosine and multiplies it by the measurement of (B), thus obtaining the measurement of the cathetus (A) which is equal to (Rr), rolling radius of the wheel. Once the measurement of (Rr) has been obtained, the instrument multiplies it by 2 Fl, obtaining the rolling circumference (Cr) of the wheel and therefore the distance traveled by the vehicle at each single revolution of the wheel (Pv). The calculation unit is programmed to automatically carry out the described calculations, therefore once the circumference measurer has been positioned and the center of the hub has been pointed, the display shows in real time the measurement of the vehicle's route at each turn of the wheel.

[0012] BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 schematically illustrates the construction of the wheel circumference meter.

[0014] Figure 2 schematically illustrates the wheel circumference meter device used with a pedestal support.

[0015] Figure 3 schematically illustrates the wheel circumference meter device used with a magnetic support anchored to the wheel rim.

[0016] Figure 4 highlights the right triangle that appears when the instrument takes the measurement.

[0017] BEST MODE FOR CARRYING OUT THE INVENTION

[0018] The wheel circumference gauge can be made as follows:

[0019] The magnetic strip and the sensor are of the type normally used in the industrial automation sector for measurements of submillimetric linear displacements;

[0020] The indicator panel of the instrument is an alphanumeric LCD type display; The electronic control circuit, on a small printed circuit, can be created with an 8 / 32 bits microprocessor and enclosed in a container, built ad hoc or even of the commercial type, which can allow a sealable closure to guarantee the integrity of the instrument set-up from possible tampering;

[0021] The instrument is powered in direct current by batteries;

[0022] The interconnection support and the rod can be made with aluminum profiles which make the instrument both resistant and light;

[0023] The pedestal support Fig. 2 can be made with a metal base on which a ground steel rod with a section that allows the slider of the interconnection support to slide, without play, must be fixed perpendicularly to it;

[0024] The magnetic support anchored to the wheel rim Fig. 3 can be made with a ground steel rod (7), of such a length that it can be applied to all wheel sizes and of such a section that it can allow sliding, without play, of the interconnection support slider. Two magnetic spacers (8 and 8') slide on the rod to be positioned on the wheel rim. This support is provided with a level (9) to ensure, during positioning, that it is perpendicular to the wheel support surface.

[0025] INDUSTRIAL APPLICABILITY

[0026] The wheel circumference meter is intended to be used to measure the route of a vehicle at each single revolution of the wheel. For example, it can be used by technical centres, workshops authorized for the repair and control of tachographs, as part of the measurements to be carried out for their calibration.

Claims

CLAIMS1 . A wheel circumference meferwhich is configured to calculate and display the route Pv of a vehicle at each single revolution of the wheel, comprising:- an interconnection support (1 );- a laser pointer (2) which is hinged to the interconnection support (1) and is configured_to point the center of the hub with its beam;- a rod (3) having a known lenght and being anchored by a hinge to the interconnection support (1), wherein the fulcrum of the hinge is at the same height as the laser beam, said rod being free to rotate on the plane perpendicular to the plane of the wheel circumference, wherein said rod (3), when touching the ground at whatever height the instrument is positioned, allows once the center of the hub has been pointed with the laser beam to outline the hypotenuse of a right triangle;- a magnetic band (4) housed on a circular crown integral with the interconnection support (1);- a sensor (5) integral with the rod (3) and positioned so as to graze the magnetic band (4) when the rod (3) rotates; and- a calculation unit with display (6) which is configured to process the impulses coming from the sensor (5) based on a calculation and automatically display the distance travelled by the vehicle at each turn of the wheel, wherein the calculation is carried out by measuring using the sensor (5) the angle a that is created between the vertical segment (A) which goes from the center of the wheel to the support surface of the same and the segment (B) corresponding to the rod (3) of known lenght extending between the center of the wheel and the support surface and determining said route Pv based on the following equation: Pv = Rr multiplied by 2TT, wherein Rr is the tyre rolling radius given by Rr = A = B multiplied by cos(a)2. The device according to claim 1 is characterized by the fact that to ensure the sliding of the instrument along an axis perpendicular to the support surface of the wheel it is equipped with a pedestal support (Figure 2) to be positioned near the wheel and is made up of a base on which a shaft with a section such as to allow the slider of the interconnection support to slide without play must be fixed perpendicular to it3. The device according to claim 1 is characterized by the fact that if the rim is made of ferrous material as an alternative to the pedestal support, the magnetic support (Figure 3) can be used to be anchored to the wheel rim and is made up of a shaft (7) from the section such as to allow the slider of the interconnection support (1) to be housed and slid on it without play, as well as being equipped with a level (9) to monitor the perpendicularity to the wheel support surface and two magnetic sliders (8 and 8') which are free to slide on it to place them at the upper and lower edge of the wheel rim.

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