Patent Application
20140260585
The invention relates generally to tire monitoring systems for collecting measured tire parameter data during vehicle operation and, more particularly, to a system and method for estimating vehicle tire deflection and load based upon analytic assessment of such measurements.
Vehicle-mounted tires may be monitored by tire pressure monitoring systems (TPMS) which measure tire parameters such as pressure and temperature during vehicle operation. Data from TPMS tire-equipped systems is used to ascertain the status of a tire based on measured tire parameters and alert the driver of conditions, such as low tire pressure or leakage, which may require remedial maintenance. Sensors within each tire are either installed at a pre-cure stage of tire manufacture or in a post-cure assembly to the tire.
Other factors such as tire load are important considerations for vehicle operation and safety. It is accordingly further desirable to measure tire load in a sufficiently accurate manner in order to communicate such a load estimation to a vehicle operator and/or vehicle systems such as braking and control systems in conjunction with the measured tire parameters of pressure and temperature.
According to an aspect of the invention a system and method estimating a vehicle tire load includes a tire static load estimating means for estimating a static tire load; tire deflection estimating means for estimating a deflection-based tire load calculated from a measurement of a tire vertical deflection; load variation estimation means estimating the instantaneous tire load variation by using the tire vertical deflection information; output tire load estimation means for calculating substantially an output load estimation mathematically fusing the static tire load with the load variation.
In another aspect, the calculation of output load estimation from the deflection-based tire load and the load variation occurs substantially instantaneously.
Pursuant to a further aspect, the tire deflection estimating means includes a chassis accelerometer measuring a chassis vertical acceleration; and a hub accelerometer measuring a wheel hub vertical acceleration of the tire.
A linear filter model such as a Kalman Filter, in a further aspect, receives as inputs the chassis vertical acceleration and the wheel hub vertical acceleration.
“ANN” or “Artificial Neural Network” is an adaptive tool for non-linear statistical data modeling that changes its structure based on external or internal information that flows through a network during a learning phase. ANN neural networks are non-linear statistical data modeling tools used to model complex relationships between inputs and outputs or to find patterns in data.
“Aspect ratio” of the tire means the ratio of its section height (SH) to its section width (SW) multiplied by 100 percent for expression as a percentage.
“Asymmetric tread” means a tread that has a tread pattern not symmetrical about the center plane or equatorial plane EP of the tire.
“Axial” and “axially” means lines or directions that are parallel to the axis of rotation of the tire.
“CAN bus” or “controller area network” 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 automotive applications.
“Chafer” is a narrow strip of material placed around the outside of a tire bead to protect the cord plies from wearing and cutting against the rim and distribute the flexing above the rim.
“Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.
“Equatorial Centerplane (CP)” 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 as the tire rotates or rolls.
“Groove” means an elongated void area in a tire wall that may extend circumferentially or laterally about the tire wall. The “groove width” is equal to its average width over its length. A grooves is sized to accommodate an air tube as described.
“Inboard side” means the side of the tire nearest the vehicle when the tire is mounted on a wheel and the wheel is mounted on the vehicle.
“Kalman Filter” is a set of mathematical equations that implement a predictor-corrector type estimator that is optimal in the sense that it minimizes the estimated error covariance—when some presumed conditions are met.
“Lateral” means an axial direction.
“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.
“Luenberger Observer” is a state observer or estimation model. A “state observer” is a system that provide an estimate of the internal state of a given real system, from measurements of the input and output of the real system. It is typically computer-implemented, and provides the basis of many practical applications.
“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.
“Non-directional tread” means a tread that has no preferred direction of forward travel and is not required to be positioned on a vehicle in a specific wheel position or positions to ensure that the tread pattern is aligned with the preferred direction of travel. Conversely, a directional tread pattern has a preferred direction of travel requiring specific wheel positioning.
“Outboard side” means the side of the tire farthest away from the vehicle when the tire is mounted on a wheel and the wheel is mounted on the vehicle.
“Peristaltic” means operating by means of wave-like contractions that propel contained matter, such as air, along tubular pathways.
“Piezoelectric Film Sensor” a device in the form of a film body that uses the piezoelectric effect actuated by a bending of the film body to measure pressure, acceleration, strain or force by converting them to an electrical charge.
“Radial” and “radially” means directions radially toward or away from the axis of rotation of the tire.
“Rib” means a circumferentially extending strip of rubber on the tread which is defined by at least one circumferential groove and either a second such groove or a lateral edge, the strip being laterally undivided by full-depth grooves.
“Sipe” means small slots molded into the tread elements of the tire that subdivide the tread surface and improve traction, sipes are generally narrow in width and close in the tires footprint as opposed to grooves that remain open in the tire's footprint.
“Slip Angle” is the angle between a vehicle's direction of ravel and the direction in which the front wheels are pointing. Slip angle is a measurement of the deviation between the plane of tire rotation and the direction of travel of a tire.
“Tread element” or “traction element” means a rib or a block element defined by having a shape adjacent grooves.
“Tread Arc Width” means the arc length of the tread as measured between the lateral edges of the tread.
The invention will be described by way of example and with reference to the accompanying drawings in which:
Referring first to
Zs=chassis vertical deflection as measured by accelerometer 22;
Zu=Hub vertical deflection as measured by accelerometer 20;
Zr=Wheel vertical deflection
Ksuspension=suspension stiffness
Csuspension=suspension dampening coefficient
Ktire=tire stiffness
Ctire=tire dampening coefficient
Ms=sprung mass
Mu=unsprung mass
The standard notational convention for describing a State-space representation is given by:
x′=Ax+Bu}state equations
y=Cx+Du}output equations
where:
x(t) State vector
x′(t) Derivative of state vector
A State matrix
B Input matrix
u(t) Input vector
y(t) output vector
C output matrix
D Direct transmission matrix
The equivalent state space representation of the “quarter car model” used in the Kalman filter has been specified below as
A=[((−Csuspension/Ms)−(Csuspension/Mu)) ((−Ksuspension/Ms)−(Ksuspension/Mu)) (Ktire/Mu)0;
1 0 0 0;
0 0 0 1;
Csuspension/Mu Ksuspension/Mu−Ktire/Mu 0]
B=[0 0 0 0]
C=[−Csuspension/Mu−Ksuspension/Mu 0 0;
Csuspension/Mu Ktire/Mu Ktire/Mu 0]
D=[0 0]
Estimated states of the Kalman linear filter 28 are (Zs′−Zu′); (Zs−Zu); (Zu−Zr); and (Zu′−Zr′). The state estimations are input into a Load Variation Estimator 30 and utilized within the expression:
[Ktire*(Zu−Zr)+Ctire*(Zu′−Zr′)] (1)
The Kalman Filter 26, in performing its state estimation, further utilizes a tire nominal static load 32 in conjunction with the tire stiffness information. The static load estimation is generated by tire attached sensors. The TPMS system produces tire identification and inflations data which is used to consult and extract tire stiffness Ktire from a tire-specific database. The Load Variation from Load Variation Estimator 30 is calculated by use of Expression (1), fusing the tire deflection information with the tire load and stiffness information.
In order to verify the accuracy of the instantaneous load estimation, actual loading on a tire 12 is measured in the
The “quarter car model” 28 estimation scheme is shown in schematic detail by
F
z,instantaneous
=F
z,static
−Ktire*(Zu−Zr)−Ctire*(Zu′−Zr′) (2)
Static loading on the tire 12 may be estimated by conducting a tire deformation analysis such as that described in co-pending U.S. patent application Ser. No. 13/609,695, filed Sep. 11, 2012, entitled “TIRE SIDEWALL LOAD ESTIMATION SYSTEM AND METHOD”, incorporated herein in its entirety by reference. The static load Fz static from the tire attached sensor 16 (
As a result, the tire vertical deflection, reconstructed using the quarter car model, is sufficiently accurate for the purpose of providing an instantaneous load estimation. The chassis and hub mounted accelerometers used in physical system of
From the foregoing, it will be appreciated that the subject system and method uses Kalman filtering techniques to estimate the vertical deflection of a tire by starting with the measures of the vehicle suspension dynamics. The observer is based on a “quarter car model” as replicated in
Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.
