Patent Description:
The load on each tire of a vehicle plays an important role in vehicle factors such as handling, safety, reliability, and performance. Measurement or estimation of the load on a tire during the operation of a vehicle is often used by vehicle control systems such as braking, traction, stability, and suspension systems. For instance, information about individual tire loads enables precise estimation of the load distribution between the front and the rear axle of the vehicle, which can then be used to optimize the brake control system. Alternatively, knowledge of tire loads and consequently the vehicle mass may enable more accurate estimation of the remaining range of an electric vehicle. Thus, it is desirable to estimate the load on a tire in an accurate and reliable manner for input or use in such systems.

Prior art approaches have involved attempts at directly measuring tire load using load or strain sensors. Such direct-measurement techniques have experienced disadvantages due to the difficulty in achieving a sensor with a construction and placement on the tire that enables accurate and consistent measurement of tire load, particularly over the life of a tire.

Other prior art approaches have been developed that involve estimation of tire load using fixed parameters. Such prior art approaches have experienced disadvantages since techniques relying upon fixed parameters often lead to less-than-optimum predictions or estimations, which in turn reduces the accuracy and/or reliability of the tire load predictions.

As a result, there is a need in the art for a system and method that accurately and reliably estimates tire load.

<CIT> describes a system in accordance with the preamble of claim <NUM>.

According to a preferred aspect of the invention, a counter-deflection load estimation system for a tire is provided. The tire includes a pair of sidewalls extending to a circumferential tread and supporting a vehicle, and the vehicle includes a controlled area network bus. The system includes a sensor that is mounted to the tire and measures a parameter of the tire. A counter-deflection of the tire is determined from the measured parameter, and a linear vehicle speed signal is received through the controlled area network bus. A processor is in electronic communication with the sensor and with the controlled area network bus. A load estimation module is in electronic communication with the processor, receives the linear vehicle speed signal and the counter-deflection of the tire, and determines a load on the tire.

According to another preferred aspect of the invention, a method for estimating the load of a tire using counter-deflection is provided. The tire includes a pair of sidewalls extending to a circumferential tread and supporting a vehicle. In the method, a sensor is mounted to the tire, and a parameter of the tire is measured with the sensor. A counter-deflection of the tire is determined from the measured parameter, and a linear vehicle speed signal is received through a controlled area network bus of the vehicle. A processor is provided in electronic communication with the sensor and with the controlled area network bus. The linear vehicle speed signal and the counter-deflection of the tire are receiving in a load estimation module that is in electronic communication with the processor. A load on the tire is determined with the load estimation module.

"CAN bus" is an abbreviation for controller area network, which is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer. CAN bus is a message-based protocol, designed specifically for vehicle applications.

"Equatorial Centerplane" means the plane perpendicular to the tire's axis of rotation and passing through the center of the tread.

"Footprint" means the contact patch or area of contact created by the tire tread with a flat surface, such as the ground, as the tire rotates or rolls.

"Lateral edges" means a line tangent to the axially outermost tread contact patch or footprint as measured under normal load and tire inflation, the lines being parallel to the equatorial centerplane.

"Net contact area" means the total area of ground contacting tread elements between the lateral edges around the entire circumference of the tread divided by the gross area of the entire tread between the lateral edges.

"Tread element" or "traction element" means a rib or a block element defined by a shape having adjacent grooves.

An exemplary embodiment of the counter-deflection tire load estimation system <NUM> of the present invention is shown in <FIG>. The system <NUM> and accompanying method attempt to overcome the above-described challenges posed by prior art systems and methods that seek to measure the tire load through direct sensor measurements. As such, the subject system and method is referred herein as an "indirect" load estimation system and method.

With particular reference to <FIG>, the system <NUM> estimates the load on each tire <NUM> supporting a vehicle <NUM> based on counter-deflection of the tire, as will be described in greater detail below. While the vehicle <NUM> is depicted as a passenger car, the invention is not to be so restricted. The principles of the invention find application in other vehicle categories such as commercial trucks in which vehicles may be supported by more or fewer tires than shown in <FIG>. For the purpose of convenience, analysis of a single tire <NUM> will be made except as specifically described below, with the understanding that a similar analysis is contemplated for each tire supporting the vehicle <NUM>.

The tire <NUM> is of conventional construction and is mounted on a respective wheel <NUM>. The tire <NUM> includes a pair of sidewalls <NUM> that extend to a circumferential tread <NUM>, which engages the ground during vehicle operation. The tire <NUM> preferably is equipped with a sensor <NUM> that is mounted to the tire for the purpose of detecting certain real-time tire parameters. For example, the sensor <NUM> may be a commercially available tire pressure monitoring system (TPMS) module or sensor, which may be affixed to an inner liner <NUM> of the tire <NUM> by suitable means such as adhesive. The sensor <NUM> preferably includes a pressure sensor to sense an inflation pressure <NUM> (<FIG>) within a cavity <NUM> of the tire <NUM>, and a temperature sensor to sense a temperature <NUM> of the tire and/or the temperature in the cavity. The sensor <NUM> preferably also senses a revolution time of the tire <NUM>, and also senses counter deflection of the tire, as will be explained in greater detail below.

The sensor <NUM> preferably also includes a processor and memory to store tire identification (tire ID) information <NUM> (<FIG>) for the tire <NUM>. For example, the tire ID may include manufacturing information for the tire <NUM>, including: the location of the tire on the vehicle <NUM>; the tire model; size information, such as rim size, width, and outer diameter; manufacturing location; manufacturing date; a tread cap code that includes or correlates to a compound identification; and a mold code that includes or correlates to a tread structure identification. The tire ID may also include a service history or other information to identify specific features and parameters of the tire <NUM>. The sensor <NUM> preferably further includes an antenna for transmitting measured parameters and tire ID data to a remote processor <NUM>, which may be a processor that is integrated into a vehicle CAN bus <NUM>, for analysis.

Aspects of the tire load estimation system <NUM> preferably are executed on a processor <NUM> (<FIG>) that is accessible through the vehicle CAN bus <NUM>. The processor <NUM> may be a vehicle-mounted processor or may be a remote Internet or cloud-based processor (<FIG>). Use of such a processor <NUM>, and accompanying memory, enables input of data into the system <NUM> from the tire-based sensor <NUM> and data from certain vehicle-based sensors, as well as data from a database that may be stored in a suitable storage medium which is in electronic communication with the processor. The CAN bus <NUM> enables the tire load estimation system <NUM> to interface with other electronic components and systems of the vehicle <NUM>.

Turning to <FIG>, as the tire <NUM> rotates or rolls on a surface <NUM> such as the ground, the tread <NUM> creates a contact patch <NUM> with the surface, which is also known as a footprint. In the contact patch <NUM>, the tire <NUM> experiences a deflection <NUM>. Due to the deflection <NUM>, a surface <NUM> of the tire <NUM> outside of the contact patch <NUM> experiences a counter-deflection <NUM>. More particularly, the counter-deflection <NUM> is an increase in a radius of the tire <NUM> away from the contact patch <NUM> and is proportional to the deflection <NUM> that occurs in the contact patch.

With additional reference to <FIG>, as the tire <NUM> rotates, it exhibits radial acceleration <NUM>. The radial acceleration <NUM> of the tire <NUM> may be plotted over time <NUM>, and when the vehicle <NUM> is traveling at a constant speed, a mid-region <NUM> between radial acceleration minimums <NUM> corresponds to the counter-deflection <NUM> of the tire. A mean value <NUM> for the radial acceleration mid-region <NUM> may be determined, which corresponds to a specific value for the counter-deflection <NUM>, as will be described in greater detail below. In this example, the mean value <NUM> for the radial acceleration mid-region <NUM> is about <NUM>, where g is a gravitational force equivalent. The radial acceleration mean value <NUM> corresponds to a counter-deflection <NUM> or a counter-deflected radius of about <NUM> meters (M) for the tire <NUM> under a load of <NUM>,<NUM> newtons (N) at a speed of <NUM> kilometers per hour (kph).

The sensor <NUM> (<FIG>) includes a radial accelerometer to sense the radial acceleration <NUM> of the tire <NUM>, from which the counter-deflection <NUM> may be determined. The determination of counter-deflection <NUM> of the tire <NUM> from the radial acceleration <NUM> may be performed within the sensor <NUM>, or in the processor <NUM>, as the processor is in electronic communication with the sensor. It is to be understood that other measuring devices which measure deformation of the tire <NUM> may be employed to determine counter-deflection <NUM>.

Turning to <FIG>, the counter-deflection tire load estimation system <NUM> includes a load estimation module <NUM>, which is stored on or is in electronic communication with the processor <NUM>. The load estimation module <NUM> receives a linear vehicle speed <NUM> through the vehicle CAN bus <NUM>, and tire data <NUM> from the sensor <NUM>. The tire data <NUM> preferably includes the radial acceleration <NUM> of the tire <NUM>, from which the counter-deflection <NUM> may be determined, or another tire parameter that enables the determination of the counter deflection. The tire data <NUM> also preferably includes a revolution time <NUM> of the tire <NUM> to enable determination of the radial acceleration mid-region <NUM>, and thus the counter-deflection <NUM>. The tire data <NUM> preferably also includes the tire inflation pressure <NUM>, the tire temperature <NUM>, the tire ID information <NUM>, and/or an identification code <NUM> for the sensor <NUM>.

The load estimation module <NUM> preferably includes a regression model, which may be a linear regression model or a nonlinear regression model, to estimate a tire load <NUM> from the linear vehicle speed <NUM> and the tire data <NUM>, including the counter-deflection <NUM>. Preferably, a linear regression model is employed. However, if greater accuracy in the load estimation model <NUM> is desired, a nonlinear regression model may be employed.

By way of example, the tire <NUM> includes a vertical stiffness Kf, which is a proportionality constant between the deflection <NUM> (also indicated as f) and a normal load F on the tire: <MAT>.

A counter-deflection stiffness Kλ of the tire <NUM> is a proportionality constant between the counter-deflection <NUM> (also indicated as λ) and the normal load F: <MAT>.

The counter-deflection stiffness Kλ is directly proportional to a vertical stiffness of the tire <NUM>. The counter-deflection stiffness Kλ may be described as a regression model with a first variable, indicated as m, which is proportional to the inflation pressure <NUM> (also indicated as p), and a second variable, indicated as b, which represents structural characteristics of the tire <NUM> identified from the tire ID information <NUM>, such as a sidewall shear stiffness and a size of the tire: <MAT>.

The counter-deflection <NUM> (λ) may be determined using a counter-deflected radius r of the tire <NUM>, subtracting an unloaded tire radius ro: <MAT>.

The radius r, as obtained from the measured radial acceleration <NUM> (also indicated as a), is equivalent to the square of the linear vehicle speed <NUM> (also indicated as v) divided by the radial acceleration: <MAT>.

The counter-deflection <NUM> (λ) is thus determined as: <MAT>.

From this, the tire load <NUM> (also indicated as F), is determined: <MAT>.

Which may also be generally expressed as F = f (p, ro, v, a).

In this manner, the load estimation module <NUM> estimates the tire load <NUM> from the linear vehicle speed <NUM> and the tire data <NUM>. The estimated load <NUM> on the tire <NUM> may be communicated through the vehicle CAN bus system <NUM> from the counter-deflection tire load estimation system <NUM> for use by a vehicle control system, such as a braking, traction, stability, and/or suspension system.

Turning to <FIG>, the counter-deflection tire load estimation system <NUM> preferably is executed on a processor <NUM> that is accessible through the vehicle CAN bus <NUM>, which may be mounted on the vehicle <NUM>, or which may be in an Internet or cloud-based computing system <NUM>, referred to herein as a cloud-based computing system. The counter-deflection tire load estimation system <NUM> preferably employs wireless data transmission <NUM> between the vehicle <NUM> and the cloud-based computing system <NUM>. The counter-deflection tire load estimation system <NUM> may also employ wireless data transmission <NUM> between the cloud-based computing system <NUM> and a display device <NUM> that is accessible to a user of the vehicle <NUM>, such as a smartphone, or to a fleet manager. Alternatively, the system <NUM> may also employ wireless data transmission <NUM> between the vehicle CAN bus <NUM> and the display device <NUM>.

In this manner, the counter-deflection tire load estimation system <NUM> of the present invention indirectly estimates tire load <NUM> in an accurate and reliable manner using counter-deflection <NUM> of the tire <NUM>. The counter-deflection tire load estimation system <NUM> employs the linear vehicle speed <NUM> and the tire data <NUM> for a real-time estimation of the tire load <NUM>.

Claim 1:
A counter-deflection load estimation system for a tire, the tire (<NUM>) including a pair of sidewalls (<NUM>) extending to a circumferential tread (<NUM>) and supporting a vehicle (<NUM>), the vehicle (<NUM>) including a controlled area network bus (<NUM>), the system (<NUM>) comprising:
a sensor (<NUM>) being mounted to the tire (<NUM>), the sensor (<NUM>) being configured for measuring a parameter of the tire (<NUM>) including a radial acceleration (<NUM>) of the tire (<NUM>);
means for determining a counter-deflection (<NUM>) of the tire (<NUM>) from said measured parameter;
means for receiving a linear vehicle speed signal (<NUM>) through the controlled area network bus (<NUM>);
a processor (<NUM>) in electronic communication with the sensor (<NUM>) and with the controlled area network bus (<NUM>); and
a load estimation module (<NUM>) in electronic communication with the processor (<NUM>), the load estimation module being configured for receiving the linear vehicle speed signal (<NUM>) and the counter-deflection (<NUM>) of the tire (<NUM>) and for determining a load (<NUM>) on the tire (<NUM>); characterized in that
the system (<NUM>) is configured for determining the counter-deflection (<NUM>) from a mid-region (<NUM>) between radial acceleration minimums (<NUM>).