| CPC B60C 23/064 (2013.01) [B60C 19/00 (2013.01); B60C 2019/004 (2013.01)] | 18 Claims |
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1. System for measuring a length of a footprint of a tyre (10), said system comprising:
a first electronic device (1) to be positioned, in use, on an inner surface (10A) or on an outer surface (10B) of the tyre (10),
a second electronic device (2), to be positioned, in use, in contact with a rim (20), on which said tyre (10) is mounted,
a processing unit (3), external to said electronic devices (1, 2),
wherein:
a first reference system x1, y1, z1 is associated with the first electronic device (1) in such a way that an axis x1 is tangent to a rotation of a first point (P1) which is a point of said tyre (10) in which said first electronic device (1) is applied, and an axis z1 is perpendicular to said axis x1,
a second reference system x2, y2, z2 is associated to the second electronic device (2) in such a way that an axis x2 is tangent to a rotation of a second point (P2) which is a point of said rim (20) in which said second electronic device (2) is applied, and an axis z2 is perpendicular to said axis x2,
said first electronic device (1) is configured at least to send data to said processing unit (3) and comprises inside:
a first inertial measurement unit (12) comprising a first gyroscope (121) and a first accelerometer (122), configured to acquire, by means of said first gyroscope (121), a plurality of values associated at least to an angular velocity around a y axis (ω1y), or, by means of said first accelerometer (122), a plurality of values associated at least to a linear acceleration along an x axis (A1x) or a plurality of values associated at least to a linear acceleration along a z axis (A1z),
a first storage means (15) for storing data,
a first logic control unit (11), connected with said first inertial measurement (12) and to said first storage means (15), and configured to:
receive from said first inertial measurement unit (12):
each value of said linear acceleration along the x axis (A1x), or
each value of said linear acceleration along the z axis (A1z), or
each value of said angular velocity around the y axis (ω1y),
filter by means of a first digital filter:
each value of said linear acceleration along the x axis (A1x) to obtain a filtered linear acceleration along the x axis (A1x′), or
each value of said linear acceleration along the z axis (A1z) to obtain a filtered linear acceleration along the z axis (A1z′), or
each value of said angular velocity around the y axis (ω1y) to obtain a filtered linear angular velocity around the y axis (ω1y′),
identify a first time instant (t1,1D), in correspondence of a first contact point (CP1) between a portion of said tyre (10) and a ground surface, when said portion of said tyre (10) comes into contact with the ground surface, and a second time instant (t1,2D), in correspondence of a second contact point (CP2) between said portion of said tyre (10) and the ground surface, beyond which said portion of said tyre (10) loses contact with the ground surface; said first time instant (t1,1D) and said second time instant (t1,2D) being respectively:
an initial time instant and a final time instant of a discontinuity portion of a sinusoid (S1F) associated with said filtered linear acceleration along the x axis (A1x′), or
an initial time instant and a final time instant of a discontinuity portion of a sinusoid (S1F′) associated with said filtered linear acceleration along the z axis (A1z′), or
an initial time instant and a final time instant of a discontinuity portion of a sinusoid (S1F″) associated with said filtered angular velocity around the y axis (ω1y′),
calculate a time interval (ΔtD) between said first time instant (t1,1D) and said second time instant (t1,2D),
store said first time instant (t1,1D), said second time instant (t1,2D) and said time interval (ΔtD) in said first storage means (15),
send said first time instant (t1,1D), said second time instant (t1,2D) and said time interval (ΔtD) to said processing unit (3),
said second electronic device (2) is configured at least to send data to said processing unit (3) and comprises inside:
a second inertial measurement unit (22) comprising a second gyroscope (221), configured to acquire, by means of said second gyroscope (221), a plurality of values associated at least to an angular velocity around the y axis (ω2y),
a second storage means (25) for storing data,
a second logic control unit (21), connected to said second inertial measurement unit (22) and to said second storage means (25), and configured to:
receive from the second inertial measurement unit (22) the values of said angular velocity around the y axis (ω2y),
filter by means of a second digital filter each value of said angular velocity around the y axis (ω2y) to obtain a respective filtered angular velocity around the y axis (ω2y′),
identify a respective time instant t2y′ associated with each value of said filtered angular velocity around the y axis (ω2y′),
store in predetermined time intervals in said second storage means (25) each value of said filtered angular velocity around the y axis (ω2y′) and the respective time instants, t2y′,
send to said processing unit (3) each value of said filtered angular velocity around the y axis (ω2y′) and the respective time instants t2y′,
said processing unit (3) is configured at least to receive data from said first electronic device (1) and from said second electronic device (2) and comprises inside:
a third storage means (35) for storing data,
a third logic control unit (31), connected to said third storage means (35), and configured to:
receive said first time instant (t1,1D), said second time instant (t1,1D) and said time interval (ΔtD) from said first electronic device (1),
receive the values of said filtered angular velocity around the y axis (ω2y′) sent by said second electronic device (2), as well as the respective time instants t2y′,
calculate a mean value (ω′2y) of the filtered angular velocities around the y axis associated with said second electronic device (2) in correspondence of each of the respective time instants t2y′ that are within said time interval (ΔtD),
calculate an angle (B) between a first axis (B1) passing through a centre (O) of the tyre (10) and said first contact point (CP1) and a second axis (B2) passing through the centre (O) of the tyre (10) and said second contact point (CP2), according to the following formula:
β=ω′2y·ΔtD,
calculate the length (L) of the footprint of the tyre (10) with the following formula:
 wherein R0 is a rolling radius of the tyre (10).
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