Patent Description:
In order to use four-wheel drive effectively, the running distance of front tyres must be bigger than that of the rear tyres - this is referred to as the lead ratio, and it is conditioned by the tyres rolling circumferences and tractor's inter axle ratio. Tractor manufacturers normally recommend which tyres can be mounted as standard, based on the rolling circumference data (at rated pressure and load, and full original tread depth) of new tyres published by tyre manufacturers. In many cases, several sizes are possible so long as they comply with the stipulated lead ratio. To use four-wheel drive effectively, the lead ratio should amount preferably to between +<NUM>% and +<NUM>% (the running distance of the front tyres is longer than the running distance of the rear tyres). The permitted lead ratio is normally accepted by the industry between <NUM>% and +<NUM>%. A lead ratio less than <NUM>% and greater than +<NUM>% can have a negative impact on the tractor's driving performance and steering behavior (particularly when less than <NUM>%), and can cause excessive wear and tear in front and rear tyres, as well as possible damages to the tractor's transmission. In four-wheel drive mechanisms, the relationship between the total number of revolutions of the front and rear axle is a constant factor (and is determined by the cogs in the gear box). This relationship is referred to as the inter axle ratio or transference ratio and, depending on the tractor brand and type, is normally between <NUM> and <NUM>.

Once you know the rolling circumference for front and rear tyres, as well as the tractor's inter axle ratio, it is possible to calculate the lead ratio with the following formula: (rolling circumference front tyre * inter axle ratio / rolling circumference rear tyre) - <NUM>.

But it is also necessary to consider that the standard calculations could be affected along the tractor's life, as many factors can affect to the rolling circumferences of the tyres, for example the load per axle, the tyre pressure applied by the customer, the wear rate, etc. or simply by replacing one axle worn out tyres by new ones, and keeping in the other axle partially worn tyres. All these situations will change the theoretical lead ratio and could therefore affect the proper performance of the tractor and/or tyres.

Nowadays, at least three people are necessary for determining characteristic parameters of an agricultural tractor: one person driving the agricultural tractor along a test straight path and two persons looking at the tyres to visually measure the total number of revolutions of the tyres.

<CIT> discloses an electro-hydraulic arrangement regulating the lifting mechanism actuatable by a hydraulic motor, on an agricultural working vehicle having a driven wheel, comprising a plurality of sensors including a position sensor forming an actual value position signal, a force sensor forming an actual value force sensor, and an additional sensor forming an actual value slippage signal dependent on slippage of the driven wheel, a nominal value transmitter, a first summation point connected with the additional sensor and with the force sensor so as to obtain the slippage-dependent signal and the actual value force signal therefrom and to produce an output signal, a mixing device having a first input connected with the first summation point and for receiving the output signal and a second input connected with the position sensor for receiving the actual value position signal and producing an output signal, and a second summation point connected with the mixing device for receiving the output signal of the mixing device and also connected with the nominal value transmitter for receiving a signal from the latter so as to form a regulating deviation for the lifting mechanism.

<CIT> discloses a device for operating an all-wheel-drive agricultural commercial vehicle with a driven rear axle and a front axle that can be engaged for performing an all-wheel-drive mode. A control unit determines, during the all-wheel-drive mode, a front wheel slip parameter that characterizes a drive wheel slip occurring on the front axle of the agricultural commercial vehicle. The control unit deactivates the all-wheel-drive mode independent of the driver if this unit detects that the determined front wheel slip parameter is greater than a specified threshold value.

<CIT> discloses a system and method for determining the wheel load for a wheel of a first axle, based on the wheel load for a wheel of a second axle, and the wheel speed ratio between the first and second axle. As a result, wheel load can be calculated for axles not easily adapted to receive load sensors, e.g. a rear axle of an agricultural tractor. The system uses a characteristic map of the relationship between wheel load and wheel geometry, e.g. wheel circumference, for different tire pressure values of a wheel to provide an efficient and effective mechanism for the determination of wheel load.

The aim of the present invention is to provide a tyre analysis method and a tyre analysis system for determining characteristic parameters of an agricultural tractor that are easy, quick and precise to implement. In particular, the tyre analysis method and a tyre analysis system of the present invention will easily help to verify and choose the best combinations of tyres and/or the best set up for optimal performance.

According to the present invention, a tyre analysis method and a tyre analysis system for determining characteristic parameters of an agricultural tractor are provided, as set forth in the appended claims.

The present invention is now described in reference to the attached drawings, which illustrate a non-limiting exemplary embodiment, wherein:.

In <FIG> an agricultural tractor is indicated as a whole by the number <NUM>.

The agricultural tractor <NUM> comprises two front wheels <NUM> (only one is visible in <FIG>) equipped with two front tyres <NUM>, two rear wheels <NUM> (only one is visible in <FIG>) equipped with two rear tyres <NUM> (bigger than the front tyres <NUM>), and a four-wheel drive powertrain <NUM> which is powered by an internal combustion engine <NUM> and transmits the motion to all the four wheels <NUM> and <NUM> in the case of Mechanical Front Wheel Drive (MFWD) or Four Wheel Drive tractors (4WD).

The agricultural tractor <NUM> is provided by a tyre analysis system <NUM> designed to determine some data connected to the wheels <NUM> and <NUM> and in particular to the tyres <NUM> and <NUM> mounted on the wheels <NUM> and <NUM>.

The tyre analysis system <NUM> comprises (at least) two rotation sensors <NUM> coupled, in the embodiment shown in <FIG> and <FIG>, to the right front wheel <NUM> and to the right rear wheel <NUM>; each rotation sensor <NUM> is designed to measure the number of rotations made by each wheel <NUM> or <NUM>. In the embodiment shown in <FIG> and <FIG> the two rotation sensors <NUM> are coupled to the front and rear wheels <NUM> and <NUM> of the same (right) side, while in the embodiment shown in <FIG> the two rotation sensors <NUM> are coupled to the two rear wheels <NUM> of the same (rear) axle. According to a preferred embodiment, the rotation sensors <NUM> are developed by using Hall effect encoders and high quality bearings (of course other types of encoders could be used).

The tyre analysis system <NUM> comprises a (at least one) distance sensor <NUM> designed to measure a (linear) distance D (shown in <FIG>) traveled by the agricultural tractor <NUM>. According to a preferred embodiment, the distance sensor <NUM> is formed by two different elements: a receiver <NUM> which is attached to a body <NUM> of the agricultural tractor <NUM> and a beacon <NUM> placed in a fixed position on the ground nearby the travelling path of the agricultural tractor <NUM>. In particular, the beacon <NUM> is housed on a support <NUM> laying on the ground. According to a preferred embodiment, the receiver <NUM> is attached to the rearmost part of the body <NUM> of the agricultural tractor <NUM> and the beacon <NUM> is placed behind the agricultural tractor <NUM> (i.e. facing the receiver <NUM>): in this manner the distance sensor <NUM> (composed by the receiver <NUM> and by the beacon <NUM>) can measure without any interference the distance between the receiver <NUM> and the beacon <NUM> and thus can measure the distance D (shown in <FIG>) traveled by the agricultural tractor <NUM>. According to a preferred embodiment, the distance sensor <NUM> uses the Ultra Wideband (UWB) Technology and allows to determine the distance D (shown in <FIG>) traveled by the agricultural tractor <NUM> with a precision of at least <NUM>-<NUM> centimeters.

It is preferable to attach the receiver <NUM> to the rearmost part of the body <NUM> of the agricultural tractor <NUM> and thus to place the beacon <NUM> behind the agricultural tractor <NUM> so that the metallic mass of the agricultural tractor <NUM> or attached equipment cannot (negatively) interfere with the electromagnetic waves exchanged between the receiver <NUM> and the beacon <NUM>.

The tyre analysis system <NUM> comprises a control unit (operating console) <NUM> which is wireless connected to the sensors <NUM> and <NUM> (for example using the Bluetooth® standard) so as to receive the measures from the sensors <NUM> and <NUM>. The control unit <NUM> performs the system and operation management and the data collection.

The tyre analysis system <NUM> can comprise a software application <NUM> running on a personal (portable) electronic device <NUM> like a mobile phone or a tablet computer. The software application <NUM> constitutes a Human-Machine Interface (HMI) for using the tyre analysis system <NUM>. The software application <NUM> can be used by an operator to manual input some data (agricultural tractor <NUM> data, tyres <NUM> and <NUM> data, location. ) and to visualize the final reports. The software application <NUM> can memorized the agricultural tractor <NUM> (vehicle) data, the tyres <NUM> and <NUM> data (size, brand, model, version, year, Remaining Tread Depth -RTD-, pressure, wear condition, photographs. ), the location, the date, and several sets of system readings.

The tyre analysis system <NUM> can comprise also an Internet web site <NUM>, which can be browsed in Internet and can exchange data with the software application <NUM>. For example, the Internet web site <NUM> can be used to data analysis, add manual comments, add data to a centralized database, and generate reports (the web site <NUM> can generate a PDF report and send back the PDF report to the software application <NUM>).

According to a preferred embodiment shown in <FIG>, each rotation sensor <NUM> is provided with a (permanent) magnet <NUM> for magnetically attaching the rotation sensor <NUM> to the rim of a respective wheel <NUM> or <NUM> (and in particular to the central hub of the wheel or to the wheel disc). Magnetically attaching the rotation sensor <NUM> to the rim of a respective wheel <NUM> or <NUM> allows a fast and easy connection/disconnection and, at the same time, a safe and reliable fixing, and allows to avoid possible interferences with fixed parts of the vehicle (for example a Central Tyre Inflation System -CTIS-pipes if installed).

According to a preferred embodiment shown in <FIG>, the receiver <NUM> of the distance sensor <NUM> is provided with a (permanent) magnet <NUM> for magnetically attaching the receiver <NUM> to the body <NUM> of the agricultural tractor <NUM>. Magnetically attaching the receiver <NUM> to the body <NUM> allows a fast and easy connection/disconnection and, at the same time, a safe and reliable fixing.

The tyre analysis system <NUM> can be used to perform an axle inspection when the two rotation sensor <NUM> are coupled to the two wheels <NUM> or <NUM> of the same (front or rear) axle (as shown in <FIG>). When the two rotation sensor <NUM> are coupled to the two wheels <NUM> or <NUM> of the same (front or rear) axle (as shown in <FIG>), the agricultural tractor <NUM> has to be driven (generally at a maximum speed of <NUM>-<NUM>/h) for a test run on hard (i.e. stable) soil and along a (approximately) straight path enough long to allow the checked axle to make at least <NUM>-<NUM> revolutions (but of course a greater number of revolutions could be done, for example as many as <NUM>-<NUM> revolutions or even more). At the end of the test run, the control unit <NUM> compares the total revolutions done by the left wheel <NUM> or <NUM> with the total revolutions done by the right wheel <NUM> or <NUM>: if the total number of revolutions of both wheels <NUM> or <NUM> (right and left) is the same (within a certain tolerance margin) then it is established that the two wheels <NUM> or <NUM> (right and left) of the (front or rear) axle are balanced, otherwise it is established that and two wheels <NUM> or <NUM> (right and left) of the (front or rear) axle are unbalanced and therefore a correct intervention is necessary to avoid subjecting to unnecessary mechanical stress (and thus wear) the powertrain <NUM>.

In other words, the control unit <NUM> calculates an axle balance by dividing the total number of revolutions of the right wheel <NUM> or <NUM> by the total number of revolutions of the left wheel <NUM> or <NUM>; when the axle balance is equal to <NUM> (within a certain tolerance margin) then it is established that the two wheels <NUM> or <NUM> (right and left) of the (front or rear) axle are balanced, otherwise it is established that and two wheels <NUM> or <NUM> (right and left) of the (front or rear) axle are unbalanced. The unbalance can be also calculated as absolute rotation difference among the wheels of the same axle.

Referring to <FIG>, the axle inspection checks if the rotation speed ω<NUM> is equal or not to rotation speed ω<NUM> (front axle) and checks if the rotation speed ω<NUM> is equal or not to rotation speed ω<NUM> (rear axle), as the rotation speed is directly proportional to the total number of revolutions. Of course the tyre analysis system <NUM> can be used to perform an axle inspection of the front axle (by coupling the two rotation sensors <NUM> to both the front wheels <NUM>) and successively the tyre analysis system <NUM> can be used to perform an axle inspection of the rear axle (by coupling the two rotation sensors <NUM> to both the rear wheels <NUM>). According to a different embodiment, four rotation sensors <NUM> can be used to perform at the same an axle inspection of the front axle and also of the rear axle.

The tyre analysis system <NUM> can be used to determine the real slip when at least one rotation sensor <NUM> is coupled to the rear wheels <NUM> of the rear axle (as shown in <FIG>): during a first test the agricultural tractor <NUM> has to be driven (generally at a maximum speed of <NUM>-<NUM>/h) on operating conditions, on hard soil, and without working load (equipment no in operating position) applied till the rear wheels <NUM> turns a given number of times (for example <NUM>, <NUM>, <NUM>. revolutions) and it is measured the first running distance D1 at the end of the given number of revolutions, while during a second test the agricultural tractor <NUM> has to be driven (generally at a maximum speed of <NUM>-<NUM>/h) on operating conditions, on the working field, and with load applied (equipment on operating position) till the rear wheels <NUM> turns the given number of times of the first test (it is not strictly necessary exactly the same turns as the tyre analysis system <NUM> will do the required calculation in any case), and it is measured the second running distance D2 at the end of the given number of revolutions. At the end of the two tests, the control unit <NUM> calculates the real slip by dividing the second running distance D2 traveled divided by the number of revolutions done with load applied, by the first running distance D1 traveled divided by the number of revolutions without load applied (in other words, the tyre analysis system <NUM> is calculating the distance driven by each rear tyre revolution with and without working load, and then calculates the ratio between both results to determine the slip percentage instead of driving exactly the same number of rear tyre revolutions on each condition).

The tyre analysis system <NUM> can be used to determine the real (effective) rolling circumferences of each tyre <NUM> and <NUM>, the real (effective) inter-axle ratio ("IAR"), and the real (effective) lead ratio when the two rotation sensor <NUM> are coupled to a front wheel <NUM> and to a rear wheel <NUM> as shown in <FIG> and <FIG>.

To determine the rolling circumferences, the agricultural tractor <NUM> has to be driven (generally at a maximum speed of <NUM>-<NUM>/h) with 4x4 (four-wheel drive) off on operating conditions on hard soil and without load applied, for a certain number of revolutions of the rear tyre (normally <NUM>) and the control unit <NUM> measures the total number of revolutions done by the wheels <NUM> and <NUM> and also the total running distance D: the control unit <NUM> calculates the real (effective) rolling circumferences of the front and rear tyres <NUM> and <NUM> by dividing the total running distance D by the total number of revolutions of each axle.

In four-wheel drive mechanisms, the relationship between the total number of revolutions of the front and rear axle (in 4x4 drive mode) is a constant factor (and is determined by the cogs in the gear box, transfer case and hub reduction); this relationship is referred to as the inter axle ratio or transference ratio (also known as mechanical drive ratio) and, depending on the tractor brand and type, is normally between <NUM> and <NUM>. Of course the inter axle ratio or transference ratio is a fixed and known parameter of the agricultural tractor 1that is sometimes indicated in any of the tractor's plates, or can be obtained from the tractor's manufacturer, but if that information is not available or is difficult to obtain, it could be calculated by the system with a high degree of precision.

Referring to <FIG>, the inter axle ratio or transference ratio is the ratio between the rotation speed ω<NUM> (front axle) and the rotation speed ω<NUM> (rear axle); the inter axle ratio or transference ratio can be determined also dividing the rotation speed ω<NUM> (ω<NUM>) by the rotation speed ω<NUM> (ω<NUM>).

Traditionally, the theoretical lead ratio is calculated by using the tyre's official rolling circumference (that manufacturers published at rated conditions, i.e. at the rated inflation pressure, rated load of each tyre and at <NUM>/h), using the following formula: <MAT>.

If the actual rolling circumference of the tyres, under the actual load, inflation pressure, etc., is known, the actual lead can be calculated.

But the system can calculate the actual (real) lead ratio under the actual operating conditions just based on the measured revolutions of each axle, in 4x4 On and 4x4 Off conditions, even without knowing the inter axle ratio. Once the control unit <NUM> knows the revolutions for front and rear tyres <NUM> and <NUM>, in 4x4 On and 4x4 Off conditions, the control unit <NUM> calculates the lead ratio as follows: <MAT>.

It will also calculate the inter axle ratio as follows: <MAT>.

Generally, in the agricultural tractor <NUM> the front axle must actually pull the rear axle slightly when the front axle is engaged: the calculation of this difference in traction, where the front axle pulls slightly faster than the rear axle, is called front-wheel lead. When the lead ratio is too high (for example higher than <NUM>%), then the rear axle is turning too slowly compared to the front axle, so the rear axle is holding back the front axle, which is likely to cause front wheel slippage; the front axle undergoes too much mechanical pressure which may result in a rattling noise when you engage the front axle as well as excessive mechanical heating, and a rapid tyre wear. When the lead ratio is too low (for example lower than <NUM>%) the rear axle turns quicker than the front axle, so the rear axle pushes the front axle, which is likely to cause rear wheel slippage; the front axle loses efficiency and steering is less responsive on loose soil.

According to a preferred embodiment, the control unit <NUM> is configured to measure and register the ambient air pressure, the ambient air moisture, and/or the ambient air temperature as all these values influence the dimensions of the tyres <NUM> and <NUM>.

The embodiments described herein can be combined with each other without departing from the scope of protection of the present invention.

The method described above has many advantages.

First and foremost, the aforementioned method allows a very easy, quick and precise determination of many characteristic parameters of the tyres <NUM> and <NUM>.

Furthermore, the aforementioned method requires the presence of only one person, while the known manual determination requires the presence of at least three people (one driving the agricultural tractor <NUM> and two looking at the tyres <NUM> and <NUM>); in other words, in the aforementioned method the two persons looking at the tyres <NUM> and <NUM> are substituted by the rotation sensors <NUM> and by the distance sensor <NUM> which are much more precise (the rotation sensors <NUM> have easily a resolution of <NUM>,<NUM>° while a skilled person could have a maximum resolution of <NUM>°) and easy to use (the rotation sensors <NUM> can be mounted/dismounted to/from the wheels <NUM> and <NUM> in few seconds).

Claim 1:
A tyre analysis method for determining characteristic parameters of an agricultural tractor (<NUM>) provided with two front wheels (<NUM>) supporting two front tyres (<NUM>) and with two rear wheels (<NUM>) supporting two rear tyres (<NUM>); the method comprises the steps of:
mounting a first rotation sensor (<NUM>) on a first wheel (<NUM>, <NUM>);
mounting a second rotation sensor (<NUM>) on a second wheel (<NUM>, <NUM>);
driving the agricultural tractor (<NUM>) along a straight path;
measuring, while driving the agricultural tractor (<NUM>) along the straight path, the total number of revolutions made by the first wheel (<NUM>, <NUM>) and by the second wheel (<NUM>, <NUM>) ;
determining at least one characteristic parameter using the total number of revolutions made by the first wheel (<NUM>, <NUM>) and by the second wheel (<NUM>, <NUM>); and
measuring with a distance sensor (<NUM>) a distance (D) traveled by the agricultural tractor (<NUM>);
said method being characterized in that the distance sensor (<NUM>) is formed by:
a receiver (<NUM>) which is attached to a body (<NUM>) of the agricultural tractor (<NUM>); and
a beacon (<NUM>) placed in a fixed position on the ground nearby the travelling path of the agricultural tractor (<NUM>).