Vehicle operating parameter determination system and method
First Claim
1. A method of estimating a steering angle offset value in a vehicle having a relative position steering angle sensor, said method comprising:
- providing a mathematical expression for calculating an estimated steering angle offset value, {circumflex over (δ
)}off, based upon at least one measured value of a vehicle operating parameter wherein said mathematical expression is definable by;
selecting a mathematical model to describe the dynamic behavior of the vehicle which includes a first variable, δ
, representing the steering angle of the vehicle, wherein said mathematical model includes at least one of a Kalman filter and a state observer; and
substituting, for said first variable, δ
, the sum of a second variable, δ
Uncenter, representing the relative steering angle position and a third variable, δ
off, representing the steering angle offset in said model to provide said mathematical expression;
obtaining said at least one measured value for said vehicle; and
estimating said steering angle offset value using said at least one measured value and said mathematical expression.
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Abstract
A system and method for estimating an operating parameter of a vehicle such as the steering angle offset or body slip angle. The method includes providing a dynamic vehicle model which is valid when the yaw rate and slip angle of the vehicle are either constant or changing. The vehicle model is reformulated to allow for the direct estimation of the steering angle offset value and/or the body slip angle. Estimation of an operating parameter of the vehicle may also include the use of a model difference term which is defined by the difference between a value estimated using the model and a measured value. A method for filtering the steering angle offset value is also provided. The filtering method may utilize a variable filter coefficient which varies in response to changes in the dynamic behavior of the vehicle.
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Citations
18 Claims
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1. A method of estimating a steering angle offset value in a vehicle having a relative position steering angle sensor, said method comprising:
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providing a mathematical expression for calculating an estimated steering angle offset value, {circumflex over (δ
)}off, based upon at least one measured value of a vehicle operating parameter wherein said mathematical expression is definable by;
selecting a mathematical model to describe the dynamic behavior of the vehicle which includes a first variable, δ
, representing the steering angle of the vehicle, wherein said mathematical model includes at least one of a Kalman filter and a state observer; and
substituting, for said first variable, δ
, the sum of a second variable, δ
Uncenter, representing the relative steering angle position and a third variable, δ
off, representing the steering angle offset in said model to provide said mathematical expression;
obtaining said at least one measured value for said vehicle; and
estimating said steering angle offset value using said at least one measured value and said mathematical expression. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
wherein; β
represents the body slip angle;
{dot over (ψ
)} represents the yaw rate;
δ
represents the steering angle;
m represents the mass of the vehicle;
v represents the longitudinal speed of the vehicle;
Jz represents the inertia moment of the vehicle around its mass center point;
is represents the steering angle ratio;
Cv represents the cornering stiffness value of front tires;
Ch represents the cornering stiffness value of the rear tires;
lv represents the distance from the front axle to the mass center point of the vehicle; and
ih represents the distance from the rear axle to the mass center point of the vehicle.
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8. The method of claim 7 wherein said step of substituting the sum of said second and third variables in said model provides a mathematical expression which states:
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9. The method of claim 8 wherein said step of substituting the sum of said second and third variables further comprises reformulating said model after substituting said sum, said step of reformulating said model provides a mathematical expression which comprises:
x(k+1)=A(k)x(k)+b(k)·
u(k)+v(k)
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10. The method of claim 1 wherein said step of estimating said steering angle offset value includes use of the mathematical expression which comprises:
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11. The method of claim 1 further comprising the steps of:
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estimating a plurality of steering angle offset values; and
filtering said plurality of estimated steering angle offset values.
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12. The method of claim 10 wherein said filtering step comprises using a variable filter coefficient, Fk.
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13. The method of claim 11 wherein said variable filter coefficient is calculated using an uncertainty factor, Uk, said uncertainty factor, Uk, being determined using at least one value from the group including the yaw rate of the vehicle, the estimated steering angle position and the lateral acceleration of the vehicle.
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14. The method of claim 12 wherein said uncertainty factor, Uk, is determined using the following equation:
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15. A method of filtering a plurality of time indexed values in a process for determining a steering angle position of a vehicle having a relative position steering angle sensor, said method comprising:
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estimating a plurality of time indexed steering angle offset values using at least one of a Kalman filter and a state observer;
filtering a plurality of time indexed values which are a function of said plurality of time indexed steering angle offset values using a variable filter coefficient, Fk, said variable filter coefficient, Fk, being determined using an uncertainty factor, Uk, said uncertainty factor, Uk, being determined using at least one value from the group including yaw rate of the vehicle, estimated steering angle position and the lateral acceleration of the vehicle. - View Dependent Claims (16, 17, 18)
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18. The method of claim 17 wherein said filtering step comprises the use of the formula:
Specification